bluuebunny/crossref_metadata_2025 huggingface dataset:
Universal Differential Equation for Diffusion-Sorption Problem in Porous Media Flow
Authors: Praditia Timothy , Oladyshkin Sergey , Nowak Wolfgang
Published: March 2021

Artificial Neural Networks (ANNs) have been widely applied to model hydrological problems with the increasing availability of data and computing power. ANNs are particularly useful to predict dynamic variables and to learn / discover constitutive relationships between variables. In the hydrology field, a specific example of the relationship takes the form of the governing equations of contaminant transport in porous media flow. Fluid flow in porous media is a spatio-temporal problem and it requires a certain numerical structure to solve. The ANNs, on the other hand, are black-box models that lack interpretability especially in their structure and prediction. Therefore, the discovery of the relationships using ANNs is not apparent. Recently, a distributed spatio-temporal ANN architecture (DISTANA) was proposed. The structure consists of transition kernels that learn the connectivity between one spatial cell and its neighboring cells, and prediction kernels that transform the transition kernels output to predict the quantities of interest at the subsequent time step. Another method, namely the Universal Differential Equation (UDE) for scientific machine learning was also introduced. UDE solves spatio-temporal problems by using a Convolutional Neural Network (CNN) structure to handle the spatial dependency and then approximating the differential operator with an ANN. This differential operator will be solved with Ordinary Differential Equation (ODE) solvers to administer the time dependency. In our work, we combine both methods to design an improved network structure to solve a contaminant transport problem in porous media, governed with the non-linear diffusion-sorption equation. The designed architecture consists of flux kernels and state kernels. Flux kernels are necessary to calculate the connectivity between neighboring cells, and are especially useful for handling different types of boundary conditions (Dirichlet, Neumann, and Cauchy). Furthermore, the state kernels are able to predict both observable states and mass-conserved states (total and dissolved contaminant concentration) separately. Additionally, to discover the constitutive relationship of sorption (i.e. the non-linear retardation factor R), we regularize its training to reflect the known monotonicity of R. As a result, our network is able to approximate R generated with the linear, Freundlich, and Langmuir sorption model, as well as the contaminant concentration with high accuracy.
Middle Miocene rise of the Greater Himalaya establishing a new orographic barrier
Authors: Thiede Rasmus , Scherler Dirk , Glotzbach Christoph
Published: March 2021

The Himalaya is the highest and steepest mountain range on Earth and an efficient north-south barrier for moisture-bearing winds. The close coupling of changes in topography, erosion rates, and uplift has previously been interpreted as an expression of a climatic control on tectonic deformation. Here, we present 17 new zircon U/Th-He (ZHe) bedrock-cooling ages from the Sutlej Valley that – together with >100 previously published mica 40Ar/39Ar, zircon and apatite fission track ages – allow us to constrain the crustal cooling and exhumation history over the last ~20 Myr. Using 1D-thermal modeling, we observe a rapid decrease in exhumation rates from >1 km/Myr to <0.5 km/Myr that initiated at ~17-15 Ma across the entire Greater and Tethyan Himalaya, as far north as the north-Himalayan Leo Pargil gneiss dome. This decrease is recognized both in the hanging and footwall of major Miocene shear zones and suggests that cooling is associated to surface erosion rather than to tectonic unroofing. We explain the middle Miocene deceleration of exhumation with major reorganization of Himalayan deformation and the onset of the growth of the Lesser Himalayan duplex. This resulted in accelerated uplift of the Greater Himalaya above a mid-crustal ramp, and thus forming a new efficient orographic barrier. The period of slow exhumation in the upper Sutlej Valley coincides with a period of internal drainage in the south-Tibetan Zada Basin further upstream, which we interpret to be a consequence of tectonic damming of the upper Sutlej River. External drainage of the Zada Basin was re-established ~1 Ma, when we observe exhumation rates in the upper Sutlej Valley to accelerate again. Our new finding document that the location of tectonic deformation processes control the first order spatial pattern of both climatic zones and erosion across the orogen.
Multiphase buffer theory explains contrasts in atmospheric aerosol acidity
Authors: Zheng Guangjie , Su Hang , Wang Siwen , Andreae Meinrat , Pöschl Ulrich , Cheng Yafang
Published: March 2021

Aerosol acidity largely regulates the chemistry of atmospheric particles, and resolving the drivers of aerosol pH is key to understanding their environmental effects. We find that an individual buffering agent can adopt different buffer pH values in aerosols and that aerosol pH levels in populated continental regions are widely buffered by the conjugate acid-base pair NH4+/NH3 (ammonium/ammonia). We propose a multiphase buffer theory (Zheng et al., 2020, Science) to explain these large shifts of buffer pH, and we show that aerosol water content and mass concentration play a more important role in determining aerosol pH in ammonia-buffered regions than variations in particle chemical composition. Our results imply that aerosol pH and atmospheric multiphase chemistry are strongly affected by the pervasive human influence on ammonia emissions and the nitrogen cycle in the Anthropocene.

References:

Zheng, G., Su, H.*, Wang, S., Andreae, M. O., Pöschl, U., and Cheng, Y.*: Multiphase buffer theory explains contrasts in atmospheric aerosol acidity, Science, 369, 1374-1377, 2020.
Ice flow localisation enhanced by composite ice rheology 
Authors: Räss Ludovic , Duretz Thibault
Published: March 2021

Ice’s predominantly viscous rheology exhibits a significant temperature and strain-rate dependence, commonly captured as a single deformation mechanism by Glen's flow law. However, Glen’s power-law relationship may fail to capture accurate stress levels at low and elevated strain-rates ultimately leading to velocity over- and under-estimates, respectively. Alternative more complex flow laws such as Goldsby rheology combine various creep mechanisms better accounting for micro-scale observations resulting in enhanced localisation of ice flow at glacier scales and internal sliding.

The challenge in implementing Goldsby rheology arises with the need of computing an accurate partitioning of the total strain-rate among the active creep mechanisms. Some of these mechanisms exhibit grain-size evolution sensitivity potentially impacting the larger scale ice dynamics.

We here present a consistent way to compute the effective viscosity of the ice using Goldsby rheology for temperature and strain-rate ranges relevant to ice flow. We implement a local iteration procedure to ensure accurate implicit partitioning of the total strain-rate among the active creep mechanisms including grain-size evolution. We discuss the composite deformation maps and compare the results against Glen's flow law. We incorporate our implicit rheology solver into an implicit 2D thermo-mechanical ice flow solver to investigate localisation of ice flow over variable topography and in shear margin configurations. We quantify discrepancies  in surface velocity patterns when using Goldsby rheology instead of Glen's flow law.
Comparison between IPSL Venus Global Climate Model results and aerobraking data
Authors: Martinez Antoine , Lebonnois Sébastien , Chaufray Jean-Yves , Millour Ehouarn , Pierron Thomas
Published: March 2021

For fifteen years, a Global Climate Model (GCM) has been developed for the Venus atmosphere at Institut Pierre-Simon Laplace (IPSL), in collaboration between LMD and LATMOS, from the surface up to 150 km altitude. Its recent extension up to the exobase (roughly 250 km) within the framework of the VCD project now allows us to simulate the Venusian upper atmosphere and the key atmospheric parameters of the aerobraking phases. The aim of this presentation is to study the evolution of the density of the Venusian upper atmosphere as a function of different parameters such as solar irradiance, latitude, local time and zenith solar angle (SZA), for regions from 130 to 180 km of altitude. We will present here several comparisons of the upper atmosphere of Venus between our model results and a selection of aerobraking data from different missions such as Venus Express, Pioneer Venus and Magellan.
Rainfall simulation experiments in vineyards comparing two different plot scales
Authors: Neumann Martin , Kavka Petr , Devátý Jan , Strouhal Luděk , Tejkl Adam , Stašek Jakub , Kubínová Romana , Rodrigo-Comino Jesús
Published: March 2021

Vineyards are vulnerable to soill loss due to the several inherent factors highly discussed in the literature. A lot of research is being carried out on this topic and hundreds of experiments were conducted around the world in past decades. The use of rainfall simulators is very extensive with prominent results; however, the use of different scales is scarce in exact places but using different plot sizes. Small (1-4 m2) and big plots (>4 m2) can detect the initiation of specific processes such as surface runoff and initial of soill particle detachment. However, mechanisms such as connectivity, sedimentation or linear erosion differ among plot sizes. Also, the size, high water consumption and time-consuming of the big rainfall simulator makes its use something scarce. Therefore, the main goal of this research was to compare the big and small rainfall simulators and the obtained results considering the continuous development of various rainfall simulators on the CTU’s Department of Landscape Water Management (Prague, Czech Republic). The small rainfall simulator with 1x1 m plot and the big one covering two experimental plots of 8x1 m size were used next to each other in a conventional vineyard in the viticultural region of Moravia. The results showed different processes both of them key to understand from a holistic point of view the inititaion of soil erosion processes in vineyards.

This study has been supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS20/156/OHK1/3T/11 and the Project QK1910029.
Hydrological modeling in data sparse environments
Authors: Anwar Faizan , Bárdossy András , Seidel Jochen
Published: March 2021

We demonstrate that in data sparse environments, model parameter uncertainty is not the only cause of concern. To get a meaningful outcome, input data uncertainty has to be taken into account as well. The procedure involved calibration of a hydrological model using recent daily data rich time period along with validation. A historical flood was simulated (after warmup) for which the input data were relatively sparse in space, namely precipitation and temperature, using the calibrated model parameters. Precipitation was assumed to be the main driver of this event. Results showed that by only using interpolated precipitation (e.g. IDW or Kriging), the magnitude and timing of the peak were incorrect, even after using very many different parameter vectors that performed equally well for the recent times. Subsequently, the model was inverted for precipitation i.e. input fields that produced the correct timing, magnitude, dependence in space and distributions were searched for. This was done using a previously developed simulation algorithm. The new fields showed that the same hydrograph could have been produced by two main types of conditions, namely, early snow cover that melted and heavy rain. The plausibility of the simulated fields was also assessed by comparing their structure in space to events in recent times.
Controlled source electromagnetic measurements offshore the Maltese Islands: Implications for offshore freshened groundwater in a carbonate shelf
Authors: Haroon Amir , Micallef Aaron , Faghih Zahra , Jegen Marion , Schwalenberg Katrin , Karstens Jens , Berndt Christian , Garcia Xavier , Kuehn Michel , Rizzo Enzo , Fusi Nicoletta Chiara , Ahaneku Chibuzo Valeria , Petronio Lorenzo , Weymer Bradley A.
Published: March 2021

Carbonate lithologies host considerable quantities of the Earth’s freshwater resources and partially supply a significant amount of the global population with drinkable water.  Although they comprise substantial amounts of the coastlines, it is not known if these carbonate lithologies can sustain freshened groundwater offshore, and if this can help meet future water demands in coastal regions. To date, predicting volumes of freshened groundwater within marine carbonates has been challenging. Here, we integrate controlled source electromagnetic profiles with seismic reflection and core log data to derive a lithological model for the eastern carbonate margin of the Maltese Islands, one of the most water-starved countries in the world. Electrical resistivity models are used to guide lithological inference where seismic data provide limited information due to the superimposed seafloor multiple. We show that resistivity values within the Upper Coralline and Globigerina Limestone formations exceed the measured resistivity of seawater-saturated core log samples by at least a factor of four. This could be indicative of offshore freshened groundwater that occupies the pore space of the low permeability limestone along the eastern Maltese shelf. To validate this observation without further ground-truthing data, we use extensive forward modelling to show that a similar resistivity footprint can be achieved by localized interbedded low-porosity or highly cemented units. However, the spatial extent of such units across the entire eastern Maltese margin is geologically improbable. This points to the occurrence of offshore freshened groundwater that was likely emplaced during the last sea-level lowstand.
Mars’ ionosphere: from our current knowledge to the way forward
Authors: Sanchez-Cano Beatriz
Published: March 2021

The ionosphere of Mars is the conducting layer embedded within the thermosphere and exosphere that is mostly the result of solar EUV photoionization. It is also the layer that links the neutral atmosphere with space, and acts as the main obstacle to the solar wind. The ionosphere’s interaction with the solar wind is a critical aspect that determines the Martian atmospheric evolution, and ultimately the planet’s habitability. This interaction is often referred to as planetary Space Weather, the forecast of which is currently challenging due to the lack of a permanent in-situ solar wind monitor at Mars. Understanding the ionospheric response to solar wind variability is, therefore, essential in order to assess the response of the Martian plasma environment to the dissipation of energy from solar storms, and their impact on current technology deployed on the red planet.

This lecture will focus on our current knowledge of the Martian ionosphere. In particular, I will focus on our recent advances in the understanding of the Martian ionospheric reaction to different Space Weather events during the solar cycle, both from the data analysis and ionospheric modelling perspectives. Some important aspects to consider are the bow shock, magnetic pileup boundary, and ionopause characterization, as well as the behaviour of the topside and bottomside of the ionosphere taking into account the planet’s orbital eccentricity. Moreover, I will show the effect of electron precipitation from large Space Weather events in the very low Martian ionosphere, a region that it is not accessible to in-situ spacecraft observations. Finally, I will conclude the presentation by giving my perspective on some of the key outstanding questions that remain unknown, and I consider they constitute the next generation of Mars’ ionospheric science and exploration.

 
Two-dimensional impurity imaging in polar ice cores sparks new demand for automated image analysis
Authors: Bohleber Pascal , Roman Marco , Vascon Sebastiano , Pelillo Marcello , Barbante Carlo
Published: March 2021

Due to its micron-scale resolution and micro-destructiveness, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is especially suited for the analysis of the oldest and highly thinned sections of polar ice cores. State-of-the-art 2D elemental imaging by LA-ICP-MS has great potential for investigating the location of impurities on the ice sample surface and is crucial to avoid misinterpretation of ultra-fine resolution signals. The impurity imaging with LA-ICP-MS comprises several millions of laser shots fired over just a few square mm. This technique combines new chemical images with visual analysis and, in so doing raises new questions that may be answered through techniques in automated image analysis and computer vision. As an illustration of this new frontier, a selected set of key problems is presented, with first examples of how automated image analysis techniques can help solving them. This concerns the relationship between impurity localization and the grain boundary network as well as the paleoclimate significance of single line profiles along the main core axis. Ultimately, this demonstrates that it is the right time to spark an intensified exchange among the two scientific communities of computer vision and ice core science.
Stochastic modelling of injection-induced seismicity in the Cooper Basin enhanced geothermal system
Authors: Michas Georgios , Vallianatos Filippos
Published: March 2021

Fluid-injections under high pressures into deep “hot” rock formations are routinely performed during the development of Enhanced Geothermal Systems (EGS). Such fluid-injections, which aim to enhance the permeability in the targeted rock formation, can induce intense microseismicity and in some cases even larger magnitude earthquakes. A characteristic of injection-induced seismicity is its spatial migration with time, which is considered indicative of pore-pressure diffusion and the geometry of the stimulated volume in which permeability is enhanced. Understanding the details of earthquake migration during stimulation operations is particularly important for the design of EGS, the management of operations, as well as for the mitigation of hazardous induced earthquakes. Herein, we develop a stochastic model to map the spatiotemporal evolution of injection-induced seismicity. The model is based on the well-established Continuous Time Random Walk (CTRW) theory that has widely been applied in nonlinear transport phenomena in complex heterogeneous media. Within this context, we describe the spatiotemporal evolution of injection-induced seismicity with an appropriate master equation and the time-fractional diffusion equation. Application of the model to two stimulation experiments in the Cooper Basin (Australia) EGS shows that induced seismicity migrates slowly with time away from the injection points according to a subdiffusive process, with waiting times between the successive earthquakes drawn from a broad probability density function with asymptotic power-law behavior. Moreover, we show that the solution of the time-fractional diffusion equation adequately describes the propagation of induced seismicity in time and space, showing a peak of earthquake concentration close to the injection point and a stretched exponential decay for the concentration of distant events. The results demonstrate that the CTRW model can efficiently describe nonlinear diffusion of injection-induced seismicity during stimulation operations in EGS.       

Acknowledgements

The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Number: 00256).
Factors Impacting Performance of the NDSI-Based Operational Snow Cover Monitoring Algorithm in Forested Landscapes
Authors: Muhuri Arnab , Gascoin Simon , Menzel Lucas , Kostadinov Tihomir S. , Harpold Adrian A. , Sanmiguel-Vallelado Alba , López-Moreno Juan I.
Published: March 2021

In cold regions of the world with significant forest cover, a notable volume of precipitated snow resides under the forest cover. In such regions, snow is an abundant and valuable natural resource and assessing the winter extent of snow precipitation is particularly important for forecasting hydroelectric power potential, managing forests for maximizing the spring snowmelt yield, and monitoring animal habitats.

Forest presents challenging scenarios by obscuring much of the underlying snow over the forest floor from the view of the imaging spaceborne sensors. Moreover, due to the prevalence of mixed pixels, particularly in the forested landscapes, merely binarizing pixels into snow/snow-free can introduce errors while integrating the snow-covered area (SCA) information for hydro-climatological modeling. Therefore, the fractional snow-covered area (fSCA), which is a finer representation of the binary SCA and defines the snow-covered fraction of the pixel area, is a more reliable indicator. 

The recently launched High Resolution Snow & Ice (HRSI) monitoring service by Copernicus allows exploitation of the high-resolution Sentinel-2 data by facilitating free distribution of NDSI-based operational snow cover maps. It also offers the feasibility to estimate the fractional snow cover (FSC) without the requirement of any end-member spectra. In this investigation, we assessed the performance of the NDSI-based operational snow cover area (SCA) monitoring algorithm and the associated FSC with respect to factors influencing the algorithm's performance. The investigation focused over test sites located in the northern Sierra Nevada mountain range in California, US and the central Spanish Pyrenees. The analyses indicated that terrestrial characteristics like tree cover density (TCD) and meteorological factors like incoming solar irradiance impacts the performance of the optical satellite-based snow cover monitoring algorithms. A strong dependence of the algorithm's performance on TCD (negatively correlated) and solar irradiance (positively correlated) was observed.
Observational evidence of polar mesospheric ozone loss following substorm events
Authors: Chapman-Smith Keeta , Seppälä Annika , Rodger Craig , Hendry Aaron
Published: March 2021

Ozone in the polar middle atmosphere is known to be affected by charged energetic particles precipitating into the atmosphere from the magnetosphere. In recent years there has been increased interest in the sources and consequences of electron precipitation into the atmosphere. Substorms are an important source of electron precipitation. They occur hundreds of times a year and drive processes which cause electrons to be lost into our atmosphere. The electrons ionise neutrals in the atmosphere resulting in the production of HOx and NOx, which catalytically destroy ozone. Simulations have examined substorm driven ozone loss and shown it is likely to be significant. However, this has not previously been verified from observations. Here we use polar mesospheric ozone observations from the Global Ozone Monitoring by Occultation of Stars (GOMOS) and Microwave Limb Sounder (MLS) instruments to investigate the impact of substorms. Using the superposed epoch technique we find consistent 10-20% reduction in mesospheric ozone in both data sets. This provides the first observational evidence that substorms are important to the ozone balance within the atmosphere. 
Wind effects change in Taihu Lake with climate change background
Authors: Liu Sien , Ye Qinghua , Zhou Jie
Published: March 2021

Large shallow lakes globally are threatened by eutrophication, and climate change is believed to aggregate the situation. Wind, as the most important momentum source and the major contributor to consistently change the hydrodynamic patterns inside the large shallow lakes, is highly susceptible to climate change. Taihu Lake, which is the 3rd largest shallow lake in China and pertains crucial social and economic values, is chosen in this study as an example. Due to climate change, the wind condition of Taihu Lake shows a significantly decreasing trend of wind speed and the frequency of extreme wind events. Previous studies have paid little attention to the climate change effects on wind hydrodynamics and its implications on water quality has not yet been thoroughly described. Here in this study, we use a well-calibrated and validated three-dimensional Delft3D model to investigate the spatial and temporal heterogeneity of wind induced hydrodynamics and its water quality implications with climate change. The model results give a prediction of less current speed, lower wave height and bottom shear stress compared to the reference scenario, while the three dimensionality of flow field remains. Further, water age is used to demonstrate the influence of external nutrient sources, i.e. the input from adjacent river networks in the basin. Large water ages are observed and potentially it would enhance the accumulation of nutrients and deterioration of water quality.
Geomorphic and sedimentary characteristics of ancient Dora Kamiyama rockslide in Tibet Plateau - implications of dynamic process and frictional heating
Authors: Yang Zongji , Liu Shihao , Wang Liyong , Liu Gang , Fu Xiaolong
Published: March 2021

The mechanisms of high-speed and long-runout landslides are mainly reflected in the geomorphological morphology and internal sedimentology of the deposits. The geomorphic and sedimentary characteristics of ancient Dora Kamiyama rockslide in Tibet Plateau was discussed based on field investigation and multidisciplinary tests. The landslide area is divided into three zones: the source area (I), the translation area (II), and the accumulation area (III). Geomorphic features include toreva block, the levee, the transverse ridge, the longitudinal ridge, the hummock and the ridge confined by troughs and the carapace composed of giant blocks were analysed,which are considered as indicators of the dynamic process of the landslide during transport. 3 stages of the rockslide dynamic motion were proposed, including extensional, compressional and radial motions, respectively. Sedimentary features of facies in the rockslide was revealed, including carapace facies, blocky facies, fragmented facies, shear zones, and basal mixed zones, the mineral change process of the rockslide during the movement process and the temperature change of the sliding surface can be obtained based on analyzing the minerals change near the shear zone. The temperature field of the landslide and its movement process can be reconstructed through the temperature change of the shear zone. The results show that frictional heating was generated during complex dynamics interactions. The friction temperature generated by sliding near the fragmented facies was about 870–1470 °C. Based on sedimentary evidence, the dynamic evolution of the rockslide in response to temperature changes were reconstructed based on frictional thermal analysis.
Solar wind compression induced ULF-modulation of whistler-mode waves in the deep inner magnetosphere
Authors: Shang Xiongjun , Liu Si , Xiao Fuliang
Published: March 2021

With observations of Van Allen Probes, we report a rare event of quasiperiodic whistler-mode waves in the dayside magnetosphere on 20 February 2014 as a response to the enhancement of solar wind dynamic pressure (Psw). The intensities of whistler-mode waves and anisotropy distributions of energetic electrons exhibit a ~5 mins quasi-periodic pattern, which is consistent with the period of synchronously observed compressional ULF waves. Based on the wave growth rates calculation, we suggest that the quasiperiodic whistler-mode waves could be generated by the energetic electrons with modulated anisotropy. The Poynting vectors of the whistler-mode waves alternate between northward and southward direction with a period twice the compressional ULF wave's near the equator, also exhibiting a clear modulated feature. This is probably because the intense ULF waves slightly altered the location of the local magnetic minimum, and thus modulated the relative direction of the wave source region respect to the spacecraft. Current results provide a direct evidence that the Psw play an important role in the generation and propagation of whistler-mode waves in the Earth's magnetosphere.
Temperate Alpine glacier surface dynamics linked to collapsing subglacial conduits
Authors: Egli Pascal , Lane Stuart , Irving James , Belotti Bruno
Published: March 2021

If tongues of temperate Alpine glaciers are subjected to high temperatures their topography may change rapidly due to the effects of differential melt related to aspect and debris cover. Independent of local surface melt, the position of subglacial conduits may have an important influence on ice creep and so on changes in topography at the ice surface. This reflects analyses that suggest that subglacial conduits at glacier margins may not be permanently pressurised; and that creep closure rates are insufficient to close subglacial conduits completely. Rapid climate warming may exacerbate this process, due both to surface-melt driven glacier thinning and over-enlargement of conduits due to high upstream melt rates. Over-enlarged conduits that are not permanently pressurised would lead to the development of structural weaknesses and eventual collapse of the ice surface into the conduits. We hypothesise that this collapse mechanism could represent an important and alternative driver of rapid glacier retreat.

In this paper we combine: (1) an extensive survey of glacier margin collapse in the Swiss Alps with (2) intensive monitoring of the dynamics of such collapse at the Otemma Glacier in the south-western Swiss Alps. Daily UAV surveys were undertaken at a high spatial resolution and with precise and accurate ground control. These datasets were used to generate surface change information using SfM-MVS photogrammetry. Surfaces of difference showed surface loss that could not be related to ablation alone. Combining them with three-dimensional ground-penetrating radar (GPR) surveys in the same zone showed that the surface loss was coincident spatially with the positions of sub-glacial conduits, for ice thicknesses between 20 m and 50 m. We show that this form of subglacial conduit collapse is also happening for several other glaciers in the Swiss Alps, and that this mechanism of snout collapse and glacier retreat has become more common than has hitherto been the case. It also leads to temporal patterns of glacier margin retreat that differ from those that might be expected due to glacier mass balance and ice mass flux effects alone.
The 2020 Haenam earthquake sequence: The first observation of a seismic front on the Korean Peninsula migrating in a manner similar to fluid diffusion
Authors: Son Minkyung , Cho Chang Soo , Choi Jin-Hyuck , Jeon Jeong-Soo , Park Yun Kyung
Published: March 2021

Low-magnitude earthquakes (maximum Mw: 3.2) were recorded from late April 2020 onward in the county of Haenam, southwestern South Korea. Moderate to strong earthquakes had not previously been documented in instrumental, historical, or geological records. We identified 226 hypocentres in this earthquake sequence from April 25 to May 11, 2020. The seismic front of this sequence migrated in a manner similar to a diffusing fluid, with a hydraulic diffusivity of 0.012 m2/s. This is the first observation of natural seismicity on the Korean Peninsula imitating fluid diffusion. We applied a cross-correlation approach to detect unrecorded events, and relocated the hypocentres of the 71 previously recorded and 155 newly detected events using data collected at permanent seismic stations; clear linearity was observed at the metre scale. Spatially, the hypocentres were distributed within a 0.3 km × 0.3 km fault plane at a depth of ~20 km, trending west-northwest–east-southeast with a dip of ~70° in the south-southwestern direction. The moment tensor solution of the largest event had a strike of 98°, dip of 65°, and rake of 7°, which correspond to the fault geometry of the relocated hypocentres. The hypocentres progressed toward the upper eastern edge of the lineament. The largest event occurred at a shallow region of the fault plane, in the direction of hypocentre migration. Together, these results showed that the migration sequence of the 2020 Haenam earthquake mimicked the flow of a diffusing fluid. The structural data indicate that a fault–fracture mesh geometry channelled fluid flow, supporting the concept of a “fluid-driven earthquake swarm” for the 2020 Haenam earthquake sequence. Regarding the final parts of the sequence, there appeared to be a second intrusion at the western end, and a permeability barrier at the eastern end, of the fault plane. The well-constrained hypocentre locations in our study provide essential data for future research, and our interpretations of hypocentre migration during this earthquake sequence may help to elucidate the mechanisms driving earthquake swarms under conditions of intraplate stress.
Tectonic regime variety and stability in mantle convection with strain-induced weakening
Authors: Rolf Tobias , Arnould Maëlis
Published: March 2021

Earth's tectonic evolution and its link to global mantle dynamics are controlled by the pre-existing structure of the lithosphere which guides how strain localizes and causes the necessary weakness to (re-)activate plate boundaries. Recent models of global-scale mantle convection have self-consistently reproduced Earth-like tectonic regimes, consistent with several aspects of today’s observed tectonics. In many cases these models ignore the memory on pre-existing deformation though. Here, a mantle convection model is advanced to include the associated rheological inheritance via a parameterization of strain-induced plastic (brittle) weakening. Based on more than 180 simulations in a wide 2D cartesian box, the control of strain-induced weakening on the resulting tectonic regime is demonstrated. Strain-induced brittle weakening impacts the stability fields of the different tectonic regimes observed, but to first order it does not generate new tectonic regimes or change the dynamics of a given regime (e.g., its characteristic surface mobility). A time-dependent plate-like regime similar to Earth's becomes more feasible with decreasing critical strain at (and above) which maximum weakening is observed. It is less feasible with increasing temperature-dependence of the healing rate, but remains a possibility at small critical strain. While the critical yield stress that still allows for plate-like behavior is apparently larger with strain-induced weakening considered, the effective shift (incorporating the yield stress reduction due to strain weakening) is relatively small and only about 10% under the tested conditions. Strain accumulation in stable continental lithosphere is generally small because of the necessity of high rheological strength. This holds true even for continental collision events, although at least some strain is accumulated and preserved following such events in the immediate proximity of the colliding continental margins.

 
Cause-and-effect relations between cosmic rays, electric field, aerosols and clouds
Authors: Stathopoulos Stavros , Misios Stergios , Kourtidis Konstantinos
Published: March 2021

Here we examine the cause-and-effect relations between galactic cosmic rays, electric field, aerosols and clouds over a region of Atlantic Ocean, during a Forbush Decrease (FD) event on 07/12/2015, using Convergent Cross Mapping (CCM) method. For this purpose, we used FD data from the Neuron Monitor Database (NMDB), Potential Gradient data (PG) from Global Coordination of Atmospheric Electricity Measurements (GLOCAEM) and remote sensing data from MODIS/Aqua, namely Aerosol Optical Depth at 550nm (AOD), Cloud Fraction (CF), Cloud Optical Thickness (COT), Cloud Top Pressure (CTP), Cirrus Reflectance (CR) and Cloud Effective Radius-Liquid (CERL). A cause-and-effect relation was found between FD and AOD, CERL, CF and PG, over the region. On the other hand, no causal effect was found between FD and COT, CTP and CR. This research is funded in the context of the project "Cosmic and electric effects on aerosols and clouds” (MIS: 5049552) under the call for proposals “Support for researchers with emphasis on young researchers - Cycle B” (EDULL 103). The project is co-financed by Greece and the European Union (European Social Fund - ESF) by the Operational Programme Human Resources Development, Education and Lifelong Learning 2014-2020.
Bedding into Bags: The material and temporal assemblages of upcycling
Authors: Holdsworth Clare
Published: March 2021

This paper presents an upcycling creative project: bedding into bags. The premise of the project is straightforward; to take an unused everyday household item (a duvet cover) and upcycle this into new products (8 different types of bags). The project develops a growing body of geographical research on the embodied practices of making, wherein the researcher is maker rather than observer. Through close attention to the materiality of making this project reveals the intricate assemblages of  materials and time that upcycling requires. This project responds to calls for a practice-based approach to sustainability that can reveal the possibilities and limitations of ‘doing’ sustainability.
Predicting laboratory earthquakes using machine learning
Authors: van Klaveren Silke , Vasconcelos Ivan , Niemeijer Andre
Published: March 2021

The successful prediction of earthquakes is one of the holy grails in Earth Sciences. Traditional predictions use statistical information on recurrence intervals, but those predictions are not accurate enough. In a recent paper, a machine learning approach was proposed and applied to data of laboratory earthquakes. The machine learning algorithm utilizes continuous measurements of radiated energy through acoustic emissions and the authors were able to successfully predict the timing of laboratory earthquakes. Here, we reproduced their model which was applied to a gouge layer of glass beads and applied it to a data set obtained using a gouge layer of salt. In this salt experiment different load point velocities were set, leading to variable recurrence times. The machine learning technique we use is called random forest and uses the acoustic emissions during the interseismic period. The random forest model succeeds in making a relatively reliable prediction for both materials, also long before the earthquake. Apparently there is information in the data on the timing of the next earthquake throughout the experiment. For glass beads energy is gradually and increasingly released whereas for salt energy is only released during precursor activity, therefore the important features used in the prediction are different. We interpret the difference in results to be due to the different micromechanics of slip. The research shows that a machine learning approach can reveal the presence of information in the data on the timing of unstable slip events (earthquakes). Further research is needed to identify the responsible micromechanical processes which might be then be used to extrapolate to natural conditions.
Investigation of future climate characteristics over the Carpathian Region by “tuning” CORDEX temperature time series – a new perspective
Authors: Torma Csaba Zsolt
Published: March 2021

The answers to the following questions ‘What are the consequences of climate change (warming)…?’ and ‘By when do we have to be prepared for that level of climate change (warming)?’ must be given only with caution. On the one hand, regional or local changes can be inconsistent with global changes, as local processes might not accurately interpreted by global climate models (GCMs) due to their relative coarse resolution. On the other hand, climate model simulations’ outputs are prone to biases compared to observations; furthermore, climate projections can be very different in modelling future temperature characteristics. In this context, while the magnitude of expected change described by a climate model may seem to be reasonable, but the projected temperature is not necessarily realistic (considering the model’s relative bias compared to observations). More specifically, the standard procedure of assessing climate change can be illustrated by taking the mean for a future period (e.g. 2070–2099) and compute the change relative to a reference period (e.g. 1976−2005). Keeping in mind the expected changes based on those projections might come with high degree of uncertainty as simulations might show different mean temperature values for the same assessed periods with even a range of few degrees of °C. When regional climate change is assessed based on at a given regional warming level (WL, e.g. 1.5 °C) added to the observed mean, then the aforementioned uncertainty range is reduced as the models (GCM or regional climate models) are assessed with respect to the same 30-year mean temperature value, but not for the same periods (noting that the WL is defined at regional and not at global scale). Thus the uncertainty of expected changes with regard to temperature can be significantly reduced. In this case an additional uncertainty factor might rise: time, as climate models can reach that WL at different times. Accordingly, we can give information on relative changes with a specific uncertainty as a metric based on the timing of reaching the assessed WL. Aim of the present work is to illustrate the feasibility of this concept for the region of the Carpathian Basin based on high-resolution EURO- and Med-CORDEX simulations.
Estimation of the scale lengths of turbulence from GPS single difference phase observations 
Authors: Kermarrec Gaël , Schön Steffen
Published: March 2021

Signals from the Global Navigation Satellite System (GNSS) travel through the whole atmosphere and encounter fluctuations of the index of refraction. The long-term variations of the tropospheric refractive index delay the signals, whereas its random variations correlate with the phase measurements. The power spectral density of microwave phase difference can be derived from physical considerations by combining results from the Kolmogorov theory and electromagnetic wave propagation. Four different dominant noise regimes are expected. Their cutoff frequencies can be estimated with the unbiased Whittle Maximum Likelihood estimator; They provide information about the scale lengths of turbulence which are directly linked with the size of the eddies or swirling motion present in the free atmosphere. Dependencies of these parameters with the satellite geometry or the time of the day pave the way for a better comprehension of how tropospheric turbulence acts as correlating GNSS phase observations. The result is less empirical modeling of GNSS phase correlations to improve the positioning results and avoid an overestimation of their precision. We use GPS single differences from 290 m distant antenna positions recorded during two days in 2013 in a common clock experiment at the Physikalisch Technische Bundesanstalt in Braunschweig Germany to explain our methodology, based on adequate filtering of the residuals to mitigate multipath effects.
Assessing the hydrologic regime alteration of a Wadi system as a proxy on initial ecological responses to climate change and growing water demand
Authors: Mahmoodi Nariman , Kiesel Jens , Wagner Paul , Fohrer Nicola
Published: March 2021

Most Wadi systems of the world are threatened by climate change and unsustainable consumption through different water use systems (WUS) which can result in an alteration of the hydrologic regime, a deterioration of water resources, and their valuable ecosystems. The objective of this study is to assess the impact of climate change and growing water demand on the alteration of the Halilrood River’s flow regime and the associated impacts on the ecosystem of the Jazmorian wetland in central Iran. The Soil and Water Assessment Tool (SWAT) model is used to simulate the flow regime of the near and far future (2030-2059 and 2070-2099). Based on 32 Indicators of Hydrologic Alteration (IHA) in conjunction with the Range of Variability Approach (RVA) alterations in the flow regime are evaluated. Impacts of three scenarios for future water use (No-, Constant-, and Projected-WUS) are assessed. No-WUS assumes pristine conditions in the future when no water use system are included in the model (no demand) and we only account for the impact of climate change; Constant-WUS assumes unaltered groundwater demand in the future; and Projected-WUS corresponds to the increases in the number of water use systems in the future (increasing demand). Flow regime alteration assessment indicates that climate change will severely affect the magnitude of monthly and annual extreme flows, frequency and duration of high and low Pulses in the Halilrood Basin, especially in the far future. The comparison of model simulations under different scenarios shows that the impact of climate change was more intense when growing water demand in the future is taken into account. The result of the RVA test indicates moderate and high level of changes for 18 indicators, thus likely affecting the environmental flows required for the health of the downstream wetland.
Dust Aerosol trends over the Eastern Mediterranean region during 2003-2019
Authors: Shaheen Abdallah , Wu Renguang , Yousefi Robabeh
Published: March 2021

Dust Aerosol Optical Depth (DAOD) is considered as one of the main sources of uncertainty in the assessment of climate change. In this talk, we present results of DAOD trend over the Eastern Mediterranean (EM) region in the dusty season (April- May- June- and July: AMJJ) during the years 2003-2019 using long-term DAOD from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and the Copernicus Atmosphere Monitoring Service Reanalysis (CAMSRA). MERRA-2 and CAMSRA DAOD displayed significant positive trends during the years 2003-2010 over the region at the rates of 0.007 year−1 and 0.005 year−1, respectively. In contrast, significant negative MERRA-2 and CAMSRA DAOD trends occurred during the years 2010 -2017 with the rates of -0.009 year−1 and -0.004 year−1, respectively. Moreover, trend analysis was also attempted for the Angstrom Exponent (AE440-870) and Fine Mode Fraction (FMF500) from 3 AERONET sits in the region.  AERONET data are compatible with the trend of MERRA-2 and CAMSRA DAOD. This suggests that the aerosols trend on the EM region is influenced by aeolian dust level.