bluuebunny/crossref_metadata_2025 huggingface dataset:
Air Quality Impacts of COVID-19 Lockdown Measures using high-resolution observations of multiple trace gases from S5P/TROPOMI
Authors: Eskes Henk , Levelt Pieternel , Stein Deborah , DeSmedt Isabelle , Aben Ilse , van Roozendael Michel , Stavrakou Jenny , Bauwens Maite , Lerot Christophe , Veefkind Pepijn , Borsdorff Tobias , Verhoelst Tijl , Loyola Diego , Romahn Fabian
Published: March 2021

The lockdown measures taken to combat the COVID-19 virus implemented in a majority of countries worldwide have had a dramatic impact on the anthropogenic pollutant emissions, related to a drastic reduction of road and air traffic, as well as part of the industrial activities. In our contribution we investigate the presence of COVID-19-related imprints in air quality as observed from space, focussing on worldwide industrial/highly populated regions where strong lockdown measures have been taken (e.g., China, Europe, US). This is done by exploiting the observations of the TROPOMI instrument onboard the Copernicus Sentinel-5P platform, for a number of trace gases which are indicators of anthropogenic activity. We make use of the TROPOMI operational product portfolio, which includes tropospheric NO2, CO, SO2, and HCHO. These operational data products are complemented by other scientific products such as the BIRA-IASB glyoxal (CHOCHO) retrievals and a new SO2 retrieval algorithm called COBRA. The reductions in NO2 observed by TROPOMI have been documented already in the recent literature for several regions and countries worldwide. In our contribution we focus on the combined observations of multiple trace gases, which provides not only information about how much primary (NOx) emissions decreased, but also gives region-to-region insights and constraints on the overall changes in atmospheric composition as a result of these lockdowns.
Future Holiday Climate Index (HCI) Performances of Urban and Beach Destinations in the Mediterranean
Authors: Saygili Araci F. Sibel , Demiroglu O. Cenk , Pacal Aytac , Hall C. Michael , Kurnaz M. Levent
Published: March 2021

Tourism is a major socioeconomic contributor to established and emerging destinations in the Mediterranean region. Recent studies introducing the Holiday Climate Index (HCI) highlight the significance of climate as a factor in sustaining the competitiveness of coastal and urban destinations. The aim of this study is to assess the future HCI performances of urban and beach destinations in the greater Mediterranean region. For this purpose, HCI scores for the reference (1971-2000) and future (2021-2050, 2070-2099) periods were computed with the use of two latest greenhouse gas concentration trajectories, RCP 4.5 and 8.5, based on the Middle East North Africa (MENA) Coordinated Regional Downscaling Experiment (CORDEX) domain and data. The outputs were adjusted to a 500 m resolution via the use of lapse rate corrections that extrapolate the climate model topography against a resampled digital elevation model. All periodic results were seasonally aggregated and visualized on a (web) geographical information system (GIS). The web version of the GIS also allowed for a basic climate service where any user can search her/his place of interest overlaid with index ratings. Exposure levels are revealed at the macro scale while sensitivity is discussed through a validation of the climatic outputs against visitation data for one of Mediterranean's leading destinations, Antalya. HCI:Urban results showed that Canary Islands hold suitable conditions for tourism during almost all four seasons and all five periods which will have certain implications when other core Mediterranean competitors lose their relative climatic attractiveness. HCI:Beach results for the summer season showed that Las Canteras, Alicate, Pampelonne, Myrtos, Golden Sands and Edremit all pose Very Good to Excellent conditions without any Humidex risks for the extreme future scenario (2070-2099 RCP8.5).
Much detailed outputs of the study can be viewed from the web service at:
http://climatechange.boun.edu.tr/en/holiday-climatology-of-the-mediterranean/

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Strategies for the environmental recovery of abandoned mining areas
Authors: Hernández-Córdoba Manuel , Martinez-Sánchez Maria Jose , Martinez López Salvadora , Martinez-Martinez Lucia Belén , Hernández-Pérez Carmen , García-Lorenzo Mari Luz , Bech Jaume , Pérez-Sirvent Carmen
Published: March 2021

Abandoned mining areas are a clear example of the failure of the different administrations to solve the environmental problems they pose, due to the lack of unified legislation and management and the activity of geological processes. It is therefore important to have a clear vision of the environmental problems that occur and the possible actions to solve them.

The Sierra Minera (Cartagena, SE Spain) presents situations of risk of soil contamination that coincide with those areas with the highest content of soluble and/or bioavailable PTEs (potentially toxic elements) for the health of people and ecosystems, especially in those sites of concentration of polluting sources (flotation mud pools and heterogeneous dumps), with a very fine texture. These areas present numerous points with an urgent need for risk management due to the possible mobilization in different environmental conditions of arsenic and heavy metals, with a control of both soluble and particulate dispersion. Special interest presents arsenic mobilisation in an acidic environment together with reducing situations and the presence of organic matter (waterlogged marshes).

The recovery technologies to be applied in the Sierra Minera require a great diversity of techniques, depending on the uses of the land. In the contamination foci it is necessary to carry out actions with containment, stabilisation and solidification technologies in situ. Phytoremediation techniques, given the high content of PTEs present, may not all be appropriate in the different situations. Phytoextraction should only be applied in areas with low concentrations of PTEs, and by plants that do not transfer to their aerial part, to avoid the risk of ingestion by animals. Phytostabilisation will be important in combined techniques, in order to ensure that contaminants are not transferred to the environment, and by non-accumulating plants in the aerial part. Wetlands can be a complementary solution to the projects developed at the heading of wadis, providing a double purpose, natural attenuation of contamination and lamination of turbulence and floods.

A generic overview is given of the most important regeneration approaches from a geochemical point of view, without going into structural solutions, selecting those technologies that are most suitable to the environment in which they are located, trying to imitate natural attenuation processes and using eco-efficient and sustainable materials.
Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations
Authors: Latessa Gaston , Busse Angela , Valyrakis Manousos
Published: March 2021

The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.

In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.

Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.

The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.

A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.

Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.
Evaluating synthetic vulnerability functions in flood risk modelling – a case study from Switzerland
Authors: Keiler Margreth , Zischg Andreas , Fuchs Sven
Published: March 2021

The selection of vulnerability models has a significant influence on the overall uncertainty when quantifying flood loss. Several scholars reported a limited spatial transferability of available vulnerability functions to case studies other than those they have been empirically deduced from. As a result, there is a need for computation and validation of regionally specific vulnerability functions. As in many data-scarce regions this option is not feasible, the physical processes of flood impact model chains can be developed using synthetic vulnerability function and validating them by expert opinion. The function presented in our study is based on expert heuristics using a small sample of representative buildings. We applied the vulnerability function in a meso-scale river basin and evaluated the new function by comparing the resulting flood damage with the damage computed by other approaches, (1) an ensemble of vulnerability functions available from the literature, (2) an individual vulnerability function calibrated with region-specific data, and (3) the vulnerability function used in flood risk management by the Swiss government. The results show that synthetic information can be a valuable alternative for developing flood vulnerability models in regions without any data or only few data on flood loss.
Modelling dynamic fault slip and seismic wavefield for production-induced seismicity in Groningen
Authors: Ruan Jingming , Ghose Ranajit , Mulder Wim
Published: March 2021

Induced seismicity from a gas-producing region such as Groningen is believed to be caused by reservoir depletion due to long-term gas production. However, because of the complexity and uncertainty regarding the underground structure and composition, it is difficult to quantify the effect on induced seismicity due to gas production. Here we use finite-element modelling to investigate the seismogenic potential of a pre-existing fault reactivated due to fluid depletion, considering different model settings. By applying quasi-static poroelastic loading representing reservoir depletion, the stress and strain fields are derived from the resulting displacement field. The equilibrium of the fault is then evaluated using either rate-and-state or slip-weakening behaviour for friction. When the critical state is reached on the fault, where the shear stress is greater than the friction, the reactivation of the fault takes place. This reactivation is simulated by using a dynamic solver to observe the propagation and the arrest of the dynamic faulting, as well as the resultant wavefield due to seismic slip. By comparing the depletion value at both aseismic and seismic ruptures, and looking at the stress distribution on the fault, the pattern of rupture nucleation, and the resulting seismic wavefield, we are able to evaluate separately the effect of different model settings, including the geometry and material property of both caprock and reservoir, reservoir depletion pattern, and the friction law. Furthermore, by combining our study with the observed seismic wavefield, it is possible to obtain useful insights on the spatial variation in the source region.
On ion temperature dependence of symmetric magnetic reconnection
Authors: Zaitsev Ivan , Divin Andrey , Semenov Vladimir , Korovinskiy Daniil , Deca Jan , Khotyaintsev Yuri , Markidis Stefano
Published: March 2021

Various simulations of collisionless magnetic reconnection reveal that the process is typically fast, with the reconnection rate being of the order of 0.1. Systematic numerical and observational studies of upstream parameters dependence (density, magnetic field) concord the basic Sweet-Parker-like predictions that the dynamical properties scale globally with the Alfven speed, with particle heating scaling as the Alfven speed squared. In this study, we perform a set of symmetric 2D PIC simulations starting from Harris current sheet but differ in upstream background plasma ion temperature. The exhaust velocity in such a setup is known to have explicit temperature dependence, leading to a reduction of the jet velocity at high temperatures. We suggest that the global reconnection rate is controlled by this outflow velocity since the reconnection electric field in the quasi-steady stage is the motional (convective) electric field of the ion bulk flow within the exhaust. Consequently, if the upstream thermal speed is above the Alfven velocity, then the reconnection rate drops. On top of that, the electron-ion temperature partition in the exhaust depends strongly on the upstream ion temperature, which we attribute to the scaling in plasma compression and development of the parallel electrostatic potential in the exhaust. 
Preliminary morpho-structural analyses of the summit craters of Etna, in the last 4 Years, based on data extracted through SfM technique
Authors: Proietti Cristina , Cantarero Massimo , De Beni Emanuela
Published: March 2021

Morphological changes of the summit craters of active volcanoes are of pivotal interest in volcano monitoring because they could be the consequences of volcanic activities and represent the prelude of dangerous events.
Several methodologies have been used during the years in the volcanological monitoring, starting from ground measurements and remote sensing techniques such as aerial observation and satellite data analysis.  However, in the last decade UAVs have emerged in monitoring active volcanoes. In fact, they represent tools of indisputable value due to their relatively low cost, speed in mission planning, repeatability of surveys for data acquisition and increased operator safety.
During the last 4 Years we performed 15 UAVs surveys and 3 from helicopter to monitor the four summit craters of ETNA. The acquired data have been processed through structure-from-motion photogrammetric software to extract DEMs and orthomosaics with resolution ranging between 5 and 20 cm. A multi-temporal comparison of the extracted data has been successively performed on a GIS platform with the final aims of performing morpho-structural analyses of Etna summit craters, identifying areas of structural weakness, that could indicate areas of possible lateral collapses, and computing volume balances between gained and lost volumes.
The presented elaborations could help to quantify the hazard related to Etna summit eruptive activity and to mitigate the risk on an area visited by several tourists, especially in summer time.
Design flood estimation at locations with no data or short records in a Bayesian framework
Authors: Engeland Kolbjorn , Reitan Trond , Stenius Seija Maria , Glad Per
Published: March 2021

Estimating design floods at location with no measurements or short records is a major challenge for operational hydrology. The aims of this study are to (i) develop a regional flood frequency model that consists of a regression model for the index flood and the parameters in the growth curve; (ii) assess and attribute the uncertainty to the components of the regional flood frequency model, (iii) develop flexible approaches for combining a regional flood frequency model with local data and provide recommendations for how to combine local and regional data. Annual maximum flood data from 529 gauging stations were used for the model development. We re-parametrized the Generalized Extreme Value (GEV) distribution into an index flood component and growth curve component, and we used the median flood as the index flood. The model was estimated using a MCMC algorithm within a Bayesian framework. The Bayesian approach was also used to combine local and regional data. Two approaches were used (i) combining local and regional data to estimate the index flood (ii) combining local and regional data to estimate both the index flood and the growth curve. Simulation experiments were carried out to assess the performance of these approaches. We see that in particular for data records shorter than 10 years, we can benefit from combining the local and the regional model by both approaches. We also constructed a prior for use in local analysis that complied with the distribution of the regional model for three key quantiles.  For the index flood, the regression model was successfully estimated and evaluated using a three-step cross validation approach. The most important variables for predicting the index flood were mean annual runoff, river length and lake percentage. The attribution of uncertainty showed that most of the uncertainty was found in the index flood component.

 
Tracing gold nuggets back to the source: a microchemical analysis of tertiary gold placers in Central Spain.
Authors: Barrios Santos , Gómez Barreiro Juan , Lozano Fernández Rafael Pablo , Merinero Palomares Raúl , Suárez Barrios Mercedes , dos Santos Alves Kelvin , Morales Sánchez-Migallón Juan , Malecki Jeremi
Published: March 2021

Gold placers are abundant and intensively surveyed in western Iberia since antiquity. Three Cenozoic gold placers covering Neoproterozoic-Lower Paleozoic basement rocks have recently been revealed, which stand out for the number and size of the samples recovered: Salvatierra de Tormes (ST), Santibáñez el Alto (SA) and Casas de Don Pedro-Talarrubias (CSDP). To date, primary sources remain undiscovered. We have combined microchemical, inclusion analysis and morphology of gold nuggets to define the placer gold signature and its relationship with bedrock primary sources and infer mineralization styles. Coarse gold particles prevent secondary resetting of source signature and increase the chances to investigate mineral assemblages. Nuggets morphology analysis have reveled that ST and SA deposit are fluvial "trunk" placers, while CSDP represents an autochthon or colluvial placer type. Four different types of gold have been defined in nuggets: core gold (T1), rim gold (T2) fine grained gold in Fe-oxyhydroxides aggregates (T3) and "mustard" gold (Au+Sb-Pb-Fe-oxides) (T4).

Based on those categories we have explored primary and secondary signatures in the deposits. Lode signature is observed in the core of nuggets (T1) with a fineness between 800 and 1000. Alloy composition ranges from binary (Au:Ag) in SA to ternary (Au:Ag:Cu) in ST and CSDP. Sulphides and sulfarsenides dominates inclusions association in ST, while Sb- and Sb-Pb-Fe phases appear in ST and CSDP respectively. CSDP primary gold shows a distinct Hg content. The identification of mineral phases non-compatible with supergene conditions in gold and textural remnants of annealing microstructures, point to an hypogenic origin of T1 in all deposits and coul be compatible with a mesothermal system (<400ºC) in which, CSDP represents the higher T and SA the lower T end. A hybrid hydrothermal-magmatic system is proposed.

Secondary signature is complex and reveals several stages. Older evidence of in-situ modification of primary gold was found in CSDP gold-bearing quart fragments, with pervasive alteration under oxidizing and alkaline conditions. This process liberated gold from T1 and primary phases (e.g., aurostibite), leading to the formation of auroatimonades and "mustard" gold (T4), showing a complex textural pattern. Gold particles were subsequently modified during fluvial transport and deposition through the interaction with fluids, which activated Ag-leaching processes, resulting in the development of gold-rich rims (T2). Partial dissolution and re-precipitation of gold in reduction conditions formed very fineness gold particles embedded in Fe oxy-hydroxides (T3).
Storm-runoff processes in a mainly waterlogged low mountain range catchment in the national park Hunsrück-Hochwald, SW-Germany
Authors: Zemke Julian
Published: March 2021

This study investigates potential effects of wetland restoration on storm flow dynamics in a mainly waterlogged low mountain range catchment located in SW-Germany. Here, wetland drainage networks are being sealed, aiming to achieve rising soil water tables and reestablished peat vegetation. With the help of hydrograph separation, multiple linear regression (MLR) and covariance analysis (ANCOVA), runoff-governing storm properties and sealing influences were analyzed. Results show, that not only natural storm parameters (precipitation sum, rainfall intensity, antecedent precipitation and temperature) exert influence on storm-runoff, but sealings also led to significantly altered processes: On the one hand, storm-runoff coefficients increased in sealed catchments, resulting most likely from more saturated soils, providing a smaller infiltration capacity. This is a desired effect of rewetting but coincidently a downside regarding storm flood prevention. On the other hand, lag times, meaning the timespan between rainfall occurrence and the hydrograph starting to rise, were noticeably prolonged. This effect can be potentially beneficial when it comes to storm flood prevention. Overall, statistical models including sealings showed more satisfactory results describing stormflow variance compared to models without sealings. Therefore, sealings do exert – statistically proven – an effect on storm runoff. The heterogeneity of the results, representing a dense gauge network spread over an investigation area of roughly 7.5 km² shows, that a high-resolution sampling, both spatially and temporally, is vital. That is since runoff processes in waterlogged low mountain range catchments are still poorly understood.
Fine root exudation rate increases in drier soils, but tree level carbon exudation does not change under drought in mature Fagus sylvatica - Picea abies trees
Authors: Hafner Benjamin D. , Brunn Melanie , Zwetsloot Marie J. , Hikino Kyohsuke , Pritsch Karin , Weikl Fabian , Rühr Nadine K. , Sayer Emma J. , Bauerle Taryn L.
Published: March 2021

Drought is a severe natural risk that increases drying-rewetting frequencies of soils. Yet, it remains largely unknown how forest ecosystems respond to dry-wet cycles, hampering our ability to evaluate the overall sink and source functionality for this large carbon pool. Recent investigations suggest that the release of soluble carbon via root exudation increases under drought, influencing soil carbon stabilization and mineralization. However, an integration of root exudation into the carbon allocation dynamics of drought stressed trees is missing. We hypothesized that roots in dry soil layers have a higher exudation rate than roots in more moist layers across different soil depths. Further, we tested if higher exudation rates under drought are attenuated by reduced root abundance in dry soils and if the fraction of root exudation from total carbon allocation increases with decreasing photosynthesis rates under drought. At the KROOF experimental site in southern Germany, where mature beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.) trees were exposed to artificial drought stress for five consecutive growing seasons, we show that at the root level root exudation rate increases in drier soils. Especially roots in the upper soil profile and roots of spruce trees increased root exudation under drought. When scaled to whole tree level, we did not find differences in total exudation between drought stressed and control trees, indicating sustained root exudation at the tree level under drought. As photosynthesis rates and therefore total carbon assimilation was substantially reduced under drought (by 50 % in beech and almost 70 % in spruce), the fraction of root exudation from total assimilation slightly increased for drought stressed trees. Our results demonstrate that stimulation of root exudation rates with drought exists in natural temperate forest ecosystems but might be mitigated by reduced fine root abundance under drought. Nevertheless, increased exudation per root surface area will have localized impacts on rhizosphere microbial composition and activity especially in the topsoil exposed to more extreme dry-wet cycles. Finally, also the exudate composition can help to determine how priming of soil organic matter relates to belowground carbon allocation dynamics and to disclose processes of complementary species interaction and should be emphasised in future studies.
Impact and uncertainty of climate projections on Alpine catchments using high-resolution models
Authors: Moraga Jorge Sebastian , Peleg Nadav , Fatichi Simone , Molnar Peter , Burlando Paolo
Published: March 2021

Hydrological processes in mountainous catchments will be subject to climate change on all scales, and their response is expected to vary considerably in space. Typical hydrological studies, which use coarse climate data inputs obtained from General Circulation Models (GCM) and Regional Climate Models (RCM), focus mostly on statistics at the outlet of the catchments, overlooking the effects within the catchments. Furthermore, the role of uncertainty, especially originated from natural climate variability, is rarely analyzed. In this work, we quantified the impacts of climate change on hydrological components and determined the sources of uncertainties in the projections for two mostly natural Swiss alpine catchments: Kleine Emme and Thur. Using a two-dimensional weather generator, AWE-GEN-2d, and based on nine different GCM-RCM model chains, we generated high-resolution (2 km, 1 hour) ensembles of gridded climate inputs until the end of the 21st century. The simulated variables were subsequently used as inputs into the fully distributed hydrological model Topkapi-ETH to estimate the changes in hydrological statistics at 100-m and hourly resolutions. Increased temperatures (by 4°C, on average) and changes in precipitation (decrease over high elevations by up to 10%, and increase at the lower elevation by up to 15%) results in increased evapotranspiration rates in the order of 10%, up to a 50% snowmelt, and drier soil conditions. These changes translate into important shifts in streamflow seasonality at the outlet of the catchments, with a significant increase during the winter months (up to 40%) and a reduction during the summer (up to 30%). Analysis at the sub-catchment scale reveals elevation-dependent hydrological responses: mean annual streamflow, as well as high and low flow extremes, are projected to decrease in the uppermost sub-catchments and increase in the lower ones. Furthermore, we computed the uncertainty of the estimations and compared them to the magnitude of the change signal. Although the signal-to-noise-ratio of extreme streamflow for most sub-catchments is low (below 0.5) there is a clear elevation dependency. In every case, internal climate variability (as opposed to climate model uncertainty) explains most of the uncertainty, averaging 85% for maximum and minimum flows, and 60% for mean flows. The results highlight the importance of modelling the distributed impacts of climate change on mountainous catchments, and of taking into account the role of internal climate variability in hydrological projections.
The hydroclimate-vegetation relationship in the Amazon basin during the last 20 years: an analysis focused on the southwestern region
Authors: Gutierrez-Cori Omar , Espinoza Jhan Carlo , Z X Li Laurent , Wongchuig-Correa Sly , Arias Paola A. , Ronchail Josyane , Segura Hans
Published: March 2021

The relationship between multiple hydroclimatic variables and vegetation conditions in the upper Madeira Basin (southwestern Amazon) has been analyzed. Vegetative dynamics are characterized using NDVI dataset as an indicator of the photosynthetic capacities of vegetation. Hydroclimatic variability is analyzed using satellite-based precipitation datasets, observed river discharge, and satellite measurements of terrestrial water storage (TWS). Our results show that the vegetation in the Basin varies from energy- to water-limited. During the peak of the wet season (January-February), rainfall, discharge, and TWS are negatively correlated with NDVI (r=-0.48 to -0.65), suggesting that during this period the vegetation is mainly energy-dependent. Outside this period, these correlations are positive (r=0.55 to 0.9), suggesting that vegetation depends mainly on water availability. This higher water dependence is more noticeable during the vegetation dry season (VDS; June-October). Considering the predominant land cover types, differences in the hydroclimate-NDVI relationship are observed. Evergreen forests remain energy-limited during the beginning of the VDS, but they become water-dependent almost at the end. Savannas show a different behavior, where water dependence occurs months before the onset of the VDS. On the other hand, unlike the other variables, the TWS better explains the NDVI in evergreen forests during the VDS (r=0.7 to 0.85). This is probably because evergreen forests are more dependent on deep soil water. A spatial analysis between hydroclimatic variables and the NDVI shows the predominance of positive correlations in most of the basin. However, specific areas do not show significant correlations. The weak relationship in these areas is explained by two factors i) very wet conditions during most of the year in the "rainfall hotspot" regions, where the vegetation is not water-limited, and ii) recent land-use changes (deforestation) that break the natural response in the hydroclimate-vegetation system. These findings provide new evidence on the impacts of the land cover changes on the natural relationship between vegetation and hydroclimatic variability, which is particularly relevant given the increasing rates of deforestation in this region during recent years.
Saturn's Diffuse Core from Ring Seismology
Authors: Mankovich Christopher , Fuller Jim
Published: March 2021

Gravity field measurements only weakly constrain the deep interiors of Jupiter and Saturn, stymieing efforts to measure the mass and compactness of these planets' cores, crucial properties for understanding their formation pathways and evolution. However, studies of Saturn's rings by Cassini have revealed waves driven by pulsation modes within Saturn, offering independent seismic probes of Saturn's interior. The observations reveal gravity mode (g mode) pulsations that indicate that a part of Saturn's interior is stably stratified by composition gradients, and the g mode frequencies directly probe the buoyancy frequency within the planet.

We compare structure models with gravity and new seismic measurements from Cassini to show that the data can only be explained by a diffuse, stably stratified core-envelope transition region in Saturn extending to approximately 60% of the planet's radius. This predominantly stable interior imposes significant constraints on Saturn's intrinsic magnetic field generation. The gradual distribution of heavy elements required by the seismology constrains mixing processes at work in Saturn, and it may reflect the planet's primordial structure and accretion history.
Determining Bridge Deck Chloride Quantities Using Ground Penetrating Radar
Authors: Alongi Anthony
Published: March 2021

Chlorides from deicing salts attack the steel reinforcement in bridge decks which can ultimately cause delamination and deterioration of the concrete. For transportation agencies, the repair cost from these defects are estimated to exceed $5B per year in USA and make up between 50% - 85% of bridge maintenance budgets. While, the removal and replacement of chloride contaminated concrete is the most long-lasting and cost-effective remediation, few methods exist to determine chloride content in bridge decks. This research describes an entirely new method for determining chloride quantity in bridge decks using ground penetrating radar (GPR) technology and establishes and quantifies the relationship between chlorides in concrete (which cause corrosion of reinforcing steel and delamination of concrete) and the effect on GPR signal propagation. Specifically, it shows that there is a deterministic relationship between radar signal attenuation and the amount of chloride and moisture in bridge deck concrete, and that when moisture content is known it is possible to estimate chloride quantity based on signal loss or attenuation measurements. Our research also demonstrates the practical application of this concept by utilizing GPR along with limited coring (three or more core samples) and laboratory chloride measurements to produce an accurate and quantitative, spatial mapping of chlorides in bridge decks.
Processes influencing groundwater in the coastal aquifer of Troia Portugal
Authors: Juchem Marlin , da Conceição Neves Maria , Dill Amélia
Published: March 2021

Groundwater fluctuation in coastal aquifers depends on a number of processes which interact with each other in a complex way. In this work, we analyzed the response of the groundwater’s quality and quantity indicators of Troia costal aquifer to several forcing factors. Troia peninsula is underlayed by a multi-layer aquifer consisting of an upper phreatic layer freshwater porous aquifer, a salt water sandy layer with interbeded clay lenses and a deeper semi-confined karst aquifer. This study focuses on the upper aquifer region (10m depth), where influences of oceanic and atmospheric drivers are expected to be strongest. Groundwater data was collected from a borehole located approx. 200m from the shoreline. Hourly records of the piezometric level, conductivity, and temperature data from the hydrological year 2006-2007 were related to data of barometric pressure, rainfall and tides using correlation and singular spectral analytical methods. All variables (precipitation, barometric pressure and tidal cycles) uniquely affect the groundwater’s level and quality with different magnitudes and time scales. Regarding the long-term and larger scales, precipitation seems to be the most influential factor, contributing to 46 % of the variability of the groundwater time series. This percentage of variabillity is due the seasonality of the water cycle, with 29% related to the semi-annual cycle and 17% related to the quarterly cycle. The barometric pressure seems to affect the groundwater in similar scales as the precipitation, however tidal cycles have a much smaller impact. The tidal data was modelled with WxTides software with an interval of 15 minutes. The cyclic patterns of semidiurnal and fortnightly tidal-induced sea level changes can clearly be observed in the records of the groundwater level throughout the entire time series. Tides and groundwater level present a maximum positive correlation coefficient of 0.58 in the month of August, when other forcing factors, such as precipitation, are the lowest. Groundwater level displays a 16-day time lag with the precipitation, a two-day time lag with the barometric pressure and a two-hour time lag with the modelled tides. The correlations and lags found in this study are being used as a basis for ongoing research on the complexity of groundwater level oscillations in littoral zones. The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.
Short-term effects of experimental fire on CO2, CH4 and N2O exchange in a well-drained arctic tundra
Authors: Hermesdorf Lena , D'Imperio Ludovica , Elberling Bo , Ambus Per Lennart
Published: March 2021

Wildfire frequency in the Arctic has increased in recent years and is projected to increase further with changes in climatic conditions due to warmer and drier summers. Yet, there is a lack of knowledge about the impacts such events may have on the net greenhouse gas (GHG) balances in ecosystems. During three consecutive growing seasons, we investigated the immediate and short-term effects of experimental fire on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) surface fluxes in a well-drained tundra ecosystem in West Greenland. During the fire, we monitored litter and surface temperature, as well as the soil temperature in the top 0-5 cm. The results showed that surface temperatures exceeded 400 °C during the burning process and combusted all aboveground biomass, which significantly affected the ecosystem carbon (C) balance. Burned plots continued to be a net CO2 source for at least two years after burning. Meanwhile, soil temperature did not exceed 60 °C during the fire, and soil GHG cycling appeared relatively resistant to these conditions. Burning had an effect on soil properties and CH4 fluxes only immediately after the fire event and it had no significant effect on ecosystem respiration (ER). Instead net CH4 uptake and ER correlated (p<0.05) with soil moisture and soil temperature, respectively. No significant fire effects were observed in net N2O fluxes which suggests that processes linked to the nitrogen (N) cycle are driven by factors that were not affected by this moderate fire event.   
Joint Inversion for Surface Accumulation and Geothermal Heat Flow from Ice-Penetrating Radar Observations at Dome A, East Antarctica. 
Authors: Wolovick Michael , Moore John , Zhao Liyun
Published: March 2021

Dome A is the summit of the East Antarctic Ice Sheet (EAIS), underlain by the rugged Gamburtsev Subglacial Mountains (GSM).  The rugged basal topography produces a complex hydrological system featuring basal melt, water transport and storage, and freeze-on.  Here, we present the results of an inverse model used to infer the spatial distributions of geothermal heat flow (GHF) and accumulation rate that best fit a variety of observational constraints.  Our model agrees well with the observed water bodies and freeze-on structures, while also predicting a significant amount of unobserved water and suggesting a change in stratigraphic interpretation that reduces the volume of the freeze-on units.  Our model stratigraphy agrees well with observations, and we predict that there will be two distinct patches of ice up to 1.5 Ma suitable for ice coring underneath the divide.  Past divide migration could have interrupted stratigraphic continuity at the old ice patches, but various indirect lines of evidence suggest that the divide has been stable for about the last one and a half glacial cycles, which is a hopeful but by no means definitive sign for stability in the longer term.  Finally, our GHF estimate is higher than previous estimates for this region, but consistent with possible heterogeneity in crustal heat production.     
Multi-scale mountain waves observed with the ALIMA lidar during SOUTHTRAC-GW above the southern Andes
Authors: Kaifler Natalie , Kaifler Bernd , Dörnbrack Andreas , Gisinger Sonja , Mixa Tyler , Rapp Markus
Published: March 2021

During the SOUTHTRAC-GW (Southern hemisphere Transport, Dynamics and Chemistry – Gravity Waves) field campaign, gravity waves above the Southern Andes mountains, the Drake passage and the Antarctic Peninsula were probed with airborne instruments onboard the HALO research aircraft. The Airborne Lidar for Middle Atmosphere research (ALIMA) detected particularly strong mountain waves in excess of 25 K amplitude in cross-mountain legs above the Southern Andes of research flight ST08 on 12 September 2019. The mountain waves propagated well into the mesosphere up to 65 km altitude with possible generation of smaller-scale secondary waves during wave breaking above 65 km. A superposition of mountain waves with horizontal wavelengths in the range 15-200 km and vertical wavelengths 7-24 km dominated the wave field between 18 and 65 km altitude. Vertical wavelengths predicted by the hydrostatic equation and horizontal wind from the European Center for Medium-Range Weather Forecasts’ Integrated Forecasting System are in good agreement with observed vertical wavelengths. We apply wavelet analysis to the measured temperature field along the flight track in order to identify and separate dominant scales, and estimate their relative contributions to the total gravity wave momentum flux as well as the local and zonal-mean gravity wave drag. Furthermore, we compare our observations to results obtained by Fourier ray analysis of the terrain of the Southern Andes. The Fourier model allows the investigation of the 3d-wave field and trapped waves which are not well sampled by the ALIMA instrument because of the relative alignment between the wave fronts and the flight track. These sampling biases are quantified from virtual flights through the model domain at multiple angles and taken into account in the estimation of the total momentum flux derived from ALIMA observations. The combination of high-resolution observations and model data reveals the significance of this and similar mountain wave events in the Southern Andes region for the atmospheric dynamics at ~60° S.
Passive acoustic determination of wave breaking dissipation rate across the spectrum
Authors: Zou Xiaochen , Babanin Alexander
Published: March 2021

The ambient sound near the ocean surface is controlled by many processes, while wave breaking becomes the dominant factor once it occurs. Laboratory experiment shows that a severer breaker will result in a higher sound level and a larger mean bubble size. This relationship indicates a potential to extract information about wave breaking from acoustic records. Based on both laboratory and field experiments, a passive acoustic method has been developed to determine the wave breaking dissipation rate across the spectrum which had been extremely difficult to obtain in the open sea. The laboratory experiments were carried out in a flume at the University of Adelaide. Waves of different amplitudes and periods were generated and triggered to break by an underwater obstacle. The wave profiles before and after breaking were measured by two capacitance probes to calculate their breaking severities. The acoustic noise emitted by bubbles was recorded by a hydrophone located right under the breaking zone and the mean bubble sizes were computed on the basis of the relationship between bubble radius and acoustic frequency. A non-dimensional empirical formula between breaking severity and mean bubble size was established then applied to acoustic measurements in Lake George, New South Wales, Australia. Acoustic pulse amplitude, power spectral density of acoustic spectrum and the ratio between acoustic pulse amplitude and period were analyzed to identify the acoustic pulses truly produced by bubbles. The mean bubble sizes of each breaker were deduced from the acoustic records and further converted into their breaking severities. Combined with the wave scale information extracted from wave surface records, the spectral dissipation rates in Lake George were finally obtained. The acoustic based results are compared with various kinds of whitecapping dissipation source terms of WAVEWATCH III® and their differences are discussed.
Integrating variable traits and inheritance into the individual-based model LAVESI for evaluation of their importance for larch forest performance under future adverse conditions
Authors: Gloy Josias , Kruse Stefan , Herzschuh Ulrike
Published: March 2021

With changing climate boreal forest need to shift their distribution further north and become threatened by droughts in the south. However, whether boreal forest species can adapt to novel situations and reduce their extinction risk is largely unknown but crucial to predict future performance of populations. Exploring variable traits and ultimately trait inheritance in an individual-based model could improve our understanding and help future projections.

 

Hence, we updated the individual-based spatially explicit vegetation model LAVESI to allow for variation in traits values that are normally distributed and the option of determining the trait values based on the parental values, thus allowing full inheritance.

 

Using historical climate data and future projections, we ran simulation experiments of Larix gmelinii stands in the two areas of interest, the northern treeline expanding due to increasing temperatures, and the southern area experiencing increased drought. At these regions, the trait of ‘seed weight’ regulate migration further north and the ‘drought resistance’ protecting stands in the south, a comparison of the model variants: uniform, variable and inherited traits is being performed.

The results will be presented and will allow to disentangle how far migration rate and survival rate are influenced by this. In preliminary tests, it was already shown that both the allowing trait variation and inheritance led to an increase in migration rate, with the latter having a stronger impact. Similarly, the early tests for the drought resistance show that in changing temperatures leading to droughts the trait variation allows for adaption and leads to better surviving populations.

 

We expect that variable traits ensure that if the environment changes necessary trait variants are available. Inheritance could let the populations adapt to environments and promote successful trait values and therefore lead to more optimised populations, that are able to spread faster and be as resilient as needed.

 

With this, we show that implementing trait variation and inheritance may contribute to creating more accurately predicting models and understanding responses of boreal forests to global change.
Selective mineral dissolution and permeability enhancement of fractured volcanic rocks by chelating agent flooding in geothermal environments 
Authors: Salala Luis , Watanabe Noriaki , Takahashi Kaori , Erazo Jose , Tsuchiya Noriyoshi
Published: March 2021

Chemical stimulation using high-concentration hydrofluoric and hydrochloric acids has been a classic method to enhance the permeability of a geothermal reservoir. Our research group has recently proposed a new chemical stimulation using a weakly acidic (moderate-reactivity) aqueous solution containing an environmentally friendly chelating agent to create voids, which are sustained under crustal stress, by selective mineral dissolution with preventing precipitation by chelation of metal ions. In the present study, we have conducted chelating agent flooding experiments using an aqueous solution of pH 4 containing readily biodegradable chelating agent (GLDA) on various types of fractured volcanic rocks at 200 oC and effective confining stress of 15 MPa. The experiments have revealed fast permeability enhancement of up to approximately four times, from the initial value, in two hours. Further analyses have revealed phenocrysts of Fe-bearing minerals (ex. Hematite) dissolved faster than the groundmass of the rocks to create the voids. These results show the possibility of the new chemical stimulation.

Keywords: Chemical stimulation, Chelating agents, Geothermal energy, EGS