bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Sea Sea Surface Waves In Hurricane Basing On Self-Similarity Concept
Authors: Yurovskaya Mariya , Kudryavtsev Vladimir , Chapron Bertrand
Published: March 2020

The study is based on a simple parametric model, which is an extension of the self-similarity theory for surface waves generated by a wind field. According to the original similarity concept, the development of wind waves can be fully described using the scale of the fetch length (or time) and wind velocity. The aim of the work is to develop a parametric model to describe the wave generation in arbitrary spatio-temporal wind field. We assume that in this case similarity laws are also fulfilled, i.e., the rate of spectral the peak frequency and wave energy change is completely determined by the wave age. The source function is written in a form providing the stationary solution that corresponds to the well-known fetch law, confirmed in numerous experiments.

In order to extend the equations to the two-dimensional case, when the wind change occurs in both directions, it is assumed that the relations stay valid if the wind speed is replaced by its component in spectral peak direction. In this case, the system of equations should be supplemented by an expression for the evolution of spectral peak direction, describing its adaptating to the direction of non-uniform wind.

The algorithm for solving the complete system of equations describing the evolution of wave height, spectral peak frequency, its propagation direction and focusing/defocusing of wave energy, is based on the method of characteristics. To simulate the evolution of waves in a hurricane, we use the calculation in a non-stationary reference system associated with the hurricane. Coordinates, wave peak frequency, energy and direction are calculated along ray trajectory at every discrete time moment. To increase the stability of the numerical scheme, an implicit 4th-order Runge-Kutta method is used.

Test calculations were carried out for the case of the wave development from the coast with a uniform wind and then for an inhomogeneous cyclonic wind field for different hurricane speeds. The calculations reproduce the anisotropy of the energy distribution inside the hurricane and the effect of wave trapping by a moving cyclone. A comparison of the results with available field measurements of wave parameters in tropical cyclones showed their good agreement. The proposed algorithm can be used in wave forecast models and can serve for deeper understanding the wave field formation in extreme conditions.

The work was supported by Russian Science Foundation via grant 17-77-30019 and the Ministry of Education and Science of the Russian Federation under the State Assignment No. 0827-2018-0003.
In-situ Experiment on the Influence of Humidity on the Cyclic and Long-Term Deformation Behavior (CD-A) of the Opalinus Clay at the Mont Terri Rock Laboratory, Switzerland: Excavation of the Twin Niches, First Measurements, Simulations and Analysis
Authors: Maßmann Jobst , Ziefle Gesa , Costabel Stephan , Furche Markus , Graupner Bastian , Hesser Jürgen , Jaeggi David , Königer Franz , Rink Karsten , Schuhmann Rainer , Vowinckel Bernhard , Wieczorek Klaus
Published: March 2020

Claystone is characterized by a complex, highly coupled hydraulic-mechanical behavior. The physical understanding of the related effects is of great importance concerning the stability during the construction phase as well as for the safety assessment of the integrity of a potential repository for high-level nuclear waste. The rock laboratory Mont Terri, Switzerland, provides the unique possibility to conduct in-situ experiments in the Opalinus Clay for a broad international community. The experiment on the influence of humidity on the cyclic and long-term deformation behavior (CD-A experiment) is conducted in the new part of the rock laboratory, which has been finalized in 2019.

To compare the coupled hydraulic-mechanical effects under different conditions, two parallel oriented niches, called twins, have been excavated in autumn 2019. The twins have a length of 11 m and a diameter of 2.3 m and no shotcrete support. The first twin remains under “natural conditions”. Here, the atmospheric conditions are characterized by a seasonal change in air humidity and temperature. This leads to a desaturation of the claystone around the niche. The second twin is locked. In this area, the air conditions imply a high humidity and the desaturation of the claystone will be avoided as much as possible.

In both twins, a geological characterization of drill cores and of rocks exposed in the niches have been carried out. Furthermore, a long-term measurement program of the related parameters has been launched. It includes measurements of the air humidity, the temperature, the deformation (extensometer), the convergence of the niches, the pore water pressure (piezometer) and the water content (Taupe). Additionally, periodic measurements of the permeability, electrical resistivity (ERT), and nuclear magnetic resonance (NMR) on the niche walls as well as petrophysical analyses of drilled cores are planned. Seismic borehole measurements will also be carried out. The measuring program will be accompanied by the numerical simulation of the coupled hydraulic-mechanical effects in the vicinity of the niches. The comparison of the measurements with simulation results considering different model approaches should support the identification of significant physical effects of the complex coupled material behavior.

This contribution will focus on the observations during the excavation of the twin niches and analysis of the first measured data as well as numerical investigations carried out with OpenGeoSys.
Evaluation of the potential of Sentinel-1 and Sentinel-1 data for clay content mapping
Authors: Bousbih Safa , Zribi Mehrez , Lili-Chabaane Zohra , Baghdadi Nicolas , Gorrab Azza , Ben Aissa Nadhira
Published: March 2020

Soil texture is a key parameter in agricultural processes and an important measure for agricultural prediction, water cycle, filtering of pollutants and carbon storage. Besides, its estimation is essential for agronomists, hydrologists, geologists and environmentalists and for modeling in these application areas. Several studies have been based on understanding and modeling the biological, physical and chemical processes in the soil. Regarding the texture of the soil, few researches propose soil texture spatialization, and are generally based on ground measurements. Among other things, field observations or laboratory analyzes are very expensive and are not very representative. Indeed, the soil texture presents a strong heterogeneity even at the scale of a field. It is then necessary to use precise and spatialized information on soils.

These methods are generally based on remote sensing data and particularly optical data to restore soil component. However, these techniques are strongly affected by atmospheric conditions. This constraint is not valid for Radar sensors (Radio Detection And Ranging). Radar data are mainly sensitive to soil moisture and soil roughness, and has also been evaluated for its ability to perform texture measurements.

The aim of this study is evaluate the potential of these techniques based on optical and radar data for soil texture estimation. By its composition, its structure, its texture and its porosity, soil moisture is strongly influenced by the soil nature. With the arrival of Sentinel-1 (S-1) and Sentinel-2 (S-2) ESA spatial missions, data are acquired with high spatial and temporal resolution between July and early December 2017, on a semi-arid area in central Tunisia. This study is therefore conducted using S-2 SWIR (Short-Wave Infrared) bands (B11 and B12, most sensitive to clay) and soil moisture products derived from radar data. And algorithms based on the support vector machine (SVM) and random forest (RF) methods are proposed for the classification and mapping of clay content.

In order to evaluate the approach and determine the adequate data (between optical and radar data) allowing to precisely characterize the clay content, a cross-validation was used. The SWIR bands lead to less satisfactory outcomes compared to soil moisture. With an overall accuracy of approximately 65%, soil moisture achieved the best performance for estimating soil texture. The results also showed that RF and SVM are robust classifiers for texture estimation despite the small number of training data. However, RF displays greater accuracy and speed of simulation compared to SVM.
Model based climate change impact assessment of river water quality in Wales
Authors: Dallison Richard , Patil Sopan
Published: March 2020

Climate change is likely to threaten the consistent provision of clean drinking water in the UK, in terms of both water quantity and quality. Water quality could be especially problematic due to projected increases in extreme weather events such as droughts and flooding, both of which have a deleterious impact on water quality.

This study uses the Soil and Water Assessment Tool (SWAT) with UK Climate Projections (UKCP) 2018 data to model the impacts of a worst-case global emissions scenario (RCP8.5), on water quality for five catchments in Wales, UK. Our five study catchments (Clwyd, Conwy, Dyfi, Teifi, and Tywi) cover approximately 21% of the total area of Wales and are an important source of water supply for the North, West, and South-West Wales regions. We use an ensemble of 12 regionally downscaled Global Climate Models as inputs to account for uncertainty in the projections and temporal snapshots are taken for the 2020-39, 2040-59 and 2060-78 periods. We focus on the concentrations of four specific water quality variables: nitrogen (N), phosphorous (P), suspended sediment (SS), and dissolved oxygen (DO).

At all five catchments, SWAT is calibrated using river flow data only, due to the lack of water quality measurements. SWAT parameters related to water quality are kept at their default values. While this approach increases the uncertainty related to the specific values of water quality variables, it does provide the relative changes in specific water quality variables under future climate conditions. Results show that changing river flow patterns, both long term averages and extreme events, have a large impact on water quality. Concentrations of all four water quality variables show clear correlations with river flow. The largest changes in seasonal water quality are generally observed in spring and autumn, especially for P and N concentrations. Sediment concentrations and DO levels have an inverse relationship, with SS levels increasing with increased river flow and DO levels decreasing.

Results of this study are useful for water resource management and planning, especially in terms of the potential adaptation measures required to cope with the additional treatment required at water treatment works. By taking twenty-year snapshots our study also allows for short, medium and long term solutions to be planned.
Small-scale variations of helium abundance in different large-scale solar wind structures
Authors: Khokhlachev Alexander , Riazantseva Maria , Rakhmanova Liudmila , Yermolaev Yuri , Lodkina Irina , Zastenker Georgy
Published: March 2020

The boundaries between large-scale solar wind streams are often accompanied by sharp changes in helium abundance.  Wherein the high value of relative helium abundance is known as a sign of some large-scale solar wind structures ( for example magnetic clouds). Unlike the steady slow solar wind where the helium abundance is rather stable and equals ~5%, in magnetic clouds its value can grow significantly up to 20% and more, and at the same time helium component becomes more variable.  In this paper we analyze the small-scale variations of solar wind plasma parameters, including the helium abundance variations in different large-scale solar wind streams, especially in magnetic clouds and Sheath regions before them. We use rather long intervals of simultaneous measurements at Spektr-R (spectrometer BMSW) and Wind (spectrometer 3DP) spacecrafts.  We choose the intervals with rather high correlation  level of plasma parameters as a whole to be sure that we are deal with the same plasma stream.  The intervals associated with different large scale-solar wind structures are selected by using of our catalog ftp://ftp.iki.rssi.ru/pub/omni/catalog/. For selected intervals we examine cross-correlation function for Spektr-R and Wind measurements  to reveal the local spatial inhomogeneities by helium abundance which can be observed only at one of spacecrafts, and we determine properties of ones. Such inhomogeneities can be generate by turbulence, which is typically getting more intense in the considered disturbed intervals in the solar wind. The work is supported by Russian Science Foundation grant 16-12-10062.
Eastward Tectonic Escape of Sicily Microplate: preliminary results
Authors: Penza Giulia , Macchiavelli Chiara , Pierantoni Pietro Paolo , Turco Eugenio
Published: March 2020

The complex processes affecting the Tyrrhenian-Apennine System are inevitably reflected in Sicily, here considered as an independent plate starting from 5 Ma and located between Europe and Africa plates and Calabria microplate.

In particular the retreat of the Adriatic-Ionian slab and its fragmentation involve Sicily in a process of escape towards east-southeast due to the space that the slab is creating. At the same time Africa acts as an intender during its convergence with the European plate.

We show here the preliminary results of a study that aims to reconstruct the kinematic evolution of Sicily and its role in the framework of the Tyrrhenian-Apennine System.

First of all we found the margins of the plate, searching for lithospheric structures that can be considered as plate boundaries, using different types of data (high resolution bathymetric maps, seismic sections, geodetic data, focal mechanism of recent earthquakes, gravimetric maps, lithosphere thickness maps…) together with the literature.

The margins are:

-The Sicily Channel, characterized by a series of pull-apart basins related to a dextral trascurrent zone (Sicily-Africa margin);

-The Malta escarpment and the Taormina Line characterized by transpression (Sicily-Calabria margin);

-The Drepano-Ustica seamount also characterized by transpression (Sicily Europe margin).

 

Starting from the structures in the Sicily Channel, we found the Euler pole of rotation between Sicily and Africa using the GPlates software. Thanks to the software we were able to find also Sicily-Europe and Sicily-Calabria poles and the velocity vectors.

Finally, we compared the Euler poles and the velocity vectors with the geological data, trying the best fit of the two and better refine the model.

 

Key Words: Sicily microplate, Sicily Channel, Malta Escarpment, Tyrrhenian-Apennine System.
Impact of reservoir operations and climate variability on regulated flow regimes
Authors: Ferrazzi Marta , Vivian Roberto , Botter Gianluca
Published: March 2020

The simultaneous growth in climate-driven fluctuations of river flow regimes and global freshwater demand threatens the security of anthropogenic and ecologic uses of streamflows. Dams have long been designed to reconcile the conflict between patterns of human water uses and the temporal variability of flows, and are operated worldwide. In this context, there is a need to understand the combined influence of reservoir operations and climate variability on regulated streamflow regimes, and disclose whether observed hydroclimatic fluctuations can be accommodated by existing reservoirs. Here, these issues are addressed through a quantitative analysis of flow regime alterations by dams as driven by heterogeneous uses and variable regulation capacities (i.e., storage capacity scaled to the average inflow). In particular, the concept of streamflow stability is used to compare inter-annual changes in the occurrence probability of synchronous flows observed upstream and downstream of dams. The selection of structures considered in this study is distributed throughout the entire Central-Eastern United States, so as to span heterogeneous hydroclimatic settings and reservoir functions (i.e., flood control, water supply, hydropower production and multi-purpose). Our results reveal that reservoirs devoted to flood control and those operating for water supply produce distinctive impacts on flow regimes. Flood control does not alter the mean discharge downstream, but decreases long-term discharge variability and, thus, homogenize regional flow dynamics. However, regulation for flood control is unable to mitigate the impact of variable climate drivers on the stability of streamflows and hydroclimatic fluctuations typical of unregulated regimes are transferred unaltered in downstream reaches, or even amplified. Water supply, instead, reduces the mean flow of regulated reaches but increases the long-term streamflow variability, thereby enhancing the regional heterogeneity of flows. In this case, regulation smooths inter-annual changes of flow regimes, though at the cost of systematically filtering out medium-to-high discharges, with negative consequences on stream ecosystems. The observed connection between reservoir functions and the features of downstream flow regime alterations by dams represents a critical step forward for a sustainable management of water resources.
Beyond single model and single domain : Using big data to answer fundamental questions in rock magnetism
Authors: Nagy Lesleis , Williams Wyn , Tauxe Lisa , Muxworthy Adrian , Fabian Karl
Published: March 2020

Interpretation of palaeointensity measurements is difficult since natural samples are made up of magnetic grains of different size, shape and chemical composition. Néels single-domain (SD) model is the main theoretical tool used to understand paleomagnetic measurements, but it is limited since it only applies to uniformly magnetized grain assemblies.

Recent work has shown that the single-vortex (SV) state is not only significantly more common than SD as it occupies a much larger range of grain sizes but is also surprisingly thermally stable [1]. As these grains likely account for the majority of the signal measured in the laboratory, they must also be responsible for the range of observations that lead to large inaccuracies in measurement, for example, pTRM tails. Additionally, if we have a clear understanding of the SV state, can we account for the true cooling rate dependence of grain assemblies, and also find a physical link between magnetic coercivity and blocking temperature.

We present a framework of tools for paleomagnetists to interpret measurements in the light of advances in numerical modelling and the increase in speed of modern computers. We hope that these tools will advance our understanding of the basic mechanisms by which samples record and preserve the Earth’s magnetic field and so will allow for the quantification of errors observed in real samples.

[1] L.  Nagy,  W.  Williams,  A.  R.  Muxworthy,  K.  Fabian,  T.  P.  Almeida, P. Ó Conbhuí, and V. P. Shcherbakov. Stability of equidimensional pseudo–single-domain magnetite over billion-year timescales. PNAS 114(39):10356–10360, 2017
Clustering mechanisms of flood occurrence; modelling and relevance to insurance practices
Authors: Manolis Georgios T. , Papoulakos Konstantinos , Iliopoulou Theano , Dimitriadis Panayiotis , Tsaknias Dimosthenis , Koutsoyiannis Demetris
Published: March 2020

Population growth, economic development and risk-blind urbanization often increase exposure to risk, including that due to floods. While rural flooding may affect much larger areas of land, urban floods are more challenging to manage, since the higher population and asset density in the urban environment increase the environmental and social impacts of floods and make the potential flood damages more costly. Therefore, the need for integrated flood insurance policy and products on extended parts of the world is pronounced in order to reduce the financial consequences of extreme flood events, which endanger in many cases the environmental, social and economic stability. As the assessment of the so-called collective risk is a typical issue faced in insurance and reinsurance practices, in this study we investigate the stochastic dynamics of daily stream flow series with particular interest to the existence of clustering mechanisms in floods, which is known to increase the potential risk. We analyse collective risk on the US-CAMELS dataset, treating the streamflow exceedances over given thresholds as proxies for insurance claim amounts. Moreover, we develop modelling and simulation approaches of extreme flows as a step towards the deeper understanding of the relationship between the stochastic patterns of flood occurrence and proxies of insurance claims, paving the way for a more efficient use of the available streamflow records.

Acknowledgement: This research is conducted within the frame of the course "Stochastic Methods" of the National Technical University of Athens (NTUA). The School of Civil Engineering of NTUA provided moral support for the participation of the students in the Assembly.
Observation of dynamic fine structure in ocean using pre-stack seismic data
Authors: Gong Yi , Song Haibin , Fan Wenhao , Guan Yongxian , Zhang Kun
Published: March 2020

We propose a method for observing the dynamic thermohaline fine structure using pre-stack seismic data, and combine it with PIV(Particle-Image-Velocimetry) technology to obtain a series of vertical two-dimensional flow velocity sections.
Because of the redundancy of the multi-channel reflection seismic data, the reflection seismic structure at the same location can be observed multiple times from pre-stack seismic data. First, we extract the common-midpoint gathers (CMPs) from the multi-channel reflection seismic data. Then extract the common-offset gathers (COGs) from CMPs. Finally, a seismic processing sequence, such as noise attenuation, normal move out (NMO), velocity analysis and migration, is applied for imaging the reflection structure in COG sections. These COG sections with different offsets are the images of the thermohaline fine structure of seawater at different times. We apply this method to study a typical internal solitary wave in the Dongsha plateau of the South China Sea. We find that the waveform of the internal solitary wave(ISW) in shallow water region does not change much during propagation, but the front becomes flatter and the rear becomes steeper in deep water region, so there is a ISW shoaling change vertically. 
We apply the PIV technique to the COG pre-stack migrated sections and calculate the flow velocity sections of the internal solitary wave. To verify the correctness of the flow velocity sections, we compare it with the theoretical flow velocity section calculated from the KdV equation. It is found that the two sections are consistent in flow directions, and the PIV result shows the structure of wave induced velocity well. In the PIV calculation results, the average value of the velocity in the horizontal direction is 1.7 m/s, and in the vertical direction is 0.3 m/s. This result is larger than the theory, especially the horizontal velocity. We speculate that the horizontal velocity contains not only the wave induced velocity component of the internal solitary wave but also the phase velocity component.
In summary, we use pre-stack seismic data to observe changes in the thermohaline fine structure during the propagation of internal solitary waves, and find that the waveforms of internal solitary waves vary differently at different depths. We use the PIV technique to calculate the flow velocity section of the internal solitary wave and compare it with the theoretical results. We find that our method is feasible to describe the flow velocity qualitatively, but it needs further improvement in quantitative description. This method has great potential in studying the dynamic evolution of mesoscale or submesoscale ocean processes.
Recent studies on troposphere delay modeling for SLR
Authors: Drożdżewski Mateusz , Boisits Janina , Zus Florian , Balidakis Kyriakos , Sośnica Krzysztof
Published: March 2020

Recent studies on troposphere delay in Satellite Laser Ranging (SLR) show that the compliance of horizontal gradients of troposphere delay reduces the observation residuals, as well as improves the consistency between SLR results and other space geodetic techniques, all of which are essential for the realization of the terrestrial reference frame. In this work, we examine 3 novel approaches of troposphere delay modeling in SLR, with respect to the standard Mendes-Pavlis approach. We test Potsdam Mapping Function (PMF) with mapping function coefficients and linear horizontal gradients which are based on ERA5 reanalysis provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) model with improved time and spatial resolution in comparison to ERA-Interim reanalysis. We also test a solution based on Vienna Mapping Function 3 for optical observations (VMF3o) which considers the separation of the mapping functions for hydrostatic and non-hydrostatic delays and horizontal gradients. Eventually, we test a solution based on Mendes – Pavlis model with a parameterized model for horizontal gradients based on the 16-year time series of horizontal gradients from PMF. To conduct this experiment, we use SLR observations to passive geodetic satellites LAGEOS-1 and LAGEOS-2. From differences of residual standard deviations for all proposed solutions, we observe an improvement of the SLR observation residuals, for low elevation angles above 10% and improvement of the consistency between estimated pole coordinates and the combined solution IERS-14-C04 series with respect to the currently recommended solutions that neglect the horizontal gradients in SLR solutions.
Did the evolution of tropical river systems impact the Cenozoic climate system ? A preliminary study with the IPSL-CM5A2 earth system model.
Authors: Sepulchre Pierre , Bres Julia
Published: March 2020

Driven by plate tectonics and geodynamics, Earth surface has been reshaped during the Cenozoic, with the uplift of numerous mountain ranges. Climate modellers have been tackling the direct impact of these changes on climate for decades, essentially thanks to sensitivity experiments to topography, aiming at quantifying the impact of mountains on atmospheric and ocean dynamics. An indirect consequence of mountain uplift is changes in the continental river routing system, that can be relocated and provide the ocean with freshwater fluxes very different from the present. Here we focus on the Amazon and the Congo river, which routing are known to have been altered by the uplifts of the Andes and the East African Rift System, respectively. We carried out numerical simulations with the IPSL-CM5A2 earth system model in which we alternatively relocated or cut the runoff of these two rivers, and compared the results to simulations where topography only has been changed. We analyze the consequences of the changes in routing in terms of ITCZ position, precipitation spatial patterns, and salinity budgets and associated AMOC strength over the oceans. We show that depending on the region considered, the direct (mechanical) and indirect (hydrology) consequences of uplift on climate can either add up or counteract each other.

 
Experimental study of visco-elasto-plastic deformation of sedimentary rocks
Authors: Sabitova Alina , Yarushina Viktoriya , Stanchits Sergey , Stukachev Vladimir , Myasnikov Artyom , Cheremisin Alexey
Published: March 2020

It is known that understanding of long-term hydrocarbon recovery or CO2 storage problems depend on proper addressing the physical coupling between the fluid flow and mechanical deformation. The success of geo-energy applications such as hydraulic fracturing, wellbore stability, and geological storage of CO2 is directly connected to the comprehensive formulation of appropriate rock rheology. Effective viscosity is an important parameter that allows to couple fluid flow and deformation processes occurring in the Earth. However, this parameter is rarely measured in the laboratories as it is a challenging task. Moreover, few existing measurements were made in the compaction regime and make no reckoning of decompaction. However, decompaction may affect fluid flow distribution in a porous medium and create highly porous channels such as chimneys observed in the subsea reservoirs and caprocks. In this study, we present results of multistage laboratory creep and relaxation experiments that were conducted on different materials including artificial specimens, limestones, heterogeneous shales with sandstone inclusions, and pure sandstones and shales. Both compaction and (de)compaction regimes were considered. We studied the influence of historical changes in the thermal regime during the glaciation and deglaciation cycles, water saturation, preliminary damage of the samples on their viscous behavior. The first stage of the experiment is the initial fast loading to dilation point, where the transition from compaction to dilatancy occurs. The second stage is a purely viscous creep. The third stage is the stress relaxation phase. During the fourth stage, repeated cycles of fast visco-elasto-plastic loading/ unloading were conducted. Effective viscosity was calculated for all samples. Experimental curves are explained using the theoretical model for visco-elasto-plastic (de)compaction of porous rocks.
Detecting active subglacial lakes beneath the Greenland Ice Sheet using ArcticDEM
Authors: Bowling Jade , Leeson Amber , McMillan Malcolm , Livingstone Stephen , Sole Andrew
Published: March 2020

A total of 63 subglacial lakes have been documented beneath the Greenland Ice Sheet using a combination of radio-echo sounding and surface elevation change measurements. Of these, only 7 lakes have shown evidence of hydrological activity over the period 2001-2018. Draining lakes have been observed to drive transient changes in local ice flow speeds in Antarctica. The sudden discharge of water during a subglacial lake outburst event causes the subglacial lake roof to subside, which propagates to the surface, resulting in the formation of collapse basins (typically ~50-70 m in depth). These surface features can be detected using remote sensing techniques.

Whilst over 100 active subglacial lakes have been identified in Antarctica, predominantly beneath ice streams, little is known about the extent, volume of water stored and residence times of active subglacial lakes in Greenland, together with any potential influence of drainage events on local ice dynamics and sediment evacuation rates. Here, we explore the potential of the high resolution ArcticDEM stereogrammetric digital surface model (DSM) open source dataset, generated from satellite optical imagery, to identify and monitor subglacial lake-derived collapse basins. The ArcticDEM provides 2 m time-stamped surface elevation data, covering ~160 million km2, offering an exciting opportunity to map elevation changes between 2009-2017. This study presents the first effort to utilise ArcticDEM data at an ice-sheet scale to identify and monitor active subglacial lakes beneath the Greenland Ice Sheet, which we hope will ultimately improve our understanding of its complex subglacial hydrological system.
After the fire: biogeochemical effects of charcoal and ash on fire-affected landscapes
Authors: Santin Cristina , Jones Matthew W. , Neris Jonay , Doerr Stefan H.
Published: March 2020

Vegetation fires are a global phenomenon that affect 3-5 million km2 every year. Both natural and caused by humans, fire burns through a very broad range of ecosystems, from boreal forest to tropical savannahs, exerting also a very broad range of effects. Despite this huge variability, there are two components always present after a fire: charcoal and ash.

Charcoal, also known as pyrogenic carbon, is a key player in the carbon cycle from fires, due to its ability to act as a carbon sink. In addition, it can play a major role in the functioning of soils via its interactions with other elements and priming of native soil organic matter. Meanwhile, ash, the powdery fire residue, can be an important source of nutrients for the post-fire regrowing vegetation, but it can also be a source of water contamination when transported by wind and water to the hydrological networks after fire. This presentation will give an overview on the current knowledge of these two interlinked components of the wildfire-affected landscapes, highlighting current gaps and future research directions.
Is Climate Change Reversible? CDRMIP simulations of the Earth system response to a massive CO2 increase and decrease (emissions followed by negative emissions).
Authors: Keller David , Lenton Andrew , Scott Vivian , Vaughan Naomi ,   Modelling groups who contributed to the carbon dioxide removal model intercomparison project and CDRMIP steering committee members
Published: March 2020

To stabilize long-term climate change at well-below 2°C (ideally below 1.5°C) above pre-industrial levels, large and sustained CO2 emission reductions are needed.  Despite pledges from numerous governments, the world is not on track to achieve the required reductions within the timeframes outlined in the Paris Agreement, and it appears increasingly likely that an overshoot of the 1.5 or 2 °C temperature target will occur.  If this happens, it may be possible to use carbon dioxide removal methods to return atmospheric CO2 concentrations to lower levels or even to reduce the magnitude of the overshoot, with the hope that lower CO2 will rapidly lead to lower temperatures and reverse or limit other climate change impacts.  Here we present a multi-model analysis of how the Earth system and climate respond during the CMIP6 CDRMIP cdr-reversibility experiment, an idealized overshoot scenario, where CO2 increases from a pre-industrial level by 1% yr-1 until it is 4 times the initial value, then decrease again at 1% yr-1 until the pre-industrial level is again reached, at which point CO2 is held constant.  For many modelled quantities climate change appears to eventually be reversible, at least when viewed at the global mean level.  However, at a local level the results suggest some changes may be irreversible, although spatial patterns of change differ considerably between models.  For many variables the response time-scales to the CO2 increase are very different than to the decrease in CO2 with a many properties exhibiting long time lags before responding to decreasing CO2, and much longer again to return to their unperturbed values (if this occurs).
Changes in European surface ozone air quality over the 21st century
Authors: Stähle Christoph , Rieder Harald , Mayer Monika
Published: March 2020

Surface ozone is a criteria air pollutant, formed by photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs). Despite recent reductions in the surface ozone burden following precursor emission controls (predominantly concerning NOx) the recent European air quality report published by the European Environment Agency (EEA) highlights that to date still 17 EU member states are reporting ozone concentrations that exceed the target value set for the protection of human health (120 µg/m³, maximum daily 8-hour average (MDA8) not to be exceeded more than 25 times per year (3-year average)). In total, 20 percent of all ozone monitoring sites showed ozone concentrations exceeding the EU target value for the protection of human health, and only 5% of monitoring sites showed ozone concentrations in compliance with the more stringent WHO target value. Here we focus on past and future changes in European surface ozone abundances in a set of simulations performed with the Geophysical Fluid Dynamics Laboratory (GFDL) chemistry-climate model CM3. First, we evaluate the general model performance for the recent past by comparing model output to observations available from the EEA Airbase database. The evaluation is performed on the basis of interpolation of the historic site level observations to a grid of 2.5° x 2°, matching the dimensions of the CM3 model. Our results for the recent past show that the modelled ozone abundances are biased high compared to observations. Therefore, we apply a suite of correction techniques (quantile mapping, delta function) to obtain modelled ozone fields in agreement with observations. Emanating from remediated model data the correction functions derived are applied to transient (2006-2100) simulations following selected Representative Concentration Pathways (RCPs). Using these bias-corrected future simulations we illustrate next potential changes in future European surface ozone air pollution over the course of the 21st century.
From machine learning to sustainable taxation: GPS traces of trucks circulating in Belgium
Authors: Adam Arnaud , Thomas Isabelle
Published: March 2020

Transport geography has always been characterized by a lack of accurate data, leading to surveys often based on samples that are spatially not representative. However, the current deluge of data collected through sensors promises to overpass this scarcity of data. We here consider one example: since April 1st 2016, a GPS tracker is mandatory within each truck circulating in Belgium for kilometre taxes. Every 30 seconds, this tracker collects the position of the truck (as well as some other information such as speed or direction), leading to an individual taxation of trucks. This contribution uses a one-week exhaustive database containing the totality of trucks circulating in Belgium, in order to understand transport fluxes within the country, as well as the spatial effects of the taxation on the circulation of trucks.

Machine learning techniques are applied on over 270 million of GPS points to detect stops of trucks, leading to transform GPS sequences into a complete Origin-Destination matrix. Using machine learning allows to accurately classify stops that are different in nature (leisure stop, (un-)loading areas, or congested roads). Based on this matrix, we firstly propose an overview of the daily traffic, as well as an evaluation of the number of stops made in every Belgian place. Secondly, GPS sequences and stops are combined, leading to characterise sub-trajectories of each truck (first/last miles and transit) by their fiscal debit. This individual characterisation, as well as its variation in space and time, are here discussed: is the individual taxation system always efficient in space and time?

This contribution helps to better understand the circulation of trucks in Belgium, the places where they stopped, as well as the importance of their locations in a fiscal point of view. What are the potential modifications of the trucks routes that would lead to a more sustainable kilometre taxation? This contribution illustrates that combining big-data and machine learning open new roads for accurately measuring and modelling transportation.
An overview of the evolution of global debris flow related research from 2010 to 2019 — A bibliometric analysis on based on Web of Science Core Collection
Authors: Xiang Li
Published: March 2020

Abstract: Based on 2246 research articles focusing on the topic of “debris flow” derived from Science Citation Index (SCI) database which were published from 2010 to 2019, this article presents a comprehensive review on the global scientific outputs in this research field. By adopting bibliometric analysis, the most productive journals, authors, institutions and countries were identified. Combining with the visual software, the temporal change of the cooperation scope, degree and intensity on country- and institution- level were discussed. It also provides in-depth investigations on the co-occurrence of author key words, which may contribute to reveal the current research hotspots and future development trends. The results of this study can provide a broad insight for scientific community devoting to debris flow related research field and support for the development of other related research work.
Data quality of Aeolus wind measurements
Authors: Krisch Isabell ,   Aeolus DISC
Published: March 2020

The European Space Agency (ESA)’s Earth Explorer Aeolus was launched in August 2018 carrying the world’s first spaceborne wind lidar, the Atmospheric Laser Doppler Instrument (ALADIN). ALADIN uses a high spectral resolution Doppler wind lidar operating at 355nm to measure profiles of line-of-sight wind components in near-real-time (NRT). ALADIN samples the atmosphere from 30km altitude down to the Earth’s surface or to the level where the lidar signal is attenuated by optically thick clouds.

The global wind profiles provided by ALADIN help to improve weather forecasting and the understanding of atmospheric dynamics as they fill observational gaps in vertically resolved wind profiles mainly in the tropics,  southern hemisphere, and over the northern hemisphere oceans. In January 2020, the European Centre for Medium-Range Weather Forecasts (ECMWF) became the first numerical weather prediction (NWP) centre to assimilate Aeolus observations for operational forecasting.

A main prerequisite for beneficial impact is data of sufficient quality. Such high data quality has been achieved through close collaboration of all involved parties within the Aeolus Data Innovation and Science Cluster (DISC), which was established after launch to study and improve the data quality of Aeolus products. The tasks of the Aeolus DISC include the instrument and platform monitoring, calibration, characterization, retrieval algorithm refinement, processor evolution, quality monitoring, product validation, and impact assessment for NWP.

The achievements of the Aeolus DISC for the NRT data quality and the current status of Aeolus wind measurements will be described and summarized. Further, an outlook on future improvements and the availability of reprocessed datasets with enhanced data quality will be provided.
The FastScape software stack: reusable tools for landscape evolution modelling
Authors: Bovy Benoit , Braun Jean , Cordonnier Guillaume , Lange Raphael , Yuan Xiaoping
Published: March 2020

The name “FastScape” has been used to describe a landscape evolution model as well as a set of efficient algorithms to simulate various processes of erosion, transport and deposition (e.g., fluvial, hillslope and marine). We also use this name for a set of software components (https://github.com/fastscape-lem) aimed at making those models and algorithms readily accessible to a wide range of users, from experts in landscape evolution modelling to scientists, researchers and teachers in the broader Earth science community. Those software components are organised as a stack where each level has a distinct scope. At the bottom of this stack, “fastscapelib-fortran” is the original, full-featured implementation of the FastScape model, which provides a Fortran API as well as Python bindings. Its successor “fastscapelib” is a library written in modem C++ that directly exposes the FastScape algorithms (e.g., flow-routing, depression-resolving, channel erosion, hillslope diffusion) through basic APIs in C++, Python and potentially other languages such as R or Julia in the future. Built on top of those core libraries, “fastscape” is a high-level yet flexible tool that helps anyone who wants to quickly build, extend or simply run FastScape model variants in a user-friendly, interactive environment. Through its xarray-centric interface, it is deeply integrated with the rest of the Python scientific ecosystem, therefore offering great capabilities at user’s fingertips for pre/post-processing, visualisation and simulation management. One of our primary concern is following good practices (API design, testing, documentation, distribution...) while developing each of these tools. We show through a gallery of examples how the FastScape software stack has been used in research and outreach projects. We plan to provide better integration with other tools for topographic analysis/modelling (e.g., Landlab, LSDTopotools) in the future and we also greatly encourage contributions from the broader community.
Geomorphological evidence of active faulting in low seismicity regions - examples from the Valley of Lakes, southern Mongolia
Authors: van der Wal Jorien L.N. , Nottebaum Veit C. , Stauch Georg , Lehmkuhl Frank , Reicherter Klaus
Published: March 2020

The tectonically active northern margin of the Gobi Altai in southern Mongolia is best known for the 1957 Mw 8.1 Bogd earthquake. Cumulative offsets along the Bogd fault indicate that the area was subject to repeated earthquakes in the past. North of the Bogd fault, the Valley of Lakes characterises a seismically quiescent zone between the Gobi Altai and the central Mongolian Hangay dome, with little to no instrumentally recorded earthquakes. However, Quaternary alluvial fans of rivers that drain toward the endorheic lakes in this basin are crosscut by multiple fault scarps with displacements up to 15 m. Additionally, river channel morphology is significantly altered by tectonic lineaments indicating that, despite the lack of recorded seismicity, this area may indeed have been seismically active in the recent past. By applying remote sensing techniques, UAV photogrammetry, and morphometric studies, we aim to understand i) the effect these faults had on the landscape evolution of the Valley of Lakes, ii) their relationship to deformation along the Bogd fault and iii) whether these faults accommodate a significant amount of strain related to the India-Eurasia collision.

The lack of available material for dating requires palaeoseismological studies to make use of morphotectonic observations as an alternative, relative dating method. At the Bogd fault, such studies were combined with sparsely available cosmogenic nuclide age data to determine that vertical slip rates vary between 0.1 and 1 mm/yr on individual faults and at the scale of the entire mountain front, respectively. In the Valley of Lakes, a total lack of age data complicates the extrapolation of slip rates, however scarp degradation indicates that slip rates are likely lower than at the Bogd fault. Fluvial terraces of the Tuyn Gol river are crosscut by at least three major fault scarps, which contribute to valley width variations of the river from ±3500 m to ±20 m at the current fan apex, and which are reflected in steepness index variations along minor drainages. Additionally, a large paleochannel suggests that major drainage reorganisation events took place in Quaternary times, either reflecting periods of high tectonic activity or as a result of significant climate variations. The transtensional nature of some faults in the Valley of Lakes is unique; however fault mechanisms in the area are generally in line with the active deformation in the Gobi Altai. Our results stress the earthquake potential of regions with low instrumental seismicity and demonstrate that deformation in the Gobi Altai may reach further north than previously expected.