bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial variability of topsoil δ13C across Qinghai-Tibet Plateau
Authors: Lai Yunsen , Li Shaoda , Tang Xiaolu , Luo Xinrui , Liu Liang , Shi Yuehong , Yu Peng
Published: March 2021

Soil carbon isotopes (δ13C) provide reliable insights at the long-term scale for the study of soil carbon turnover and topsoil δ13C could well reflect organic matter input from the current vegetation. Qinghai-Tibet Plateau (QTP) is called “the third pole of the earth” because of its high elevation, and it is one of the most sensitive and critical regions to global climate change worldwide. Previous studies focused on variability of soil δ13C at in-site scale. However, a knowledge gap still exists in the spatial pattern of topsoil δ13C in QTP. In this study, we first established a database of topsoil δ13C with 396 observations from published literature and applied a Random Forest (RF) algorithm (a machine learning approach) to predict the spatial pattern of topsoil δ13C using environmental variables. Results showed that topsoil δ13C significantly varied across different ecosystem types (p < 0.05).  Topsoil δ13C was -26.3 ± 1.60 ‰ for forest, 24.3 ± 2.00 ‰ for shrubland, -23.9 ± 1.84 ‰ for grassland, -18.9 ± 2.37 ‰ for desert, respectively. RF could well predict the spatial variability of topsoil δ13C with a model efficiency (pseudo R2) of 0.65 and root mean square error of 1.42. The gridded product of topsoil δ13C and topsoil β (indicating the decomposition rate of soil organic carbon, calculated by δ13C divided by logarithmically converted SOC) with a spatial resolution of 1000 m were developed. Strong spatial variability of topsoil δ13C was observed, which increased gradually from the southeast to the northwest in QTP. Furthermore, a large variation was found in β, ranging from -7.87 to -81.8, with a decreasing trend from southeast to northwest, indicating that carbon turnover rate was faster in northwest QTP compared to that of southeast. This study was the first attempt to develop a fine resolution product of topsoil δ13C for QTP using a machine learning approach, which could provide an independent benchmark for biogeochemical models to study soil carbon turnover and terrestrial carbon-climate feedbacks under ongoing climate change.
Future changes in Beijing haze events under different shared socioeconomic pathways
Authors: Guo Liang , Wilcox Laura , Bollasina Massimo , Turnock Steven , Lund Marianne , Zhang Lixia
Published: March 2021

The occurrence of severe haze events remains a serious problem in Beijing. Previous studies suggested that the frequency of weather patterns conducive to haze may increase with global warming. The new Shared Socioeconomic Pathways (SSPs) cover a wide range of uncertainties in aerosol and greenhouse gases emissions. Global and Chinese aerosol emissions are projected to decrease in most SSPs, while increases in greenhouse gases and global warming will continue for the rest of the century. The future, therefore, remains unclear.

We quantified the air pollution over Beijing and associated weather patterns using multiple indices calculated from the SSPs

We show that the occurrence of weather patterns conducive to the formation of haze significantly increases by the end of the century due to increases in greenhouse gases. Aerosol reductions also cause an increase in their occurrence, but reduce the severity of haze, and overall reducing aerosol emissions will be beneficial.
 Prediction of peat depths using airborne radiometric data: optimization of ground surveys. 
Authors: Marchant Ben
Published: March 2021

The use of remote sensing data can lead to great efficiencies when mapping soil variables across broad regions. However, remote sensors rarely make direct measurements of the soil property of interest. Instead, an empirical model is required to relate the remote sensing data to ground measurements of the property of interest. We discuss how a survey of ground measurements required to calibrate such a model can be optimized. We make reference to the mapping of peat depth within the Dartmoor National Park (UK) using radiometric potassium data from an airborne survey of the region (http://www.tellusgb.ac.uk/). We expand the standard linear mixed model to accommodate nonlinear relationships between radiometric potassium and peat depths. The attenuation of the radiometric signal is seen to increase with peat depth, but the depth is particularly uncertain when the radiometric signal is small. When a spatial simulated annealing algorithm is used to optimize the locations for a survey of peat depth measurements to minimize the errors in the maps of peat depth upon use of the radiometric data, the complete range of the radiometric data are sampled but ground measurements are particularly focussed where the radiometric signal is small. We see that an optimized survey of 30 ground measurements combined with the radiometric data lead to more accurate maps than can be achieved from interpolation of more than 200 peat depth measurements.
What does the 2A Event observed in the oceanic crust actually represent?
Authors: Hobbs Richard , Peirce Christine
Published: March 2021

The transition zone between the more porous upper extrusive layer (2A) and the less porous lower dyke layer (2B) within the oceanic crust is characterised by a high velocity gradient based on inversion of controlled-source, long-offset refraction data. In these data the phase associated with this high velocity gradient, termed the 2A Event, has an anomalously high amplitude over a limited range of offsets and appears to form a triplication with refractions from layer 2A above and 2B below. These characteristics fit the accepted model that this event is a caustic or retrograde phase, generated by a distinct layer whose thickness and velocity gradient can be determined by ray-trace modelling. Hence, a velocity model for Layer 2 (derived from seismic data acquired near ODP 504B) consists of a ~500 m-thick 2A with a velocity gradient of ~1.0 s-1; a ~200 m-thick transition zone with a high velocity gradient of ~4.0 s-1; and a ~1300 m-thick 2B with a velocity gradient of ~0.3 s-1. However, this model is at odds with observation of Layer 2 lithology obtained from coring and ophiolites where the 2A is composed of a mixture of higher velocity basalt flows and lower velocity pillow lavas and breccia, with the transition zone represented by an increasing number of dykes which eventually make up 100% of the section in layer 2B combined and the effects of high-temperature alteration. Starting with a simplified but plausible geologically-based model, we show that it is possible to synthetically generate the observed 2A Event, and gain insight into what controls its visibility and variability in refraction data. Our primary findings show that the 2A Event will only form and propagate in the base of layer 2A, above the level where the higher velocities dominate. We also show that the amplitude of the 2A Event is sensitive to the local velocity structure of the extrusive layer and is most visible when seismic energy is focused by a low velocity layer. Hence, we conclude that the 2A Event is not a simple caustic, as defined by geometrical optics, but instead caused by the incident seismic energy being briefly concentrated in a leaky waveguide close to, but above, the mean depth of the dykes and the onset of high temperature alteration.
Elucidating soil moisture dynamics in agricultural landscapes under varying weather patterns
Authors: Fritz Veronica , Thaasan Thakshajini , Williams Andrew , Udawatta Ranjith , Mendis Sidath , Aloysius Noel
Published: March 2021

Changing weather patterns and anthropogenic land use change significantly alter the terrestrial water cycle. A key variable that modulates the water cycle on the land surface is soil moisture and its variability in time and space. Hydrological models are used to simulate key components of the water cycle including infiltration, soil storage and uptake by plants. However, uncertainties remain in accurately representing soil moisture dynamics in models. Here, with the aid of several sensors installed at a 30-ha experimental research facility, we attempt to quantify differences in soil water storage across multiple land use types – cropped area, mosaic of turf grass and native plants, and an unkept weeded area as control land use. We will also discuss the accuracy of sensors to correctly measure soil water storage. Our study was conducted at an agricultural experimental station in Columbia, Missouri, USA. We use a variety of instruments to measure weather, evapotranspiration, and soil water. We used boundary layer scintillometers to measure near-surface turbulence, sensors to continuously track soil moisture and temperature, as well as weather stations for precipitation, air temperature, solar radiation and wind speed.  Changes in volumetric water content and soil temperature are measured at 5-minute intervals at 10-, 20-, and 40-cm soil depths to compare soil water storage among the three land use types. We also took soil samples before and after several storm events to calibrate the sensor readings at three sites. We, then, analyzed several storm events over a period of five months and compared the actual soil moisture and soil temperature dynamics at finer time intervals. With additional measurements of weather and boundary layer turbulence, we hope to reveal the landscape and weather control on soil moisture distribution across multiple land uses, and their subsequent impact on plant water uptake. Our preliminary results indicate that continuously disturbed agricultural lands depletes soil moisture at faster rates, which may present challenges in maintaining land productivity in the long term.
Comparative overview of reservoir siltation assessment techniques depending on the type of sediment
Authors: Hilgert Stephan , Sotiri Klajdi , Fuchs Stephan
Published: March 2021

Over many decades it has become evident, that sediment accumulation threatens the fundamental operation of reservoirs by reducing the storage volume, hindering technical functions and deteriorating water quality over time. Most scientists, operators and authorities are aware of this, often “silent” but enduring process. However, not often mitigation measures are applied with foresight and in an appropriate manner according to this global problem. One fundamental reason for the often hesitant implementation of measures is the lack of precise and applicable assessment techniques. The type of reservoir, available historic data and especially the composition of the sediment may allow only for one available method to be applied successfully. In this study we present a workflow to select the best available method to detect the sediment thickness correctly. We compare topographic differencing, dual-frequency echo sounding, sub-bottom echo sounding, free-fall penetrometer measurements and sediment coring. Next to the general applicability, the precision (vertical resolution) and the time requirement for the measurement are relevant factors. A special point of discussion is the presence of free gas inside the sediment, often creating measurement errors, leading to underestimation of the sediment thickness.
The ice nucleating ability of macromolecules in immersion freezing decreases in the presence of salts: Implications for freezing point depression calculations
Authors: Went Jon F. , Wheeler Jeanette D. , Peaudecerf François J. , Borduas-Dedekind Nadine
Published: March 2021

Cloud formation represents a large uncertainty in current climate predictions. In particular, ice in mixed-phase clouds requires the presence of ice nucleating particles (INPs) or ice nucleating macromolecules (INMs). An influential population of INPs has been proposed to be organic sea spray aerosols in otherwise pristine ocean air. However, the interactions between INMs present in sea water and their freezing behavior under atmospheric immersion freezing conditions warrants further research to constrain the role of sea spray aerosols on cloud formation. Indeed, salt is known to lower the freezing temperature of water, through a process called freezing point depression (FPD). Yet, current FPD corrections are solely based on the salt content and assume that the INMs’ ice nucleation abilities are identical with and without salt. Thus, we measured the effect of salt content on the ice nucleating ability of INMs, known to be associated with marine phytoplankton, in immersion freezing experiments in the Freezing Ice Nuclei Counter (FINC) (Miller et al., AMTD, 2020). We measured eight INMs, namely taurine, isethionate, xylose, mannitol, dextran, laminarin, and xanthan as INMs in pure water at temperatures relevant for mixed-phase clouds (e.g. 50% activated fraction at temperatures above –23 °C at 10 mM concentration). Subsequently, INMs were analyzed in artificial sea water containing 36 g salt L-1. Most INMs, except laminarin and xanthan, showed a loss of ice activity in artificial sea water compared to pure water, even after FPD correction. Based on our results, we hypothesize sea salt has an inhibitory effect on the ice activity of INMs. This effect influences our understanding of how INMs nucleate ice as well as challenges our use of FPD correction and subsequent extrapolation to ice activity under mixed-phase cloud conditions.
Using a water budget model to anticipate the impact of climate change on groundwater recharge at the regional scale in cold and humid climates - example of southern Quebec (Canada)
Authors: Dubois Emmanuel , Larocque Marie , Gagné Sylvain
Published: March 2021

In cold and humid climates, rivers and superficial water bodies are often fed by groundwater with relatively constant inflows that are most visible during the summer (limited net precipitation) and the winter (limited runoff and infiltration). The harsh winter – short growing season succession could be drastically affected by climate change. Although water is abundant, extreme low flows are expected in the near future, most likely due to warmer summer temperatures, increased summer PET and possible lower summer precipitation. It is thus crucial to provide stakeholders with scenarios of future groundwater recharge (GWR) to anticipate the impacts of climate change on groundwater resources at the regional scale. This study aims to test the contributions of a superficial water budget model to estimate the impact of climate change on the regional GWR. The methodology is tested in a forested and agricultural region of southern Quebec, located between the St. Lawrence River and the Canada-USA border, and between the Quebec-Ontario border and Quebec City (36,000 km²). Scenarios of GWR for the region are simulated with the HydroBudget model, performing a transient-state spatialized superficial water budget, and 12 climate scenarios (RCP 4.5 and 8.5, 1951-2100 period). The model was previously calibrated in the study area for the 1961-2017 period and provides spatially distributed runoff, actual evapotranspiration, and GWR fluxes at a 500 x 500 m resolution with a monthly time step. Climate scenarios show warming of the annual temperature from +2 to +5°C and up to 20% increase of annual precipitation at the 2100 horizon compared to the 1981-2010 reference period. By the end of the century, the number of days above 0°C could double between November and April, dividing by almost two the quantity of snow during winter. The clear trends of warming temperature leads to a clear actual evapotranspiration (AET) increase while the increasing variability in annual precipitation translates into more variable annual runoff and GWR. Although no annual GWR decrease is simulated, an increase of winter GWR (up to x2) is expected, linked to warmer winters and unfrozen soils, followed by a decrease for the rest of the year, linked to a longer growing season producing higher AET rates. Although simple in its simulation process, the use of a superficial water budget model simulating soil frost provides new insights into the possible future trends in the different hydrologic variables based on a robust understanding of past condition. Aside from providing scenarios of spatialized GWR (also runoff and AET) at the 2100 horizon for a large region, this study shows that a simple water budget model is an appropriate and affordable tool to provide stakeholders with useful data for water management in a changing climate.
The use of CMEMS Black Sea Physical Reanalysis (1993-2019) to understand better the Black Sea variability
Authors: Peneva Elisaveta , Lima Leonardo , Aydogdu Ali , Masina Simona , Stanev Emil , Ciliberti Stefania , Azevedo Diana , Coppini Giovanni , Palazov Atanas , Marinova Veselka , Valcheva Nadezdha
Published: March 2021

The recently upgrated CMEMS product Black Sea Physical Reanalysis (BLKSEA_MULTIYEAR_PHY_007_004) covers the period 1993-2019 presenting a base for reliable long-term estimates on different aspects of the Black Sea physical processes. The data archive provides monthly and daily fields for the Black Sea basin including 3D variables (temperature, salinity, zonal and meridional velocity components) and 2D variables (mixed layer depth, bottom temperature and sea surface height). 

The good spatial and temporal resolution of the reanalysis gives possibility to evaluate the trend and variability of the subsurface temperature and salinity, as well as the general circulation changes. In the last two decades significant tendency for warming is observed at the surface and in deeper layers, reaching down ~100 m depth. This trend is associated with a slight positive salinity trend seen down to ~200 m depth, which is present almost in the entire Black Sea except for the north-western shelf close to the Danube and Dnestr river delta. Both temperature and salinity show strong interannual variability.  

The calculated Ocean Heat Content (OHC) in the Black Sea basin over the last ~30 year period suggests that the Black Sea water had experienced a general heating tendency after 2013. The increase of OHC is mostly due to the layer 0-200 m and the deeper layers are rather conservative in time. Nevertheless, the cold winter conditions in 2006, 2012 and 2017 led to significant surface water cooling and replenishment of the Cold Intermediate Layer. 

The variation in the main dynamic feature of the basin, the Black Sea Rim current, is studied using the reanalysis data. It shows that the surface current speed varies within ~30% in the period 1993-2019 with a slight positive tendency. The main factor which triggers the inter-annual variability of the Rim current is found to be the atmospheric forcing. Comparison with the surface wind curl from the ERA5 reanalysis data shows significant correlation, predominantly positive (cyclonic) curl for both sea and atmosphere circulation and similar positive trend of the wind/current speed. This proves that the Black Sea Rim Current could be considered a Sverdrup balanced flow and thus strongly related to the regional air circulation.
Sr isotope fractionation in a karst river: case study of Krka, Croatia
Authors: Lojen Sonja , Jamil Qasim , Zuliani Tea , Rovan Leja , Kanduč Tjaša , Vreča Polona , Štrok Marko , Bura Nakić Elvira , Cukrov Neven
Published: March 2021

Precipitation of calcite from water fractionates strontium (Sr) isotopes because of preferential incorporation of light (86Sr) isotopes into the solid phase, making continental carbonates one of the most 88Sr depleted reservoirs. It was suggested that carbonate precipitation is the most likely process controlling δ88/86Sr composition of karst water. Therefore, the 88Sr enrichment of river water could be used for the estimation of Sr and carbonate precipitation at catchment scale.

In the present study, we report on trace element partitioning and Sr isotope fractionation between tufa and water in the groundwater fed karst river Krka (Croatia). Water and tufa along with samples of bedrock and soil as the main contributors of dissolved and particulate Sr at seven main waterfalls and cascades along a 33 km section of the river were analysed for trace element and Sr isotope composition (δ88/86Sr).

The highest δ88/86Sr values were measured in soils and in siliciclastic rocks, while in limestone, the δ88/86Sr values were similar to those of old tufa precipitated in the period between 96 and 141 ky BP. Recent tufa, however, was considerably depleted in 88Sr. The isotope fractionation between water and recent tufa varied a lot and was inversely correlated with Mg and Sr partitioning coefficients, while correlations with precipitation rates and temperature were rather weak. The δ88/86Sr of recent tufa was strongly correlated with the stable isotope composition of organic carbon, which indicates that apart from hydrochemical, hydraulic parameters and temperature, plants and microbial communities that knowingly stimulate the tufa formation also affect the isotope fractionation of Sr.
Temporal stability of Salmonella enterica and Listeria monocytogenes levels across irrigation water types
Authors: Kim Seongyun , Pachepsky Yakov , White Chanelle , Gerdes Megan , Goldstein Rachel , Sapkota Amy , Micallef Shirley , Kniel Kali , Parveen Salina , Hashem Fawzy , Sharma Manan
Published: March 2021

Enteric bacterial pathogens in irrigation water can be a public health and food safety issue when contaminating produce. Microbial water quality varies depending on the location and type of water source. We hypothesis temporally stable spatial patterns in levels of Salmonella enterica and Listeria monocytogenes exist in individual water sources in the same region. To test this hypothesis, samples were collected from six water sources in the mid-Atlantic U.S over two years, twice every month during growing season (May to September) and once a month during non-growing seasons (October to April). The sampling sites represented four rivers and two ponds. Several environmental covariates (conductivity, ORP, pH, salinity, dissolved oxygen, turbidity, cumulative rainfall for one and seven day prior to sampling dates) were measured in conjunction with quantitative pathogen recovery. Temporal stability was quantified by computing the mean relative difference (MRD) of pathogen levels from the average across the monitoring location at the same sampling dates. The Spearman rank correlation coefficient between each pathogen level on successive sampling dates was calculated. Levels of both pathogens at each location demonstrated temporally stable spatial patterns. The overall MRD values of pathogens in river water were higher than MRD values of pathogens in pond water. The MRD values for S. enterica were similar to the MRD values of cumulative 7-day rainfall. An inverse relationship between the MRD values of L. monocytogenes and water temperature were found.  The Spearman rank correlation for both pathogens indicated moderate to strong relationship between consecutive sampling events in approximately 80% of cases. These can be used to improve regional monitoring of microbial quality of irrigation water.
A climatological approach for operational radar rainfall bias correction 
Authors: Imhoff Ruben , Brauer Claudia , van Heeringen Klaas-Jan , Leijnse Hidde , Overeem Aart , Weerts Albrecht , Uijlenhoet Remko
Published: March 2021

Most radar quantitative precipitation estimation (QPE) products systematically deviate from the true rainfall amount. This makes radar QPE adjustments unavoidable for operational use in hydro-meteorological (forecasting) models. Most correction methods require a timely available, high-density network of quality-controlled rain gauge observations. Here, we introduce a set of fixed bias reduction factors for the Netherlands, which vary per grid cell and day of the year. With this approach, we aim to provide an alternative to current practice, because the climatological factors are both operationally available and independent of the real-time rain gauge availability.

The correction factors were based on 10 years of 5-min radar QPE and reference rainfall data. We tested this method on the resulting rainfall estimates and subsequent discharge simulations for twelve Dutch catchment and polder areas. In addition, we compared the results to the operational mean field bias (MFB) corrected rainfall estimates and a reference dataset. This reference consisted of the radar QPE, spatially adjusted with a network of 356 validated rain gauge observations. Of this network, only 31 are automatic gauges. Hence, only these were available in real-time for the operational MFB corrections.

The climatological correction factors show clear spatial and temporal patterns. The factors are higher far from the radars and higher during winter than in summer. The latter pattern is likely a result of sampling above the melting layer during the months December–March, which causes higher underestimations. Estimated yearly rainfall sums are generally comparable to the reference and outperform the MFB corrected rainfall estimates for catchments far from the radars (south and east of the country). This difference is absent for catchments closer to the radars, where both products tend to marginally overestimate the rainfall sums. The differences amplify when both QPE products are used to force the hydrologic models. Discharge simulations based on the proposed QPE product outperform the MFB corrected rainfall estimates for all but one basin. Moreover, the climatological factor derivation shows little sensitivity to the moving window length and to leaving individual years out of the training dataset. The presented method provides a robust and straightforward operational alternative. It can serve as a benchmark for further QPE algorithm development in the Netherlands and elsewhere.
Cosmic rays at ground level; a brief introduction
Authors: Strauss Du Toit
Published: March 2021

Galactic cosmic rays, and sporadic high energy solar energetic particles, are energetic enough to pierce the Earth’s protective magnetosphere and interact with the atmosphere. Here, a secondary particle cascade leads to enhanced radiation levels which is of importance, for instance, to aviation dosimetry and related studies. At ground level, these secondary particles can be observed (indirectly) by means of neutron monitors, and this has been done for more than 70 years, providing a valuable long-term cosmic ray record. In this talk, we introduce the different primary particle populations, discuss their acceleration and modulation, and connect this with long-term neutron monitor measurements.
Biostratigraphically constrained Neogene palaeoenvironments of the Red Sea rift
Authors: Hughes Geraint , Varol Osman
Published: March 2021

Marine sediments deposited in response to the Neogene opening of the Red Sea during divergence of the African-Arabian plate margin provide micropalaeontological chronological evidence to calibrate synchronous palaeoenvironmental events from the Gulf of Suez to the Gulf of Aden. This facility provides insights to the timing and relative rates of tectonic subsidence associated with the rifting episodes of the region. Biostratigraphic index forms include planktonic and benthonic foraminifera and calcareous nannofossils. These, combined with various associated microfossils and macrofossil fragments, permit interpretation of a range of depositional environments that span intertidal to bathyal regimes. Onset and recovery from various hypersaline events are similarly interpreted by integrating microfossils and lithology. Following an episode of emergence and sporadic volcanicity, subsidence and the first Neogene marine transgression created brackish to shallow marine lagoons during the Early Miocene (Foraminiferal Letter Stage Upper Te). Rapid subsidence and accumulation of deep marine mudstones, of local hydrocarbon source-rock quality, with thinly interbedded siliciclastic and calciclastic debris flows commenced in the Early Miocene (Planktonic foraminiferal zones N5-N8; Nannofossil zones NN3-NN5). The debris flows increased in abundance and provide good hydrocarbon reservoirs. The Gulf of Suez and Red Sea experienced episodic isolation from the Indian Ocean during the latest Early Miocene and earliest Middle Miocene (Planktonic foraminiferal zones N8-N9; Nannofossil zone NN5 Foraminiferal Letter Stage Middle-Upper Tf1), resulting in hypersaline events with precipitation of submarine gypsum and halite. The isolation is attributed to constriction of the southern Red Sea, in the vicinity of the Bab El Mandab Straits, by eustatic sea level fall as well as probable tectonic activity; the synchronous Gulf of Aden succession does not display evidence for such hypersaline events. A prolonged hypersaline phase extended over most of the Middle Miocene, for which absence of biostratigraphic data precludes age control. During the latest Middle Miocene to Late Miocene, rejuvenation of the hinterland cause rapid deposition of terrestrial and fluviatile coarse and fine siliciclastics, with similar biostratigraphic paucity except for rare diatoms and palynomorphs. Renewed subsidence, associated with opening of the Aqaba Fault, combined with eustatic sea level rise caused marine deposition to recommence in the Pliocene.
Investigating erosion and entrainment of snow avalanches using the material point method
Authors: Li Xingyue , Sovilla Betty , Ligneau Camille , Jiang Chenfanfu , Gaume Johan
Published: March 2021

Erosion and entrainment are critical processes in gravity-driven mass flows like snow avalanches, as they can significantly change the flow mass and momentum and thus affect the flow dynamics. In snow avalanches, snow cover can be considerably eroded but only partially entrained into the flow. Differentiating erosion and entrainment gives more accurate prediction of the increased flow mass and offers information on eroded snow cover remaining on the slope, but is challenging in practice. This study investigates snow avalanche erosion and entrainment with the material point method, focusing on exploring various erosion mechanisms, differences in erosion and entrainment, and their possible influences on runout distance. By using different mechanical properties for the flowing snow, distinct erosion patterns are observed and the corresponding temporal evolutions of entrainment, erosion, and deposition in the erodible bed are examined. Erosion and entrainment require an appropriate combination of snow friction and cohesion of the bed. If cohesion and/or friction are too low, the bed will naturally be unstable. On the other hand, highly cohesive and frictional bed will prevent erosion. For intermediate values, erosion and entrainment can be notable, and the amount of eroded snow shows a clear negative correlation with snow friction and cohesion while the entrained snow does not demonstrate a strong tendency. Furthermore, the release and erodible bed lengths are varied to study their effect on erosion and entrainment propensity. It is found that the increase in the lengths of the release zone and erodible bed leads to more erosion and entrainment as expected, but not necessarily to a longer runout distance. In our simulations, the release and erodible bed lengths are positively and negatively correlated with the runout distance, respectively. This implies that the runout distance can have opposite trends with erosion and entrainment, which might be closely related to the energy change of the simulated avalanches from the outlet of the erodible bed to the final deposit. Our results shed more light into the erosion and entrainment mechanisms and may contribute to improve related parametrizations in large-scale avalanche dynamics models.
Adaptive Multi-Physics Simulations of Collisionless Plasmas
Authors: Lautenbach Simon , Grauer Rainer
Published: March 2021

Collisionless plasmas, mostly present in astrophysical and space environments, often require a kinetic treatment given by the Vlasov equation. Unfortunately, the six-dimensional Vlasov equation is inherently expensive to compute and usually can only be solved on very small parts of the considered spatial domain. However, in some cases, e.g. magnetic reconnection, it is sufficient to solve the Vlasov equation in a localized domain and solve the remaining domain with appropriate fluid models. We present an adaptive hierarchical treatment of collisionless plasmas ranging from fully kinetic, to a 10-moment fluid model incorporating a simplified treatment of Landau damping, to a 5-moment fluid description. To account for separation of electron and ion physics, hybrid stages of mixed electron and ion models are also allowed. As a proof of concept, the full physics-adaptive hierarchy is applied to the Geospace Environmental Modeling (GEM) challenge of magnetic reconnection.
Geochemical evidence of tropical cyclone controls on shallow-marine sedimentation (Pliocene, Taiwan) 
Authors: Dashtgard Shahin , Löwemark Ludvig , Wang Pei-Ling , Setiaji Romy , Pan Yu-Yen , Vaucher Romain
Published: March 2021

 Shallow-marine sediment typically contains a mix of marine and terrestrial organic mate­rial (OM). Most terrestrial OM enters the ocean through rivers, and marine OM is incorpo­rated into the sediment through both suspension settling of marine plankton and sediment reworking by tides and waves under fairweather conditions. River-derived terrestrial OM is delivered year-round, although sediment and OM delivery from rivers is typically highest during extreme weather events that impact river catchments. In Taiwan, tropical cyclones (TCs) are the dominant extreme weather event, and 75% of all sediment delivered to the surrounding ocean occurs during TCs.

Lower Pliocene shallow-marine sedimentary strata in the Western Foreland Basin of Taiwan comprises mainly completely bioturbated intervals that transi­tion upward into strata dominated by tidally generated sedimentary structures, indicating extensive sediment reworking under fairweather conditions. Physical evidence of storm deposition is limited. However, lower Pliocene strata contain OM that is effectively 100% terrestrial OM in sediment that accumulated in estimated water depths <35 m. The overwhelming contribution of terrestrially sourced OM is attributed to the dominance of TCs on sedimentation, whereby ∼600,000 TCs are estimated to have impacted Taiwan during accumulation of a ~200 m long succession. In contrast, the virtual absence of marine OM indicates that organic contributions from suspension settling of marine OM is negligible regardless of the preserved evidence of extensive reworking via fairweather processes (i.e., waves and tides). These data suggest that (1) even in the absence of physical expressions of storm deposition, TCs still completely dominate sedimentation in shallow-marine environments, and (2) the organic geochemical signal of preserved shallow-marine strata is not reflective of day-to-day depositional conditions in the environment.
Crop transitions can drive economic and ecological shifts in an established farming landscape: a case study from California
Authors: Wartenberg Ariani , Moanga Diana , Potts Matthew , Butsic Van
Published: March 2021

Meeting growing challenges to maintain food production and rural livelihoods while minimizing land degradation will require significant changes in the way existing farming landscapes are managed. A systemic understanding of the agroecological impacts of land-use change in established farming landscapes, and the identification of significant trade-offs or synergies, are crucial to inform farm management and land-use governance solutions. Here, we focus on land-use change impacts in an already established farming landscape. We investigate spatial and temporal dynamics of agricultural land-use change from 2002 to 2018, in Kern County, California. Our study region is one of the major agricultural production hotspots in the United States, and has undergone a recent agricultural land-use transition from annual to perennial cropping systems. In this study we analyzed parcel-level data documenting changes in the land-use footprint for individual crops, ranging from annual crops like wheat and cotton to perennial tree crops like almonds and pistachios. We assess how land-use change impacted ecosystem pressures and service indicators selected for their relevance in an agricultural context, including water-use, soil erosion, profit and carbon sequestration. Our results indicate no salient trade-offs or synergies among individual crops, and illustrate the possibility of limited economic-ecological trade-offs associated with a shift from annual to perennial crops in a well-established agricultural landscape. We further discuss the relevance of our findings in the context of land-ownership consolidation and changing export dynamics in the study area.
Diffuse electron precipitation in magnetosphere-ionosphere-thermosphere coupling
Authors: Lin Dong , Wang Wenbin , Merkin Viacheslav , Pham Kevin , Bao Shanshan , Sorathia Kareem , Toffoletto Frank , Shi Xueling , Meers Oppenheim , Khazanov George , Michael Adam , Lyon John , Garretson Jeffrey , Anderson Brian
Published: March 2021

Auroral precipitation plays an important role in magnetosphere-ionosphere-thermosphere (MIT) coupling by enhancing ionospheric ionization and conductivity at high latitudes. Diffuse electron precipitation refers to scattered electrons from the plasma sheet that are lost in the ionosphere. Diffuse precipitation makes the largest contribution to the total precipitation energy flux and is expected to have substantial impacts on the ionospheric conductance and affect the electrodynamic coupling between the magnetosphere and ionosphere-thermosphere. Kinetic theory and observational analysis also demonstrate that diffuse precipitation is subject to multiple reflection effects, i.e. secondary electrons produced by the primary precipitation are reflected between the north and south hemispheres multiple times before they are fully lost in the atmosphere. In this study, we make use of the newly developed Multiscale Atmosphere-Geospace Environment (MAGE) model developed at the NASA DRIVE Science Center for Geospace Storms (CGS) to explore the role of diffuse electron precipitation in MIT coupling. Diffuse precipitation in MAGE is derived from the electron distribution in the Rice Convection Model (RCM), a ring current model that solves for energy dependent drifts of electrons and ions. Diffuse precipitation, together with mono-energetic electron precipitation based on parameterization of the magnetohydrodynamic (MHD) parameters from the Grid Agnostic MHD with Extended Research Applications (GAMERA) magnetosphere model, are input to the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) to calculate the ionospheric ionization rate and conductivity and height-integrated conductance. With controlled numerical experiments, we investigate 1. how the diffuse precipitation affects the location and structure of a mesoscale ionospheric convection process, i.e., subauroral polarization streams (SAPS); 2. How multiple reflection effects impact the ionosphere-thermosphere and their coupling with the magnetosphere. Our study demonstrates that diffuse electron precipitation plays a critical role in determining the location and structure of SAPS. The multiple reflection effects make diffuse precipitation number flux and energy flux a few times higher than the unmodified precipitation, resulting in a greatly enhanced auroral ionospheric conductance, lower cross polar cap potential,  higher total field-aligned currents, and changes in global thermospheric winds and temperature. Therefore, diffuse electron precipitation has both local and global impacts on MIT coupling.
Latent seismicity driven by aseismic creep and enhanced pore-fluid pressure in NE British Columbia
Authors: Salvage Rebecca O. , Eaton David W.
Published: March 2021

The global pandemic of COVID-19 furnished an opportunity to study seismicity in the Kiskatinaw area of British Columbia, noted for hydraulic-fracturing induced seismicity, during a period of anthropogenic quiescence. A total of 389 events were detected from April to August 2020, encompassing a period with no hydraulic-fracturing operations during a government-imposed lockdown. During this time period, observed seismicity had a maximum magnitude of ML 1.2 and lacked temporal clustering that is often characteristic of hydraulic-fracturing induced sequences. Instead, seismicity was persistent over the lockdown period, similar to swarm-like seismicity with no apparent foreshock-aftershock type sequences. Hypocenters occurred within a corridor orientated NW-SE, just as seismicity had done in previous years in the area, with focal depths near the target Montney formation or shallower (<2.5 km). Based on the Gutenberg-Richter relationship, we estimate that a maximum of 21% of the detected events during lockdown may be attributable to natural seismicity, with a further 8% possibly due to dynamic triggering of seismicity from teleseismic events. The remaining ~70% cannot be attributed to direct pore pressure increases induced by fluid injection, and therefore is inferred to represent latent seismicity i.e. seismicity that occurs after an unusually long delay following primary activation processes, with no obvious triggering mechanism. We can exclude pore-pressure diffusion from the most recent fluid injection, as is there is no clear pattern of temporal or spatial seismicity migration. If elevated pore pressure from previous injections became trapped in the subsurface, this could explain the localization of seismicity within an operational corridor, but it does not explain the latency of seismicity on a timescale of months. However, aseismic creep on weak surfaces such as faults, in response to tectonic stresses, in addition to trapped elevation pore-pressure could play a role in stress re-loading to sustain the observed pattern of seismicity.
Simulation of High-Frequency Rotational Motion in a Two-Dimensional Laterally Heterogeneous Half-Space
Authors: Lokmer Ivan , Singla Varun Kumar , McCloskey John
Published: March 2021

The seismic waves responsible for vibrating civil engineering structures undergo interference, focusing, scattering, and diffraction by the inhomogeneous medium encountered along the source-to-site propagation path. The subsurface heterogeneities at a site can particularly alter the local seismic wave field and amplify the ground rotations, thereby increasing the seismic hazard. The conventional techniques to carry out full wave field simulations (such as finite-difference or spectral finite element methods) at high frequencies (e.g., 15 Hz) are computationally expensive, particularly when the size of the heterogeneities is small (e.g., <100 m). This study proposes an alternative technique that is based on the first-order perturbation theory for wave propagation. In this technique, the total wave field due to a particular source is obtained as a superposition of the ‘mean’ and ‘scattered’ wave fields. Whereas the ‘mean’ wave field is the response of the background (i.e., heterogeneity-free) medium due to the given source, the ‘scattered’ wave is the response of the background medium excited by fictitious body forces. For a two-dimensional laterally heterogeneous elastic medium, these body forces can be conveniently evaluated as a function of the material properties of the heterogeneities and the mean wave field. Since the problem of simulating high-frequency rotations in a laterally heterogeneous medium reduces to that of calculating rotations in the background medium subjected to the (1) given seismic source and (2) body forces that mathematically replace the small-scale heterogeneities, the original problem can be easily solved in a computationally accurate and efficient manner by using the classical (analytical) wavenumber-integration method. The workflow is illustrated for the case of a laterally heterogenous layer embedded in a homogeneous half-space excited by plane body-waves.
Impact of the spaciotemporal variability of the snowpack conditions on internal liquid water fluxes
Authors: Valence Eole , Baraër Michel
Published: March 2021

In cold regions, the seasonal snowpack plays an important hydrological role. By storing and releasing solid precipitation, the snowpack gives shape to the yearly hygrogram. In addition, by modulating liquid water pathway and residence time, snowpack internal conditions have a strong implication on the partitioning of meltwater among streamflow, groundwater recharge and soil moisture storage. During rain on snow (ROS) events, snowpack conditions influence timing and amount of liquid water inflow to the surface drainage system, with winter floods and ice jams as potential consequences.

Recent observations and projections show an increase in ROS frequency in many cold regions of the world. This trend raises concern about a possible increase in winter floods and ice jams events with climate change. In order to better anticipate the hydrological consequences of the increasing ROS phenomenon, a good understanding of the processes and conditions influencing liquid water release from the snowpack is required. 

The present study articulates around a multimethod approach to characterize liquid water storage and movement in a snowpack in a non-mountainous environment. By combining drone-based high frequency GPR, NIR photogrammetry, time domain reflectometry, stable isotopes of water and other manual measurements throughout a winter season, we aim monitoring the spatiotemporal evolution of the snowpack liquid water content as well as the water fluxes at the snowpack margins.

Preliminary results show that, combining the selected methods allows tracking liquid water storage and movements in the snowpack throughout an entire season.
The Temporal Propagation Processes of Multiple Types of Drought in Central Asia
Authors: Tian Lu , Ho Sarah , Disse Markus , Tuo Ye
Published: March 2021

Drought propagation processes interlink closely with the water cycle, which has so far been mostly investigated without tracking temporal propagation across multiple types of drought. Central Asia, including Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan, and Xinjiang (China) areas, is one of the most drought-prone areas in the world and extremely vulnerable to water scarcity. Understanding the multiple pathways of drought propagation over time in Central Asia is necessary for food security, human health, and poverty alleviation. In this study, we quantify the propagation time and track the details of temporal propagation processes of drought across the atmosphere, the geosphere, and the hydrosphere. The standardized indices are calculated using variables directly related to each type of drought: precipitation (SPI), evapotranspiration (SEDI), soil moisture (SSI), and runoff (SRI)1, 2. The drought propagation processes are divided into the development stage and recovery stage. The propagation time at different stages between multiple types of drought is calculated by the Pearson correlation coefficient (p<0.05)3 and run theory method4. Besides, the potential influencing factors on the temporal propagation are explored from the meteorological, land cover, and water management aspects. As the main results, the propagation time in winter is longer than in summer. And topography has a significant impact on drought propagation time. These key findings could further benefit the early warning of drought and facilitate the drought mitigation-adaptation in both Central Asia and other continents.

Keywords: Temporal propagation, Central Asia, Influencing factors, Land cover

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