bluuebunny/crossref_metadata_2025 huggingface dataset:
The impacts of drought on the microbial states and processes in the hyporheic zone of temperate streams
Authors: Coulson Laura E. , Attermeyer Katrin , Griebler Christian , Schelker Jakob , Hein Thomas , Weigelhofer Gabriele
Published: March 2020

Intermittent streams as well as extreme events are expected to become more common as the climate changes. Therefore, it is important to understand how drought affects the biofilms that are essential for nutrient and DOM processing within streams. Previous work has largely focused on Mediterranean streams. This project evaluates how drought affects the state and processes of the microbial biofilms in the hyporheic zone of temperate intermittent streams. The experiment was conducted with outdoor experimental hyporheic flumes (5 m long, 0.6 m wide, 1.2 m deep) that were allowed to fall dry for periods ranging from 4 to 100 days. Sediment was sampled before drying, during the drought, and at several time points after rewetting. Samples were analyzed for extracellular enzymatic activity, respiration, bacterial growth, live to dead cell ratios, bacterial abundances, and extracellular polymeric substances.

Extracellular enzymatic activities remained unaffected by the drought in the hyporheic zone but showed an increase on the surface during the dry phase. Upon rewetting, the enzymatic activities generally fell to pre-drought levels on the surface. Extracellular polymeric substances also remained unaffected by drought in the hyporheic zone. However, surface values for extracellular polymeric substances showed a similar pattern to enzymatic activities during the longer dry periods (70+ days) and subsequent rewetting. These results indicate that the hyporheic zone retained enough moisture in the sediment to continue functioning, while the surface sediment was impacted by the loss of flowing water.
Automatic glacier outlines extraction from Sentinel-1 and Sentinel-2 time series
Authors: Barella Riccardo , Callegari Mattia , Marin Carlo , Notarnicola Claudia , Zebisch Marc , Sailer Rudolf , Klug Christoph , Galos Shtephan , Dinale Roberto , Benetton Stefano
Published: March 2020

Glaciers represent an important part of the hydrologic cycle in the Alps and they are very sensitive to climate change. Satellite remote sensing is an efficient tool for glacier monitoring because it provides a synoptic view over large areas. In literature, well-established methods for glacier delineation based on the Red and Short Wave Infrared (SWIR) ratio have been presented. These methods depend on a manual selection for each glacier of the “best scene”, i.e. absence of cloud coverage and minimum snow cover. A further manual refinement step is needed to handle possible errors, mainly due to cloud cover or shadows, and to include debris covered ice.

A manual approach for glacier outline extraction, especially if applied over large areas and beside the respective extraordinary amount of work, may be inadequate for at least two reasons:

1) The increased amount of available satellite data provided by the recently launched Sentinel-2 mission, which ensure at least one acquisition every 5 days on a given area;

2) The need for a more frequent update of the glacier outlines i.e. few years, due to the faster changes affecting glaciers during the last years.

In this work, we present an automatic method for glacier mapping, including bare ice and debris covered ice through the synergetic use of Sentinel-1 and Sentinel-2. The information of the Sentinel-2 time series is first classified with a Support Vector Machine (SVM) to detect cloud and snow. The snow and cloud masks are then used to select the non-cloudy pixels with the lowest snow coverage in the surrounding area. This is done by applying a moving window on the entire multi-temporal classified stack. The selected pixels for each band compose a multi-temporal cloud free mosaic, which represents the glaciers with the minimum snow cover for the current ablation season i.e., the “best scene”. If we compose the mosaic with classified pixels instead of the reflectance, we obtain the glacier – non glacier map that we use for outlines extraction. On the other hand, the Sentinel-1 coherence is used to detect the debris-covered ice over the areas classified as non-glacier from Sentinel-2. In detail, the Sentinel-1 time series is exploited to generate a multi-temporal coherence mosaic, which is representative of the loss of coherence due to the movement of the debris only. By properly thresholding this mosaic and considering the topographic information, the outlines of debris covered glaciers can be extracted.

The results obtained with the proposed method are compared with the recent official glacier inventory of South Tyrol (Italy) and Tyrol (Austria), which was derived from the manual interpretation of aerial orthophotos and lidar data by glacier experts.
Response of tropical terrestrial gross primary production to the super El Niño event in 2015
Authors: Zhu Jiawen , Zhang Minghua , Zhang Yao , Zeng Xiaodong , Xiao Xiangming
Published: March 2020

The Gross Primary Production (GPP) in tropical terrestrial ecosystems plays a critical role in the global carbon cycle and climate change. The strong 2015–2016 El Niño event offers a unique opportunity to investigate how GPP in the tropical terrestrial ecosystems responds to climatic forcing. This study uses two GPP products and concurrent climate data to investigate the GPP anomalies and their underlying causes. We find that both GPP products show an enhanced GPP in 2015 for the tropical terrestrial ecosystem as a whole relative to the multi-year mean of 2001–2015, and this enhancement is the net result of GPP increase in tropical forests and decrease in non-forests. We show that the increased GPP in tropical forests during the El Nino event is consistent with increased photosynthesis active radiation as a result of a reduction in clouds, while the decreased GPP in non-forests is consistent with increased water stress as a result of a reduction of precipitation and an increase of temperature. These results reveal the strong coupling of ecosystem and climate that is different in forest and non-forest ecosystems, and provide a test case for carbon cycle parameterization and carbon-climate feedback simulation in models.
Study on the correlation between meteorological and agricultural drought, based on remotely sensed indices
Authors: Mansorian Ruja , Zare Mohammad , Schumann Guy
Published: March 2020

In this study, long-term time series of precipitation data were used for determining the drought condition using the standard precipitation index (SPI) for 3, 6 and 12 month time scales. The indicators were calculated with two methods: a) using a gamma distribution and transforming the probability of occurrence to standard normal distribution, b) using the non-parametric plotting position method. Then, the SPI values for two consequent years 2013-14 and 2014-15 were extracted from data to study on meteorological drought. The SPI index calculations showed that the first year had near normal, whereas the second year had extreme drought condition. In parallel, 34 Landsat 8 satellite images were downloaded during the indicated time period to determine normalized difference vegetation index (NDVI) and vegetation condition index (VCI) as agricultural drought indices. The mean values of VCI for each month were considered as representative value for drought condition of the area. When the agricultural and meteorological drought indices were determined, the correlation coefficient (r) were calculated for finding the relation between these types of droughts. the results show that the highest correlation between SPI-3,6 and 12-month time scales and VCI occurred in 4, 2 and 4 months lag time respectively, with corresponding r value of 0.67, 0.65 and 0.69. The best agreement between these indices with calculated lag time proves the hypothesis that agricultural drought occurs after meteorological drought. Therefore, the results could be applied by farmers to plan an appropriate irrigation scheduling for upcoming droughts, specially, in arid and semi-arid areas. It could be concluded that for having suitable planning in water scarcity condition, understanding the situation helps water planners have better insight about management polices to minimize the effects of this natural hazard on human. To sum up, finding a relation between different types of droughts is helpful for monitoring, predicting and detecting droughts to better prepare for drought phenomena and to minimize losses
Crop Yield Estimation Using Multi-source Satellite Image Series and Deep Learning
Authors: Ghazaryan Gohar , Skakun Sergii , König Simon , Eyshi Rezaei Ehsan , Siebert Stefan , Dubovyk Olena
Published: March 2020

Timely monitoring of agricultural production and early yield predictions are essential for food security. Crop growth conditions and yield are related to climate variability and extreme events. Remotely sensed time-series can be used to study the variability in crop growth and agricultural production. However, the choice of remotely sensed data and methods is still an issue, as different datasets have different spatiotemporal characteristics. Thus, our primary goal was to study the impact of applying different remotely sensed time series on yield estimation in U.S. at the county and field scale. Furthermore, the impact of crop growth conditions on yield variability was assessed. For county-level analysis, MODIS-based surface reflectance, Land Surface Temperature, and Evapotranspiration time series were used as input datasets. Whereas field-level analysis was carried out using NASA’s Harmonized Landsat Sentinel-2 (HLS) product. 3D convolutional neural network (CNN) and CNN followed by long-short term memory (LSTM) were used. For county-level analysis, the CNN-LSTM model had the highest accuracy, with a mean percentage error of 10.3% for maize and 9.6% for soybean. This model presented robust results for the year 2012, which is considered a drought year. In the case of field-level analysis, all models achieved accurate results with R2 exceeding 0.8 when data from mid growing season were used. The results highlight the potential of yield estimation at different management scales.
Impact of disturbed ionospheric conditions in EGNOS performance
Authors: Magdaleno Sergio , Rupiewicz Joanna
Published: March 2020

The European Geostationary Navigation Overlay Service (EGNOS) is the Europe's regional satellite-based augmentation system (SBAS). It provides an augmentation service to the Global Positioning System (GPS) L1 Coarse/ Acquisition (C/A) civilian signal by providing corrections and integrity information for GPS space vehicles (ephemeris, clock errors) and information to estimate the ionosphere delays affecting the user. This information provided by EGNOS improves the accuracy and reliability of GNSS positioning information while also providing a crucial integrity message. This is especially relevant for civil aviation community, which, thanks to this improvement, can perform precision approaches (APV-I and LPV200) using GNSS, with a clear optimisation of the cost of the infrastructure with no impact in the safety of the operations.

One of the most important figures for EGNOS is the availability of the system, which is characterized by the proportion of time during which reliable navigation information is presented to the crew, autopilot, or other system managing the flight of the aircraft. (ICAO SARPS).

ESSP, as EGNOS Service Provider, monitors the daily availability for these flight operations (APV-I, LPV200), considering the system available when operational requirements defined in ICAO SARPS are met. In this case, EGNOS is considered available when the Protection Levels, an upper bound of the aircraft position error with the specified integrity risk, are lower than the Alarm limits defined by ICAO for these operations.

One of the main degradation sources in the EGNOS availability (and others SBAS) is the ionosphere, especially under disturbance conditions (e.g. geomagnetic storms, scintillation …) (Pintor et al., 2015; Haddad, 2016).

In the frame of the H2020 project - TechTIDE, the impact of disturbed ionospheric conditions in the EGNOS availability has been analysed. TechTIDE project is generating a warning system which will provide Travelling Ionospheric Disturbances (TID) information and some ionospheric activity indicators. These products would be used for the definition of mitigation strategies in some operational systems (EGNOS, N-RTK and HF communications).

As part of TechTIDE project, ESSP has assessed the impact of disturbed ionospheric conditions in EGNOS availability and defined a relationship with an ionospheric activity indicator provided by TechTIDE warning system. This paper presents the outcomes of this assessment.

References:

Haddad, F. (2016). Latest SBAS Performances under Severe and Equatorial Ionosphere Conditions, ICAO Workshop, August, 15-17, 2016.

Pintor, P., Roldan, R., Gomez, J., de la Casa, C., Fidalgo, R. M. (2015). The impact of the high ionospheric activity in the EGNOS performance, Coordinates, March 2015.
Cycling of carbon and water in mountain ecosystems under changing climate and land use (CYCLAMEN)
Authors: Kitz Florian , Wohlfahrt Georg , Rotach Mathias W , Tasser Erich , Tscholl Simon , Bartkowiak Paulina , Castelli Mariapina , Notarnicola Claudia , Dabhi Hetal , Simon Thorsten
Published: March 2020

Land ecosystems presently sequester around 25% of the carbon dioxide (CO2) that is emitted into the atmosphere by human activity and thus, along with the oceans (absorbing a similar fraction), slow down the increase of atmospheric CO2. Whether land ecosystems will be able to continue to sequester atmospheric CO2 at similar rates in the future or whether carbon cycle-climate feedbacks will cause the land sink to saturate or even turn into a source, is a topic of controversial discussion. While taking up CO2 through the stomata, plants inevitably lose water through transpiration. Terrestrial evapotranspiration (ET) can have a feedback to (local) precipitation and therefore modulate near-surface climate. The terrestrial carbon and water cycles are highly connected and controlled by complex interactions between biological and abiotic drivers. Mountain ecosystems in the European Alps are a hot spot of climate and land-use changes. Over the last century, temperatures have increased in the region with a rate double that of the global average and are expected to rise rapidly. In addition, precipitation changes are highly complex with an increasing and a decreasing trend in the northern and southern Alps, respectively and different seasonal patterns. Socio-economic development in the Alps during the past centuries have caused large-scale changes in land-use and its intensity, which has contributed to the uncertainty about future land-atmosphere interactions. The objective of the CYCLAMEN project is to quantify and project the resilience and vulnerability of carbon and water cycling in North and South Tyrol. We aim at providing information for predicting likely future changes in climate and land-use over the region.

In the study we used a comprehensive and multidisciplinary approach to model biosphere-atmosphere interactions in the Alps. Data from eddy covariance stations spread across the region were chosen to test and calibrate the biosphere model SiB4. The meteorological data from the same stations was used to train a stochastic Weather Generator and simulate weather conditions under climate scenarios RCP8.5 and RCP2.6 until 2100. To account for future land- use/ land- cover (LULC) changes the SPA-LUCC model was used. Both the simulated weather conditions and the expected LULC were fed back to the SiB4 model to calculate ecosystem parameters, including carbon dioxide net ecosystem exchange and evapotranspiration. In parallel, an enhanced thermal remote sensing dataset was produced, specifically adapted for mountainous areas. This dataset will be the main driver for modelling ET with an energy balance model whose output will be cross compared with the one of the biosphere model SiB4.
Understory biomass measurement based on SfM data by a manual low-flying drone under the canopy
Authors: Zhang Yupan , Onda Yuichi , Kato Hiroaki , Sun Xinchao , Gomi Takashi
Published: March 2020

Understory vegetation has the important effect that cannot be ignored on Evapotranspiration. In previous studies, laser scanner was used to measure small-scale biomass and airborne LiDAR was used to assess light availability to understory vegetation, which in turn was converted to understory biomass production. However, it is difficult to measure watershed-scale understory biomass with high resolution. In this study, Structure from Motion (SfM) was used to reconstruct understory vegetation structure by a manual low-flying drone under the canopy with radial paths in a line thinning plantation and a spot thinning plantation made by Japanese cedar and cypress. By generating Orthomosaic image and dense point cloud data, we then extracted Excess Green Index (ExG) and Canopy Height Model (CHM), combining with understory biomass data from field harvesting to establish a quantitative relationship between the CHM and biomass, which was then used to map biomass and vegetation coverage in the study area. The results indicated that (1) a flight height of 7-10 meters is more conducive to understory vegetation reconstruction, with a photo quality greater than 0.8 and a point cloud density of more than 20 points/cm2. (2) a regression cubic model based on the CHM has acceptable accuracy and biomass estimate capability (P<0.01), with a coefficient of determination of 0.75. (3) compared with the spot thinning, the understory biomass under the line thinning scenario was higher(average biomass 3.03kg/m2). (4) vegetation coverage based on the ExG index of visible light analysis was affected by ambient light(strong sunlight on a sunny day), and it cannot reflect the seasonal changes of understory vegetation biomass. These results disclosed the potential of the dense point cloud from drone SfM for estimating understory biomass. With this method, we will measure more than 5000m2 of headwater catchment and output a understory biomass map.

 
Explicit nonlinear waves of fluid models on extended domains and unbounded growth with backscatter
Authors: Prugger Artur , Rademacher Jens
Published: March 2020

Large scale motions in geophysical fluid models are often characterised by linear waves, which are obtained by linearising the equations. But there are also many explicit solutions of the fully nonlinear equations when posed the full space. The exact solutions we are investigating often characterise Rossby waves, since they are in geostrophic balance. They also can be compositions of waves, some are interacting with each other and some do not, showing wave interactions as explicit solutions in the fully nonlinear problem.

In this talk I will briefly introduce the idea behind these explicit nonlinear waves and show some of their properties, and their occurrence in different fluid models in extended domains.

As an application, we especially focus on a rotating shallow water model with simplified backscatter. In this case one finds not only geostrophic explicit solutions, but also ageostrophic ones. Moreover, here energy accumulates in selected scales due to the backscatter terms and causes exponentially and unboundedly growing ageostrophic nonlinear waves. This also relates to instability of coexisting stationary waves and is an instance of the role of nonlinear waves in energy transfer, and illustrates their role in preventing energy equidistribution for general data.
science-policy interface: the italian experience
Authors: angela corina
Published: March 2020

Over the last 15 years, in the framework of the Italian early warning system, managed directly by the civil protection authorities, the gap between science and policy have been positively bridged with the Knowledge Centres: a national strategy, with a formal architecture that has build a dialogue between scientific community and responsibility services.
The applied research, tailored on operational user needs, has been funded and supported leading to the development of advanced applications in coupled meteo-hydrological modelling, satellite rapid damage analysis, hydraulic modelling, levees vulnerability estimation etc.
Similar interface models are being created in the European institutions (DRMKC, European Commission) or in the international expert Agencies ( Research Panel, WMO).
The general positive dialogue among science and policy, in a mutual enrichment, is presented in this paper. 
Parquet Cube to store and process gridded data
Authors: lambert elisabeth , Zigna Jean-michel , Zilio Thomas , Gouillon Flavien
Published: March 2020

The volume of data in the earth data observation domain grows considerably, especially with the emergence of new generations of satellites providing much more precise measures and thus voluminous data and files. The ‘big data’ field provides solutions for storing and processing huge amount of data. However, there is no established consensus, neither in the industrial market nor the open source community, on big data solutions adapted to the earth data observation domain. The main difficulty is that these multi-dimensional data are not naturally scalable. CNES and CLS, driven by a CLS business needs, carried out a study to address this difficulty and try to answer it.

Two use cases have been identified, these two being complementary because at different points in the value chain: 1) the development of an altimetric processing chain, storing low level altimetric measurements from multiple satellite missions, and 2) the extraction of oceanographic environmental data along animal and ships tracks. The original data format of these environmental variables is netCDF. We will first show the state of the art of big data technologies that are adapted to this problematic and their limitations. Then, we will describe the prototypes behind both use cases and in particular how the data is split into independent chunks that then can be processed in parallel. The storage format chosen is the Apache parquet and in the first use case, the manipulation of the data is made with the xarray library while all the parallel processes are implemented with the Dask framework. An implementation using Zarr library instead of Parquet has also been developed and results will also be shown. In the second use case, the enrichment of the track with METOC (Meteo/Oceanographic) data is developed using the Spark framework. Finally, results of this second use case, that runs operationally today for the extraction of oceanographic data along tracks, will be shown. This second solution is an alternative to Pangeo solution in the world of industrial and Java development. It extends the traditional THREDDS subsetter, delivered by the Open source Unidata Community, to a bigdata implementation. This Parquet storage and associated service implements a smoothed transition of gridded data in Big Data infrastructures.
A text-mining approach to assess impacts and benefits of Nature-Based Solutions
Authors: Castellanos Diaz Leydy Alejandra , Versini Pierre Antoine , Tchiguirinskaia Ioulia , Bonin Olivier
Published: March 2020

Worldwide, research community has studied the benefits of green and blue spaces implementation in urban areas, generating a great amount of literature regarding this topic. Since these solutions are of interest to face climate change impacts in cities, the European Commission (EC) has funded several projects to make an extensive review of the available literature. Three of these projects were especially studied here, namely EKLIPSE, Mapping Assessment of Ecosystem and their Services- Urban Ecosystem (MAES: Urban Ecosystems), and NATure-based URban innoVATION (NATURVATION). They all aim to identify the physical and social impacts, benefits and trade-offs of Nature-Based Solutions (NbS).

To objectively compare findings presented in the deliverable reports, a text-mining approach was carried out. This methodology coupled with a data visual representation allowed to convert the EC projects reports (corpus) into a meaningful structured analysis. As a result, a graphical representation was created, making possible to recognize concepts, patterns and attributes addressed by each text, as well as stakeholders and their position with respect to the topic.

 The text mining analysis was implemented through Gargantex Blue Jasmine Version (an open source software developed by ISC-PIF). Gargantex results permitted to recover a list of key-terms from each corpus based in their co-occurrence in the whole text. These terms were used to elaborate a visual representation or network, placing the words strongly related close to each other and characterizing the obtained clusters by a similar color.

This approach underlined the specific focus of each project: the conciliation between urbanisation and urban ecosystems (MAES), or the economic valuation and monetisation of NbS (NATURVATION) for instance. Moreover, it demonstrated that despite the different literature review methodologies of each report/project, there are some common trends exhibited by the obtained graphical networks and their statistical attributes. For instance, the need to assess the NbS performance with some adapted indicators; and the important EC supporting role in the implementation of NbS. Similarly, some regulating (e.g. water quality or temperature reduction) and cultural (e.g. recreation or health benefits) services are more addressed.  

This analysis can be applied to all kind of corpus, which makes it easy to understand different and similar concepts and approaches of a set of text data. A text-mining analysis can be conducted over the direct references of NbS benefits, on a collection of publications of a research database like Scopus or Science Direct. 
Morphology and sedimentary filling of an ancient estuarine valley in an urban environment (Gijón, NW Spain)
Authors: Pando Luis , Flor-Blanco Germán , Rey Díaz de Rada Jorge , García-Rodríguez Adrián
Published: March 2020

The city of Gijón is located on the Cantabrian Coast (NW, Spain), and its subsurface is formed mainly by sand linked to an old estuarine mouth barrier (beach and dunes), sand bay and marshes. Under these sediments, there is a layer of clays related to the weathering of a Jurassic rock basement. This research addresses the setting of the estuary sediments in both the submerged area, located north of the city, and under the built-up area.

The seafloor morphology was investigated by means of a bathymetric survey with multi-beam echo sounder. A geophysical survey using high-resolution reflection seismic profiles allowed studying the thickness of the unconsolidated deposits that fill the bay of Gijón. Likewise, the distribution of coastal sediments under the city was reviewed from boreholes collected within a GIS-based geotechnical database.

The bathymetric reconstruction led to the identification of a paleo-valley supposedly excavated by the main river of the city, with N-S orientation that evolves to NNE-SSW towards the north. It shows a sandy bottom with a very low slope, a length of about 4 km and a width that ranges between 400 and 800 m. In this channel, the unconsolidated deposits reach a maximum thickness of around 15 m while at S, in the urban subsurface, the thickness exceeds 20 m locally. With these data, it was also possible to investigate the geometry of the bedrock under the sedimentary filling.
Dynamics of seepage mobile inventory in forest and agricultural soils - Results from a comparative multi-year lysimeter study
Authors: Lehmann Katharina , Lehmann Robert , Totsche Kai Uwe
Published: March 2020

The mobile inventory in soil seepage is of fundamental importance for soil development and for functioning of subsurface ecosystem compartments. The mobile inventory may encompass inorganic, organo-mineral and organics, dissolved and colloidal, but also particulate matter and microbiota. Still unknown are the conditions and factors that trigger the release and export of seepage-contained mobile matter within soil, and its translocation through the subsurface of the critical zone. Long-term and high-resolution field studies that includes the mobile particulate inventory are essentially lacking. To overcome this knowledge gap, we established long-term soil monitoring plots in the Hainich Critical Zone Exploratory (HCZE; NW-Thuringia, central Germany). Soil seepage from 22 tension-supported lysimeters in topsoil and subsoil, covering different land use (forest, pasture, cropland) in the topographic recharge area of the HCZE, was collected and analyzed by a variety of analytical methods (physico-/chemical and spectroscopic) on a regular (biweekly) and event-scale cycle. With our study we proved that substances up to a size of 50 µm are mobile in the soils. The material spectra comprised minerals, mineral-organic particulates, diverse bioparticles and biotic detritus. Atmospheric forcing was found to be the major factor triggering the translocation of the mobile inventory. Especially episodic infiltration events during hydrological winter seasons (e.g. snow melts) with high seepage volume influences seepage hydrochemistry (e.g. pH, EC) and is important for transport of mobile matter to deeper compartments. Seasonal events cause mobilization of significant amounts of OC. On average, 21% of the total OC of the seepage was particulate (>0.45 µm). Furthermore, our results suggest that the formation environment and the geopedological setting (soil group, parent rock, land use) are controlling factors for the composition and the amount of soil-born mobile inventory. Our study provides evidence for the importance of the mobile inventory fraction >0,45 µm for soil element dynamics and budgets and highlights the role of weather events on soil and subsoil development and subsurface ecosystem functioning.
Does the seismic cycle slip toward randomness?
Authors: Ghazoui Zakaria , Grasso Jean-Robert , Watlet Arnaud , Caudron Corentin , Karimov Abror , Bertrand Sebastien , Yokoyama Yusuke , van der Beek Peter
Published: March 2020

Seismology and paleoseismology seem to be two distant sisters when we address earthquake time-interval distributions. One observation stands out; an apparent discrepancy in time-interval models, i.e. periodic to cluster, within similar tectonic context. As a departure point, we will use the Himalayan context where according to instrumental or paleoseismic catalogues, time-interval distributions are presented as Poisson to periodic. We report on a new 6000-year lake-sediment seismic record and perform statistical analyses to show that time intervals between large (M≥6.5) earthquakes are robustly described by a Poisson distribution, while second-order fluctuations imply event clustering. These patterns are calibrated against an instrumental catalogue for the entire Himalaya; we show that both catalogues are inconsistent with periodic models. Throughout this presentation, we will compare the Himalayan results with paleoseismic catalogues from three distinct tectonic settings (Indonesia, New-Zealand and Jordan). Each of them displays a close to Poisson distribution, in consonance with instrumental catalogues results. Our results imply that the occurrence of major seismic events is as uncertain as smaller events on any time scale, increasing drastically previous estimate of the seismic hazard.
Fidelity of CORDEX experiments over Himalayan Watersheds
Authors: Hasson Shabehul
Published: March 2020

How much water will come in future from the Himalayan watersheds under changing climate is a growing concern for ensuring sustainable development of downstream agrarian economies and for socioeconomic wellbeing of dependent communities. However, robust assessment of future water availability largely depends upon fidelity of climate modelling experiments simulating future change scenarios, beyond the debate of their possibility and plausibility. Thus, I assess the fidelity of CORDEX experiments over the Himalayan watersheds for the historical period against a broader set of observational datasets, in terms of reproducibility of the observed climatology of temperature and precipitation. Changes in these basic variables relevant for impact studies will also be presented under different scenarios and their robustness will be discussed in view of their fidelity for the historical period. The study will suggest the suitability of CORDEX experiments for the impact studies and further possibilities for improvement.
The influence of wind on the evolution of freshwater fronts in the Rhine ROFI
Authors: Keyzer Lennart , Rijnsburger Sabine , Zijl Firmijn , Verlaan Martin , Snellen Mirjam , Slobbe Cornelis , Audibert Raul Flores , Horner-Devine Alexander , Souza Alejandro , Pietrzak Julie
Published: March 2020

The Rhine River discharges freshwater into the North Sea, forming one of the largest Regions of Freshwater Influence (ROFI) in Europe. Every tidal cycle, a freshwater lens is released. These fronts were captured by the STRAINS (STRAtification Impacts Near-shore Sediment) field campaign of 2014. The data consists of current velocity, temperature and salinity at a fixed location 10 km northeast of the river mouth. Here, we explore the effect of the wind on the evolution of the freshwater lenses using a high-resolution 3D model, which is validated against the field data. We find a stratified river plume that consists of multiple freshwater fronts. On every ebb tide, a new freshwater lens is formed, which is subsequently advected by the tidal flow. Remaining lenses from previous tidal cycles are still present when the next one is formed. The properties and evolution of the lenses strongly depends on the wind magnitude and direction. Under upwelling winds, they evolve separately and the downstream plume is detached from the coast. The thickest lenses are found under downwelling winds, when their propagation speed is maximum and the downstream river plume is pushed against the coast. During storm conditions, when the wind speed exceeds 15 m/s, the river plume becomes well-mixed and no separate lenses are found. The model shows a detailed picture of the formation and evolution of the freshwater lenses in the Rhine ROFI and the vertical structure of the water column. We find a multiple front system, where lenses interact under the influence of tidal flow and prevailing winds; diverging flows causes the lenses to separate, while they seem to merge under converging flows.
Assessing the climate response to regional sea ice change across all Arctic regions.
Authors: Levine Xavier , Cvijanovic Ivana , Ortega Pablo , Donat Markus
Published: March 2020

Climate models predict that sea ice cover will shrink--even disappear-- in most regions of the Arctic basin by the end of the century, triggering local and remote responses in the surface climate via atmospheric and oceanic circulation changes. In particular, it has been suggested that seasonal anomalies over Europe and North America in recent years could have been caused by record low Arctic sea ice cover. Despite an intense research effort toward quantifying its effect, the contribution of regional sea ice loss to climate change and its mechanisms of action remain controversial. 

In this study, we prescribe sea ice loss in individual sectors of the Arctic within a climate model, and study its effect on climatic anomalies in the Northern Hemisphere. Using the EC-EARTH3.3 model in its atmospheric-only and fully coupled configuration, and following the PAMIP protocol, sea ice cover is set to either its present day state, or a hypothetical future distribution of reduced sea ice cover in the Arctic. This pan-Arctic sea ice loss experiment is then complemented by 8 regional sea ice loss experiments.

Comparing those experiments, we assess the contribution of sea ice loss in each region of the Arctic to climate change over Europe, Siberia and North America. We find that sea ice loss in some sectors of the Arctic appears to matter more for Northern Hemisphere climate change than others, even after normalizing for differences in surface cover. Furthermore, the climatic effect of regional sea ice loss is compared to that of a pan-Arctic sea ice loss, whose associated climate anomalies are found to be strikingly different from that expected from a simple linear response to regional sea ice loss. We propose a mechanism for this nonlinear climate response to regional sea ice loss, which considers regional differences in the strength of the thermal inversion over the Arctic, as well as the relative proximity of each Arctic region to features critical for stationary wave genesis (e.g. the Tibetan plateau).
Trapped particles around Jupiter detected by Advanced Stellar Compass
Authors: Herceg Matija , Jørgensen John L. , Jørgensen Peter S. , Merayo Jose M. G. , Benn Mathias , Denver Troelz , Connerney John E. P.
Published: March 2020

The Advanced Stellar Compass (ASC), attitude reference for the MAG investigation onboard Juno, has continuously monitored high energy particles fluxes in Jupiter’s magnetosphere since Juno’s orbit insertion. The instrument performs this function by tracking the effects of radiation with sufficient energy to transit the instrument’s radiation shielding. Particles that Juno ASC observes have energy >15MeV for electrons, >80MeV for protons, and >~GeV for heavier elements.

Completing 24 highly elliptical orbits around Jupiter, results in a fairly detailed mapping of the trapped high energy flux at up to 20 Jupiter radius distances.

Traveling at velocities close to the speed of light, electrons measured by the ASC, maintain the motion governed by the three adiabatic invariants: gyrating motion around the magnetic field line, a north-south magnetic pole particle bounce, and a charge dependent drift around the planet.

The bounce period is much smaller than the Jovian rotation period, and a large east-west drift component is caused by the magnetic field gradient. For these reasons, the drift shell description traditionally used for dipolar fields, are far from adequate to describe the behavior of energetic particles travelling close to Jupiter.

In this work, we present the distribution of the trapped high energy electrons around Jupiter. Furthermore, we have constrained the spatial extent of the stable trapped regions and are presenting the distinctive pitch angle and its correlation with ”life” of a particle. At certain distances from Jupiter, pitch angle dependency is not as important to keep the particle trapped as is the injected energy. We also develop an adiabatic map which describes the radial bands for stable trapped particles as a function of the pitch angle and energy.

 
Quantifying the contribution of three competing pathways to total degradation in groundwater by a triple-isotope analysis approach
Authors: Thullner Martin , Centler Florian , Hofstetter Thomas
Published: March 2020

In groundwater and other environmental compartments, compound-specific stable isotope analysis (CSIA) has been used for the determination of specific degradation pathways by analyzing the stable isotopes of two elements. This ‘dual-isotope’ or two-dimensional isotope’ analysis also allows for an estimation of the contribution of two different pathways contributing both to the overall degradation and stable isotope fractionation. Heterogeneous groundwater flow patterns lead to some yet acceptable uncertainities in the results of this method.  Recent CSIA approaches also allow for investigating the simultaneous stable isotope fractionation effects for three different elements. Such information on the stable isotope fractionation of three different elements of a degradable compound could be used for a quantitative analysis of the contribution of different degradation pathways in systems with three different pathways, but up to know there is no theoretical concepts providing such quantitative estimate.

The aim of the present study is to overcome this shortage and to present such theoretical concept for the quantification of single pathway contribution to the overall biodegradation in groundwater and other systems with three parallel degradation pathways. For this purpose the approach of Centler et al. (2013) for the analysis of dual-isotope analysis has been expanded to consider the fractionation of three different elements affected by three different pathways. The obtained analytical expression allows for the quantification of each pathway to total degradation based stable isotope enrichment factors and measured stable isotope signatures. The applicability of the concept is demonstrated using data from Wijker et al. (2013).

 

Centler, F., Hesse, F., and Thullner, M. (2013) Journal of Contaminant Hydrology, 152, 97-116.

Wijker, R. S., Bolotin, J., Nishino, S. F., Spain, J. C., and Hofstetter, T. B. (2013) Environmental Science & Technology, 47, 6872-6883.

 
Linking soil physical properties to the tea bag index for different land uses
Authors: Fu Yuting , de Jonge Lis , Greve Mogens , Arthur Emmanuel , Moldrup Per , Norgaard Trine , Paradelo-Perez Marcos
Published: March 2020

Organic matter decomposition is an important process in global carbon cycling and its rate is altered by various factors. Changes in land use can have a significant effect on decomposition rates, with consequences on CO2 emissions. The tea bag index (TBI) method is recognized as a simple and effective approach to investigate decomposition. Despite the fact that TBI has been globally applied, most research mainly focuses on soil microbiological aspects; the role of soil physical properties have earned less attention. Linking the soil physical properties to TBI can give us a broad understanding on how land use affects the soil microhabitat, and in turn influence carbon sequestration. Here, we measured the decomposition of green and rooibos tea in a transect from the east to west coast of Denmark across four land uses categorized into two groups (natural and cultivated). The natural group comprised forest and heath, and the cultivated group was composed of cereal and grass. Decomposition rate (k) and stabilization factor (S) were calculated after three months tea bag incubation. Soil physical properties including volumetric water content (VWC), air permeability and relative gas diffusivity (Dp/D0) were measured at matric potential of –10 and –100 kPa. The cultivated land uses had higher k and S values compared to natural systems. The S was positively correlated with VWC and negatively correlated with Dp/D0 in natural systems while no relationship was found for cultivated land. However, there was a negative correlation of k-VWC and positive correlation of k-Dp/D0 in cultivated land, suggesting an impact of soil management and anthropogenic influence on litter decomposition and carbon sequestration.
Can Teleseismic Travel-Times Constrain 3D Anisotropic Structure in Subduction Zones? Insights from Realistic Synthetic Experiments
Authors: VanderBeek Brandon , Faccenda Manuele
Published: March 2020

Despite the well-established anisotropic nature of Earth’s upper mantle, the influence of elastic anisotropy on teleseismic tomographic images remains largely ignored. In subduction zones, unmodeled anisotropic heterogeneity can lead to substantial isotropic velocity artefacts that may be misinterpreted as compositional heterogeneities (e.g. Bezada et al., 2016). Recent studies have demonstrated the possibility of inverting P-wave delay times for the strength and orientation of seismic anisotropy assuming a hexagonal symmetry system (e.g. Huang et al., 2015; Munzarová et al., 2018). However, the ability of P-wave delay times to constrain complex anisotropic patterns, such as those expected in subduction settings, remains unclear as the aforementioned methods are tested using ideal self-consistent data (i.e. data produced using the assumptions built into the tomography algorithm) generated from simplified synthetic models. Here, we test anisotropic P-wave imaging methods on data generated from geodynamic simulations of subduction. Micromechanical models of polymineralic aggregates advected through the simulated flow field are used to create an elastic model with up to 21 independent coefficients. We then model the teleseismic wavefield through this fully anisotropic model using SPECFEM3D coupled with AxiSEM. P-wave delay times across a synthetic seismic array are measured using conventional cross-correlation techniques and inverted for isotropic velocity and the strength and orientation of anisotropy using travel-time tomography methods. We propose and validate approximate analytic finite-frequency sensitivity kernels for the simplified anisotropic parameters. Our results demonstrate that P-wave delays can reliably recover horizontal and vertical changes in the azimuth of anisotropy. However, substantial isotropic artefacts remain in the solution when only inverting for azimuthal anisotropy parameters. These isotropic artefacts are largely removed when inverting for the dip as well as the azimuth of the anisotropic symmetry axis. Due to the relative nature of P-wave delay times, these data generally fail to reconstruct anisotropic structure that is spatially uniform over large scales. To overcome this limitation, we propose a joint inversion of SKS splitting intensity with P-wave delay times. Preliminary results demonstrate that this approach improves the recovery of the magnitude and azimuth of anisotropy. We conclude that teleseismic P-wave travel-times are a useful observable for probing the 3D distribution of upper mantle anisotropy and that anisotropic inversions should be explored to better understand the nature of isotropic velocity anomalies in subduction settings.
From time series analysis to hydrodynamic modelling in a complex hydrosystem: applications for the hydrodynamic characterization and modelling of a karst aquifer with sparse data (Oeillal spring, France).
Authors: Sivelle Vianney , Jourde Hervé
Published: March 2020

The Narbonne-Sigean sedimentary basin is composed by Oligocene sediment, alluvions from the Aude River and the Fontfroide-Montredon limestone massif. The significant tectonics during the Oligocene rifting brought all of these formations to the surface in the Malvesi area. A normal fault affects the area and causes the Jurassic unit to rise in the form of a horst: the Montlaures massif. The Oeillal spring is located on the south border of this massif. The karst spring outflows at 4 pools with different physico-chemical signature. Each of these pools is equipped with a CTD probe. Moreover, the area is monitored with piezometric and temperature measurements that allow characterizing each of the main geological formations near the Oeillal spring. Though measurements started more than ten years ago (2007), continuous monitoring is available on one hydrological cycle, only. Indeed, only sparse data are available over the period 2007-2018, which required proposing a methodology to allow the optimal use of the available data in the modelling workflow.  The present study thus focuses on this methodology and on the use of numerical tools such as time series analysis (auto and cross-correlation analysis, spectral analysis) to determine a suitable modelling approach (lumped or distributed model) adapted to the hydrodynamic modelling of karst springs with sparse data.