bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial analysis of return periods of hydrological drought of Nile River Basin
Authors: Mengistu Tsidu Gizaw
Published: March 2020

The Nile River Basin has been vital source of water to Riparian countries in both upper and lower catchments of the Basin. However, the states in the lower catchment namely Sudan and Egypt have exploited this resource without significant competition from countries in the upper catchments in the past. Recently, due to population increase in the basin and climate change, there are some initiatives by Riparian States such as Ethiopia to use this vital water resource (e.g., for energy generation). Therefore, it is important to understand recurrent drought characteristics and its potential impacts on the water resource in the basin. Drought events in the Nile Basin have been extracted using run theory based on the Standardized Precipitation Evapotranspiration Index (SPEI) accumulated on the time scale of 12 months using CRU rainfall and evapotranspiration data, which covers the period 1901–2018. The drought events are characterized by four variables: duration, severity. Intensity and Inter-arrival time. The mean duration and severity of drought during the last 118 years over the Basin are generally short and moderate over upper catchments. Conversely, the mean duration various from 4 to 8 months and up to 14 months over the middle and lower catchments of the Basin respectively while the mean drought severity increases from -2 at upper catchment to -7 at lower catchment. Gamma, Weibull, Gamma and Exponential functions are then selected to describe the marginal distribution of severity, duration, intensity and inter-arrival time, respectively. The Gumbel–Hougaard Copula was used to construct the joint distribution of duration, severity, intensity and/or inter-arrival time. The results indicate that the return period is dependent on the location within the basin, variable type and the combination of variables. For extreme droughts with severity index of -10 and duration of 14 months, return periods are longer than 40 years over south parts of the Basin and it barely exceeds 25 years over northern parts of the Basin. Generally, the short return period is mainly distributed in lower catchments of the Basin. This study on the identification of spatial distributions of drought return periods across the Basin is therefore important for drought mitigation and strategic planning on the water resource.
Source-to-Sink Systems in the Central Atlantic: Cretaceous Climate Transitions and the Consequences for Reservoir Distribution
Authors: Nicoll Graeme , Smith Joss , Gréselle Benjamin
Published: March 2020

In frontier settings where data are limited or nonexistent, exploration often relies on predictive models to define uncertainty and derisk decisions. However, helping predict the spatial and temporal extent of geological elements in ancient systems is often challenging and requires a combined multidisciplinary methodology and mindset. The benefits of following a holistic Earth system science approach to the global-scale prediction of petroleum system elements are discussed.

Building on spatial and temporal frameworks provided by plate tectonic and sequence stratigraphic modelling, palinspastic gross depositional environment maps can be integrated with numerous data sets to generate useful paleo-digital elevation models (PDEM) for discrete time slices of the Earth’s history. With a reliable depiction of ancient landscapes and bathymetry, these global PDEMs are instrumental in identifying sediment source areas, which facilitates modelling of paleodrainage pathways. These PDEMs form an essential input to run global paleoclimate and paleotidal simulations, which, in turn, provide a wide range of useful parameters. In combination, paleodrainage and paleoclimate outputs allow for a predictive source-to-sink approach, which provides useful insights away from data constraints.

To highlight the predictive capabilities of this approach, the focus is on the Cretaceous paleo-margin from Guyana in northeast South America to Morocco in northwest Africa. The generation, quality, and distribution of clastic and carbonate systems related to the changing geomorphological and climatic evolution of the central Atlantic domain are discussed.

Within this prospective region, climatic trends are demonstrated (i.e., an intensification of precipitation along the equatorial margin and a progressive aridification in northern Africa) and their implications are discussed. For a range of Cretaceous time-slices, predictions of sediment flux, submarine fan dimensions, and hinterland composition, which provide useful insight into potential reservoir extent and quality along this margin, are demonstrated. By integrating climate, sediment flux, and sediment composition predictions, a margin-wide screening for clastic reservoir potential highlighting areas where existing plays could be extended (MSGBC) and where climatic controls add significant potential risk to reservoir presence and quality (Morocco) are presented.
Real time data quality control applied on an IOT sensor water quality network
Authors: Maeyens Matthias , Pagán Brianna , Seuntjens Piet , Maiheu Bino , Desmet Nele , van Loo Maarten , van Hoey Stijn
Published: March 2020

In recent years, extend periods of drought have been affecting the water quality and availability in  the Flanders region in Belgium. Especially the coastal region experienced an increased salinization of ground and surface water. The Flemish government therefore decided to invest in a dense IoT water quality monitoring network aiming to deploy 2500 water quality sensors  primarily in surface water but also in ground water and sewers. The goal of this "Internet of Water" project is to establish an operational state of the art monitoring and prediction system in support of future water policy in Flanders. 

Since Flanders is a relatively small region (13,522 km²), placing this many sensors will result in one of the most dense surface water quality sensor networks in the world. Each sensor will continuously measure several indicators of water quality and transmit the data wirelessly. This allows us to continuously monitor the water quality and build a big enough data set to be able to use a more data driven approach to predicting changes  in water quality. However, as with any sensor system, the quality of the data can vary in time due to problems with the sensors, incorrect calibration or unforeseen issues. Real-time data quality control is crucial to prevent unsound decisions due to faulty data.

This contribution will give a general overview of the network and it’s specifications, but mainly focus on the implementation of the data stream as well as methods that are implemented to guarantee good data quality. More specifically the architecture and setup of a real-time data quality control system is described. Which will add quality control flags to measurements.  This system is  integrated with the NGSI API introduced by FIWARE, which forces us to make specific design decisions to acommodate to the NGSI API.
Recent Subsidence Rates in the Mekong Delta derived from Sentinel-1 SAR-Interferometry
Authors: Dörr Nils , Schenk Andreas , de Wit Kim , Lexmond Bente R. , Minderhoud Philip S.J. , Neussner Olaf , Nguyen Diem K. , Nguyen T. Loi
Published: March 2020

Coastal subsidence increases the vulnerability to flooding risk, salinization of water resources and permanent inundation. For the Mekong Delta, whose mean elevation is less than 2 m above sea level, subsidence rates of up to several centimeters per year have been reported recently. This leads to a growing risk for the resident population, infrastructure and economy, increased by the accelerating sea level rise. Land subsidence in Mekong Delta has different causes, most prominently natural compaction of young deltaic sediments, but also overexploitation of groundwater aquifers with accompanying head decline. Precise monitoring of the subsidence rate is necessary for analyses of cause and hazard as well as planning and assessment of countermeasures. Here, we present and discuss recent land subsidence rates in the Mekong Delta derived from satellite-based SAR-Interferometry.

We use Sentinel-1 scenes acquired between 2015 and 2019 to analyze recent land subsidence in the lower Mekong Delta. The Persistent Scatterer Interferometry technique (PS-InSAR) is applied, which allows for the estimation of displacement rates of coherent backscatter targets with mm-accuracy. Separate analyses of time series from ascending and descending observations and comparison with other studies based on data of the same sensor give insight into the accuracy of the parameter estimation and the error budget.

The observed subsidence rates of up to 6 cm/yr feature mainly three different spatial characteristics: (i) interconnected areas of little to no subsidence, (ii) isolated urban hot-spots with high subsidence rates and (iii) larger regions with increased subsidence rates covering urban as well as rural areas. Points on deeply founded infrastructure frequently exhibit lower subsidence rates than adjacent ground surface points. We study this phenomenon at different buildings since subsidence rates with respect to different foundation depths can be used as a proxy to constrain the effective depths of sediment compaction. Further, the correlation of observed subsidence rates and spatial distribution of lithostratigraphic units from quaternary sedimentary depositions is investigated. Finally, we show changes and commons in the spatial distribution of the subsidence rates compared to a previously published study on subsidence in the Mekong Delta covering data from 2006 to 2010.
Assessing underground heat exchange and solar heat storage capabilities based on ground thermo-physical properties: the Euganean hills demo site (Italy)
Authors: Di Sipio Eloisa , Sassi Raffaele , Buggiarin Stefano , Ceccato Silvia , Galgaro Antonio
Published: March 2020

The utilization and development of renewable energy sources (RES) is currently a topic of great interest in energy field. In detail, the coupling of different RES and related technologies, as solar thermal and shallow geothermal, for heating/cooling purpose of residential buildings is a promising sector. The possibility to store the thermal energy produced by solar panels in the underground during the summer season, when the insolation is greater, and to use the heat accumulated during the coldest periods, is strictly related, among others, both to the thermo-physical properties of rocks and to the solar radiation locally available. As the ground is the invariant component of the whole system, a better knowledge of its thermal properties (i.e. thermal conductivity, volumetric heat capacity…) is fundamental to evaluate the amount of heat that can be stored.

This paper presents an innovative methodological approach combining information related to underground thermal energy exchanging and storage capacity with the solar radiation, taking also into account the location of the possible end-users, that is the distribution of the residential buildings in the territory. The Euganean Hills area, located in the Po River Plain (north-east Italy), is selected as demonstration test site. A qualitative map, created using Geographycal Information System (GIS) application, has been realized in order to represent the “Ground thermal suitability” of a territory to sensible heat storage, that is the possibility to store solar energy in the underground for a later use.

This thematic map is a really promising tool, suitable for local administrator and professionals, for planning the possible exploitation of solar thermal renewable resources available in the area.
NOC GNSS-R Global Ocean Wind Speed and Sea-Ice Products
Authors: Hammond Matthew , Foti Giuseppe , Gommenginger Christine , Srokosz Meric , Unwin Martin , Rosello Josep
Published: March 2020

Global Navigation Satellite System-Reflectometry (GNSS-R) is an innovative and rapidly developing approach to Earth Observation that makes use of signals of opportunity from Global Navigation Satellite Systems, which have been reflected off the Earth’s surface. Using GNSS-R data collected by the UK TechDemoSat-1 (TDS-1) between 2014 and 2018, the National Oceanography Centre (NOC) has developed a GNSS-R wind speed retrieval algorithm called the Calibrated Bistatic Radar Equation (C-BRE), which now features updated data quality control mechanisms including flagging of radio frequency interference (RFI) and sea-ice detection based on the GNSS-R waveform. Here we present an assessment of the performance of the latest NOC GNSS-R ocean wind speed and sea-ice products (NOC C-BRE v1.0) using validation data from the ECMWF ERA-5 re-analysis model output. Results show the capability of spaceborne GNSS-R sensors for accurate wind speed retrieval and sea-ice detection. Additionally, ground-processed Galileo returns collected by TDS-1 are examined and the geophysical sensitivity of reflected Galileo data to surface parameters is investigated. Preliminary results demonstrate the feasibility of spaceborne GNSS-R instruments receiving a combination of GNSS signals transmitted by multiple navigation systems, which offers the opportunity for frequent, high-quality ocean wind and sea-ice retrievals at low relative cost. Other advancements in GNSS-R technology are represented by future mission concepts such as HydroGNSS, a proposed ESA Scout mission opportunity by SSTL offering support for enhanced retrieval capabilities exploiting dual polarisation, dual frequency, and coherent reflected signal reception.
Catchment exports and monitoring
Authors: Moatar Florentina , Renard Benjamin , Floury Mathieu , Gold Arthur , Meybeck Michel , Minaudo Camille , Ferréol Martial , Chandesris André , Addy Kelly , Piffady Jeremy , Pinay Gilles
Published: March 2020

Solute and sediment catchment exports from drainage basins are difficult to quantify because they are exported during “hot moments”, generally during high water periods.  

We present here a simple model for predicting load flashiness (M2, proportion of load exported during the highest 2% of flows) from flow flashiness (W2, proportion of flows exported during the highest 2% of flows) and export pattern (b50high, linear slope of the log concentration-log discharge relationship based on data above the median flow only). The model is parameterised based on an extensive monthly-sample data set from France, and validated using an independent daily-sample long-term data set from US including several rivers near Lake Erie (altogether over 1.5 Million discharge-concentration

Based on this model, we constructed a load-flashiness diagram to determine optimal monitoring frequency of dissolved or particulate constituents as a function of b50high and W2. Based on M2, optimal temporal monitoring frequency of the studied constituents decreases in the following order: TSS, TP, DOC, NO3, and TDS. Finally, we analyzed relationships between these metrics and catchments characteristics. Depending on the constituent, we explained between 30 to 40% of their M2 variance with simple catchment characteristics, such as stream network density or percentage of intensive agriculture. Therefore, catchment characteristics can be used as a first approach to set up water quality monitoring design where no hydrological and/or water quality monitoring exist.

The load flashiness M2 can also be used to optimize monitoring frequency to reach a certain level of annual load uncertainty (here 10%) for loads trend detection required for instance by international conventions such as OSPAR and HELCOM. Regulatory monitoring in Europe, recommended by the WFD, promotes the monthly sampling for any monitored constituents (dissolved and particulate) and for any basin size. Such standardized monitoring does not take into account the actual variability of the constituent concentration and loads, particularly for the small (100 – 1000 km²) and very small (< 100 km²) basins. For instance, our results show that a 30 days sampling frequency is not appropriate to calculate loads with a reasonable uncertainty (+/- 10%) in more than 90% of cases.
A fragmentation model approach for low velocity impact charging
Authors: Antonsen Tarjei , Mann Ingrid , Vaverka Jakub , Nouzak Libor
Published: March 2020

This work addresses the generation of charge during impacts of nano- to microscale projectiles on metal surfaces at speeds from 0.1 to 10 km/s. These speeds are well above the range of elastic deformation and well below speeds where volume ionization occures. Earlier models have utilized impurity diffusion through molten grains together with a Saha-equation to model impact ionization at these speeds. In this work we employ a model of capacitive contact charging in which we allow for projectile fragmentation upon impact. We show that this model well describes laboratory measurements of metal projectiles impacting metal targets. It also can describe in-situ measurements of dust in the Earth’s atmosphere made from rockets. We also address limitations of the currently most used model for impact ionization.
Observing System Simulation Experiment (OSSE) of future ALTIUS ozone profiles
Authors: Errera Quentin , Debosscher Jonas , Dekemper Emmanuel , Demoulin Philippe , Fussen Didier , Piroux Didier , Vanhellemont Filip , Mateshvili Nina
Published: March 2020

ALTIUS (Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere) is a satellite mission dedicated to continue Earth limb measurements for atmospheric sciences (Fussen et al., JQSRT, 2019). It is an element of the ESA Earth Watch programme and is expected to be launched in 2024 on a low earth polar orbit. The instrument is based on three spectral imagers that will measure in UV-vis-NIR wavelength range and will operate in different viewing geometry: limb scattering and occultation of the sun, the moon, the planets and the stars. ALTIUS will retrieve vertical profiles of ozone, nitrogen dioxide, aerosol extinction, among others.

In this study, we present an Observing System Simulation Experiment (OSSE) of ALTIUS ozone profiles that we have compared with the existing observations from Aura Microwave Limb Sounder (MLS). For this purpose, we have created a stratospheric ozone reference dataset between June and September 2008 based on the assimilation of MLS data with the Belgian Assimilation System for Chemical Observations (BASCOE). During the MLS assimilation experiment, the ozone state is saved in the space of ALTIUS previously determined with the ALTIUS orbit simulator, then perturbed according to the ALTIUS error budget, which creates ALTIUS synthetic observations. The assimilation of these ALTIUS ozone profiles agrees well with those of MLS. The assimilation of the different modes of ALTIUS reveals that all modes are necessary to constrain ozone during the polar night: solar and stellar occultations are the most constraining during the June-August period while limb scattering profiles are the most constraining from September onward.

 
Rate enhancement in collisions of sulfuric acid molecules due to long-range intermolecular forces
Authors: Halonen Roope , Zapadinsky Evgeni , Kurtén Theo , Vehkamäki Hanna , Reischl Bernhard
Published: March 2020

Collisions of molecules and clusters play a key role in determining the rate of atmospheric new particle formation and growth. Traditionally the statistics of these collisions are taken from kinetic gas theory assuming spherical noninteracting particles, which may significantly underestimate the collision coefficients for most atmospherically relevant molecules. Such systematic errors in predicted new particle formation rates will also affect large-scale climate models. We studied the statistics of collisions of sulfuric acid molecules in a vacuum using atomistic molecular dynamics simulations. We found that the effective collision cross section of the H2SO4 molecule, as described by an optimized potentials for liquid simulation (OPLS) all-atom force field, is significantly larger than the hard-sphere diameter assigned to the molecule based on the liquid density of sulfuric acid. As a consequence, the actual collision coefficient is enhanced by a factor of 2.2 at 300 K compared with kinetic gas theory. This enhancement factor obtained from atomistic simulation is consistent with the discrepancy observed between experimental formation rates of clusters containing sulfuric acid and calculated formation rates using hard-sphere kinetics. We find reasonable agreement with an enhancement factor calculated from the Langevin model of capture, based on the attractive part of the atomistic intermolecular potential of mean force.
Precision Heterodyne Oxygen-Calibration Spectrometry: Vertical Profiling of Water and Carbon Dioxide in the Troposphere and Lower Stratosphere
Authors: Miller J. Houston , Flores Monica , Bomse David
Published: March 2020

We describe the continued development of a new laser heterodyne radiometry (LHR) technique:  Precision Heterodyne Oxygen-Calibration Spectrometry, or PHOCS. The prototype instrument is equipped with two active laser channels for oxygen and water (measured near 1.28 µm) and carbon dioxide (near 1.57 µm) determination. The latter may be substituted by a heterodyne receiver module equipped with a laser to monitor atmospheric methane near 1.65 µm). Oxygen measurements provide dry gas corrections and – more importantly – determine accurate temperature and pressure profiles that, in turn, improve the precision of the CO2 and H2O column retrievals. Vertical profiling is enabled by interrogating the very low-noise, absorption lines shapes collected by the O(10-3 cm-1) instrument. The presentation will describe (1) the continued development of column concertation retrieval protocols and (2) the results of initial tests performed at the Smithsonian Environmental Research Center in Edgewater, Maryland during the summer/fall of 2019 and spring of 2020.
Determination of rock transport parameters using short-term radionuclides and nanoparticles
Authors: Zuna Milan , Dobrev David , Havlová Václava , Kůs Pavel , Doubravová Daniela , Parma Petr
Published: March 2020

The aim of the project is to develop and test the short-lived radionuclides in order to describe the contaminant transport processes radionuclides, tracer metals and nanoparticles in the environment. Furthermore, the aim is also to develop on-line detection methods to quantify the processes that influence their movement towards the biosphere. Use of short lived radionuclide in tracer tests brings an advantage of excellent detection and avoids contamination of rock samples/environment during experiments.

The research is focused predominantly on radio-tracers in various forms (solute/nanoparticles) and on development of advanced detection techniques for their monitoring and display. The following pre-selected radionuclides were considered for potential  irradiation (24Na, 42K, 64Cu, 72Ga, 76As, 82Br, 99Mo, 140La, 142Pr, 198Au, 166Ho, 188Re, 153Sm). After thorough evaluation, holmium and rhenium compounds were selected for irradiation in the LVR- 15 reactor (CVŘ Řež), namely holmium oxide (Ho2O3) and ammonium perphenate (NH4ReO4). Those compounds were selected based on the computational analyses. Solutions of 50, 200, 300 MBq (188Re) and 300 MBq (166Ho) were finally prepared for detection tests. Paralelly, a method for the preparation of chromium oxide nanoparticles was introduced and tested.

A miniaturized spectral camera MiniPIX TPX3 has been developed for radionuclide detection. It is similar to the MiniPIX with a Timepix3 chip, a new generation of chips developed by the collaboration Medipix3. The camera has a resolution of 256 x 256 pixels with a pixel size of 55 x 55 µm (2 mm CdTe sensor).

The developed measurement system enables on-line monitoring and 3D visualization of the radioactivity distribution in the studied rock samples with respect to radionuclide distribution within the rock. Various measurement configurations were tested with respect to source activity, detector/collimator distance, and rock thickness to find optimal measurement parameters.

The work described herein was funded by the project of the Ministry of Industry and Trade in the TRIO program (FV30430)
A multi-approach skill-score procedure to optimize continental-scale ice-sheet models
Authors: Tabone Ilaria , Robinson Alexander , Alvarez-Solas Jorge , Blasco Javier , Moreno Daniel , Montoya Marisa
Published: March 2020

Simulations of large-scale ice sheet models are crucial to understand the long-term evolution of an ice sheet and its response to climate forcings. However, solving the ice-flow equations and processes proper of the ice sheet at large spatial scales requires reducing the model computational complexity to a certain degree. To do so, coarse-resolution models represent several physical processes and ice characteristics through model parameterisations. Ice-sheet boundary conditions (e.g. basal sliding, surface ablation, grounded and marine basal melting) as well as unconstrained ice-flow properties (e.g. ice-flow enhancement factor) are some examples. However, choosing the best parameter values to well represent such processes is a demanding exercise. Statistical methods, from simple to advanced techniques involving Bayesian approaches, have been taken into account to evaluate the model performance. Here we optimise the performance of a new state-of-the-art hybrid ice-sheet-shelf model by applying a skill-score method based on a multi-misfits approach. A large ensemble of paleo-to-present transient simulations of the Greenland ice sheet (GrIS) is produced through the Latin Hypercube Sampling technique. Results are then evaluated against a variety of information, comprising the present-day state of the ice sheet (e.g. ice thickness, ice velocity, basal thermal state) as well as available paleo reconstructions (e.g. glacial maximum extent, past elevation at the ice core sites). Results are then assembled to generate a single skill-score value based on a gaussian approach. The procedure is applied to various model parameters to evaluate the best choice of values associated with their parameterisations. 
Compositional heterogeneity amongst salt-rich grains emitted from Enceladus’ subsurface ocean
Authors: Zou Zenghui , Postberg Frank , Hillier Jon , Khawaja Nozair , Klenner Fabian , Nölle Lenz
Published: March 2020

Salt-rich icy particles within Saturn’s E-Ring are relatively young (<~200 years), and originate from frozen aerosolized droplets of the salty seawater of Enceladus’ subsurface ocean, ejected into space, through fractures in the moon’s south polar region, within a plume of gas and ice particles. The salt-rich grains are therefore believed to reflect the composition of the ocean water. In situ mass spectra of the plume and E-ring icy particles, obtained by the Cosmic Dust Analyzer (CDA) impact ionization mass spectrometer onboard the Cassini spacecraft, indicate significant compositional diversity within the salt-rich population. Understanding the compositions of dissolved salts within the grains, and thus the ocean, can provide important constraints for geochemical models of Enceladus’ core/ocean environment.

To investigate and quantify variations in grain composition, a Laser Induced Liquid Beam Ion Desorption (LILBID) technique has been used to desorb and ionize a wide range of Enceladean ocean-like solutions containing dissolved salts. The resulting ions were then measured by a reflectron-type time of flight mass spectrometer. As the laser desorption mechanism simulates the ice grain impact process occurring on the CDA target, spectra produced in the laboratory from a large range of well-characterized salt solutions can be used to determine the CDA-applicable spectral appearances of substances within the ice grains emitted from Enceladus’ ocean.

Here we present the results of an investigation of CDA E-ring spectra, supported by laboratory analogue experiments, which show significant compositional heterogeneity within the salt-rich grains originating from Enceladus’ subsurface ocean. Two main spectral subtypes, representing endmember compositions within the salt-rich grains, are identified. These mass spectra are dominated by features from chloride-rich or carbonate-rich compounds and the laboratory detectability of other, additional, compounds within these brines is discussed.
Building a climate service to support an Εarly Warning System for the West Nile Virus disease in Greece
Authors: Katragkou Eleni , Karypidou Maria Chara , Kartsios Stergios , Gewehr Sandra , Mourelatos Spiros
Published: March 2020

According to the National Public Health Organization in Greece, cases of West Nile Virus (WNV) infection in humans and animals have been recorded in various areas over Greece during the years 2010-2014 and 2017-2019 (https://eody.gov.gr). In this work we present a climate service which supports an Early Warning System (EWS) for the mosquito-borne WNV disease, operated for the first time over the Region of Central Macedonia in Greece. The EWS is based on a platform fed by time-dependent data (climate information and mosquito population data (Culex sp.)) and time invariant data (topography, density of mosquito breeding sites taken from field campaigns and distance to water-related land cover categories). The climate data are produced on a daily basis by the WRF-AUTH-MC weather forecast model over a 2x2 Km grid covering the Region of Central Macedonia, which operates from April to October (mosquito circulation period). Mosquito samples are collected every 2 weeks by the company ECODEVELOPMENT, using CO2 mosquito traps. The mosquito data along with the climatic and static environmental information are utilized within a Generalized Linear Model (GLM). Based on an empirical relationship derived from the GLM, the overall environmental suitability for the Culex mosquito is assessed over the study region. The work is performed in the framework of the German-Greek bilateral project “Establishment of an Early Warning System for mosquito borne diseases” (http://www.wnvalert.eu/), which is focusing on improved measures on proactive mosquito control and disease prevention activities.
Greenhouse gas emissions from a Mediterranean floodplain forest: the role of tree emissions under a changing flooding regime.
Authors: Poblador Sílvia , Martínez-Sancho Elisabet , Menéndez-Serra Mateu , Casamayor Emilio O. , Estiarte Marc , Lupon Anna , Martí Eugènia , Peñuelas Josep , Sabaté Santiago , Sabater Francesc
Published: March 2020

The increase of greenhouse gas (GHG) emissions into the atmosphere is promoting and accelerating climate warming. Among GHG sources, soils are an important natural source of GHG to the atmosphere through aerobic soil respiration that release carbon dioxide (CO2). However, in riparian areas, soils can also release relevant amounts of methane (CH4) and nitrous oxide (N2O) through anaerobic processes promoted by high groundwater levels or flooded conditions. Recent studies have highlighted the role of trees in CH4 emissions, but little is still known about the origin of these emissions, the processes involved, and their contribution to the global carbon and nitrogen cycles. To shed light on this issue, we measured GHG emissions (i.e. CO2, CH4, and N2O) from the stems of two riparian tree species (Fraxinus agustifolia and Quercus robur) located along a gradient of soil moisture conditions (i.e. from wet to completely flooded soils) in a Mediterranean floodplain forest. Moreover, we also analyzed the isotopic carbon signature of the GHG emitted and the microbial communities inhabiting within tree stems by 16S rRNA gene analysis. Our results showed that CH4 emitted by riparian tree stems was 100-fold higher at the flooded than at wet soil locations, while CO2 and N2O emissions did not vary across moisture conditions. When considering together emissions form soil surface and tree stems under flooded conditions, riparian trees contributed up to 20%, 40% and 60% of the total CH4, CO2, and N2O emissions, respectively. Keeling plots suggested that CO2 emitted through tree stems was produced within the soil compartment and thus transported to the atmosphere through the tree stems, whereas CH4 emissions may have a different origin. However, methanogens were almost absent on the wood microbiome. The substantially higher presence of methanotrophs on the wood than on the soil compartment suggested that, despite CH4 emitted by stems could come from soil microbial activity, the microbial consumption of that CH4 within the tree stem could have changed its isotopic signature. Overall, our findings suggest that the riparian trees growing in this Mediterranean floodplain forest may mainly act as passive transporters of GHG produced in soils instead of being active GHG producers.
Exploration of electromagnetic induction potential to understand groundwater infiltration within the Chalk critical zone
Authors: Dumont Marc , Guillemoteau Julien , Cavalcante-Fraga Luis , Guérin Roger , Schamper Cyril , Chen Ningxin , Valdés Danièle
Published: March 2020

The underground quarry of Chalk at Saint-Martin le Nœud (80km north of Paris, France) is an instrumented site of particular interest to study infiltration processes in the Chalk critical zone. The outcropping of the water table creates permanent underground lakes (20 and 30m below the surface) showing spatial and temporal variations of groundwater hydrodynamics and geochemistry within the 1.2km long quarry. Previous studies showed a correlation between infiltration variations and the geometry of the clay covering the Chalk. Here, we present a methodology coupling electrical and electromagnetic surveys to analyze the control of the critical zone structures on infiltration processes.

In 2019, the whole quarry has been covered by an electromagnetic induction (EMI) mapping, providing an estimation of the shallow bulk electrical conductivity at several depths of investigation with a good lateral resolution (0.5m spacing along lines spaced 5 to 25m apart). The EMI instrument used for this study requires a calibration with conductivity/resistivity values as provided by rocks samples or electrical resistivity tomography (ERT). For this purpose, and additionally to characterize deeper structures, five ERT profiles have been acquired above underground lakes with contrasted hydrodynamical behaviors. Such setting poses several challenges for the calibration of EMI data as (i) the EMI and ERT methods have, by definition, different lateral sensitivities and (ii) the numerical modellings used for both methods in the calibration procedure are based on different geometric assumptions (2D for ERT, and 1D for EMI).

Our study explores an approach to refine and improve EMI calibration using contrasted ERT profiles. The first step tackles, for each ERT profile, the difference between EMI and ERT resolution in order to improve the consistency between the imagery of both methods. The second step analyzes the consistency of the five calibrations for each ERT profiles and the calibration validity in regards to the lateral heterogeneity at the quarry scale. As a result, we are able to provide reliable EMI calibration while taking advantage of deeper ERT imagery in areas of interest. These results are improving our understanding of the geometry of the clay covering the Chalk formations. This geometry is confronted with previous geochemical and hydrodynamical results to understand how the critical zone structures control temporal variations of groundwater infiltration within the critical zone.
Observation of gravity fluctuations due to tide-induced groundwater table fluctuations with two superconducting gravimeters
Authors: Goto Hiroki , Sugihara Mituhiko , Nishi Yuji , Ikeda Hiroshi
Published: March 2020

Estimation of aquifer hydraulic properties is necessary for predicting groundwater flow and hence managing groundwater resources. Analysis of tide-induced groundwater table fluctuations in unconfined aquifers is one of the methods to estimate aquifer properties. Changes in groundwater level affect surface gravity. Consequently, surface gravity in coastal regions is expected to fluctuate due to the groundwater table fluctuations and is potentially useful for estimating aquifer properties. Moreover, gravity measurements are sensitive to mass redistribution around the observation location and therefore are useful for estimating the storage coefficient of an aquifer. In this study, surface gravity and unconfined groundwater level were measured continuously near the coast of Japan to observe gravity fluctuations due to the tide-induced groundwater table fluctuations. Groundwater level measured in two wells at 60 and 90 m distances from the coastline fluctuated in response to ocean tides. Two superconducting gravimeters (SGs) were installed at 70 and 80 m distances from the coastline and at an elevation of 8 m. After taking the difference between gravity values recorded with the two SGs and then correcting the gravity difference for ocean loading effects, diurnal and semi-diurnal gravity fluctuations, which are possibly due to tide-induced groundwater table fluctuations, were recognized. These results suggest that gravity monitoring with two SGs at different distances from the coastline can be useful for observing gravity fluctuations due to tide-induced groundwater table fluctuations and possibly for estimating aquifer hydraulic properties.
Exospheric Na distributions along the Mercury orbit with the THEMIS telescope
Authors: Milillo Anna , Mangano Valeria , Massetti Stefano , Mura alessandro , Plainaki christina , Alberti Tommaso , Ivanovski Stavro , De Angelis Elisabetta , Rispoli Rosanna
Published: March 2020

The variability of Na exosphere of Mercury shows time scales from less than one hour to seasonal variations. While the faster variations, accounting of about 10-20% of fluctuations are probably linked to the planet response to solar wind and IMF variability, the seasonal variations (up to about 80%) should be explained by a complex mechanisms involving different surface release processes, loss, source and migrations of the exospheric Na atoms. Eventually, a Na annual cycle can be identified. In the past, integrated disk emission from ground-based observations and equatorial density from MESSENGER have been analysed. In this study, for a better investigation of the exospheric Na features, we have studied the local time and latitudinal distributions of the exospheric Na column density as a function of the True Anomaly Angle (TAA) of Mercury by means of the extended dataset of images, collected from 2009 to 2013, by the THEMIS solar telescope. In particular, THEMIS images, in agreement with previous results, registered a strong general increase at aphelion and a dawn ward emission predominance with respect to dusk ward and subsolar region between 90° and 150° TAA. We find a predominance of subsolar column density along the rest of the Mercury orbit. Also an unexpected relation between Northward or Southward peak emission and both TAA and local time is evidenced by our analysis requiring further investigations. Possible relationship with distance from the dust disk or IMF polarity is being considering.
A Robust Error Characterization Method for SAR Altimetry over the Inland Water Domain
Authors: Wenzl Martina , Restano Marco , Benveniste Jérôme
Published: March 2020

The advent of SAR (delay-Doppler) altimetry allowed the production of data with a high spatial resolution (300 m along-track). Investigations in the inland water domain clearly benefited from SAR data and future processing strategies (e.g. the fully-focused SAR, FF-SAR) are expected to improve further the quantity of data points over water bodies of a reduced size.

The proposed work aims at investigating the quality of Sentinel-3 water level retrievals over three targets of different characteristics: the Ohio River, the Columbia River and the Great Salt Lake. Data are processed through the ESA G-POD SARvatore online and on-demand processing service for the exploitation of CryoSat-2 and Sentinel-3 data (https://gpod.eo.esa.int/services/SENTINEL3_SAR/) and obtained by using the SAMOSA2, SAMOSA+ & SAMOSA++ retrackers. The selected posting rate of measurements is 80 Hz to optimize the location of data points over the Ohio and Columbia River (an estimate every 80 m along-track), however a comparison with the 20 Hz posting rate is being made. Empirical retrackers outputs, available in the official 20 Hz Sentinel-3 LAN products, are also considered for comparison and water masks from (Pekel et al., 2016) are used to select data points acquired over water bodies.

The main goal of this study is to analyse the key parameters characterizing both the L1b SAR waveform and the retracking (e.g. the Pulse Peakiness, the Misfit…) to define a robust error characterization method that is expected to filter out an increased number of outliers. A validation exercise using in situ data will be presented to demonstrate that the proposed method leads to the definition of a reduced, highly reliable dataset, associated with a realistic error characterization model.

The study is expected to unlock possible synergies with SWOT and support the comparison of SAR estimates to FF-SAR estimates obtained at a comparable along-track resolution.
Reconstruction of LGM ice extents in Europe indicates a cold and dry climate with precipitation patterns similar to present day
Authors: Višnjević Vjeran , Herman Frederic , Prasicek Günther
Published: March 2020

 

During the pinnacle of the last glacial period 21 kyr ago, the Alps and the Pyrenees were largely covered by ice. Climate was colder and most likely drier, but the magnitudes of temperature and precipitation changes remain poorly constrained. This is in part because climate proxies are not sufficiently accurate, and because there are unknowns on the past position of the Westerly winds and, consequently, the intensity of the moisture flow towards Europe. A new inverse method combined with an ice flow model enables us to infer past climate from mapped ice extents. In the case of the Alps, all of the presented scenarios recover an increase in the position of the ELA across the mountain range from west to east, and a decrease from north to south, pointing to a dominantly zonal circulation with Westerlies bringing moisture from the Atlantic. This is supported by the Pyrenees reconstruction, where the method recovers a clear N-S gradient for all scenarios, indicating that the moisture source from the direction of the Atlantic. While the precipitation pattern was probably not much different from today, mean temperatures were ~9.3 ± 2.97˚C lower in the Alps and ~6.6 ± 1.6˚C lower in the Pyrenees. Our results match pollen-based reconstructions if the climate was 60% dryer than today.

 
Towards space-borne monitoring of localized CO2 emissions: an instrument concept and first performance assessment
Authors: Strandgren Johan , Wilzewski Jonas , Krutz David , Paproth Carsten , Sebastian Ilse , Gurney Kevin , Liang Jianming , Roiger Anke , Butz André
Published: March 2020

Independent verification of reported carbon dioxide (CO2) emissions is a corner stone for advancing towards emission accounting and reduction measures agreed upon in the Paris agreement. Here, we present the concept and first performance assessment of a compact space-borne imaging spectrometer that could support the task of "monitoring, verification, reporting'' (MVR) of CO2 emissions worldwide. With a ground resolution of 50m x 50m, the goal is to estimate the CO2 emissions from localized sources down to a source strength of approx. 1 MtCO2/yr, hence complementing other planned CO2 monitoring missions, like the European Carbon Constellation (CO2M).

Such fine ground resolution requires a trade-off towards coarse spectral resolution in order to achieve sufficient noise performance. Since fine ground resolution also implies limited ground coverage, a fleet of satellites, each carrying such an instrument is envisioned, requiring a relatively low-cost and simple design, e.g. by restricting the spectrometer to a single spectral window. To demonstrate that column-averaged dry-air mole-fractions of CO2 (XCO2) can be reliably retrieved with a single spectral window and at the required coarse spectral resolution, we use degraded GOSAT short-wave infrared spectra of the CO2 bands near 1.6 and 2.0 µm, respectively.

Through radiative transfer simulations, including a realistic instrument noise model and a global trial ensemble covering various geophysical scenarios, it is further shown that an instrument noise error of 1.1 ppm (1sigma) can be achieved for the XCO2 retrieval. Despite the limited amount of information from a single spectral window and a relatively coarse spectral resolution, scattering by atmospheric aerosol and cirrus can be partly accounted for, with deviations of at most 4.0 ppm from the true abundance for 68 % of the scenes in the global trial ensemble.

Finally we simulate the ability of the proposed instrument concept to observe CO2 plumes from single power plants in an urban environment using high-resolution CO2 emission and surface albedo data for the city of Indianapolis. Given the preliminary instrument design and the corresponding instrument noise error, emission plumes from point sources with an emission rate down to the order of 0.3 MtCO2/yr can be resolved, i.e. well below the target source strength of 1 MtCO2/yr. Hence, some margin for additional error sources like scattering particles and complex meteorology exists.
Ice melting in a turbulent stratified shear flow
Authors: Couston Louis-Alexandre , Hester Eric , Favier Benjamin , Jenkins Adrian , Holland Paul
Published: March 2020

In this talk I will present preliminary results of direct numerical simulations of ice melting in a turbulent stratified shear flow. The model solves the evolution of the turbulent fluid phase and of the diffusive solid ice phase, due to melting and freezing, in a fully coupled way. This is done by combining a Direct Numerical Simulation (DNS) code with a novel formulation of the equations for the solid and liquid phases of water based on the phase-field method. DNS enables turbulent motions to be simulated without approximation, i.e. solving Navier Stokes equations, while the phase-field method allows the ice-ocean interface to be rough and evolve in response to melting. I will present results on the turbulent boundary layer and on the self-generated basal topography at the ice-water interface. The ultimate goal of this work is to propose a new DNS-based parameterization of the melting process at rough ice-ocean boundaries that takes into account the effects of temperature and salt stratification, and flow velocities.