bluuebunny/crossref_metadata_2025 huggingface dataset:
Calibrating the Tropospheric Delays of VLBI Observations using Numerical Weather Prediction Models
Authors: Nilsson Tobias , Balidakis Kyriakos
Published: March 2021

The observations of geodetic Very Long Baseline Interferometry (VLBI) are affected by the troposphere, and this effect needs to be considered in the VLBI data analysis. The normal way of doing this is to estimate the zenith tropospheric delays and tropospheric gradients as additional parameter in the analysis. However, due to the poor geometric distributions of the observations in some VLBI sessions, like the Intensives, the tropospheric parameters cannot be estimated with a high accuracy. An alternative is to use external information on the tropospheric delay from Numerical Weather Prediction Models (NWM). Due to the increasing accuracy of the NWM, this alternative is becoming more and more interesting. In this work, we use tropospheric delays from the fifth ECMWF reanalysis, ERA5, in the analysis of VLBI data and evaluate the impacts on the results. We study the impact of different types of VLBI sessions, like Intensives, local networks, and global networks. The results of this study will show to what extent ERA5 data can be used to correct the tropospheric delays in geodetic VLBI. Furthermore, the results also give information on the accuracy of the tropospheric delays from NMW.
Expansion of hot plasma with Kappa distribution in coronal flare sources
Authors: Benáček Jan , Karlický Marian
Published: March 2021

We study how hot plasma that is released during a solar flare can be confined in its source and interact with surrounding colder plasma. The X-ray emission of coronal flare sources is well explained using Kappa velocity distribution. Therefore, we compare the difference in the confinement of plasma with Kappa and Maxwellian distribution. We use a 3D Particle-in-Cell code, which is large along magnetic field lines, effectively one-dimensional, but contains all electromagnetic effects. In the case with Kappa distribution, contrary to Maxwellian distribution, we found formation of several thermal fronts associated with double-layers that suppress particle fluxes. As the Kappa distribution of electrons forms an extended tail, more electrons are not confined by the first front and cause formation of multiple fronts. A beam of electrons from the hot part is formed at each front; it generates return current, Langmuir wave density depressions, and a double layer with a higher potential step than in the Maxwellian case. We compare the Kappa and Maxwellian cases and discuss how these processes could be observed.
Results of measurements of the state of the ozone layer in East Antarctica
Authors: Borisovets Aliaksei , Bruchkouski Ilya , Svetashev Aliaksandr , Krasouski Aliaksandr
Published: March 2021

Regions with an expected low anthropogenic load are of particular interest for monitoring small gas components of the atmosphere. Under such conditions, the concentration of ozone is determined by natural processes. One of these regions is East Antarctica.

The experimental part of the research included:

- Complex of meteorological observations;

- Measurement of total ozone column (TOC) in the vertical column of the atmosphere;

- Monitoring of spectra, levels and doses of surface solar radiation;

The research was carried out in the areas where the Belarusian Antarctic expeditions were based: the stations “Mount Vechernaya” and “Progress”.

The measurements were carried out by a two-channel filter photometer PION-F and an ultraviolet spectroradiometer PION-UV, developed at the NOMREC. When determining the TOC values, the method was used, which consists in restoring the TOC values by analyzing the spectral distribution of the illumination density of the Earth's surface in the UV range. According to this method, the TOC values can be obtained using the ratio of illuminances at two wavelengths of the solar spectrum, one of which falls in the region of sufficiently strong absorption of atmospheric ozone, and the other is outside this region.

During the Belarusian Antarctic expeditions, a significant amount of experimental data was obtained (more than 100,000 spectra of energy illumination, more than 1,000 average daily values of TOC, etc.). The accumulated array of experimental data can be used to study theoretical problems and solve applied problems.

This paper presents a description of the dynamics of TOC in the atmosphere of East Antarctica during the period of seasonal expeditions 2014-2020.
Numerical simulations of wet snow avalanches: interplay between cohesion and friction
Authors: Chambon Guillaume , Faug Thierry , Naaim Mohamed
Published: March 2021

Wet snow avalanches present distinctive features such as unusual trajectories, peculiar deposit shapes, and a rheological behavior displaying a combination of granular and pasty features depending on the actual snow liquid water content. Complex transitions between dry (cold) and wet (hot) flow regimes can also occur during a single avalanche flow. In an attempt to account for this complexity, we report on numerical simulations of avalanches using a frictional-cohesive rheology implemented in a depth-averaged shallow-flow model. Through extensive sensitivity studies on synthetic and real topographies, we show that cohesion plays a key role to enrich the physics of the simulated flows, and to represent realistic avalanche behaviors. First, when coupled to a proper treatment of the yielding criterion, cohesion provides a way to define objective stopping criteria for the flow, independently of the issues incurred by artificial diffusion of the numerical scheme. Second, and more importantly, the interplay between cohesion and friction gives raise to a variety of nontrivial physical effects affecting the dynamics of the avalanches and the morphology of the deposits. The relative weights of frictional and cohesive contributions to the overall stress are investigated as a function of space and time during the propagation, and related to the formation of specific features such as lateral levées, hydraulic jumps, etc. This study represents a first step towards robust avalanches simulations, spanning the wide range of possible flow regimes, through shallow-flow approaches. Future improvements involving more refined cohesion parameterizations will be discussed.
Near-past evolution of the magnitude and intensity of European heat waves
Authors: Ye Zhuyun , Christensen Jesper , Geels Camilla , Im Ulas
Published: March 2021

This work presents results from downscaling experiments using the Weather Research and Forecasting (WRF) in frame of the H2020-EXHAUSTION project for the period of 1980-2010 at 20km horizontal resolution over the European domain. Two simulations were carried out driven by ERA5 input by grid nudging (WRF_ERA5) and CESM2 output using 6 waves spectral nudging (WRF_CESM2), respectively. These near-past simulations have been rigorously evaluated with observations and reanalysis data including European Climate Assessment & Dataset (ECA&D), EOBS, and ERA5-land for the daily mean (TG), maximum (TX), and minimum (TN) surface temperatures over the whole Europe as well as five climate zones. The WRF simulations compared reasonably well with the observations. WRF_ERA5 showed a smaller root mean square error (RMSE) and higher correlations (r), while WRF_CESM2 performed better in terms of mean and normalized mean bias (MB and NMB). WRF_CESM2 is overall reliable to be used for future simulations.  In terms of the 30-year trend of TG, TX, and TN, WRF_CESM2 (0.6-0.66 °C/10yrs) showed faster increasing trends than WRF_ERA5 (0.29-0.35 °C/10yrs) and observations (0.27-0.41 °C/10yrs). Evaluations in different climate zones show smaller bias in north-western Europe and southern Europe. In terms of temporal evolution, eastern Europe showed the highest correlations. The worst model performance has been calculated for northern Europe. 

In addition, the Warm Spell Duration Index (WSDI) and the Heat Wave Magnitude Index daily (HWMId) have been calculated to represent the duration and magnitude of heat waves, respectively, for both simulations and observations. Strong and significant increasing trends are shown in eastern Europe and northern Europe for both WSDI and HWMId in all cases, with the fastest trends shown in EOBS (4 days/10yrs for WSDI, and 2/10yrs for HWMId), slowest trends in ECA&D (2 days/10yrs for WSDI, and 1/10yrs for HWMId), and trends in two WRF simulations are in between. No significant trends were found in southern Europe and north-western Europe in ECA&D, EOBS, and WRF_ERA5 simulation, while significant increasing trends were simulated in WRF_CESM2 in these two zones. The preliminary results suggested an increasing trend in the evolution of the future heat waves over Europe with implications on both direct impacts on human health, as well as indirect impacts through changes in exposure to pollutants such as ozone and particulate matter. Various future simulations are ongoing to address the impacts of climate change on the severity of heat waves under different levels of mitigation.
Energetic particles and radar blackouts at Mars
Authors: Lester Mark , Sanchez-Cano Beatriz , Potts Daniel , Lillis Rob , Cartacci Marco , Bernardini Fabrizio , Orosei Roberto , Perry Matthew , Putzig Nathaniel , Campbell Bruce , Blelly Pierre-Louis , Milan Steve , Opgenoorth Hermann , Witasse Olivier
Published: March 2021

We present the first long-term characterization of the lower ionosphere of Mars, a region previously inaccessible to orbital observations, based on an analysis of radar echo blackouts observed by MARSIS on Mars Express and SHARAD on the Mars Reconnaissance Orbiter from 2006 to 2017.  A blackout occurs when the expected surface reflection is partly to fully attenuated for portions of an observation.  Enhanced ionization at altitudes of 60 to 90 km, below the main ionospheric electron density peak, results in the absorption of the radar signal, leading to a radar blackout.  MARSIS, operating at frequencies between 1.8 and 5 MHz suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz).  More events are seen during solar maximum while  there is no apparent relationship between blackout occurrence and crustal magnetic fields. Blackouts do occur during both nightside and dayside observations, and have an interesting variation with solar zenith angle.   Analysis of MAVEN Solar Energetic Particle (SEP) electron counts between 20 and 200 keV during selected events demonstrates that these electrons are responsible for such events, and we investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce  measurable attenuation.  When both radars observe a radar blackout at the same time, the SEP electron fluxes are at their highest. For certain events, we find that the average spectrum responsible for a blackout is particularly enhanced at the higher energy end of the spectrum, i.e. above 70 keV .   This study is, therefore, important for future communications for human exploration of Mars.
 Water management in the Mucille area (NE Italy) through hydrologic balance estimation
Authors: Zini Luca , Turpaud Philippe , Calligaris Chiara
Published: March 2021

After abundant rainfalls, the Mucille area (Ronchi dei Legionari, Northeastern Italy) is subject to frequent flooding. Although this area has always been exposed to such hazard, these inundations become problematic since 2001 as they more frequently affect housing and recreational areas, leading the population to believe that the swallow holes draining the area stopped functioning. The increased frequency of intense rainfall events led the municipal technicians to involve the Department of Mathematics and Geosciences of the University of Trieste to assess the situation. The Mucille karstic depression is fed by a spring area and drained by two swallow holes one of which is permanently active while the other operates only during floods. The Mucille springs represent the westernmost drain of the Classical Karst aquifer. During floods, as in-situ discharge measurements are impossible, only a hydrologic balance model may assess the inflow or outflow discharges. The extension of the flooded areas has been mapped. The obtained flooded surface together with high resolution DEM coverage allows to calculate the volume of surface water. Combined with water table levels recorded in an adjacent piezometer, this volume can be computed over time. Thus, the hydrologic balance (inflow minus outflow) can be estimated. This model has been applied to several flood events among which, two were the most important in terms of flooded areas: one in December 2017 and the other in November 2019. During the event of December 2017, the water level reached 7,5 m a.s.l. and the difference between the inflow and the outflow was 880 l/s. The day following the peak, the discharge difference decreased to 273 l/sand the 5 subsequent days the water balance was close to equilibrium. From the eighth day on, the outflow became predominant resulting in a negative budget between -233 and -78 l/s. The flood event of November 2019 reached the maximum inundated area at a water level of 7,8 m a.s.l. with a difference between the inflow and the outflow of 750 l/s . Two days after the peak a negative balance of -200 l/s was recorded and remained negative for the next 5 days. A period of intermittent precipitations increased again the inflow up to 600 l/s. Following a period of ten days with a negative balance the water level returned to the initial values of 5 m a.s.l. This study provides evidences fundamental for the design of measures to mitigate the risk. It estimates the discharge of the swallow holes, confirming their efficiency. Nonetheless it also emphasises the need to improve their draining capacity, especially considering the unsuspected high outflow of the springs at the onset of the flood.
Short-term Glacial Dynamics Detection of a Maritime Glacier in Southeastern Tibetan Plateau using Cost-effective UAV and Rapid Photogrammetry Techniques
Authors: Xu Shuyang , Fu Ping
Published: March 2021

Glacier mechanical ablation, such as ice calving, collapsing and flaking, plays a significant role in amplifying glacier recession. Mechanical ablation, as a non-linear response to climatic changes, caused by structural instabilities are mainly attributed to interactions of water-ice/glacier, which could be strengthened by the enhanced meltwater runoffs when rain season meets with ablation season. Similar to water-terminating glaciers, ice calving (or large-scale ice collapsing) events have happened in land-terminating glaciers in the southeastern Tibetan Plateau such as Hailuogou (HLG) glacier. However, other than ice calving events with water involved and dry calving events, ice calving of HLG glacier is roughly in the middle state between them. Previous studies have shown that HLG glacier have maintained negative mass balance in recent years with sustaining retreat, accompanied by mechanical ice loss events. Seven field trips to HLG glacier were conducted from 2017 to 2020 (concentrated from June to November). A cost-effective Unmanned Aerial Vehicle (UAV; DJI Mavic Pro) was used to capture images from ice fall to glacier terminus. Agisoft Metashape Pro was used to produce dense point cloud, digital surface model and ortho-images, etc. Results indicate that, under the intense interactions of water-ice/glacier, glacier terminus has been retreating continually, the terminal ice cliffs have gone through a succession of structural changes, the proglacial river have diverted several times, and the position of subglacial channel outlet had multi-times shifts accompanied with the periodic occurrences of terminal ice cave. The surrounding glacial landscapes have been altered accordingly such as the increasing runoffs from glacier river, the narrowing glacier ice fall, upward invasions by periglacial vegetation, and etc. The combination of repeated UAV mapping and rapidly streamlined terrain reconstruction technique provides a cost-effective option for short-term monitoring of glacier dynamics, especially for more precise detection on mechanical ablation, compared with datasets from commercial satellites.
Fully kinetic PIC simulations of particle acceleration and non-Maxwellian distribution functions due to current sheets in solar wind turbulence
Authors: Munoz Patricio A. , Büchner Jörg , Jain Neeraj
Published: March 2021

Turbulence is ubiquitous in solar system plasmas like those of the solar wind and Earth's magnetosheath. Current sheets can be formed out of this turbulence, and eventually magnetic reconnection can take place in them, a process that converts magnetic into particle kinetic energy. This interplay between turbulence and current sheet formation has been extensively analyzed with MHD and hybrid-kinetic models. Those models cover all the range between large Alfvénic scales down to ion-kinetic scales. The consequences of current sheet formation in plasma turbulence that includes electron dynamics has, however, received comparatively less attention. For this sake we carry out 2.5D fully kinetic Particle-in-Cell simulations of kinetic plasma turbulence including both ion and electron spectral ranges. In order to further assess the electron kinetic effects, we also compare our results with hybrid-kinetic simulations including electron inertia in the generalized Ohm's law. We analyze and discuss the electron and ion energization processes in the current sheets and magnetic islands formed in the turbulence. We focus on the electron and ion distribution functions formed in and around those current sheets and their stability properties that are relevant for the micro-instabilities feeding back into the turbulence cascade. We also compare pitch angle distributions and non-Maxwellian features such as heat fluxes with recent in-situ solar wind observations, which demonstrated local particle acceleration processes in reconnecting solar wind current sheets [Khabarova et al., ApJ, 2020].
Navigating the challenges of explicitly including ocean-ice shelf interactions in a global ocean model using an adapted ISOMIP+ configuration as a fit-for-purpose tool
Authors: Hutchinson Katherine , Deshayes Julie , Mathiot Pierre
Published: March 2021

Currently, none of the global 1° ocean-climate coupled models used for the Coupled Model Intercomparison Project (CMIP) explicitly simulate sub-ice shelf cavity circulation. This circulation plays a critical role in global ocean overturning as it transforms salty water formed at the surface in Antarctica into the parent waters of Antarctic Bottom Water (AABW). A challenge that the ocean-climate modelling community faces is the inclusion of these ocean-ice shelf interactions in global ocean 1° resolution models, so as to explicitly simulate dense water production and export. Choices regarding various numerical schemes and parameterizations need to be made, but in testing sensitivity to these choices and feedback effects of biases, large super-computing costs associated with running a global configuration are incurred. To address this we present an adapted configuration of the Ice Shelf-Ocean Model Intercomparison Project (ISOMIP), named ISOMIP+K, as the default idealised ISOMIP+ setup is not appropriate for modelling the deep, cold Antarctic cavities responsible for forming the dense parent waters of AABW. ISOMIP+K is currently adapted for the NEMO ocean model, motivated by the fact that this model is used for 6 of the climate groups participating in CMIP. We present results from ISOMIP+K configurations for Filchner-Ronne, Larsen-C and Ross ice shelves, which are important for dense water formation and large enough to be resolved, albeit coarsely, in a global 1° Earth System Model. This adapted ISOMIP+K test case, which is now far from idealized, is used to test the effect of initial conditions, the choice of values for lateral diffusion of momentum, mixing, drag coefficients and bathymetry on key indicators describing melt, sub-ice shelf circulation and dense water export. As opposed to regional high resolution Southern Ocean configurations, the ISOMIP+K configurations are designed so that the lessons learnt are directly transferable to a global ocean configuration where each choice made is backed-up by extensive, yet affordable, testing.
Impacts of COVID-19 lockdown restrictions on urban NO2 and O3 level in Germany with consideration of meteorological impacts and seasonal variation
Authors: Balamurugan Vigneshkumar , Bi Xiao , Gensheimer Johannes , Chen Jia , Keutsch Frank , Bhattacharjee Shrutilipi , Shekhar Ankit
Published: March 2021

In 2020, the entire world population has witnessed an unprecedented virus outbreak in terms of COVID-19, which led to restrictions in human activities across the world. Strict measures in Germany started on March-21, 2020 and ended on April-30, 2020, while more relaxed measures continued until July 2020. Vehicle traffic volume and industrial activities were drastically reduced, and, as a result, pollutant emission rates were expected to be reduced. Changes in atmospheric pollutant concentrations are an indicator for changes in emission rates although they are not directly proportional as concentrations are heavily influenced by meteorological conditions and as atmospheric photochemical reactions can be non-linear. Without accounting for the influence of meteorology and atmospheric photochemical reactions, a simple comparison of the lockdown period pollutant concentration values with pre-lockdown only to estimate emissions could be misleading. To normalize the effects of meteorological conditions and atmospheric chemical transformation and reactions, we adopted a method of comparing the predicted Business As Usual (BAU) NO2 and O3 concentrations, i.e., the expected value of NO2 and O3 concentration for 2020 meteorological conditions without lockdown restrictions, with the observed NO2 and O3 concentrations. BAU NO2 and O3 concentrations corresponding to 2020 meteorological conditions were predicted based on wind speed and sunshine duration (and season of the day) using the previous year NO2 and O3 concentrations as the references. Compared to BAU levels, big metropolitan cities in Germany show a decline in observed NO2 level (-24.5 to -37.7 %) in the strict lockdown period and rebound to the BAU level at the end of July 2020. In contrast, there is a marginal change in O3 level (+9.6 to -7.4 %). We anticipate that the imbalanced changes in precursors emission (decrease in NOX and increase in volatile organic compounds (VOCs) emission) are attributed to the marginal changes in observed O3 level compared to BAU level; decreased NOX would decrease the O3 concentration due to NOX-limited conditions, and increased VOCs would increase the O3 concentration. These results imply that the balanced emission control between the VOCs and NOX are required to limit the secondary pollutant (O3) formation.
Using rock magnetics to resolve composite magmatic state fabrics: a case study from the Younger Giant Dyke Complex, SW Greenland
Authors: Koopmans Lot , McCarthy William
Published: March 2021

Understanding the geometry of magma chambers plays a critical role in determining the igneous petrogenic processes that occur as intrusions cool. Quantitative fabric analysis methods, such as anisotropy of magnetic susceptibility (AMS), are routinely used to measure magma flow dynamics and determine the mechanism of magma transport and emplacement. However, magma mushes typically experience multiple flow events; e.g. emplacement, convection, and interstitial melt percolation. There is thus a need to develop a more a sophisticated approach to unravelling complex rock fabrics that record more than one magmatic state process. This study uses novel rock magnetic datasets to untangle the evolution of the 1163 Ma Younger Giant Dyke Complex (YGDC) of SW Greenland, a multi-sheeted troctolite dyke system that attains widths up to 800 m and encloses several evolved and/or modally layered ovoid pods.

Field results identify that ovoid pods occur in the thickest dyke segments. Several pods are defined by gently inward dipping modal layers and/or a parallel mineral foliations, and in-phase AMS magnetic foliations lie parallel to the observed field fabrics. Critically, imbricated plagioclase crystals record a magma transport direction toward the center of each pod, and this observation is substantiated by in-phase AMS lineations that plunge down dip of the foliation and shallow toward the center of each pod. These observations are interpreted to show gravitational settling under a convective flow regime.

In addition, 66% of out-of-phase AMS fabrics are non-parallel with in-phase AMS results. Out-of-phase AMS is a relatively new technique and is thought to reflect anisotropy controlled by a restrictive group of ferromagnetic minerals such as single domain magnetite and pyrrhotite. Out-of-phase lineations in layered pods are relatively steeply inclined and do not shallow towards the center, we therefore hypothesize that these lineations record a late stage filter-pressing process within the crystal mush. To test this hypothesis, anisotropy of anhysteretic remanent magnetism (AARM) data were collected from 15 samples. Results show that the AARM and out-of-phase AMS tensor axes are parallel, indicating that the sub-fabric detected by out-of-phase AMS is normal and most likely controlled by single domain magnetite.

Our results show that the application of rock magnetic techniques is effective in unravelling magma convection fabrics from later melt migration fabrics in mushy magmas.
Effect of gravity curvature on large-scale atomic gravimeters
Authors: Tell Dorothee , Wodey Étienne , Meiners Christian , Zipfel Klaus H. , Schilling Manuel , Schubert Christian , Rasel Ernst M. , Schlippert Dennis
Published: March 2021

In terrestrial geodesy, absolute gravimetry is a tool to observe geophysical processes over extended timescales. This requires measurement devices of high sensitivity and stability. Atom interferometers connect the free fall motion of atomic ensembles to absolute frequency measurements and thus feature very high long-term stability. By extending their vertical baseline to several meters, we introduce Very Long Baseline Interferometry (VLBAI) as a gravity reference of higher-order accuracy.

By using state-of-the-art vibration isolation, sensor fusion and well controlled atomic sources and environments on a 10 m baseline, we aim for an intrinsic sensitivity σg ≤ 5 nm/s² in a first scenario for our Hannover VLBAI facility. At this level, the effects of gravity gradients and curvature along the free fall region need to be taken into account. We present gravity measurements along the baseline, in agreement with simulations using an advanced model of the building and surroundings [1]. Using this knowledge, we perform a perturbation theory approach to calculate the resulting contribution to the atomic gravimeter uncertainty, as well as the effective instrumental height of the device depending on the interferometry scheme [2]. Based on these results, we will be able to compare gravity values with nearby absolute gravimeters and as a first step verify the performance of the VLBAI gravimeter at a level comparable to classical devices.

The Hannover VLBAI facility is a major research equipment funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). This work was supported by the DFG Collaborative Research Center 1464 “TerraQ” (Project A02) and is supported by the CRC 1227 “DQ-mat” (Project B07), Germany’s Excellence Strategy EXC-2123 “QuantumFrontiers”, and the computing cluster of the Leibniz University Hannover under patronage of the Lower Saxony Ministry of Science and Culture (MWK) and the DFG. We acknowledge support from “Niedersächsisches Vorab” through the “Quantum- and Nano-Metrology (QUANOMET)” initiative (Project QT3), and for initial funding of research in the DLR-SI institute, as well as funding from the German Federal Ministry of Education and Research (BMBF) through the funding program Photonics Research Germany.

[1] Schilling et al. “Gravity field modelling for the Hannover 10 m atom interferometer”.  Journal of Geodesy 94, 122 (2020)

[2] Ufrecht, Giese,  “Perturbative operator approach to high-precision light-pulse atom interferometry”. Physical Review A 101, 053615 (2020).
New insights into magmatic processes from integrated satellite observation, trajectory analysis and magma ascent modelling
Authors: Burton Mike , La Spina Giuseppe , Hayer Catherine , Esse Benjamin
Published: March 2021

Analysis of TROPOMI data with plume trajectory tools opens the possibility of new insights into volcanic / magmatic processes from two data sources: SO2 flux time series and plume height time series. In this paper we investigate results from explosive eruptions and attempt to explain the results with a magma ascent conduit model. The combination of plume height and gas flux data with a model of the magma ascent process provides a toolkit which allows us to constrain magma reservoir processes from satellite monitoring data. The combination of modelling and observations opens a new volcanological research frontier, because the TROPOMI sensor has daily global coverage, a high spatial resolution and is sensitive enough to detect many small-medium explosions globally, so that a large inventory of explosive activity can be characterised. 
Exploring the deep interior of ice giants with shock-compression experiments and ab initio simulations: The case of metallic ammonia 
Authors: Bethkenhagen Mandy , Hernandez Jean-Alexis , Benuzzi-Mounaix Alessandra , Datchi Frederic , French Martin , Guarguaglini Marco , Lefevre Frederic , Ninet Sandra , Redmer Ronald , Vinci Tommaso , Ravasio Alessandra
Published: March 2021

Ammonia is predicted to be one of the major components in the depths of the ice giant planets Uranus and Neptune. Their dynamics, evolution, and interior structure are insufficiently understood and models rely imperatively on data for equation of state and transport properties [1,2]. Despite its great significance, the experimentally accessed region of the ammonia phase diagram today is still very limited in pressure and temperature [3, 4].

We investigate the equation of state, the optical properties and the electrical conductivity of warm dense ammonia by combining laser-driven shock experiments and state-of-the-art density functional theory molecular dynamics (DFT-MD) simulations [5]. The equation of state is probed along the Hugoniot of liquid NH3 up to 350 GPa and 40000 K and in very good agreement with earlier DFT-MD results [6]. Our temperature measurements show a subtle slope change at 7000 K and 90 GPa, which coincides with the gradual transition from a liquid dominated by molecules to a plasma state in our new ab initio simulations. The reflectivity data furnish the first experimental evidence of electronic conduction in high pressure ammonia and are in excellent agreement with the reflectivity computed from atomistic simulations. Corresponding electrical conductivity values are found up to one order of magnitude higher than in water in the 100 GPa regime, with possible implications on the generation of magnetic dynamos in large icy planets’ interiors.

 

[1] Scheibe, Nettelmann, Redmer, Astronomy & Astrophysics 632, A70 (2019).

[2] Vazan & Helled, Astronomy & Astrophysics 633, A50 (2020).

[3] Nellis, Hamilton, Holmes, Radousky, Ree, Mitchell, Nicol, Science 240, 779 (1988).

[4] Radousky, Mitchell, Nellis, Journal of Chemical Physics 93, 8235 (1990).

[5] Ravasio, Bethkenhagen, Hernandez, Benuzzi-Mounaix, Datchi, French, Guarguaglini, Lefevre, Ninet, Redmer, Vinci, Physical Review Letters 126, 025003 (2021).

[6] Bethkenhagen, French, Redmer, Journal of Chemical Physics 138, 234504 (2013).
Study of water salinity in the Chtouka plain (Morocco) using TEM geophysical method, chemical and isotopes tracers
Authors: Schreiber Henrik , Danni Saadou Oumarou , Touab Amine , Abourig Fatima , Montcoudiol Nelly , Ez-Zaouy Yassine , Hssaisoune Mohammed , Bouchaou Lhoussaine
Published: March 2021

The Chtouka plain in Morocco suffers from groundwater overexploitation and a significant increase in water salinity. In this study, a multidisciplinary approach combining water chemistry, stable isotopes of water (18O, 2H) and Transient Electromagnetic (TEM) method was used. The main objective was to identify the water salinity sources and the extension of the marine intrusion. Water samples were collected from wells and boreholes, springs, the Massa river and the main source of freshwater in the region, the Youssef Ibn Tachfine Dam. Geophysical (TEM) measurements (12 profiles comprising 83 measurement points) were carried out along the coastal zone and around the northern bank of the Massa river. The results show a spatial variability of water salinity, indicating rock-water interaction, seawater intrusion and anthropogenic influence. The interpretation of the TEM soundings allow to draw the front line of the marine intrusion in the aquifer. The results, compared to previous numerical simulations, show a significant progress of the marine intrusion into the coastal aquifer. The intrusion indeed reaches a distance of 2.5 km from the coast, far beyond models’ predictions. The local water authorities can use these results to improve their monitoring network and better assess the progress of the seawater intrusion.
Keywords: Water salinity, TEM geophysical method, chemical and isotopes tracers, marine intrusion
CHANGES IN COMBINED EFFECT OF EXTREMES BASED ON MODIFIED CLIMATE EXTREMES INDEX (mCEI) OVER THE EUROPE-MEDITERRANEAN REGION
Authors: Kelebek Mehmet Barış , Batıbeniz Fulden , Önol Barış
Published: March 2021

Multiple climate extremes have diverse impacts on the human environment and the natural ecosystem. The use of a compact set of climate change indices enhances our understanding of the combined impacts of extreme climatic conditions. In this study, we calculated percentile based extreme temperature and precipitation indices, and self-calibrating Palmer Drought Severity Index over the Europe-Mediterranean (EURO-MED) region for 1979-2016 period. Moreover, we extended the Climate Extremes Index (CEI) as the modified Climate Extremes Index (mCEI) to obtain combined information regarding the extremes on the grid basis. As a holistic approach mCEI provides detailed spatiotemporal information on annual timescale, and high-resolution grid-based data allows us to do detailed country-based and city-based analyses. For temperature, we use the last generation ERA5 reanalysis dataset, and for precipitation, we use MSWEP gridded observational dataset. The results indicate that warm temperature extremes are significantly on the rise over the EURO-MED region whereas the cold temperature extremes decrease. The extreme drought has a significant increasing trend. Although there are heterogeneous regional distributions, extreme precipitation indices have a significant increasing tendency. Additionally, we found that the Mediterranean coasts, the Balkan countries, the Eastern Europe, Iceland, the parts of western Russia, the parts of Turkey, and the parts of Syria and Iraq are the major hot-spots for the combined extremes based on mCEI. Among the major urban agglomerations of the EURO-MED region, 28 cities exhibit a significant increasing trend of the mCEI greater than 1.5% decade-1. These results agree with the previous findings related to the climatic extremes of the EURO-MED climate hotspot, and strengthen the findings on human-induced climate change.
The Global Emergence of Hotter-Drought Drivers of Forest Disturbance Tipping Points
Authors: Allen Craig D. , Hammond William M.
Published: March 2021

Current research is presented on global-scale patterns and trends of forest responses to increasingly hotter droughts, particularly extensive tree mortality and forest die-offs involving a range of interactive disturbances (e.g., water stress, insect outbreaks, high-severity wildfire), illustrating emerging ecological changes and growing tipping-point risks to forests worldwide from hotter-drought extremes.  Cross-scale observations and empirical findings – ranging from controlled experiments in pots and local plot-level vegetation data, to networks of carbon flux monitoring sites and globally synoptic remote-sensing data – increasingly indicate that amelioration of hotter-drought stress via fertilization of photosynthesis from elevated atmospheric CO2concentrations may soon be overwhelmed by heat and accelerated atmospheric drought.  These findings highlight some current challenges in realistically projecting the future of global forest ecosystems (and their associated carbon pools and fluxes) with process-based Earth system models.  In particular there is substantial evidence that ‘historical forests’ – established by circa 1880 and dominated by larger, older trees – may be disproportionately vulnerable to increased growth stress and mortality under hotter-drought conditions from ongoing anthropogenic climate change.  The fates of the world’s biggest, oldest trees and historical forests in response to global change are of vital importance, given that they are essential as:  a) disproportionately large carbon sinks;  b) among the most biodiverse and rare terrestrial ecosystems;  c) irreplaceable archives of environmental history;  and d) venerated for many spiritual, aesthetic, and other cultural reasons.  Key scientific uncertainties that impede modeling progress are outlined, and examples of promising empirical modeling approaches are illustrated.
Landscapes to Lifescapes - Sociotechnical interventions in public engagement 
Authors: Skinner Christopher , Lloyd Wiliams Alison , Mort Maggie , Coles Joanne
Published: March 2021

Flooding is recognised as a powerful agent of geomorphology. During a few hours of a flood event, more change can occur to a river and its valley than accumulated changes over several decades. Floods are also a powerful force of change in our human experience. Floods (re)shape lives, communities and societies, causing devastation and upheaval but also creating experience and enhanced understanding among flood-affected people of the need to adapt and live with water. So, to appreciate the full of impacts of flooding it is important to consider and communicate the ways it changes both 'landscapes and lifescapes'.

In the Landscapes to Lifescapes online exhibition, hosted on The Flood Hub (https://thefloodhub.co.uk/), social scientists and geomorphologists collaborate to explore the material and social meaning of flooding. ‘Landscapes’ shows the complex and varied forms of flooding and how these alter rivers and valleys, visualised by digital activities from the SeriousGeoGames Lab. ‘Lifescapes’ illuminates some of the effects of flooding on families and communities, using flood testimonies gathered from a series of qualitative participative studies. The exhibition culminates in a 360 virtual reality experience, telling the true story of a young boy caught up in flooding. Help Callum was created combining software designed for videogames and a real flood narrative, allowing visitors to experience Callum’s journey from flood victim to flood activist, through his eyes and using his words.

The aim of the exhibition is to promote flood resilience knowledge and actions to the users through: raising awareness of flood risk and recovery, including particular impacts on children and young people; encouraging the users’ agency by highlighting actions that can be taken at household and community level; and modelling positive behaviours by providing examples and case studies. Evaluation is conducted throughout using feedback boards and polls. 
NMR spectroscopy approach to study soil organic matter formation under different plant composition during 50 years
Authors: Kauer Karin , Pärnpuu Sandra
Published: March 2021

The aim of this research was to study the effect of different plants on soil organic matter (SOM) composition. The composition of SOM was studied in a field experiment established in 1964 on a carbonaceous glacial till soil with very low initial SOC concentration (1.28 g kg-1). The effects on SOM composition of bare fallow, barley, grasses, and clover-grasses mixture, were studied using 13C nuclear magnetic resonance (NMR) spectroscopy which is a common tool to characterize SOM. In 2014 the soil samples were collected from 0-5 cm soil layer, air-dried samples sieved through a 2-mm sieve and pretreated with 10% HF solution before NMR spectroscopy analysis. Samples of bulk soil and density fractionated mineral fraction (John et al., 2005) were analyzed. Also, a sample from barley treatment collected in 1966 was analyzed.

O/N-alkyl C was the most abundant C type at the start of the experiment and also in all treatments after 50 years. During 50 years the proportions of O/N-alkyl C and alkyl C increased but contributions of carboxyl C and aromatic C decreased. The ratio of alkyl C/O-alkyl C, which describes the degree of soil organic matter decomposition, decreased from 0.47 (in 1966) to 0.40-0.44 in treatments with plants. In bare fallow treatment, the SOM decomposition stage did not change a lot during the time. In soil mineral fraction the differences between treatments appeared more clearly and the degree of decomposition decreased in line: bare fallow>barley>clover-grasses>grasses (0.49>0.40>0.36>0.34) and this was due to higher O/N-alkyl-C content in treatments with plants. The higher O/N-alkyl C contribution in soil heavy fraction can be attributed to microbially synthesized carbohydrates (Yeasmin et al., 2020) and depended on the amount and properties of C input into the soil in different treatments.

In conclusion, the SOM composition was influenced by plant composition and the effect was more pronounced in soil mineral fraction. The SOM degree of decomposition was higher in treatment with annual crop (barley during 50 years). Under perennial grasses and clover-grasses mixture, the soil organic matter decomposition degree was lower.

This work was supported by the Estonian Research Council grant PSG147.

References

John, B., Yamashita, T., Ludwig, B., & Flessa, H. (2005). Storage of organic carbon in aggregate and density fractions of silty soils under different types of land use. Geoderma, 128(1–2), 63–79. https://doi.org/10.1016/j.geoderma.2004.12.013

Yeasmin, S., Singh, B., Smernik, R. J., & Johnston, C. T. (2020). Effect of land use on organic matter composition in density fractions of contrasting soils: A comparative study using 13C NMR and DRIFT spectroscopy. Science of the Total Environment, 726, 138395. https://doi.org/10.1016/j.scitotenv.2020.138395
Updated land use and land cover change (LULCC) emission estimates based on new high-resolution LULCC forcing data
Authors: Ganzenmüller Raphael , Bultan Selma , Winkler Karina , Fuchs Richard , Pongratz Julia
Published: March 2021

Land use and land cover change (LULCC) has a significant role for the global carbon cycle. Despite big improvements in LULCC emission modelling, related uncertainties remain relatively high. Major uncertainties in quantifying LULCC emissions stem from uncertainties in underlying LULCC datasets. The novel, high-resolution (~1 km×1 km) LULCC dataset HIstoric Land Dynamics Assessment+ (HILDA+) reflects gross transitions derived from multiple remote sensing products and offers an alternative to existing land use change datasets, serving as forcing for process-based and bookkeeping models. By incorporating HILDA+ in the “bookkeeping of land use emissions” (BLUE) model, which is one of the three bookkeeping models used in the Global Carbon Budget 2020, we gain a different temporal and spatial perspective on LULCC estimates and related sources of uncertainty. 

We compare our results to emission estimates based on LUH2, which is broadly used as LULCC forcing for process-based and bookkeeping models. First results of our analysis show overall lower LULCC emissions for the estimates based on HILDA+. For the time period 1990-2019, mean yearly emission estimates based on HILDA+ are 0.595 GtC yr−1 compared to 1.368 GtC yr−1 based on LUH2. Reasons are lower emissions from cropland expansion and less carbon uptake from vegetation regrowth after abandonment of managed land (i.e. a smaller carbon sink). Furthermore, fewer discontinuities in the BLUE runs with the HILDA+ forcing compared to the LUH2-based estimates suggests a better representation of land use dynamics and their effects. Overall, the simulations based on HILDA+ capture spatial heterogeneity to a greater degree and provide a more detailed picture of local sources and sinks, which is crucial for (1) a better representation of component fluxes (e.g. deforestation, degradation) and (2) effective mitigation and adaptation policies.
Food vs water security in cities: A georeferenced sustainability assessment of peri-urban agriculture in metropolitan Barcelona using water vulnerability maps.
Authors: Madrid-Lopez Cristina , Ventura Sergi , Gilabert Joan , Marull Joan , Domene Elena , Villalba Gara
Published: March 2021

The Fitness Check on EU water legislation concluded that there is a need to integrate water issues into other policies such as those related to urban planning. The increase of population in urban areas is expected to raise urban food demand about 50% to 60% globally by 2050. This intensifies the use of water for irrigation purposes as urban planners implement peri-urban agriculture as a way to increase food security and protect ecosystem services from urbanization. If not properly planned, urban and peri-urban agriculture can result in increasing pressures over water resources, such as aquifer depletion or nitrate pollution which impact the overall status of the water bodies. As cities start promoting local agriculture, it is important to provide policy makers with tools to determine the impacts of food production on water resources, from a geo-referenced, systemic water-energy-food perspective.

In this work, we propose a method for the regionalized assessment of the tradeoffs between peri-urban food production potential and the associated impacts over water resources and apply it to the Metropolitan Area of Barcelona (AMB). AMB is the most populated urban area of the Mediterranean coast and sixth in Europe. With over 5 million people, the AMB only produces between 7% and 10% of its food demand and the new Metropolitan Urban Master Plan (PDU) scenarios foresee a growth in agricultural land of up to 20%.

The method we propose includes three stages. First, we map peri-urban agricultural land uses available from the local land use classification by CREAF and reclassify them to Copernicus’ CORINE land cover taxonomy in order to facilitate replicability and comparability of results. Second, we use the Water Framework Directive water body status index (high, good, moderate, poor, bad) to create physical vulnerability maps of water bodies. Third, we study how water use relates to water impacts using the vulnerability maps. Following this method, we assess the water-food tradeoffs for four scenarios of agricultural land change, classifying agricultural land according to their food supply potential and water impacts. This method can be used to assess agriculture in other metropolitan regions.

This work is part of the research developed in the ERC Project URBAG: Integrated System Analysis of Urban Vegetation and Agriculture.