bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying the dependence of electron fluxes in the Earth’s radiation belts with radial diffusion drivers through the use of information theory.
Authors: Osmane Adnane , Savola Mikko , Kilpua Emilia , Koskinen Hannu , Borovsky Joe , Kalliokoski Milla
Published: March 2021

We describe the use of information-theoretic methodologies to characterise statistical dependencies of energetic electron fluxes (130 keV and >1 MeV) with a wide range of solar wind and magnetospheric drivers. We focus specifically on drivers associated with radial diffusion processes and revisit the events studied by Rostoker et al. Geophys. Res. Lett. (1998) in terms of mutual information. The main benefit of mutual information, in comparison to the Pearson correlation and other linear measures, lies in the capacity to distinguish nonlinear statistical dependencies from linear ones.  We find that observed enhancement in relativistic electron fluxes correlate weakly, both linearly and nonlinearly, with the ULF power spectrum, whereas less energetic electron fluxes show stronger statistical dependency with both ground and in situ ULF wave power. Our results are indicative of the need to incorporate data analysis tools that can distinguish between interdependencies of various solar wind drivers.
Empirical relationship between nightside reconnection rate and solar wind / geomagnetic measurements
Authors: Kvernhaug Andreas Lysaker , Laundal Karl M. , Reistad Jone P.
Published: March 2021

According to the expanding-contracting polar cap paradigm, dayside and nightside reconnection control magnetosphere-ionosphere dynamics at high latitudes by increasing or decreasing the open flux respectively. The dayside reconnection rate can be estimated using parameters measured in the solar wind, but there is no reliable and available proxy for the nightside reconnection rate. We want to remedy this by using AMPERE to estimate a time series of open flux content. The AMPERE data set originates from the global Iridium satellite system, enabling continuous measurements of the field-aligned Birkeland currents, from which the open magnetic flux of the polar caps can be derived. These estimates will be used to derive empirical relationships with available measurements on the ground and in the solar wind. This work can also help improve estimates of dayside reconnection rates.
Crust-Mantle Kinematics in and around the Hellenic Arc Elucidated by Local Shear Wave Splitting and Receiver Function Analyses
Authors: Keleş Derya , Eken Tuna , Confal Judith M. , Taymaz Tuncay
Published: March 2021

The fundamental knowledge on seismic anisotropy inferred from various data sets can enhance our understanding of its vertical resolution that is critical for a better interpretation of past and current dynamics and resultant crustal and mantle kinematics in the Hellenic Trench and its hinterland. To investigate the nature of deformation zones, we perform both local S-wave splitting (SWS) measurements and receiver functions (RFs) analysis. Our preliminary findings from the harmonic decomposition technique performed on radial and tangential RFs suggest relatively more substantial anisotropic signals in the lower crust and uppermost mantle with respect to upper and middle crustal structure in the region. Apparent anisotropic orientations obtained from RFs harmonic decomposition process show several consistencies with those discovered from local SWS measurements at selected stations. The actual anisotropic orientation for the structures, however, requires further modelling of the receiver functions obtained.
Climate change effects on forest floor interception in woody Cerrado ecosystem
Authors: Rosalem Livia , Gerrits-Coenders Miriam , A. A. Anache Jamil , S. Sone Julian , Schwamback Dimaghi , Campos Alessandra , Wendland Edson
Published: March 2021

The interception process is an important redistributor of water fluxes, which can considerably affect terrestrial evaporation. Not only the canopy intercepts water, but also from the forest floor significant amounts of water vapor return to the atmosphere. Remaining forests are important areas to evaluate the possible effects of climate change on the water partitioning process. Despite the hydrologic and ecosystem services offered by Cerrado forests, the interception process, as well as climate change threats on the evaporative flux of such forests, are still unknown. This study attempts to anticipate the possible impacts on the forest floor interception process in Cerrado stricto sensu considering future scenarios of climate change. To accomplish this, we used data of field monitoring from June 2017 to February 2020 in an undisturbed Cerrado s.s. forest in São Paulo State, Brazil. We calibrated and validated an improved version of the Rutter interception model (Rutter et al., 1971), which includes interception from the forest floor. Projected climate change scenarios were obtained from the National Institute for Space Research (INPE, Brazil) from 2006 to 2099 with 5km spatial resolution generated by Eta-HadGEM2-ES regional climate model under representative concentration pathway (RCP) 4.5. The results indicate increased rainfall and decreased potential evaporation in the decade 2041-2060. By the Rutter model, the total interception increased for this period (2041-2060) associated with decreased forest floor evaporation. During the first (2006-2020) and the last (2081-2099) decades, the predictions suggest an increase of 2.4% on the average annual percentage of forest floor evaporation, also an increase of minimum annual interception percentages (from 17.1% to 18.7%). Thus, our results demonstrate the relevance of forest floor to the interception process and suggest that it can be even more relevant in the future due to the climate changes.
Mobilization of particulate organic matter and minerals in Zackenberg valley, Greenland
Authors: Bröder Lisa , Hirst Catherine , Opfergelt Sophie , Lattaud Julie , Haghipour Negar , Eglinton Timothy , Vonk Jorien , Fouché Julien
Published: March 2021

Ongoing warming of the Northern high latitudes has intensified abrupt thaw processes throughout the permafrost zone. The resulting terrain disturbances are prone to release large amounts of particulate organic matter (OM) from deeper permafrost soils with thus far poorly constrained decay kinetics. Organo-mineral interactions may inhibit OM decomposition, thereby mediating the release of carbon to the atmosphere. Yet how these interactions evolve upon release and during transport along the fluvial continuum is still insufficiently understood. Here we investigate the mobilization of particulate OM from disturbed permafrost soils to the aquatic environment in the Zackenberg watershed in Northeastern Greenland. We collected soil samples in a thermo-erosion gully and a retrogressive thaw slump, as well as suspended solids and stream sediments along the glacio-nival Zackenberg River, including its tributaries, and a small headwater stream (Grænselv) affected by abrupt permafrost thaw. To evaluate the organic and mineral material transported, we compare mineral element and organic carbon (OC) concentrations, bulk carbon isotopes (13C and 14C), together with source-specific molecular biomarkers (plant-wax lipids and branched glycerol dialkyl glycerol tetraethers, brGDGTs) for the suspended load with their soil and sediment counterparts.

Preliminary results show large contrasts in OC concentrations as well as Δ14C between the glacio-nival river and the headwater stream, as well as between the different thaw features. The retrogressive thaw slump mobilizes relatively OC-poor material with very low Δ14C signatures suggesting a petrogenic contribution, while soil samples from the thermo-erosion gully had higher OC concentrations and Δ14C values. For Grænselv, Δ14C values of the particulate OC were lower close to the eroding stream bank, whereas the Zackenberg main stem displayed fairly constant Δ14C values, with some of the Zackenberg tributaries delivering relatively organic-rich particles low in Δ14C.

Molecular biomarker analyses will provide additional information on specific OM sources, while X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) analyses on the soils, sediments and suspended mineral load will give more detailed insights into the composition of the mineral matrices. By combining these analytical methods, we aim to improve our understanding of the interactions between minerals and OM and thereby help to constrain the fate of mobilized OM upon permafrost thaw.
Deep structure of the Grenada Basin from wide-angle seismic, bathymetric and gravity data
Authors: Padron Crelia , Klingelhoefer Frauke , Marcaillou Boris , Lebrun Jean-Frédéric , Lallemand Serge , Garrocq Clément , Laigle Mireille , Roest Walter , Beslier Marie-Odile , Schenini Laure , Graindorge David , Gay Aurelien , Audemard Franck , Münch Philippe
Published: March 2021

Studying back-arc basins, where sedimentation is less deformed than in the forearc, provides complementary information about formation and tectonic evolution of subduction zones. At the Lesser Antilles subduction zone, the North and South American plates are subducting underneath the Caribbean plate at a velocity of 2 cm per year. The crescent-shaped Grenada back-arc basin is located between the Aves Ridge, which hosted the remnant Early Paleogene “Great Caribbean Arc”, and the Eocene to present Lesser Antilles Arc. In this study, based on wide-angle data, we provide constraints about lateral variations in basement thickness and velocity structure in the Lesser Antilles back-arc, and to a lesser extend in the arc and forearc domain, constraining for the first time the extent of oceanic crust in the Grenada Basin and shed light on the structure and compositions of the basin’s margins.

Three combined wide-angle and reflection seismic profiles, together with gravity and bathymetric data, were acquired in the Lesser Antilles back-arc basin. Direct modeling techniques were applied to the wide-angle seismic data in order to include shallow structures imaged by the coincident reflection seismic data. The resulting velocity models were additionally constrained by gravity modeling and synthetic seismogram calculation. The final models from direct modeling image variations in thickness and velocity structure of the sedimentary and crustal layers to a depth of up to 35 km. The sedimentary cover has a variable thickness from less than a kilometer on top of the ridges to nearly 10 km in the basin. North of Guadeloupe Island, the crust is ~20 km thick from back-arc to forearc, without significant change between the Aves Ridge, the Eocene and present Lesser Antilles volcanic arc. While based on the seismic velocities, the southern part of the basin is underlain by a 6.5-7 km thick crust of of mainly magmatic origin over a width of ~80 km, the northern part is underlain by thinned continental crust. At the western flank of the Lesser Antilles Arc, the crust is 17.5-km thick, about 5 km thinner than north of Martinique island. The velocity structure is typical of volcanic arcs or oceanic plateaus. Between Aves Ridge and the Grenada basin the crust thins in a 80-100 km wide transition zone. No anomalous high velocities indicating the presence of exhumed upper mantle material were detected at the transition zone. This narrow E-W arc-ocean transition zone suggests that opening might have proceeded in a direction highly oblique to the main convergence.
Regional climate and ice shelf melt captured in an Antarctic Peninsula ice core
Authors: Emanuelsson Daniel , Thomas Elizabeth R.
Published: March 2021

In this study, we present the stable water isotope record (δ18O) from an ice core drilled in Palmer Land, the southern Antarctic Peninsula (AP). This unique record, records changes in eastern AP ice shelf melt on the Larsen ice shelves. We show that warm years recorded in the ice core δ18O record are associated northeasterly winds that pass over the peninsula and subsequently result in foehn-induced surface warming and melt events on the Larsen Ice shelves on the eastern coast. The recent strengthening of westerly winds that circumference Antarctica (positive trend in SAM) and the deepening of the Amundsen Sea Low drives these strong northeasterly winds. We reconstruct the number of yearly melt days on the Larsen B ice shelf using melt days estimates from the published QSCAT/ASCAT dataset. Our record shows that melting on the Larsen B ice shelf since the late 1990s was higher than at any time during the past 388 years. However, periods with a high number of melt days have occurred in the past during the latter parts of the 17th and 19th centuries, as well as more recently during the 1940s, which may indicate past foehn-induced ice shelf melting.
Coordinated observations of relativistic electron enhancements following an HSS period 
Authors: Nasi Afroditi , Daglis Ioannis A. , Katsavrias Christos , Sandberg Ingmar , Li Wen , Miyoshi Yoshizumi , Imajo Shun , Mitani Takefumi , Hori Tomo , Kasahara Satoshi , Yokota Shoichiro , Keika Kunihiro , Shinohara Iku , Matsuoka Ayako , Kasahara Yoshiya
Published: March 2021

During the second half of 2019, a sequence of solar wind high-speed streams (VSW ≥ 600 km/s)  impacted the magnetosphere, resulting in a series of recurrent, relatively weak, geomagnetic storms (Dstmin ≥ - 80 nT). During one of these storms, a longer-lasting solar wind pressure pulse and intense substorm activity were also recorded (AL ≤ - 1600 nT on August 31 and September 1).

We use particle measurements from the Van Allen Probes, Arase and Galileo 207, 215 satellites, to investigate this event; all spacecraft observed a significant enhancement of relativistic electron fluxes. We also use ULF and chorus wave measurements, as well as interplanetary parameters, for a detailed investigation of this event and of the acceleration mechanisms involved.

This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870437 for the SafeSpace project.
Downhole distributed acoustic seismic profiling at Skytrain Ice Rise, West Antarctica
Authors: Brisbourne Alex , Kendall Mike , Kufner Sofia , Hudson Thomas , Smith Andrew
Published: March 2021

Antarctic ice sheet history is imprinted in the structure and fabric of the ice column. At ice rises, the signature of ice flow history is preserved due to the low strain rates inherent at these independent ice flow centres. We present results from a distributed acoustic sensing (DAS) experiment at Skytrain Ice Rise in the Weddell Sea Sector of West Antarctica, aimed at delineating the englacial fabric to improve our understanding of ice sheet history in the region. This pilot experiment demonstrates the feasibility of an innovative technique to delineate ice rise structure. Both direct and reflected P- and S-wave energy, as well as surface wave energy, are observed using a range of source offsets, i.e., a walkaway vertical seismic profile (VSP), recorded using fibre optic cable. Significant noise, which results from the cable hanging untethered in the borehole, is modelled and suppressed at the processing stage. At greater depth, where the cable is suspended in drilling fluid, seismic interval velocities and attenuation are measured. Vertical P-wave velocities are high (VINT = 4029 ± 244 m s-1) and consistent with a strong vertical cluster fabric. Seismic attenuation is high (QINT = 75 ± 12) and contrary to observations in ice sheets over this temperature range. The signal level is too low, and the noise level too high, to undertake analysis of englacial fabric variability. However, modelling of P- and S-wave traveltimes and amplitudes with a range of fabric geometries, combined with these measurements, demonstrates the capacity of the DAS method to discriminate englacial fabric distribution. From this pilot study we make a number of recommendations for future experiments aimed at quantifying englacial fabric to improve our understanding of recent ice sheet history.

 
Forty years later: High resolution continuous flow analysis of the Dye3 ice core
Authors: Kjær Helle Astrid , Harlan Margaret , Vallelonga Paul , Svensson Anders , Blunier Thomas , Sowers Todd , Menking James Andrew , de Campo Aylin , Venkatesh Janani , Liisberg Jesper , Soestmeyer David , Morris Valerie , Vaughn Bruce , Vinther Bo
Published: March 2021

The Dye-3 ice core was drilled to bedrock at the Southern part of the central Greenland ice sheet (65°11'N, 43°50'W) in 1979-1981. The southern location is characterized by high accumulation rates compared to more central locations of the ice sheet. Since its drilling, numerous analyses of the core have been performed, and the ice has since been in freezer storage both in the USA and in Denmark.

In October and November 2019, the remaining ice, two mostly complete sections covering the depths of 1753–1820m and 1865–1918m of the Dye-3 core, were melted during a continuous flow analysis (CFA) campaign at the Physics of Ice, Climate, and Earth (PICE) group at the University of Copenhagen. The data represents both Holocene, Younger Dryas and Glacial sections (GS 5 to 12).

 

The measured data consist chemistry and impurities contained in the ice, isotopes, as well as analysis of methane and other atmospheric gases. 

The chemistry measurements include NH4+, Ca2+, and Na+ ions, which besides being influenced by transport, provide information about forest fires, wind-blown dust, and sea ice, respectively, as well as acidity, which aids in the identification of volcanic events contained in the core. The quantity and grain size distribution of insoluble particles was analyzed by means of an Abakus laser particle counter.

 

We compare the new high-resolution CFA record of dye3 with previous analysis and thus evaluate the progress made over 40 years. Further we compare overlapping time periods with other central Greenland ice cores and discuss spatial patterns in relation to the presented climate proxies.
Object-based image segmentation in photogrammetry for cartographic use
Authors: Kovács Béla , Pál Márton , Vörös Fanni
Published: March 2021

The use of aerial photography in topography has started in the first decades of the 20th century. Remote sensed data have become indispensable for cartographers and GIS staff when doing large-scale mapping: especially topographic, orienteering and thematic maps. The use of UAVs (unmanned aerial vehicles) for this purpose has also become widespread for some years. Various drones and sensors (RGB, multispectral and hyperspectral) with many specifications are used to capture and process the physical properties of an examined area. In parallel with the development of the hardware, new software solutions are emerging to visualize and analyse photogrammetric material: a large set of algorithms with different approaches are available for image processing.

Our study focuses on the large-scale topographic mapping of vegetation and land cover. Most traditional analogue and digital maps use these layers either for background or highlighted thematic purposes. We propose to use the theory of OBIA – Object-based Image Analysis to differentiate cover types. This method involves pixels to be grouped into larger polygon units based on either spectral or other variables (e.g. elevation, aspect, curvature in case of DEMs). The neighbours of initial seed points are examined whether they should be added to the region according to the similarity of their attributes. Using OBIA, different land cover types (trees, grass, soils, bare rock surfaces) can be distinguished either with supervised or unsupervised classification – depending on the purposes of the analyst. Our base data were high-resolution RGB and multispectral images (with 5 bands).

Following this methodology, not only elevation data (e.g. shaded relief or vector contour lines) can be derived from UAV imagery but vector land cover data are available for cartographers and GIS analysts. As the number of distinct land cover groups is free to choose, even quite complex thematic layers can be produced. These layers can serve as subjects of further analyses or for cartographic visualization.

 

BK is supported by Application Domain Specific Highly Reliable IT Solutions” project  has been implemented with the support provided from the National Research, Development and Innovation Fund of Hungary, financed under the Thematic Excellence Programme TKP2020-NKA-06 (National Challenges Subprogramme) funding scheme.

MP and FV are supported by EFOP-3.6.3-VEKOP-16-2017-00001: Talent Management in Autonomous Vehicle Control Technologies – The Project is financed by the Hungarian Government and co-financed by the European Social Fund.
Classification of landslide activity based on spaceborne interferometric SAR at the Moselle Valley, Germany
Authors: Kalia Andre C.
Published: March 2021

Landslide activity is an important information for landslide hazard assessment. However, an information gap regarding up to date landslide activity is often present. Advanced differential interferometric SAR processing techniques (A-DInSAR), e.g. Persistent Scatterer Interferometry (PSI) and Small Baseline Subset (SBAS) are able to measure surface displacements with high precision, large spatial coverage and high spatial sampling density. Although the huge amount of measurement points is clearly an improvement, the practical usage is mainly based on visual interpretation. This is time-consuming, subjective and error prone due to e.g. outliers. The motivation of this work is to increase the automatization with respect to the information extraction regarding landslide activity.

This study focuses on the spatial density of multiple PSI/SBAS results and a post-processing workflow to semi-automatically detect active landslides. The proposed detection of active landslides is based on the detection of Active Deformation Areas (ADA) and a subsequent classification of the time series. The detection of ADA consists of a filtering of the A-DInSAR data, a velocity threshold and a spatial clustering algorithm (Barra et al., 2017). The classification of the A-DInSAR time series uses a conditional sequence of statistical tests to classify the time series into a-priori defined deformation patterns (Berti et al., 2013). Field investigations and thematic data verify the plausibility of the results. Subsequently the classification results are combined to provide a layer consisting of ADA including information regarding the deformation pattern through time.
Accuracy Assessment of Recent High-Degree Global Geopotential Models Using Geodetic Control Points and Terrestrial Gravity Data in Turkey
Authors: Çevikalp Muhammed Raşit , Erol Bihter , Mutlu Bilal , Erol Serdar
Published: March 2021

The maintenance of leveling benchmark is both laborious and costly due to distortions caused by geodynamic activities and local deformations. It is necessary to realize geoid-based vertical datum, which also enables calculation from ellipsoidal heights obtained from GNSS to orthometric heights that have physical meaning. It can be considered as an important step for height system unification as it eliminates the problems stem from the conventional vertical datum. The ongoing height modernization efforts in Turkey focus to improve quality and coverage of the gravity data, eliminate errors in existing terrestrial gravity measurements in order to achieve a precise geoid model. Accuracy of the geopotential model is crucial while realizing a geoid model based vertical datum as well as unifying the regional height systems with the International Heights Reference System. In this point of view, we assessed the accuracies of recently released global geopotential models including XGM2019e_2159, GECO, EIGEN-6C4, EGM2008, SGG-UGM-1, EIGEN-6C3stat, and EIGEN-6C2 using high order GNSS/leveling control benchmarks and terrestrial gravity data in Turkey. The reason for choosing these models in the validations is their relatively higher spatial resolutions and improved accuracies compared to other GGMs in published validation results with globally distributed terrestrial data. The GNSS/leveling data used in validations include high accuracy GNSS coordinates in ITRF datum with co-located Helmert orthometric heights in regional vertical datum. 100 benchmarks are homogeneously distributed in the country with the benchmarks along the coastlines. In addition, the terrestrial gravity anomalies with 5 arc-minute resolution were also used in the tests. In order to have comparable results, residual terrain effect has been restored to the GGM derived parameters. Numerical tests revealed significant differences in accuracies of the tested GGMs. The most accurate GGM has the comparable performance with official regional geoid model solutions in Turkey. The drawn results in the study were interpreted and discussed from practical applications and height system unification points in conclusion.
The potential of using Sentinel-1 and ALOS PALSAR-2 data for characterizing West Siberian lake ice backscatter anomalies
Authors: Pointner Georg , Bartsch Annett
Published: March 2021

Millions of lakes and ponds occupy large areas of the Arctic discontinuous and continuous permafrost zones. During most of the year, the surfaces of these lakes remain covered by a thick layer of ice. Synthetic Aperture Radar (SAR) data have shown to be useful for studying the ice on Arctic lakes, especially for monitoring lake ice phenology and the grounding state of the ice (ice frozen to the lakebed versus floating lake ice). Significant backscatter is often observed from the floating ice regime in C-band due to scattering on a rough ice-water interface.

Recent research has revealed features of anomalously low backscatter in Sentinel-1 C-band SAR imagery on some of the West Siberian lakes that likely belong to the floating ice regime. These anomalies are characterized by prominent shapes and sizes and seem to expand throughout late winter and/or spring. It is currently assumed that some of these features are related to strong emissions of natural gas (methane from hydrocarbon reservoirs), making it important to assess their origin in detail and understand the associated mechanisms. However, in-situ data are still missing.

Here, we assess the potential of the combined use of C-band Sentinel-1 (freely available) and L-band ALOS PALSAR-2 data  (available through JAXA PI agreement #3068002) to study the backscatter anomalies. We highlight the differences between observed backscatter from the two sensors with respect to different surface types (ground-fast lake ice, floating lake ice and anomalies) and investigate backscatter differences between frozen and melting conditions. Further, polarimetric classification is performed on L-band PALSAR-2 imagery, which reveals differences in scattering mechanisms between anomalies and floating lake ice.
Natural infrastructure interventions and their effect on soil erosion mitigation in the Andes
Authors: Molina Armando , Vanacker Veerle , Rosas Miluska A. , Ochoa-Tocachi Boris , Bonnesoeur Vivien , Román-Dañobeytia Francisco , Buytaert Wouter
Published: March 2021

The Andes region is prone to soil erosion because of its steep topographic relief, high spatio-temporal variability in precipitation and heterogeneity in lithological strength. Soil erosion by water is affecting natural and anthropogenic environments through its impacts on water quality and availability, loss of soil nutrients, flood risk, sedimentation in rivers and streams, and damage to civil infrastructure. Sustainable land and water management, referred here as natural infrastructure interventions, aims to avoid, reduce and reverse soil erosion and can provide multiple benefits for the environment, population and livelihoods. In this study, we present a systematic review of peer-reviewed and grey literature involving more than 120 local case-studies from the Andes. Three major categories of natural infrastructure interventions were considered: protective vegetation, soil and water conservation measures, and adaptation measures that regulate the flow and transport of water. The analysis was designed to answer the following research questions: (1) Which soil erosion indicators allow us to assess the effectiveness of natural infrastructure interventions across the Andean range? (2) What is the overall impact of implementing natural infrastructure interventions for on-site and off-site erosion mitigation?

The systematic review shows that the effectiveness of protective vegetation on soil erosion mitigation is the most commonly studied characteristic, accounting for more than half of the empirical studies. From the suite of physical, chemical and biological indicators that were commonly used in soil erosion research, our review identified two indicators to be particularly suitable for the analyses of the effectiveness of natural infrastructure interventions: soil organic carbon (SOC) of the topsoil, and soil loss rates at plot scale. The implementation of soil and water conservation measures in areas under traditional agriculture had positive effects on SOC (1.28 to 1.29 times higher SOC than in agricultural land). Soil loss rates were 54% lower when implementing SWC than on cropland. When implementing SWC in rangeland, the data indicated an increase in soil loss rate by 1.54 times. Untreated degraded land is reported to have significantly higher soil loss and specific sediment yield compared to cropland.

The results of this systematic review allows to assess the overall effectiveness of commonly used natural infrastructure interventions, which can guide policy and decision making in the Andes. Similarly, the review identified critical gaps in knowledge that must be attended by more comprehensive research to consider the high spatiotemporal variability of the Andes region.
Fusion of rain radar images and wind forecasts in adeep learning model applied to rain nowcasting
Authors: Charantonis Anastase , Bouget Vincent , Béréziat Dominique , Brajard Julien , Filoche Arthur
Published: March 2021

Short or mid-term rainfall forecasting is a major task with several environmental applications such as agricultural management or flood risks monitoring. Existing data-driven approaches, especially deep learning models, have shown significant skill at this task, using only rainfall radar images as inputs. In order to determine whether using other meteorological parameters such as wind would improve forecasts, we trained a deep learning model on a fusion of rainfall radar images and wind velocity produced by a weather forecast model. The network was compared to a similar architecture trained only on radar data, to a basic persistence model and to an approach based on optical flow. Our network outperforms by 8% the F1-score calculated for the optical flow on moderate and higher rain events for forecasts at a horizon time of 30 minutes. Furthermore, it outperforms by 7% the same architecture trained using only rainfall radar images. Merging rain and wind data has also proven to stabilize the training process and enabled significant improvement especially on the difficult-to-predict high precipitation rainfalls. These results can also be found in Bouget, V., Béréziat, D., Brajard, J., Charantonis, A., & Filoche, A. (2020). Fusion of rain radar images and wind forecasts in a deep learning model applied to rain nowcasting. arXiv preprint arXiv:2012.05015
Coastal risks induced by Mediterranean hurricanes
Authors: Toomey Tim , Amores Angel , Marcos Marta , Orfila Alejandro , Romero Romualdo
Published: March 2021

Medicanes, for Mediterranean hurricanes, are mesoscale cyclones with morphological and physical characteristics similar to tropical cyclones. Although less intense, smaller and rarer than their Atlantic counterparts, Medicanes remain very hazardous events threatening islands and continental coasts within the Mediterranean Sea. The latest strong episode Medicane Ianos (September 2020), resulted in severe damages in Greece and several casualties. This work investigates the oceanic response to these extreme events along the Mediterranean coasts under present-day and future (21 st century) conditions. To this end, a coupled hydrodynamic-wave model is used to simulate both storm surges and wind-waves generation and propagation in the Mediterranean Sea at high resolution (~2 km) along the coastlines. A dataset of thousands of Medicanes synthetically generated from twenty global climate models and two reanalyses is used to derive the atmospheric forcing fields. Regional coastal risks assessment is performed for the present and future climate. We found increased coastal extreme sea levels in line to the reported changes in Medicane activity, with fewer events but of larger intensity projected by late 21 st century.
Data assimilation of SMAP soil moisture into the PCR-GLOBWB hydrological model to improve discharge estimates via A Novel Local Particle Filter
Authors: Wang Zhenwu , Hut Rolf , Tangdamrongsub Natthachet , van de Giesen Nick
Published: March 2021

Assimilating surface soil moisture data or GRACE data, retrieved from satellite, into hydrological models has been proven to improve the accuracy of hydrological model estimations and predictions. For data assimilation applications in hydrology, the ensemble Kalm filter(EnKF) is the most commonly used data assimilation(DA) method. Particle filters are a type of non-Gaussian filter that doesn’t need the normality assumption that the EnKF needs. Adding localization defeats the curse of dimensionality that is a problem in normal particle filters. In the present study, we investigated our adaption of the local particle filter based on the Gamma test theory(LPF-GT) to improve discharge estimates by assimilating SMAP satellite soil moisture into the PCR-GLOBWB hydrological model. The study area is the Rhine river basin, driven by forcing data from April 2015 to December 2016. The improved discharge estimates are obtained by using DA to adjust the surface soil moisture in the model. The influence of DA to discharge is not direct but works through the dynamics of the hydrological model.  To explore the potential of LPF-GT, serval sensitivity experiments were conducted to figure out the impact of localization scales and the number of particles on DA's performance. The DA estimates were validated against in situ discharge measurements from gauge stations. To demonstrate the benefit of LPF-GT, EnKF was used as a benchmark in this research. Increases in Nash-Sutcliffe (0.05%– 38%) and decreases in normalized RMSE (0.02%–3.4%) validated the capability of LPF-GT. Results showed that localization scales' impact was substantial. The optimal value of the localization scale was obtained by tuning. LPF-GT achieved a satisfactory performance when only using a few particles, even with as little as five particles. The sample errors posed an adverse impact on the open-loop results. Further improvement could be achieved by considering reduce sample errors due to a small number of particles.
Few floods govern decades of suspended sediment flux in German upland rivers
Authors: Blöthe Jan Henrik , Hoffmann Thomas
Published: March 2021

Sediment yield from lowland rivers around the globe is often dominated by suspended sediment that also acts as a carrier for pollutants and contaminants. Achieving a deeper understanding of the suspended sediment dynamics is important for river management, but often complicated by short or discontinuous time-series and scattered surveying locations. However, suspended sediment transport is highly variable in space and time, calling for decadal observations that reflect this variability. Here we make use of >130,000 measurements on water discharge (Q) and suspended sediment concentration (SSC) from twelve stations that drain large parts of the central German uplands, to investigate the spatiotemporal variability in suspended sediment flux. 
The data has been collected during working days between 1965 and 2018 in context of the suspended sediment monitoring conducted by the Federal Waterways and Shipping Administration (WSV). The contributing catchments of the twelve monitoring stations range between 2500 and 22000 km2 and cover observation periods between 27 and 53 years. 
Despite roughly similar topographic and climatic conditions, average specific (suspended) sediment yield (SSY) varies between ~6 and ~29 t km2 yr-1. Highest specific yields are observed for those catchments that drain the escarpment of the Swabian cuesta landscape. Even more pronounced than the spatial variability is the interannual variability in sediment yield, with SSY for very wet years exceeding SSY for dry years more than tenfold. Separating the hydrograph into base-flow and event-flow components, we find that sediment export during event-flows accounts for 60 to 85% of the long-term SSY, with individual floods accounting for more than 90% of the annual sediment export. We conclude that high specific (suspended) sediment yields in the central German uplands are conditioned by rapidly responding catchments (i.e. large fraction of event-flow contribution) with highly erodible lithologies of the Swabian cuesta landscapes.
Submarine groundwater discharge from coastal peatlands of northeast Germany
Authors: Racasa Erwin Don , Lennartz Bernd , Ibenthal Miriam , Janssen Manon
Published: March 2021

Submarine groundwater discharge (SGD) is an important pathway for water and compounds within the land-ocean transition zone that can impact coastal environments and marine life. Although SGD research from sandy shorelines has rapidly advanced in recent years, there is very little understanding of coastal areas dominated by coastal peatlands, where the prevailing soils are characterized by a low hydraulic conductivity. Peatlands, the world’s most efficient carbon storage, could be a potential source of carbon, nutrients, and trace metals via the SGD pathway. The objective of this study was to determine the magnitude and location of SGD in a coastal peatland in northeast Germany. We wanted to understand the factors controlling terrestrial SGD from coastal peatlands through numerical modelling employing the HYDRUS-2D modeling package. Steady-state scenarios were simulated based on soil physical properties, hydraulic heads, and geological stratifications and structure. In the model set-up, emphasis was laid upon peat layers extending from land into the sea. Our results show that terrestrial SGD occurs at a net discharge volume flux of 0.0803 m3 m-1 d-1 with seepage rates of 1.05 cm d-1 near the shore and 0.16 cm d-1 at a second discharge region above the submerged peat layer. Calculated seepage rates compare to observations from other SGD sites in the Baltic Sea region and other wetland environments. The upscaled SGD estimate for the 3-km coastal peatland is 240 m3 d-1, which is in correspondence to earlier estimates from the same site. Analysis of the model output reveals that magnitude and location of terrestrial SGD are mainly driven by the magnitude of hydraulic gradient and the hydraulic conductivity of both peat and mineral soils. Additional influencing factors are peat anisotropy, thickness of aquifer sands and peat layers, and peat elevation. Submerged peat layers extending into the sea can restrict SGD flow in deeper discharge regions but may be less critical in terms of volume flux as most SGD occurs near the shoreline. We conclude that coastal peatlands could be an essential source of carbon, nutrients, and other compounds via SGD and may influence local geochemistry budgets and marine ecosystems.
Investigation of the Upper Mantle Anisotropy Beneath the Anatolian Plate and Surroundings by Shear Wave Splitting Analysis
Authors: Erman Ceyhun , Yolsal-Çevikbilen Seda , Eken Tuna , Taymaz Tuncay
Published: March 2021

The Anatolia, one of the most actively deforming continental regions of the Earth, is considered to be a natural laboratory for studying tectonic structures, complex deformation patterns, and intense seismicity at various scales. Active tectonics of this plate has been shaped by complex interactions between the Arabian, African and Eurasian plates. In the region, there are several suture zones associated with the closure of Tethys Ocean, large-scale transform faults (e.g. North Anatolian Fault) and geological structures developed in relation to extensional and compressional tectonics. Seismic anisotropy studies are needed to better understand the relationship between surface deformation and mantle dynamics, and to establish a connection between the involved deformation models and anisotropic structures in the lithosphere and asthenosphere layers beneath Anatolia. To evaluate lateral and vertical variations in the upper mantle anisotropy and thus underlying geodynamic processes, we apply teleseismic shear wave splitting (e.g. SKS, PKS, SKKS) analyses using about 500 broad-band seismic stations located throughout Anatolia, which belong to AFAD, KOERI and NOA seismic networks. Splitting intensities (SI) were calculated for the entire data set to compare piercing parameters obtained from both SI and SWS techniques. Overall, the NE-SW fast directions were observed for the entire Anatolia. Local changes in FPDs and DTs should be interpreted with caution as they will give important clues about the correlation between existing tectonic forces and upper mantle deformation. In particular, complex anisotropy signature along the large-scale transform faults (NAF and EAF) was investigated by using multisplit approach (e.g., Eken and Tilmann, 2014) that uses a grid search over four splitting parameters of two-layer anisotropy. A bootstrap-based analysis was performed to statistically evaluate the possible variations in two-layer models. Preliminary results reveal that a two-layer anisotropy exists at the western part of the Anatolia along the NAF. The obtained two-layer anisotropy models imply that signatures of lithospheric deformation and of asthenospheric flow driven shearing remarkably differ in NW Anatolia. In this part of the Anatolian plate, we observed large time delays up to ~2.2 sec, and fast polarization directions: i) mainly consistent with the strike of NAF in the lithosphere, ii) N-S oriented in the asthenosphere that is likely attributed to the mantle flow regime under the influence of slab roll-back and trench retreat along the Hellenic subduction zone.
Mobilization of bacteriophages from soil matrix to soil water in the Attert River basin: A case study
Authors: Florent Perrine , Cauchie Henry-Michel , Ogorzaly Leslie
Published: March 2021

Bacteriophages are numerous, tremendously diverse and ubiquitous in the environment. Since the 1960s, bacteriophages have been proposed as new tracers to investigate the hydrological processes in addition to conventional tracers (i.e. isotopes, salts, dyes). Their dynamic into water (i.e. surface water, groundwater) have been well studied. However, the soil compartment known for its important microbial activity, have been few characterized in terms of bacteriophage diversity. Hence, in the present study, the objective is to investigate the transport of soil viral population from the soil matrix to the soil water compartment. This mobilization from the soil matrix is mainly driven by the adsorption/desorption mechanisms to which bacteriophages are subjected. Therefore, in order to understand the dynamics of the bacteriophage population, both soil and soil water were sampled from the Weierbach forest, located in the Attert River basin (Grand-Duchy of Luxembourg) at the topsoil level (i.e. 0-20 cm) over a period of one month. Due to a lower abundance of the microbial population in soil water, an enrichment method was carried out to increase the concentration. Subsequently, a shotgun metagenomics analysis was performed on the soil and soil water samples to obtain the DNA sequences, which were then sorted using bioinformatics and statistical analyses, allowing ultimately the identification of the viral populations. The moving of the bacteriophage populations from the soil to the soil water provides information on their transport capacity, in particular by taking into account environmental conditions such as air and soil temperatures, precipitation, soil humidity, soil pH, etc.  

 

Key words: bacteriophages, soil, water, transport, environmental conditions
Stratospheric residence time and the lifetime of volcanic aerosol
Authors: Toohey Matthew , Jia Yue , Tegetmeier Susann
Published: March 2021

The cumulative radiative impact of major volcanic eruptions depends strongly on the length of time volcanic sulfate aerosol remains in the stratosphere. Observations of aerosol from recent eruptions have been used to suggest that residence time depends on the latitude of the volcanic eruption, with tropical eruptions producing aerosol loading that persists longer than that from extratropical eruptions. However, the limited number of eruptions observed make it difficult to disentangle the roles of latitude and injection height in controlling aerosol lifetime. Here we use satellite observations and model experiments to explore the relationship between eruption latitude, injection height and resulting residence time of stratospheric aerosol. We find that contrary to earlier interpretations of observations, the residence time of aerosol from major tropical eruptions like Pinatubo (1991) is on the order of 24 months. Model results suggest that the residence time is greatly sensitive to the height of the sulfur injection, especially within the lowest few kilometers of the stratosphere. As injection heights and latitudes are unknown for the majority of eruptions over the common era, we estimate the impact of this uncertainty on volcanic aerosol forcing reconstructions. 
Modeling recent permafrost thaw and associated hydrological changes in an endorheic Tibetan watershed
Authors: Immerzeel Walter , Martin Léo , Brun Fanny , Westermann Sebastian , Fiddes Joel , Kraaijenbrink Philip , Mathys Tamara
Published: March 2021

Permafrost has a crucial influence on sub-surface water flow and thus on the hydrology of catchments. Its thawing drives the release of frozen water and a transition from surface-water-dominated systems to groundwater-dominated systems. In the context of global warming, these hydrological modifications are of critical importance for extensive headwater regions such as the Qinghai-Tibet Plateau (QTP) and the Himalayas. Permafrost covers a significant proportion of these regions (40% of the QTP), which are major water towers of the world. Therefore, improving our understanding and ability to quantify these changes are a key scientific challenge.

Many watersheds of the QTP have seen their hydrologic budget modified over the last decades as evidenced by strong lake level variations observed in endorheic basins. Yet, the possible contribution of permafrost thaw to these variations has not been assessed. The Paiku basin (central Himalayas, southern TP) finds itself in a similar situation. The Paiku lake at the lowest point of this endorheic basin has exhibited important level decreases since the 70’s and thus offers the possibility to test the potential role of permafrost thaw on these hydrologic changes. We present permafrost simulations at the scale of the basin over the last four decades that reproduce its degradation as result of regional climatic change. We use the Cryogrid model to simulate the surface energy balance, snow pack dynamics and the ground thermal regime while accounting for the phase changes and the soil water budget. Because the surface radiative, sensitive and latent heat fluxes in alpine environments are strongly dependent on the physiography the model is forced with distributed downscaled forcing data produced with the TOPOSCALE model to account for this spatial variability. Simulated surface conditions are evaluated against meteorological data acquired within the basin and remotely sensed surface temperatures.

The simulations show that, contrary to large scale estimates of permafrost occurrence probability, an important part of the basin is underlaid by permafrost. During the simulated period, permafrost distribution and active layer exhibit limited variations (active layer deepening neighboring 10 cm) yet deeper ground temperatures (7-8 m) show a warming close to 0.8 degree (0.2 degree per decade). These first results tend to indicate a limited contribution of permafrost to the catchment hydrology over the last decades, a trend that could be significantly modified in the future if the simulated warming rates persist and lead to increased permafrost thawing.