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  • 538.7  (10)
  • 631.4  (10)
  • English  (20)
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  • 2020-2022  (20)
  • 2021  (20)
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  • English  (20)
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  • 2020-2022  (20)
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  • 2021  (20)
  • 1
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    A Statistical Classifier for Historical Geomagnetic Storm Drivers Derived Solely From Ground-Based Magnetic Field Measurements (2021)
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    Publication Date: 2021-07-26
    Description: Solar wind observations show that geomagnetic storms are mainly driven by interplanetary coronal mass ejections (ICMEs) and corotating or stream interaction regions (C/SIRs). We present a binary classifier that assigns one of these drivers to 7,546 storms between 1930 and 2015 using ground-based geomagnetic field observations only. The input data consists of the long-term stable Hourly Magnetospheric Currents index alongside the corresponding midlatitude geomagnetic observatory time series. This data set provides comprehensive information on the global storm time magnetic disturbance field, particularly its spatial variability, over eight solar cycles. For the first time, we use this information statistically with regard to an automated storm driver identification. Our supervised classification model significantly outperforms unskilled baseline models (78% accuracy with 26[19]% misidentified interplanetary coronal mass ejections [corotating or stream interaction regions]) and delivers plausible driver occurrences with regard to storm intensity and solar cycle phase. Our results can readily be used to advance related studies fundamental to space weather research, for example, studies connecting galactic cosmic ray modulation and geomagnetic disturbances. They are fully reproducible by means of the underlying open-source software (Pick, 2019, http://doi.org/10.5880/GFZ.2.3.2019.003)
    Keywords: 538.7 ; geomagnetic observatory data ; geomagnetic storm drivers ; historical geomagnetic storms ; supervised machine learning
    Language: English
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  • 2
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    Suprathermal Fe in the Earth's Plasma Environment: Cluster RAPID Observations (2021)
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    Publication Date: 2021-07-26
    Description: Baryonic matter in geospace is almost exclusively in a plasma state, with protons (H +) and to some extent ionized helium (He) and oxygen (O) being the dominant ion species. But also other heavier ion species and even molecular ions are present in geospace. The Research with Adaptive Particle Imaging Detectors (RAPID) on board the Cluster satellites can identify and characterize some of these ions by utilizing their measured time of flight and energy. Usually, the measurements are then assigned into three discrete species channels; protons (H +), helium (He), and a common channel for carbon, nitrogen, and oxygen (CNO), each with flux, energy, and angular information. But RAPID also has a Direct Event (DE) diagnostic mode in which the full time of flight and energy information for a limited number of incident particles are stored. With knowledge about energy losses in the various detector parts, it is then possible to derive the atomic mass of the incident particle. In this paper we report on results from a study of Cluster DE events during the years 2001–2018, with a particular emphasis of iron (Fe) ions. We show that suprathermal Fe ions can be found all over geospace covered by Cluster, and that the time variation is consistent with modulation by geomagnetic disturbances and solar activity. We do not find any clear correlations between detection of suprathermal Fe and meteor showers or sputtering off the moon.
    Keywords: 538.7 ; composition ; ion outflow ; energetic particles
    Language: English
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  • 3
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    Residuals to the CHAOS-6 Geomagnetic Field Model Caused by Magnetospheric Currents During Enhanced Magnetic Activity (2021)
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    Publication Date: 2021-07-26
    Description: Thanks to mapping missions, like Ørsted, CHAMP, and Swarm, we have gained a detailed understanding of the geomagnetic field. High-resolution models like POMME, GRIMM, or CHAOS are able to describe the main parts of the Earth's magnetic field reliably. These models represent well contributions from the core and crustal fields. But their validity of describing magnetospheric field effects is limited to low activity periods (Kp ~ 0–2). Here, we study the differences between CHAMP magnetic observations and the predictions from CHAOS-6-x9, a recent version, outside this validity range. Systematic residuals appear at times of elevated activity. Mean amplitudes at the equator grow up to 12 nT around 20 hr magnetic local time for magnetic activity around Kp = 4.7. Negative residuals are obtained in the evening to midnight sector and positive ones in the morning. A seasonal dependence of the magnetospheric currents causes more negative deflections of the residuals in the winter than in the summer hemisphere. This hemispheric asymmetry cannot be accounted for by a degree 1 spherical harmonics function. A surprising observation is that the residuals show a clear longitude dependent pattern, which changes with local time. The analysis reveals that this feature can be interpreted as a Universal Time dependence of the residuals with a peak-to-peak amplitude of about 8 nT and a period of 12 hr at an activity level of Kp = 4.7. All these results call for a better parameterization of the magnetospheric current effects in a geomagnetic field model that is reliable at least up to moderate activity levels.
    Keywords: 538.7 ; geomagnetic field ; geomagnetic field model ; magnetospheric currents ; ring current ; near-Earth magnetic effect
    Language: English
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  • 4
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    One Hundred Thousand Years of Geomagnetic Field Evolution (2021)
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    Publication Date: 2021-07-26
    Description: Paleomagnetic records from sediments, archeological artifacts, and lava flows provide the foundation for studying geomagnetic field changes over 0–100 ka. Late Quaternary time-varying spherical harmonic models for 0–100 ka produce a global view used to evaluate new data records, study the paleomagnetic secular variation on centennial to multimillennial timescales, and investigate extreme regional or global events such as the Laschamp geomagnetic excursion. Recent modeling results (GGF100k and LSMOD.2) are compared to previous studies based on regional or global stacks and averages of relative geomagnetic paleointensity variations. Time-averaged field structure is similar on Holocene, 100 ky, and million-year timescales. Paleosecular variation activity varies greatly over 0–100 ka, with large changes in field strength and significant morphological changes that are especially evident when field strength is low. GGF100k exhibits a factor of 4 variation in geomagnetic axial dipole moment, and higher-resolution models suggest that much larger changes are likely during global excursions. There is some suggestion of recurrent field states resembling the present-day South Atlantic Anomaly, but these are not linked to initiation or evolution of excursions. Several properties used to characterize numerical dynamo simulations as “Earth-like” are evaluated and, in future, improved models may yet reveal systematic changes linked to the onset of geomagnetic excursions. Modeling results are useful in applications ranging from ground truth and data assimilation in geodynamo simulations to providing geochronological constraints and modeling the influence of geomagnetic variations on cosmogenic isotope production rates.
    Keywords: 538.7 ; Holocene ; paleomagnetic records ; geomagnetic field variations
    Language: English
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  • 5
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    Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ (2021)
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    Publication Date: 2021-10-28
    Description: The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long-term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day-to-day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet-time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day-to-day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long-term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.
    Keywords: 538.7 ; geomagnetism ; space physics ; geomagnetic daily variation ; solar quiet currents ; equatorial electrojet ; equatorial ionosphere
    Language: English
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  • 6
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    Natural and anthropogenic compaction in North Germany (Schleswig-Holstein): Verification of harmful subsoil compactions (2021)
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    Publication Date: 2021-10-15
    Description: Many soil types in the federal state of Schleswig-Holstein (North Germany) are naturally compacted in the subsoil due to pedo- or geogenic processes (42% of the area) but, due to anthropogenic impacts, the percentage of subsoil compaction has increased further. To determine the overall subsoil compaction status of seven representative soil types in Schleswig-Holstein (≤ 60 cm depth), air capacity (AC), saturated hydraulic conductivity (Ks) and effective bulk density (ρBeff) of 342 soil profiles from the database of the State Agency for Agriculture, Environment and Rural Areas of Schleswig-Holstein (LLUR) were evaluated with respect to critical threshold values (AC 〈 5 Vol.-%, Ks 〈 10 cm day−1, ρBeff 〉 1.7 g cm−3). The compaction status was classified into Classes I–IV, where a harmful subsoil compaction was assumed if both values of AC and Ks simultaneously exceeded (are smaller than) their threshold value (Class IV). Subsoils of (Stagnic) Luvisols and Stagnosols derived from glacial till, as well as those of Fluvic Gleyic Stagnosols of the marshlands, showed a high degree of natural compaction (46%–65% in Class IV). In contrast, sandy subsoil horizons of Podzols and Brunic Arenosols derived from glacifluvial sediments were rarely compacted (〈 13% in Class IV), and possessed the lowest ρBeff, which were similar to Anthrosols. Only 5%–18% of their subsoil horizons exceeded the critical value of 1.7 g cm−3. Additionally, anthropogenic subsoil compaction of at least 6%–10% was verified for (Stagnic) Luvisols and Stagnosols.
    Keywords: 631.4 ; air capacity ; hydraulic conductivity ; soil database ; subsoil compaction
    Language: English
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  • 7
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    Towards a standardization of soil-related ecosystem service assessments (2021)
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    Publication Date: 2021-10-15
    Description: The concept of ecosystem services (ES) creates understanding of the value of ecosystems for human well-being. With regard to soils, it provides a framework for assessments of soil contributions and soil management impacts. However, a lack of standardization impedes comparisons between assessment studies and the building of synthesis information. The Common International Classification of Ecosystem Services (CICES) is an important step forward, although its application to soils is not without difficulty. CICES version 5.1 defines 83 ES classes, of which only some are relevant for soils. We compiled two subsets of CICES classes: one set of soil-related ES comprising 29 services defined as directly and quantifiably controlled by soils and their properties, processes and functions, and another set of 40 ES defined as being affected by agricultural soil management. Additionally, we conducted a systematic literature review, searching for published lists of soil-related ES that claim completeness. We identified 11 relevant lists. Of all CICES classes, 12 were included in more than 75% of the lists, whereas another 36 classes were included in 25–75% of them. Regarding the suitability of the CICES classification for addressing ES in the context of soils and their agricultural management, we identified constraints, such as overlaps, gaps, and highly specific or very broad class definitions. Close cooperation between the soil research and ES communities could ensure better consideration of soils in future CICES updates. A shortlist of 25 service classes affected by agricultural soil management facilitates a standardized approach and may function as checklists in impact assessments. Highlights: Standardized definitions are needed to allow meta-analysis of ecosystem service studies and improve assessments. CICES defines 83 detailed classes of ecosystem services, suggested as a “default list”. We identified 29 classes as soil related and 40 classes as affected by agricultural soil management. Both subsets facilitate ecosystem service assessments in soil research and comparability of results.
    Keywords: 631.4 ; agriculture ; arable ; CICES ; impact area ; impact assessment ; soil functions ; soil management ; soil properties ; standardization
    Language: English
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  • 8
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    Permafrost soil complexity evaluated by laboratory imaging Vis-NIR spectroscopy (2021)
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    Publication Date: 2021-10-15
    Description: The biogeochemical functioning of soils (e.g., soil carbon stabilization and nutrient cycling) is determined at the interfaces of specific soil structures (e.g., aggregates, particulate organic matter (POM) and organo-mineral associations). With the growing accessibility of spectromicroscopic techniques, there is an increase in nano- to microscale analyses of biogeochemical interfaces at the process scale, reaching from the distribution of elements and isotopes to the localization of microorganisms. A widely used approach to study intact soil structures is the fixation and embedding of intact soil samples in resin and the subsequent analyses of soil cross-sections using spectromicroscopic techniques. However, it is still challenging to link such microscale approaches to larger scales at which normally bulk soil analyses are conducted. Here we report on the use of laboratory imaging Vis–NIR spectroscopy on resin embedded soil sections and a procedure for supervised image classification to determine the microscale soil structure arrangement, including the quantification of soil organic matter fractions. This approach will help to upscale from microscale spectromicroscopic techniques to the centimetre and possibly pedon scale. Thus, we demonstrate a new approach to integrate microscale soil analyses into pedon-scale conceptual and experimental approaches. Highlights: Quantification of soil constituents using Vis-NIR spectroscopy. New approach to use resin embedded soil core sections with intact structure. Reproducible quantification of soil constituents important for soil carbon storage. Vis-NIR as promising tool for upscaling from microscale to pdeon scale.
    Keywords: 631.4 ; Alaska ; HySpex ; mineral associated organic matter ; occluded particulate organic matter ; particulate organic matter ; pedogenic iron oxides ; supervised image classification
    Language: English
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  • 9
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    The Norwegian-Greenland Sea, the Laschamps, and the Mono Lake Excursions Recorded in a Black Sea Sedimentary Sequence Spanning From 68.9 to 14.5 ka (2021)
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    Publication Date: 2021-10-15
    Description: A full-vector paleomagnetic record, comprising directional data and relative paleointensity (rPI), was derived from 16 sediment cores recovered from the southeastern Black Sea. The obtained data were used to create a stack covering the time window between 68.9 and 14.5 ka. Age models are based on radiocarbon dating and correlations of warming/cooling cycles monitored by high-resolution X-ray fluorescence (XRF) elementary ratios and by ice-rafted debris (IRD) in Black Sea sediments to the sequence of “Dansgaard-Oeschger” (D-O) events defined from the Greenland ice core oxygen isotope stratigraphy. The reconstructed prominent lows in paleointensity at about 64.5, 41.2, and 34.5 ka are coeval with the Norwegian-Greenland Sea, the Laschamps, and the Mono Lake excursions, respectively. For a further analysis, the stacked Black Sea paleomagnetic record was converted into one component being parallel to the direction expected from a geocentric axial dipole (GAD) and two components perpendicular to it (EW, inclined NS), representing definitely only non-GAD components of the geomagnetic field. Discussions of the field configurations at the Black Sea site are focused on the three excursional events. The Norwegian-Greenland Sea excursion was dominated by a decaying axial dipole and persisting weak nondipole field, with directional variations still within the range of normal secular variations. The Laschamps excursion comprises two full polarity transitions and a short stable interval of reversed polarity in between. The Mono Lake excursion was mostly dominated by a nondipole field, though with a less pronounced weakening of the axial dipole component.
    Keywords: 538.7 ; Black Sea ; Norwegian-Greenland Sea excursion ; Laschamps excursion ; Mono Lake excursion ; paleosecular variations
    Language: English
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  • 10
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    Spatial Heterogeneity Enables Higher Root Water Uptake in Dry Soil but Protracts Water Stress After Transpiration Decline: A Numerical Study (2021)
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    Publication Date: 2021-10-27
    Description: A common assumption in models of water flow from soil to root is that the soil can be described in terms of its representative or effective behavior. Microscale heterogeneity and structure are thereby replaced by effective descriptions, and their role in flow processes at the root-soil interface is neglected. Here the aim was to explore whether a detailed characterization of the microscale heterogeneity at the scale of a single root impacts the relation between flow rate and pressure gradient. Numerical simulations of water flow toward a root surface were carried out in a two-dimensional domain with a randomized configuration of spatially variable unsaturated hydraulic conductivities and varying boundary conditions, that is, increasing and decreasing root water uptake rates. By employing Matheron's method, the soil hydraulic properties were varied, while the effective hydraulic conductivity (corresponding to the geometric mean) remained unchanged. Results show that domains with a uniform conductivity could not capture important features of water flow and pressure distribution in spatially variable domains. Specifically, increasing heterogeneity at the root-soil interface allowed to sustain higher root water uptake rates but caused a slower recovery in xylem suction after transpiration ceased. The significance of this is that, under critical conditions, when pressure gradients and flow rates are high, microscale heterogeneity may become an important determinant and should not be neglected in adequate descriptions of water flow from soil to root in dry soil.
    Keywords: 631.4 ; effective soil hydraulic conductivity ; leaf water potential ; soil water potential ; root water uptake ; root-soil interface ; soil heterogeneity
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  • 11
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    Recordings of Fast Paleomagnetic Reversals in a 1.2 Ma Greigite-Rich Sediment Archive From Lake Ohrid, Balkans (2021)
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    Publication Date: 2021-10-11
    Description: State-of-the-art paleoclimate research strongly depends on the availability of time-equivalent markers as chronological control to disentangle interrelationships in the climate system from regional to global scale. Geomagnetic reversals are regarded as excellent age constraints because they are global events and independent from climatic conditions. However, spatial variations of timing and internal dynamics of reversals may limit their precision. Our 1.2 Ma high-resolution (~25 cm/kyr) sediment record from Lake Ohrid is promising to precisely depict the Matuyama-Brunhes (MB) reversal and the Jaramillo subchron. Two generations of diagenetic ferrimagnetic minerals are present in glacial intervals of the Lake Ohrid record. Early diagenetic greigite acquired a quasi synsedimentary chemical magnetization, while a late diagenetic greigite formation, triggered by the upward diffusion of H2S-rich waters, obscures the polarity record at the top of the Jaramillo. Interglacial intervals are unaffected by greigite formation, likely due to low iron concentrations. Based on an orbitally tuned age model with tephrostratigraphic markers, the base of Jaramillo can be precisely dated to 1072.4 ka, and the MB reversal to 778.5 ka. Both polarity reversals occurred very rapidly in our record, lasting 2.3 and 1 kyr, respectively. Our results reveal that the dipole component of the Earth's magnetic field fell below the nondipole components only for a short duration in the Mediterranean region. The comparison of the timing of the MB boundary across different archives implies that the onset of the reversal provides a more synchronous age marker compared to often used midpoint ages.
    Keywords: 538.7 ; magnetostratigraphy ; diagenesis ; rock magnetism ; greigite ; fast magnetic reversals ; Matuyama-Brunhes
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  • 12
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    Nowcasting and Predicting the Kp Index Using Historical Values and Real-Time Observations (2021)
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    Publication Date: 2021-10-11
    Description: Current algorithms for the real-time prediction of the Kp index use a combination of models empirically driven by solar wind measurements at the L1 Lagrange point and historical values of the index. In this study, we explore the limitations of this approach, examining the forecast for short and long lead times using measurements at L1 and Kp time series as input to artificial neural networks. We explore the relative efficiency of the solar wind-based predictions, predictions based on recurrence, and predictions based on persistence. Our modeling results show that for short-term forecasts of approximately half a day, the addition of the historical values of Kp to the measured solar wind values provides a barely noticeable improvement. For a longer-term forecast of more than 2 days, predictions can be made using recurrence only, while solar wind measurements provide very little improvement for a forecast with long horizon times. We also examine predictions for disturbed and quiet geomagnetic activity conditions. Our results show that the paucity of historical measurements of the solar wind for high Kp results in a lower accuracy of predictions during disturbed conditions. Rebalancing of input data can help tailor the predictions for more disturbed conditions.
    Keywords: 538.7 ; Kp index ; geomagnetic activity ; empirical prediction ; solar wind ; forecast ; AI
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  • 13
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    Estimating Shortwave Clear-Sky Fluxes From Hourly Global Radiation Records by Quantile Regression (2021)
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    Publication Date: 2021-10-13
    Description: Estimates of radiative fluxes under cloud-free conditions (“clear-sky”) are required in many fields, from climatic analyses of solar transmission to estimates of solar energy potential for electricity generation. Ideally, these fluxes can be obtained directly from measurements of solar fluxes at the surface. However, common standard methods to identify clear-sky conditions require observations of both the total and the diffuse radiative fluxes at very high temporal resolution of minutes, which restricts these methods to a few, well-equipped sites. Here we propose a simple method to estimate clear-sky fluxes only from typically available global radiation measurements (Rsd) at (half-)hourly resolution. Plotting a monthly sample of observed Rsd against the corresponding incoming solar radiation at the top of atmosphere (potential solar radiation) reveals a typical triangle shape with clear-sky conditions forming a distinct, linear slope in the upper range of observations. This upper slope can be understood as the fractional transmission of solar radiation representative for cloud-free conditions of the sample period. We estimate this upper slope through quantile regression. We employ data of 42 stations of the worldwide Baseline Surface Radiation Network to compare our monthly estimates with the standard clear-sky identification method developed by Long and Ackerman (2000, https://doi.org/10.1029/2000JD900077). We find very good agreement of the derived fractional solar transmission (R2 = 0.73) across sites. These results thus provide confidence in applying the proposed method to the larger set of global radiation measurements to obtain further observational constraints on clear-sky fluxes and cloud radiative effects.
    Keywords: 538.7 ; cloud-free ; clear-sky ; global radiation ; transmission ; quantile regression
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  • 14
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    Converting forests into rubber plantations weakened the soil CH4 sink in tropical uplands (2021)
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    Publication Date: 2021-10-13
    Description: Large-scale conversion of natural forest to rubber plantations has taken place for decades in Southeast Asia, help to make it a deforestation hot spot. Besides negative changes in biodiversity, ecosystem water, and carbon budgets, converting forests to plantations often reduced CH4 uptake by soils. The latter process, which might be partly responsible for resumed increase in the growth rate of CH4 atmospheric concentrations since 2006, has not been adequately investigated. We measured soil surface CH4 fluxes during 2014 and 2015 in natural forests and rubber plantations of different age and soil textures in Xishuangbanna, Southwest China—a representative area for this type of land-use change. Natural forest soils were stronger CH4 sinks than rubber soils, with annual CH4 fluxes of −2.41 ± 0.28 and −1.01 ± 0.23 kg C ha−1 yr−1, respectively. Water-filled pore space was the main factor explaining the differences between natural forests and rubber plantations, even reverting rubber soils temporarily from CH4 sink into a methane source during the rainy season in older plantations. Soil nitrate content was often lower under rubber plantations. Added as a model covariate, this factor improved explanation power of the CH4 flux—water-filled pore space regression. Although soils under rubber plantation were more clayey than soils under natural forest, this was not the decisive factor driving higher soil moisture and lower CH4 uptake in rubber soils. Thus, the conversion of forests into rubber plantations exerts a negative impact on the CH4 balance in the tropics and likely contributes to global climate.
    Keywords: 631.4 ; deforestation ; land-use change ; methane ; rubber plantation ; soil moisture ; soil texture ; tropics
    Language: English
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  • 15
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    Influence of soil structure on the spread of Pseudomonas fluorescens in soil at microscale (2021)
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    Publication Date: 2021-10-14
    Description: For over a half a century, researchers have been aware of the fact that the physical and chemical characteristics of microenvironments in soils strongly influence the activity, growth and metabolism of microorganisms. However, many aspects of the effect of soil physical characteristics, such as the pore geometry, remain poorly understood. Therefore, the objective of the present research was to determine the influence of soil pore characteristics on the spread of bacteria, observed at the scale relevant to microbes. Pseudomonas fluorescens was introduced in columns filled with 1–2 mm soil aggregates, packed at different bulk densities. Soil microcosms were scanned at 10.87 μm voxel resolution using X-ray computed tomography (CT) to characterize the geometry of pores. Thin sections were prepared to determine the spread and colonization of bacteria. The results showed that average bacterial cell density was 174 cells mm−2 in soil with bulk density of 1.3 g cm−3 and 99 cells mm−2 in soil with bulk density of 1.5 g cm−3. Soil porosity and solid-pore interfaces influence the spread of bacteria and their colonization of the pore space at lower bulk density, resulting in relatively higher bacterial densities in larger pore spaces. The study also demonstrates that thin sectioning of resin-impregnated soil samples can be combined with X-ray CT to visualize bacterial colonization of a 3D pore volume. This research therefore represents a significant step towards understanding how environmental change and soil management impact bacterial diversity in soils. Highlights: We used a quantitative approach to study bacterial spread in soil at scales relevant to microbes. The rate of pseudomonas spread decreased with increased bulk density of soil. Soil porosity and soil-pore interface influence Pseudomonas in lower bulk density soil. Soil structure with different pore characteristics effects spread and activity of bacteria in soil.
    Keywords: 631.4 ; bacterial spread ; fluorescence microscopy ; pore geometry ; soil thin sections ; X-ray computed tomography
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  • 16
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    Could oxalate-extractable phosphorus replace phosphorus fractionation schemes in soil phosphorus prospections?—A case study in the prehistoric Milseburg hillfort (Germany) (2021)
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    Publication Date: 2021-10-14
    Description: A geoarchaeological soil phosphorus (P) prospection is used to identify a gate within the prehistoric rampart of the Milseburg hillfort (Hesse, Germany). This study compares the application of a P fractionation scheme and P extraction with ammonium-oxalate. We hypothesized that oxalate-extractable P (P-ox) and the related degree of P saturation (DPS) could replace the more expensive and time-consuming fractionation schemes for geoarchaeological investigations. Comparing the results, the P fractionation helped to verify the existence of another section of the prehistoric ramparts and to identify the location of a gate within it. It also helped to discover the archaeologically relevant soil depths in the investigated area. This information could not be retrieved from the P-ox data alone. Soil P-ox contents and DPS values are relatively unspecific with regard to prehistoric land use. However, DPS at least indicates settled versus unsettled areas. Still, the results of the P fractionation more clearly delineate Iron Age land use areas including settlement, non-settlement, rampart, and rampart gap (probable gate). Thus, in geoarchaeological contexts, this method seems to be preferable to a singular P-ox extraction. However, for better results, P-ox determination could be integrated into a P fractionation scheme.
    Keywords: 551.9 ; 631.4 ; Milseburg ; oxalate-extractable phosphorus ; phosphorus fractionation ; phosphorus saturation ; soil phosphorus prospection
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  • 17
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    Classification of buried soils, cultural, and colluvial deposits in the Viking town Hedeby (2021)
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    Publication Date: 2021-10-14
    Description: Objective classification of settlement deposits is a prerequisite for understanding human-environment interactions at habitation sites. This paper presents a novel approach combining a relatively fine-scale sampling strategy, a multimethod geoarchaeological investigation of cores and multivariate statistics to aid in the classification and interpretation of complex and intricately stratified archaeological deposits. Heterogeneous settlement deposits, buried soils, colluvial, fluvial, and fluvioglacial sediments from cores retrieved in the Viking settlement Hedeby were investigated using six cost-effectively measurable geoecological parameters: loss on ignition at 550°C, magnetic susceptibility, contents of stones, artifacts, bones, and charcoal with wood. Principal component analysis allowed identifying variables that would sufficiently describe data and cluster analysis enabled the classification of the materials. As a result, 13 classes were distinguished with a detailed and reliable differentiation of materials of natural and cultural genesis. Based on spatial distribution patterns of the classes, hypotheses regarding land use in the adjacent areas were made: Waste disposal in the valley of Hedeby-brook and metallurgic activities north of it. This approach is valuable for coring-based research at settlements, in particular at tightly managed heritage sites, and for surveys to identify potential excavation sites, whereas the set of variables must be adjusted according to local conditions.
    Keywords: 631.4 ; 930.1 ; classification ; cultural layers ; Hedeby ; multivariate statistics ; soil horizons ; Viking Age
    Language: English
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  • 18
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    Relationships between spectral features, iron oxides and colours of surface soils in northern Jordan (2021)
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    Publication Date: 2021-09-06
    Description: Ground data on spectral characteristics of Jordan's soils remain sparse, which makes the interpretation of remote sensing datasets challenging. These are, however, very useful for predicting soil properties and agricultural suitability. Previous studies have shown that soil colours correlate well with degrees of weathering intensity, as indicated by magnetic parameters and dithionite-extractable iron (Fed) contents along a climosequence in northern Jordan. This study enlarges the database by the results of 160 bulk samples that were collected systematically from the soil surface at 40 locations. In addition to soil colour and contents of Fed, we explore mean soil reflectance spectra (MSRS) measured by analytical spectral devices (ASD) and analyse the morphological conditions of the spectra referring to the effects of iron oxides on spectral behaviours. Results show a high correlation of spectral behaviours and colour variations with Fe oxides, and no correlation with soil organic carbon Corg. The influence of the Fe oxide contents is clearly apparent in the visible range (VIS). The presence of CaCO3 increases the reflectance in all spectral ranges. Six soil groups (Gr. I - Gr. VI) were discerned qualitatively and quantitatively in the study area, which largely mirror the intensity of red colour expressed by redness indices. Highlights In northwestern Jordan there is an evident connection between the spectral properties, chemistry and soil colour. This study established a preliminary spectral library of soils in NW Jordan to facilitate the use of remote sensing in soil studies. The morphological properties and statistical analysis of the spectral data show that spectra of soils in NW Jordan are dominated by iron oxides. Spectral properties can be used to characterize the soil colours and types of Fe oxides in soils of Jordan.
    Keywords: 631.4 ; ASD laboratory soil spectroscopy ; CIELAB colour system ; iron oxides ; Mediterranean soils ; soil colour
    Language: English
    Type: article
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    The Effect of Plasma Boundaries on the Dynamic Evolution of Relativistic Radiation Belt Electrons (2021)
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    Publication Date: 2021-10-01
    Description: Understanding the dynamic evolution of relativistic electrons in the Earth's radiation belts during both storm and nonstorm times is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) focus group “Quantitative Assessment of Radiation Belt Modeling” has selected two storm time and two nonstorm time events that occurred during the second year of the Van Allen Probes mission for in-depth study. Here, we perform simulations for these GEM challenge events using the 3D Versatile Electron Radiation Belt code. We set up the outer L* boundary using data from the Geostationary Operational Environmental Satellites and validate the simulation results against satellite observations from both the Geostationary Operational Environmental Satellites and Van Allen Probe missions for 0.9-MeV electrons. Our results show that the position of the plasmapause plays a significant role in the dynamic evolution of relativistic electrons. The magnetopause shadowing effect is included by using last closed drift shell, and it is shown to significantly contribute to the dropouts of relativistic electrons at high L*. We perform simulations using four different empirical radial diffusion coefficient models for the GEM challenge events, and the results show that these simulations reproduce the general dynamic evolution of relativistic radiation belt electrons. However, in the events shown here, simulations using the radial diffusion coefficients from Brautigam and Albert (2000) produce the best agreement with satellite observations.
    Keywords: 538.7 ; radiation belt ; simulation ; relativistic electrons ; magnetopause shadowing ; wave-particle interaction ; plasmapause
    Language: English
    Type: map
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  • 20
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    Soil organic carbon allocation and dynamics under perennial energy crops and their feedbacks with soil microbial biomass and activity (2021)
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    Publication Date: 2021-12-07
    Description: The cultivation of perennial instead of annual energy crops has received growing interest. Previous studies identified numerous beneficial effects of perennial energy crop (PEC) cultivation for the agricultural landscape such as promotion of agrobiodiversity, reduced requirements for agrochemicals and fertilizers as well as a large potential for carbon accumulation in soil. However, the mere presence of soil organic matter (SOM) accumulation gives no indication about the persistence of the SOM for example after a recultivation of the stands. Therefore, this study focused on SOM pools of different density fractions and soil microbial parameters. Six different PECs were tested against a typical benchmark system as feedstock for anaerobic digestion. The study has shown that all PEC species increased soil microbial activity and provided an insight how they sequester carbon in soil. Moreover, significant modifications in basic soil properties caused by plant growth were observed. For example, the cultivation of giant knotweed has lowered the soil pH by more than 0.5 pH units compared to the benchmark system. After 5 years of PEC cultivation, total soil organic carbon stocks were increased between 1,500 ± 400 and 4,500 ± 1,500 kg C ha-1 for the upper 10 centimetres of soil. The distribution among different soil fractions showed species-specific patterns. Tall wheatgrass and Virginia mallow showed particular high accumulation rates in the mineral-associated SOM fraction which indicates long residence times of the SOM after a possible recultivation of the fields.
    Keywords: 631.4 ; perennial energy crop ; soil carbon accumulation ; soil microbiological activity
    Language: English
    Type: map
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