bluuebunny/crossref_metadata_2025 huggingface dataset:
The Drac paleo-valleys: a long-term archive of fluvial dynamics in the periglacial zone of the western French Alps
Authors: Mai Yung Sen Vivien
Published: March 2021

The evolution of the Alpine mountain belt during the Quaternary is strongly controlled by periodic glaciations and deglaciations. The significant erosion during these glacial/interglacial cycles has left very few sedimentary archives to study the surface dynamics within the mountain belt over the last hundreds of thousands of years. Valleys within the periglacial zone are the best candidates to target long-term geological archives in the Alps because they potentially preserve ancient fluvial deposits that have been preserved from glacial abrasion. The Drac River in the French western Alps preserves the alluvial fills of three generations of paleo-valleys, which were filled in response to glacial damming of the river and subsequently re-incised during glacial retreat. Detailed 3D mapping of the paleo-valleys was carried out to constrain their geometry and reconstruct the evolution of the Drac fluvial profile over time. The age of the fills of the three paleo-valleys was constrained by measuring the luminescence signal of feldspars, targeting sandy intervals within the coarse fluvial deposits. Dating these fills allows to quantitatively constrain the alluviation and incision dynamics of the Drac paleo-valleys. The onset of alluviation of the most recent paleo-valley occurred before the Last Glacial Maximum, between 40 ka and 90 ka BP (MIS 3 -5). The fill of the intermediate paleo-valley is dated to the previous cold period at 134±20 ka BP (MIS 6). Finally, the oldest paleo-valley was filled more than 200 ka ago. The filling periods correspond to the global climatic cooling stages and are much longer than the incision phases, which took place during global warm intervals. The pattern of sedimentary filling implies it is controlled by an increase in sediment flux in the context of glacial advance, while the incision phases are due to rapid base-level lowering linked to the retreat of glaciers damming the Drac basin. Complementary luminescence dating is currently carried out on the terraces, at the tops of the fillings, and will lead to a better understanding of the control of glaciations on the dynamics of alluvial deposits in the periglacial zone.
Correcting Late Cenozoic Sea-Level Records for Dynamic Topography: Examples from Australia
Authors: Richards Fred , Coulson Sophie , Austermann Jacqueline , Hoggard Mark , Mitrovica Jerry
Published: March 2021

Much of our understanding of ice sheet sensitivity to climatic forcing is derived from palaeoshoreline records of past sea-level. However, the present-day elevations of these sea-level markers reflect the integrated effect of both ice volume change and solid Earth processes. Accurately quantifying the latter contribution is therefore essential for making reliable inferences of past ice volume. While uncertainties associated with glacial isostatic adjustment (GIA) can be mitigated by focusing on sites far from ice sheets, the same is not true for mantle flow-driven dynamic topography, which is ubiquitous and can generate vertical motions of ~±100 m on million-year timescales. As a result, improved knowledge of the spatio-temporal evolution of this transient topography is required to refine constraints on ice sheet stability and to guide modelling of future trajectories.

Since the shortest wavelength and fastest evolving contributions to dynamic topography originate in the shallow mantle, reconstructing dynamic topography over 1–10 Myr timescales requires accurate models of Earth’s lithosphere and asthenosphere. Here, we construct these models by mapping upper mantle shear wave velocities from high-resolution surface wave tomographic models into thermomechanical structure using calibrated parameterisations of anelasticity at seismic frequency. Resulting numerical predictions of present-day dynamic topography are in good agreement with residual depth measurements, with particularly good fits obtained around Australia. In this region, predicted temperatures are also compatible with palaeogeotherms extracted from xenolith suites, indicating that present-day upper mantle structure is well characterised and that numerical “retrodictions” of vertical motions are more likely to be reliable. In addition, Australia is sufficiently distant from major ice sheets that uncertainty in GIA contributions to sea-level change are relatively small. These considerations, combined with new compilations of continent-wide sea-level indicators, make Australia a particularly promising location for separating out ice volume-driven global mean sea-level changes from local sea-level variations related to vertical land motions and gravitational effects.

By back-advecting density perturbations from an ensemble of Earth models, we demonstrate that ~±200 m relative sea-level changes across Australia since the Mid-Pliocene Warm Period (MPWP; ∼3 Ma) can be tied directly to changes in dynamic topography. Significantly, after removing this signal from observed relative sea-level changes,  a consistent global mean sea-level during the MPWP of 12±8 m above present is obtained, towards the lower end of previous estimates.
Complex resistivity inversion using controlled source electromagnetic data
Authors: Porté Julien , Girard Jean-François , Bretaudeau François
Published: March 2021

In some Earth materials, induced polarization (IP) phenomena are occurring when an electric perturbation is applied. These mechanisms are described by a frequency dependent complex resistivity. The study of relaxation model parameters describing these phenomena allows to access indirectly to several properties of interest of the underground, as properties linked to the pore space geometry, fluid content or presence and discrimination of disseminated metallic particles. Nevertheless, complex resistivity is usually studied using electrical method with a direct current hypothesis, neglecting by the way electromagnetic induction that can occurs in the data. Thus, strong limitations appear to recover a complex resistivity image as EM induction increase with frequencies and larger offset.

 

We implemented a frequency dependent complex resistivity in POLYEM3D, a 3D finite-difference modelling and inversion code for controlled-source electromagnetic data (CSEM) in order to fully recover IP information contained in EM data. CSEM method is a resistivity imaging technique using multi-frequency electromagnetic signals fully taking into account EM induction with larger investigation depth. Following a preliminary sensitivity study, a multi-stages inversion strategy was defined to undertake the multi-parameters problem. Furthermore, to manage the increasing number of parameters, a second order polynomial parametrization is used to describe frequency variation of complex resistivity.

 

We show through 1D synthetic data inversions and preliminary 3D results that we are able to recover a complex resistivity and its frequency variation from CSEM data in the IP/EM coupling domain, when IP signals are sufficiently large compared to EM induction. Our inversion strategy allows then to access to IP parameters of the medium in an extended frequency domain as well as for greater depth of investigation. A 3D CSEM survey was undertaken in December 2020 on the former mining site of La Porte-Aux-Moines (Côtes-d'Armor, France) presenting strong IP responses, to validate our inversion method for a 3D in-situ dataset.
Updates and Early Results from the Heavy Ion Sensor on Solar Orbiter
Authors: Lepri Susan T. , Livi Stefano A. , Raines Jim M. , Galvin Antoinette B. , Kistler Lynn M. , Dewey Ryan M. , Alterman Benjamin L. , Allegrini Frederic , Collier Michael R. , Owen Christopher J.
Published: March 2021

 

The Solar Orbiter mission was launched in 2020 into an orbit that will explore the inner heliosphere. During its orbit, periods of quasi-corotation with the Sun will enable determination of the source regions on the Sun for solar wind structures.  The Solar Wind Analyser (SWA) is a suite of instruments that provide in-situ measurements of solar wind electrons, protons, alpha particles, and heavy ions.  The SWA-Heavy Ion Sensor (HIS) is optimized to measure heavy ions in the solar wind, pickup ions, and suprathermal ions in an energy range spanning from 0.5- 75keV/e.  We present measurements of heavy ion composition from SWA-HIS taken during the cruise phase of the mission to highlight the capabilities of the instrument and the observations we expect to collect over the next 10 years. We discuss how SWA-HIS will enable linkages between the Sun and the solar wind to reveal the nature of the acceleration and release of the solar wind and the sources and structure of the solar wind.  We will also provide an overview of the available data and accessibility of the public datasets. 
A sequence of temporally separated element peaks; the fingerprint of a biogeochemical event initiated by sedimentary exhalative (SEDEX) brine expulsion
Authors: Arts Michiel , Cramer Bradley , Calner Mikael , Rasmussen Christian , Bancroft Alyssa , Oborny Stephan , Hartke Emma , Biebesheimer Ellie , Da Silva Anne-Christine
Published: March 2021

The Ireviken Biogeochemical Event (IBE) consists of the Ireviken Extinction Event (IEE) and is superseded by the Ireviken positive d13Ccarb Excursion (ICIE). During the Ireviken Extinction Event 80% of the conodont species and 50% of the trilobite species went extinct and Acritarchs, chitinozoans, graptolites, corals, and brachiopods communities were severely affected as well. Currently there are no indications that the Ireviken Biogeochemical event can be linked to a LIP or a bolide impact which are the usual triggers for most known biogeochemical events. The IBE has been tentatively linked to SEDEX brine expulsion, however convincing high-resolution data supporting the SEDEX brine expulsion theory was lacking.

The Altajme core from Gotland Sweden covers the entirety of the Ireviken Biogeochemical Event and using an ITRAX XRF core scanner  we were able to create a new dataset with a 1cm(~150-400 yr.) resolution. This dataset enables us to shed new light on the origin of the IBE and serves as a template for a cyclostratigraphic age model (using the detrital proxies of Ti and Al) which puts the IBE within a precise temporal framework.

The occurrence of peak values of Nb, Mn, Cu, Ba, Pb, Zn, As, Ag in the Altajme core follows the temporal sequence of element peaks which is characteristic for the cooling of a hydrothermal system. A Pb:Zn ratio of >1 and low Cu/(Zn+Pb) ratio categorises the hydrothermal system as being the sedimentary exhalative (SEDEX) brine expulsion type system. Through these results we can undoubtedly link the Ireviken Biogeochemical Event to a SEDEX brine expulsion. Numerous SEDEX style ore deposits of Proterozoic to Cenozoic age are known, but it has been difficult to connect them with similarly aged biogeochemical events.  This study demonstrates that through extremely high resolution XRF/element data we can observe the far-field signature of a SEDEX brine expulsion and thus showing us the way to recognize more biogeochemical events triggered by SEDEX brine expulsions. 
Soil organic carbon dynamics and sequestration potential in cropland-grassland agro-ecosystems
Authors: Guillaume Thomas , Makowski David , Libohova Zamir , Bragazza Luca , Sinaj Sokrat
Published: March 2021

Increasing soil organic carbon (SOC) in agro-ecosystems enables to address simultaneously food security as well as climate change adaptation and mitigation. Croplands represent a great potential to sequester atmospheric C because they are depleted in SOC. Hence, reliable estimations of SOC deficits in agro-ecosystems are crucial to evaluate the C sequestration potential of agricultural soils and support management practices. Using a 30-year old soil monitoring networks with 250 sites established in western Switzerland, we identified factors driving the long-term SOC dynamics in croplands (CR) and permanent grasslands (PG) and quantified SOC deficit. A new relationship between the silt + clay (SC) soil particles and the C stored in the mineral-associated fraction (MAOMC) was established. We also tested the assumption about whether or not PG can be used as carbon-saturated reference sites. The C-deficit in CR constituted about a third of their potential SOC content and was mainly affected by the proportion of temporary grassland in the crop rotation. SOC accrual or loss were the highest in sites that experienced land-use change. The MAOMC level in PG depended on the C accrual history, indicating that C-saturation level was not coincidental. Accordingly, the relationship between MAOMC and SC to determine soil C-saturation should be estimated by boundary line analysis instead of least squares regressions. In conclusion, PG do provide an additional SOC storage capacity under optimal management, though the storage capacity is greater for CR.
Optical properties of smoke particules from Australian 2019-20 wildfires derived from lidar measurements at the French Antarctic station Dumont d’Urville
Authors: Tencé Florent , Jumelet Julien , Sarkissian Alain , Bekki Slimane , Khaykin Sergey
Published: March 2021

Australia experienced an unprecedented fire season from August 2019 to March 2020, now colloquially named as Black Summer. As a warming climate could tend to enhance wildfire seasons, it is critical to study their impact on a large scale : pyrocumunolimbus (pyroCb) events directly inject large quantities of material into the stratosphere, from which aerosols can then be transported due to the general circulation patterns. Stratospheric aerosols have an important impact on the radiative budget of the Earth : directly, through the change in albedo they imply, and indirectly, enhancing nucleation processes.

The pyrocumunolimbus events triggered by these wildfires between 2019/12/29 and 2020/01/04 raised the stratospheric aerosol load of the Southern Hemisphere to a rarely observed level and we hereby present the optical signatures and characterization of the smoke-related aerosols detected at the French Antarctic station Dumont d’Urville (66.6°S – 140°E) since their first detection in november 2019 and their presence throughout the 2020 year after long range transport. Combined with satellite measurements from OMI and OMPS, lidar measurements allow us to follow the time evolution of these aerosol layers, their vertical distribution in altitude as well as their optical properties and assessment of the lidar ratio. As the groundbased instrumental coverage remains sparse in the Southern Hemisphere and especially in Antarctica, such events highlight the importance of running monitoring programs at high latitudes.
Field measurements of soil denitrification using 15N gas flux
Authors: Matson Amanda , Lempio Dirk , Höppner Frank , Well Reinhard
Published: March 2021

Accurate models of soil N cycling are an important tool for optimizing N use efficiency within agricultural systems and predicting N emissions to the environment. However, within such models, denitrification remains a challenge to describe and predict. One issue in achieving accurate denitrification estimates is the limited number of soil N2 flux datasets that can be used to validate model estimates. Measurements of soil denitrification, which include both N2O and N2 fluxes, are challenging, however, due to methodological limitations for the measurement of N2 and the heterogeneity of denitrification in soils.

As part of the DFG-research unit “Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)”, we are building on previous data collected from laboratory incubations to take in situ field measurements. We use soil flushing and stable isotope techniques, combined with real-time monitoring of soil conditions, to assess the response of soil denitrification to a variety of control factors. These include: soil texture, previous crop, irrigation, and fertilizer application, in addition to the ambient changes in field conditions over one growing season of winter wheat. Both natural abundance and 15N labeling of the soil mineral N pool will be used to assess denitrification pathways.

Here we introduce the experimental field setup, summarize key elements of method testing and present early results of N2 and N2O. Once complete, this data set will provide valuable insight into the temporal and spatial heterogeneity of denitrification in agricultural soils. Data will be used to calibrate newly developed DASIM models as well as denitrification sub-modules of existing biogeochemical models.
Transect across the External Pamir thrust belt and Main Pamir Thrust along the Altyn Darya valley, Kyrgyzstan
Authors: Kley Jonas , Voigt Thomas , Sobel Edward R. , Rembe Johannes , Jie Chen
Published: March 2021

The ca. 35 km long, N-S-trending Altyn Darya valley in Kyrgyzstan exposes a nearly complete cross-section of the External Pamir thrust belt (EP), extending from the active Pamir Frontal Thrust in the north to the Main Pamir Thrust (MPT) and some distance into its hanging-wall. The EP comprises a northward imbricated stack of Carboniferous to Late Neogene rocks. From north to south, young clastics of the Alai Valley foreland basin are overthrust by an intensely folded and thrust-repeated frontal stack of Upper Cretaceous to Paleogene limestone, shale and evaporite. Lower Cretaceous red sandstones first emerge above north- and south-verging thrusts forming a triangle zone whose core comprises spectacular isoclinal folds in Upper Cretaceous strata. Towards the south, another thrust imbricate of Lower Cretaceous is overthrust by Late Triassic-Jurassic sandstones and mafic volcanics which are themselves overthrust by an internally deformed, Carboniferous to Triassic succession of, from bottom to top, greywacke and shale, limestone, volcanoclastic conglomerates, variegated sandstone-shale and pink conglomerates. The Carboniferous units in the south are truncated by the MPT which emplaces a succession of greenschist, marble and chert overlain by a km-thick sequence of metamorphosed and deformed, pillow-bearing lavas of Carboniferous age. Structural geometries and fault preference indicate that the basal detachment of the EP deepens southward very gently, stepping down from a detachment in Upper Cretaceous shale to another one near the base of the Lower Cretaceous and eventually a third one in Triassic shale. Cross-section balancing suggests minimum shortening of 75 km for units in the MPT´s footwall. The displacement on the MPT is poorly constrained due to eroded hanging-wall cutoffs, but must exceed 15 km. The basal detachment cuts into basement no earlier than 100 km from the present thrust front, too far south to link up with the top of the Pamir slab.

The stratigraphic succession exposed in Altyn Darya can be readily correlated with less deformed and less metamorphosed transects in westernmost China (Qimgan and Kawuke), some 250 km to the east. A marble-greenschist sequence similar to that carried on the MPT in Altyn Darya has been identified there as a tectonic nappe of the Karakul-Mazar unit, emplaced from the south already in an Upper Triassic to Lower Jurassic (Late Cimmerian) event. If the correlation is correct, then the MPT had a Mesozoic precursor structure extending over much of the E-W striking segment of the Northern Pamir.
The first result of geodetic implications on intra-graben subsidence along the eastern part of the Gediz graben
Authors: Gül Yavuz , Duman Hüseyin , Hastaoğlu Kemal Özgür , Poyraz Fatih , Tiryakioğlu İbrahim , Erdoğan Hediye , Doğan Alperen , Güler Süleyman
Published: March 2021

The Western Anatolian extensional tectonic regime results in developing a set of approximately E-W trending Horst-Graben morphology. The Gediz graben accommodating many fertile lands is one of the significant tectonic structures associated with that regime. Intensive grape cultivation requiring irrigation has been conducted in these lands for many years, which causes a permanent decrease in the water budget as a consequence of increasing farming activities. Hence, we have aimed to clarify better spatial subsidence of the eastern part of the Gediz graben and performed at first InSAR data to obtain land-surface deformations. Towards the middle of graben, the line-of-sight deformation rates of InSAR from LiCSAR products reach gradually up to nearly 10 cm/yr. To confirm these rates, we monumented four continuous GNSS stations.  One of which was located out of the graben while the rest were at the graben in June 2020. Analysis of such a short time-series does not make sense; however, the vertical displacements for the closest stations to the center of the graben reach up to about 8 cm. while out of the graben station seems to be stable visually. It is worth stating that the givens are biased due most likely to the periodic signals. Consequently, the gradually increasing subsidence rates towards the graben center showed that have not been driven only by tectonic settlements but could also be driven by other phenomena. These results are the first results of the ongoing project no 119Y180 supported by TUBITAK.

Keywords: Land subsidence, GPS, InSAR, Gediz Graben
New build homes, resilience and environmental justice – current and future trends in flood risk under climate change across England and Wales
Authors: Rözer Viktor , Surminski Swenja
Published: March 2021

Despite improvements in the management of risk from climate related hazards and the introduction of new regulations, loss and damage caused by climate related hazards remains high. An important driver in many parts of the world is the continuation of new assets being built in hazard prone locations. Over the last decade over 120,000 new homes in England and Wales have been built in areas affected by different types of flooding. While the yearly rates of new homes in areas affected by river, coastal or surface water flooding have increased only moderately on the national level, significant differences between and within regions as well as between different flood types exist. Using property level data on new homes built over the last decade and information on the socio-economic development of neighbourhoods, we analyse spatial clusters of disproportional increase in exposure to single or multiple types of flooding from recently built homes and investigate how these patterns evolve under different future climate change scenarios. We find that a disproportionately higher number of homes built in struggling or declining neighbourhoods between 2008 and 2018 is expected to end up in areas at a high risk of flooding over their lifetime as a result of climate change. Based on these findings, we discuss issues regarding future spending on flood protection and affordability of flood insurance in the face of climate change as well as the transferability of the findings to other climate related hazards.
Conditional Simulation of Precipitation Time Series Using Phase Annealing 
Authors: Mehrvand Masoud , Bárdossy András , Anwar Faizan
Published: March 2021

Precipitation is one of the main inputs for hydrological models. For design purposes observed precipitation at high temporal resolution is often not available. In this case weather generators can be used to simulate realistic precipitation. Synthetic precipitation time series are often produced directly from observed time series using the stochastic methods which are able to reproduce the properties of the observed time series. The main difference and advantage of this research is to generate time series by focusing on the specific properties of the observed time series and trying to obtain these properties indirectly by conducting through investigation on the phases and power spectra and their individual effects using the phase annealing method.

Phase annealing is mainly based on annealing the phases of precipitation time series which are obtained from Fourier transform in order to meet the desired properties. These are obtained from observed time series and defined in the objective function. The outcome is synthetic time series with altered phases while the power spectrum is kept intact yielding new precipitation time series with properties matching those of the observed time series.
Morphological evolution of the middle and lower Seine valley during the Quaternary period.
Authors: Genuite Kim , Nehme Carole , Ballesteros Daniel , Todisco Dominique , Mouralis Damase
Published: March 2021

The Seine river (France) drains today a catchment area of 80,000 km2 covering almost the northern part of France. Despite its importance, few studies focused on the Seine catchment and its landscape evolution, unlike the Somme basin, which remains a European reference for the Quaternary, because of to the numerous archaeological sites it contains. The middle and lower Seine valley in Normandy shows nevertheless a particular meandering fluvial dynamic and a succession of fluvial terraces over 120 m height, dated back to Early Quaternary. Previous works focused on the stratigraphy of alluvial sequences and led to the accurate characterization of lower fluvial and estuarine levels from Marine Isotope Stage (MIS) 1 to MIS 11. The alluvial terraces comprise also various Acheulean industries, showing human settlements in the valley for at least 400,000 years. Such archaeological remnants were retrieved in Saint-Pierre-Lès-Elbeuf, Tourville-la-Rivière, Vernon and La Celle.

Nowadays, the Seine connects to the drowned lower Seine course which continues in the Channel. This submerged part was subaerial during the last glacial cycle. Presently, the lower Seine course is still under the influence of marine tidal effects up to la Bouille (around 30 km from the coast). Additionally, estuarine deposits filled the valley up to Les Andelys (around 80 km from the coast) during the Holocene transgression and cover the penultimate and last glacial alluvial terraces. Nevertheless, the dynamic of the Seine river is broadly identified with few chronological constraints, but without any morphometric analysis combined with stratigraphical study.

This work provides a review of the stratigraphy of the quaternary alluvial deposits in the lower part of the Seine Valley, together with new morphometrical analysis of the paleo-meanders located at higher altitudes. The analysis of the paleo-morphologies compared with high-resolution digital elevation model (DEM), provides new means for constraining the fluvial incision and deposition over long distances and periods, and helps to discuss the river evolution related with quaternary uplift, catchment evolution and glacio-eustatic dynamics.
Investigating the effectiveness of bubble-plume destratification systems in a temperate, shallow, drinking water reservoir
Authors: Waterhouse Jack , Kjeldsen Thomas , Bryant Lee
Published: March 2021

Thermal destratification of lakes and reservoirs is a primary control on dissolved-oxygen levels below the thermocline. In such waterbodies, internal biogeochemical processes are often controlled by a complex set of oxygen-controlled forcing mechanisms. Therefore, preventing stratification by artificial processes has long been an important tool in maintaining dissolved oxygen concentrations and corresponding water quality and ecosystem health in drinking water reservoirs. Blagdon Lake in Somerset, SW England is a medium-size (1.8km2), shallow depth (max: 13.1m) drinking water reservoir. An extensive 6-month field campaign was undertaken in the summer of 2019 at the reservoir, measuring depth profiles of dissolved oxygen, turbidity, conductivity, temperature and pH using an EXO3 multiparameter sonde and a CastAway® CTD. In addition, two thermistor chains were permanently installed measuring temperature and dissolved oxygen concentrations using Onset TidbiT v2 loggers (1m depth intervals) through the water column at 30-minute temporal resolution and a miniDOT oxygen logger at the sediment-water interface respectively. These thermistor chains collected data from summer 2019 – autumn 2020. The data from this field campaign were analysed to investigate the effectiveness of the installed bubble-plume destratification system present at Blagdon Lake, SW England. Similar systems are used in 66% of UK reservoirs employing artificial mixing infrastructure, though very little has been published evaluating their effectiveness in such temperate, shallow, drinking water reservoirs. Initial analysis of the results indicates that the bubble-plume system, nor wind shear is effectively preventing spring/summer destratification for long periods, and that neither are the main factor controlling thermal stratification in Blagdon Lake. The data provides a unique opportunity to directly assess the impact of bubble-plume aerators and their effectiveness at thermal destratification to control dissolved oxygen and water quality in temperate, shallow water bodies.
Identifying and linking flash flood prone atmospheric conditions to flooding occurrences in central Western Europe
Authors: Meyer Judith , Douinot Audrey , Neuper Malte , Mathias Luca , Tamez-Meléndez Carol , Zehe Erwin , Pfister Laurent
Published: March 2021

In recent years, flash floods occurred repeatedly in temperate regions of central Western Europe (e.g., Orlacher Bach (GER), Hupselsebeek (NL), White Ernz (LUX)). This type of extreme flood events is unusual for these regions, as opposed to Mediterranean catchments that are more prone to flash floods. In the second half of the 20th century, and more specifically in the 1990’s, westerly atmospheric fluxes were the dominating triggering factor of large scale (winter) floods in central Western Europe.

With a view to gain a better understanding of the mechanisms controlling the recent flash flood events at higher latitudes, we explore various avenues related to the non-stationarity of environmental systems. We hypothesize that an increase in the occurrence of flash flood prone atmospheric conditions has recently led to higher precipitation totals and a subsequent increase in flash flood events in central Western Europe.

Therefore, we first analysed relevant atmospheric parameters from the ERA 5 reanalysis dataset. Second, we linked the atmospheric parameters to the concept of general circulation patterns as per Hess and Brezowsky (1977). Third, we analysed precipitation data from a set of stations located in the Moselle river basin (35.000 km2). These three pillars build the base for identifying flash flood prone atmospheric conditions over space and time that are then compared to actual occurrences of extreme discharge events in streams within the Moselle river basin.

To validate our hypothesis, spatial and temporal patterns in the occurrence of extreme precipitation and discharge events need to match atmospheric patterns. Preliminary results suggest that daily precipitation data and meridional circulation patterns do not show a clear trend towards an increased occurrence of precipitation events or higher precipitation amounts. Due to the limitations inherent to the available long-term dataset of daily data, the hypothesis can only be partly evaluated, and more detailed analyses are added. For that reason, discharge data with a 15-minute resolution, along with precipitation radar data of 5-minute time steps will be employed at a limited spatial extent in future analyses. In case of rejection of our working hypothesis this may pinpoint to other flash flood triggering mechanisms, such as changes in land use, soil moisture conditions or cultivation methods.
Evolution of Dryness/Wetness conditions and their characteristics (duration and severity) across Upper Jhelum Basin, Pakistan
Authors: Ansari Rubina , Grossi Giovanna
Published: March 2021

Global warming and anthropogenic activities have significantly altered the hydrological cycle and amplified the extreme events (floods and droughts) in many regions of the world, with associated environmental, economic, and social losses. For effective hydro extremes hazards management, it is significant to understand how climate change influences the occurrence, duration, and severity of the regional dryness/wetness conditions (droughts/floods). The present study was carried out over Upper Jhelum Basin (UJB) in Pakistan which lies in the western Himalaya, a most effected mountainous range by Climate Change. Firstly, a suitable gridded precipitation dataset was selected/chosen among various datasets (APHRODITE, CHIRPS, ERA5, PGMFD, MSWEP) through spatio-temporal comparison against in situ data at monthly, seasonal, and annual scale. Secondly, selected gridded data was adjusted for biases using linear (Linear scaling-LS, Local intensity scaling-LOCI) and nonlinear (Power transformation-PT and Distribution mapping-DM) statistical methods. Finally, standardized precipitation index (SPI) at multiple time scale was used to analyses dryness/wetness conditions in the Upper Jhelum Basin over a 35-year period (1981–2015). Results show the higher capability of ERA5 data to represent the UJB precipitation patterns with correlation coefficient (r=0.79) and normalized standard deviation (nSD=1.1), despite of overestimation especially during peak months. Regarding precipitation bias adjustment, all methods were able to correct the mean values while LOCI and DM take advantage over other two methods to correct wet-day probability and precipitation intensity. The SPI analysis at different time scales showed that wet periods occurred more in the first half of the study period, but at later years, drying periods ranging from moderate to severe continue to be seen with increasing frequency. A strong change in dry/wet conditions was observed around years 1997/1998. This change may be the result of the strongest El Nino event (1997-98) occurred in the history. However, further studies are still needed to check whether there is only a large multi-decadal variation or dry conditions will prevail in future. Overall, these findings would assist to better understand the changing pattern of extreme events with climate variability and help water resources managers to develop basin wide appropriate mitigation and adaptation measures to combat climate change and its consequences. 
Actual evaporation from bare soils - A comparison of numerical modelling and field lysimeter data
Authors: Joshi Deep Chandra , Peters Andre , C. Iden Sascha , Zimmermann Beate , Durner Wolfgang
Published: March 2021

Predicting evaporation from drying soils under limited water supply conditions, where water transfer to the atmosphere is limited primarily by soil hydraulic conductivity, is challenging. The parameterization of soil hydraulic properties (SHP) plays a crucial role in reliable predictions of evaporation. In particular, there are expected differences between traditional functions that consider water flow only in capillaries and functions that additionally consider non-capillary processes, i.e., water storage and film flow on particle surfaces and in corners and channels of pores. The non-capillary processes in simulating evaporation from soil surfaces become more important when the soil dries.

The purpose of this study was to investigate the applicability of different soil hydraulic function types in modelling the actual evaporation under water-limited conditions. Data were obtained from a large bare-soil field lysimeter (2.5 m height; 1 m2 surface area), where the lysimeter mass and outflow were measured in hourly time intervals. Precipitation and actual evaporation were calculated from the mass changes of the lysimeter, using a simplified version of the AWAT filter approach of Peters et al. (2017). Meteorological parameters to calculate the potential evaporation were taken from the nearest weather station. Potential evaporation rates were obtained by (i) using the FAO-56 version of the Penman-Monteith equation and (ii) scaling these values to match the bare soil potential evaporation.

The evaporation was simulated using two different models for soil hydraulic properties: i) van Genuchten Mualem (VGM) (only capillary storage and flow), and ii) Peters-Durner-Iden (PDI) (capillary and non-capillary storage and flow). The results show a systematic difference in evaporation prediction by applying the PDI and VGM models, with higher evaporation rates for the PDI model under dry conditions.
Statistical estimates of auroral Pedersen conductance using electric and magnetic measurements by the Swarm spacecraft
Authors: Vanhamäki Heikki , Aikio Anita , Kauristie Kirsti , Käki Sebastian , Knudsen David
Published: March 2021

Height-integrated ionospheric Pedersen and Hall conductances play a major role in ionospheric electrodynamics and Magnetosphere-Ionosphere coupling. Especially the Pedersen conductance is a crucial parameter in estimating ionospheric energy dissipation via Joule heating. Unfortunately, the conductances are rather difficult to measure directly in extended regions, so statistical models and various proxies are often used.

We discuss a method for estimating the Pedersen Conductance from magnetic and electric field data provided by the Swarm satellites. We need to assume that the height-integrated Pedersen current is identical to the curl-free part of the height integrated ionospheric horizontal current density, which is strictly valid only if the conductance gradients are parallel to the electric field. This may not be a valid assumption in individual cases but could be a good approximation in a statistical sense. Further assuming that the cross-track magnetic disturbance measured by Swarm is mostly produced by field-aligned currents and not affected by ionospheric electrojets, we can use the cross-track ion velocity and the magnetic perturbation to directly estimate the height-integrated Pedersen conductance.

We present initial results of a statistical study utilizing 5 years of data from the Swarm-A and Swarm-B spacecraft, and discuss possible applications of the results and limitations of the method.
Seafloor topography variations mapped by regional gravity tensor analysis 
Authors: Seoane Lucia , Ramillien Guillaume , Darrozes José , Frappart Frédéric , Rouxel Didier , Schmitt Thierry , Salaun Corinne
Published: March 2021

The AGOSTA project initially proposed by our team and lately funded by CNES TOSCA consists of developing efficient approaches to restore seafloor shape (or bathymetry), as well as lithospheric parameters such as the crust and elastic thicknesses, by combining different types of observations including gravity gradient data. As it is based on the second derivatives of the potential versus the space coordinates, gravity gradiometry provides more information inside the Earth system at short wavelengths. The GOCE mission has measured the gravity gradient components of the static field globally and give the possibility to detect more details on the structure of the lithosphere at spatial resolutions less than 200 km. We propose to analyze these satellite-measured gravity tensor components to map the undersea relief more precisely than using geoid or vertical gravity previously considered for this purpose. Inversion of vertical gravity gradient data derived from the radar altimetry technique also offers the possibility to reach greater resolutions (at least 50 km) than the GOCE mission one. The seafloor topography estimates are tested in areas well-covered by independent data for validation, such as around the Great Meteor guyot [29°57′10.6″N, 28°35′31.3″W] and New England seamount chain [37°24′N 60°00′W, 120° 10' 30.4" W] in the Atlantic Ocean as well as the Acapulco seamount [13° 36' 15.4" N, 120° 10' 30.4" W] in the Central Pacific.
Tectonic stylolites as a valuable stress archive – new insights from Late Cretaceous intra-plate stresses in Europe
Authors: Köhler Saskia , Koehn Daniel
Published: March 2021

The importance of paleostress analysis is dramatically increasing due to its application in diverse fields, such as sustainable exploration of resources, reservoir potential or storage sites. A good understanding of the subsurface geology, the geological stress-history and associated fracture and fault networks is essentially for these applications. Understanding of the complete paleostress history is not only of interest for applied research, but also for an understanding of the dynamics of geological processes in general. In recent years a diverse toolbox of stress inversion methods has been developed including stress inversion from tectonic stylolites (and slikolites). The pressure solution structures not only preserve the direction of the largest principle stress – they are an archive for the complete stress tensor and the absolute stress magnitude at the moment of their development. Here we present the first results of a systematic study of this upcoming method. For comparison we preformed roughness analysis of tectonic stylolites from Mesozoic limestone from SE Germany. In late Cretaceous the area was affected by shortening in a NE-SW direction, which is clearly illustrated by fault-slip analysis and the orientation of tectonic stylolites. During this tectonic event the stress regime changed from thrusting to strike-slip, with the sampled stylolites persevering the transition between these two stress events. With our preliminarily results we show that roughness analysis of tectonic stylolites enables us to record short time intervals during phases of contraction, and therefore offers crucial insights into stress history and tectonic processes with pulsating stress fields.
A hemispheric-wide performance assessment of the CMIP models based on recurrent atmospheric circulation patterns for use in regional climate studies
Authors: Brands Swen
Published: March 2021

The present study provides an exhaustive performance assessment of the the global climate models participating in the Coupled Model Intercomparison Project Phase 5 and 6 for the northern hemisphere extratropics. Meant as a direct answer to the request for model selection criteria tailored to the requirements of the downscaling and bias correction communities, the evaluation is based on the climatological frequencies of recurrent regional atmospheric circulation patterns as defined by Lamb (1972). In total, 126 historical integrations from 51 different models are assessed, taking into account the effects of internal model variability and reanalysis uncertainty. Three problematic regions (the southwestern United States, the Gobi desert, Greenland and the surrounding seas) are detected where reanalysis uncertainty considerably alters any attempt to rank the models. In the remaining regions, this kind of uncertainty is generally negligible. It is shown that the best performing models are not necessarily the most complex ones, where complexity is here defined as the number of realms considered by the coupled model configuration. Internal model variability only has a small effect on the overall results and, even at the grid-box scale, shifts the ranks only by a few integers. On average, the model versions used in CMIP6 perform better than their CMIP5 predecessors and so do classical atmosphere-ocean global circulation models (AOGCMs) if compared with fully comprehensive Earth System Models (ESMs). Both findings can be explained by a moderately strong relationship between the models’ performance and the horizontal resolution of the atmospheric model component (r = 0.65), which tends to be finer in CMIP6 if compared with CMIP5 and in the AOGCMs if compared with the ESMs. The study provides an objective model ranking based on performance for any region of then northern hemisphere extratropics that can be used for model selection in regional climate studies. Since model complexity should be also taken into account, the overall ranking is complemented by separate rankings for the AOGCM and ESM families. The role of model complexity as a selection criteria should be further discussed in the future.

Reference: Lamb, H.: British Isles Weather types and a register of daily sequence of circulation patterns, 1861-1971, Geophysical Memoir, 116, 85pp., HMSO, 1972.

 
Consistent retrieval of cloud/aerosol single scattering properties and surface reflectance
Authors: Luffarelli Marta , Govaerts Yves
Published: March 2021

The CISAR (Combined Inversion of Surface and AeRosols) algorithm is exploited in the framework of the ESA Aerosol Climate Change Initiatiave (CCI) project, aiming at providing a set of atmospheric (cloud and aerosol) and surface reflectance products derived from S3A/SLSTR observations using the same radiative transfer physics and assumptions. CISAR is an advance algorithm developed by Rayference originally designed for the retrieval of aerosol single scattering properties and surface reflectance from both geostationary and polar orbiting satellite observations.  It is based on the inversion of a fast radiative transfer model (FASTRE). The retrieval mechanism allows a continuous variation of the aerosol and cloud single scattering properties in the solution space.

 

Traditionally, different approaches are exploited to retrieve the different Earth system components, which could lead to inconsistent data sets. The simultaneous retrieval of different atmospheric and surface variables over any type of surface (including bright surfaces and water bodies) with the same forward model and inversion scheme ensures the consistency among the retrieved Earth system components. Additionally, pixels located in the transition zone between pure clouds and pure aerosols are often discarded from both cloud and aerosol algorithms. This “twilight zone” can cover up to 30% of the globe. A consistent retrieval of both cloud and aerosol single scattering properties with the same algorithm could help filling this gap.

 

The CISAR algorithm aims at overcoming the need of an external cloud mask, discriminating internally between aerosol and cloud properties. This approach helps reducing the overestimation of aerosol optical thickness in cloud contaminated pixels. The surface reflectance product is delivered both for cloud-free and cloudy observations.  

 

Global maps obtained from the processing of S3A/SLSTR observations will be shown. The SLSTR/CISAR products over events such as, for instance, the Australian fire in the last months of 2019, will be discussed in terms of aerosol optical thickness, aerosol-cloud discrimination and fine/coarse mode fraction.