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  • ddc:551.5  (64)
  • ddc:551.9  (33)
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  • 2020-2024  (98)
  • 1
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    “Seeing” Beneath the Clouds—Machine‐Learning‐Based Reconstruction of North African Dust Plumes (2024)
    Details
    Publication Date: 2024-05-22
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Mineral dust is one of the most abundant atmospheric aerosol species and has various far‐reaching effects on the climate system and adverse impacts on air quality. Satellite observations can provide spatio‐temporal information on dust emission and transport pathways. However, satellite observations of dust plumes are frequently obscured by clouds. We use a method based on established, machine‐learning‐based image in‐painting techniques to restore the spatial extent of dust plumes for the first time. We train an artificial neural net (ANN) on modern reanalysis data paired with satellite‐derived cloud masks. The trained ANN is applied to cloud‐masked, gray‐scaled images, which were derived from false color images indicating elevated dust plumes in bright magenta. The images were obtained from the Spinning Enhanced Visible and Infrared Imager instrument onboard the Meteosat Second Generation satellite. We find up to 15% of summertime observations in West Africa and 10% of summertime observations in Nubia by satellite images miss dust plumes due to cloud cover. We use the new dust‐plume data to demonstrate a novel approach for validating spatial patterns of the operational forecasts provided by the World Meteorological Organization Dust Regional Center in Barcelona. The comparison elucidates often similar dust plume patterns in the forecasts and the satellite‐based reconstruction, but once trained, the reconstruction is computationally inexpensive. Our proposed reconstruction provides a new opportunity for validating dust aerosol transport in numerical weather models and Earth system models. It can be adapted to other aerosol species and trace gases.〈/p〉
    Description: Plain Language Summary: Most dust and sand particles in the atmosphere originate from North Africa. Since ground‐based observations of dust plumes in North Africa are sparse, investigations often rely on satellite observations. Dust plumes are frequently obscured by clouds, making it difficult to study the full extent. We use machine‐learning methods to restore information about the extent of dust plumes beneath clouds in 2021 and 2022 at 9, 12, and 15 UTC. We use the reconstructed dust patterns to demonstrate a new way to validate the dust forecast ensemble provided by the World Meteorological Organization Dust Regional Center in Barcelona, Spain. Our proposed method is computationally inexpensive and provides new opportunities for assessing the quality of dust transport simulations. The method can be transferred to reconstruct other aerosol and trace gas plumes.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We present the first fast reconstruction of cloud‐obscured Saharan dust plumes through novel machine learning applied to satellite images〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The reconstruction algorithm utilizes partial convolutions to restore cloud‐induced gaps in gray‐scaled Meteosat Second Generation‐Spinning Enhanced Visible and Infrared Imager Dust RGB images〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉World Meteorological Organization dust forecasts for North Africa mostly agree with the satellite‐based reconstruction of the dust plume extent〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: GEOMAR Helmholtz Centre for Ocean Research Kiel
    Description: University of Cologne
    Description: https://doi.org/10.5281/zenodo.6475858
    Description: https://github.com/tobihose/Masterarbeit
    Description: https://dust.aemet.es/
    Description: https://ads.atmosphere.copernicus.eu/cdsapp#!/dataset/cams-global-reanalysis-eac4?tab=overview
    Description: https://navigator.eumetsat.int/product/EO:EUM:DAT:MSG:DUST
    Description: https://navigator.eumetsat.int/product/EO:EUM:DAT:MSG:CLM
    Description: https://doi.org/10.5067/KLICLTZ8EM9D
    Description: https://disc.gsfc.nasa.gov/datasets?project=MERRA-2
    Description: https://doi.org/10.5067/MODIS/MOD08_D3.061
    Description: https://doi.org/10.5067/MODIS/MYD08_D3.061
    Description: https://doi.org/10.5281/ZENODO.8278518
    Keywords: ddc:551.5 ; mineral dust ; North Africa ; MSG SEVIRI ; machine learning ; cloud removal ; satellite remote sensing
    Language: English
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  • 2
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    Horizontal Correlation Functions of Wind Fluctuations in the Mesosphere and Lower Thermosphere (2023)
    Details
    Publication Date: 2023-06-21
    Description: Measurements of kinetic energy in vortical and divergent fluctuations in the mesosphere and lower thermosphere can be used to study stratified turbulence (ST) and gravity waves. This can be done using horizontal correlation functions of the fluctuating component of velocity. This study introduces a novel method for estimating these correlation functions using radars that observe Doppler shifts of ionized specular meteor trails. The technique solves the correlation functions directly on a longitudinal‐transverse‐up coordinate system, assuming axial symmetry. This procedure is more efficient and leads to smaller uncertainties than a previous approach. The new technique is applied to a year‐long data set from a multistatic specular meteor radar network in Germany, to study the annual variability of kinetic energy within turbulent fluctuations at 87–93 km of altitude. In monthly averages, the kinetic energy is found to be nearly equipartitioned between vortical and divergent modes. Turbulent fluctuations maximize during the winter months with approximately 25% more energy in these months than at other times. The horizontal correlation functions are in agreement with the inertial subrange of ST, exhibiting a 2/3 power law in the horizontal lag direction, with an outermost scale of ST to be about 380 km. This suggests that horizontal correlation functions could be used to estimate turbulent energy transfer rates.
    Description: Plain Language Summary: Flows exhibit a phenomenon called turbulence, which transfers energy from large scales into smaller scales. This effect is important to quantify the energy budget of the Earth's upper atmosphere. The range of length scales where this phenomenon occurs is called the inertial subrange of turbulence. The classical theory of isotropic turbulence predicts that this energy transfer occurs on length scales smaller than ∼100 m, at 60–110 km altitude. Recent work has shown that horizontal velocity fluctuations can extend the inertial subrange to length scales of up to hundreds of kilometers horizontally. This type of turbulence is called stratified turbulence (ST). So far no comprehensive study has been made to experimentally examine ST in the mesosphere and lower thermosphere (MLT) region on horizontal mesoscales. This study introduces a method for doing so by measuring how the wind fluctuations are correlated as a function of horizontal separation. This is achieved by using meteor radar measurements. The technique is applied to a year‐long data set over Germany. It is found that the MLT wind fluctuations are compatible with ST theory. The introduced method could potentially be used for routinely measuring how kinetic energy flows from large‐scale to small‐scale atmospheric fluctuations.
    Description: Key Points: A more efficient estimator for horizontal correlation functions is introduced. The rotational and divergent correlation functions of mesosphere and lower thermosphere wind fluctuations are found to be balanced at horizontal mesoscales. Horizontal correlations of wind fluctuations follow a 2/3‐power law for horizontal separations of up to 300–400 km.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: French Ministry of Foreign and European Affairs
    Description: Leibniz SAW project FORMOSA
    Keywords: ddc:551.5 ; mesosphere ; lower thermosphere ; wind fluctuations
    Language: English
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  • 3
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    Fingerprinting Kinetic Isotope Effects and Diagenetic Exchange Reactions Using Fluid Inclusion and Dual‐Clumped Isotope Analysis (2023)
    Details
    Publication Date: 2023-06-19
    Description: Geochemical analyses of carbonate minerals yield multiple parameters which can be used to estimate the temperature and water composition at which they formed. Analysis of fluid trapped in minerals is a potentially powerful tool to reconstruct paleotemperatures as well as diagenetic and hydrothermal processes, as these could represent the parent fluid. Internal fluids play important roles during the alteration of carbonate fossils, lowering energetic barriers associated with resetting of clumped isotopes, as well as mediating the transport of elements during diagenesis. Here, we explore the behavior of the ∆47–∆48 “dual‐clumped” isotope thermometer during fluid‐carbonate interaction and demonstrate that it is highly sensitive to the water/carbonate ratio, behaving as a linear system in “rock buffered” alteration, and as a decoupled system in water‐dominated systems due to non‐linear mixing effects in ∆48. Dry heating experiments show that the extrapolated “heated” end‐member is indistinguishable from the predicted ∆47 and ∆48 value expected for the experimental temperature. Furthermore, we evaluate two common laboratory sampling methods for their ability to thermally alter samples. We find that the temperature of the commonly used crushing cells used to vapourize water for fluid inclusion δ18O analyses is insufficient to cause fluid‐carbonate oxygen isotope exchange, demonstrating its suitability for analyses of fluid inclusions in carbonates. We also find that belemnites sampled with a hand‐drill yield significantly warmer paleotemperatures than those sampled with mortar and pestle. We conclude that thermally‐driven internal fluid‐carbonate exchange occurs indistinguishably from isotopic equilibrium, limited by the extent to which internal water and carbonate can react.
    Description: Plain Language Summary: Carbonate minerals contain multiple, independent, chemical and isotopic parameters which can be used to calculate the temperature at which the mineral formed. If these proxies agree with one another, it has been confidently assumed that the temperature is indeed genuine. Here, we investigate three such parameters and show how they record kinetic processes during mineral formation, as well as thermally‐driven processes which may alter a climate record. We find that this method could potentially be used to study the kinetic factors at play during biomineralization, even if the “true” temperature is unknown. We also find that some thermal processes result in all three parameters agreeing with one another. Because thermal alteration poses a potential dilemma for climate researchers, we investigate two common laboratory preparation techniques that involve heating a sample before analysis: drilling and heating sample for fluid inclusion analysis. We find that the heat of a drill is sufficient to facilitate these reactions, and potentially imparts a warm bias onto paleotemperatures, however the apparatus used for analyzing fluid inclusions does not appear to significantly alter the material. We conclude our approach using fluid inclusion analysis and dual‐clumped isotopes has the potential to resolve many ambiguities in interpreting climate records.
    Description: Key Points: We explore the behavior of dual‐clumped and fluid‐inclusion isotope paleothermometers during thermal alteration. Different conditions during diagenesis may result in discrepant paleotemperature estimates, which may be used to identify altered records. Hand‐drilling belemnites produces sufficient heat to reset paleotemperatures, but the heat during analysis of fluid inclusions does not.
    Description: DFG
    Description: https://doi.org/10.5281/zenodo.7565557
    Keywords: ddc:551.9 ; diagenesis ; clumped isotopes ; fluid inclusions ; numerical modeling
    Language: English
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  • 4
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    Zur Land- und Bodendegradation – ein Rück- und Ausblick deutschland- und weltweit (2023)
    Details
    Publication Date: 2023-06-12
    Description: Soils and landscapes are bridges of space and time, as they simultaneously and authentically show essential aspects that were previously separated by time and space (such as cultural and activity-related aspects from past and present) to the trained observer - albeit only in excerpts. Therefore, this article presents a series of impact indicators for soil changes, starting with extreme (anthropogenic) interventions and ending with equally extreme ("natural") events. An essential difference to specifically planning-relevant or human ecological concepts, which, for example, specify land use/load categories, is that the following impact indicators perceive soils as a phenomenon in themselves and do not define them through attributed functions. Particular attention is focused on their changeability and vital development potential, as well as on their property as a sphere of penetration of living and material things, with emphasis on the noetic effect. The intervention or event spaces on the earth's surface can be differentiated quantitatively through the type, strength, and duration of the phenomena. The intensity of all processes can be described by amplitude (the strength of the interventions/events) and frequency (the repetition rate of the interventions/events) and can be specifically identified and quantified by, for example, material inputs or outputs per unit of time. For the first time, there would be a system for measuring the ecological quality of anthropogenic land use, which could serve as an "alert system for the external technological culture," and could help us become aware of our "inner" culture.
    Description: research
    Keywords: ddc:550 ; Boden ; Landschaft ; Bodendegeneration ; Deutschland ; Anthropogene Bodenveränderung
    Language: German
    Type: doc-type:article
    Format: 9
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  • 5
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    Investigation of a Dissipating Mesospheric Bore Using Airglow Imager and Direct Numerical Simulation (2023)
    Details
    Publication Date: 2023-10-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Atmospheric gravity waves play an important role in driving the dynamics of the Mesosphere and Lower Thermosphere and the basic structure of this region is determined by momentum deposition of these waves. Mesospheric bores are a type of non‐linear response that cause the amplification of gravity wave, due to trapping, that is characterized by a propagating step‐like jump followed by undulating waves. They require a stable layer or duct to travel horizontally with little attenuation thereby capable of transporting wave energy and momentum over larger distances. We present a prominent bright undular bore event observed in the mesospheric O(〈sup〉1〈/sup〉S), O〈sub〉2〈/sub〉, and OH emission layers on 16 March 2021 over Germany. A striking feature of this observation is the capture of bore's rapid dissipation around the center of the imager's field of view. The vertical temperature profile obtained from the satellite data indicates the presence of temperature inversion layer which acted as a thermal duct for the bore propagation. In addition, we have performed idealized two dimensional direct numerical simulations (DNS) of Navier‐Stokes equations under Boussinesq approximation. The DNS results reproduce many important characteristics of the observed airglow event like the nonlinear wave‐steepening, number of trailing waves, and its dissipation by implementing a thermal duct and a wave‐like perturbation. Furthermore, the DNS results also indicate that the duct width and amplitude of the initial perturbation have a considerable effect on the bore morphology.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Observation of a mesospheric bright bore event that dissipated within the field of view〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The duct that enabled the bore propagation was near the O(〈sup〉1〈/sup〉S) emission layer based on the observational data〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The majority of the observed features are reproduced with idealized 2D direct numerical simulations using Boussinesq approximation〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: https://doi.org/10.22000/809
    Description: http://sirius.bu.edu/data/
    Description: http://saber.gats-inc.com/coin.php
    Keywords: ddc:551.5 ; bores ; direct numerical simulations ; gravity waves ; inversion layers
    Language: English
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  • 6
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    On the Temperature Dependence of the Cloud Ice Particle Effective Radius—A Satellite Perspective (2023)
    Details
    Publication Date: 2023-12-05
    Description: Cloud ice particle effective radius in atmospheric models is usually parametrized. A widely‐used parametrization comprises a strong dependence on the temperature. Utilizing available satellite‐based estimates of both cloud ice particle effective radius and cloud‐top temperature we evaluate if a similar temperature‐dependence exists in these observations. We find that for very low cloud‐top temperatures the modeled cloud ice particle effective radius generally agrees on average with satellite observations. For high sub‐zero temperatures however, the modeled cloud ice particle effective radius becomes very large, which is not seen in the satellite observations. We conclude that the investigated parametrization for the cloud ice particle effective radius, and parametrizations with a similar temperature dependence, likely produce systematic biases at the cloud top. Supporting previous studies, our findings suggest that the vertical structure of clouds should be taken into account as factor in potential future updates of the parametrizations for cloud ice particle effective radius.
    Description: Plain Language Summary: Atmospheric models are often used to diagnose and predict the atmospheric state including clouds. One very important property of clouds that consist of ice particles is the cloud ice particle effective radius. This ice effective radius is based on assumptions about the size and shapes of the ice particles in clouds, and thus parametrized, and is one of the important variables needed for calculating the effect of clouds on electromagnetic radiation, in particular on the solar radiation that enters the Earth's atmosphere. In our study we found that the parametrized ice effective radius agrees well on average and global scale with the ice effective radius inferred from satellite observations for cold clouds. However, we also found that for warmer ice clouds the parametrized ice effective radius is much higher than in satellite observations. Our study suggests that parametrizations of the ice effective radius used in atmospheric models show potential for improvements.
    Description: Key Points: Comparisons of modeled cloud ice particle effective radius with satellite observations are presented. For very low cloud temperatures the modeled cloud ice particle effective radius agrees on average with satellite observations. Modeled large cloud ice particle effective radii for high sub‐zero temperatures are not found in satellite observations.
    Description: European Space Agency http://dx.doi.org/10.13039/501100000844
    Description: https://doi.org/10.5281/zenodo.7445152
    Description: https://doi.org/10.5676/DWD/ESA_Cloud_cci/AVHRR-PM/V003
    Description: https://doi.org/10.5676/EUM_SAF_CM/CLARA_AVHRR/V002
    Description: http://doi.org/10.5067/MODIS/MYD06_L2.NRT.061
    Keywords: ddc:551.5 ; clouds ; ice particle effective radius ; parametrization ; model ; satellite observations
    Language: English
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  • 7
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    The Climatology of Elevated Stratopause Events in the UA‐ICON Model and the Contribution of Gravity Waves (2023)
    Details
    Publication Date: 2023-11-23
    Description: The climatologies of the stratopause height and temperature in the UA‐ICON model are examined by comparing them to 17‐years (2005–2021) of Microwave Limb Sounder (MLS) observations. In addition, the elevated stratopause (ES) event occurrence, their main characteristics, and driving mechanisms in the UA‐ICON model are examined using three 30‐year time‐slice experiments. While UA‐ICON reasonably simulates the large‐scale stratopause properties similar to MLS observations, at polar latitudes in the Southern Hemisphere the stratopause is ∼8 K warmer and ∼3 km higher than observed. A time lag of about two months also exists in the occurrence of the tropical semiannual oscillation of the stratopause compared to the observations. ES events occur in ∼20% of the boreal winters, after major sudden stratospheric warmings (SSWs). Compared to the SSWs not followed by ES events (SSW‐only), the ES events are associated with the persistent tropospheric forcing and prolonged anomalies of the stratospheric jet. Our modeling results suggest that the contributions of both gravity waves (GW)s and resolved waves are important in explaining the enhanced residual circulation following ES events compared to the SSW‐only events but their contributions vary through the lifetime of ES events. We emphasize the role of the resolved wave drag in the ES formation as in the sensitivity test when the non‐orographic GW drag is absent, the anomalously enhanced resolved wave forcing in the mesosphere gives rise to the formation of the elevated stratopause at about 85 km.
    Description: Plain Language Summary: Using 17 years (2005–2021) of Microwave Limb Sounder (MLS) observations, we show negative (cooling stratopause temperatures and decreasing stratopause heights) trends in most regions and seasons. The largest negative trend in the stratopause temperature (by considering all regions and all seasons) is found in the Southern Hemisphere (SH)'s polar region during austral spring. The seasonal average of cooling rates is comparable in the mid‐latitudes of Northern Hemisphere and SH. In the UA‐ICON simulations, the elevated stratopause events (ESEs) occur after major sudden stratospheric warmings (SSWs). ESEs frequency is 2 events per decade in UA‐ICON simulations. Our results show that the wind reversal is stronger and long‐lasting in the ESEs compared to SSW‐only events. In addition, the easterlies extend to the mesosphere in the composites of ESEs, but the reversed winds are limited to below 60 km in the case of SSW‐only events. We show that the non‐orographic gravity wave drag induces anomalous residual circulation after SSW that causes the ESEs. We also show that the ESEs form even in the absence of non‐orographic gravity wave drag. In this case, the anomalous residual circulation is due to the anomalously enhanced resolved wave forcing in the mesosphere that gives rise to the formation of the ESEs at about 85 km.
    Description: Key Points: The largest stratopause trend is found in the Southern Hemisphere polar region during austral springbased on Microwave Limb Sounder observations. The suppression of gravity waves in UA‐ICON reveals the importance of resolvedwaves and their ability to compensate missing drag. In the polar regions, the simulated stratopause is too warm and the tropical semi‐annual oscillation is about two months out of phase.
    Description: Deutsche Forschungsgemeinschaft
    Description: Transregional Collaborative Research Centre
    Description: GACR
    Description: MS‐GWaves
    Description: https://code.mpimet.mpg.de/projects/iconpublic
    Description: https://doi.org/10.26050/WDCC/UAICON_timesl_ctrl
    Description: https://doi.org/10.26050/WDCC/UAICON_timesl_nonon
    Description: https://doi.org/10.26050/WDCC/UAICON_timesl_nosso
    Keywords: ddc:551.5 ; gravity waves ; elevated stratopause ; middle atmosphere
    Language: English
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  • 8
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    Toward Better Constrained Scattering Models for Natural Ice Crystals in the Visible Region (2023)
    Details
    Publication Date: 2023-11-23
    Description: In this work, we introduce a method for constraining the optical scattering models of natural ice crystals based on in‐situ measurements. Specifically the measured angular scattering functions for ice crystals can be used to compute a set of the asymmetry parameter (g) and the corresponding complexity parameter (C〈sub〉p〈/sub〉). It is demonstrated that the g‐C〈sub〉p〈/sub〉 relation can give valuable information on the morphology of ice crystal. The validity of the methods is shown from theoretical perspectives and the geometric‐optics ray‐tracing simulations. As an application, we investigate rimed ice crystals from in‐situ measurements and found that (a) the C〈sub〉p〈/sub〉 parameter is very well correlated with the surface riming degree and (b) only those models with both roughness and internal scattering can explain the observed g‐C〈sub〉p〈/sub〉 relation for rimed particles.
    Description: Plain Language Summary: Light scattering models of ice crystals are important for remote sensing and climate studies. Yet, many physical parameters, such as shape, aspect ratio, and inhomogeneity of the ice crystal can impose significant uncertainty in the single‐scattering properties predicted by light scattering models. To reduce such uncertainty and constrain the physical parameters in modeling, we introduce a novel method by analyzing the in‐situ measurement of the phase functions of ice crystals. We demonstrate the validity and usefulness of the method using both geometric ray‐tracing simulations and a case study on rimed crystals from two campaigns.
    Description: Key Points: A method is developed for analyzing in‐situ polar nephelometer measurements, aiming for constraining the light scattering models for natural ice crystal. Validity of the method is demonstrated by geometric‐optics ray‐tracing simulations and in‐situ measurements. A case study of rimed crystals measured in‐situ during two aircraft field campaigns using the Particle Habit Imaging and Polar Scattering probe is presented.
    Description: Helmholtz Association's Initiative and Networking Fund
    Description: https://doi.org/10.1594/PANGAEA.902611
    Description: https://doi.org/10.5065/D6639NKQ
    Description: https://zenodo.org/badge/latestdoi/440147565
    Keywords: ddc:551.5 ; light scattering ; ice crystals
    Language: English
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  • 9
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    Triple‐Element Stable Isotope Analysis of Chloromethane Emitted by Royal Fern and Degraded by Club Moss (2023)
    Details
    Publication Date: 2023-09-12
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Chloromethane (CH〈sub〉3〈/sub〉Cl) is the most abundant natural chlorinated organic compound in the atmosphere playing an important role in catalyzing stratospheric ozone loss. Vegetation emits the largest amounts of CH〈sub〉3〈/sub〉Cl to the atmosphere but its source strength is highly uncertain leading also to large uncertainties in the global budget of CH〈sub〉3〈/sub〉Cl. Triple‐element stable isotope analysis may help to reduce uncertainties because it provides additional process‐level information compared to conventional quantification methods. In this study we performed experiments to obtain a first triple‐elemental isotopic fingerprint (〈sup〉2〈/sup〉H, 〈sup〉13〈/sup〉C, 〈sup〉37〈/sup〉Cl) of CH〈sub〉3〈/sub〉Cl emitted by a relevant plant species (royal fern, 〈italic〉Osmunda regalis〈/italic〉). Isotopic values of all three elements showed considerable differences compared to isotopic values of industrially manufactured CH〈sub〉3〈/sub〉Cl which bodes well for future applications to distinguish individual sources. Isotopic analysis of potential precursors (rain, methoxy groups) of CH〈sub〉3〈/sub〉Cl in plants revealed no measurable change of hydrogen and chlorine isotopic ratios during formation which may provide a simpler route to estimate the isotopic composition of CH〈sub〉3〈/sub〉Cl emissions. Plant degradation experiments of CH〈sub〉3〈/sub〉Cl were carried out with club moss (〈italic〉Selaginella kraussiana〈/italic〉) revealing significant isotopic fractionation for all three elements. The fractionation pattern characterized by epsilon and lambda is inconsistent with known biotic dechlorination reactions indicating a yet unreported biotic degradation mechanism for CH〈sub〉3〈/sub〉Cl. Overall, this study provides first insights into the triple‐elemental isotopic fingerprint of plant emissions and degradation. The results may represent important input data for future isotope‐based models to improve global budget estimates of CH〈sub〉3〈/sub〉Cl and to explore the yet unknown degradation pathways.〈/p〉
    Description: Plain Language Summary: Chloromethane is the most abundant chlorinated organic compound in the atmosphere. It contributes to the destruction of the ozone layer that protects us from skin cancer and genetic damage. Currently, we do not have a good understanding of the sources and removal processes of chloromethane in the atmosphere. In this paper, we use a technique that takes advantage of the different varieties of a chemical element. These so‐called isotopes behave differently during chemical reactions that lead to individual isotopic fingerprints depending on the source or removal process. We used isotopic fingerprints of all three chemical elements in chloromethane and showed that chloromethane produced by a plant (royal fern) differs substantially from chloromethane manufactured by industry. Other plant species such as club moss are able to remove chloromethane from the atmosphere but it is often not clear how this occurs. Isotopic analysis revealed that the studied club moss uses a unique, thus far unknown, way to break down chloromethane. This study demonstrates how information extracted from isotopic fingerprints will help to improve our understanding of sources and removal processes of chloromethane in the atmosphere. It can help to better predict how ozone destruction in the stratosphere affects us in the future.〈/p〉
    Description: Key Points: First triple‐element isotopic characterization of plant CH〈sub〉3〈/sub〉Cl emission and degradation. Plant degradation experiments suggest another yet unknown transformation pathway. Important input data for future isotope based models to improve understanding of global CH〈sub〉3〈/sub〉Cl budget.
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.48758/ufz.13388
    Keywords: ddc:551.9 ; CH3Cl ; ozone depletion ; isotopes ; plant emissions ; halogens
    Language: English
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  • 10
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    The Sensitivity of Moisture Flux Partitioning in the Cold‐Point Tropopause to External Forcing (2023)
    Details
    Publication Date: 2023-07-20
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The dryness of the stratosphere is the result of air entering through the cold tropical tropopause layer (TTL). However, our understanding of the moisture flux partitioning into water vapor and frozen hydrometeors is incomplete. This raises concerns regarding the ability of General Circulation Models to accurately predict changes in stratospheric water vapor following perturbations in the radiative budget due to volcanic aerosol or stratospheric geoengineering. We present the first results using a global storm‐resolving model investigating the sensitivity of moisture fluxes within the TTL to an additional heating source. We address the question how the partitioning of moisture fluxes into water vapor and frozen hydrometeors changes under perturbations. The analysis reveals the resilience of the TTL, keeping the flux partitioning constant even at an average cold‐point warming exceeding 8 K. In the control and perturbed simulations, water vapor contributes around 80% of the moisture entering the stratosphere.〈/p〉
    Description: Plain Language Summary: The stratosphere is a dry region since moisture entering it from below has to pass the cold‐point, a temperature minimum between troposphere and stratosphere. The low temperatures lead to ice formation and sedimentation of moisture. Frozen moisture within clouds rising above the cold‐point tropopause can pass this temperature barrier and be injected into the stratosphere, where temperatures increase again, promoting the melting and sublimation of ice crystals. However, little is known about the sensitivity of the split of moisture entering the stratosphere into frozen and non‐frozen moisture, especially under external influences, like heating by volcanic aerosol or stratospheric geoengineering efforts. Convective parameterizations in conventional simulations can lead to biases. The emerging km‐scale simulations, which explicitly resolve the physical processes, offer the unique possibility to study moisture fluxes under external forcing while circumventing the downsides of parameterizations. Here, the sensitivity of the moisture flux partitioning into non‐frozen and frozen components to an additional heating source is studied for the first time in global storm‐resolving simulations. The analysis reveals an unaltered flux partitioning even at an average cold‐point warming exceeding 8 K. In the control and perturbed simulations, water vapor contributes around 80% of the moisture entering the stratosphere.〈/p〉
    Description: Key Points:Water vapor dominates the stratospheric moisture budget with a contribution of around 80% in global storm‐resolving simulation. The partitioning of stratospheric moisture fluxes into vapor and frozen hydrometeors remains stable under large temperature perturbations.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Fueglistaler Group
    Keywords: ddc:551.5 ; stratospheric water vapor ; tropopause ; perturbation ; moisture budget ; geoengineering ; volcano
    Language: English
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  • 11
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    Lagrangian description of the atmospheric flow from Eulerian tracer advection with relaxation (2023)
    John Wiley & Sons, Ltd | Chichester, UK
    Details
    Publication Date: 2023-07-28
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The Lagrangian representation of fluid flows offers a natural perspective to study many kinds of physical mechanisms. By contrast, the Eulerian representation is more convenient from a diagnostic point of view. This article attempts to combine elements of both worlds by proposing an Eulerian method that allows one to extract Lagrangian information about the atmospheric flow. The method is based on the offline advection of passive tracer fields and includes a relaxation term. The latter device allows one to run the integration in a continuous fashion without the need for reinitialization. As a result one obtains accumulated Lagrangian information, for example, about the recent parcel displacement or the recent parcel‐based diabatic heating, at each point of an Eulerian grid at any time step. The method is implemented with a pseudospectral algorithm suitable for gridded global atmospheric data and compared with the more traditional trajectory method. The method's utility is demonstrated on the basis of a few examples, which relate to cloud formation and the development of temperature anomalies. The examples highlight that the method provides a convenient diagnostic of parcel‐based changes, paving an intuitive way to explore the physical processes involved. Due to its gridpoint‐based nature, the proposed method can be applied to large data sets in a straightforward and computationally efficient manner, suggesting that the method is particularly useful for climatological analyses.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The Lagrangian representation of fluid flows offers the most natural perspective to study many kinds of physical mechanisms; by contrast, the Eulerian representation is more convenient from a diagnostic point of view. This article attempts to combine elements of both worlds by proposing an Eulerian method that allows one to extract Lagrangian information about the atmospheric flow. The method enables one to easily produce a sequence of maps showing accumulated Lagrangian changes. 〈boxed-text position="anchor" id="qj4453-blkfxd-0001" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:00359009:media:qj4453:qj4453-toc-0001"〉 〈/boxed-text〉〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.5 ; air‐parcel approach ; atmospheric fluid dynamics ; atmospheric transport ; Eulerian tracer technique ; Lagrangian analysis ; Lagrangian tracking ; synoptic‐scale meteorology ; trajectories
    Language: English
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  • 12
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    Oblique Propagation and Refraction of Gravity Waves Over the Andes Observed by GLORIA and ALIMA During the SouthTRAC Campaign (2023)
    Details
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Gravity waves (GW) carry energy and momentum from the troposphere to the middle atmosphere and have a strong influence on the circulation there. Global atmospheric models cannot fully resolve GWs, and therefore rely on highly simplified GW parametrizations that, among other limitations, account for vertical wave propagation only and neglect refraction. This is a major source of uncertainty in models, and leads to well‐known problems, such as the late break‐up of polar vortex due to the “missing” GW drag around 60°S. To investigate these phenomena, GW observations over Southern Andes were performed during SouthTRAC aircraft campaign. This paper presents measurements from a SouthTRAC flight on 21 September 2019, including 3‐D tomographic temperature data of the infrared limb imager GLORIA (8–15 km altitude) and temperature profiles of the ALIMA lidar (20–80 km altitude). GLORIA observations revealed multiple overlapping waves of different wavelengths. 3‐D wave vectors were determined from the GLORIA data and used to initialize a GW ray‐tracer. The ray‐traced GW parameters were compared with ALIMA observations, showing good agreement between the instruments and direct evidence of oblique (partly meridional) GW propagation. ALIMA data analysis confirmed that most waves at 25–40 km altitudes were indeed orographic GWs, including waves seemingly upstream of the Andes. We directly observed horizontal GW refraction, which has not been achieved before SouthTRAC. Refraction and oblique propagation caused significant meridional transport of horizontal momentum as well as horizontal momentum exchange between waves and the background flow all along the wave paths, not just in wave excitation and breaking regions.〈/p〉
    Description: Plain Language Summary: Gravity waves (GW) are temperature and wind disturbances in the atmosphere that carry energy and momentum from troposphere to the middle atmosphere and have a strong influence on the circulation there. Global atmospheric models currently cannot adequately represent GW propagation: the facts that GWs can change wavefront orientation (refraction) and travel horizontally (and not just vertically) are typically neglected. This leads to important known model inaccuracies, for example, too low temperatures in southern polar regions. SouthTRAC aircraft measurement campaign observed GWs exited by wind flow over the Southern Andes in September–November 2019. Temperature measurements were conducted with the IR spectrometer GLORIA (provided 3‐D data) and the ALIMA lidar instrument. GLORIA data revealed many overlapping waves of different wavelengths, their propagation further up was investigated using ray‐tracing. Most waves seen by GLORIA were ray‐traced to ALIMA observations where their parameters were confirmed, thus validating our ray‐tracing technique and the two instruments against each other. We directly observed wave propagation in both vertical and horizontal directions and change in horizontal wave orientation (the latter was not seen before SouthTRAC). Due to these phenomena, many GWs carried momentum that had different directions and was deposited in a different location than most models typically predict.〈/p〉
    Description: Key Points: High‐resolution multi‐instrument measurements of orographic gravity waves (GWs) over the Andes were carried out. Oblique GW propagation and strong horizontal refraction were observed and analyzed using ray‐tracing. Significant redistribution of horizontal momentum due to horizontal refraction was observed all along the path of wave propagation.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: German Ministry for Education and Research
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://www.ecmwf.int/en/forecasts/datasets
    Description: https://doi.org/10.5281/zenodo.7155729
    Keywords: ddc:551.5 ; gravity waves ; refraction ; remote sensing ; lidar ; ray‐tracing
    Language: English
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  • 13
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    A Note on Aerosol Processing by Droplet Collision‐Coalescence (2023)
    Details
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The processing of aerosol by droplet collision‐coalescence is analyzed in three‐dimensional simulations of drizzling stratocumulus using a Lagrangian cloud model for the representation of aerosol and cloud microphysics. Collision‐coalescence processing is shown to create a characteristic bimodality in the aerosol size distribution. We show that the large‐scale dynamics of the stratocumulus‐topped boundary layer are key to understanding the amount of time available for collision‐coalescence processing. The large‐scale dynamics enable aerosol particles to repeat a cycle of droplet condensation, collision‐coalescence, and evaporation, which causes a steady increase in aerosol size. This process is continued until the aerosol grows so large that droplet growth is substantially accelerated and multiple collisions occur within one cycle, forming precipitation‐sized droplets that are lost to the surface, including the aerosol. An analytical relationship is derived that captures the fundamental shape of the processed aerosol size distribution.〈/p〉
    Description: Plain Language Summary: Clouds consist of cloud droplets, and cloud droplets grow from aerosol particles, which are tiny particles suspended in the atmosphere. But clouds also modify aerosol particles. This study shows that the merging of cloud droplets, a process related to the production of rain, can lead to larger aerosol particles, causing characteristic changes in the aerosol size distribution that are revealed in this study. These changes are important because larger aerosol particles will create cloud droplets more easily, with commensurate effects on the development of clouds.〈/p〉
    Description: Key Points: The effect of droplet collision‐coalescence on the aerosol size distribution is analyzed in three‐dimensional simulations. Collision‐coalescence processing introduces a characteristic bimodality in the aerosol size distribution. The large‐scale stratocumulus dynamics are key to the development of a stable population of processed aerosol particles.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Climate Program Office http://dx.doi.org/10.13039/100007298
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: http://rossby.msrc.sunysb.edu/SAM.html
    Description: https://doi.org/10.5281/zenodo.7734008
    Keywords: ddc:551.5 ; clouds ; aerosol ; processing ; collision
    Language: English
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  • 14
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    Momentum Flux and Vertical Wind Power Spectral Characteristics in the Troposphere and Lower Stratosphere Over Andøya, Norway as Observed by MAARSY (2023)
    Details
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉We used the tropospheric and lower stratospheric 3D winds for four consecutive years (2017–2020) to study the momentum flux (MF) and vertical wind power spectra (VWP) over Andøya, Norway (69.30°N, 16.04°E) using the Middle Atmosphere Alomar Radar System. The spectra range from 3.5 days〈sup〉−1〈/sup〉 > 〈italic〉f〈/italic〉 > 30 min〈sup〉−1〈/sup〉, which are categorized in terms of observed/ground‐based frequency (as the local inertial period is 13 h over Andøya), height ranges, and seasons. Our results indicate for the first time that (a) both the zonal and meridional MF display peaks around the inertial period (13 h) in the troposphere (1.80–12.00 km) during all seasons (with some exceptions), while VWP exhibits such features in the whole height range (1.80–18.00 km), (b) the minimum variability in MF, VWP, and kinetic energy is observed during summer, and (c) both the MF and VWP demonstrate height variation with maximum deviations below the tropopause.〈/p〉
    Description: Plain Language Summary: The wind measurements are used to study the height and seasonal variation of momentum flux and vertical wind power spectra during 2017–2020. We report for the first time that both the momentum flux and vertical wind power spectra depict more variations in the tropospheric heights (around 1.80–7.20 km), below the tropopause, with the minimum amplitudes in the summer months (June–July–August). Moreover, long‐period oscillations have more energy than short‐period oscillations, and therefore, contribute more to the energy or flux transfer from the lower to the higher atmosphere. The month versus height profile of kinetic energy also portrays a similar feature with considerably more magnitude for the long‐period oscillations than the short‐period ones. The kinetic energy displays an enhancement of magnitude near the tropopause (∼5.00–10.00 km).〈/p〉
    Description: Key Points: The zonal and meridional momentum flux spectra exhibit a peak around the inertial period of 13 h in the troposphere (1.80–12.00 km). Height profiles of momentum flux, vertical wind power spectra, and kinetic energy display seasonal variation with a minimum during summer. The maximum variability of momentum flux and vertical wind power spectra is noticed below tropopause and decreases with increasing height.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://doi.org/10.22000/766
    Keywords: ddc:551.5 ; atmospheric gravity waves ; momentum flux ; power spectra ; kinetic energy
    Language: English
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  • 15
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    Systematic and Temporal Geochemical Changes in the Upper Deccan Lavas: Implications for the Magma Plumbing System of Flood Basalt Provinces (2023)
    Details
    Publication Date: 2023-07-19
    Description: Large Igneous Provinces (LIPs) are unusual volcanic events in which massive amounts of melt (∼106 km3) erupt in relatively short time periods (〈106 years). Most LIP magmas have undergone extensive fractional crystallization and crustal contamination, but the crustal magmatic plumbing systems and the processes triggering eruptions are poorly understood. We present new major and trace element and radiogenic isotope data for 43 individual lava flows from a continuous 1,200 m thick stratigraphic profile through the upper, most voluminous part of the Deccan LIP (Bushe to Mahabaleshwar Formations). Eruption rates for this section are constrained by published paleomagnetic directions and absolute U‐Pb ages for zircons from weathered flow tops exposed in the profile. We find four magmatic sequences each lasting ∼104–∼105 years during which major and trace element compositions change systematically, followed by an abrupt change in geochemistry at the start of a new sequence. Within each sequence, the MgO content and proportion of crustal contamination decrease progressively, indicating a continuous replenishment of the associated magma reservoirs with less contaminated but more evolved melts. These geochemical signatures are best explained by repeated episodes of melt recharge, mixing, and eruption of variably evolved magmas originating from relatively small magma reservoir located in different crustal levels.
    Description: Plain Language Summary: Volcanism occurs predominantly at plate boundaries, either at mid‐ocean ridges or subduction zones, where most mantle melts are produced. However, the Earth's history is punctuated by volcanic events which are not related to plate boundary processes and during which large amounts of melt erupt (∼106 km3) in relatively short periods of time (〈106 years). These Large Igneous Provinces (LIPs) are associated with the activity of mantle plumes and eruption rates during their main stages are significantly higher than those of today's largest magmatic systems. However, since no LIP is currently active, the architecture of the associated plumbing systems is relatively unknown. In order to understand the magmatic processes during the emplacement of a LIP, we generated geochemical data from a continuous stratigraphic profile covering the most voluminous stage of the ∼66 Ma Deccan LIP. By combining these new data with published paleomagnetic directions and absolute U‐Pb ages for zircons, we found four eruption sequences each lasting ∼104–∼105 years. During these sequences, geochemical compositions change systematically, which is best explained by repeated episodes of melt recharge, mixing, and eruption of variably evolved magmas originating from relatively small magma reservoirs located at different crustal levels.
    Description: Key Points: Four recharge‐crystallization‐eruption sequences fed the most voluminous Deccan lava. Magmatic plumbing system with interconnected small‐ to medium‐sized magma reservoirs. Complex emplacement history including multiple stages of ascent, mixing, and storage.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.26022/IEDA/112672
    Keywords: ddc:551.9 ; intraplate processes ; magma chamber processes ; magma genesis and partial melting ; major and trace element geochemistry ; radiogenic isotope geochemistry
    Language: English
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  • 16
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    Authigenic and Detrital Carbonate Nd Isotope Records Reflect Pulses of Detrital Material Input to the Labrador Sea During the Heinrich Stadials (2023)
    Details
    Publication Date: 2023-07-19
    Description: Limited constraints on the variability of the deep‐water production in the Labrador Sea complicate reconstructions of the strength of the Atlantic Meridional Overturning Circulation (AMOC) during the Late Quaternary. Large volumes of detrital carbonates were repeatedly deposited in the Labrador Sea during the last 32 kyr, potentially affecting radiogenic Nd isotope signatures. To investigate this the Nd isotope compositions of deep and intermediate waters were extracted from the authigenic Fe‐Mn oxyhydroxide fraction, foraminiferal coatings, the residual silicates and leachates of dolostone grains. We provide a first order estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea. During the Last Glacial Maximum the Nd isotope signatures in the Labrador Sea would allow active water mass mixing with more radiogenic ɛNd values (−12.6 and −14) prevailing in its eastern part whereas less radiogenic values (ɛNd ∼ −18.4) were found on the western Labrador slope. The deposition of detrital carbonates during Heinrich stadials (2,1) was accompanied by negative detrital and authigenic Nd isotope excursions (ɛNd ∼ −31) that were likely controlled by dissolution of dolostone or dolostone associated mineral inclusions. This highly unradiogenic signal dominated the authigenic phases and individual water masses in the Labrador Sea, serving as potential source of highly unradiogenic Nd to the North Atlantic region, while exported southward. The Holocene authigenic ɛNd signatures of the coatings and leachates significantly differed from those of the detrital silicates, approaching modern bottom water mass signatures during the Late Holocene.
    Description: Plain Language Summary: The Labrador Sea is an important region for deep water formation and for the ocean circulation in the Atlantic region. Over the last 32 thousand years, numerous discharges from melting glaciers added freshwater to the Labrador Sea which could help understand the future effects of current melting glaciers. This information is necessary to better constrain climate predictions in order to gauge the effects on the Global Ocean Water Circulation. However, past deep water production in the Labrador is still poorly constrained, complicating reconstruction of the Atlantic Meridional Overturning Circulation on different timescales. In this study we investigated changes in deep and intermediate water mass circulation patterns over the last 32 kyr based on the radiogenic Nd isotope compositions that serve as a water mass circulation proxy. Analysis of four marine sediment cores show that the deposition of large volumes of detrital carbonates during studied period had a large effect on the recorded in the sediment column signals. New data suggest active water mass circulation during the maximum extent of glacial ice sheets. The modern day ocean circulation patterns have emerged during the Late Holocene (6 ka).
    Description: Key Points: Estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea. Dissolution of detrital dolostones in the water column during Heinrich stadials at least partially controlled ɛNd signatures. During the LGM generally more radiogenic signatures possibly indicate active water mass advection and mixing in the Labrador Sea.
    Description: GEOMAR Helmholtz‐Zentrum für Ozeanforschung Kiel http://dx.doi.org/10.13039/501100003153
    Description: Kiel University
    Description: https://doi.org/10.1594/PANGAEA.952659
    Keywords: ddc:551.9 ; Labrador Sea ; Late Quaternary ; Paleoceanography ; neodymium isotopes ; dolostone ; AMOC ; carbonate dissolution ; Heinrich stadials
    Language: English
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  • 17
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    Fitting Cumulus Cloud Size Distributions From Idealized Cloud Resolving Model Simulations (2023)
    Details
    Publication Date: 2023-07-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Whereas it is now widely accepted that cumulus cloud sizes are power‐law distributed, characteristic exponents reported in the literature vary greatly, generally taking values between 1 and >3. Although these differences might be explained by variations in environmental conditions or physical processes organizing the cloud ensembles, the use of improper fitting methods may also introduce large biases. To address this issue, we propose to use a combination of maximum likelihood estimation and goodness‐of‐fit tests to provide more robust power‐law fits while systematically identifying the size range over which these fits are valid. The procedure is applied to cloud size distributions extracted from two idealized high‐resolution simulations displaying different organization characteristics. Overall, power‐laws are found to be outperformed by alternative distributions in almost all situations. When clouds are identified based on a condensed water path threshold, using power‐laws with an exponential cutoff yields the best results as it provides superior fits in the tail of the cloud size distributions. For clouds identified using a combination of water content and updraft velocity thresholds in the free troposphere, no substantial improvement over pure power‐laws can be found when considering more complex two‐parameter distributions. In this context however, exponential distributions provide results that are as good as, if not better than power‐laws. Finally, it is demonstrated that the emergence of scale free behaviors in cloud size distributions is related to exponentially distributed cloud cores merging as they are brought closer to each other by underlying organizing mechanisms.〈/p〉
    Description: Plain Language Summary: Clouds constitute an important element of the climate system reflecting incoming solar radiation and emitting infra‐red radiation that heats the atmosphere. The net radiative impact of clouds however depends on many factors including their size. It is thus of prime importance to characterize the size of clouds, in particular convective clouds, and understand the underlying processes controlling them. In this study, a numerical model is used to simulate two convective situations at horizontal resolutions providing a fine description of cloud processes. After identifying individual clouds and calculating their size, statistical methods are employed to characterize the cloud size distributions. Depending on the situation, cloud size distributions are found to be best represented by either power‐laws with an exponential cutoff or exponential functions. Pure power‐laws, which constitute the most popular model used to represent cloud size distributions, are generally found to yield poorer fits. Finally, it is demonstrated that power‐laws in cloud size distributions emerge when individual cloud cores, that are exponentially distributed in size, are brought closer to each other and merge as the cloud ensemble organizes.〈/p〉
    Description: Key Points: A combination of statistical methods is used to fit cloud size distributions from two simulated convective cloud ensembles.〈/p〉〈/list-item〉 〈list-item〉〈p〉Depending on the situation, exponential distributions and power‐laws with an exponential cutoff may constitute superior alternatives to pure power‐laws.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The merging of individual cloud cores is found to control the emergence of power‐law cloud size distributions.〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: https://bitbucket.org/julien_savre/pycloudfit/src/master/
    Description: https://doi.org/10.5281/zenodo.7005140
    Keywords: ddc:551.5 ; Moist convection ; cloud resolving modeling ; cloud size distributions ; cloud merging
    Language: English
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  • 18
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    Do Optically Denser Trade‐Wind Cumuli Live Longer? (2023)
    Details
    Publication Date: 2023-07-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉This study investigates the lifetime and temporal evolution of physical properties of trade‐wind cumuli based on tracking individual clouds in observations with the Advanced Baseline Imager aboard the geostationary GOES‐16 satellite during the “ElUcidating the RolE of Cloud–Circulation Coupling in ClimAte” (EUREC〈sup〉4〈/sup〉A) campaign east of Barbados in winter 2020. A first application of our upgraded cloud‐tracking toolbox to measurements with high spatio‐temporal resolution (2 × 2 km〈sup〉2〈/sup〉 and 1 min) provides probability density functions of lifetime and area of clouds that develop as a consequence of meso‐to‐synoptic scale motions. By separately considering clouds that exist during daytime and live in distinct lifetime intervals, we find that shallow marine cumuli live longer when they cover a larger surface area and show higher cloud optical thickness (COT). Besides the effect of COT, the scale of the atmospheric motions with which the clouds interact is also critical to their lifetime.〈/p〉
    Description: Plain Language Summary: We present a detailed investigation of the lifetime of Caribbean trade‐wind cumulus clouds and the temporal evolution of their physical properties based on geostationary observations with the Advanced Baseline Imager aboard the geostationary GOES‐16 satellite during the “ElUcidating the RolE of Cloud–Circulation Coupling in ClimAte” (EUREC〈sup〉4〈/sup〉A) field experiment in winter 2020. The tracking of 2.7 million individual clouds in measurements with high spatio‐temporal resolution enables the investigation of processes that control the lifetime of shallow marine cumulus (SMC) clouds. Our analysis reveals that SMC clouds live longer when they span over a surface area that exceeds an order of tens of square kilometers. While these clouds show similar median cloud droplet size and number concentration compared to shorter‐lived clouds, they contain more liquid water and, thus, show a COT that is increased by about one third. Besides the effect of COT, we find that the scale of the atmospheric motions with which the clouds interact is also critical to their lifetime.〈/p〉
    Description: Key Points: First study of the life cycle of shallow marine cumulus based on observations with the Advanced Baseline Imager aboard GOES‐16.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Confirmation of the double power law in the distribution of cloud lifetime from measurements with a temporal resolution of 1 minute.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Cloud lifetime is related to large‐scale circulation and affects cloud optical thickness.〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Description: https://observations.ipsl.fr/thredds/catalog/EUREC4A/SATELLITES/GOES-E/2km_01min/2020/catalog.html
    Keywords: ddc:551.5 ; shallow convection ; trade‐wind cumuli ; life cycle ; EUREC4A ; GOES‐16 ABI
    Language: English
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  • 19
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    Partial analysis increments as diagnostic for LETKF data assimilation systems (2023)
    John Wiley & Sons, Ltd | Chichester, UK
    Details
    Publication Date: 2023-07-25
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Local ensemble transform Kalman filters (LETKFs) allow explicit calculation of the Kalman gain, and by this the contribution of individual observations to the analysis field. Though this is a known feature, the information on the analysis contribution of individual observations (partial analysis increment) has not been used as systematic diagnostic up to now despite providing valuable information. In this study, we demonstrate three potential applications based on partial analysis increments in the regional modelling system of Deutscher Wetterdienst and propose their use for optimising LETKF data assimilation systems, in particular with respect to satellite data assimilation and localisation. While exact calculation of partial analysis increments would require saving the large, five‐dimensional ensemble weight matrix in the analysis step, it is possible to compute an approximation from standard LETKF output. We calculate the Kalman gain based on ensemble analysis perturbations, which is an approximation in the case of localisation. However, this only introduces minor errors, as the localisation function changes very gradually among nearby grid points. On the other hand, the influence of observations always depends on the presence of other observations and settings for the observation error and for localisation. However, the influence of observations behaves approximately linearly, meaning that the assimilation of other observations primarily decreases the magnitude of the influence, but it does not change the overall structure of the partial analysis increments. This means that the calculation of partial analysis increments can be used as an efficient diagnostic to investigate the three‐dimensional influence of observations in the assimilation system. Furthermore, the diagnostic can be used to detect whether the influence of additional experimental observations is in accordance with other observations without conducting computationally expensive single‐observation experiments. Last but not least, the calculation can be used to approximate the influence an observation would have when applying different assimilation settings.〈/p〉
    Keywords: ddc:551.5 ; analysis influence ; convective‐scale ; ensemble data assimilation ; localisation ; NWP ; satellite data assimilation
    Language: English
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  • 20
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    Scale interactions between the meso‐ and synoptic scales and the impact of diabatic heating (2023)
    John Wiley & Sons, Ltd | Chichester, UK
    Details
    Publication Date: 2023-07-25
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉For both the meso‐ and synoptic scales, reduced mathematical models give insight into their dynamical behaviour. For the mesoscale, the weak temperature gradient approximation is one of several approaches, while for the synoptic scale the quasigeostrophic theory is well established. However, the way these two scales interact with each other is usually not included in such reduced models, thereby limiting our current perception of flow‐dependent predictability and upscale error growth. Here, we address the scale interactions explicitly by developing a two‐scale asymptotic model for the meso‐ and synoptic scales with two coupled sets of equations for the meso‐ and synoptic scales respectively. The mesoscale equations follow a weak temperature gradient balance and the synoptic‐scale equations align with quasigeostrophic theory. Importantly, the equation sets are coupled via scale‐interaction terms: eddy correlations of mesoscale variables impact the synoptic potential vorticity tendency and synoptic variables force the mesoscale vorticity (for instance due to tilting of synoptic‐scale wind shear). Furthermore, different diabatic heating rates—representing the effect of precipitation—define different flow characteristics. With weak mesoscale heating relatable to precipitation rates of 〈mml:math id="jats-math-1" display="inline" overflow="scroll"〉〈mml:mrow〉〈mml:mi〉𝒪〈/mml:mi〉〈mml:mo stretchy="false"〉(〈/mml:mo〉〈mml:mn〉6〈/mml:mn〉〈mml:mspace width="0.3em"/〉〈mml:mtext〉mm〈/mml:mtext〉〈mml:mo〉·〈/mml:mo〉〈mml:msup〉〈mml:mrow〉〈mml:mi mathvariant="normal"〉h〈/mml:mi〉〈/mml:mrow〉〈mml:mrow〉〈mml:mo form="prefix"〉−〈/mml:mo〉〈mml:mn〉1〈/mml:mn〉〈/mml:mrow〉〈/mml:msup〉〈mml:mo stretchy="false"〉)〈/mml:mo〉〈/mml:mrow〉〈/mml:math〉, the mesoscale dynamics resembles two‐dimensional incompressible vorticity dynamics and the upscale impact of the mesoscale on the synoptic scale is only of a dynamical nature. With a strong mesosocale heating relatable to precipitation rates of 〈mml:math id="jats-math-2" display="inline" overflow="scroll"〉〈mml:mrow〉〈mml:mi〉𝒪〈/mml:mi〉〈mml:mo stretchy="false"〉(〈/mml:mo〉〈mml:mn〉60〈/mml:mn〉〈mml:mspace width="0.3em"/〉〈mml:mtext〉mm〈/mml:mtext〉〈mml:mo〉·〈/mml:mo〉〈mml:msup〉〈mml:mrow〉〈mml:mi mathvariant="normal"〉h〈/mml:mi〉〈/mml:mrow〉〈mml:mrow〉〈mml:mo form="prefix"〉−〈/mml:mo〉〈mml:mn〉1〈/mml:mn〉〈/mml:mrow〉〈/mml:msup〉〈mml:mo stretchy="false"〉)〈/mml:mo〉〈/mml:mrow〉〈/mml:math〉, divergent motions and three‐dimensional effects become relevant for the mesoscale dynamics and the upscale impact also includes thermodynamical effects.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉We develop a two‐scale asymptotic model for the meso‐ and synoptic scales following a weak temperature gradient balance and quasigeostrophic theory, but with explicit scale interactions and dependent on the mesoscale diabatic heating. With weak mesoscale heating, the mesoscale dynamics resembles 2D incompressible vorticity dynamics and the upscale impact on the synoptic scale is only of a dynamical nature. With strong mesoscale heating, divergent motions and 3D effects become relevant for the mesoscale and the upscale impact also includes thermodynamical effects. 〈boxed-text position="anchor" id="qj4456-blkfxd-0001" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:00359009:media:qj4456:qj4456-toc-0001"〉
    Description: German Research Foundation (DFG)
    Keywords: ddc:551.5 ; asymptotics ; atmospheric dynamics ; mesoscale ; multiscale scale interactions ; quasigeostrophic ; synoptic scale
    Language: English
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  • 21
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    Stable Carbon Isotope Signature of Methane Released From Phytoplankton (2023)
    Details
    Publication Date: 2023-07-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Aquatic ecosystems play an important role in global methane cycling and many field studies have reported methane supersaturation in the oxic surface mixed layer (SML) of the ocean and in the epilimnion of lakes. The origin of methane formed under oxic condition is hotly debated and several pathways have recently been offered to explain the “methane paradox.” In this context, stable isotope measurements have been applied to constrain methane sources in supersaturated oxygenated waters. Here we present stable carbon isotope signatures for six widespread marine phytoplankton species, three haptophyte algae and three cyanobacteria, incubated under laboratory conditions. The observed isotopic patterns implicate that methane formed by phytoplankton might be clearly distinguished from methane produced by methanogenic archaea. Comparing results from phytoplankton experiments with isotopic data from field measurements, suggests that algal and cyanobacterial populations may contribute substantially to methane formation observed in the SML of oceans and lakes.〈/p〉
    Description: Plain Language Summary: Methane plays an important role in atmospheric chemistry and physics as it contributes to global warming and to the destruction of ozone in the stratosphere. Knowing the sources and sinks of methane in the environment is a prerequisite for understanding the global atmospheric methane cycle but also to better predict future climate change. Measurements of the stable carbon isotope composition of carbon—the ratio between the heavy and light stable isotope of carbon—help to identify methane sources in the environment and to distinguish them from other formation processes. We identified the carbon isotope fingerprint of methane released from phytoplankton including algal and cyanobacterial species. The observed isotope signature improves our understanding of methane cycling in the surface layers of aquatic environments helping us to better estimate methane emissions to the atmosphere.〈/p〉
    Description: Key Points: Stable carbon isotope values of methane emitted from six phytoplankton cultures incubated in the laboratory. Isotope fractionation between methane source signature and biomass of widespread algal and cyanobacterial species. Isotopic patterns of methane released by phytoplankton may be clearly distinguished from methane formed by methanogenic archaea.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Spanish Ministry of Universities
    Description: https://doi.org/10.11588/data/YYLEKU
    Keywords: ddc:551.9 ; methane ; stable isotopes ; phytoplankton ; algae ; cyanobacteria ; methane paradox
    Language: English
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  • 22
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    Detecting Extreme Temperature Events Using Gaussian Mixture Models (2023)
    Details
    Publication Date: 2024-02-12
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Extreme temperature events have traditionally been detected assuming a unimodal distribution of temperature data. We found that surface temperature data can be described more accurately with a multimodal rather than a unimodal distribution. Here, we applied Gaussian Mixture Models (GMM) to daily near‐surface maximum air temperature data from the historical and future Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations for 46 land regions defined by the Intergovernmental Panel on Climate Change. Using the multimodal distribution, we found that temperature extremes, defined based on daily data in the warmest mode of the GMM distributions, are getting more frequent in all regions. Globally, a 10‐year extreme temperature event relative to 1985–2014 conditions will occur 13.6 times more frequently in the future under 3.0°C of global warming levels (GWL). The frequency increase can be even higher in tropical regions, such that 10‐year extreme temperature events will occur almost twice a week. Additionally, we analyzed the change in future temperature distributions under different GWL and found that the hot temperatures are increasing faster than cold temperatures in low latitudes, while the cold temperatures are increasing faster than the hot temperatures in high latitudes. The smallest changes in temperature distribution can be found in tropical regions, where the annual temperature range is small. Our method captures the differences in geographical regions and shows that the frequency of extreme events will be even higher than reported in previous studies.〈/p〉
    Description: Plain Language Summary: Extreme temperature events are unusual weather conditions with exceptionally low or high temperatures. Traditionally, the temperature range was determined by assuming a single distribution, which describes the frequency of temperatures at a given climate using their mean and variability. This single distribution was then used to detect extreme weather events. In this study, we found that temperature data from reanalyses and climate models can be more accurately described using a mixture of multiple Gaussian distributions. We used the information from this mixture of Gaussians to determine the cold and hot extremes of the distributions. We analyzed their change in a future climate and found that hot temperature extremes are getting more frequent in all analyzed regions at a rate that is even higher than found in previous studies. For example, a global 10‐year event will occur 13.6 times more frequently under 3.0°C of global warming. Furthermore, our results show that the temperatures of hot days will increase faster than the temperature of cold days in equatorial regions, while the opposite will occur in polar regions. Extreme hot temperatures will be the new normal in highly populated regions such as the Mediterranean basin.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Extreme temperature events are detected with Gaussian Mixture Models to follow a multimodal rather than a unimodal distribution〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉10‐year temperature extremes will occur 13.6 times more frequently under 3.0°C future warming〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Colder days are getting warmer faster than hotter days in high latitudes, whereas it is the opposite for many regions in low latitudes〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: European Research Council http://dx.doi.org/10.13039/501100000781
    Description: https://github.com/EyringMLClimateGroup/pacal23jgr_GaussianMixtureModels_Extremes
    Description: https://doi.org/10.5281/zenodo.3401363
    Keywords: ddc:551.5 ; extreme events ; Gaussian mixture models ; daily maximum temperatures ; return periods ; bimodal distributions ; multimodal distributions
    Language: English
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  • 23
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    Upper Bounds of Maximum Land Surface Temperatures in a Warming Climate and Limits to Plant Growth (2023)
    Details
    Publication Date: 2024-02-28
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Extremely high land surface temperatures affect soil ecological processes, alter land‐atmosphere interactions, and may limit some forms of life. Extreme surface temperature hotspots are presently identified using satellite observations or deduced from complex Earth system models. We introduce a simple, yet physically based analytical approach that incorporates salient land characteristics and atmospheric conditions to globally identify locations of extreme surface temperatures and their upper bounds. We then provide a predictive tool for delineating the spatial extent of land hotspots at the limits to biological adaptability. The model is in good agreement with satellite observations showing that temperature hotspots are associated with high radiation and low wind speed and occur primarily in Middle East and North Africa, with maximum temperatures exceeding 85°C during the study period from 2005 to 2020. We observed an increasing trend in maximum surface temperatures at a rate of 0.17°C/decade. The model allows quantifying how upper bounds of extreme temperatures can increase in a warming climate in the future for which we do not have satellite observations and offers new insights on potential impacts of future warming on limits to plant growth and biological adaptability.〈/p〉
    Description: Plain Language Summary: While satellite imagery can identify extreme land surface temperatures, land and atmospheric conditions for the onset of maximum land surface temperature (LST) have not yet been globally explored. We developed a physically based analytical model for quantifying the value and spatial extent of maximum LST and provide insights into combinations of land and atmospheric conditions for the onset of such temperature extremes. Results show that extreme LST hotspots occur primarily in the Middle East and North Africa with highest values near 85°C. Importantly, persistence of surface temperatures exceeding 75°C limits vegetation growth and disrupts primary productivity such as in Lut desert in Iran. The study shows that with global warming, regions with prohibitive land surface temperatures will expand.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Hotspots for high land surface temperatures (LSTs) were globally identified using a physically based analytical approach incorporating land and atmospheric conditions〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉High LSTs primarily occur in Middle East and North Africa with values exceeding 85°C〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Maximum LSTs rising at a rate of 0.17°C/decade may limit plant growth and biological adaptability in a warming world〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Hamburg University of Technology
    Description: European Union's Horizon Europe Research and Innovation Programme
    Description: https://disc.gsfc.nasa.gov/datasets/M2I1NXLFO_5.12.4/summary
    Description: https://disc.gsfc.nasa.gov/datasets/M2T1NXRAD_5.12.4/summary
    Description: https://doi.org/10.5067/MODIS/MCD12C1.006
    Description: https://doi.org/10.3133/ofr20111073
    Description: https://www.nccs.nasa.gov/services/data-collections/land-based-products/nex-gddp-cmip6
    Description: https://doi.org/10.3334/ORNLDAAC/1247
    Keywords: ddc:551.5 ; maximum land surface temperature (LST) ; land conditions ; atmospheric conditions ; LST hotspots
    Language: English
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  • 24
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    Large‐eddy simulation of soil moisture heterogeneity‐induced secondary circulation with ambient winds (2023)
    John Wiley & Sons, Ltd. | Chichester, UK
    Details
    Publication Date: 2024-03-05
    Description: Land surface heterogeneity in conjunction with ambient winds influences the convective atmospheric boundary layer by affecting the distribution of incoming solar radiation and forming secondary circulations. This study performed coupled large‐eddy simulation (ICON‐LEM) with a land surface model (TERRA‐ML) over a flat river corridor mimicked by soil moisture heterogeneity to investigate the impact of ambient winds on secondary circulations. The coupled model employed double‐periodic boundary conditions with a spatial scale of 4.8 km. All simulations used the same idealized initial atmospheric conditions with constant incident radiation of 700 W⋅m〈sup〉−2〈/sup〉 and various ambient winds with different speeds (0 to 16 m⋅s〈sup〉−1〈/sup〉) and directions (e.g., cross‐river, parallel‐river, and mixed). The atmospheric states are decomposed into ensemble‐averaged, mesoscale, and turbulence. The results show that the secondary circulation structure persists under the parallel‐river wind conditions independently of the wind speed but is destroyed when the cross‐river wind is stronger than 2 m⋅s〈sup〉−1〈/sup〉. The soil moisture and wind speed determine the influence on the surface energy distribution independent of the wind direction. However, secondary circulations increase advection and dispersive heat flux while decreasing turbulent energy flux. The vertical profiles of the wind variance reflect the secondary circulation, and the maximum value of the mesoscale vertical wind variance indicates the secondary circulation strength. The secondary circulation strength positively scales with the Bowen ratio, stability parameter (−Z〈sub〉i〈/sub〉/L), and thermal heterogeneity parameter under cross‐river wind and mixed wind conditions. The proposed similarity analyses and scaling approach provide a new quantitative perspective on the impact of the ambient wind under heteronomous soil moisture conditions on secondary circulation.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.5 ; ambient winds ; Bowen ratio ; land surface model ; large‐eddy simulation ; moisture spatial heterogeneity ; secondary circulation ; similarity theory ; turbulence
    Language: English
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  • 25
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    Regional Impact of Snow‐Darkening on Snow Pack and the Atmosphere During a Severe Saharan Dust Deposition Event in Eurasia (2023)
    Details
    Publication Date: 2024-03-05
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Light‐absorbing impurities such as mineral dust can play a major role in reducing the albedo of snow surfaces. Particularly in spring, deposited dust particles lead to increased snow melt and trigger further feedbacks at the land surface and in the atmosphere. Quantifying the extent of dust‐induced variations is difficult due to high variability in the spatial distribution of mineral dust and snow. We present an extension of a fully coupled atmospheric and land surface model system to address the impact of mineral dust on the snow albedo across Eurasia. We evaluated the short‐term effects of Saharan dust in a case study. To obtain robust results, we performed an ensemble simulation followed by statistical analysis. Mountainous regions showed a strong impact of dust deposition on snow depth. We found a mean significant reduction of −1.4 cm in the Caucasus Mountains after 1 week. However, areas with flat terrain near the snow line also showed strong effects despite lower dust concentrations. Here, the feedback to dust deposition was more pronounced as increase in surface temperature and air temperature. In the region surrounding the snow line, we found an average significant surface warming of 0.9 K after 1 week. This study shows that the impact of mineral dust deposition depends on several factors. Primarily, these are altitude, slope, snow depth, and snow cover fraction. Especially in complex terrain, it is therefore necessary to use fully coupled models to investigate the effects of mineral dust on snow pack and the atmosphere.〈/p〉
    Description: Plain Language Summary: Dust particles such as Saharan dust can darken snow surfaces, leading to increased absorption of solar radiation. The result is earlier snow melt in the spring and a warming of the land surface. Predicting dust deposition and subsequent regional impacts is difficult because the distribution of snow and dust appears in complex patterns depending on the landscape. We extended an atmospheric and land surface model system to investigate the impact of Saharan dust particles across Eurasia during a Saharan dust transport event. We found that mountainous regions are particularly affected by the dust particles, leading to increased snowmelt. In addition, regions with thin and patchy snow cover show a strong response to the dust particles, mainly causing a warming of the land surface. We found that the effects of dust particles depend on different regional characteristics. Therefore, when investigating dust on snow, it is important to use model systems that represent both the atmospheric process and surface properties properly.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉There are regional effects due to the high spatial variability in mineral dust and snow properties〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Thin snow layers favor a rise in temperature, higher elevations mainly show accelerated snow melt〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉We found a significant impact on surface radiation, temperature and snow cover properties〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Initiative and Networking Fund of the Helmholtz Association
    Description: https://doi.org/10.35097/1579
    Keywords: ddc:551.5 ; light‐absorbing impurities ; dust on snow ; snow albedo ; regional impact ; modeling ; ensemble simulation
    Language: English
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  • 26
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    Bulk Transfer Coefficients Estimated From Eddy‐Covariance Measurements Over Lakes and Reservoirs (2023)
    Details
    Publication Date: 2024-03-06
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The drag coefficient, Stanton number and Dalton number are of particular importance for estimating the surface turbulent fluxes of momentum, heat and water vapor using bulk parameterization. Although these bulk transfer coefficients have been extensively studied over the past several decades in marine and large‐lake environments, there are no studies analyzing their variability for smaller lakes. Here, we evaluated these coefficients through directly measured surface fluxes using the eddy‐covariance technique over more than 30 lakes and reservoirs of different sizes and depths. Our analysis showed that the transfer coefficients (adjusted to neutral atmospheric stability) were generally within the range reported in previous studies for large lakes and oceans. All transfer coefficients exhibit a substantial increase at low wind speeds (〈3 m s〈sup〉−1〈/sup〉), which was found to be associated with the presence of gusts and capillary waves (except Dalton number). Stanton number was found to be on average a factor of 1.3 higher than Dalton number, likely affecting the Bowen ratio method. At high wind speeds, the transfer coefficients remained relatively constant at values of 1.6·10〈sup〉−3〈/sup〉, 1.4·10〈sup〉−3〈/sup〉, 1.0·10〈sup〉−3〈/sup〉, respectively. We found that the variability of the transfer coefficients among the lakes could be associated with lake surface area. In flux parameterizations at lake surfaces, it is recommended to consider variations in the drag coefficient and Stanton number due to wind gustiness and capillary wave roughness while Dalton number could be considered as constant at all wind speeds.〈/p〉
    Description: Plain Language Summary: In our study, we investigate the bulk transfer coefficients, which are of particular importance for estimation the turbulent fluxes of momentum, heat and water vapor in the atmospheric surface layer, above lakes and reservoirs. The incorrect representation of the surface fluxes above inland waters can potentially lead to errors in weather and climate prediction models. For the first time we made this synthesis using a compiled data set consisting of existing eddy‐covariance flux measurements over 23 lakes and 8 reservoirs. Our results revealed substantial increase of the transfer coefficients at low wind speeds, which is often not taken into account in models. The observed increase in the drag coefficient (momentum transfer coefficient) and Stanton number (heat transfer coefficient) could be associated with the presence of wind gusts and capillary waves. In flux parameterizations at lake surface, it is recommended to consider them for accurate flux representation. Although the bulk transfer coefficients were relatively constant at high wind speeds, we found that the Stanton number systematically exceeds the Dalton number (water vapor transfer coefficient), despite the fact they are typically considered to be equal. This difference may affect the Bowen ratio method and result in biased estimates of lake evaporation.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Bulk transfer coefficients exhibit a substantial increase at low wind speed〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The increase is explained by wind gustiness and capillary wave roughness〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉At higher wind speed, drag coefficient and Stanton number decrease with lake surface area〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: SHESF, Sao Francisco Hydroelectric Company
    Description: DOE Ameriflux Network Management Project
    Description: NSF North Temperate Lakes LTER
    Description: U.S. Department of Energy Office of Science
    Description: Japan Society for the Promotion of Science KAKENHI
    Description: Swedish Research Council
    Description: ÚNKP‐21‐3 New National Excellence Program of the Ministry for Innovation and Technology, Hungary
    Description: Russian Science Foundation http://dx.doi.org/10.13039/501100006769
    Description: Helmholtz Young Investigators Grant
    Description: Helmholtz Association of German Research Centers
    Description: Austrian Academy of Sciences
    Description: Autonome Provinz Bozen‐Südtirol
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Russian Ministry of Science and Higher Education
    Description: National Research, Development and Innovation Office
    Description: ICOS‐Finland, University of Helsinki
    Description: https://doi.org/10.5281/zenodo.6597828
    Keywords: ddc:551.5 ; bulk transfer coefficients ; eddy‐covariance ; lakes ; reservoirs
    Language: English
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  • 27
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    Between Broadening and Narrowing: How Mixing Affects the Width of the Droplet Size Distribution (2023)
    Details
    Publication Date: 2024-02-15
    Description: Entrainment and mixing play an essential role in shaping the droplet size distribution (DSD), with commensurate effects on cloud radiative properties or precipitation formation. In this paper, we use a model that considers all relevant scales related to entrainment and mixing by employing the linear eddy model (LEM) as a subgrid‐scale (SGS) mixing model, coupled with a large‐eddy simulation model and a Lagrangian cloud model (LCM) for a single cumulus congestus cloud. We confirm that the DSD is broadened toward small‐size droplets during homogeneous mixing. During inhomogeneous mixing, the DSD width remains almost unchanged. The DSD width can also be narrowed after mixing. We show that this happens when DSD is broadened toward small‐size droplets, which evaporate rapidly, while larger droplets are almost unaffected. In addition, when droplets ascend during mixing, DSD narrowing is caused when the adiabatic increase in supersaturation is slower than the average droplet evaporation, allowing only the largest droplets to benefit from the newly produced supersaturation. The narrowing mixing scenario prevents clouds from having too broad DSDs and causes the DSD relative dispersion to converge around 0.2 to 0.4. As this scenario is more frequent when the LEM SGS model is used, our results indicate that adequately modeling turbulent mixing is necessary to represent a realistic DSD shape.
    Description: Plain Language Summary: Clouds are always in contact with the surrounding air. Because the air outside the cloud is drier than the cloud, cloud droplets tend to evaporate when it enters the cloud. The size of the cloud droplets after evaporation can vary depending on the timescales of turbulent mixing and droplet evaporation. If the dry air mixes quickly, all droplets evaporate simultaneously. If the dry air is mixed slowly, only the droplets exposed to the dry air evaporate. However, this mixing occurs on small scales that traditional cloud models cannot account for. To account for this, we use a special model capable of representing all relevant scales. We confirm previous theoretical work that when mixing is fast, all droplets evaporate and the mean droplet size decreases. When mixing is slow, some droplets evaporate completely, but the average droplet size remains constant. We also observe cases where only small droplets evaporate while large droplets barely change. This scenario happens when there are many small droplets to evaporate or when additional moisture from cloud motion prevents larger droplets from evaporating completely.
    Description: Key Points: Changes in the droplet spectrum width under different mixing scenarios are investigated using a Lagrangian cloud model. While droplet spectrum broadening is common, narrowing occurs when the droplet size relative dispersion is large, or when droplets ascend. The interaction of these different mixing scenarios favors a relative dispersion of the droplet spectrum between 0.2 and 0.4.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: http://rossby.msrc.sunysb.edu/SAM.html
    Description: https://doi.org/10.5281/zenodo.7120916
    Keywords: ddc:551.5 ; entrainment and mixing ; cumulus clouds ; droplet size distribution ; Lagrangian cloud model ; mixing scenarios
    Language: English
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  • 28
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    Uncertainty Quantification for Machine Learning‐Based Ionosphere and Space Weather Forecasting: Ensemble, Bayesian Neural Network, and Quantile Gradient Boosting (2023)
    Details
    Publication Date: 2024-02-15
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Machine learning (ML) has been increasingly applied to space weather and ionosphere problems in recent years, with the goal of improving modeling and forecasting capabilities through a data‐driven modeling approach of nonlinear relationships. However, little work has been done to quantify the uncertainty of the results, lacking an indication of how confident and reliable the results of an ML system are. In this paper, we implement and analyze several uncertainty quantification approaches for an ML‐based model to forecast Vertical Total Electron Content (VTEC) 1‐day ahead and corresponding uncertainties with 95% confidence intervals (CI): (a) Super‐Ensemble of ML‐based VTEC models (SE), (b) Gradient Tree Boosting with quantile loss function (Quantile Gradient Boosting, QGB), (c) Bayesian neural network (BNN), and (d) BNN including data uncertainty (BNN + D). Techniques that consider only model parameter uncertainties (a and c) predict narrow CI and over‐optimistic results, whereas accounting for both model parameter and data uncertainties with the BNN + D approach leads to a wider CI and the most realistic uncertainties quantification of VTEC forecast. However, the BNN + D approach suffers from a high computational burden, while the QGB approach is the most computationally efficient solution with slightly less realistic uncertainties. The QGB CI are determined to a large extent from space weather indices, as revealed by the feature analysis. They exhibit variations related to daytime/nightime, solar irradiance, geomagnetic activity, and post‐sunset low‐latitude ionosphere enhancement.〈/p〉
    Description: Plain Language Summary: Space weather describes the varying conditions in the space environment between the Sun and Earth that can affect satellites and technologies on Earth, such as navigation systems, power grids, radio, and satellite communications. The manifestation of space weather in the ionosphere can be characterized using the Vertical Total Electron Content (VTEC) derived from Global Navigation Satellite Systems observations. In this study, the machine learning (ML) approach is applied to approximate the nonlinear relationships of Sun‐Earth processes using data on solar activity, solar wind, magnetic field, and VTEC. However, the measurements and the modeling approaches are subject to errors, increasing the uncertainty of the results when forecasting future instances. For reliable forecasting, it is necessary to quantify the uncertainties. Quantifying the uncertainty is also helpful for understanding the ML‐based model and the problem of VTEC and space weather forecasting. Therefore, in this study, ML‐based models are developed to forecast VTEC within the ionosphere, including the manifestation of space weather, while the degree of reliability is quantified with a target value of 95% confidence.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Machine learning‐based Vertical Total Electron Content models with 95% confidence intervals (CI) are developed for the first time using four approaches to quantify uncertainties〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Bayesian Neural Network quantifying model and data uncertainties contains ground truth within CIs, but is computationally intensive〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Quantile Gradient Boosting is fastest with comparable performance in terms of uncertainty; CIs largely determined from space weather indices〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Description: https://www.tensorflow.org/
    Description: https://doi.org/10.21105/joss.03021
    Description: http://www.aiub.unibe.ch/download/CODE
    Description: https://kauai.ccmc.gsfc.nasa.gov/instantrun/iri
    Description: https://doi.org/10.5281/zenodo.7741342
    Description: https://doi.org/10.5281/zenodo.7858906
    Description: https://doi.org/10.5281/zenodo.7858661
    Keywords: ddc:551.5 ; machine learning ; uncertainty quantification ; confidence intervals ; probabilistic ionosphere forecast ; space weather ; ensemble ; Bayesian neural network ; quantile gradient boosting
    Language: English
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  • 29
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    Correcting Hargreaves‐Samani formula using geographical coordinates and rainfall over different timescales (2023)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2024-02-14
    Description: The United Nations Food and Agricultural Organization (FAO) approved the Hargreaves‐Samani formula (HAR‐85) as an alternative to the standard Penman‐Monteith method (FAO‐PM) for estimating grass reference evapotranspiration (ETo). With much less data demand, HAR‐85 is unequivocally useful where meteorological variables are often scarce, incomplete or unavailable. Herein, we evaluate HAR‐85 against FAO‐PM across 2.505 million km2, representing Sudan and South Sudan and encompassing wide hydroclimate domains including the Nile River. We further propose simple year‐round and seasonal adjustment models to correcting HAR‐85 across the entire study area. The models express HAR‐85's error in multiple linear regressions in terms of latitude, longitude, altitude and/or monthly rainfall. Varying data periods, including odd, even and all years, are used in the evaluation and the adjustment models development and validation processes to investigate the influence of changing data period. A suit of eight performance indicators shows dependency of the original bias of HAR‐85 on the geographical location, monthly rainfall amount, season of the year and data period. All error indicators amplify southward from the hyper‐arid region to the dry sub‐humid zone. For example, the mean bias error (MBE) ranges from −0.51 to 1.29 mm/day, respectively. Study area‐wide, HAR‐85 least represents FAO‐PM during the hottest month and the transitional month (between the wet and dry‐cool seasons) with MBE of 0.65 and 0.70 mm/day, respectively. Conversely, it represents FAO‐PM the most in the wettest month, with smallest MBE of 0.32 mm/day. Beholding this spatiotemporal trait, the final yearly and seasonal adjustment models developed herein enormously moderate the predominant overestimation of the original HAR‐85. The former model explains 46.7% of the error variance whereas 36.9% to 62.3% of the variation in the error is explainable by the latter models. These adjustment models narrow the monthly MBE among the stations from −0.71‐2.17 to −0.80‐1.20 and −0.65‐0.99 mm/day, respectively. Without undermining the accuracy, the year‐round adjustment model can still be feasibly recommended for general use across the study area.
    Description: For the vast area encompassing Sudan and South Sudan, with hyper‐arid, arid, semi‐arid and dry sub‐humid climates, the performance of the simple Hargreaves‐Samani formula is evaluated against FAO Penman‐Monteith method for estimating grass reference evapotranspiration (ETo). ETo is essentially latitude, rainfall, season and timescale dependent with dominant overestimation. Adjustment is proposed through year‐round and seasonal multiple linear regressions on latitude, altitude, longitude and monthly rainfall, explaining ~37‐62% of the bias error.
    Keywords: ddc:551.5 ; arid climates ; evaluation ; FAO Penman‐Monteith method ; grass reference evapotranspiration ; Hargreaves‐Samani method ; sub‐humid climates ; Sudan ; validation
    Language: English
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  • 30
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    Not All Clear Air Turbulence Is Kolmogorov—The Fine‐Scale Nature of Atmospheric Turbulence (2023)
    Details
    Publication Date: 2024-02-14
    Description: We study a strong clear air turbulence (CAT) event experienced by the German High‐Altitude Long‐Range research aircraft (HALO) during the Southern Hemisphere Transport, Dynamics, and Chemistry campaign. HALO encountered CAT leeward of the southern Andes Mountains, where tropospheric airflow favored vertically propagating mountain waves that were refracted southeastward into the core of tropopause jet. Turbulence is quantified using spectral quantities and structure functions computed from in situ 100 Hz flight level data. The detected CAT region exhibits strong patchiness, characterized by separated bursts in turbulent kinetic energy and energy dissipation rate. The high resolution in situ observations reveal different turbulent scaling within each patch, in both spectra and structure functions, and following Monin and Yaglom's conversion law. One patch follows power laws with exponents −1.71 ± 0.06, −1.771 ± 0.006, and −1.56 ± 0.05 for the velocity components w, v, and u, respectively, while another patch has exponents −2.17 ± 0.12, −2.50 ± 0.08, and −1.92 ± 0.09. These patches are mediated by a third patch with less clear scaling. While the patches can deviate from Kolmogorov scaling due to the anisotropy of the airflow, they still display evidence of CAT with enhanced energy dissipation rates.
    Description: Plain Language Summary: Clear air turbulence (CAT) is a common phenomenon in upper layers of the atmosphere, often triggered by the instability of internal gravity waves or by strong wind shear. CAT can be disruptive for airplanes and uncomfortable for pilots and passengers. Nevertheless, the relationship between CAT formation and the resulting strength of bumpiness experienced by an aircraft is not fully understood. Most of these turbulent regions are patchy and exhibit sudden inhomogeneous bursts of velocity and temperature variations. However, CAT is often quantified using spectral quantities assuming isotropic and homogeneous turbulence. Here, we present a case study of a CAT event observed in the lowermost stratosphere during a research flight in the lee of the Andes Mountains near the Drake Passage in South America. The unique 100 Hz high resolution in situ observations allow the study of individual patches within the turbulent event. Their statistical properties can deviate significantly from those of homogeneous and isotropic turbulence, indicating thermal stratification as an important parameter determining the spectral response.
    Description: Key Points: Moderate‐to‐severe clear air turbulence (CAT) over the Southern Andes is analyzed using 100 Hz in situ data obtained during a flight of the Southern Hemisphere Transport, Dynamics, and Chemistry campaign. Vertical propagation of mountain waves in the lee of the Southern Andes is recognized as the main source for the turbulence observed. Anisotropy due to thermal stratification results in turbulent patches within the CAT region with non‐Kolmogorov turbulence scaling.
    Description: Ministerio de Defensa, Argentina http://dx.doi.org/10.13039/501100016156
    Description: Federal Ministry for Education and Research
    Description: https://doi.org/10.5281/zenodo.6918363
    Description: https://halo-db.pa.op.dlr.de/mission/116
    Description: https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5
    Keywords: ddc:551.5 ; southern Andes ; clear air turbulence (CAT) ; gravity waves dynamics ; German High-Altitude Long-Range research aircraft (HALO)
    Language: English
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  • 31
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    Temperature Calibration of Elevated Mg/Ca in Planktic Foraminifera Shells From the Hypersaline Gulf of Aqaba (2023)
    Details
    Publication Date: 2024-02-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The Mg/Ca of marine calcareous Planktic Foraminifera (PF) shells is commonly used for sea surface temperature reconstructions. However, compared to open marine environments, hypersaline (>40) oligotrophic seas have been shown to accommodate PF with higher Mg/Ca and divergent temperature to Mg/Ca relationships. To investigate influencing factors of PF Mg uptake in hypersaline regions, we measured the Mg/Ca of two flux‐dominating PF species, 〈italic〉Globigerinoides ruber albus〈/italic〉 and 〈italic〉Turborotalita clarkei〈/italic〉, derived from a monthly resolved time series of sediment traps in the Gulf of Aqaba, northern Red Sea as well as the corresponding temperature, salinity, and 〈italic〉p〈/italic〉H values. The PF exhibit elevated Mg/Ca which cannot be explained by post‐deposition or interstitial sediment diagenetic processes. 〈italic〉G. ruber albus〈/italic〉 displays Mg/Ca trends that strongly follow seasonal mixed layer temperature changes. Conversely, 〈italic〉T〈/italic〉. 〈italic〉clarkei〈/italic〉 Mg/Ca trends do not follow temperature but rather show significant Mg/Ca enrichment following mixing of the surface water column. We present a framework for incorporating elevated Mg/Ca into global Mg/Ca‐T calibrations for 〈italic〉G〈/italic〉. 〈italic〉ruber albus〈/italic〉 and present a new Mg/Ca‐T calibration suitable for hypersaline marine environments.〈/p〉
    Description: Plain Language Summary: Past seawater temperature is reconstructed from the magnesium‐to‐calcium ratio (Mg/Ca) in the calcareous shells of a group of marine microplankton called foraminifera. Two foraminifer species, 〈italic〉Globigerinoides ruber albus〈/italic〉 and 〈italic〉Turborotalita clarkei〈/italic〉, are abundant in the Gulf of Aqaba, northern Red Sea, at year‐round high temperatures and salinities. The shells of these foraminifera have elevated Mg/Ca relative to other marine regions, and here, we explore the factors causing this. The Mg/Ca values of both 〈italic〉G〈/italic〉. 〈italic〉ruber albus〈/italic〉 and 〈italic〉T〈/italic〉. 〈italic〉clarkei〈/italic〉 reflect the environmental conditions of the water column. For 〈italic〉G〈/italic〉. 〈italic〉ruber albus〈/italic〉, temperature and salinity appear to be factors responsible for the Mg/Ca trends and elevated values. We incorporate the new Mg/Ca data for 〈italic〉G〈/italic〉. 〈italic〉ruber albus〈/italic〉 to calibrate elevated Mg/Ca with temperature for high‐salinity (>40) marine environments. The Mg/Ca of the deeper dwelling 〈italic〉T〈/italic〉. 〈italic〉clarkei〈/italic〉 show higher ratios following deep mixing of the surface water column and may indicate annually recurring phytoplankton blooms caused by nutrient input into the sunlit ocean surface.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉A new Mg/Ca temperature calibration for high salinity environments is presented for 〈italic〉Globigerinoides ruber albus〈/italic〉〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉A framework for incorporating high salinity environments into global Mg/Ca‐T calibrations is provided〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Enhanced Mg/Ca in subsurface dwelling 〈italic〉Turborotalita clarkei〈/italic〉 may indicate seasonal deep mixing of the upper water column〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Israel Science Foundation http://dx.doi.org/10.13039/501100003977
    Description: Minerva PhD Fellowship Stipend
    Description: Advance School for Environmental Studies
    Description: https://doi.org/10.1594/PANGAEA.959629
    Description: https://doi.org/10.17617/3.EXFQC2
    Keywords: ddc:551.9 ; Gulf of Aqaba ; Planktic Foraminifera shells ; Mg/Ca ; sea surface temperature reconstructions
    Language: English
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    Cyclone Impacts on Sea Ice Concentration in the Atlantic Arctic Ocean: Annual Cycle and Recent Changes (2023)
    Details
    Publication Date: 2024-02-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉We quantify sea ice concentration (SIC) changes related to synoptic cyclones separately for each month of the year in the Greenland, Barents and Kara Seas for 1979–2018. We find that these SIC changes can be statistically significant throughout the year. However, their strength varies from region to region and month to month, and their sign strongly depends on the considered time scale (before/during vs. after cyclone passages). Our results show that the annual cycle of cyclone impacts on SIC is related to varying cyclone intensity and traversed sea ice conditions. We further show that significant changes in these cyclone impacts have manifested in the last 40 years, with the strongest changes occurring in October and November. For these months, SIC decreases before/during cyclones have more than doubled in magnitude in the Barents and Kara Seas, while SIC increases following cyclones have weakened (intensified) in the Barents Sea (Kara Sea).〈/p〉
    Description: Plain Language Summary: We study how the sea ice cover in the Arctic Ocean changes due to the passage of low‐pressure systems (cyclones). Our study covers all years between 1979 and 2018 and each individual month of the year. Our results show that the passage of cyclones can affect the sea ice year around, but the strength and the sign (less or more sea ice concentration due to cyclones) of this impact varies strongly. These variations in cyclone impacts throughout the year are related to variations in the strength of the cyclones and changes in the state of the sea ice cover (e.g., thinner vs. thicker ice). We further show that the cyclone impact on the Arctic sea ice has changed during the last 40 years. These changes are strongest in autumn, particularly in October and November. In these months, the strength of the destructive cyclone impacts on sea ice has more than doubled in some regions of the Arctic compared to previous times. In some regions, however, also the strength of ice preserving cyclone impacts (more sea ice due to cyclones) has intensified recently.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Cyclones can significantly impact the sea ice in the Atlantic Arctic in all months of the year, but with strong spatiotemporal variations〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Impacts are stronger in the cold season than in summer due to variations in cyclone intensity and traversed sea ice conditions〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Significant changes emerged throughout the year, recently strongest in the Barents Sea in autumn due to a reduced mean ice concentration〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: https://doi.org/10.24381/cds.adbb2d47
    Description: https://www.cen.uni-hamburg.de/icdc/data/ocean/easy-init-ocean/ecmwf-oras5.html
    Keywords: ddc:551.5 ; cyclones ; sea ice ; Arctic ; atmosphere‐sea ice interactions ; climate change
    Language: English
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  • 33
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    Added value of an atmospheric circulation pattern‐based statistical downscaling approach for daily precipitation distributions in complex terrain (2023)
    John Wiley & Sons, Ltd. | Chichester, UK
    Details
    Publication Date: 2024-01-24
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Reliable prediction of heavy precipitation events causing floods in a world of changing climate is crucial for the development of appropriate adaption strategies. Many attempts to provide such predictions have already been conducted but there is still much potential for improvement left. This is particularly true for statistical downscaling of heavy precipitation due to changes present in the corresponding atmospheric drivers. In this study, a circulation pattern (CP) conditional downscaling to the station level is proposed which considers occurring frequency changes of CPs. Following a strict circulation‐to‐environment approach we use atmospheric predictors to derive CPs. Subsequently, precipitation observations are used to derive CP conditional cumulative distribution functions (CDFs) of daily precipitation. Raw precipitation time series are sampled from these CDFs. Bias correction is applied to the sampled time series with quantile mapping (QM) and parametric transfer functions (PTFs) as methods being tested. The added value of this CP conditional downscaling approach is evaluated against the corresponding common non‐CP conditional approach. The performance evaluation is conducted by using Kling–Gupta Efficiency (KGE), root mean squared error (RMSE), and mean absolute error (MAE) metrics. In both cases the applied bias correction is identical. Potential added value can therefore only be attributed to the CP conditioning. It can be shown that the proposed CP conditional downscaling approach is capable of yielding more reliable and accurate downscaled daily precipitation time series in comparison to a non‐CP conditional approach. This can be seen in particular for the extreme parts of the distribution. Above the 95th percentile, an average performance gain of +0.24 and a maximum gain of +0.6 in terms of KGE is observed. These findings support the assumption of conserving and utilizing atmospheric information through CPs can be beneficial for more reliable statistical precipitation downscaling. Due to the availability of these atmospheric predictors in climate model output, the presented method is potentially suitable for downscaling precipitation projections.〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-pressure-levels?tab=overview
    Description: https://cdc.dwd.de/portal/
    Keywords: ddc:551.5 ; bias correction ; circulation patterns ; ERA5 ; extreme events ; heavy precipitation ; simulated annealing ; statistical downscaling
    Language: English
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    Enhanced Polar Vortex Predictability Following Sudden Stratospheric Warming Events (2023)
    Details
    Publication Date: 2024-01-24
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Sudden stratospheric warming (SSW) events can form a window of forecast opportunity for polar vortex predictions on subseasonal‐to‐seasonal time scales. Analyzing numerical ensemble simulations, we quantify the associated enhanced predictability due to reduced upward planetary wave fluxes during the mostly radiatively driven recovery phase following SSWs. Ensembles that predict an SSW show reduced ensemble spread in terms of polar vortex strength for several weeks to follow, as well as a corresponding reduction in forecast errors. This increased predictability is particularly pronounced for strong SSWs and even occurs if not all ensemble members predict a major SSW. Furthermore, we found a direct impact of the occurrence of SSWs on the date of the final warming (FW): the decrease in upward wave fluxes delays the FW significantly. The reduced spread after SSWs and the delay in FW date have potentially further implications for (subseasonal) predictions of the tropospheric and mesospheric circulations.〈/p〉
    Description: Plain Language Summary: The polar vortex is a large scale circulation active during winter in the higher levels of the polar atmosphere. Changes in the strength of the polar vortex can have an impact on the weather over mid‐latitude regions like Europe. This is the case especially for the period after so‐called sudden stratospheric warming (SSW) events, where the polar vortex breaks down very abruptly and then slowly recovers over several weeks. Such a break‐down of the polar vortex tends to suppress wave activity and hence reduces the dynamical variability in the polar stratosphere, leading to a more predictable evolution of the circulation. We quantify the strength and timescale of this increase in predictability of the polar vortex after an SSW using a large set of winter time model forecasts.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Sudden stratospheric warmings (SSWs) lead to reduced forecast spread in the polar stratosphere for several weeks after the event〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Reduced forecast spread after SSWs is driven by suppressed vertical planetary wave propagation due to persistent negative wind anomalies〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Final warmings are delayed for winters with SSW, consistent with reduced upward wave fluxes following the SSW〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://apps.ecmwf.int/datasets/data/s2s-realtime-instantaneous-accum-ecmf/levtype=sfc/type=cf/
    Description: https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-pressure-levels?tab=overview
    Description: https://doi.org/10.5282/ubm/data.395
    Keywords: ddc:551.5 ; sudden stratospheric warming ; final warming ; strat‐trop‐coupling ; polar vortex ; predictability ; window of forecast opportunity
    Language: English
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  • 35
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    Non‐Orographic Gravity Waves and Turbulence Caused by Merging Jet Streams (2023)
    Details
    Publication Date: 2024-01-24
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Jet streams are important sources of non‐orographic internal gravity waves and clear air turbulence (CAT). We analyze non‐orographic gravity waves and CAT during a merger of the polar front jet stream (PFJ) with the subtropical jet stream (STJ) above the southern Atlantic. Thereby, we use a novel combination of airborne observations covering the meso‐scale and turbulent scale in combination with high‐resolution deterministic short‐term forecasts. Coherent phase lines of temperature perturbations by gravity waves stretching along a highly sheared tropopause fold are simulated by the ECMWF IFS (integrated forecast system) forecasts. During the merging event, the PFJ reverses its direction from approximately antiparallel to parallel with respect to the STJ, going along with strong wind shear and horizontal deformation. Temperature perturbations in limb‐imaging and lidar observations onboard the research aircraft HALO during the SouthTRAC campaign show remarkable agreement with the IFS data. Ten hours earlier, the IFS data show an “X‐shaped” pattern in the temperature perturbations emanating from the sheared tropopause fold. Tendencies of the IFS wind components show that these gravity waves are excited by spontaneous emission adjusting the strongly divergent flow when the PFJ impinges the STJ. In situ observations of temperature and wind components at 100 Hz confirm upward propagation of the probed portion of the gravity waves. They furthermore reveal embedded episodes of light‐to‐moderate CAT, Kelvin Helmholtz waves, and indications for partial wave reflection. Patches of low Richardson numbers in the IFS data coincide with the CAT observations, suggesting that this event was accessible to turbulence forecasting.〈/p〉
    Description: Plain Language Summary: Gravity waves play an in important role in vertical and horizontal energy transport in the atmosphere and are significant factors in wheather forecasting and climate projections. Among other processes, tropospheric jet streams are known to be sources of gravity waves. They furthermore can be accompanied by tropopause folds (i.e., local tropopause depressions, where stratospheric air can reach deeply into the troposphere) and turbulence, which is relevant for aviation safety. Using a novel combination of airborne observations and data by a state‐of‐the‐art forecasting system, we analyze gravity waves and turbulence during a merger of tropospheric jet streams above the southern Atlantic. The observations show a high degree of agreement with the forecast data from the troposphere to the stratosphere. Ten hours earlier, the forcast data show an “X‐shaped” gravity wave structure that emerges from a highly sheared tropopause fold between the merging jet streams. Fast in situ observations at the flight level provide information on the characteristics of the observed waves and show light‐to‐moderate turbulence, small‐scale waves and indications for partial wave reflection. The observed turbulence events are consistently located in regions where the forecast data suggest potential for turbulence.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Non‐orographic internal gravity waves and clear air turbulence are observed in merging jet streams〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉State‐of‐the art high resolution forecast agrees with novel combination of airborne sensors〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉“X‐shaped” gravity wave feature resulting from merging jet streams at a highly sheared tropopause fold〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.5445/IR/1000151856
    Description: https://www.ecmwf.int/en/forecasts
    Description: https://www.ready.noaa.gov/
    Keywords: ddc:551.5 ; gravity waves ; jet streams ; clear air turbulence ; remote sensing ; in situ observations ; field campaigns
    Language: English
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    Origin of 182W Anomalies in Ocean Island Basalts (2023)
    Details
    Publication Date: 2023-11-13
    Description: Ocean island basalts (OIB) show variable 〈sup〉182〈/sup〉W deficits that have been attributed to either early differentiation of the mantle or core‐mantle interaction. However, 〈sup〉182〈/sup〉W variations may also reflect nucleosynthetic isotope heterogeneity inherited from Earth's building material, which would be evident from correlated 〈sup〉182〈/sup〉W and 〈sup〉183〈/sup〉W anomalies. Some datasets for OIB indeed show hints for such correlated variations, meaning that a nucleosynthetic origin of W isotope anomalies in OIB cannot be excluded. We report high‐precision W isotope data for OIB from Samoa and Hawaii, which confirm previously reported 〈sup〉182〈/sup〉W deficits for these samples, but also demonstrate that none of these samples have resolvable 〈sup〉183〈/sup〉W anomalies. These data therefore rule out a nucleosynthetic origin of the 〈sup〉182〈/sup〉W deficits in OIB, which most likely reflect the entrainment of either core material or an overabundance of late‐accreted materials within OIB mantle sources. If these processes occurred over Earth's history, they may have also been responsible for shifting the 〈sup〉182〈/sup〉W composition of the bulk mantle to its modern‐day value. We also report Mo isotope data for some Hawaiian OIB, which reveal no resolved nucleosynthetic Mo isotopic anomalies. This is consistent with inheritance of 〈sup〉182〈/sup〉W deficits in OIB from the addition of either core or late‐accreted material, but only if these materials have a non‐carbonaceous (NC) meteorite‐like heritage. As such, these data rule out significant contributions of carbonaceous chondrite (CC)‐like materials to either Earth's core or late accretion.
    Description: Plain Language Summary: Some ocean island basalts (OIB) may contain a record of processes and characteristics of the deepest parts of Earth's mantle, including at the boundary between the iron‐rich core and mantle. Like some prior studies, we measured tungsten isotopes within OIB from Hawaii and Samoa, and report that tungsten isotopes in these OIB differ in their characteristics compared to what is observed in modern rocks that are most representative of the upper part of Earth's mantle. One explanation for these tungsten isotope anomalies is that they are a signature of chemical interaction between the core and lower mantle, suggesting that the core 'leaks' into the lower mantle. Another possibility proposed here is that these tungsten isotope anomalies reflect ancient crust that contained dense, meteorite‐like materials, which sank to the bottom of the mantle during Earth's early history. Using isotopes of another element, molybdenum, we show that the source(s) of these tungsten isotope anomalies do not contain a significant number of materials that originated from the outer Solar System before being added to Earth during its formation.
    Description: Key Points: 〈sup〉182〈/sup〉W deficits in ocean island basalts are confirmed, but correlated 〈sup〉182〈/sup〉W–〈sup〉183〈/sup〉W anomalies present in prior datasets are not confirmed. 〈sup〉182〈/sup〉W deficits may reflect core‐mantle interaction or an overabundance of late‐accreted materials, but not nucleosynthetic effects. Mo isotope data similar to BSE estimate; W‐Mo data rule out significant contribution of CC‐like material to Earth's core or late accretion.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.35003/YCUKOX
    Keywords: ddc:551.9 ; core‐mantle interaction ; late accretion ; tungsten isotopes ; molybdenum isotopes ; ocean island basalts ; nucleosynthetic effects
    Language: English
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    Microphysical Pathways Active Within Thunderstorms and Their Sensitivity to CCN Concentration and Wind Shear (2023)
    Details
    Publication Date: 2023-11-02
    Description: The impact of cloud condensation nuclei (CCN) concentration on microphysical processes within thunderstorms and the resulting surface precipitation is not fully understood yet. In this work, an analysis of the microphysical pathways occurring in these clouds is proposed to systematically investigate and understand these sensitivities. Thunderstorms were simulated using convection‐permitting (1 km horizontal grid spacing) idealized simulations with the ICON model, which included a 2‐moment microphysics parameterization. Cloud condensation nuclei concentrations were increased from 100 to 3,200 CCN/cm3, in five different wind shear environments ranging from 18 to 50 m/s. Large and systematic decreases of surface precipitation (up to 35%) and hail (up to 90%) were found as CCN was increased. Wind shear changes the details, but not the sign, of the sensitivity to CCN. The microphysical process rates were tracked throughout each simulation, closing the mass budget for each hydrometeor class, and collected together into “microphysical pathways,” which quantify the different growth processes leading to surface precipitation. Almost all surface precipitation occurred through the mixed‐phase pathway, where graupel and hail grow by riming and later melt as they fall to the surface. The mixed‐phase pathway is sensitive to CCN concentration changes as a result of changes to the riming rate, which were systematically evaluated. Supercooled water content was almost insensitive to increasing CCN concentration, but decreased cloud drop size led to a large reduction in the riming efficiency (from 0.79 to 0.24) between supercooled cloud drops and graupel or hail, resulting in less surface precipitation.
    Description: Plain Language Summary: The amount of rain and hail from thunderstorms can be influenced by the amount of pollution in the form of aerosol particles, which determine how many cloud droplets form and how large they are. Unfortunately, different numerical models give different answers on whether rain and hail increase or decrease if pollution increases. In this article, we present a new analysis method helping to identify the small‐scale processes which are responsible for the increase or decrease in a specific numerical scheme. We apply it to simulations of thunderstorms and show that the decrease of rain and hail in the numerical model used here is mostly linked to the riming process. Riming is the collision of cloud droplets and frozen particles at temperatures below 0°C, such that the liquid water freezes to the surface of the ice particles and makes them bigger. Less riming occurs when pollution increases, because cloud droplets are smaller. This process is very important because nearly all rain reaching the surface consists of melted ice particles.
    Description: Key Points: Microphysical pathways are constructed by tracking microphysical processes rates and closing the hydrometeor mass budget. More cloud condensation nuclei lead to less surface precipitation and hail, due to smaller cloud drop sizes and reduced riming collection efficiency. Simulations with constant riming collection efficiency reveal two different hail formation pathways.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: HORIZON EUROPE European Research Council http://dx.doi.org/10.13039/100019180
    Description: https://doi.org/10.5445/IR/1000156063
    Keywords: ddc:551.5 ; convective clouds ; hail ; riming ; precipitation ; CCN ; convection‐permitting simulation
    Language: English
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    The Linkage of Serial Cyclone Clustering in Western Europe and Weather Regimes in the North Atlantic‐European Region in Boreal Winter (2023)
    Hauser, Seraphine ; Mueller, Sebastian ; Chen, Xiaoyang ; [et al.]
    Details
    Publication Date: 2023-11-02
    Description: Extra‐tropical cyclones are an important source of weather variability in the mid‐latitudes. Multiple occurrences in a short period of time at a particular location are denominated serial cyclone clustering (SCC), and potentially lead to large societal impacts. We investigate the relationship between SCC affecting Western Europe and large‐scale weather regimes (WRs) in the North Atlantic‐European region in boreal winter. We find that SCC in low latitudes (45°N) is predominantly associated with the anticyclonic Greenland Blocking WR. In contrast, SCC in mid and high latitudes (55°N, 65°N) is mostly linked to different cyclonic WRs. Thereby, SCC occurs typically within a well‐established WR that builds up prior to SCC and decays after SCC. Thus, SCC events are closely associated with recurrent, quasi‐stationary and persistent large‐scale flow patterns (WRs). This mutual relationship reveals the potential of WRs in forecasting storm series and associated impacts on sub‐seasonal to seasonal time scales.
    Description: Plain Language Summary: Serial cyclone clustering describes the occurrence of multiple extra‐tropical cyclones within a certain time frame and a spatially restricted region. Since extra‐tropical cyclones can be associated with strong winds and heavy precipitation, multiple occurrences can lead to large cumulative impacts in the affected areas. We analyze the relationship between serial cyclone clustering (SCC) in Western Europe and so‐called weather regimes (WRs) in the North Atlantic‐European region in boreal winter. These regimes describe slow evolving and enduring large‐scale atmospheric circulation patterns. Relationships with certain regime types are identified but depend on the latitude at which the clustered frequency of extra‐tropical cyclones is found. When SCC occurs in low latitudes (45°N), it mostly appears coincident with anticyclonic large‐scale flow patterns. In contrast, SCC in mid and high latitudes (55°N, 65°N) often occurs simultaneously with different cyclonic regimes. We find that periods of SCC occur typically within WR life cycles pointing to the fact that both, the WRs and SCC periods, are interlinked. This relationship may facilitate forecasting storm series and associated impacts on time scales beyond 2 weeks.
    Description: Key Points: A close relationship is found between serial cyclone clustering (SCC) at 5°W and weather regimes (WRs) in the North Atlantic‐European region. SCC in mid and high latitudes (55°N, 65°N) is mainly associated with cyclonic and in low latitudes (45°N) with anticyclonic WR life cycles. Regardless of the selected latitude, SCC occurs mostly during an active regime life cycle and is manifested in a well‐established WR.
    Description: German Research Foundation
    Description: AXA Research Fund http://dx.doi.org/10.13039/501100001961
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: BMBF ClimXtreme
    Description: https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era-interim
    Keywords: ddc:551.5 ; serial cyclone clustering ; weather regimes ; atmospheric dynamics ; sub‐seasonal prediction
    Language: English
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    Observations of Gravity Wave Refraction and Its Causes and Consequences (2023)
    Details
    Publication Date: 2023-11-28
    Description: Horizontal gravity wave (GW) refraction was observed around the Andes and Drake Passage during the SouthTRAC campaign. GWs interact with the background wind through refraction and dissipation. This interaction helps to drive midatmospheric circulations and slows down the polar vortex by taking GW momentum flux (GWMF) from one location to another. The SouthTRAC campaign was composed to gain improved understanding of the propagation and dissipation of GWs. This study uses observational data from this campaign collected by the German High Altitude Long Range research aircraft on 12 September 2019. During the campaign a minor sudden stratospheric warming in the southern hemisphere occurred, which heavily influenced GW propagation and refraction and thus also the location and amount of GWMF deposition. Observations include measurements from below the aircraft by Gimballed Limb Observer for Radiance Imaging of the Atmosphere and above the aircraft by Airborne Lidar for the Middle Atmosphere. Refraction is identified in two different GW packets as low as ≈4 km and as high as 58 km. One GW packet of orographic origin and one of nonorographic origin is used to investigate refraction. Observations are supplemented by the Gravity‐wave Regional Or Global Ray Tracer, a simplified mountain wave model, ERA5 data and high‐resolution (3 km) WRF data. Contrary to some previous studies we find that refraction makes a noteworthy contribution in the amount and the location of GWMF deposition. This case study highlights the importance of refraction and provides compelling arguments that models should account for this.
    Description: Plain Language Summary: Gravity waves (GWs) are very important for models to reproduce a midatmospheric circulations. But the fact is that models oversimplify the GW physics which results in GWs being underrepresented in models. GW refraction is one of the processes not captured by the physics in model parameterization schemes. This article uses high‐resolution observations from the SouthTRAC campaign to show how GWs refract and highlight the importance there‐of. This case study shows a 25% increase in the GWMF during propagation. The increase in momentum flux is linked to refraction which results in a shortening in the GW horizontal wavelength. This article shows that refraction is important for the amount as well as the location of GWMF deposition. This case study highlights the importance of refraction and provides compelling arguments that models should account for this.
    Description: Key Points: A case study reveals that refraction results in a 25% increase in gravity wave momentum flux (GWMF). Including refraction dynamics affects the location of GWMF deposition. Refraction is prominent in strong wind gradients (i.e., displaced vortex conditions).
    Description: ANPCYT PICT
    Description: DFG
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Instituto de Física de Buenos Aires
    Description: SNCAD MinCyT initiative
    Description: HALO‐SPP
    Description: ROMIC WASCLIM
    Description: https://doi.org/10.5281/zenodo.6997443
    Description: https://cds.climate.copernicus.eu/cdsapp%23%21/home
    Keywords: ddc:551.5 ; gravity wave ; mountain wave ; refraction ; Andes ; Drake Passage ; gravity wave momentum flux
    Language: English
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    Wind Power Input to Ocean Near‐Inertial Waves Diagnosed From a 5‐km Global Coupled Atmosphere‐Ocean General Circulation Model (2023)
    Details
    Publication Date: 2023-11-27
    Description: Using the 5 km coupled general circulation model ICON, the surface internal wave energy source, crucial for the oceanic circulation, is quantified as the wind‐induced wave energy flux that radiates from the mixed layer bottom (MLB) into the ocean interior. Our result lowers the previous estimates of the wind power input to surface near‐inertial motions from up to more than 1 TW down to about 0.23–0.27 TW, depending on season. We point out that the estimate of the wind input to ocean depends not only on the wind stress used—as suggested by previous studies—but also on the ocean model used. While the surface currents in a slab ocean model or a non‐eddying ocean circulation model are strongly determined by the wind forcing, the surface currents in the 5 km ICON model can be more strongly determined by internal instability process (eddy) than by wind stress forcing from less‐extreme weather disturbances. The resulting more or less random alignment of surface current and wind stress can presumably lead to a lower wind input to surface near‐inertial motions. Of the surface wave energy source, about 30% is fluxed down into the interior ocean. This percentage roughly doubles those from previous studies, due to the stronger wave energy flux related to stronger inertial waves generated by the tropical cyclones simulated by the 5 km ICON model. Overall, the low wind input at near‐inertial frequencies produces a wind‐induced wave energy source at the MLB that is well below 0.1 TW.
    Description: Plain Language Summary: For maintaining the oceanic overturning circulation, energy is needed to mix the dense water up and light water down. The main energy source for mixing arises from breaking of internal waves. A considerable portion of this source comes from waves excited by winds at the sea surface. This paper quantifies this wave energy source based on a frontier simulation of a coupled atmosphere‐ocean general circulation model at a horizontal resolution of 5 km. This model is capable to simulate tropical cyclones (hurricanes and typhoons) and less‐extreme small‐scale and short‐living weather disturbances and oceanic mesoscale eddies, which were not represented by the models used in most of the previous studies. Taking these new features into account, we find that the wind‐induced wave energy source is less than 0.1 TW.
    Description: Key Points: Relatively low wind power input to near‐inertial motions in a 5 km global coupled simulation. Energy flux radiating from the mixed layer bottom as interior wave energy source. Strong internal waves excited by tropical cyclones simulated by a 5 km global coupled general circulation model.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: http://hdl.handle.net/21.11116/0000-000A-C1FA-2
    Keywords: ddc:551.5 ; wind‐induced wave energy source ; km‐scale coupled GCM ; internal waves generated by tropical cyclones
    Language: English
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    On the Dynamical Importance of Gravity Wave Sources Distributed Over Different Heights in the Atmosphere (2023)
    Details
    Publication Date: 2023-11-27
    Description: Gravity waves (GWs) are generated at all altitudes in the atmosphere, but sources above the lower stratosphere are rarely considered by parameterizations employed in general circulation models. This study assesses the potential impact on the thermosphere produced by small‐scale waves originating at different heights. Within the proposed numerical framework, GW sources are represented by wave momentum forcing, whose values are expressed relative to the forcing required to obtain typical wave spectra around the tropopause. The relative importance of tropospheric and extra‐tropospheric sources and the response in the thermosphere are studied in a series of sensitivity experiments. They demonstrate that the accumulation of wave momentum steeply drops with height as a consequence of decreasing density, even when the forcing is maintained at a uniform level throughout the middle atmosphere. When a broad spectrum is forced at twice the tropospheric rate, the thermospheric drag is increased by only a factor of two, and that increase is produced by waves that were forced in the lower stratosphere. With increasing altitude, vertically localized sources contribute progressively less. For example, for GWs excited near the mesopause to produce an impact comparable with that due to waves propagating from below, the forcing must be orders of magnitude stronger than in the troposphere. The estimated forcing of the so‐called secondary harmonics by breaking primary waves is much weaker, such that the systematic dynamical effect of secondary waves in the thermosphere is negligible compared to that of the primary GWs generated in the troposphere.
    Description: Plain Language Summary: Multiple observations demonstrate that gravity waves (GWs) are generated at all atmospheric levels, however numerical general circulation models employing parameterizations that account for wave sources only in the troposphere are able to reproduce the state and dynamics of the middle and upper atmosphere reasonably well. Assessing the role of GWs generated above the troposphere is extremely challenging, because such waves are difficult to separate from those of tropospheric origin in observations. The mechanisms of wave generation in the middle atmosphere are very complex and not fully understood. We developed a numerical framework, in which the strength of the extra‐tropospheric sources is represented by multiples of those in the troposphere. In the series of sensitivity tests, we demonstrate that the contribution of sources to the total wave momentum drops with height following the density decrease, and that the tropospheric sources capture the major part of the total momentum and of the associated GW drag in the thermosphere. One of the conclusions of this study is that the impact in the thermosphere of secondary waves, which are believed to be excited near the mesopause, is negligible compared to that of primary waves propagating from the troposphere.
    Description: Key Points: A framework for assessing impacts of gravity waves generated by sources distributed over all heights in the middle atmosphere is developed. The thermospheric response to sources above the tropopause is primarily produced by waves generated in the lower. stratosphere Localized sources produce negligible thermospheric drag unless the forcing is orders of magnitude stronger than in the troposphere.
    Description: Earth Sciences Division http://dx.doi.org/10.13039/100014573
    Description: https://kauai.ccmc.gsfc.nasa.gov/instantrun/hwm
    Description: https://ccmc.gsfc.nasa.gov/modelweb/models/nrlmsise00.php
    Keywords: ddc:551.5 ; gravity waves ; wave sources ; thermosphere ; secondary waves ; middle atmosphere
    Language: English
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    Systematic Across‐Arc Variations of Molybdenum Isotopes in a Fluid‐Dominated Subduction Zone System (2023)
    Details
    Publication Date: 2023-11-27
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Mass‐dependent Mo isotope variations are a promising new tracer to study magmatic processes in different geological settings. We report the first Mo isotope data for the Kamchatka arc system in the Northwest Pacific, comprising basaltic lavas of a complete Southeast‐Northwest traverse from the volcanic arc front through to the back arc region. The majority of volcanic centers investigated directly override the Hawaii‐Emperor Seamount Chain, which is currently being subducted underneath the arc system. Our Mo isotope data show systematic trends with Ce/Pb, Ce/Mo, Nb/Zr, La/Sm, and 〈sup〉143〈/sup〉Nd/〈sup〉144〈/sup〉Nd ratios from the volcanic arc front to the back arc. Arc front lavas have higher δ〈sup〉98/95〈/sup〉Mo and lower Ce/Pb, Ce/Mo, Nb/Zr, La/Sm compared to back arc lavas. Because the involvement of subducted sediments can be excluded, we attribute the observed variations to a change in the mantle source composition from the arc front to the back arc regions. The isotopic and chemical budget of arc front lavas is dominated by a slab fluid component (high δ〈sup〉98/95〈/sup〉Mo, low Ce/Pb, Ce/Mo), whereas mantle‐like Ce/Pb, Ce/Mo, elevated Nb/Zr and La/Sm in the back arc samples suggest an enriched mantle source. Combined δ〈sup〉98/95〈/sup〉Mo, Nd, and Pb isotope data in back arc lavas are very similar to those observed for modern ocean island basalts from Hawaii. We thus explore the possibility that the back arc mantle was contaminated by a Hawaii‐type, enriched asthenospheric mantle component from the subducted Hawaii‐Emperor Seamount Chain.〈/p〉
    Description: Plain Language Summary: In subduction zones, tectonic plates—tens of kilometers thick and making up the outer shell of our planet—are on a collision course. Although the absolute convergence rates of these plates are minute (a few cm/year), the forces in this process are so large that one plate is pushed under the other, causing the lower plate to be recycled into the Earth's mantle over time scales of millions of years. The tangible consequences are high‐magnitude earthquakes and large‐volume volcanic eruptions along these convergent plate margins. It is thus important to better understand the geological processes that operate in subduction zones. Here, we have studied the chemical and isotopic composition of volcanic rocks from the Kamchatka subduction zone. Our results confirm that water, locked into the subducting plate while residing on the surface, is released into the hot, overlying mantle after subduction, causing the formation of large volumes of magma that eventually erupt in volcanoes on the Kamchatka Peninsula. Our data also indicate that the subducting plate, once pushed into the mantle, is being ripped apart, allowing buoyant mantle material from greater depth to rise and contribute to the large‐scale volcanism observed along this convergent plate margin.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Molybdenum isotope systematics in arc basalts from Kamchatka are consistent with presence of a slab‐derived fluid in their mantle source〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Back arc basalts also show contribution from a geochemically enriched source〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Combined Mo, Nd, and Pb isotope and trace element data for back arc basalts suggest involvement of Hawaii‐type asthenospheric mantle〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.25625/P5BBFL
    Keywords: ddc:551.9 ; molybdenum isotopes ; slab fluid ; enriched mantle ; subduction ; Kamchatka ; Hawaii
    Language: English
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    Temporal Variability of Fluvial Sand Composition: An Annual Time Series From Four Rivers in SW Germany (2023)
    Details
    Publication Date: 2023-09-13
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The sampling of fluvial sediment is subject to many sources of uncertainty, for example, time and location, and the number of samples collected. It is nevertheless commonly assumed that a sample taken at one time and location provides a somewhat averaged compositional signal. Any spatial or temporal variability of this signal is often neglected. This study investigates how the composition of bed load sand changes over an observation period of 1 year in four river basins with differing bedrock geology in southwestern Germany. Up to 12 bulk sediment samples were taken at the same locations using the same approach and analyzed for their granulometry and geochemistry. The results indicate that (a) different grain sizes yield different compositions due to source rock composition and hydraulic sorting effects, (b) bulk sediment composition changes temporally due to changing grain‐size distribution, and (c) compared to the bulk sample, the composition of narrow grain sizes is temporally more stable but nevertheless has an average variability of 15%. Because heavy mineral‐bound elements such as Zr have the highest variability, we relate a major component of compositional variability to temporally varying heavy mineral concentrations in response to hydrodynamic processes. Mixing modeling demonstrates that the fluvial sand faithfully reflects its catchment geology and that the sediment sources do not change substantially during the observation period, even during a flooding event. We conclude (a) that the causes for compositional variability may be disentangled using chemical and granulometric time series data and (b) that narrow grain sizes yield representative source rock contributions.〈/p〉
    Description: Plain Language Summary: Sediment transported by rivers is generated by the erosion of the rocks present within the river catchment area. The composition of this sediment is controlled by various processes in the catchment, for example, climate, rock type, weathering, and flow strength. Geoscientists can use modern river sediment to understand how these processes impact sediment composition, and then apply this information to the geologic time. Sampling the river sediment is often the first step in such studies, but few studies consider the sources of uncertainty during sampling, for example, time and location of sampling, and number of collected samples. For this study, we returned to the same river location during the course of 1 year to take bulk sediment samples and analyzed how variable the size of sediment grains and the sediment chemistry are. We discovered that different grain sizes yield different chemical compositions, and this is caused by differences in rock type and hydraulic processes. Because the proportion of different grain sizes in the bulk sediment changes over the year due to water flow conditions, the chemistry of the bulk sediment sample changes over the year. We provide some quantitative estimates for this variability that should be considered in similar studies.〈/p〉
    Description: Key Points: Bed load sand from 4 rivers was sampled monthly over the course of 1 year to analyze the temporal compositional variability. Composition is grain‐size‐dependent, and narrow grain‐size fractions show less variability than bulk sediment samples. Composition changes during the year, and this is related to changing grain‐size distributions rather than changing sediment sources.
    Description: https://doi.pangaea.de/10.1594/PANGAEA.959006
    Keywords: ddc:551.9 ; geochemistry ; provenance ; grain‐size ; variability ; bed load ; fluvial sediment
    Language: English
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    The Role of Mineral Dust Aerosol Particles in Aviation Soot‐Cirrus Interactions (2023)
    Details
    Publication Date: 2023-12-19
    Description: Predicting cirrus cloud properties with confidence requires a sound understanding of the relative roles of homogeneous and heterogeneous ice formation. This study explores the effect of mineral dust and contrail‐processed aviation soot particles as ice‐nucleating particles (INPs) competing with liquid solution droplets in cirrus formation. We study aerosol‐cirrus interactions by accounting for atmospheric variability in updraft speeds and INP number concentrations. Our results confirm the dominant role of mineral dust in ice nucleation events in cirrus clouds. In addition, we show that pre‐existing thin cirrus may suppress ice formation when updraft speeds are low. We find that homogeneous freezing of liquid solution droplets dominates clear‐sky aerosol‐cirrus interaction above a threshold updraft speed determined by total number concentrations and ice nucleation abilities of INPs. When mineral dust particles exceed number concentrations of 10 L〈sup〉−1〈/sup〉, they reduce homogeneously nucleated ice crystal numbers significantly and even prevent homogeneous freezing for frequently observed local updraft speeds between 10 and 20 cm s〈sup〉−1〈/sup〉. When both mineral dust and aviation soot particles coexist with solution droplets, dust typically prevents ice nucleation by aviation soot. Aviation soot exerts a notable impact on cirrus ice numbers only if updrafts are weak, large soot particles are present in number concentrations that are considerably higher than typically observed in emission measurements, and/or number concentrations of mineral dust and other INPs are low. Overall, our results elucidate the role of aviation soot‐cirrus interactions in the presence of other INP types.
    Description: Plain Language Summary: Understanding ice formation from atmospheric aerosol particles in cirrus clouds is important to correctly predict the impact of cirrus on climate. Here, we study for the first time on the process level cirrus ice formation from freezing of liquid solution droplets in competition with ice nucleation on mineral dust and aviation‐produced soot particles. Our results show that in the majority of cloud‐forming updrafts, mineral dust particles dominate cirrus formation over droplet freezing and that they outcompete aviation soot in producing cloud ice. Moreover, already existing cirrus clouds often prevent ice formation from these particle types altogether. Our results help evaluate cirrus parameterizations within global models and constrain model‐based estimates of the global climate impact of aviation.
    Description: Key Points: Mineral dust outcompetes contrail‐processed aviation soot in aerosol‐cirrus interactions. Mineral dust reduces homogeneously nucleated ice crystal numbers more effectively than aviation soot. Strong potential of pre‐existing cirrus clouds to suppress new cloud ice formation.
    Description: European Commission http://dx.doi.org/10.13039/501100000780
    Description: https://doi.org/10.5281/zenodo.7404707
    Keywords: ddc:551.5 ; ice nucleating particles ; cirrus ; aerosol cloud interactions
    Language: English
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    The Role of Stratified Turbulence in the Cold Summer Mesopause Region (2023)
    Details
    Publication Date: 2024-01-22
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The summer mesopause at middle and high latitudes is the coldest place on Earth, and atmospheric gravity waves are responsible for the emergence of this extreme thermal phenomenon. Although the main physical mechanism behind the latter is understood, a deeper insight into it can be gained from the investigation of the mesoscale energy spectrum. In this work, we decompose the frequency spectra into divergent and rotational parts and find that their energy contributions are equipartitioned at high frequencies. This mesoscale energy equipartition is a feature of stratified turbulence and illustrates the complexity of the mesoscale dynamics in the summer mesopause region. We also analyze the power spectra of observed and simulated mesoscale zonal and meridional winds at middle latitudes in the Southern Hemisphere and show that stratified turbulence plays a role in the mesopause region during summer.〈/p〉
    Description: Plain Language Summary: Given its complexity to be measured at different spatio‐temporal scales, the exploration of the mesosphere and lower thermosphere remains an active area of research. In this work, we have applied velocity filtering techniques to both multistatic specular meteor radar measurements and global circulation model simulations to analyze horizontal wind frequency spectra over southern Patagonia. We consider the theory of layered anisotropic stratified turbulence to study the summer mesopause region and hypothesize that this type of turbulence (in the statistical sense) plays a role in the transition of internal gravity waves to small‐scale turbulence.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Spatially filtered horizontal wind residuals are explored for the first time at mesopause altitudes over Patagonia〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Frequency spectra of horizontal wind residuals follow a −2 slope〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Simulated divergent and rotational parts of the mesoscale kinetic energy are equipartitioned at high frequencies〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Leibniz Society
    Description: https://doi.org/10.22000/1737
    Keywords: ddc:551.5 ; stratified turbulence ; gravity waves ; mesopause ; meteor radar ; energy spectrum
    Language: English
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  • 46
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    Monthly Climatologies of Zonal‐Mean and Tidal Winds in the Thermosphere as Observed by ICON/MIGHTI During April 2020–March 2022 (2023)
    Details
    Publication Date: 2024-01-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Version 5 (v05) of the thermospheric wind data from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) instrument on the Ionospheric Connection Explorer (ICON) mission has been recently released, which largely avoids local‐time dependent artificial baseline drifts that are found in previous versions of the ICON/MIGHTI wind data. This paper describes monthly climatologies of zonal‐mean winds and tides based on the v05 ICON/MIGHTI data under geomagnetically quiet conditions (Hp30 〈 3o) during April 2020–March 2022. Green‐line winds in the lower thermosphere (90–110 km) and red‐line winds in the middle thermosphere (200–300 km) are analyzed, as these data cover both daytime and nighttime. The latitude and height structures of zonal‐mean winds and tides are presented for each month, and the results are compared with the widely used empirical model, Horizontal Wind Model 2014 (HWM14). The ICON/MIGHTI and HWM14 results are in general agreement, providing a validation of the v05 ICON/MIGHTI data. The agreement is especially good for the zonal‐mean winds. Amplitudes of lower thermospheric tides from ICON/MIGHTI tend to be larger than those from HWM14 as well as from an empirical model, Climatological Tidal Model of the Thermosphere (CTMT). This could be due to the influence of interannual variability of the tides. The amplitude structure of lower thermospheric tides in HWM14 does not match those from ICON/MIGHTI and CTMT in some months. Also, HWM14 underestimates the meridional‐wind amplitude of the migrating diurnal tide in the middle thermosphere. These results highlight the need for improved tidal representation in HWM14.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Monthly climatologies of zonal‐mean winds and tides at 90–110 km and 200–300 km are determined using v05 Ionospheric Connection Explorer/Michelson Interferometer for Global High‐resolution Thermospheric Imaging (ICON/MIGHTI) observations〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉ICON/MIGHTI and Horizontal Wind Model 2014 results are in general agreement, providing a validation of the Version 5 ICON/MIGHTI data〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The agreement is especially good for the zonal‐mean winds, while some discrepancies are found in tidal amplitudes〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: NASA
    Description: https://icon.ssl.berkeley.edu/Data
    Description: https://kp.gfz-potsdam.de/en/hp30-hp60/data
    Description: https://doi.org/10.5880/Hpo.0002
    Description: https://spaceweather.gc.ca/forecast-prevision/solar-solaire/solarflux/sx-5-mavg-en.php
    Description: https://globaldynamics.sites.clemson.edu/articles/ctmt.html
    Description: https://doi.org/10.5281/zenodo.5541913
    Keywords: ddc:551.5 ; thermosphere ; zonal‐mean winds ; tides ; ionospheric connection explorer (ICON) ; MIGHTI ; HWM14
    Language: English
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  • 47
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    Extreme Horizontal Wind Perturbations in the Mesosphere and Lower Thermosphere Over South America Associated With the 2022 Hunga Eruption (2023)
    Details
    Publication Date: 2024-04-03
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉On 15 January 2022, the Hunga volcano produced a massive explosion that generated perturbations in the entire atmosphere. Nonetheless, signatures in the mesosphere and lower thermosphere (MLT) have been challenging to identify. We report MLT horizontal wind perturbations using three multistatic specular meteor radars on the west side of South America (spanning more than 3,000 km). The most notorious signal is an exceptional solitary wave with a large vertical wavelength observed around 18 UT at all three sites, with an amplitude of ∼50 m/s mainly in the westward direction. Using a customized analysis, the wave is characterized as traveling at ∼200 m/s, with a period of ∼2 hr and a horizontal wavelength of ∼1,440 km in the longitudinal direction, away from the source. The perturbation is consistent with an 〈italic〉L〈/italic〉〈sub〉1〈/sub〉 Lamb wave mode. The signal's timing coincides with the arrival time of the tsunami triggered by the eruption.〈/p〉
    Description: Plain Language Summary: The eruption of the Hunga volcano in January 2022 had a widespread impact on the atmosphere, affecting various layers. We describe a perturbation in horizontal winds caused by the event, which was observed over the west coast of South America by three different meteor radar systems separated by more than 3,000 km between them. The perturbation behaved similarly in the altitude range of 80–100 km, and the wave parameters observed were consistent with high‐order Lamb wave solutions from simulations carried out using the Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension. This finding complements other studies that have explored the impacts of the eruption on different atmospheric levels. Overall, this study provides valuable insights into the complex and far‐reaching effects of volcanic eruptions on the atmosphere.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Hunga eruption generated extreme horizontal wind perturbations at 80–100 km of altitude over South America〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The signal was detected almost simultaneously by three multistatic meteor radar systems spanning more than 3,000 km〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The perturbation had a period of ∼2 hr, a horizontal phase velocity of ∼200 m/s, and a horizontal wavelength of ∼1,440 km〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Leibniz SAW project FORMOSA
    Description: https://doi.org/10.22000/956
    Keywords: ddc:551.5 ; South America ; 2022 Hunga Eruption ; mesosphere ; lower thermosphere ; horizontal wind perturbations
    Language: English
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  • 48
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    Horizontal Wavenumber Spectra Across the Middle Atmosphere From Airborne Lidar Observations During the 2019 Southern Hemispheric SSW (2023)
    Details
    Publication Date: 2024-04-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Horizontal wavenumber spectra across the middle atmosphere are investigated based on density measurements with the Airborne Lidar for Middle Atmosphere research (ALIMA) in the vicinity of the Southern Andes, the Drake passage and the Antarctic peninsula in September 2019. The probed horizontal scales range from 2000 to 25 km. Spectral slopes are close to 〈italic〉k〈/italic〉〈sup〉−5/3〈/sup〉 in the stratosphere and get shallower for horizontal wavelengths 〈200 km in the mesosphere. The spectral slopes are shown to be statistically robust with the presented number of flight legs despite the unknown orientation of true wave vectors relative to the flight track using synthetic data and a Monte Carlo approach. The largest spectral amplitudes are found over the ocean rather than over topography. The 2019 sudden stratospheric warming caused a critical level for MWs and a reduction of spectral amplitudes at horizontal wavelengths of about 200 km in the mesosphere.〈/p〉
    Description: Plain Language Summary: The spectral analysis of observations along extended flight tracks helps to determine the contribution of different length scales to atmospheric processes. In this study we calculate horizontal wavenumber spectra in the altitude range between 20 and 80 km, the middle atmosphere, based on observations from the Airborne Lidar for Middle Atmosphere research onboard the HALO aircraft. The observations were performed in the vicinity of the Southern Andes, the Drake passage and the Antarctic peninsula during September 2019. The observed horizontal scales range from 2000 km to about 25 km and cover almost the entire mesoscale range of atmospheric dynamics in the middle atmosphere. This study finds that vertical oscillations in the atmosphere, called gravity waves, cause the slopes and power of the spectra at the observed horizontal scales in the middle atmosphere. The slopes and power of the horizontal spectra vary with varying gravity wave activity during the period of observations.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Horizontal wavenumber spectra across the middle atmosphere are computed using airborne lidar observations during the 2019 sudden stratospheric warming (SSW)〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Horizontal wavenumber spectra are close to 〈italic〉k〈/italic〉〈sup〉−5/3〈/sup〉 in the stratosphere, and become shallower in the mesosphere during the SSW〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Observational evidence is provided that the mesoscale spectral slope in the middle atmosphere is caused by the occurrence of gravity waves〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: German Federal Ministry for Education and Research
    Description: Internal Funds of the German Aerospace Center
    Description: Karlsruhe Institute of Technology
    Description: Forschungszentrum Jülich
    Description: German Science Foundation
    Description: https://doi.org/10.5281/zenodo.7861915
    Keywords: ddc:551.5 ; gravity waves ; middle atmosphere ; airborne lidar ; horizontal wavenumber spectrum ; SSW
    Language: English
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  • 49
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    Mobilization of Tungsten in Greenstone Belts of the Archean Kaapvaal and Singhbhum Cratons (2023)
    Details
    Publication Date: 2024-05-22
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Due to the inherently fluid‐mobile nature of W, the 〈sup〉182〈/sup〉W record of the early Earth may have been obscured by fluid‐induced mobilization of W. To investigate W mobilization in Archean greenstone sequences, we analyzed 〈sup〉182〈/sup〉W isotope systematics and major and trace element concentrations in samples from the 3.53 Ga old Onverwacht Group of the Kaapvaal Craton (South Africa) and the >3.51 Ga old Badampahar Group of the Singhbhum Craton (India). Our results for mafic and ultramafic metavolcanic rocks show W/Th ratios significantly higher than primary magmatic values, which suggests fluid‐induced W enrichment. Samples least affected by secondary W enrichment (W/Th 〈 0.26) show no resolvable W isotope anomalies from modern mantle values in both cratons. Samples from the Kaapvaal Craton with elevated W/Th exhibit deficits in 〈sup〉182〈/sup〉W as low as −8.1 ± 4.3 ppm compared to the modern mantle. Covariations of μ〈sup〉182〈/sup〉W with W/Th, and Ce/Pb suggest that negative isotope signatures were introduced during secondary fluid‐mediated processes. The enrichment of W is most evident in altered ultramafic rocks comprising serpentine, resulting in additional covariations between MgO, LOI, and W/Th. The W isotope composition of serpentinized komatiites reflects the composition of younger intruding granitoids. We therefore infer the latter as a possible source of W‐rich fluids. The Badampahar Group samples exhibit little W isotope variability. A well‐resolved 〈sup〉182〈/sup〉W deficit of −6.2 ± 2.9 ppm was determined in a single komatiite sample, which indicates an unknown fluid source, currently not represented in any other unit of the Singhbhum Craton.〈/p〉
    Description: Plain Language Summary: The tungsten (W) isotope composition of ancient rocks can be used to trace processes that occurred during Earth's early evolution. However, interactions between rocks and fluids may alter the W concentration and therefore influence the interpretation of W isotope data. To identify the source of such fluids and the processes by which they affect the W isotope composition of rocks, we analyzed ancient rock samples from South Africa and India. The isotope composition of rocks with a low W concentration reflects that of the modern Earth. Therefore, they do not trace the processes that occurred during Earth's early evolution. Samples from South Africa with untypically high W concentrations show a different isotopic composition. The variation in the W isotope signature correlates with other chemical indices that are susceptible to modification by fluid‐related processes. This shows that the W within the rocks is derived from an external fluid source and not from their original magmatic source. Samples with the highest W enrichment have a similar isotope composition as spatially associated intrusive rocks. By inference, the latter likely represent the source of W‐rich fluids. The samples from India show similar enrichment in W, indicating similar fluid‐related processes and W sources at both localities.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉The magmatic sources of metavolcanic rocks from the Onverwacht Group and the Badampahar Group do not exhibit W isotope anomalies〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Negative W isotope signatures in the Onverwacht Group are likely derived from fluids sourced from younger intrusive granitoids〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Felsic intrusive rocks are a major source of W‐rich fluids in Paleoarchean greenstone units〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.5880/digis.2023.005
    Keywords: ddc:551.9 ; fluid‐mobility ; Kaapvaal ; Singhbhum ; 182W ; tungsten isotopes
    Language: English
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  • 50
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    Using continuous electrical conductivity measurements to derive major solute concentrations in karst systems (2023)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2024-05-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Hydrochemical data of karst springs provide valuable insights into the internal hydrodynamical functioning of karst systems and support model structure identification. However, the collection of high‐frequency time series of major solute species is limited by analysis costs. In this study, we develop a method to retrieve the individual solute concentration time series and their uncertainty at high temporal resolution for karst springs by using continuous observations of electrical conductivity (EC) and low‐frequency ionic measurements. Due to the large ion content and non‐negligible concentrations of aqueous complexes in karst systems, the concentration of each solute species occurring as free ion and as part of aqueous complexes are computed separately. The concentration of species occurring as free ions are computed considering their contributions to the total EC, whereas the concentration of the species as part of complexes are obtained from speciation calculations. The pivotal role of the complexation processes for the reconstruction of solute concentration time series starting from the EC signal is investigated in two karstic catchments with different geologies and temporal resolution of the available hydrochemical datasets, that is the Kerschbaum dolostone system in Austria and the Baget limestone system in France. The results show that complexation processes are significant and should be considered for the estimation of the total solute concentration in case of SO〈sub〉4〈/sub〉, Ca, Mg and HCO〈sub〉3〈/sub〉. The EC signal of a karst spring can be used to interpolate and quantify the dynamics of those solutes characterized by large contribution (approximately >6%) to the total EC and low relative variability, that is HCO〈sub〉3〈/sub〉, Ca and Mg. Moreover, the presented method can be used to estimate concentrations of solutes when applied to karst systems with stationary and hydrogeochemical homogeneous contributing area. On the contrary, the method is affected by large uncertainty in case of dynamic systems characterized by varying contributions of water from different geological areas. This study aims to contribute to the problem of hydrogeochemical data availability and to support future works on karst systems conceptualization.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: École Polytechnique Fédérale de Lausanne http://dx.doi.org/10.13039/501100001703
    Description: European Regional Development Fund http://dx.doi.org/10.13039/501100008530
    Description: http://www.hydroshare.org/resource/fb92daaffced415fb7a991747e73adfa
    Keywords: ddc:551.9 ; electrical conductivity decomposition ; high‐resolution hydrochemical data ; hydrochemical modelling ; karst
    Language: English
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  • 51
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    The inner life of the Atlantic Intertropical Convergence Zone (2023)
    John Wiley & Sons, Ltd | Chichester, UK
    Details
    Publication Date: 2024-05-30
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The Intertropical Convergence Zone (ITCZ) is a central component of the atmospheric general circulation, but remarkably little is known about the dynamical and thermodynamical structure of the convergence zone itself. This is true even for the structure of the low‐level convergence that gives the ITCZ its name. Following on from the major international field campaigns in the 1960s and 1970s, we performed extensive atmospheric profiling of the Atlantic ITCZ during a ship‐based measurement campaign aboard the research vessel 〈italic toggle="no"〉SONNE〈/italic〉 in summer 2021. Combining data collected during our north–south crossing of the ITCZ with reanalysis data shows the ITCZ to be a meridionally extended region of intense precipitation, with enhanced surface convergence at its edges rather than in the center. Based on the location of these edges, we construct a composite view of the structure of the Atlantic ITCZ. The ITCZ, far from being simply a region of enhanced deep convection, has a rich inner life, that is, a rich dynamical and thermodynamic structure that changes throughout the course of the year, and has a northern edge that differs systematically from the southern edge.〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Horizon 2020 Framework Programme CONSTRAIN http://dx.doi.org/10.13039/100010661
    Description: https://doi.org/10.5281/ZENODO.7051674
    Description: https://doi.org/10.24381/cds.adbb2d47
    Keywords: ddc:551.5 ; ITCZ ; Atlantic ; convergence ; observations ; reanalysis
    Language: English
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  • 52
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    A Decentralized Approach for Modeling Organized Convection Based on Thermal Populations on Microgrids (2022)
    Details
    Publication Date: 2023-01-17
    Description: In this study, a spectral model for convective transport is coupled to a thermal population model on a two‐dimensional horizontal “microgrid,” covering the typical gridbox size of general circulation models. The goal is to explore new ways of representing impacts of spatial organization in cumulus cloud fields. The thermals are considered the smallest building block of convection, with thermal life cycle and movement represented through binomial functions. Thermals interact through two simple rules, reflecting pulsating growth and environmental deformation. Long‐lived thermal clusters thus form on the microgrid, exhibiting scale growth and spacing that represent simple forms of spatial organization and memory. Size distributions of cluster number are diagnosed from the microgrid through an online clustering algorithm, and provided as input to a spectral multiplume eddy‐diffusivity mass flux scheme. This yields a decentralized transport system, in that the thermal clusters acting as independent but interacting nodes that carry information about spatial structure. The main objectives of this study are (a) to seek proof of concept of this approach, and (b) to gain insight into impacts of spatial organization on convective transport. Single‐column model experiments demonstrate satisfactory skill in reproducing two observed cases of continental shallow convection. Metrics expressing self‐organization and spatial organization match well with large‐eddy simulation results. We find that in this coupled system, spatial organization impacts convective transport primarily through the scale break in the size distribution of cluster number. The rooting of saturated plumes in the subcloud mixed layer plays a key role in this process.
    Description: Plain Language Summary: Recent studies have emphasized the importance of the spatial structure of convective cloud fields in Earth's climate, yet this phenomenon is not yet represented well in Earth System Models (ESMs). This study explores a new way to achieve this goal, by considering spatial organization at the scale of small bubbles of rising air called thermals that together make up convective clouds. Populations of interacting thermals are modeled in a computationally efficient way on a small two‐dimensional grid. This microgrid is then coupled to a convection scheme, which stands for the set of equations used to statistically represent the impact of convective transport at scales that remain unresolved in ESMs. The coupling makes the scheme decentralized, in that the transport becomes dependent on a population of longer‐lived convective structures that slowly develop and evolve on the microgrid. The new scheme is tested for observed conditions at a meteorological site in the Southern Great Plains area of the United States, making use of a combination of high‐resolution simulations and measurements to evaluate performance. Apart from proof of concept for the new modeling approach, the results provide new insights into how the spatial structure of convective cloud populations can affect its vertical transport.
    Description: Key Points: A multiplume spectral convection scheme is coupled to a binomial thermal population model on a horizontal microgrid. Observed diurnal cycles of continental shallow convection are reproduced, including good agreement on scale growth and spatial organization. Spatial organization impacts convective transport through the scale break in the cluster number density, with a key role played by plume rooting.
    Description: U.S. Department of Energy http://dx.doi.org/10.13039/100000015
    Description: https://doi.org/10.5281/zenodo.6044338
    Keywords: ddc:551.5 ; convective parameterization ; spatial organization ; population dynamics ; thermals ; microgrid modeling ; shallow cumulus
    Language: English
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  • 53
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    Horizontal Wavenumber Spectra of Vertical Vorticity and Horizontal Divergence of Mesoscale Dynamics in the Mesosphere and Lower Thermosphere Using Multistatic Specular Meteor Radar Observations (2022)
    Details
    Publication Date: 2023-01-14
    Description: Specular meteor radars (SMRs) have significantly contributed to the understanding of wind dynamics in the mesosphere and lower thermosphere (MLT). We present a method to estimate horizontal correlations of vertical vorticity (Qzz) and horizontal divergence (P) in the MLT, using line‐of‐sight multistatic SMRs velocities, that consists of three steps. First, we estimate 2D, zonal, and meridional correlation functions of wind fluctuations (with periods less than 4 hr and vertical wavelengths smaller than 4 km) using the wind field correlation function inversion (WCFI) technique. Then, the WCFI's statistical estimates are converted into longitudinal and transverse components. The conversion relation is obtained by considering the rotation about the vertical direction of two velocity vectors, from an east‐north‐up system to a meteor‐pair‐dependent cylindrical system. Finally, following a procedure previously applied in the upper troposphere and lower stratosphere to airborne wind measurements, the longitudinal and transverse spatial correlations are fitted, from which Qzz, P, and their spectra are directly estimated. The method is applied to a special Spread spectrum Interferometric Multistatic meteor radar Observing Network data set, obtained over northern Germany for seven days in November 2018. The results show that in a quasi‐axisymmetric scenario, P was more than five times larger than Qzz for the horizontal wavelengths range given by ∼50–400 km, indicating a predominance of internal gravity waves over vortical modes of motion as a possible explanation for the MLT mesoscale dynamics during this campaign.
    Description: Key Points: We investigate the horizontal correlation functions of vertical vorticity and horizontal divergence for mesoscale wind fluctuations in the mesosphere and lower thermosphere. 2D zonal and meridional correlation functions and 1D longitudinal and transverse correlation functions as a function of horizontal lags are analyzed. The divergence dominated over the vorticity during November 2018 in northern Germany.
    Description: Leibniz SAW
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: French Ministry of Foreign and European
    Description: https://doi.org/10.22000/536
    Keywords: ddc:551.5 ; MLT ; vorticity ; correlation function ; meteor radar ; mesoscales ; divergence
    Language: English
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  • 54
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    High‐Resolution Aircraft Observations of Turbulence and Waves in the Free Atmosphere and Comparison With Global Model Predictions (2022)
    Details
    Publication Date: 2023-01-14
    Description: High‐resolution flight data obtained from in situ measurements in the free atmosphere aboard the High Altitude and Long Range Research Aircraft (HALO) are used to determine eddy dissipation rates along extended flights during the recent Southern Hemisphere Transport, Dynamics, and Chemistry aircraft campaign (SOUTHTRAC) in the 2019 austral winter. These data are analyzed and correlated with quantities characterizing the ambient airflow and the magnitudes of vertical energy propagation through internal gravity waves. The observed turbulence events are strongly correlated with elevated shear values, and overturning gravity waves do not appear to play a role. A highlight of the analysis is the validation of a recently implemented Clear Air Turbulence (CAT) forecast index in the European Centre for Medium‐Range Weather Forecast integrated forecast system. Here we find a slightly better correlation of the CAT prediction with the HALO research aircraft observations compared to those of commercial aircraft. The observed turbulence during SOUTHTRAC was never stronger than moderate, as EDR values remained below 0.3 m2/3 s−1. In general, light and light‐to‐moderate turbulence events were extremely rare, occurring in only about 5% of the flight time, and stronger events in less than 0.2%. These results are also reflected in the local atmospheric conditions, which were dominated by a thermally very stable airflow with low vertical shear and large Richardson numbers.
    Description: Plain Language Summary: This study analyzes high‐resolution data of velocity components in the upper troposphere and lower stratosphere collected with the German research aircraft High Altitude and Long Range Research Aircraft during the Southern Hemisphere Transport, Dynamics, and Chemistry (SOUTHTRAC) campaign in September–November 2019. Flights were conducted predominantly over the southern part of South America, the Drake Passage, and the Antarctic Peninsula. The objective of the analysis was to determine the eddy dissipation rates during the 22 flights. The cubic root of eddy dissipation rates is a common measure used to characterize turbulent regions in the atmosphere. High quality observations with a very accurately calibrated sensor are rare, especially in the remote areas of the SOUTHTRAC campaign. Observed eddy dissipation rates have been correlated with gravity wave activity, but these correlations are very small. A much stronger dependence of the eddy dissipation rates exists on the vertical shear of the horizontal wind. Thus, mechanical generation of turbulence appears to dominate in the observed cases. Overall, the observed turbulence was never stronger than moderate. Turbulence events were extremely rare, occurring in only about 5% of the flight time, and stronger events less than 0.2%. Finally, the observed eddy dissipation rates were compared with weather model forecasts, demonstrating their reliability in predicting turbulent regions.
    Description: Key Points: Small eddy dissipation rates were observed in the free atmosphere along extended research flights during Southern Hemisphere Transport, Dynamics, and Chemistry in austral winter 2019. Stronger turbulence events are rare and are mostly correlated with enhanced vertical shear of the horizontal wind. EDR predictions of a 15‐member ensemble shows higher correlation with research aircraft observations than with those by commercial aircraft.
    Description: Federal Ministry for Education and Research
    Description: German Science Foundation
    Description: https://halo-db.pa.op.dlr.de/mission/116
    Description: https://halo-db.pa.op.dlr.de/dataset/8497
    Description: https://halo-db.pa.op.dlr.de/dataset/8496
    Description: https://apps.ecmwf.int/codes/grib/param-db/?id=260290
    Description: https://doi.org/10.21957/xbar-5611
    Description: https://halo-db.pa.op.dlr.de/dataset/8955
    Description: https://madis.ncep.noaa.gov/acars_variable_list.shtml
    Keywords: ddc:551.5 ; turbulence in the free atmosphere ; eddy dissipation rate ; clear‐air turbulence predictions ; ECMWF integrated forecast system
    Language: English
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    Ice Aggregation in Low‐Level Mixed‐Phase Clouds at a High Arctic Site: Enhanced by Dendritic Growth and Absent Close to the Melting Level (2022)
    Details
    Publication Date: 2023-01-13
    Description: Low‐level mixed‐phase clouds (MPCs) occur extensively in the Arctic, and are known to play a key role for the energy budget. While their characteristic structure is nowadays well understood, the significance of different precipitation‐formation processes, such as aggregation and riming, is still unclear. Using a 3‐year data set of vertically pointing W‐band cloud radar and K‐band Micro Rain Radar (MRR) observations from Ny‐Ålesund, Svalbard, we statistically assess the relevance of aggregation in Arctic low‐level MPCs. Combining radar observations with thermodynamic profiling, we find that larger snowflakes (mass median diameter larger than 1 mm) are predominantly produced in low‐level MPCs whose mixed‐phase layer is at temperatures between −15 and −10°C. This coincides with the temperature regime known for favoring aggregation due to growth and subsequent mechanical entanglement of dendritic crystals. Doppler velocity information confirms that these signatures are likely due to enhanced ice particle growth by aggregation. Signatures indicative of enhanced aggregation are however not distributed uniformly across the cloud deck, and only observed in limited regions, suggesting a link with dynamical effects. Low Doppler velocity values further indicate that significant riming of large particles is unlikely at temperatures colder than −5°C. Surprisingly, we find no evidence of enhanced aggregation at temperatures warmer than −5°C, as is typically observed in deeper cloud systems. Possible reasons are discussed, likely connected to the ice habits that form at temperatures warmer than −10°C, increased riming, and lack of particle populations characterized by broader size distributions precipitating from higher altitudes.
    Description: Plain Language Summary: Low‐level mixed‐phase clouds (MPCs), that is, shallow clouds containing both liquid droplets and ice crystals, form frequently in the Arctic region. Their characteristic structure—consisting of one or multiple liquid layers at sub‐zero temperatures, from which ice crystals form and precipitate—is nowadays well understood. However, the processes that lead to the growth of ice crystals into snow have been overlooked. Using a 3‐year data set of radar observations from Ny‐Ålesund, in Svalbard, Norway, we are able to identify situations when the ice particle growth is dominated by aggregation of several individual crystals. Combining radar observations with temperature information, we find that larger snowflakes are only produced in MPCs if their liquid portion is at temperatures between −15 and −10°C. This coincides with the temperature regime known for favoring aggregation due to growth and subsequent entanglement of branched crystals. Surprisingly, we find no evidence of enhanced ice aggregation at temperatures warmer than −5°C, as is typically observed in deeper cloud systems. Possible reasons are discussed, likely connected to the ice crystal shapes that develop at temperatures warmer than −10°C, increased liquid droplet production, and lack of particles precipitating from higher altitudes.
    Description: Key Points: Low‐level mixed‐phase clouds (MPCs) at Ny‐Ålesund produce large aggregates predominantly at dendritic‐growth temperatures. Enhanced aggregation due to dendritic growth occurs intermittently in limited regions of the MPC. The typically observed enhanced aggregation zone close to 0°C is absent in low‐level MPCs at the site.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.5 ; Arctic mixed‐phase clouds ; aggregation ; riming ; dendritic‐growth zone ; radar
    Language: English
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    Towards a more comprehensive assessment of the intensity of historical European heat waves (1979–2019) (2022)
    John Wiley & Sons, Ltd. | Chichester, UK
    Details
    Publication Date: 2023-01-19
    Description: Europe has been affected by record‐breaking heat waves in recent decades. Using station data and a gridded reanalysis as input, four commonly used heat wave indices, the heat wave magnitude index daily (HWMId), excess heat factor (EHF), wet‐bulb globe temperature (WBGT) and universal thermal climate index (UTCI), are computed. The extremeness of historical European heat waves between 1979 and 2019 using the four indices and different metrics is ranked. A normalisation to enable the comparison between the four indices is introduced. Additionally, a method to quantify the influence of the input parameters on heat wave magnitude is introduced. The spatio‐temporal behaviour of heat waves is assessed by spatial–temporal tracking. The areal extent, large‐scale intensity and duration are visualized using bubble plots. As expected, temperature explains the largest variance in all indices, but humidity is nearly as important in WBGT and wind speed plays a substantial role in UTCI. While the 2010 Russian heat wave is by far the most extreme event in duration and intensity in all normalized indices, the 2018 heat wave was comparable in size for EHF, WBGT and UTCI. Interestingly, the well‐known 2003 central European heat wave was only the fifth and tenth strongest in cumulative intensity in WBGT and UTCI, respectively. The June and July 2019 heat waves were very intense, but short‐lived, thus not belonging to the top heat waves in Europe when duration and areal extent are taken into account. Overall, the proposed normalized indices and the multi‐metric assessment of large‐scale heat waves allow for a more robust description of their extremeness and will be helpful to assess heat waves worldwide and in climate projections.
    Description: Europe has been affected by record‐breaking heat waves in recent decades. Using station data and a gridded reanalysis, the extremeness of European heat waves between 1979 and 2019 is ranked using four indices: heat wave magnitude index daily (HWMId), excess heat factor (EHF), wet‐bulb globe temperature (WBGT) and universal thermal climate index (UTCI). In order to assess heatwaves worldwide and in climate projections, the spatial extent, large‐scale intensity and duration of heatwaves are visualized using bubble plots.
    Description: AXA Research Fund http://dx.doi.org/10.13039/501100001961
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Karlsruher Institut für Technologie http://dx.doi.org/10.13039/100009133
    Keywords: ddc:551.5 ; duration ; heat wave ; indices ; intensity ; large‐scale ; spatial extent
    Language: English
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    A Parameterization of Cirrus Cloud Formation: Revisiting Competing Ice Nucleation (2022)
    Details
    Publication Date: 2023-01-20
    Description: This study develops an advanced physically‐based parameterization of heterogeneous ice nucleation in cirrus clouds that includes an updated parameterization of stochastic homogeneous freezing of supercooled solution droplets. Both components are formulated based on the same methodology and level of approximation, without numerical integration of the underlying ice supersaturation equation. The new scheme includes measured ice nucleation spectra describing deterministic ice activation from an arbitrary number of types of ice‐nucleating particles (INPs), tracks the competition for available water vapor between the different ice nucleation modes, and allows for new ice formation and growth within pre‐existing cirrus clouds. The computationally efficient scheme works with a minimal set of physical input parameters and predicts total nucleated ice crystal number concentrations (ICNCs) along with the maximum ice supersaturation attained during cirrus formation events. Aspects of its implementation into host models are discussed, including the provision of suitably parameterized vertical wind speeds. The parameterization is validated by comparisons to numerical simulations. First off‐line applications to mineral dust and aviation soot particles are presented, including ICNC ensemble statistics resulting from the coupling with statistics of updraft speed variability.
    Description: Plain Language Summary: Two decades after introduction of the first parameterization of cirrus cloud formation by freezing of ubiquitous liquid solution droplets, an improved version is developed based on the latest experimental findings regarding solid ice‐nucleating particles, a small subset of the atmospheric aerosol. The new scheme allows to predict ice crystal formation in cirrus from competing homogeneous freezing and heterogeneous ice activation more realistically and with greater computational efficiency. It considers new developments regarding the properties of vertical wind speeds (triggering ice formation) and the molecular kinetics of water vapor uptake onto ice crystals (controlling ice growth). This study explains the foundation of cirrus ice formation and growth based on cloud physical theory, derives and explains the parameterization, discusses its use in host models to facilitate applications, checks its performance by comparison to comprehensive numerical simulations, and presents first results involving mineral dust and aircraft‐emitted soot particles as examples for good and poor atmospheric ice‐nucleating particles, respectively.
    Description: Key Points: Competing ice nucleation processes in cirrus are predicted reliably and efficiently. Partial activation of dust particles may occur frequently in cirrus formation. Nucleation of ice within already‐existing cirrus requires high updraft speeds.
    Keywords: ddc:551.5 ; cirrus ; ice nucleation ; parameterization ; dust
    Language: English
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    Minimal Recipes for Global Cloudiness (2022)
    Details
    Publication Date: 2023-12-05
    Description: Clouds are primary modulators of Earth's energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low‐level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies.
    Description: Plain Language Summary: Clouds are important for Earth's climate, because they affect a large portion of the planet's energy balance, and hence its mean temperature. To better understand how the interplay between cloudiness and energy balance would change in a changing climate, a better theoretical understanding of how clouds are distributed over the planet, and how this connects with the state variables of the climate system such as temperature and wind speed, is required. As theoretical understanding is currently limited, in this work we explore the possibility of very simply representing the spatiotemporal distribution of clouds over the whole planet. We believe that these simple representations advance the field in the direction of a conceptual theory of global cloudiness and its impact on the energy balance. We show that the impact of cloudiness on both solar and terrestrial radiation balance can be captured well globally with only a few predictive fields, like surface temperature or vertical wind speed, combined simply and using only three tunable parameters, and without using any supplementary information such as the particular season or location on the planet.
    Description: Key Points: Model fits are performed to the spatiotemporal observed cloudiness over all oceans, using a minimal set of predictors and parameters. Models capture global‐mean, spatial, and most of seasonal variability of cloud radiative effects. Cloud albedo and longwave effect are captured by pressure velocity and its variance, surface temperature, and lower tropospheric stability.
    Description: CONSTRAIN project EU Horizon 2020
    Keywords: ddc:551.5 ; global cloudiness ; energy balance ; cloud controlling factors
    Language: English
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    Deep Learning Based Cloud Cover Parameterization for ICON (2022)
    Details
    Publication Date: 2023-12-05
    Description: A promising approach to improve cloud parameterizations within climate models and thus climate projections is to use deep learning in combination with training data from storm‐resolving model (SRM) simulations. The ICOsahedral Non‐hydrostatic (ICON) modeling framework permits simulations ranging from numerical weather prediction to climate projections, making it an ideal target to develop neural network (NN) based parameterizations for sub‐grid scale processes. Within the ICON framework, we train NN based cloud cover parameterizations with coarse‐grained data based on realistic regional and global ICON SRM simulations. We set up three different types of NNs that differ in the degree of vertical locality they assume for diagnosing cloud cover from coarse‐grained atmospheric state variables. The NNs accurately estimate sub‐grid scale cloud cover from coarse‐grained data that has similar geographical characteristics as their training data. Additionally, globally trained NNs can reproduce sub‐grid scale cloud cover of the regional SRM simulation. Using the game‐theory based interpretability library SHapley Additive exPlanations, we identify an overemphasis on specific humidity and cloud ice as the reason why our column‐based NN cannot perfectly generalize from the global to the regional coarse‐grained SRM data. The interpretability tool also helps visualize similarities and differences in feature importance between regionally and globally trained column‐based NNs, and reveals a local relationship between their cloud cover predictions and the thermodynamic environment. Our results show the potential of deep learning to derive accurate yet interpretable cloud cover parameterizations from global SRMs, and suggest that neighborhood‐based models may be a good compromise between accuracy and generalizability.
    Description: Plain Language Summary: Climate models, such as the ICOsahedral Non‐hydrostatic climate model, operate on low‐resolution grids, making it computationally feasible to use them for climate projections. However, physical processes –especially those associated with clouds– that happen on a sub‐grid scale (inside a grid box) cannot be resolved, yet they are critical for the climate. In this study, we train neural networks that return the cloudy fraction of a grid box knowing only low‐resolution grid‐box averaged variables (such as temperature, pressure, etc.) as the climate model sees them. We find that the neural networks can reproduce the sub‐grid scale cloud fraction on data sets similar to the one they were trained on. The networks trained on global data also prove to be applicable on regional data coming from a model simulation with an entirely different setup. Since neural networks are often described as black boxes that are therefore difficult to trust, we peek inside the black box to reveal what input features the neural networks have learned to focus on and in what respect the networks differ. Overall, the neural networks prove to be accurate methods of reproducing sub‐grid scale cloudiness and could improve climate model projections when implemented in a climate model.
    Description: Key Points: Neural networks can accurately learn sub‐grid scale cloud cover from realistic regional and global storm‐resolving simulations. Three neural network types account for different degrees of vertical locality and differentiate between cloud volume and cloud area fraction. Using a game theory based library we find that the neural networks tend to learn local mappings and are able to explain model errors.
    Description: EC ERC HORIZON EUROPE European Research Council
    Description: Partnership for Advanced Computing in Europe (PRACE)
    Description: NSF Science and Technology Center, Center for Learning the Earth with Artificial Intelligence and Physics (LEAP)
    Description: Deutsches Klimarechenzentrum
    Description: Columbia sub‐award 1
    Description: https://github.com/agrundner24/iconml_clc
    Description: https://doi.org/10.5281/zenodo.5788873
    Description: https://code.mpimet.mpg.de/projects/iconpublic
    Keywords: ddc:551.5 ; cloud cover ; parameterization ; machine learning ; neural network ; explainable AI ; SHAP
    Language: English
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    The Interface Between Magma and Earth's Atmosphere (2022)
    Details
    Publication Date: 2023-07-20
    Description: Volatiles released from magma can form bubbles and leave the magma body to eventually mix with atmospheric air. The composition of those volatiles, as derived from measurements made after their emission, is used to draw conclusions on processes in the Earth's interior or their influences on Earth's atmosphere. So far, the discussion of the influence of high‐temperature mixing with atmospheric air (in particular oxygen) on the measured volcanic gas composition is almost exclusively based on thermodynamic equilibrium (TE) considerations. By modeling the combined effects of C‐H‐O‐S reaction kinetics, turbulent mixing, and associated cooling during the first seconds after magmatic gas release into the atmosphere we show that the resulting gas compositions generally do not represent TE states, with individual species (e.g., CO, H2, H2S, OCS, SO3, HO2, H2O2) deviating by orders of magnitude from equilibrium levels. Besides revealing the chemical details of high‐temperature emission processes, our results question common interpretations of volcanic gas studies, particularly affecting the present understanding of auto‐catalytic conversion of volcanic halogen species in the atmosphere and redox state determination from volcanic plume gas measurements.
    Description: Plain Language Summary: A major fraction of magmatic gas emissions are released into the atmosphere from open vents. The emission processes are characterized by fast turbulent mixing with atmospheric air (within seconds) and associated rapid cooling. Hardly anything is known about the chemical kinetics within this brief mixing and cooling period. We simulate the chemical kinetics during the first seconds of hot magmatic gases in the atmosphere and find severe deviation to common interpretations and central thermodynamic equilibrium assumptions prevailing in volcanic gas geochemistry.
    Description: Key Points: We model the chemical kinetics of high‐temperature volcanic gas emissions within the first seconds of mixing with atmospheric air. We identify key chemical processes within the magma‐atmosphere interface and quantify influences on the volcanic plume composition. Our results question common assumptions prevailing in volcanic gas geochemistry and refine interpretations of gas emissions from open vents.
    Description: German Research Foundation
    Keywords: ddc:551.9 ; volcanic gas emissions ; kinetic chemistry modeling ; atmospheric chemistry ; magmatic redox states ; reactive halogen chemistry
    Language: English
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    Modeling cloud properties over the 79 N Glacier (Nioghalvfjerdsfjorden, NE Greenland) for an intense summer melt period in 2019 (2022)
    John Wiley & Sons, Ltd. | Chichester, UK
    Details
    Publication Date: 2023-07-25
    Description: Long believed to be insignificant, melt activity on the Northeast Greenland Ice Stream (NEGIS) has increased in recent years. Summertime Arctic clouds have the potential to strongly affect surface melt processes by regulating the amount of radiation received at the surface. However, the cloud effect over Greenland is spatially and temporally variable and high‐resolution information on the northeast is absent. This study aims at exploring the potential of a high‐resolution configuration of the polar‐optimized Weather Research & Forecasting Model (PWRF) in simulating cloud properties in the area of the Nioghalvfjerdsfjorden Glacier (79 N Glacier). Subsequently, the model simulations are employed to investigate the impact of Arctic clouds on the surface energy budget and on surface melting during the extensive melt event at the end of July 2019. Compared to automatic weather station (AWS) measurements and remote‐sensing data (Sentinel‐2A and the Moderate Resolution Imaging Spectroradiometer, MODIS), PWRF simulates cloud properties with sufficient accuracy. It appears that peak melt was caused by an increase in solar radiation and sensible heat flux (SHF) in response to a blocking anticyclone and foehn winds in the absence of clouds. Cloud warming over high‐albedo surfaces helped to precondition the surface and prolonged the melting as the anticyclone abated. The results are sensitive to the surface albedo and suggest spatiotemporal differences in the cloud effect as snow and ice properties change over the course of the melting season. This demonstrates the importance of including high‐resolution information on clouds in analyses of ice sheet dynamics.
    Description: German Federal Ministry for Education and Research http://dx.doi.org/10.13039/501100002347
    Description: https://doi.org/10.5065/EM0T-1D34
    Description: https://cds.climate.copernicus.eu/cdsapp/#!/search?type=dataset
    Description: https://ladsweb.modaps.eosdis.nasa.gov/search/
    Keywords: ddc:551.5 ; cloud properties ; cloud radiative effect ; Northeast Greenland Ice Stream ; regional climate modeling ; surface energy balance ; surface melt ; surface energy balance ; surface melt
    Language: English
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    Laboratory Assessment of the Impact of Chemical Oxidation, Mineral Dissolution, and Heating on the Nitrogen Isotopic Composition of Fossil‐Bound Organic Matter (2022)
    Details
    Publication Date: 2023-01-21
    Description: Fossil‐bound organic material holds great potential for the reconstruction of past changes in nitrogen (N) cycling. Here, with a series of laboratory experiments, we assess the potential effect of oxidative degradation, fossil dissolution, and thermal alteration on the fossil‐bound N isotopic composition of different fossil types, including deep and shallow water scleractinian corals, foraminifera, diatoms and tooth enamel. Our experiments show that exposure to different oxidizing reagents does not significantly affect the N isotopic composition or N content of any of the fossil types analyzed, demonstrating that organic matter is well protected from changes in the surrounding environment by the mineral matrix. In addition, we show that partial dissolution (of up to 70%–90%) of fossil aragonite, calcite, opal, or enamel matrixes has a negligible effect on the N isotopic composition and N content of the fossils. These results suggest that the isotopic composition of fossil‐bound organic material is relatively uniform, and also that N exposed during dissolution is lost without significant isotopic discrimination. Finally, our heating experiments show negligible changes in the N isotopic composition and N content of all fossil types at 100°C. At 200°C and hotter, any N loss and associated nitrogen isotope changes appear to be directly linked to the sensitivity of the mineral matrix to thermal stress, which depends on the biomineral type. These results suggest that, so long as high temperature does not compromise the mineral structure, the biomineral matrix acts as a closed system with respect to N, and the N isotopic composition of the fossil remains unchanged.
    Description: Plain Language Summary: The ratio of the heavy and light isotopes of nitrogen (15N and 14N) in the organic material contained within the mineral structure of fossils can be used to reconstruct past changes in biological and chemical processes. With a series of laboratory experiments, we evaluate the potential effects of chemical conditions, fossil dissolution, and heating on the nitrogen isotopic composition (15N/14N ratio) of corals, foraminifera, diatoms and tooth enamel. Our results indicate that these processes do not have a significant effect on the 15N/14N of fossils, suggesting that the mineral matrix provides a barrier that isolates a fossil's organic nitrogen from the surrounding environment, preventing alteration of its 15N/14N. In addition, we show that if part of the fossil‐bound organic nitrogen is exposed by dissolution or heating, it is lost without affecting the 15N/14N of the organic material that remains in the mineral. These findings imply that the original 15N/14N ratio incorporated by the organism is preserved in the geologic record. Therefore, measurements of the nitrogen isotopes on fossils can provide faithful biological, ecological, and environmental information about the past.
    Description: Key Points: Fossil‐bound organic matter is well protected by the mineral matrix from chemical changes in the surrounding environment. Partial dissolution of fossil calcite, aragonite, opal, and enamel has a negligible effect on their N isotopic composition and N content. During heating, fossil N content and isotopic composition remains unchanged if the structure of the inorganic matrix is not compromised.
    Description: Max Planck Society
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: US National Science Foundation
    Description: Paul Crutzen Nobel Prize Fellowship
    Description: https://doi.org/10.5281/zenodo.6884681
    Keywords: ddc:551.9 ; nitrogen isotopes ; diagenesis ; foraminifera ; corals ; diatoms ; teeth
    Language: English
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    Observational Evidence for Multivariate Drought Hazard Amplifications Across Disparate Climate Regimes (2022)
    Details
    Publication Date: 2023-01-25
    Description: Drought poses significant challenges to global water security in a warming world. A global‐scale synthesis of the multivariate drought risk considering interdependencies between drought attributes across disparate climate regimes is still lacking. Leveraging precipitation and streamflow observations of 270 large catchments over the globe, we show that multivariate drought hazard amplifies significantly (at ∼65–76% of catchments) considering dependence between drought duration and severity. A signifying nature of this amplification (A) is the power‐law scaling with dependence metric (A∝τλ;λ=5−12; $A\propto {\tau }^{\lambda };\,\lambda =5-12;$ where τ and λ are Kendall's correlation and the scaling exponent), revealing current approaches considering drought attributes as independent or linearly dependent will severely underestimate likelihood of extreme droughts. Furthermore, we find disparate responses in the multivariate imprints of meteorological to hydrological droughts across climate types, with strengths varying from large to modest in Tropics and Mid‐latitudes, which indicates weaker overlap between rain‐deficit and streamflow droughts. In contrast, a strong overlap in multivariate hazards of rain‐deficit and streamflow droughts is apparent across transitional Subtropics. Our study highlights the relevance of accounting for multivariate aspects of drought hazards to inform adaptation to water scarcity in a changing climate.
    Description: Plain Language Summary: The world's large river basins support a huge population and diverse ecosystems. A growing body of the literature suggests holistic risk management requires a “multivariate event perspective” to analyze interacting drought attributes rather than each of these drivers in isolation. Using the gauge‐based observational framework, we show a robust amplification in multivariate drought hazard and this response co‐vary among distinct climate regimes. Our multivariate hazard framework shows a contrasting response in multivariate imprints (or degree of overlap) of rain‐deficit (drivers) to streamflow (response)‐droughts across disparate climate regimes for milder and extreme categories of droughts; from substantial regional variations in multivariate drought hazard in tropics and mid‐latitudes, revealing a weak imprint between drought types. In contrast, the transitional subtropics show a modest variation in the multivariate imprint of drought types, indicating stronger imprint. We emphasize that failure to account for nonlinear interactions among interacting drought attributes will severely underestimate the extreme drought hazard, jeopardizing the adequacy of resilient water infrastructure design. The insights will aid in adaptation to extreme droughts under global warming.
    Description: Key Points: Global synthesis of multivariate drought imprints between rain‐deficit and streamflow droughts. Observational assessment showed strong amplifications in bivariate drought hazards to dependence. Strong imprints between rain‐deficit and streamflow droughts in transitional sub‐tropics.
    Description: Department of Science and Technology, Ministry of Science and Technology, India http://dx.doi.org/10.13039/501100001409
    Description: German Academic Exchange Service New Delhi http://dx.doi.org/10.13039/501100001650
    Description: Science and Engineering Research Board http://dx.doi.org/10.13039/501100001843
    Description: Indian Institute of Technology Kharagpur http://dx.doi.org/10.13039/501100008984
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Description: https://portal.grdc.bafg.de/applications/public.html?publicuser=PublicUser
    Description: https://opendata.dwd.de/climate_environment/GPCC/html/download_gate.html
    Keywords: ddc:551.5 ; hydrological drought ; meteorological drought ; multivariate drought hazard
    Language: English
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    Combining Commercial Microwave Link and Rain Gauge Observations to Estimate Countrywide Precipitation: A Stochastic Reconstruction and Pattern Analysis Approach (2022)
    Details
    Publication Date: 2024-02-28
    Description: Accurate spatiotemporal precipitation quantification is a crucial prerequisite for hydrological analyses. The optimal reconstruction of the spatial distribution, that is, the rainfall patterns, is particularly challenging. In this study, we reconstructed spatial rainfall on a countrywide scale for Germany by combining commercial microwave link and rain gauge observations for a better representation of the variability and spatial structure of rainfall. We further developed and applied the Random‐Mixing‐Whittaker‐Shannon method, enabling the stochastic reconstruction of ensembles of spatial fields via linear combinations of unconditional random fields. The pattern of rainfall objects is evaluated by three performance characteristics, that is, ensemble Structure‐, Amplitude‐, and Location‐error. Precipitation estimates obtained are in good agreement with the gauge‐adjusted weather radar product RADOLAN‐RW of the German Weather Service (DWD) which was used as a reference. Compared to reconstructions by Ordinary Kriging, Random Mixing showed clear advantages in the pattern representation via a five times smaller median structure error.
    Description: Plain Language Summary: Rainfall is commonly measured by dedicated sensors such as rain gauges or weather radars. Commercial microwave links (CMLs), which have the primary purpose of signal forwarding within cellular networks, can be used for rainfall measurements too. The signal, which is transmitted from one antenna to another, is being attenuated if it rains along the path. From the amount of attenuation an average rain rate can be retrieved. For many hydrological applications, it is of major interest to estimate area‐wide rainfall (i.e., rainfall maps) while observations provide only scattered information. In this study, we used the local information from almost 1,000 rain gauges and the information along the paths of 3,900 CMLs distributed over Germany to reconstruct rainfall maps. We did this by applying a method of stochastic simulation (called Random Mixing) which we compared to a more common method of estimation (Ordinary Kriging). To evaluate the quality of the obtained maps, we compared them to rainfall information from weather radars. We found that the general agreement is high, and that maps reconstructed by Random Mixing have particular advantages in representing the spatial structure, that is, the shape of rainfall cells.
    Description: Key Points: Geostatistical Random Mixing simulation now capable of countrywide spatial rainfall interpolation. Variability assessment via commercial microwave link path consideration and ensemble estimation. Realistic rainfall pattern representation quantified by ensemble Structure‐, Amplitude‐, and Location‐error metrics.
    Description: German Research Foundation
    Description: Federal Ministry of Education and Research
    Description: https://doi.org/10.5281/zenodo.4810169
    Description: https://opendata.dwd.de/climate_environment/CDC
    Description: https://maps.dwd.de/geoserver/web/wicket/bookmarkable/org.geoserver.web.demo.SRSDescriptionPage?10 26code=EPSG:1000001
    Description: https://doi.org/10.5281/zenodo.5380342
    Description: https://doi.org/10.5281/zenodo.7048941
    Description: https://doi.org/10.5281/zenodo.7049826
    Description: https://doi.org/10.5281/zenodo.7049846
    Keywords: ddc:551.5 ; precipitation estimation ; geostatistical simulation ; spatial pattern analysis ; commercial microwave links ; rain gauges ; random mixing
    Language: English
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    When Do Subpollen Particles Become Relevant for Ice Nucleation Processes in Clouds? (2022)
    Details
    Publication Date: 2024-02-09
    Description: When exposed to sufficiently humid environments, pollen grains burst and release large quantities of small subpollen particles (SPPs) which carry ice nucleating macromolecules. In this study, for the first time we develop a physically based parameterization describing the bursting process of pollen by applying a turgor pressure parameterization and quantify the impact SPPs have on overall ice nucleation in clouds. SPPs are generated from simulated birch pollen emissions over Europe for a 10‐day case study in spring. We found SPP concentrations to surpass pollen grain concentrations by 4–6 orders of magnitude leading to an abundance of biological ice nuclei from SPPs in the range of 103−104 m−3. However, it is found that these concentrations lead to only small changes in hydrometeor number densities and precipitation. Addressing the question when SPPs become relevant for ice nucleation in clouds, we conducted a sensitivity investigation. We find that amplifying ice nucleation efficiency of biological particles by factors greater 100 increases the ice particle numbers by up to 25% (T ≈ 268 K). Strong reductions show in cloud droplet number concentration and water vapor at these temperatures while water vapor is increasing at 600 m. Overall, we found a net reduction of water in the atmosphere as liquid and particularly water vapor density is reduced, while frozen water mass density increases above 257 K. Findings indicate an alteration of mixed‐phase cloud composition and increased precipitation (up to 6.2%) when SPPs are considered as highly efficient biological ice nuclei.
    Description: Key Points Subpollen particles (SPPs) reach freezing altitudes in large number concentrations. Nucleation efficiency of SPPs affects both amplitude and sign of impact on nucleation processes. Relevant impact requires greatly increased nucleation efficiency of the SPPs.
    Description: H2020 European Research Council http://dx.doi.org/10.13039/100010663
    Description: University of Toronto Scarborough Department of Physical and Environmental Sciences Travel Award
    Description: Ministry of Science, Research and the Arts Baden‐Württemberg
    Description: Deutsche Forschungsgemeinschaft
    Description: https://doi.org/10.35097/830
    Keywords: ddc:551.5 ; subpollen particle ; SPP ; biological ice nucleation ; burst parameterization
    Language: English
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    Fast Atmospheric Response to a Cold Oceanic Mesoscale Patch in the North‐Western Tropical Atlantic (2022)
    Details
    Publication Date: 2023-11-13
    Description: Low‐level clouds over the tropical and sub‐tropical oceans play a crucial role in the planetary radiative energy budget. However, they are challenging to model in climate simulations because they are affected by local processes that are still partially unknown. The control that mesoscale sea surface temperature (SST) structures have on the dynamics of the lower atmosphere on daily scales is emerging to be non‐negligible and calls for more effort to be understood. During the EUREC〈sup〉4〈/sup〉A field campaign, two of the research vessels (R/Vs) involved in the experiment sampled the edge of a cold mesoscale SST patch in the north‐western tropical Atlantic, crossing a gradient of roughly 0.75°C/100 km. The comprehensive set of instruments carried by the R/Vs allows an unprecedented characterization of the atmospheric response to the cold water forcing. The cold ocean patch weakens the vertical atmospheric mixing, reducing the boundary layer depth of roughly 200 m and the horizontal wind intensity of approximately 3 m s〈sup〉−1〈/sup〉. At the same time, the humidity content in the sub‐cloud layer increases and these conditions decrease the latent heat flux (by roughly 80 W m〈sup〉−2〈/sup〉) and reduce vertical velocity fluctuations, making it less likely that moisture exceeds the lifting condensation level. As a consequence, fewer and thinner low‐level clouds form over cold water. Independent satellite measurements are found to agree with the in situ observations. The observed link between sea temperature and low‐level clouds highlights its importance in the puzzle of modeling the sea‐air‐cloud interactions.
    Description: Plain Language Summary: Puffy clouds typically visible at sea strongly challenge climate models that struggle to represent their interaction with the sea surface and solar radiation. And as a consequence, these climate models cannot precisely estimate how much the Earth's temperature will increase 100 years from now and its uncertainty. We went into the western Atlantic ocean for a month in January–February 2020 to measure sea surface temperature and cloud properties and observe how these changes occur. We saw clouds grow deeper over the warm water patches, holding more water and eventually raining. Weaker winds and more humid air occur on cold patches. Satellite observations seem to record the same behavior over a larger area in the same region. We detected a clear difference in cloud properties and amounts over warm and cold patches from all sensors, recording essential evidence of a feature that is hard to predict. We hope these observations will help to properly simulate the intensity and signs of low‐cloud feedback over warm and cold oceanic patches of water to improve climate models.
    Description: Key Points: Ship‐based observations are used to characterize the lower atmospheric response to a cold patch in the north‐western subtropical Atlantic. Signatures in dynamical and thermodynamical atmospheric properties agree with a reduced vertical mixing over the cold patch. Such a weaker vertical mixing is linked to a reduced shallow cloud cover because less moisture reaches the level of saturation.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: ESA ESRIN
    Description: MIUR 2018–2022
    Description: COST European Cooperation in Science and Technology
    Description: Helmholtz Association of German Research Centers
    Description: https://doi.org/10.5281/zenodo.6365636
    Description: https://github.com/ClauClouds/SST-impact/
    Keywords: ddc:551.5 ; mesoscale SST structures ; low clouds ; cloud feedbacks ; marine boundary layer ; air‐sea interactions ; ship‐based remote sensing
    Language: English
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    Projecting Stratocumulus Transitions on the Albedo—Cloud Fraction Relationship Reveals Linearity of Albedo to Droplet Concentrations (2022)
    Details
    Publication Date: 2023-09-13
    Description: Satellite images show solid marine stratocumulus cloud decks (Sc) that break up over the remote oceans. The Sc breakup is initiated by precipitation and is accompanied by a strong reduction in the cloud radiative effect. Aerosol has been shown to delay the Sc breakup by postponing the onset of precipitation, however its climatic effect is uncertain. Here we introduce a new approach that allows us to re‐cast currently observed cloud cover and albedo to their counterfactual cleaner world, enabling the first estimate of the radiative effect due to delayed cloud breakup. Using simple radiative approximation, the radiative forcing with respect to pre‐industrial times due to delayed Sc breakup is −0.39 W m−2. The radiative effect changes nearly linearly with aerosol due to the droplet concentration control on the cloud cover, suggesting a potentially accelerated warming if the current trend of reduction in aerosol emissions continues.
    Description: Plain Language Summary: The response of cloud cover to aerosol is a climatologically important quantity that has been extremely difficult to estimate. The challenge is that one would need to estimate the fractional area that is currently overcast, but which would have been partly overcast in a cleaner atmosphere. Global climate models (GCMs) are one tool to address such a problem. They allow one to change aerosol levels and to evaluate the cloud response. However, representation of warm, low‐level cloud processes, and in particular aerosol‐cloud interactions in GCMs, is inadequate. Here we introduce an observational method that allows us to re‐cast the currently observed cloud cover and albedo of oceanic warm clouds to their counterfactual state in a cleaner world. We find a linear relationship between the cloud radiative effect and droplet concentration. If we continue to experience a decrease in aerosol emissions then we anticipate a reduction in the aerosol‐cloud radiative effect. The global annual radiative forcing associated with anthropogenic aerosol delaying closed cell breakup is found to be −0.39 W m−2.
    Description: Key Points: A simple model is presented to describe closed cell breakup by initiation of precipitation. The model demonstrates that the global annual radiative effect due to delayed closed cells breakup changes nearly linearly with emissions. The linearity emerges from the nearly linear relationship between cloud cover and albedo.
    Description: German Research Foundation
    Description: Department of Energy's Atmospheric System Research
    Description: Royal Society University Research Fellowship
    Description: https://ladsweb.modaps.eosdis.nasa.gov/archive/allData/61/MOD06_L2/
    Description: https://ceres-tool.larc.nasa.gov/ord-tool/jsp/SSF1degEd41Selection.jsp
    Description: https://doi.org/10.24381/cds.bd0915c6
    Description: https://doi.org/10.5281/zenodo.7072605
    Keywords: ddc:551.5 ; cloud radiative effect ; stratocumulus ; aerosol cloud interactions ; transitions ; closed cells ; open cells
    Language: English
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    Impact of Parametrizing Microphysical Processes in the Jet and Vortex Phase on Contrail Cirrus Properties and Radiative Forcing (2022)
    Details
    Publication Date: 2023-12-15
    Description: Contrail ice nucleation and ice crystal loss during the vortex phase control ice crystal numbers in young contrails and can have a strong impact on the properties and the life cycle of contrail cirrus. For current soot number emissions, ice nucleation is controlled by the number of emitted soot particles and atmospheric conditions while the vortex phase loss depends predominantly on the nucleated ice crystal numbers and the ambient relative humidity. Initial ice crystal numbers after the vortex phase are close to the emitted soot particle number only for very low ambient temperatures (〈210 K) and for highly ice‐supersaturated conditions. Higher temperatures and lower relative humidities lead to significantly decreased ice crystal numbers. Global climate model simulations show that initial contrail ice crystal numbers per fuel mass are on average 50%–65% decreased relative to the soot number emission index in the extratropics and more in tropics. In the extratropics, this is mainly caused by a high ice crystal loss during the vortex phase and in the (sub)tropics and at lower flight levels by decreased ice nucleation. Simulated ice crystal numbers per newly formed contrail length agree well with in situ measurements over central Europe within the variability of present‐day soot number emissions. Our estimated global mean contrail cirrus radiative forcing (RF) for the year 2006 is 44 (31–49) mWm〈sup〉−2〈/sup〉, around 22% lower than estimated in a previous study. When reducing soot number emissions by 80%, RF decreases by 41%, slightly less than suggested by a recent study.
    Description: Plain Language Summary: Contrail cirrus are known to be a major contribution to the aviation climate impact connected with a large uncertainty. Earlier research has shown that the ice crystal number in newly formed contrails has a large impact on the average contrail cirrus climate impact. But the properties of newly formed contrails are not well captured within the climate models. We have improved the representation of the contrail formation processes in our contrail cirrus module within the ECHAM climate model by including parameterizations for contrail ice nucleation and the ice crystal survival in the vortex phase. We could show that young contrail properties agree well with available campaign measurements over central Europe, given the large variability in soot number emissions, when matching geographical locations, cruise level, and atmospheric variables. The improvements within our contrail cirrus parameterization lead to a decrease in our estimate of contrail cirrus radiative forcing by slightly more than 20% relative to our earlier estimates in which we prescribed constant initial ice crystal numbers. Furthermore, our improved model indicates that the decrease in the contrail cirrus climate impact due to introducing biofuels, which lead to a decrease in soot number emissions, is slightly smaller than estimated earlier.
    Description: Key Points: For current soot emissions, young contrail ice numbers are limited by vortex phase loss in extratropics and ice nucleation in tropics. Modeled young contrail ice crystal numbers agree well with measurements over Europe considering the variability of soot number emissions. Sensitivity of contrail cirrus radiative forcing to soot number emissions decreased if capturing variability in young contrail ice numbers.
    Description: Emission and Climate Impact of Alternative Fuels
    Description: Scientific Steering Committee
    Description: https://zenodo.org/record/6902742
    Description: https://www.qtiplot.com/
    Description: http://ferret.pmel.noaa.gov/Ferret/
    Keywords: ddc:551.5 ; contrail formation ; soot number emissions ; ice crystal numbers ; contrail cirrus properties ; radiative forcing
    Language: English
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    Precipitation Over Southern Africa: Moisture Sources and Isotopic Composition (2022)
    Details
    Publication Date: 2023-12-14
    Description: Southern Africa, with its vast arid to semiarid areas, is considered vulnerable to precipitation changes and amplifying weather extremes. However, during the last 100 ka, huge lakes existed in the currently dry central Kalahari. It has been suggested that these lakes could have existed due to altered atmospheric circulation pattern, leading to an increase in precipitation or to changes in the annual precipitation distribution. Past climate changes are recorded in paleo‐archives, yet, for a proper interpretation of paleo‐records, for example, from sedimentological archives or fossils, it is essential to put them in a context with recent observations. This study’s objective is, therefore, to analyze spatially differing annual precipitation distributions at multiple locations in southern Africa with respect to their stable water isotope composition, moisture transport pathways, and sources. Five different precipitation distributions are identified by end‐member modeling and respective rainfall zones are inferred, which differ significantly in their isotopic compositions. By calculating backward trajectories, different moisture source regions are identified for the rainfall zones and linked to typical circulation patterns. Our results furthermore show the importance of the seasonality, the amount effect, and the traveled distance of the moisture for the general isotopic composition over the entire southern Africa. The identified pattern and relationships can be useful in the evaluation of isotope‐enabled climate models for the region and are potentially of major importance for the interpretation of stable water isotope composition in paleo‐records in future research.
    Description: Key Points: We identified five different annual precipitation distributions in southern Africa that cluster in space and define rainfall zones. Lagrangian source diagnostic shows that the rainfall zones have notably different moisture sources. The isotopic composition differs significantly between rainfall zones.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://nucleus.iaea.org/wiser
    Description: https://doi.pangaea.de/10.1594/PANGAEA.944811
    Description: https://doi.org/10.24381/cds.bd0915c6
    Description: http://iacweb.ethz.ch/staff/sprenger/lagranto/
    Description: https://forobs.jrc.ec.europa.eu/products/glc2000/products.php
    Description: https://doi.org/10.6084/m9.figshare.7504448.v3
    Description: https://doi.org/10.5066/F7J38R2N
    Description: https://cran.r-project.org/bin/windows/base/old/
    Description: https://cran.r-project.org/web/packages/EMMAgeo/index.html
    Description: https://cran.r-project.org/web/packages/party/index.html
    Keywords: ddc:551.5 ; Lagrangian moisture source diagnostic ; stable water isotopes ; precipitation end‐member ; random forest ; annual rainfall distribution ; moisture pathways
    Language: English
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    Impacts of the Desiccation of the Aral Sea on the Central Asian Dust Life‐Cycle (2022)
    Details
    Publication Date: 2023-12-19
    Description: The formation of the Aralkum (Aral Desert), following the severe desiccation of the former Aral Sea since the 1960s, has created what may be regarded as one of the world's most significant anthropogenic dust sources. In this paper, focusing on dust emission and transport patterns from the Aralkum, the dust life‐cycle has been simulated over Central Asia using the aerosol transport model COSMO‐MUSCAT (COnsortium for Small‐scale MOdelling‐MUltiScale Chemistry Aerosol Transport Model), making use of the Global Surface Water data set to take into account the sensitivity to changes in surface water coverage over the region between the 1980s (the “past”) and the 2010s (the “present”). Over a case study 1‐year period, the simulated dust emissions from the Aralkum region increased from 14.3 to 27.1 Tg year〈sup〉−1〈/sup〉 between the past and present, an increase driven solely by the changes in the surface water environment. Of these simulated modern emissions, 14.5 Tg are driven by westerly winds, indicating that regions downwind to the east may be worst affected by Aralkum dust. However a high degree of interannual variability in the prevailing surface wind patterns ensures that these transport patterns of Aralkum dust do not occur every year. Frequent cloud cover poses substantial challenges for observations of Central Asian dust: in the Aralkum, over two‐thirds of the yearly emissions are emitted under overcast skies, dust which may be impossible to observe using traditional satellite or ground‐based passive remote sensing techniques. Furthermore, it is apparent that the pattern of dust transport from the Aralkum under clear‐sky conditions is not representative of the pattern under all‐sky conditions.
    Description: Plain Language Summary: Since the 1960s the Central Asian lake that used to be known as the Aral Sea has almost completely dried out, due to human activity. This environmental disaster has created a new desert known as the Aralkum (the “Aral Desert”), which now has a size of 245 km × 245 km across. Dried lakes such as the Aralkum can be very effective sources of wind‐driven atmospheric dust. The soils of the Aralkum are also contaminated with agricultural chemicals from nearby croplands, making the Aralkum a major regional threat to human health. Using an atmospheric computer model, we explore the consequences of the new Aralkum for the patterns of atmospheric dust and their potential impacts in Central Asia. We find that the new Aralkum has contributed an extra 7% per year to the total dust quantity over Central Asia, however due to thick cloud cover over two thirds of this dust from the Aralkum cannot be seen by Earth‐observing satellites. The wind patterns over the Aralkum vary from year to year, so while our simulations predict that most of the Aralkum's dust is transported to the east during the simulation year, during other years plenty more dust will be transported elsewhere.
    Description: Key Points: The impact of changes in surface water coverage over the Aralkum (the former Aral Sea) for dust emission and transport is investigated. There is a high degree of interannual variability in the directions of dust‐emitting winds over the Aralkum. Over two thirds of Aralkum dust activity occurs under thick cloud cover, limiting the possibility of it being observed by satellites.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.5281/zenodo.6022747
    Description: https://global-surface-water.appspot.com/download
    Description: https://soilgrids.org/
    Description: https://search.earthdata.nasa.gov/search
    Description: https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels
    Description: https://ads.atmosphere.copernicus.eu/cdsapp#!/dataset/cams-global-reanalysis-eac4
    Description: https://ladsweb.modaps.eosdis.nasa.gov/search/
    Description: https://aeronet.gsfc.nasa.gov/
    Description: https://worldview.earthdata.nasa.gov/
    Keywords: ddc:551.5 ; dust aerosol ; Aralkum ; Central Asia ; modeling
    Language: English
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    Zircon Dates Long‐Lived Plume Dynamics in Oceanic Islands (2022)
    Details
    Publication Date: 2024-04-25
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉In this contribution we report the first systematic study of zircon U‐Pb geochronology and δ〈sup〉18〈/sup〉O‐〈italic〉ε〈/italic〉Hf〈sub〉(〈italic〉t〈/italic〉)〈/sub〉 isotope geochemistry from 10 islands of the hot‐spot related Galapagos Archipelago. The data extracted from the zircons allow them to be grouped into three types: (a) young zircons (0–∼4 Ma) with 〈italic〉ε〈/italic〉Hf〈sub〉(〈italic〉t〈/italic〉)〈/sub〉 (∼5–13) and δ〈sup〉18〈/sup〉O (∼4–7) isotopic mantle signature with crystallization ages dating the islands, (b) zircons with 〈italic〉ε〈/italic〉Hf〈sub〉(〈italic〉t〈/italic〉)〈/sub〉 (∼5–13) and δ〈sup〉18〈/sup〉O (∼5–7) isotopic mantle signature (∼4–164 Ma) which are interpreted to date the time of plume activity below the islands (∼164 Ma is the minimum time of impingement of the plume below the lithosphere), and (c) very old zircons (∼213–3,000 Ma) with mostly continental (but also juvenile) 〈italic〉ε〈/italic〉Hf〈sub〉(〈italic〉t〈/italic〉)〈/sub〉 (∼−28–8) and δ〈sup〉18〈/sup〉O (∼5–11) isotopic values documenting potential contamination from a number of sources. The first two types with similar isotopic mantle signature define what we call the Galápagos Plume Array (GPA). Given lithospheric plate motion, this result implies that GPA zircon predating the Galápagos lithosphere (i.e., >14–164 Ma) formed and were stored at sublithospheric depths for extended periods of time. In order to explain these observations, we performed 2D and 3D thermo‐mechanical numerical experiments of plume‐lithosphere interaction which show that dynamic plume activity gives rise to complex asthenospheric flow patterns and results in distinct long‐lasting mantle domains beneath a moving lithosphere. This demonstrates that it is physically plausible that old plume‐derived zircons survive at asthenospheric depths below ocean islands.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Our data define the Galápagos Plume Array defined by mantle 〈italic〉ε〈/italic〉Hf〈sub〉(〈italic〉t〈/italic〉)〈/sub〉 and δ18O values in the range ∼0–164 Ma〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉This finding allows dating back plume activity to, at least, early Middle Jurassic (∼164 Ma)〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Numerical experiments confirm it is plausible that old Plume‐derived zircons survive in the asthenosphere for extended periods of time〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Ministerio de Asuntos Económicos y Transformación Digital, Gobierno de España http://dx.doi.org/10.13039/501100010198
    Description: Ministerio de Ciencia e Innovación http://dx.doi.org/10.13039/501100004837
    Description: European Research Council http://dx.doi.org/10.13039/501100000781
    Description: https://doi.org/10.5281/zenodo.7047729
    Description: https://doi.org/10.5281/zenodo.6967187
    Keywords: ddc:551.9 ; mantle plume ; galapagos zircon ages ; asthenospheric zircon ; oceanic islands ; thermo‐mechanical numerical experiments
    Language: English
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    Stratus over rolling terrain: Large‐eddy simulation reference and sensitivity to grid spacing and numerics (2022)
    John Wiley & Sons, Ltd | Chichester, UK
    Details
    Publication Date: 2024-01-15
    Description: The formation of low stratus cloud over idealized hills is investigated using numerical model simulations. The main driver for the cloud formation is radiative cooling due to outgoing longwave radiation. Despite a purely horizontal flow, the advection terms in the prognostic equations for heat and moisture produce vertical mixing across the upper cloud edge, leading to a loss of cloud water content. This behavior is depicted via a budget analysis. More precisely, this spurious mixing is caused by the diffusive error of the advection scheme in regions where the sloping surfaces of the terrain‐following vertical coordinate intersect the cloud top. This study shows that the intensity of the (spurious) numerical diffusion depends strongly on the horizontal resolution, the order of the advection schemes, and the choice of scalar advection scheme. A large‐eddy simulation with 4‐m horizontal resolution serves as a reference. For horizontal resolutions of a few hundred meters and simulations carried out with a model setup as used in numerical weather prediction, a strong reduction of the simulated liquid‐water path is observed. In order to keep the (spurious) numerical diffusion at coarser resolutions small, at least a fifth‐order advection scheme should be used. In the present case, a weighted essentially nonoscillatory scalar advection scheme turns out to increase the numerical diffusion along a sharp cloud edge compared with an upwind scheme. Furthermore, the choice of vertical coordinate has a strong impact on the simulated liquid‐water path over orography. With a modified definition of the sigma coordinate, it is possible to produce cloud water where the classical sigma coordinate does not allow any cloud formation.
    Description: Diffusive errors of the advection scheme reduce the cloud water content of low stratus over idealized hills. This is due to the terrain‐following vertical coordinate and depends strongly on the horizontal resolution. Orographic features should be represented by at least 𝒪(10) grid points and a fifth‐order advection scheme (or higher) should be used. A weighted essentially nonoscillatory scalar advection scheme increases numerical diffusion along a sharp cloud edge compared with an upwind scheme. Modifying the definition of the sigma coordinate leads to a strong gain in the simulated liquid‐water path.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Hans Ertel Centre for Weather Research
    Keywords: ddc:551.5 ; advection ; fog ; low stratus ; resolution ; rolling terrain ; vertical coordinate
    Language: English
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    Dissolved, Labile, and Total Particulate Trace Metal Dynamics on the Northeast Greenland Shelf (2022)
    Chen, Xue‐Gang ; Krisch, Stephan ; Al‐Hashem, Ali ; [et al.]
    Details
    Publication Date: 2024-03-22
    Description: We present high‐resolution profiles of dissolved, labile, and total particulate trace metals (TMs) on the Northeast Greenland shelf from GEOTRACES cruise GN05 in August 2016. Combined with radium isotopes, stable oxygen isotopes, and noble gas measurements, elemental distributions suggest that TM dynamics were mainly regulated by the mixing between North Atlantic‐derived Intermediate Water, enriched in labile particulate TMs (LpTMs), and Arctic surface waters, enriched in Siberian shelf‐derived dissolved TMs (dTMs; Co, Cu, Fe, Mn, and Ni) carried by the Transpolar Drift. These two distinct sources were delineated by salinity‐dependent variations of dTM and LpTM concentrations and the proportion of dTMs relative to the total dissolved and labile particulate ratios. Locally produced meltwater from the Nioghalvfjerdsbræ (79NG) glacier cavity, distinguished from other freshwater sources using helium excess, contributed a large pool of dTMs to the shelf inventory. Localized peaks in labile and total particulate Cd, Co, Fe, Mn, Ni, Cu, Al, V, and Ti in the cavity outflow, however, were not directly contributed by submarine melting. Instead, these particulate TMs were mainly supplied by the re‐suspension of cavity sediment particles. Currently, Arctic Ocean outflows are the most important source of dFe, dCu, and dNi on the shelf, while LpTMs and up to 60% of dMn and dCo are mainly supplied by subglacial discharge from the 79NG cavity. Therefore, changes in the cavity‐overturning dynamics of 79NG induced by glacial retreat, and alterations in the transport of Siberian shelf‐derived materials with the Transport Drift may shift the shelf dTM‐LpTM stoichiometry in the future.
    Description: Plain Language Summary: Trace metals (TMs) including cobalt (Co), iron (Fe), manganese (Mn), copper (Cu), and nickel (Ni) are essential micronutrients for marine productivity. The Northeast Greenland shelf is a climatically sensitive region, influenced by both outflowing Arctic waters and local glacier melting. We lack knowledge on how these Arctic surface waters affect TM dynamics on the Greenland shelf and how climatic shifts may influence TM dynamics. Here, we distinguish local submarine meltwater from Arctic surface waters using distinct tracers; noble gases and radium isotopes. We show that the TM dynamics on the shelf are largely controlled by the intrusion of Arctic surface waters which creates a near‐surface plume of dissolved and labile particulate TMs. Conversely, submarine meltwater creates a subsurface plume enriched in dissolved TMs but depleted in particulate TMs, which is exported from underneath a floating ice tongue. In the future, increasing Arctic river discharge and local glacial melting may both significantly change shelf micronutrient ratios demonstrating downstream impacts of a changing cryosphere on marine biogeochemical cycles.
    Description: Key Points: The overall dissolved and particulate trace metal (TM) dynamics were mainly regulated by the mixing with Arctic surface waters. Resuspension of cavity sediments is a major localized source of labile and total particulate Cd, Co, Fe, Mn, Ni, Cu, Al, V, and Ti. Whilst dissolved and particulate TMs are mostly coupled on the Greenland shelf, cavity outflow decouples both phases.
    Description: Kuwait Institute for Scientific Research
    Description: Deutsche Forschungsgemeinschaft
    Description: https://doi.pangaea.de/10.1594/PANGAEA.871030
    Description: https://doi.pangaea.de/10.1594/PANGAEA.871030
    Description: https://doi.pangaea.de/10.1594/PANGAEA.871028
    Description: https://doi.pangaea.de/10.1594/PANGAEA.905347
    Description: https://doi.pangaea.de/10.1594/PANGAEA.933431
    Description: https://doi.pangaea.de/10.1594/PANGAEA.948466
    Description: https://doi.pangaea.de/10.1594/PANGAEA.936029
    Description: https://doi.pangaea.de/10.1594/PANGAEA.936027
    Description: https://doi.org/10.1594/PANGAEA.931336
    Keywords: ddc:551.9 ; Arctic ; trace metals ; labile particulate ; glacier ; meltwater ; GEOTRACES
    Language: English
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  • 74
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    Accessories in Kaiserstuhl carbonatites and related rocks as accurate and faithful recorders of whole rock age and isotopic composition (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-06
    Description: The accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites and carbonate-rich foidites from the Kaiserstuhl are variously suited for the in situ determination of their U–Pb ages and Sr, Nd- and Hf-isotope ratios by LA-ICP-MS. The 143Nd/144Nd ratios may be determined precisely in all five phases, the 176Hf/177Hf ratios only in calzirtite and the 87Sr/86Sr ratios in perovskites and pyrochlores. The carbonatites and carbonate-rich foidites belong to one of the three magmatic groups that Schleicher et al. (1990) distinguished in the Kaiserstuhl on the basis of their Sr, Nd and Pb isotope ratios. Tephrites, phonolites and essexites (nepheline monzogabbros) form the second and limburgites (nepheline basanites) and olivine nephelinites the third. Our 87Sr/86Sr isotope data from the accessories overlap with the carbonatite and olivine nephelinite fields defined by Schleicher et al. (1990) but exhibit a much narrower range. These and the εNd and εHf values plot along the mantle array in the field of oceanic island basalts relatively close to mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar and fission track ages for the Kaiserstuhl lie between 16.2 and 17.8 Ma. They stem entirely from the geologically older tephrites, phonolites and essexites. No ages existed so far for the geologically younger carbonatites and carbonate-rich foidites except for one apatite fission track age (15.8 Ma). We obtained precise U–Pb ages for zirconolites and calzirtites of 15.66, respectively 15.5 Ma (± 0.1 2σ) and for pyrochlores of 15.35 ± 0.24 Ma. Only the perovskites from the Badberg soevite yielded a U–P concordia age of 14.56 ± 0.86 Ma while the perovskites from bergalites (haüyne melilitites) only gave 206Pb/238U and 208Pb/232Th ages of 15.26 ± 0.21, respectively, 15.28 ± 0.48 Ma. The main Kaiserstuhl rock types were emplaced over a time span of 1.6 Ma almost 1 million years before the carbonatites and carbonate-rich foidites. These were emplaced within only 0.32 Ma.
    Description: Frankfurt Institute for Advanced Studies (FIAS) (4401)
    Keywords: ddc:551.9 ; In situ determination of Sr, Nd and Hf isotope ratios ; In situ determination of U–Pb ages ; Accessories in carbonatites ; Kaiserstuhl
    Language: English
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    Oxygen Consumption of Resuspended Sediments of the Upper Elbe Estuary: Process Identification and Prognosis (2021)
    Springer Netherlands
    Details
    Publication Date: 2023-08-25
    Description: The resuspension of sediment leads to an increased release of nutrients and organic substances into the overlying water column, which can have a negative effect on the oxygen budget. Especially in the warmer months with a lower oxygen saturation and higher biological activity, the oxygen content can reach critical thresholds in estuaries like the upper Elbe estuary. Many studies have dealt with the nutrient fluxes that occur during a resuspension event. However, the sediment properties that influence the oxygen consumption potential (OCP) and the different biochemical processes have not been examined in detail. To fill this gap, we investigated the biogeochemical composition, texture, and OCP of sediments at 21 locations as well as the temporal variability within one location for a period of 2 years (monthly sampling) in the upper Elbe estuary. The OCP of sediments during a seven-day resuspension event can be described by the processes of sulphate formation, nitrification, and mineralisation. Chlorophyll, total nitrogen (Ntotal), and total organic carbon showed the highest correlations with the OCP. Based on these correlations, we developed a prognosis model to calculate the OCP for the upper Elbe estuary with a single sediment parameter (Ntotal). The model is well suited to calculate the oxygen consumption of resuspended sediments in the Hamburg port area during the relevant warmer months and shows a normalised root mean squared error of 〈 0.11 ± 0.13. Thus, the effect of maintenance measures such as water injection dredging and ship-induced wave on the oxygen budget of the water can be calculated.
    Description: Hamburg Port Authority
    Description: Universität Hamburg (1037)
    Keywords: ddc:551.9 ; Sediment ; Resuspension ; Oxygen consumption ; Nutrients ; Elbe estuary ; Modelling
    Language: English
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  • 76
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    Sub-arc mantle enrichment in the Sunda rear-arc inferred from HFSE systematics in high-K lavas from Java (2021)
    Kirchenbaur, M. ; Schuth, S. ; Barth, A. R. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: Many terrestrial silicate reservoirs display a characteristic depletion in Nb, which has been explained in some studies by the presence of reservoirs on Earth with superchondritic Nb/Ta. As one classical example, K-rich lavas from the Sunda rear-arc, Indonesia, have been invoked to tap such a high-Nb/Ta reservoir. To elucidate the petrogenetic processes active beneath the Java rear-arc and the causes for the superchondritic Nb/Ta in some of these lavas, we studied samples from the somewhat enigmatic Javanese rear-arc volcano Muria, which allow conclusions regarding the across-arc variations in volcanic output, source mineralogy and subduction components. We additionally report some data for an along-arc sequence of lavas from the Indonesian part of the Sunda arc, extending from Krakatoa in the west to the islands of Bali and Lombok in the east. We present major and trace element concentrations, Sr–Nd–Hf–Pb isotope compositions, and high-field-strength element (HFSE: Nb, Ta, Zr, Hf, W) concentrations obtained via isotope dilution and MC-ICP-MS analyses. The geochemical data are complemented by melting models covering different source compositions with slab melts formed at variable P–T conditions. The radiogenic isotope compositions of the frontal arc lavas in combination with their trace element systematics confirm previously established regional variations of subduction components along the arc. Melting models show a clear contribution of a sediment-derived component to the HFSE budget of the frontal arc lavas, particularly affecting Zr–Hf and W. In contrast, the K-rich rear-arc lavas tap more hybrid and enriched mantle sources. The HFSE budget of the rear-arc lavas is in particular characterized by superchondritic Nb/Ta (up to 25) that are attributed to deep melting involving overprint by slab melts formed from an enriched garnet–rutile-bearing eclogitic residue. Sub-arc slab melting was potentially triggered along a slab tear beneath the Sunda arc, which is the result of the forced subduction of an oceanic basement relief ~ 8 Myr ago as confirmed by geophysical studies. The purported age of the slab tear coincides with a paucity in arc volcanism, widespread thrusting of the Javanese basement crust as well as the short-lived nature of the K-rich rear-arc volcanism at that time.
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Description: Gottfried Wilhelm Leibniz Universität Hannover (1038)
    Keywords: ddc:551.9 ; Rear-arc volcanism ; Superchondritic Nb/Ta ; Muria ; Sunda arc
    Language: English
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    The composition of subduction zone fluids and the origin of the trace element enrichment in arc magmas (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-21
    Description: The partitioning of major and trace elements between eclogite and aqueous fluids with variable salinity was studied at 700–800 °C and 4–6 GPa in piston cylinder and multi anvil experiments. Fluid compositions were determined using the diamond trap technique combined with laser ablation ICP-MS measurements in the frozen state. In addition to NaCl, SiO2 is the main solute in the fluids. The fluid/eclogite partition coefficients of the large ion lithophile elements (LILE), such as Rb, Cs, Sr, and Ba as well as those of the light rare earths (LREE), of Pb, and of U increase by up to three orders of magnitude with salinity. These elements will therefore be efficiently transported by saline fluids. On the other hand, typical high field strength elements, such as Ti, Nb, and Ta, are not mobilized even at high salinities. Increasing temperature and pressure gradually increases the partitioning into the fluid. In particular, Th is mobilized by silica-rich fluids at 6 GPa already at low salinities. We show that we can fully reproduce the trace element enrichment pattern of primitive arc basalts by adding a few percent of saline fluid (with 5–10 wt% Cl) released from the basaltic slab to the zone of melting in the mantle wedge. Assuming 2 wt% of rutile in the eclogite equilibrated with the saline fluid produces a negative Nb Ta anomaly that is larger than in most primitive arc basalts. Therefore, we conclude that the rutile fraction in the subducted eclogite below most arcs is likely 〈 1 wt%. In fact, saline fluids would even produce a noticeable negative Nb Ta anomaly without any rutile in the eclogite residue. Metasomatism by sediment melts alone, on the other hand, is unable to produce the enrichment pattern seen in arc basalts. We, therefore, conclude that at least for primitive arc basalts, the release of hydrous fluids from the basaltic part of the subducted slab is the trigger for melting and the main agent of trace element enrichment. The contribution of sediment melts to the petrogenesis of these magmas is likely negligible. In the supplementary material, we provide a “Subduction Calculator” in Excel format, which allows the calculation of the trace element abundance pattern in primitive arc basalts as function of fluid salinity, the amount of fluid released from the basaltic part of the subducted slab, the fluid fraction added to the source, and the degree of melting.
    Description: DFG
    Description: Universität Bayreuth (3145)
    Keywords: ddc:551.9 ; Subduction zone fluids ; Fluid/eclogite partitioning ; Arc magmas ; Salinity ; Trace elements ; Nb Ta anomaly ; Primitive arc basalts
    Language: English
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    Intercomparison of different state-of-the-art formulations of the mass density of humid air (2021)
    Springer International Publishing
    Details
    Publication Date: 2024-02-23
    Description: The differences between one classical and three state-of-the-art formulations of the mass density of humid air were quantified. Here, we present both the calculi for direct determination of the humid-air mass density employing the virial form of the thermodynamic equation of state, and a sufficiently accurate look-up-table for the quick-look determination of the humid-air mass density, which is based on the advanced Thermodynamic Equation of Seawater 2010.
    Description: Leibniz-Institut für Troposphärenforschung e.V. (3489)
    Keywords: ddc:551.5 ; Mass density ; Humid air ; Real-gas effects ; TEOS-10
    Language: English
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    Solar noble gases in an iron meteorite indicate terrestrial mantle signatures derive from Earth’s core (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2023-11-18
    Description: Noble gases are important tracers of planetary accretion and acquisition of volatiles to planetary atmospheres and interiors. Earth’s mantle hosts solar-type helium and neon for which 〈sup〉20〈/sup〉Ne/〈sup〉22〈/sup〉Ne ratios advocate either incorporation of solar wind irradiated solids or solar nebula gas dissolution into an early magma ocean. However, the exact source location of primordial signatures remains unclear. Here we use high-resolution stepwise heating gas extraction experiments to analyse interior samples of the iron meteorite Washington County and find that they contain striking excesses of solar helium and neon. We infer that the Washington County protolith was irradiated by solar wind and that implanted noble gases were partitioned into segregating metal melts. The corollary that solar signatures are able to enter the cores of differentiated planetesimals and protoplanets validates hypotheses that Earth’s core may have incorporated solar noble gases and may be contributing to the solar signatures observed in Earth’s mantle.
    Description: Incorporation of iron meteorites in the core could explain variable noble gas signatures in different mantle reservoirs, according to stepwise heating experiments which show that the Washington County meteorite carries solar wind-derived He and Ne.
    Description: Klaus Tschira Stiftung (Klaus Tschira Foundation) https://doi.org/10.13039/501100007316
    Description: https://doi.org/10.26022/IEDA/111938
    Keywords: ddc:551.9 ; Core processes ; Early solar system ; Geochemistry ; Geodynamics ; Meteoritics
    Language: English
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  • 80
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    Trace-element behaviour in sediments of Ugandan part of Lake Victoria: results from sequential extraction and chemometrical evaluation (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-11-18
    Description: Lake Victoria is the second largest freshwater lake and the largest tropical lake in the world. The transboundary lake has the fastest growing population in its catchment, which can impact the water and sediment quality. To determine the extent of anthropogenic effects on sediment quality in the Ugandan part of Lake Victoria, the contents and binding behaviour of trace elements were analysed, as well as organic matter and phosphorus in different sediment layers of both deep and coastal sediments near the coastal cities of Entebbe, Kampala and Jinja. The data were assessed using the German LAWA criteria for trace-element pollution, the Geo-Index, Cluster- and Factor analyses. Mostly, no critical trace-element contamination in the sediments of the investigated area was observed. However, changes in element distributions caused by anthropogenic influences from around the lake were detected, like higher contents of Cu, Ti and V in near shore sediments with urban surrounding. Near Jinja, industrial wastewaters caused particularly elevated contents of Cu in the sediments (70–121 mg/kg, 3.5–6 times the geogenic background), exceeding the LAWA criteria and potentially harming the aquatic habitat. In addition, temporally growing organic matter contents in the lake sediments near the estuary of River Nzoia (from 4.2 to 17.6% in around 60 years) due to increased soil erosion in the river’s catchment area and blooms of the water hyacinth became visible. This study demonstrates that the whole catchment area is responsible to ensure a healthy aquatic ecosystem in Lake Victoria.
    Description: International Foundation for Science (IFS)
    Description: Organisation for the Prohibition of Chemical Weapons http://dx.doi.org/10.13039/501100004766
    Description: Helmholtz-Zentrum für Umweltforschung GmbH - UFZ (4215)
    Keywords: ddc:551.9 ; Lake Victoria ; Sediments ; Trace elements and heavy metals ; BCR extraction ; Igeo and LAWA ; Chemometrical judge- and assessment
    Language: English
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    Bioavailable DOC: reactive nutrient ratios control heterotrophic nutrient assimilation—An experimental proof of the macronutrient-access hypothesis (2021)
    Graeber, Daniel ; Tenzin, Youngdoung ; Stutter, Marc ; [et al.]
    Springer International Publishing
    Details
    Publication Date: 2023-11-28
    Description: We investigate the "macronutrient-access hypothesis", which states that the balance between stoichiometric macronutrient demand and accessible macronutrients controls nutrient assimilation by aquatic heterotrophs. Within this hypothesis, we consider bioavailable dissolved organic carbon (bDOC), reactive nitrogen (N) and reactive phosphorus (P) to be the macronutrients accessible to heterotrophic assimilation. Here, reactive N and P are the sums of dissolved inorganic N (nitrate-N, nitrite-N, ammonium-N), soluble-reactive P (SRP), and bioavailable dissolved organic N (bDON) and P (bDOP). Previous data from various freshwaters suggests this hypothesis, yet clear experimental support is missing. We assessed this hypothesis in a proof-of-concept experiment for waters from four small agricultural streams. We used seven different bDOC:reactive N and bDOC:reactive P ratios, induced by seven levels of alder leaf leachate addition. With these treatments and a stream-water specific bacterial inoculum, we conducted a 3-day experiment with three independent replicates per combination of stream water, treatment, and sampling occasion. Here, we extracted dissolved organic matter (DOM) fluorophores by measuring excitation-emission matrices with subsequent parallel factor decomposition (EEM-PARAFAC). We assessed the true bioavailability of DOC, DON, and the DOM fluorophores as the concentration difference between the beginning and end of each experiment. Subsequently, we calculated the bDOC and bDON concentrations based on the bioavailable EEM-PARAFAC fluorophores, and compared the calculated bDOC and bDON concentrations to their true bioavailability. Due to very low DOP concentrations, the DOP determination uncertainty was high, and we assumed DOP to be a negligible part of the reactive P. For bDOC and bDON, the true bioavailability measurements agreed with the same fractions calculated indirectly from bioavailable EEM-PARAFAC fluorophores (bDOC r〈sup〉2〈/sup〉 = 0.96, p 〈 0.001; bDON r〈sup〉2〈/sup〉 = 0.77, p 〈 0.001). Hence we could predict bDOC and bDON concentrations based on the EEM-PARAFAC fluorophores. The ratios of bDOC:reactive N (sum of bDON and DIN) and bDOC:reactive P (equal to SRP) exerted a strong, predictable stoichiometric control on reactive N and P uptake (R〈sup〉2〈/sup〉 = 0.80 and 0.83). To define zones of C:N:P (co-)limitation of heterotrophic assimilation, we used a novel ternary-plot approach combining our data with literature data on C:N:P ranges of bacterial biomass. Here, we found a zone of maximum reactive N uptake (C:N:P approx. 〉 114: 〈 9:1), reactive P uptake (C:N:P approx. 〉 170:21: 〈 1) and reactive N and P co-limitation of nutrient uptake (C:N:P approx. 〉 204:14:1). The “macronutrient-access hypothesis” links ecological stoichiometry and biogeochemistry, and may be of importance for nutrient uptake in many freshwater ecosystems. However, this experiment is only a starting point and this hypothesis needs to be corroborated by further experiments for more sites, by in-situ studies, and with different DOC sources.
    Description: Rural and Environment Science and Analytical Services Division http://dx.doi.org/10.13039/100011310
    Description: Helmholtz-Gemeinschaft http://dx.doi.org/10.13039/501100001656
    Description: Helmholtz-Zentrum für Umweltforschung GmbH - UFZ (4215)
    Keywords: ddc:551.9 ; Ecological stoichiometry ; Dissolved organic nitrogen ; PARAFAC ; Dissolved inorganic nitrogen ; Phosphate ; Ternary plots
    Language: English
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    The composition of CI chondrites and their contents of chlorine and bromine: Results from instrumental neutron activation analysis (2021)
    Details
    Publication Date: 2023-09-13
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Between 1973 and 1994, 15 samples of CI chondrites were analyzed by neutron activation analysis at the Max‐Planck‐Institute for Chemistry, Department of Cosmochemistry in Mainz, Germany. The analyses comprise nine Orgueil samples and three samples of Ivuna, two of Alais and one of Tonk. Samples came from various sources and had masses between 5 and 600 mg. Most data are published here for the first time. The results for the nine Orgueil samples demonstrate the essentially homogeneous chemical composition of Orgueil at a level of a few milligrams. The analytical results of Ivuna, Alais, and Tonk agree, with only few exceptions, with the results of Orgueil analyses. All samples agree within ±3% in their contents of Sc, Ir, Cr, Fe, Co, Zn, and Se. The elements Sc and Ir represent the refractory component; Cr, Fe, and Co the main component; and Zn and Se the volatile component. Thus, in all CI chondrites there are essentially the same fractions of the fundamental cosmochemical components. The essentially identical chemical composition of all samples shows that their water contents are constant at about 20 ± 5 wt%. There is excellent agreement between the data listed here with data reported in the relevant literature. There is no doubt that the CI composition is a well‐defined entity, which is thought to represent the non‐gaseous compositions of the solar nebula and the photosphere of the Sun. In addition, we conclude that the recently proposed new CI chondritic chlorine and Br values are too low, when compared to earlier measurements.〈/p〉
    Keywords: ddc:551.9 ; CI chondrites ; composition ; chlorine ; bromine ; neutron activation analysis
    Language: English
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    Hydrochemistry and environmental isotopes (18O, 2H, 3H, 3He/4He) of groundwater and floodwater in the great area of Hurghada, Eastern Desert of Egypt (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-09-14
    Description: Porous and fractured aquifers exist in the area of Hurghada, Eastern Desert of Egypt, whose recharge processes through the common flash floods are not identified. Hydrochemical parameters, stable isotopes 〈sup〉18〈/sup〉O, 〈sup〉2〈/sup〉H and tritium in floodwater and groundwater were applied in the area subject to study. Additionally, He isotopes were investigated in the deep wells in the faulted zone at the Abu Shaar Plateau. 〈sup〉3〈/sup〉H activity in all sampled points lies below the detection limit excluding a recent recharge component in groundwater. However, the hydrochemical ratios and the stable isotope signature confirm that the shallow wells and springs (Red Sea Hills group) are being recharged from modern precipitation. The hydrochemical parameters of the deep wells at the Abu Shaar Plateau (coastal plain group) confirm another origin for the ions rather than the modern precipitation. Together with the 〈sup〉18〈/sup〉O and 〈sup〉2〈/sup〉H values, the Br/Cl ratio of this group confirms the absence of seawater intrusion component and the role of the fault as a hydraulic barrier. These 〈sup〉18〈/sup〉O and 〈sup〉2〈/sup〉H values deviate from the GMWL confirming an evaporation effect and colder infiltration conditions and reveal strongly a possible mixing with the Nubian Sandstone in the region. The 〈sup〉3〈/sup〉He/〈sup〉4〈/sup〉He ratio confirms a mantle contribution of 2% from the total He components.
    Description: Open Access funding enabled and organized by Projekt DEAL
    Keywords: ddc:551.9 ; Groundwater ; Floodwater ; Hydrochemistry ; Water isotopes ; Helium isotopes ; Eastern desert of Egypt
    Language: English
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    Comparison of seasonal and longitudinal variation of daytime MSTID activity using GPS observation and GAIA simulations (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2024-01-19
    Description: The total electron content (TEC) data derived from the GAIA (Ground-to-topside model of Atmosphere Ionosphere for Aeronomy) is used to study the seasonal and longitudinal variation of occurrence of medium-scale traveling ionospheric disturbances (MSTIDs) during daytime (09:00–15:00 LT) for the year 2011 at eight locations in northern and southern hemispheres, and the results are compared with ground-based Global Positioning System (GPS)-TEC. To derive TEC variations caused by MSTIDs from the GAIA (GPS) data, we obtained detrended TEC by subtracting 2-h (1-h) running average from the TEC, and calculated standard deviation of the detrended TEC in 2 h (1 h). MSTID activity was defined as a ratio of the standard deviation to the averaged TEC. Both GAIA simulation and GPS observations data show that daytime MSTID activities in the northern and southern hemisphere (NH and SH) are higher in winter than in other seasons. From the GAIA simulation, the amplitude of the meridional wind variations, which could be representative of gravity waves (GWs), shows two peaks in winter and summer. The winter peak in the amplitude of the meridional wind variations coincides with the winter peak of the daytime MSTIDs, indicating that the high GW activity is responsible for the high MSTID activity. On the other hand, the MSTID activity does not increase in summer. This is because the GWs in the thermosphere propagate poleward in summer, and equatorward in winter, and the equatorward-propagating GWs cause large plasma density perturbations compared to the poleward-propagating GWs. Longitudinal variation of daytime MSTID activity in winter is seen in both hemispheres. The MSTID activity during winter in the NH is higher over Japan than USA, and the MSTID activity during winter in the SH is the highest in South America. In a nutshell, GAIA can successfully reproduce the seasonal and longitudinal variation of the daytime MSTIDs. This study confirms that GWs cause the daytime MSTIDs in GAIA and amplitude and propagation direction of the GWs control the noted seasonal variation. GW activities in the middle and lower atmosphere cause the longitudinal variation.
    Description: Japan Society for the Promotion of Science, KAKENHI (15H05815, 16H06286), Project for Solar-Terrestrial Environment Prediction (PSTEP) and Study of dynamical variation of particles and waves in the inner magnetosphere using ground-based network observation
    Description: Projekt DEAL
    Keywords: ddc:551.5 ; Daytime MSTIDs ; GAIA model ; GPS ; Gravity waves ; Meridional wind ; TEC
    Language: English
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    Sulphate reduction determines the long-term effect of iron amendments on phosphorus retention in lake sediments (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2024-01-12
    Description: Purpose: This field study aimed to guide the planning of iron amendments for phosphorus retention by investigating the long-term fate of iron added to two urban lakes (Plötzensee and Groß Glienicker See) in Berlin, Germany. The contributions of iron dosing to improve lake status as well as the relevance of competing processes for management success were evaluated. Methods: Sediment stratigraphy, as well as occurrence of iron minerals, and fluxes between water and sediment were examined using geochemical analyses (i.e. element composition, sequential extraction, X-ray diffraction, and pore water analyses). A one-box lake model was used to relate these fluxes to monitoring data from the water column and to sediment inventories. Results: In both lakes, the added iron was preserved in the sediment. Whereas phosphorus retention increased following the addition of iron to Groß Glienicker See, sulphur was retained by the excess iron in Plötzensee. This contrasting effect is attributed to significantly different sulphate reduction rates in two lakes (Wilcoxon rank sum test: W = 25, p = 0.008). According to the one-box model, sulphate reduction explained both the decrease in measured sulphate concentrations after iron application as well as the observed increase in sulphur deposition in the sediments. Conclusion: Management interventions involving iron amendments to enhance phosphorus retention must consider the competing process of iron sulphide formation during the entire management plan period, and additional iron may need to be applied to account for this effect.
    Description: Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB) im Forschungsverbund Berlin e.V. (3473)
    Keywords: ddc:551.9 ; Iron dosing ; Lake restoration ; Management implications ; Minerals ; Sulphur cycling ; Long-term field study ; One-box model
    Language: English
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    Groundwater fluoride contamination in Coimbatore district: a geochemical characterization, multivariate analysis, and human health risk perspective (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2024-04-02
    Description: In this paper, fluoride geochemistry and health risk of groundwater in Coimbatore district is studied. The order of dominance of ions were HCO〈sub〉3〈/sub〉 〉 Cl 〉 SO〈sub〉4〈/sub〉 〉 CO〈sub〉3〈/sub〉 and Na 〉 Ca 〉 Mg 〉 K. Alkaline groundwater and the dominance of HCO〈sub〉3〈/sub〉 and Na is favourable for the fluoride enrichment. Around 46% of the samples, N–NE regions, have F〈sup〉−〈/sup〉 higher than permissible limit of 1.5 mg/L. Pink granites, charnockite and gneisses in lithology is the possible origin of F〈sup〉−〈/sup〉. However, NO〈sub〉3〈/sub〉 vs F plot shows positive trend in some samples, indicating anthropogenic inputs of F〈sup〉−〈/sup〉. Correlation plots of F〈sup〉−〈/sup〉 was trending positive with pH, HCO〈sub〉3〈/sub〉 and Na and but negative for Ca, indicating the control of these ions in F〈sup〉−〈/sup〉 mobility. This result is supported by undersaturation of fluorite and supersaturation of carbonates. Four significant principal components were derived, which have explained 87% of the total variation. PC1 has high factor loadings for EC, Ca, Mg Na, Cl, SO〈sub〉4〈/sub〉, NO〈sub〉3〈/sub〉 indicating both natural and anthropogenic influences. PC2, PC3 and PC4 have higher loading for pH and HCO〈sub〉3〈/sub〉, K and HCO〈sub〉3〈/sub〉 and F〈sup〉−〈/sup〉, respectively, indicating geogenic factors in the F〈sup〉−〈/sup〉 enrichment. Human health risk assessment (HHRA) by ingestion and dermal pathways were calculated using Hazard Quotient HQ and Hazard Index (HI). 27% of males, 36% of females and 39% of the children have HI 〉 1, posing noncarcinogenic risks.
    Description: Freie Universität Berlin (1008)
    Keywords: ddc:551.9 ; Fluoride ; Geochemistry ; Multivariate analysis ; Human health risk assessment (HHRA) ; Revised permissible limits ; Coimbatore
    Language: English
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    Constraints on the pre-eruptive magmatic history of the Quaternary Laacher See volcano (Germany) (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: Ba zonation patterns in sanidine phenocrysts from mafic and intermediate phonolite and crystal-rich cumulates from the Laacher See volcano (12.9 ka) in western Germany document diffusion times suggestive of periodic recharge events throughout the magma reservoir’s entire lifespan of ~ 24 ky. Phenocrysts analysed from samples that formed late at the base of the compositionally zoned magma reservoir by mixing and mingling between a resident phonolite magma and recharging basanite show resorption and thin (2–10 μm) late-stage Ba-rich overgrowth. Short diffusion profiles across these boundaries give diffusion times of ~ 1.5–3 years at most, which are interpreted to be the maximum duration between the most recent recharge by the basanite and eruption. The lack of such late overgrowth in samples from other parts of the phonolite reservoir suggests that effect of this mixing and mingling was limited to the crystal-rich base. Sanidines in the cumulates, by contrast, are generally devoid of zoned crystals. Only rare cumulate crystals with resorbed outer boundaries and very thin overgrowths (a few microns) with very sharp compositional changes imply the remobilization of cumulates only months before eruption. Based on the diffusion timescales and storage temperatures obtained in a previous study, we present a genetic model for the conditions and timing of storage and (re-)activation of the magma system prior to the eruption of Laacher See, which is the largest volcanic event in Central Europe since the last glaciation.
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Keywords: ddc:551.9 ; Laacher see ; Diffusion chronometry ; Barium ; BSE images ; Magma storage
    Language: English
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    A wind-driven model of the ocean surface layer with wave radiation physics (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: Surface windstress transfers energy to the surface mixed layer of the ocean, and this energy partly radiates as internal gravity waves with near-inertial frequencies into the stratified ocean below the mixed layer where it is available for mixing. Numerical and analytical models provide estimates of the energy transfer into the mixed layer and the fraction radiated into the interior, but with large uncertainties, which we aim to reduce in the present study. An analytical slab model of the mixed layer used before in several studies is extended by consistent physics of wave radiation into the interior. Rayleigh damping, controlling the physics of the original slab model, is absent in the extended model and the wave-induced pressure gradient is resolved. The extended model predicts the energy transfer rates, both in physical and wavenumber-frequency space, associated with the wind forcing, dissipation in the mixed layer, and wave radiation at the base as function of a few parameters: mixed layer depth, Coriolis frequency and Brunt-Väisälä frequency below the mixed layer, and parameters of the applied windstress spectrum. The results of the model are satisfactorily validated with a realistic numerical model of the North Atlantic Ocean.
    Description: Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659
    Keywords: ddc:551.5 ; Wind-driven internal gravity waves ; Wave radiation physics
    Language: English
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  • 89
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    Biogeochemical cycling of phosphorus in subsoils of temperate forest ecosystems (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-19
    Description: Tree roots penetrate the soil to several meters depth, but the role of subsoils for the supply of nutrient elements such as phosphorus (P) to the trees is poorly understood. Here, we tested the hypothesis that increased P deficiency in the topsoil results in an increased microbial recycling of P from the forest subsoil. We sampled soils from four German temperate forest sites representing a gradient in total P stocks. We analyzed the oxygen isotopic composition of HCl-extractable phosphate (δ18OP) and identified differences in P speciation with increasing soil depth using X-ray absorption near-edge structure (XANES) spectroscopy. We further determined microbial oxygen demand with and without nutrient supply at different soil depths to analyse nutrient limitation of microbial growth and used nanoscale secondary ion mass spectrometry (NanoSIMS) to visualize spatial P gradients in the rhizosphere. We found that δ18OP values in the topsoil of all sites were close to the isotopic signal imparted by biological cycling when oxygen isotopes in phosphate are exchanged by enzymatic activity. However, with increasing soil depth and increasing HCl-P concentrations, δ18Ο values continuously decreased towards values expected for primary minerals in parent material at depths below 60 cm at sites with high subsoil P stocks and below more than 2 m at sites with low subsoil P stocks, respectively. For these depths, XANES spectra also indicated the presence of apatite. NanoSIMS images showed an enrichment of P in the rhizosphere in the topsoil of a site with high P stocks, while this P enrichment was absent at a site with low P stocks and in both subsoils. Addition of C, N and P alone or in combination revealed that microbial activity in subsoils of sites with low P stocks was mostly P limited, whereas sites with high P stocks indicated N limitation or N and P co-limitation. We conclude that subsoil P resources are recycled by trees and soil microorganisms. With continued weathering of the bedrock and mobilisation of P from the weathered rocks, P cycling will proceed to greater depths, especially at sites characterised by P limitation.
    Description: Rheinische Friedrich-Wilhelms-Universität Bonn (1040)
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Rheinische Friedrich-Wilhelms-Universität Bonn (1040)
    Keywords: ddc:551.9 ; Oxygen isotopes ; Phosphate ; NanoSIMS ; XANES ; Microbial P cycling ; Soil
    Language: English
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  • 90
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    Incorporation of Rare Earths and Yttrium in Calcite: A Critical Re-evaluation (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-20
    Description: The reported partition coefficients of REE with calcite are reviewed and critically discussed. In some of the reported experimental sets, REE concentrations are found to be supersaturated with respect to individual REE2(CO3)3 but never to REE(OH)3. Although the solutions are unsaturated with respect to individual REY carbonates, REY including Y are incorporated in calcite surfaces, where they are overgrown by calcite. Charge balances may be obtained by building {REY–Na-(CO3)2}n or by exchange of 2Ca2+ against REY3+ + blank space calcite lattice. These surface compounds may either be homogeneously distributed or clustered. Both the size and frequency of clusters increase with [REY]/[Ca] or [ΣREY3+]/[Ca2+] in solution. If these surface precipitates are removed into solutions saturated with respect to ΣREE2(CO3)3, they start growing in the aqueous phase. In this case, the apparent DREY and kREY values decrease with increasing REY concentrations in solution. In previous studies, only the individual distribution coefficients are reported not considering that the entirety of REY determines their behavior in partitioning. Given enough time, these surface clusters equilibrate with the aqueous phase before being overgrown by calcite. In the double logarithmic plots of {REY}/{Ca} versus [REY]/[Ca] or [REY3+]/[Ca2+], two relationships evolve characterizing the REY distribution in marine calcite and experimental calcites grown in Mg2+-free solutions. The double logarithmic plots of partition coefficients of REYi3+ in calcite grown from seawater show a slope exceeding unity, whereas those from fluids without Mg2+ depict slopes less than unity being both in contrast to the Henderson–Kracek rule.
    Keywords: ddc:551.9 ; Partitioning of rare earths with calcite ; Formation of REY–Na carbonate compounds ; Homogeneous partitioning ; Individual versus entirety of rare earths’ partitioning between calcite and ambient solution
    Language: English
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  • 91
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    Origin and fate of dissolved organic matter in four shallow Baltic Sea estuaries (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-20
    Description: Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.
    Description: Academy of Sciences of Finland
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: BONUS COCOA and Bundesministerium für Bildung und Forschung
    Description: Academy of Finland
    Description: Danish Research Council for Independent Research
    Description: BONUS COCOA Project
    Description: Leibniz-Institut für Ostseeforschung Warnemünde (IOW) (3484)
    Keywords: ddc:551.9 ; Coastal systems ; Dissolved organic matter ; Riverine input ; Baltic Sea
    Language: English
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  • 92
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    A statistical analysis of time trends in atmospheric ethane (2020)
    Friedrich, Marina ; Beutner, Eric ; Reuvers, Hanno ; [et al.]
    Springer Netherlands
    Details
    Publication Date: 2023-06-12
    Description: Ethane is the most abundant non-methane hydrocarbon in the Earth’s atmosphere and an important precursor of tropospheric ozone through various chemical pathways. Ethane is also an indirect greenhouse gas (global warming potential), influencing the atmospheric lifetime of methane through the consumption of the hydroxyl radical (OH). Understanding the development of trends and identifying trend reversals in atmospheric ethane is therefore crucial. Our dataset consists of four series of daily ethane columns. As with many other decadal time series, our data are characterized by autocorrelation, heteroskedasticity, and seasonal effects. Additionally, missing observations due to instrument failure or unfavorable measurement conditions are common in such series. The goal of this paper is therefore to analyze trends in atmospheric ethane with statistical tools that correctly address these data features. We present selected methods designed for the analysis of time trends and trend reversals. We consider bootstrap inference on broken linear trends and smoothly varying nonlinear trends. In particular, for the broken trend model, we propose a bootstrap method for inference on the break location and the corresponding changes in slope. For the smooth trend model, we construct simultaneous confidence bands around the nonparametrically estimated trend. Our autoregressive wild bootstrap approach, combined with a seasonal filter, is able to handle all issues mentioned above (we provide R code for all proposed methods on https://www.stephansmeekes.nl/code.).
    Description: Horizon 2020 https://doi.org/10.13039/501100007601
    Description: Fonds De La Recherche Scientifique - FNRS https://doi.org/10.13039/501100002661
    Keywords: ddc:551.5 ; Trend analysis ; Atmospheric ethane ; Bootstrapping ; Break point estimation
    Language: English
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    Geochemical focusing and sequestration of manganese during eutrophication of Lake Stechlin (NE Germany) (2020)
    Scholtysik, Grzegorz ; Dellwig, Olaf ; Roeser, Patricia ; [et al.]
    Springer International Publishing
    Details
    Publication Date: 2023-06-17
    Description: Significant sedimentation of manganese (Mn) in form of manganese oxides (MnOx) and the subsequent formation of authigenic calcium-rich rhodochrosite (Mn(Ca)CO3) were observed in the seasonally stratified hard water Lake Stechlin in north-eastern Germany. This manganese enrichment was assumed to be associated with recent eutrophication of the formerly oligotrophic lake. The mechanisms and processes involved were examined by analysing: (i) short sediment cores obtained from seven locations along a depth transect ranging from 69.5 m (the deepest point) to 38 m; (ii) sediment traps located at 20 m and 60 m water depths; (iii) water column profiles; and (iv) porewater profiles at 69.5 m and 58 m depths. Sedimentary Mn enrichment was observed at water depths below 56 m and increased to more than 25 wt% at the deepest site. Between 2010 and 2017, Mn accumulation at the deepest site was 815 g Mn m−2. Transfer of Mn from the shallower towards the deepest parts of the lake was initiated by reductive dissolution of MnOx and diffusion of dissolved Mn from the sediment to the overlying water column. Manganese was then dissipated via turbulent mixing and subsequently oxidised to MnOx before being transported towards the deepest zone. Transformation of the redeposited MnOx to Mn(Ca)CO3 favoured the final burial of Mn. We show that eutrophication and the areal spreading of anoxic conditions may intensify diagenetic processes and cause the spatial redistribution of Mn as well as its effective burial. Contrary to many previous findings, we show that increases of Mn and Mn/Fe can also be used as indicators for increasing anoxic conditions in previously oligotrophic lakes.
    Description: Leibniz-Gemeinschaft http://dx.doi.org/10.13039/501100001664
    Description: Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB) im Forschungsverbund Berlin e.V. (3473)
    Keywords: ddc:551.9 ; Lacustrine sediments ; Geochemical focusing ; Eutrophication ; Diagenesis ; Rhodochrosite ; Varves
    Language: English
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    Global Radioxenon Emission Inventory from Nuclear Power Plants for the Calendar Year 2014 (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-10-26
    Description: For the purpose of monitoring for compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the International Monitoring System (IMS) is being established that includes 40 sensor systems for atmospheric xenon radioactivity. Its purpose is to monitor the atmosphere for signatures that may indicate a nuclear explosion. Normal operational releases of radioxenon from nuclear facilities can regularly be observed by these very high-sensitive noble gas systems. Existing best estimates of releases for a generic year are unlikely to apply for any specific year at the level of individual facilities because their releases are highly variable and can change by several orders of magnitude from year to year. In this paper, best knowledge of the radioxenon emission inventory from nuclear power plants (NPPs) is collected for the calendar year 2014. The distribution function for each CTBT relevant radioxenon isotope is derived from all releases from NPPs as reported for 2014. The data of this paper can be used for developing and validating methods based on atmospheric transport modelling that are designed to enhance understanding of the impact of known sources on the IMS background observations.
    Description: Universität Hamburg (1037)
    Keywords: ddc:551.5 ; CTBT ; radioxenon ; emission inventory ; radionuclide monitoring ; atmospheric radioactivity
    Language: English
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  • 95
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    A Comprehensive Study of Infrasound Signals Detected from the Ingolstadt, Germany, Explosion of 1 September 2018 (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-11-23
    Description: The explosion at the Ingolstadt oil refinery was widely recorded at seismic and infrasound stations deployed throughout Central Europe, to distances of several hundred to a thousand kilometres. This study focuses on the wealth of data recorded at infrasound stations in Central and Eastern Europe, while from the many detecting seismic stations within 400 km range, only seismic and seismo-acoustic arrivals at the close-in Gräfenberg array are considered here. Most of the infrasound stations are acoustic arrays enabling us to apply array processing techniques to determine relevant wave field parameters, such as backazimuth and slowness (resp. trace velocity). These parameters not only confirm the source direction, but also put constraints on the observed arrivals’ propagation modes. Wave field parameters suggest that we observe tropospheric arrivals to about 150 km and stratospheric and/or thermospheric returns for longer distances. 1D, 2D and 3D ray tracing predict tropospheric arrivals to westerly directions up to distances of 100 km, beyond which only thermospheric returns are obtained azimuth-independent beyond 250–300 km. Stratospheric returns do not follow from any of the increasingly complex ray tracing models. Parabolic equation propagation modeling however suggests that in a number of cases stratospheric ducting may be possible. However, neither the tropospheric seismo-acoustic arrivals at the Gräfenberg array nor the various arrivals at IMS station IS26 could be modeled. Therefore, the Ingolstadt explosion along with the observed infrasonic phases provide an excellent test bed to investigate our ability in realistically forecasting atmospheric wave propagation with existing algorithms and available atmospheric models.
    Keywords: ddc:551.5 ; Infrasound ; explosion ; atmospheric models ; propagation modeling ; stratospheric ducting
    Language: English
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    Pseudo-total antimony content in topsoils of the Berlin Metropolitan Area (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-08
    Description: Purpose: Sb is a metalloid that naturally occurs in traces in the Northern German Lowland Area, only. Its frequent and still growing demand for industrial purposes and its release during coal combustion and by vehicular emissions lead to an enrichment of Sb in topsoils. Numerous analyses on heavy metals have been conducted in the urban environment so far, but although Sb can be ecologically harmful and potentially carcinogenic, only few studies on Sb in soils were carried out.
    Description: Materials and methods: Due to the formation of anthropogenic soils by men, especially in the course of industrialization and after World War II, more than 50% of the Berlin soils consist of anthropogenic material like redeposited natural material, debris, waste, or ashes. This composition of soils of the Berlin Metropolitan Area can function as a model for other metropolitan regions of Central Europe. In the urban and peri-urban area of Berlin, analysis of more than 900 topsoil samples has been performed measuring the content of 12 heavy metals and metalloids (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, and Zn). As a reference for the natural environment, soil profiles of typical parent rock material have been investigated taking also the regional (0.3 mg/kg), the local background value (0.61 mg/kg), and the baseline value (0.07 mg/kg) for Sb into account.
    Description: Results: By doing so, we could show the spatial distributional pattern of Sb in the Berlin Metropolitan Area and statistically evaluate our results in dependency of land-use, parent material, and soil parameters such as organic carbon content and pH. Thereby, we could prove an average enrichment two to six times over the regional background value. Median Sb content is very low in forest topsoils (0.54 mg/kg) and reaches its maximum in roadside soils (1.75 mg/kg). Technogenic materials, vehicular emissions, industrial processes, and (former) land-use are the predominant factors for Sb enrichment and distribution in the study area. Some single samples show an enrichment of up to 600% of the regional background value for topsoils.
    Description: Conclusion: Our study revealed that the Sb content in the Berlin Metropolitan Area is elevated compared to natural environments. Furthermore, we could demonstrate that Sb is a previously neglected key pollutant, specific to metropolitan areas. Due to the high environmental relevance, further Sb data from selected investigated spaces in other metropolises and specific land-use types are needed to assess the potential environmental risk of Sb in metropolitan areas.
    Description: Humboldt-Universität zu Berlin (1034)
    Keywords: ddc:551.9 ; Trace metals ; Urban geochemistry ; Pollution index ; Technogenic soils ; Antimony (Sb) ; Urban structure type
    Language: English
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    Impact of sedimentation history for As distribution in Late Pleistocene-Holocene sediments in the Hetao Basin, China (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-08
    Description: Purpose: To understand the impact of geochemical sedimentation history for arsenic (As) distribution in the sediment profiles of the Hetao Basin, we (1) evaluated sediments provenance and variations of weathering intensities, (2) attempted to reconstruct the depositional environments, and (3) explored the As and Fe speciation in the sediments. Combining the information above, different sedimentation facies were distinguished in the vertical profiles.
    Description: Methods: Two sediments cores were drilled up to 80 m depth. Major and trace element compositions, including rare earth elements (REE), were analyzed. Carbon isotope ratios (δ13Corg) of embedded organic matter in the sediments were analyzed by isotope ratio mass spectrometry (IR-MS). Arsenic and Fe speciation of the sediments were determined by sequential extractions.
    Description: Results and discussion: The similar REE geochemistry of rocks from the Lang Mountains and sediments in the Hetao Basin indicated that the sediments originated from the Lang Mountains. The C/N ratio (~ 4 to ~ 10) in combination with δ13Corg (− 27‰ to −2 4‰) suggested that sediments were mainly deposited in aquatic environments. The unconfined aquifer equaled the lacustrine deposit with less intensive weathering during last glacial maximum (LGM). Here, the As content (average, 5.4 mg kg−1) was higher than in the aquifer sediments below (average, 3.6 mg kg−1).
    Description: Conclusion: Higher content of releasable As in combination with paleolake-derived organic matter aquifer sediments probably contributes to higher groundwater As concentration in the unconfined aquifer. This study provides the first insight into the impact of sedimentation history on As distributions in sediment profiles in the Hetao Basin.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Keywords: ddc:551.9 ; Sediment basin ; Sedimentation history ; Arsenic provenance ; Weathering intensities ; Organic carbon isotopic signature ; Arsenic speciation
    Language: English
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    In situ sounding of radiative flux profiles through the Arctic lower troposphere (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-05
    Description: In situ profiles and fixed-altitude time series of all four components of net radiation were obtained at Ny-Ålesund, Svalbard (78.9° N, 11.9° E), in the period May 04–21, 2015. Measurements were performed using adapted high-quality instrumentation classified as “secondary standard” carried by a tethered balloon system. Balloon-lifted measurements of albedo under clear-sky conditions demonstrate the local dependence on altitude and on the surface inhomogeneity of this parameter over coastal terrain of Ny-Ålesund. Depending on the surface composition within the sensor’s footprint near the coastline, the albedo over predominantly snow-covered surfaces was found to decrease to 0.548 and 0.452 at 494 m and 881 m altitude compared with 0.731 and 0.788 measured with near-surface references, respectively. Albedo profiles show an all-sky maximum at 150 m above surface level due to local surface inhomogeneity, and an averaged vertical change rate of − 0.040/100 up to 750 m aboveground level (clear sky) and − 0.034/100 m (overcast). Profiling of arctic low-level clouds reveals distinct vertical gradients in all radiative fluxes but longwave upward at the cloud top. Observed radiative cooling at the top of a partly dissolving stratus cloud with heating rates of − 40.4 to − 62.1 Kd−1 in subsequent observations is exemplified.
    Description: Bundesrepublik Deutschland, Deutscher Wetterdienst, vertreten durch den Vorstand, Deutsche Meteorologische Bibliothek (4242)
    Keywords: ddc:551.5 ; Atmosphere ; Arctic ; In-situ profiling ; Albedo ; Clouds ; Heating rates
    Language: English
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