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  • 1
    Publication Date: 2022-10-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Kropp, H., Loranty, M. M., Natali, S. M., Kholodov, A. L., Rocha, A., V., Myers-Smith, I., Abbot, B. W., Abermann, J., Blanc-Betes, E., Blok, D., Blume-Werry, G., Boike, J., Breen, A. L., Cahoon, S. M. P., Christiansen, C. T., Douglas, T. A., Epstein, H. E., Frost, G., V., Goeckede, M., Hoye, T. T., Mamet, S. D., O'Donnell, J. A., Olefeldt, D., Phoenix, G. K., Salmon, V. G., Sannel, A. B. K., Smith, S. L., Sonnentag, O., Vaughn, L. S., Williams, M., Elberling, B., Gough, L., Hjort, J., Lafleur, P. M., Euskirchen, E. S., Heijmans, M. M. P. D., Humphreys, E. R., Iwata, H., Jones, B. M., Jorgenson, M. T., Gruenberg, I., Kim, Y., Laundre, J., Mauritz, M., Michelsen, A., Schaepman-Strub, G., Tape, K. D., Ueyama, M., Lee, B., Langley, K., & Lund, M. Shallow soils are warmer under trees and tall shrubs across arctic and boreal ecosystems. Environmental Research Letters, 16(1), (2021): 015001. doi:10.1088/1748-9326/abc994.
    Description: Soils are warming as air temperatures rise across the Arctic and Boreal region concurrent with the expansion of tall-statured shrubs and trees in the tundra. Changes in vegetation structure and function are expected to alter soil thermal regimes, thereby modifying climate feedbacks related to permafrost thaw and carbon cycling. However, current understanding of vegetation impacts on soil temperature is limited to local or regional scales and lacks the generality necessary to predict soil warming and permafrost stability on a pan-Arctic scale. Here we synthesize shallow soil and air temperature observations with broad spatial and temporal coverage collected across 106 sites representing nine different vegetation types in the permafrost region. We showed ecosystems with tall-statured shrubs and trees (〉40 cm) have warmer shallow soils than those with short-statured tundra vegetation when normalized to a constant air temperature. In tree and tall shrub vegetation types, cooler temperatures in the warm season do not lead to cooler mean annual soil temperature indicating that ground thermal regimes in the cold-season rather than the warm-season are most critical for predicting soil warming in ecosystems underlain by permafrost. Our results suggest that the expansion of tall shrubs and trees into tundra regions can amplify shallow soil warming, and could increase the potential for increased seasonal thaw depth and increase soil carbon cycling rates and lead to increased carbon dioxide loss and further permafrost thaw.
    Description: We thank G Peter Kershaw, LeeAnn Fishback, Cathy Wilson, and Coleen Iversen for assistance in collection of data. We thank the Permafrost Carbon Network for support and organization of the data synthesis. We thank Vladimir Romanovsky for his feedback and contribution of publicly available data. This project was supported by the National Science Foundation (Grant No. 1417745 to M L, Grant No. 1417700 to S M N, Grant No. 1417908 to A K, Grant No. 1556772 to A R, Grant No. 1637459 to L G, Grant No. 1636476 and Grant No. 1503912 to E S E, Grant No. 1806213 to B M J, Grant No. 1833056 to K D T), UK Natural Environment Research Council (Grant No. NE/M016323/1 to I H M S, Grant No. NE/K00025X/1 to G K P, Grant No. NE/K000292/1 to M W), Natural Sciences and Engineering Research (to P L, I H M S, Grant No. RGPIN-2016-04688 to D O), Council of Canada, Canadian Graduate Scholarship to (I H M -S), Greenland Ecosystem Monitoring Programme: ClimateBasis (to J A and K A), The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science (to A L B), Engineer Research and Development Center Army Direct (6.1) Research Program and the Strategic Environmental Research and Development Program (projects RC-2110 and 18-1170 to T A D), United States Geological Survey (to E E S), Arctic Challenge for Sustainability (ArCS; Grant No. JPMXD1300000000) and ArCS II (Grant No. JPMXD1420318865) (to M U and H I), the Danish National Research Foundation (Grant No. CENPERM DNRF100 to B E), the Academy of Finland (Grant No. 315519), the National Research Foundation of Korea (Grant Nos. NRF-2016M1A5A1901769; KOPRI-PN20081 to K Y and B Y L), Research Network for Geosciences in Berlin and Potsdam (to I G), the Swiss National Science Foundation (Grant No. 140631 to G S S), the URPP Global Change and Biodiversity, University of Zurich (to G S S), the University of Alberta Northern Research Awards (to D O), and the Northern Scientific Training Program (to D O), and UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE) Office of Science, Biological and Environmental Research (to V G S). S M has been supported by grants and/or in-kind from Natural Sciences and Engineering Research Council of Canada, AMAX Northwest Mining, Co. (North American Tungsten Corp., Ltd), Imperial Oil, Ltd, University of Alberta, Earthwatch International (EI), The Garfield Weston Foundation, Wapusk National Park, Churchill Northern Studies Centre, and the Northern Scientific Training Program. All code for this project are archived (DOI: 10.5281/zenodo.4041165). The data that support the findings of this study are openly available through the Arctic Data Center (Heather Kropp, Michael Loranty, Britta Sannel, Jonathan O'Donnell, Elena Blanc-Betes, et al 2020. Synthesis of soil-air temperature and vegetation measurements in the pan-Arctic. 1990-2016. Arctic Data Center. doi:10.18739/A2736M31X).
    Keywords: Arctic ; Boreal forest ; Soil temperature ; Vegetation change ; Permafrost
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2022-03-24
    Description: The correct representation of global‐scale electron density is crucial for monitoring and exploring the space weather. This study investigates whether the ground‐based Global Navigation Satellite System (GNSS) tomography can be used to reflect the global spatial and temporal responses of the ionosphere under storm conditions. A global tomography of the ionosphere electron density is constructed based on data from over 2,700 GNSS stations. In comparison to previous techniques, advances are made in spatial and temporal resolution, and in the assessment of results. To demonstrate the capabilities of the approach, the developed method is applied to the March 17, 2015 geomagnetic storm. The tomographic reconstructions show good agreement with electron density observations from worldwide ionosondes, Millstone Hill incoherent scatter radar and in‐situ measurements from satellite missions. Also, the results show that the tomographic technique is capable of reproducing plasma variabilities during geomagnetically disturbed periods including features such as equatorial ionization anomaly enhancements and depletion. Validation results of this brief study period show that the accuracy of our tomography is better than the Neustrelitz Electron Density Model, which is the model used as background, and physics‐based thermosphere‐ionosphere‐electrodynamics general circulation model. The results show that our tomography approach allows us to specify the global electron density from ground to ∼900 km accurately. Given the demonstrated quality, this global electron density reconstruction has potential for improving applications such as assessment of the effects of the electron density on radio signals, GNSS positioning, computation of ray tracing for radio‐signal transmission, and space weather monitoring.
    Description: Plain Language Summary: Computerized tomography allows the 3D imaging of several objects based on radio frequency signal measurements. Given the measurements and geometry of the current GPS (Global Positioning System) satellite constellation, there is an opportunity to apply tomography techniques and extract 3D snapshots of the Earth's atmosphere. This work presents an advanced global‐scale tomography that can represent the electron density in the Earth's upper atmosphere in a relatively high spatial and temporal resolution in the region of ∼100–1,000 km above the Earth's surface; referred to as the ionosphere. The work also validates the tomography results with multiple ionospheric observations from satellites and ground‐based radar instruments and compares with empirical and physical models. It is usually a challenge for models to reproduce the ionospheric system dynamics accurately during active space weather conditions, such as geomagnetic storms. This work, using the severe geomagnetic storm on March 17, 2015 as a case‐study, shows that the tomography is well poised for this task. The developed method could be extended to benefit several applications, such as space weather monitoring, GPS positioning and navigation, as well as to improve our understanding of the morphology and dynamics of the ionosphere.
    Description: Key Points: Presents an advanced global‐scale tomography of ionospheric electron density. Demonstrates the capability of the tomography model to reproduce the system dynamics during a severe geomagnetic storm. Validates the tomography results with multiple ground‐ and space‐based data and compares with empirical and physical models.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: Helmholtz‐Fonds (Helmholtz‐Fonds e.V.) http://dx.doi.org/10.13039/501100013655
    Keywords: ddc:551.5 ; ddc:538.7
    Language: English
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  • 3
    Publication Date: 2022-03-24
    Description: Analysis of Mars Atmosphere and Volatile Evolution (MAVEN)/Supra‐Thermal And Thermal Ion Composition observations in the Martian upper atmosphere, bounded at higher altitudes by the shocked solar wind, shows that the draping of interplanetary magnetic field penetrates down to low altitudes (∼200−250 km) and governs dynamics of the ionosphere. The upper ionospheric plasma is driven into motion flowing around Mars similar to the shocked solar wind in the adjacent magnetosheath. Such a fluid‐like motion is accompanied by ion acceleration caused by the bending of the magnetic field, leading to ion extraction and finally to ion pickup. Extraction of ions and their acceleration produces a recoil effect of the bulk ionosphere in the opposite direction. This provides a strong asymmetry in ion dynamics in two different hemispheres, accompanied by wrapping of the magnetic field lines around Mars and respective reconnection.
    Description: Plain Language Summary: Although the Martian magnetosphere is hybrid and contains components of the induced and intrinsic magnetosphere, is possible to display these components by using the specific coordinate systems. Here we study the properties of the induced magnetosphere using the data obtained by MAVEN spacecraft. The interplanetary magnetic field penetrates deep into the Martian ionosphere draping around Mars and drive to the motion dense ionospheric plasma. Draping features and the induced plasma motions occur different in two hemispheres determined by the direction of the motional electric field in the solar wind. Ion acceleration and extraction is accompanied by a recoil effect that leads to a shift and asymmetry of the ionosphere.
    Description: Key Points: Draping of the interplanetary magnetic field around Mars penetrates deep to the ionosphere enveloping the planet and driving the ionosphere to the bulk motion. Draping and motion of the ionospheric plasma is characterized by asymmetry by the direction of the motional electric field in solar wind. Ion acceleration and extraction from the ionosphere is accompanied by a shift of the bulk ionosphere in the opposite direction.
    Description: National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
    Description: DFG http://dx.doi.org/10.13039/501100001659
    Description: Russian Science Foundation http://dx.doi.org/10.13039/501100006769
    Keywords: ddc:523 ; ddc:551.5
    Language: English
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  • 4
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Estapa, M., Buesseler, K., Durkin, C. A., Omand, M., Benitez-Nelson, C. R., Roca-Marti, M., Breves, E., Kelly, R. P., & Pike, S. Biogenic sinking particle fluxes and sediment trap collection efficiency at Ocean Station Papa. Elementa: Science of the Anthropocene, 9(1), (2021): 00122, https://doi.org/10.1525/elementa.2020.00122.
    Description: Comprehensive field observations characterizing the biological carbon pump (BCP) provide the foundation needed to constrain mechanistic models of downward particulate organic carbon (POC) flux in the ocean. Sediment traps were deployed three times during the EXport Processes in the Ocean from RemoTe Sensing campaign at Ocean Station Papa in August–September 2018. We propose a new method to correct sediment trap sample contamination by zooplankton “swimmers.” We consider the advantages of polyacrylamide gel collectors to constrain swimmer influence and estimate the magnitude of possible trap biases. Measured sediment trap fluxes of thorium-234 are compared to water column measurements to assess trap performance and estimate the possible magnitude of fluxes by vertically migrating zooplankton that bypassed traps. We found generally low fluxes of sinking POC (1.38 ± 0.77 mmol C m–2 d–1 at 100 m, n = 9) that included high and variable contributions by rare, large particles. Sinking particle sizes generally decreased between 100 and 335 m. Measured 234Th fluxes were smaller than water column 234Th fluxes by a factor of approximately 3. Much of this difference was consistent with trap undersampling of both small (〈32 μm) and rare, large particles (〉1 mm) and with zooplankton active migrant fluxes. The fraction of net primary production exported below the euphotic zone (0.1% light level; Ez-ratio = 0.10 ± 0.06; ratio uncertainties are propagated from measurements with n = 7–9) was consistent with prior, late summer studies at Station P, as was the fraction of material exported to 100 m below the base of the euphotic zone (T100, 0.55 ± 0.35). While both the Ez-ratio and T100 parameters varied weekly, their product, which we interpret as overall BCP efficiency, was remarkably stable (0.055 ± 0.010), suggesting a tight coupling between production and recycling at Station P.
    Description: The authors would like to acknowledge funding support from the NASA EXPORTS program (Award 80NSSC17K0662) for all sediment trap data presented here. Net primary production data collection was supported by EXPORTS (Award 80NSSC17K568) to Oregon State University. Thorium data collection was supported by EXPORTS (Award 80NSSC17K0555) to KB, CRBN, and L. Resplandy.
    Keywords: Biological carbon pump ; Ocean Station Papa ; Sediment traps ; Carbon flux ; Particle size distribution ; Swimmers
    Repository Name: Woods Hole Open Access Server
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  • 5
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 126(7), (2021): e2020JG005977, https://doi.org/10.1029/2020JG005977.
    Description: Increasing Arctic temperatures are thawing permafrost soils and liberating ancient organic matter, but the fate of this material remains unclear. Thawing of permafrost releases dissolved organic matter (DOM) into fluvial networks. Unfortunately, tracking this material in Arctic rivers such as the Kolyma River in Siberia has proven challenging due to its high biodegradability. Here, we evaluate late summer abruptly thawed yedoma permafrost dissolved organic carbon (DOC) inputs from Duvannyi Yar. We implemented ultrahigh-resolution mass spectrometry alongside ramped pyrolysis oxidation (RPO) and isotopic analyses. These approaches offer insight into DOM chemical composition and DOC radiocarbon values of thermochemical components for a permafrost thaw stream, the Kolyma River, and their biodegraded counterparts (n = 4). The highly aliphatic molecular formula found in undegraded permafrost DOM contrasted with the comparatively aliphatic-poor formula of Kolyma River DOM, represented by an 8.9% and 2.6% relative abundance, respectively, suggesting minimal inputs of undegraded permafrost DOM in the river. RPO radiocarbon fractions of Kolyma River DOC exhibited no “hidden” aged component indicative of permafrost influence. Thermostability analyses suggested that there was limited biodegraded permafrost DOC in the Kolyma River, in part determined by the formation of high-activation energy (thermally stable) biodegradation components in permafrost DOM that were lacking in the Kolyma River. A mixing model based on thermostability and radiocarbon allowed us to estimate a maximum input of between 0.8% and 7.7% of this Pleistocene-aged permafrost to the Kolyma River DOC. Ultimately, our findings highlight that export of modern terrestrial DOC currently overwhelms any permafrost DOC inputs in the Kolyma River.
    Description: This work was funded by NSF grants ANT-1203885 and PLR-1500169 to R.G.M.S. The work was also supported by the National Science Foundation Division of Chemistry through DMR-1644779 and the State of Florida.
    Description: 2022-01-09
    Keywords: Permafrost ; Dissolved organic carbon ; Dissolved organic matter ; FT-ICR MS ; Ramped pyrolysis oxidation ; Arctic
    Repository Name: Woods Hole Open Access Server
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  • 6
    Publication Date: 2022-03-31
    Description: Compound weather and climate events are combinations of climate drivers and/or hazards that contribute to societal or environmental risk. Studying compound events often requires a multidisciplinary approach combining domain knowledge of the underlying processes with, for example, statistical methods and climate model outputs. Recently, to aid the development of research on compound events, four compound event types were introduced, namely (a) preconditioned, (b) multivariate, (c) temporally compounding, and (d) spatially compounding events. However, guidelines on how to study these types of events are still lacking. Here, we consider four case studies, each associated with a specific event type and a research question, to illustrate how the key elements of compound events (e.g., analytical tools and relevant physical effects) can be identified. These case studies show that (a) impacts on crops from hot and dry summers can be exacerbated by preconditioning effects of dry and bright springs. (b) Assessing compound coastal flooding in Perth (Australia) requires considering the dynamics of a non‐stationary multivariate process. For instance, future mean sea‐level rise will lead to the emergence of concurrent coastal and fluvial extremes, enhancing compound flooding risk. (c) In Portugal, deep‐landslides are often caused by temporal clusters of moderate precipitation events. Finally, (d) crop yield failures in France and Germany are strongly correlated, threatening European food security through spatially compounding effects. These analyses allow for identifying general recommendations for studying compound events. Overall, our insights can serve as a blueprint for compound event analysis across disciplines and sectors.
    Description: Plain Language Summary: Many societal and environmental impacts from events such as droughts and storms arise from a combination of weather and climate factors referred to as a compound event. Considering the complex nature of these high‐impact events is crucial for an accurate assessment of climate‐related risk, for example to develop adaptation and emergency preparedness strategies. However, compound event research has emerged only recently, therefore our ability to analyze these events is still limited. In practice, studying compound events is a challenging task, which often requires interaction between experts across multiple disciplines. Recently, compound events were divided into four types to aid the framing of research on this topic, but guidelines on how to study these four types are missing. Here, we take a pragmatic approach and—focusing on case studies of different compound event types—illustrate how to address specific research questions that could be of interest to users. The results allow identifying recommendations for compound event analyses. Furthermore, through the case studies, we highlight the relevance that compounding effects have for the occurrence of landslides, flooding, vegetation impacts, and crop failures. The guidelines emerged from this work will assist the development of compound event analysis across disciplines and sectors.
    Description: Key Points: Using case studies representative of four main compound event types we show how compound event‐related research questions can be tackled. We present user‐friendly guidelines for compound event analysis applicable to different compound event types. We demonstrate that compound events cause vegetation impacts, coastal flooding, landslides, and continental‐scale crop yield failures.
    Description: European COST action DAMOCLES
    Description: NERC
    Description: Swiss National Science Foundation
    Description: Helmholtz Initiative and Networking Fund
    Description: Netherlands Organisation for Scientific Research (NWO)
    Description: Fundação para a Ciência e a Tecnologia
    Description: Scientific Employment Stimulus 2017
    Description: Italian Ministry of University and Research
    Description: European Union's Horizon 2020 research and innovation programme
    Description: AXA Research Fund for support
    Description: Portuguese Foundation for Science and Technology
    Keywords: ddc:551.6
    Language: English
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  • 7
    Publication Date: 2022-03-31
    Description: Twenty‐first‐century climate change projections are uncertain, especially on regional scales. An important source of uncertainty is that climate models exhibit biases, which limits their ability to predict climate. One of the largest biases is the too warm sea surface temperature (SST) in the eastern tropical Atlantic (TA), reflecting deficient atmospheric and oceanic circulation. Here, we show that CO2‐forced TA‐sector climate changes simulated by state‐of‐the‐art climate models exhibit a strong mean‐state dependence. In particular, models simulating largest SST warming in the eastern TA, consistent with the warming observed since the mid‐20th century, typically exhibit a more realistic mean state than models simulating largest warming in the western TA. The former models exhibit a larger climate sensitivity, and predict stronger and in part qualitatively different climate changes over the TA sector, for example in precipitation. These findings may help to reducing uncertainty in TA‐climate change projections.
    Description: Plain Language Summary: Twenty‐first‐century climate change projections are uncertain, especially on regional scales. An important source of uncertainty is that climate models exhibit biases, which limits their ability to predict climate. One of the largest biases is the too warm sea surface temperature in the eastern tropical Atlantic (TA), reflecting deficient atmospheric and oceanic circulation. Here, we show that CO2‐forced TA‐sector climate changes simulated by state‐of‐the‐art climate models exhibit a strong relationship to the quality of simulating the mean state. These findings may help to reducing uncertainty in climate change projections over the TA sector.
    Description: Key Points: Climate projections for the tropical Atlantic sector depend on the quality of simulating present‐day conditions. Less biased climate models provide more reliable projections. Spread in CO2‐forced climate changes over the Tropical Atlantic region.
    Description: Helmholtz Society
    Description: JPI Climate and JPI Ocean
    Description: German Ministry of Education and Research
    Description: https://www.dkrz.de/up/services/data-management/cmip-data-pool
    Description: https://www.metoffice.gov.uk/hadobs/hadisst/
    Description: https://psl.noaa.gov/data/gridded/data.noaa.ersst.v5.html
    Description: https://psl.noaa.gov/data/gridded/data.cobe2.html
    Description: https://rda.ucar.edu/datasets/ds090.2/
    Description: https://psl.noaa.gov/data/gridded/data.hadslp2.html
    Description: http://www.esrl.noaa.gov/psd/data/gridded/data.coads.2deg.html
    Keywords: ddc:551.6
    Language: English
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  • 8
    Publication Date: 2022-03-25
    Description: Quantifying the anthropogenic fluxes of CO2 is important to understand the evolution of carbon sink capacities, on which the required strength of our mitigation efforts directly depends. For the historical period, the global carbon budget (GCB) can be compiled from observations and model simulations as is done annually in the Global Carbon Project's (GCP) carbon budgets. However, the historical budget only considers a single realization of the Earth system and cannot account for internal climate variability. Understanding the distribution of internal climate variability is critical for predicting the future carbon budget terms and uncertainties. We present here a decomposition of the GCB for the historical period and the RCP4.5 scenario using single‐model large ensemble simulations from the Max Planck Institute Grand Ensemble (MPI‐GE) to capture internal variability. We calculate uncertainty ranges for the natural sinks and anthropogenic emissions that arise from internal climate variability, and by using this distribution, we investigate the likelihood of historical fluxes with respect to plausible climate states. Our results show these likelihoods have substantial fluctuations due to internal variability, which are partially related to El Niño‐Southern Oscillation (ENSO). We find that the largest internal variability in the MPI‐GE stems from the natural land sink and its increasing carbon stocks over time. The allowable fossil fuel emissions consistent with 3 C warming may be between 9 and 18 Pg C yr−1. The MPI‐GE is generally consistent with GCP's global budgets with the notable exception of land‐use change emissions in recent decades, highlighting that human action is inconsistent with climate mitigation goals.
    Description: Key Points: We use a single‐model large ensemble to estimate uncertainties from internal climate variability in the global carbon budget. The land sink accounts for most internal climate uncertainty which may permit 9–18 Pg C yr−1 in allowable emissions by 2050 (for 3°C warming).
    Description: European Union's Horizon 2020
    Keywords: ddc:551.9 ; ddc:551.6
    Language: English
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  • 9
    Publication Date: 2022-03-28
    Description: The winter 2019/2020 showed the lowest ozone mixing ratios ever observed in the Arctic winter stratosphere. It was the coldest Arctic stratospheric winter on record and was characterized by an unusually strong and long‐lasting polar vortex. We study the chemical evolution and ozone depletion in the winter 2019/2020 using the global Chemistry and Transport Model ATLAS. We examine whether the chemical processes in 2019/2020 are more characteristic of typical conditions in Antarctic winters or in average Arctic winters. Model runs for the winter 2019/2020 are compared to simulations of the Arctic winters 2004/2005, 2009/2010, and 2010/2011 and of the Antarctic winters 2006 and 2011, to assess differences in chemical evolution in winters with different meteorological conditions. In some respects, the winter 2019/2020 (and also the winter 2010/2011) was a hybrid between Arctic and Antarctic conditions, for example, with respect to the fraction of chlorine deactivation into HCl versus ClONO2, the amount of denitrification, and the importance of the heterogeneous HOCl + HCl reaction for chlorine activation. The pronounced ozone minimum of less than 0.2 ppm at about 450 K potential temperature that was observed in about 20% of the polar vortex area in 2019/2020 was caused by exceptionally long periods in the history of these air masses with low temperatures in sunlight. Based on a simple extrapolation of observed loss rates, only an additional 21–46 h spent below the upper temperature limit for polar stratospheric cloud formation and in sunlight would have been necessary to reduce ozone to near zero values (0.05 ppm) in these parts of the vortex.
    Description: Key Points: The Arctic stratospheric winter 2019/2020 showed the lowest ozone mixing ratios ever observed and was one of the coldest on record. Chemical evolution of the Arctic winter 2019/2020 was a hybrid between typical Arctic and typical Antarctic conditions. Only an additional 21–46 h below PSC temperatures and in sunlight would have been necessary to reduce ozone to near zero locally.
    Description: International Multidisciplinary Drifting Observatory for the Study of the Arctic Climate (MOSAiC)
    Keywords: ddc:551.5 ; ddc:551.9
    Language: English
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  • 10
    Publication Date: 2022-03-23
    Description: The modeling of the atmospheric boundary layer over sea ice is still challenging because of the complex interaction between clouds, radiation and turbulence over the often inhomogeneous sea ice cover. There is still much uncertainty concerning sea ice roughness, near‐surface thermal stability and related processes, and their accurate parameterization. Here, a regional Arctic climate model forced by ERA‐Interim data was used to test the sensitivity of climate simulations to a modified surface flux parameterization for wintertime conditions over the Arctic. The reference parameterization as well as the modified one is based on Monin–Obukhov similarity theory, but different roughness lengths were prescribed and the stability dependence of the transfer coefficients for momentum, heat and moisture differed from each other. The modified parameterization accounts for the most comprehensive observations that are presently available over sea ice in the inner Arctic. Independent of the parameterization used, the model was able to reproduce the two observed dominant winter states with respect to cloud cover and longwave radiation. A stepwise use of the different parameterization assumptions showed that modifications of both surface roughness and stability dependence had a considerable impact on quantities such as air pressure, wind and near‐surface turbulent fluxes. However, the reduction of surface roughness to values agreeing with those observed during the Surface Heat Budget of the Arctic Ocean campaign led to an improvement in the western Arctic, while the modified stability parameterization had only a minor impact. The latter could be traced back to the model's underestimation of the strength of stability over sea ice. Future work should concentrate on possible reasons for this underestimation and on the question of generality of the results for other climate models.
    Description: The modeling of the atmospheric boundary layer over sea ice is challenging. This is, among others, due to the distinct sea ice surface roughness and pressure ridges as shown in the image, and the often stably stratified atmosphere. We quantified the impact of used parameterizations and show that both surface roughness and stability dependence have a considerable impact on near‐surface turbulent fluxes and atmospheric circulation in Arctic climate simulations.
    Description: German Research Foundation (DFG)
    Description: Helmholtz Association (HGF), POLEX http://dx.doi.org/10.13039/100003872
    Description: Russian Science Foundation (RSF) http://dx.doi.org/10.13039/501100006769
    Keywords: ddc:551.5
    Language: English
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