bluuebunny/crossref_metadata_2025 huggingface dataset:
Event indicator analysis using depth functions to explain the occurrence of large floods in Germany
Authors: Guse Björn , Anwar Faizan , Merz Bruno , Tarasova Larisa , Merz Ralf , Bárdossy András , Vorogushyn Sergiy
Published: March 2021

Large floods occur due to particular hydrometeorological conditions and could be characterized by different event indicators. By analyzing a large set of catchments and different events, the drivers of large flood peaks remain unclear. In addition to precipitation, also the prevailing situation in the catchment such as soil moisture conditions could control the occurrence of large floods.In this study, we analyzed a set of event indicators ranging from event precipitation via antecedent catchment state to catchment response for 169 gauges in Germany. For each gauge with a length of at least 50 years of daily observations, we derived the POT5 series. In order to test whether floods are characterized with unusual values of event indicators, we used the Tukey’s depth function. In this multivariate data analysis technique, a point cloud of different event indicators is subdivided at each point with a line into two groups. The depth value is hereby the minimum value of points in these two groups. This multivariate statistical method allows to find points in the center of the set, and those on or close to the boundary. Hence, points in the cloud center have high depth and correspond to ordinary values of the event indicators. Points at the edges of the cloud have low depth and indicate unusual indicator values. In case of low depth, the related event indicators can potentially be seen as drivers of these flood events. We compared all combinations of the event indicators with 2, 3 and 4 variables and analyzed which event indicators might cause the occurrence of large flood peaks.Our results show that the depth is reduced with increasing flood magnitude. Large floods are thus more unusual in terms of event indicators compared to smaller floods. The most relevant event indicators are maximum event precipitation and event precipitation volume. At least one of these indicators is required to explain the flood peak magnitude, but in most of the cases these two indicators are not sufficient. Inclusion of antecedent catchment state or a catchment response indicator improves the explanation in several but not all cases.Overall, we conclude that flood peak magnitudes at a specific catchment in our study region are mainly driven by the individual event characteristics. In most of the cases they cannot not be explained by typical patterns of event indicators for all large events at a given gauge.
Differential age and species growth responses to climate warming detected in old-growth Mediterranean mountain forests 
Authors: Colangelo Michele , Camarero Jesus Julio , Gazol Antonio , Borghetti Marco , Baliva Michele , Gentilesca Tiziana , Piovesan Gianluca , Rita Angelo , Lapolla Antonio , Schettino Aldo , Ripullone Francesco
Published: March 2021

Mediterranean mountainous forest ecosystems are key hotspots to study the impact of climate change, thus understanding the species-specific growth response is of great relevance. In this study, we take advantage of the few remnant patches of old-growth forests located in the Pollino Massif (southern Italy), to evaluate how the growth of conspecific young and old trees responded to climate. Indeed, thanks to their remote critical topographic conditions in which these patches are located, they have remained nearly untouched from human pressure over the last centuries. We compared two conifer species (Abies alba, Pinus heldreichii var. leucodermis) vs. two hardwood species (Fagus sylvatica, Quercus cerris) in four stands situated along an altitudinal gradient. Younger trees grew faster than their conspecific oldest trees during their juvenile stage, regardless of the environmental conditions and species studied, highlighting more favorable recent climatic and environmental conditions for growth compared to the past. Rising temperature had a positive effect on growth rate in high-elevation young and old P. leucodermis individuals. However, F. sylvatica, inhabiting mesic sites at lower elevation, had slow growth with the least difference in growth rates between young and old trees. Similarly, the growth rates of old tree species found at lower elevation (Q. cerris and A. alba, respectively) tended to be relatively stable since 1950, except for A. alba, increased over the last two decades. Climate sensitivity in recent decades differed between young and old trees in some of the species, with younger trees tending to be more sensitive in Pinus and Abies, and older trees being more sensitive in Fagus. Such disparity in climate sensitivity and long-term growth reactions to climate should be recognized and considered when forecasting the future dynamics of old-growth forests.
TRACING GROUNDWATER SYSTEMS IN UPPER AUSTRIA USING 87Sr/86Sr ISOTOPE RATIOS
Authors: Foelserl Virginia , Irrgeher Johanna , Groß Doris , Sachsenhofer Reinhard F. , Götzl Gregor , Kralik Martin , Heidinger Michael
Published: March 2021

The Upper Austrian Molasse Basin is not limited to the use of drinkable groundwater and balneological use of thermal waters. The extraction of crude oil and natural gas, the storage of natural gas and carbon dioxide, and the increasing use of thermal water as an alternative energy source are of high economic importance. In terms of water management, knowledge of the subsurface conditions, the different groundwater horizons, and their interactivity are indispensable. Already existing hydrodynamical models of the Malmian thermal aquifer, however, exhibit uncertainties due to low data density and lack of information. As part of a multi-year project funded by the ÖAW (Austrian Academy of Sciences), the data sets were expanded, among other things, by determining the strontium isotope ratios of selected water samples in Upper Austria. Therefore, concentrations of the most common cations and the strontium isotopic composition of 48 samples from 12 different aquifer horizons, ranging from shallow to artesian groundwater and geothermal and hydrocarbon wells were analyzed by using (MC) ICP-MS.
87Sr/86Sr ratios range from 0.70841 to 0.72740 and generally correlate with the respective host rock. The hydrostratigraphic horizons show characteristic strontium isotopic signatures, though they cannot be distinctly assigned to a single formation. Given variations in 87Sr/86Sr ratios can be traced in most instances. Thus, elevated 87Sr/86Sr ratios > 0.710 of a few samples of the Innviertel Group (0.70915 – 0.71167) can be explained by their sampling location at the crystalline boundary. Higher variability of results within formations, e.g., of the Linz-Melk Formation (0.70928 – 0.71160) in terms of both, 87Sr/86Sr ratio and strontium concentration suggest mixing processes with waters depleted in 87Sr. Equally large variations are shown in the results of waters from Eocene formations (0.70879 - 0.71011). In this case, supported by results of other hydrochemical data, even a multi-component mixing process is assumed. Samples of the Malmian thermal water (0.70971 - 0.71077) exhibit, with one exception, homogenous 87Sr/86Sr ratios below 0.710.
The results demonstrate the ability of strontium isotope ratio determination to confirm assumptions based on hydrochemical and physical data as well as to provide additional information about the dynamics of (deep) groundwater systems to identify mixing processes within formations.
How to reduce uncertainties in a coupled and spatialized water quality model using data assimilation?
Authors: Rouzies Emilie , Lauvernet Claire , Vidard Arthur
Published: March 2021

Intensive use of pesticides in agricultural catchments leads to a widespread contamination of rivers and groundwater. Pesticides applied on fields are transferred at surface and subsurface to waterbodies, resulting from the interaction of various physical processes. They are also highly influenced by landscape elements that can accelerate or slow down and dissipate water and contaminant flows. The PESHMELBA model has been developed to simulate pesticide fate on small agricultural catchments and to represent the landscape elements in an explicit way. It is characterized by a process-oriented approach and a modular structure that couples different models.

In the long run, we aim at setting up and comparing different landscape organization scenarios for decision-making support. However, before considering such operationnal use of PESHMELBA, uncertainties must be quantified and reduced. Additionally, the model is physically-based, fully-spatialized which leads to a large set of parameters that must be carefully estimated. To tackle both objectives, we set up a data assimilation framework based on satellite images and in situ data and we evaluate the potential of Ensemble Smoother for joint variable-parameter assimilation. Assimilating surface moisture images allows for direct correction of variables and parameters on the top part of the soil. However, due to the PESHMELBA structure based on a dynamic parallel code coupler (OpenPALM), the impact of such correction on other compartments and other physical processes has to be finely assessed.

In this preliminary study, a fairly simple virtual hillslope inspired from a realistic catchment is set up and data assimilation is performed on twin experiments, i.e., using virtual surface moisture images. The potential of such technique for improving the global performances of the model is scrutinized and the sensitivity to the assimilation framework (ensemble size, frequency of observations, errors, etc.) is assessed. Valuable information on the coupling functioning are obtained allowing for anticipating performances in a real case. Identified limitations of surface moisture assimilation also give precious indications about existing gaps and pave the way for multi-source data assimilation.

 
Improving water age estimation in a drinking water distribution network by field study and digital modeling
Authors: Rakstang Jon Kristian , B. Waak Michael , M. Rokstad Marius , Hallé Cynthia
Published: March 2021

Municipal drinking water distribution networks are complex and dynamic systems often spanning many hundreds of kilometers and serving thousands of consumers. Degradation of water quality within a distribution network can be associated to water age (i.e., time elapsed after treatment). Norwegian distribution networks often consist of an intricate combination of pressure zones, in which the transport path(s) between source and consumer is not easily ascertained. Water age is therefore poorly understood in many Norwegian distribution networks. In this study, simulations obtained from a water network model were used to estimate water age in a Norwegian municipal distribution network. A full-scale tracer study using sodium chloride salt was conducted to assess simulation accuracy. Water conductivity provided empirical estimates of salt arrival time at five monitoring stations. These estimates were consistently higher than simulated peak arrival times. Nevertheless, empirical and simulated water age correlated well, indicating that additional network model calibration will improve accuracy. Subsequently, simulated mean water age also correlated strongly with heterotrophic plate count (HPC) monitoring data from the distribution network (Pearson’s R= 0.78, P= 0.00046), indicating biomass accumulation during distribution—perhaps due to bacterial growth or biofilm interactions—and illustrating the importance of water age for water quality. This study demonstrates that Norwegian network models can be calibrated with simple and cost-effective salt tracer studies to improve water age estimates. Improved water age estimation will increase our understanding of water quality dynamics in distribution networks. This can, through digital tools, be used to monitor and control water age, and its impact on biogrowth in the network.
Error estimation of buoy, altimeter, and model significant wave height from triple collocation technique
Authors: Dodet Guillaume , Bidlot Jean-Raymond , Accensi Mickaël , Alday Mathias , Abdalla Saleh , Piolle Jean-François , Ardhuin Fabrice
Published: March 2021

Ocean wave information is of major importance for a number of applications including climate studies, safety at sea, marine engineering (offshore and coastal), and coastal risk management. Depending on the scales and regions of interest, several data sources may be considered (e.g. in situ data, VOS observations, altimeter records, numerical wave model), each one with its pros and cons. In order to optimize the use of multiple source wave information (e.g. through assimilation scheme in NWP), the error characteristics of each measurement system need to be investigated and inter-compared. In this study, we use triple collocation technique to estimate the random error variances of significant wave height from in situ, altimeter and model data. The buoy dataset is a selection of ~100 in-situ measuring stations provided by the CMEMS In-Situ Thematic Assembly Center. The altimeter dataset is composed of the ESA Sea State CCI V1.1 L2P product. The model dataset is the result of WW3 Ifremer hindcast run forced with ERA5 winds using the recently updated T475 parameterization. In comparisons to previous studies using similar techniques, the large triple collocation dataset (~450 000 matchups in total) generated for this study provides some new insights on the error variability within in situ stations, satellite missions and upon sea state conditions.Moreover, the results of the triple collocation technique help developing improved calibration of the altimeter missions included in the ESA Sea State CCI V1.1 dataset.
Reconstructing 1200 years of hydroclimate variability in the southern margins of the Arabian Desert, inferred from an ancient lake in southern Yemen
Authors: Parth Shah , Russell James M , Waldmann Nicolas
Published: March 2021

There is a major knowledge gap in the past climate oscillation of the Arabian desert, especially during the past two millennium. Reliable continuous continental records that archives at high resolution past environmental variability are useful sentinels of paleoclimate changes. Reliable interpretation from climatic proxies retrieved from lake records are crucial for identifying periodicities and the onset of climatic events and evaluating inter-annual and decadal trends driven by shifting of the Intertropical Convergence Zone (ITCZ). A multiproxy approach is presented for a ~3.3 m composite core from a karst lake located in Gayal el Bazal, southern Yemen. Sedimentary proxies, including grain size distribution and magnetic susceptibility (MS) coupled with geochemistry (XRF), provide an initial picture of centennial-scale environmental changes over the southern Arabian desert. The chronology of the core was anchored by five radiocarbon (14C) dates of terrestrial plants (wood) extracted from sediment samples and indicates the core extends to ~800 AD. Our data provides a snapshot for better understanding the impact of Indian Ocean monsoon variability at an exceptional resolution for a region that lacks sufficient information. Our data indicates that during the ‘Little Ice Age’ (~1500-1800 AD) was arid relative to the warm conditions that prevailed during the Medieval Warming Period (~800 to 1200 AD). The arid phase was marked by high Ca/(Al, Fe, Ti) values, increased inorganic carbon content, decreased MS values, and gypsum precipitation. Furthermore, end-member mixing analyses (EMMA) derived from the grain-size distribution corroborates the production of carbonate sand probably due to an increase in flash floods occurring concurrently with low lake levels under generally dry conditions. Aridity during the Little Ice Age is consistent with evidence and theory for weakened boreal summer monsoons during intervals of northern hemisphere cooling. Overall, this study will provide insight into the monsoon variability and a record for understanding the interactions between northward migrations of the ITCZ and tropical monsoonal dynamics during the late Holocene. In the context of current climate change and increasing population pressure, a deeper understanding of their long-term hydrological variability, this study is highly essential to satisfactorily forecast the sustainability of lakes as a resource in a warming world.
On the use of inverse modeling to improve subsurface drainage simulations
Authors: Chelil Samy , Oubanas Hind , Henine Hocine , Gejadze Igor , Malaterre Pierre Olivier , Tournebize Julien
Published: March 2021

The application of inverse modeling approaches has been expanded to the field of hydrology this last decade. Here, the inverse modeling has been used to adjust the input parameters of a new agricultural subsurface drainage model (SIDRA-RU) using observations of the model output. SIDRA-RU is a semi-conceptual and semi-analytical model that transforms the rainfall into a daily drainage discharge. The model is divided into two modules. The first one consists of a conceptual reservoir that converts the net rainfall into recharge; the second module simulates the drainage discharge and the water table level above the mid-drains, based on the resolution of the Boussinesq equation.

The adjoint model of SIDRA-RU has been successfully generated by means of the automatic differentiation tool (TAPENADE). First, this adjoint model is used to explore the local and global adjoint sensitivities of the valuable function defined over the drainage discharge simulations (model output), with respect to the model input parameters. Next, the most influential parameters are estimated using both the classical calibration algorithm (PAP-GR) and the variational data assimilation method (4D-VAR). For the latter method, a simple stochastic procedure has been proposed to avoid trapping the minimization process in the local minimum points.

Our results have shown that the quality of the drainage discharge simulations obtained using the 4DVAR method is better than the ones performed by the PAP-GR calibration algorithm, in terms of the water balance in particular. Indeed, less than 5 mm of the cumulative discrepancy was registered between simulated and observed water volume based on the five-year daily drainage discharge data of the Chantemerle agricultural field. However, some numerical tests, conducted to investigate the convergence of the variational calibration method, indicate the potential presence of the equifinality issues. This could be highlighted by the self-compensation of the physical soil parameters (Ksat and µ) and those managing the conceptual SIDRA-RU reservoir (Sinter and SSDI). The performed sensitivity analysis has shown that the parameters having the most impact on the drainage discharge are those controlling the nervousness and recession of the water level in soils followed by those managing the start of the drainage season.
The Daisy agroecological system model: A physically based model for preferential water flow and solute transport in drained agricultural fields
Authors: Diamantopoulos Efstathios , Holbak Maja , Abrahamsen Per
Published: March 2021

Preferential water flow and solute transport in agricultural systems affects not only the quality of groundwater but also the quality of surface waters like streams and lakes. This is due to the rapid transport of agrochemicals, immediately after application, through subsurface drainpipes and surface water. Experimental evidence attributes this to the occurrence of continuously connected pathways, connecting the soil surface directly with the drainpipes. We developed a physically-based model describing preferential flow and transport in biopores and implemented it in the agroecological model Daisy. The model simulates the often observed rapid transport of chemicals from   the upper soil layers to the drainpipes or to deeper layers of the soil matrix. Based on field investigations, biopores with specific characteristics can be parameterized as classes with different vertical and horizontal distributions. The model was tested against experimental data from a column experiment with an artificial biopore and showed good results in simulating preferential flow dynamics. We illustrate the performance of the new approach, by conducting five simulations assuming a two-dimensional simulation domain with different biopore parametrizations, from none to several different classes. The simulation results agreed with experimental observations reported in the literature, indicating rapid transport from the soil to the drainpipes. Furthermore, the different biopore parametrizations resulted in distinctly different leaching patterns, raising the expectation that biopore properties could be estimated or constrained based on observed leaching data and direct measurements.
Timeliness of earthquake magnitude estimation from the prompt elasto-gravity signal  using Deep Learning
Authors: Licciardi Andrea , Bletery Quentin , Rouet-Leduc Bertrand , Ampuero Jean-Paul , Juhel Kévin
Published: March 2021

Mass redistribution during large earthquakes produces a prompt elasto-gravity signal (PEGS) that travels at the speed of light and can be observed on seismograms before the arrival of P-waves. PEGS carries information about earthquake magnitude and the temporal evolution of seismic moment, therefore it could be used to both improve the accuracy of current early source estimation systems and speed-up early warning. However, PEGS has been detected for only a handful of very large earthquakes so far, and its potential use for operational early warning remains to be established. In this work, we study the timeliness of magnitude estimation for subduction earthquakes in Japan using PEGS waveforms by means of Deep Learning and Bayesian uncertainty analysis. Given the paucity of PEGS observations, we train the model on a database of synthetic seismograms augmented with empirical noise in order to simulate more realistic waveforms. We use about 80 stations from the Japanese F-Net network and from networks with data available through IRIS.

Under this experimental setup, we find that our model is able to track the moment release for earthquakes with a final Mw above 8.0, with a system latency that depends on the signal-to-noise ratio of PEGS. The application of our model to the Mw=9.1 Tohoku-Oki earthquake shows a latency of about 50 s after which the model is able to track well the evolving Mw of the earthquake. After about 2 minutes from the earthquake origin time, a reliable estimate of its final Mw is obtained. Similar performances in terms of timeliness of final Mw estimation are observed for the relatively smaller Hokkaido earthquake (Mw=8.1) although with higher uncertainty.

Our results highlight the potential of PEGS to enhance the performance of existing tsunami early warning systems where estimating the magnitude of very large earthquakes within few minutes is vital.

 
Assessing the Multiple Pressure Source Hypothesis for the Sakurajima Volcano and Aira Caldera Magmatic System
Authors: Backhurst Robert
Published: March 2021

Sakurajima, located on the southern rim of Aira caldera, is one of the most active volcanoes in Japan. From long term deformation trends, the volcano is showing an increased risk of large-scale eruption, emphasizing the need to better understand the magmatic system.

Deformation modelling, primarily using the Mogi method, has dominated the geodetic assessment history of Sakurajima. These methods, however, contain limitations, such as the assumption of a homogeneous crust, and have therefore not accurately depicted the magmatic system. Numerical modelling techniques have reduced this limitation by accounting for subsurface heterogeneity.

Analytical modelling studies have suggested multiple magmatic sources beneath Aira caldera and Sakurajima volcano, whilst the only numerical study undertaken so far indicated a single source. Here, we test the multiple deformation source hypothesis, whilst also incorporating subsurface heterogeneity and topography, using Finite Element (FE) numerical modelling, and geodetic data from Sakurajima.

Using a full 3D model geometry for Sakurajima and Aira caldera, preliminary forward modelling suggests a second deformation source produces our best fit to the measured geodetic data. Optimum results indicate a shallow prolate source 7-10 km below sea level (bsl), in addition to a deeper oblate source at ~13 km bsl. These preliminary findings produce greater shallow storage depths than the previous analytical models (3-6 km) and ties in with the trans-crustal magmatic system hypothesis.

Increasing our understanding of the Sakurajima magmatic system will enable improved interpretations of geodetic data prior to eruptions and will inform models for a range of similar volcanoes world-wide.
The energy budget of the tropical band in future climate 
Authors: Ferreira David , D'Agostino Roberta
Published: March 2021

The atmospheric circulation is expected to change in response to anthropogenic CO2 emissions. Both theory and model simulations of future climate suggest that the tropical overturning will weaken, with a weaker Hadley Circulation ascent, while the stratification of moist static energy (MSE) will strengthen. These two changes have opposite effects on the energy balance of the deep tropics. In the unperturbed system, the equatorward convergence of the mean flow in the lower troposphere (i.e. at low MSE) is compensated by a divergence in the upper troposphere (i.e. at high MSE), resulting in a net lateral export of MSE out of the region of ascent.

The weakening of the circulation in a future warmer climate would weaken the export of MSE while the strengthening of the stratification -- an increase of the MSE contrast between the upper and lower branches -- would reinforce it. However, previous studies suggest that these two effects do not exactly cancel out. A neglected element in this picture is the primary driver of these changes: due to the long-wave trapping by higher CO2 concentration, the tropical atmosphere will also receive more energy at the top and bottom (an increased Net Energy Input, NEI).

In this study, we attempt to reconcile changes in the circulation, stratification and NEI under climate change. Specifically, we investigate 1) to which extent the effects of circulation and stratification changes on the MSE budget compensate and 2) if inclusion of the NEI changes brings the MSE budget closer to equilibrium.

To address these questions, we compute the Gross Moist Stability in a series of simulations from the Coupled Model Intercomparison Project 5 archive. To test our understanding of the MSE budget, we consider both a future climate scenario (RCP8.5) and the mid-Holocene (6000 A.D). For the future climate, we show that, although there is a rough balance by the circulation and stratification effects, inclusion of the NEI term significantly improves the closure of the MSE budget in the deep tropics. The mid-Holocene case is, however, fundamentally different as both stratification and circulation weaken, reinforcing their effects on the MSE export. In this case, inclusion of the NEI term is critical to establish the MSE balance of the deep tropics.

Both cases underline that a three-term balance (between changes in circulation, MSE stratification and NEI) provides a robust description of the deep tropics MSE budget under climate change.
On exposure of land area and population to heat waves and cold waves in a changing climate
Authors: Hampshire Alexander , Fuckar Neven , Heaviside Clare , Allen Myles
Published: March 2021

As climate changes – potentially to a warmer state than any time during the evolution of humans – heat extremes threatening human health, global ecosystem and socio-economic fabric of our society are occurring at increasing frequency and intensity in most parts of the world. This study examines changes in global land area and population exposed to both tails of temperature distribution in changing climate since heat and cold exposure is directly associated with a range of health impacts and affects thermal comfort and occupational capacity. We first utilise the latest ECMWF atmospheric reanalysis, ERA5, to examine changes over the satellite era (since 1979), and then we explore the equivalent changes in CMIP6 archive of historical runs and future projections. Besides daily maximum and minimum of dry-bulb surface air temperature (SAT), we also consider daily extremes of the universal thermal climate index (UTCI) that includes the influence of humidity, wind and radiation encapsulating the synergetic heat exchanges between the environment and the human body. Our analysis dissects changes in spatial and temporal exposure to both heat waves and cold waves and presents metrics contrasting changes in the opposite extremes of SAT and UTCI distributions. We assess the significance of the observed, modelled and projected changes and relate them to external drivers of climate change.
Field Test of 12 serially connected FBG accelerometer parallelly with the vertical sensor of 4.5 -Hz geophones.
Authors: Ezhuthupally Reghuprasad Aarathy , Godio Alberto , Janner Davide Luca , Colombero Chiara , Franco Diego
Published: March 2021

Fibre Bragg Grating (FBG) sensors are widely used for measuring vibrations in the fields like seismology and civil engineering. FBG sensors possess several advantages when compared to the traditional vibration sensors like immunity to electromagnetic interference, multiplexing, miniature size, higher sensitivity. Highly sensitive systems are required for capturing the seismic vibrations with low magnitude of acceleration. In this work a cost-effective cantilever based FBG accelerometer is developed. The structure is modelled using the software Solid Works and fabricated with PLA by 3D printing. Finally, a comparison test was carried out by serially connecting 12 FBG accelerometers parallelly to common vertical 4.5-Hz geophones outside the lab environment. Hammer shots were acquired along the tested line and the experimental results from both the systems were analysed and compared. The FBG system demonstrated here is suitable for seismic field acquisitions with potential applications to seismic refraction surveys, surface-wave analyses and passive seismic recordings.

 
Complex rupture dynamics of the 2020 Mw 6.8 Elazığ (Sivrice) earthquake, Turkey
Authors: Gallovič František , Zahradník Jiří , Plicka Vladimír , Sokos Efthimios , Evangelidis Christos , Fountoulakis Ioannis , Turhan Fatih
Published: March 2021

The 2020 Mw 6.8 Elazığ (Sivrice) earthquake occurred on the Pütürge segment of the East Anatolian Fault zone. This strike-slip segment is situated between strong earthquakes that happened 100–150 years ago, and, since that time, the segment remained with eight Mw5-6 events, but with no Mw 6+. We relocate the mainshock and aftershock sequence and infer basic characteristics of the event using the ISOLA multiple point source approach and backpropagation of S-waveforms from local strong-motion recordings. Together with clear secondary P wave onsets identified in the recordings, the results suggest complex rupture propagation with reversal of the rupture propagation. We apply a recently developed Bayesian dynamic source inversion with slip-weakening friction and spatially inhomogeneous stress and friction parameters to gain better insight into the rupture process. Using high-quality near field recordings in the low-frequency range (<0.3Hz), we obtain a complex dynamic rupture model explaining the weak rupture initiation followed by a cascade of at least three rupture episodes, including the rupture reversal. The dynamic model explains significant features of the recordings even in a broader frequency range interesting for seismic engineering applications (<2.5Hz), e.g., a directivity pulse associated with rupturing the event’s strongest asperity with 4 m of slip and local stress drop of 40 MPa. We show that by reducing the initial stress in the top 10 km by 10%, the rupture fails to develop into the larger event, finishing as an Mw 5.8 earthquake. Considering the latter experiment corresponds to an earlier state of the fault in the seismic cycle, we hypothesize that the interseismic M5+ events on the Pütürge segment were undeveloped rudiments of potentially large events. Thus, the fault seems to have been ready for the Mw6.8 earthquake only by the time of the earthquake occurrence in 2020. This suggests that at the time of the Elazığ earthquake initiation, the final Mw6.8 magnitude was not determined, making it a treacherous case for early warning systems.
Magma system pressurisation and long-term surface deformation at Soufrière Hills Volcano, Montserrat
Authors: Hickey James , Pascal Karen , Head Matthew , Gottsmann Jo , Fournier Nico , Hreinsdottir Sigrun , Syers Racquel
Published: March 2021

Soufrière Hills Volcano (SHV) is an andesitic dome-building volcano on the island of Montserrat (British West Indies). SHV began its current, and anomalously long, eruption in 1995, but eruptive activity has been intermittent with phases of lava extrusion separated by periods of relative quiescence. The current pause in eruption started in February 2010 and is the longest yet recorded, 10 years and 11 months at the time of writing (January 2021). Continuous GPS measurements show island-wide inflation from 2010 onwards, with the rate of inflation slowly decreasing with time. However, the length of the eruptive pause raises questions as to whether there have been significant changes to the magmatic system and/or the eruption at SHV might have ended. To assess the behaviour and evolution of the SHV magmatic system since 2010 and the relation to ongoing hazard assessment, we analyse the continuous GPS temporal deformation trends using a suite of geodetic numerical models. Our models incorporate a temperature-dependent viscoelastic rheology, topography derived from a Digital Elevation Model and three-dimensional variations in mechanical properties derived from seismic tomography. The models are driven using one of four possible time-dependent source functions, to simulate differences in the temporal evolution of the magmatic system. The results show that the observed deformation data requires a temporal source function whereby the magmatic system pressure is increasing with time. A viscoelastic crustal response cannot explain the long-term deformation trends alone. The nature of the source pressurisation is unclear, and could be due, for example, to one or a combination of, magma supply, degassing/volatile influx, or overturning within a transcrustal magmatic system. Continued pressurisation within the magmatic system highlights the need for sustained vigilance in the monitoring and management of the volcano and its surroundings.
On the imprint of the mesoscale organization of tradewind clouds at cloud base and below
Authors: Bony Sandrine , Brilouet Pierre-Etienne , Chazette Patrick , Coutris Pierre , Delanoë Julien , Lothon Marie , Rochetin Nicolas , Schwarzenboeck Alfons , Stevens Bjorn
Published: March 2021

Trade-wind clouds can exhibit different patterns of mesoscale organization. These patterns were observed during the EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field campaign that took place in Jan-Feb 2020 over the western tropical Atlantic near Barbados: while the HALO aircraft was observing clouds from above and was characterizing the large-scale environment with dropsondes, the ATR-42 research aircraft was flying in the lower troposphere, characterizing clouds and turbulence with horizontal radar-lidar measurements and in-situ probes and sensors. By analyzing these data for different cloud patterns, we investigate the extent to which the cloud organization is imprinted in cloud-base properties and subcloud-layer heterogeneities. The implications of our findings for understanding the roots of the mesoscale organization of tradewind clouds will be discussed.
Validation of the ESA CCI+SSS products
Authors: Martin Adrien , Guimbard Sébastien , Boutin Jacqueline , Reul Nicolas , Catany Rafael , Cipollini Paolo , Cci+sss consortium Esa
Published: March 2021

The European Space Agency (ESA) Climate Change Initiative (CCI+) for Sea Surface Salinity (CCI+SSS) project aims at generating long-term, improved, calibrated global SSS fields from space. The project started in mid-2018 and in its second year (version 2) has produced a 10-year dataset (2010-2019) from the three available L-band radiometer satellites (SMOS: Soil Moisture and Ocean Salinity; Aquarius; SMAP: Soil Moisture Active Passive) and validated it against in situ references (Argo and ISAS: In Situ Analysis System). The comparisons with in situ ground truth indicate much better performances than the ones obtained with a single satellite data product, with global precision against in situ references of 0.15 pss. CCI SSS version 2 products show similar performance than version 1 but is one year longer. There is a very good agreement between the CCI dataset and references, including long-term stability, with differences within +-0.05 pss for global ocean within [40°S-20°N]. At higher latitude, we observe seasonal oscillation of the CCI SSS difference against references. The uncertainty provided in the CCI SSS product are in good agreement with observations (within +-25%).
Recent spatio-temporal dynamics of floods of record across Europe
Authors: Arletti Fabio , Persiano Simone , Bertola Miriam , Parajka Juraj , Blöschl Günter , Castellarin Attilio
Published: March 2021

Economic losses and social consequences caused by floods have been steadily increasing over the last decades over Europe. In such a situation, the detection of changes in flood behaviour is crucial and the scientific community itself calls for a common effort to better understand recent flood dynamics and their evolution in space and time.

In this context, our study considers an extensive dataset of annual maximum series of peak flow discharges for more than 3400 catchments across Europe for the period 1820-2016 (average record length of 53 years). Based on this extensive dataset, our study analyses the behaviour of the specific flood of record (i.e. the largest flood observed in the time interval of interest divided by the drainage area of the corresponding catchment, hereafter also referred to as SFOR) in space and time across the European continent. In particular, we consider the spatial variability of SFOR computed for the entire observation period and for two 30-years sub-samples, namely 1987-2016 and 1957-1986. We focus on three macro-regions over northwestern, southern and eastern Europe, which have been identified by previous studies as homogeneous in terms of flood regime changes and processes driving flood changes. For the selected different timespans and macro-regions, we analyse the spatial variability of the year in which SFOR was observed, and the number of times in which a new record was observed at each and every gauge, also evaluating their relationship with catchment area. By referring to the theory of record-breaking processes, we also evaluate the non-stationarity in flood sequences by accounting for the presence of spatial correlation among flood sequences.

Finally, we provide a continuous spatial representation of SFOR values across Europe by referring to the dataset of elementary catchments identified by the Joint Research Centre (JRC) of the European Commission. For each elementary catchment of the JRC dataset, we interpolate empirical SFOR values by means of the geostatistical procedure termed top-kriging, which accounts for nesting between catchments.

The outcomes of our study provide useful information on the spatio-temporal evolution of flooding potential across Europe, enabling a visualization of the current flooding potential across Europe and of significant changes and shifts of the flood of record occurred during the last five decades.
Rejuvenation events recorded in alkali feldspar from the Tuolumne Intrusive Complex
Authors: Seitz Susanne , Gualda Guilherme , Caricchi Luca
Published: March 2021

Zoned minerals preserve information about their growth conditions, by changing their composition as function of temperature, pressure and melt composition. By carefully looking at a zoned minerals we can determine characteristics of the main stages of the evolution of magmatic systems.

We study alkali feldspar megacrysts from the Tuolumne Intrusive Complex in California, with the aim of deciphering chemical signatures of rejuvenation events. We characterize the chemical zoning of alkali feldspar using X-ray tomography, BSE imaging, EDS-SEM analysis and LA-ICPMS analysis along profiles. We use hierarchical clustering based on major and trace elements to objectively identify compositional groups for each chemical profile. By reducing the complexity of chemical zoning to one dimension (i.e. cluster number) we can trace the evolution of the conditions of growth and identify rejuvenation events.

Alkali feldspar megacrysts (up to 20 cm in size) from the Cathedral Peak unit of the Tuolumne Intrusive Complex occur predominantly disperse and only make between 8 - 12 % of the total crystal population. They are mostly homogeneous in major element, and markedly oscillatory zoned in trace elements such as Ba, Sr, and Rb. Using hierarchical clustering we identify four different chemical groups within the alkali feldspar crystals. Each chemical group is repeated multiple times in a single crystal. Overall the crystals show a decreasing trend of Ba towards the rim. Extended alkali feldspar crystallization would lead to a depletion of Ba in the melt and consequently to the growth of low Ba-zones of alkali feldspar. In some crystals the sequence of decreasing Ba is repeated twice. We propose that this reflects melt recharge in a melt-rich magmatic system.
Investigating the stochastic structure of the recently published Redacted Claims data set by the FEMA National Flood Insurance Program
Authors: Papoulakos Konstantinos , Iliopoulou Theano , Dimitriadis Panayiotis , Tsaknias Dimosthenis , Koutsoyiannis Demetris
Published: March 2021

During the last decades, scientific research in the field of flood risk management has provided new insights and strong computational tools towards the deeper understanding of the fundamental probabilistic and stochastic behaviour that characterizes such natural hazards. Flood hazards are controlled by hydrometeorological processes and their inherent uncertainties. Historically, a high percentage of flood disasters worldwide are inaccurately or ineffectively reported regarding the aggregated number of the affected people, economic losses and generated flood insurance claims. In this respect, the recently published National Flood Insurance Program (NFIP) data by the Federal Emergency Management Agency (FEMA), including more than two million claims records dating back to 1978 and more than 47 million policy records for transactions, may provide new insights into flood impacts. The aim of this research is to process the actual insurance data derived from this database, in order to detect the underlying patterns and investigate its stochastic structure, paving the way for the development of more accurate flood risk assessment and modelling strategies.
A novel sampling system for radiocarbon measurements of atmospheric methane 
Authors: Zazzeri Giulia , Xu Xiaomei , Graven Heather
Published: March 2021

Radiocarbon in atmospheric methane (Δ14CH4) is a powerful tracer of fossil methane emissions and can be used to attribute methane emissions to fossil or biogenic sources. However, few Δ14CH4 measurements are reported since 20001,2, due to challenges in sampling enough carbon for 14C measurements and in assessing the influence of 14C emissions from nuclear power plants on the 14C observations.

At Imperial College London we addressed the sampling limitation by developing a unique sampling system that separates carbon at the point of sampling and uses small traps of molecular sieves. Collection of a sample is made by three main steps: 1) removal of CO2 and CO from air, 2) combustion of CH4 into CO2 and 3) adsorption of the combustion-derived CO2 onto the molecular sieve trap. 14C analysis of our samples was carried out at the accelerator mass spectrometry facility at UCI. This novel system has been used for collection of samples in central London and has been made portable for collection of samples in different settings. 

Here we describe the system and report the evaluation of the measurement uncertainty and the processing blank. We achieved a measurement precision of 6 ‰, which is similar to or better than the reported precision of the most recent observations1,3.

1 Townsend‐Small et al JGR 117(D7) 2012

2 Sparrow et al Sci. Adv 4(1) 2018

3 Espic et al Radiocarbon 61( 5) 2019
Quantum sensors for space-borne earth observation
Authors: Schubert Christian , Herr Waldemar , Ahlers Holger , Gaaloul Naceur , Ertmer Wolfgang , Rasel Ernst
Published: March 2021

Atom interferometry enables quantum sensors for absolute measurements of gravity (1) and gravity gradients (2). The combination with classical sensors can be exploited to suppress vibration noise in the interferometer, extend the dynamic range, or to remove the drift from the classical device (3). These features motivate novel sensor and mission concepts for space-borne earth observation e.g. with quantum gradiometers (4) or hybridised atom interferometers (5). We will discuss developments of atom optics and atom interferometry in microgravity in the context of future quantum sensors (6) and outline the perspectives for applications in space (4,5).

The presented work is supported by by the CRC 1227 DQmat within the projects B07 and B09, the CRC 1464 TerraQ within the projects A01, A02 and A03, by "Niedersächsisches Vorab" through "Förderung von Wissenschaft und Technik in Forschung und Lehre" for the initial funding of research in the new DLR-SI Institute, and through the "Quantum and Nano- Metrology (QUANOMET)" initiative within the project QT3.

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(2) P. Asenbaum et al., Phys. Rev. Lett. 118, 183602, 2017; M. J. Snadden et al., Phys. Rev. Lett. 81, 971, 1998.

(3) L. Richardson et al., Comm. Phys. 3, 208, 2020; P. Cheiney et al., Phys. Rev. Applied 10, 034030, 2018; J. Lautier et al., Appl. Phys. Lett. 105, 144102, 2014.

(4) A. Trimeche et al., Class. Quantum Grav. 36, 215004, 2019; K. Douch et al., Adv. Space. Res. 61, 1301, 2018.

(5) T. Lévèque et al., arXiv:2011.03382; S. Chiow et al., Phys. Rev. A 92, 063613, 2015.

(6) M. Lachmann et al., arXiv:2101.00972; K. Frye et al., EPJ Quant. Technol. 8, 1, 2021; D. Becker et al., Nature 562, 391, 2018; J. Rudolph et al., New J. Phys. 17, 065001, 2015; H. Müntinga et al., Phys. Rev. Lett. 110, 093602 , 2013.