bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Cost Air Quality Sensor Network in Munich
Authors: Zollitsch Daniel , Chen Jia , Dietrich Florian , Voggenreiter Benno , Setili Luca , Wenig Mark
Published: March 2020

As the number of official monitoring stations for measuring urban air pollutants such as nitrogen oxides (NOx), particulate matter (PM) or ozone (O3) in most cities is quite small, it is difficult to determine the real human exposure to those pollutants. Therefore, several groups have established spatially higher resolved monitoring networks using low-cost sensors to create a finer concentration map [1-3].

We are currently establishing a low-cost, but high-accuracy network in Munich to measure the concentrations of NOx, PM, O3, CO and additional environmental parameters. For that, we developed a compact stand-alone sensor systems that requires low power, automatically measures the respective parameters every minute and sends the data to our server. There the raw data is transferred into concentration values by applying the respective sensitivity function for each sensor. These functions are determined by calibration measurements prior to the distribution of the sensors.

In contrast to the other existing networks, we will apply a recurring calibration method using a mobile high precision calibration unit (reference sensor) and machine learning algorithms. The results will be used to update the sensitivity function of each single sensor twice a week.  With the help of this approach, we will be able to create a calibrated real-time concentration map of air pollutants in Munich.

[1] Bigi et al.: Performance of NO, NO2 low cost sensors and three calibration approaches within a real world application, Atmos. Meas. Tech., 11, 3717–3735, 2018

[2] Popoola et al., “Use of networks of low cost air quality sensors to quantify air quality in urban settings,” Atmos. Environ., 194, 58–70, 2018

[3] Schneider et al.: Mapping urban air quality in near real-time using observations from low-cost sensors and model information, Environ. Int., 106, 234–247, 2017
Feedback between ice dynamics and bedrock deformation with 3D viscosity in Antarctica
Authors: van der Wal Wouter , van Calcar Caroline , de Boer Bas , Blank Bas
Published: March 2020

Over glacial-interglacial cycles, the evolution of an ice sheet is influenced by Glacial isostatic adjustment (GIA) via two negative feedback loops. Firstly, vertical bedrock deformation due to a changing ice load alters ice-sheet surface elevation. For example, an increasing ice load leads to a lower bedrock elevation that lowers ice-sheet surface elevation. This will increase surface melting of the ice sheet, following an increase of atmospheric temperature at lower elevations. Secondly, bedrock deformation will change the height of the grounding line of the ice sheet. For example, a lowering bedrock height following ice-sheet advance increases the melt due to ocean water that in turn leads to a retreat of the grounding line and a slow-down of ice-sheet advance.     
               GIA is mainly determined by the viscosity of the interior of the solid Earth which is radially and laterally varying. Underneath the Antarctic ice sheet, there are relatively low viscosities in West Antarctica and higher viscosities in East Antarctica, in turn affecting the response time of the above mentioned feedbacks. However, most ice-dynamical models do not consider the lateral variations of the viscosity in the GIA feedback loops when simulating the evolution of the Antarctic ice sheet. The method developed by Gomez et al. (2018) includes the feedback between GIA and ice-sheet evolution and alternates between simulations of the two models where each simulation covers the full time period. We presents a different method to couple ANICE, a 3-D ice-sheet model, to a 3-D GIA finite element model. In this method the model computations alternates between the ice-sheet and GIA model until convergence of the result occurs at each timestep. We simulate the evolution of the Antarctic ice sheet from 120 000 years ago to the present. The results of the coupled simulation will be discussed and compared to results of the uncoupled ice-sheet model (using an ELRA GIA model) and the method developed by Gomez et al. (2018).
Calibration Test for Low Energy Ion Spectrometer onboard of Geostationary Satellites
Authors: Liu Kai , Li Yiren , Li Xin
Published: March 2020

Detections for space environment are crucial for monitoring the safety of satellites, while the parameters of space plasma are fundamental. Thus, we developed a spectrometer onboard of geostationary satellites, and it can measure the low energy ion's 3-D energy spectrum with a single sensor. To ensure the performance of the instrument, environmental tests, such as impulse test, vibration test and thermal test, were proceeded. Furthermore, a fully calibration test has been carried out to obtain all the scaling parameters. In this paper, the facilities and processes of the calibration test will be illustrated in detail, and the test's results indicate that our spectrometer will function well in the geostationary orbit.
Improved large-scale crop water requirement estimation through new high-resolution reanalysis dataset
Authors: Rolle Matteo , Tamea Stefania , Claps Pierluigi
Published: March 2020

Estimation of crop water needs is essential to understand the role of agriculture in the water balance modeling at various scales. In turn, this is relevant for water management purposes and for the fulfilling of water-related environmental regulations. In this study, a comprehensive assessment of crop water requirement at large scale is presented, both in terms of rainfall (green water) and irrigation (blue water).

A water-balance model is built to provide estimates of actual evapotranspiration and accompanying soil moisture by using high space-time resolution data. The new ERA5 reanalysis dataset, published by the ECMWF within the Copernicus monitoring system and obtained from satellite data and ground measurements, provides the precipitation and temperature input variables to the model. Data available at the hourly time scale are all aggregated on a daily scale and used in the water balance model over  a grid of cultivated areas from the MIRCA2000 dataset. Cultivated areas are available for 26 crops for year 2000 at a spatial resolution of 5 arcmin (about 9 km at the Equator). Data from MIRCA2000 are separated between rainfed areas and areas equipped for irrigation and are characterized by specific monthly calendars of the crop growing seasons.

The model performs the daily soil water balance throughout the whole year, considering all crops at their growth stage and assuming as initial condition at each crop sowing date a monthly average soil moisture. Results quantify the volumes of green and blue water necessary for crop growth and describe the spatial variability of the water requirements of each individual crop. The high spatial and temporal resolution of Copernicus ERA5 data enables a great improvement in the characterization of hydro-climatic forcings with respect to previous assessments and a greater accuracy in the crop water requirement estimates.

Finally, the knowledge of water requirements is an important step to quantify the irrigation volumes used in agriculture, on which there is a high uncertainty and little spatially distributed information. The model proposed enables the investigation of spatio-temporal variability associated to varying meteorological forcings and of the effects of different irrigation techniques, enabling an improved management of water resources.
A study of kinematic relaxation at the Venus bow shock
Authors: Pope Simon A. , Balikhin Michael A.
Published: March 2020

A new type of very-low Mach number shock in which the primary method of energy re-distribution is the kinematic relaxation of a non-gyrotropic ion population, was discovered at Venus early in the Venus Express mission. This led to the development of an associated theory and numerical analysis. The recent discovery of such a shock at the Earth using THEMIS data experimentally verified this theory using simultaneous magnetic field and plasma data. It also showed that the most favourable conditions for the formation of such a shock is the magnetic cloud phase of an ICME. Venus Express provides an excellent opportunity to study such shocks further. Here we present results from the duration of the mission, which identifies over thirty shock crossings showing evidence of kinematic relaxation. These shock crossings are investigated to understand how the upstream conditions and heavy ions (including pick-up ions) affect their formation.
Comparison of ozone profiles from the Ozone Mapping and Profiles Suite with ozonesonde measurements over Antarctica during 2012-2019
Authors: Sepulveda Edgardo , Cordero Raúl , Damiani Alessandro , Rowe Penny
Published: March 2020

The Ozone Mapping and Profiles Suite (OMPS), in orbit since October 2011 as a part of the Suomi National Polar-orbiting Partnership (Suomi NPP) Satellite includes three different spectral instruments for retrieving ozone distributions globally. One of those is the Limb Profiler (LP), which has made measurements since February 2012. The LP retrieves ozone profiles between approximately 12 km and 55 km of height.

Here we compare the OMPS LP version 2.5 ozone profiles with Electrochemical Concentration Cell (ECC) ozonesonde measurements from three Antarctic stations during the period 2012-2019: Marambio Station (-64.2413, -56.6266) on the Antarctic Peninsula, and Syowa Station (-68.3040, 49.6443) and Davis Station (-68.3110, 75.0222) in East Antarctica. The ozonesonde profiles include ozone concentration from the surface to an altitude of about 30 km. Thus, our comparisons are for altitudes of about 12 to 27 km.

During the period of highest ozone concentration (December – April), mean relative differences between OMPS LP and ozonesonde concentration typically change with height, ranging from -10% at 12-17 km altitude to 10% at 27 km altitude with slight variation between the three sites (e.g. Marambio has a higher standard deviation of 35% at 12 km). A mean relative difference of -5% is found for Syowa from about 15 km to 24 km, unlike Marambio and Davis, which have no clear difference at these heights.

Relative differences were also examined in September, when ozone concentrations are significantly lower due to the formation of the ozone hole, except for September 2019, which is excluded because a sudden stratospheric warming effect occurred. A mean relative difference of almost 30% is found in Marambio and Davis from about 12 km to 21 km, with a standard deviation of 100% at 18 km. The mean relative difference at Syowa is similar except that the relative difference peaks at almost 60% at 16 km. Marambio and Davis have similar biases above 21 km (10%), where the bias at Syowa is -5%.
The upper crustal geological and structural setting in the area of the 2016-2018 Central Apennines seismic sequence. From subsurface modeling to seismotectonics.
Authors: Maesano Francesco Emanuele , Buttinelli Mauro , Petracchini Lorenzo , D'Ambrogi Chiara , Scrocca Davide , Di Bucci Daniela , Marino Maurizio , Capotorti Franco , Cavinato Gian Paolo , Bigi Sabina , Bonini Lorenzo , Mariucci Maria Teresa , Montone Paola , Tizzani Pietro , Castaldo Raffaele , Pepe Susi , Solaro Giuseppe
Published: March 2020

Central Apennines (Italy) is a young and tectonically active mountain chain characterized by a high structural complexity where structures related to various tectonic phases are interacting with each other leading to the reactivation of inherited structures and/or to the segmentation of newly formed ones with a strong impact on the current seismotectonics of the area.

In this context, the surface geological and coseismic observations cannot always be extrapolated straightforward to depth and need to be interpreted in the context of the general upper crustal deformation history.

These considerations apply also to the area struck by the 2016-2018 Central Apennines seismic sequence where the activation of both single faults and complex fault systems has been observed.

In the framework of the RETRACE-3D project, we present a comprehensive 3D geological model derived from the interpretation of a large set of underground data acquired for hydrocarbons explorations and we discuss the implication of this geological reconstruction for the seismotectonics of the area by comparing our results with the coseismic observation.

Our results primarily show that, although the area is currently affected by an extensional tectonic regime, the main architecture of this portion of the chain is still dominated by previous compressional large-scale structures with widespread evidence of segmentation, reactivation and even inversion of various sets of inherited faults.

These results pose new points of discussion on information and input data needed to understand the seismogenesis in young and complex mountain chains, such as the Central Apennines, and strongly impact on the consequent seismic hazard assessment study.
Holocene plant community changes in the Western Alps, as inferred from sedaDNA
Authors: Garces Pastor Sandra , D. Heintzman Peter , Lammers Youri , Zetter Scarlett , Gavin Brown Antony , Walsh Kevin , Giguet Covex Charline , Tinner Willy , Schwörer Christoph , Heiri Oliver , Lavergne Sébastien , Coissac Eric , Vannière Boris , Jouffroy-Bapicot Isabelle , Tribsch Andreas , G. Alsos Inger
Published: March 2020

Climate change has already started to rapidly transform ecosystems. Predicted scenarios of future ecosystem changes inferred from contemporary ecological data may be uncertain, as these records do not provide the temporal depth needed to understand how ecosystems have responded to past periods of climatic changes and human pressure. However, palaeoecological approaches allow for the reconstruction of past ecosystem changes, including the composition of plant communities, thereby enabling researchers to improve models of future climatic change impacts.

Lakes located in high-mountain ranges, such as the Alps, are suitable ecosystems for studying long-term species turnover and environmental shifts driven by past climate changes, as they preserve a wealth of palaeoecological information in its sediment archives. The Alpine ecosystems are expected to be affected by ongoing climate warming, prompting an upward displacement of vegetation, elevated replacement rates and species losses, with projected increased intensity of impacts in the future.

Previous studies of the Alps have used pollen and macrofossil evidence to infer past vegetation dynamics. However, microscopic morphological determinations are time-consuming and some inferences have been limited by low taxonomic resolution and the biased preservation of identifiable remains. Ancient DNA from organisms is also often preserved in the sediment (sedaDNA), which can rapidly be detected and analysed using metabarcoding approaches. Together with a novel, region-specific barcode reference database for the flora of the Alps (PhyloAlps; 4500 taxa), we can bypass the morphological limitations of previous palaeobotanical studies and refine taxonomic resolution, often to the species level.

To investigate the origin and impact of past environmental changes in alpine ecosystems throughout the Holocene, we performed a multi-proxy reconstruction of 9 lake sediment cores from the Western Alps (France, Italy and Switzerland). Using metabarcoding, we reconstructed the plant community composition and used XRF, magnetic susceptibility, and loss-on-ignition data to understand lacustrine dynamics during the Holocene for each lake. We will present the major findings from these analysed records, the general ecosystem shifts inferred, and the impacts of perturbations caused by human pressure and climatic changes.
Boosting climate change research with direct access to high performance computers
Authors: Moreno de Castro Maria , Kindermann Stephan , Fiore Sandro , Nassisi Paola , Levavasseur Guillaume , Juckes Martin , Stephens Ag , Peters Karsten , Morellon Sophie , Joussaume Sylvie
Published: March 2020

Earth System observational and model data volumes are constantly increasing and it can be challenging to discover, download, and analyze data if scientists do not have the required computing and storage resources at hand. This is especially the case for detection and attribution studies in the field of climate change research since we need to perform multi-source and cross-disciplinary comparisons for datasets of high-spatial and large temporal coverage. Researchers and end-users are therefore looking for access to cloud solutions and high performance compute facilities. The Earth System Grid Federation (ESGF, https://esgf.llnl.gov/) maintains a global system of federated data centers that allow access to the largest archive of model climate data world-wide. ESGF portals provide free access to the output of the data contributing to the next assessment report of the Intergovernmental Panel on Climate Change through the Coupled Model Intercomparison Project. In order to support users to directly access to high performance computing facilities to perform analyses such as detection and attribution of climate change and its impacts, the EU Commission funded a new service within the infrastructure of the European Network for Earth System Modelling (ENES, https://portal.enes.org/data/data-metadata-service/analysis-platforms). This new service is designed to reduce data transfer issues, speed up the computational analysis, provide storage, and ensure the resources access and maintenance. Furthermore, the service is free of charge, only requires a lightweight application. We will present a demo on how flexible it is to calculate climate indices from different ESGF datasets covering a wide range of temporal and spatial scales using cdo (Climate Data Operators, https://code.mpimet.mpg.de/projects/cdo/) and Jupyter notebooks running directly on the ENES partners: the DKRZ (Germany), JASMIN (UK), CMCC(Italy), and IPSL (France) high performance computing centers.
Coastal Sea Level Change from in the North Eastern Atlantic
Authors: Fenoglio-Marc Luciana , Uebbing Bernd , Kusche Jürgen , Dinardo Salvatore
Published: March 2020

A significant part of the World population lives in the coastal zone, which is affected by coastal sea level rise and extreme events. Our hypothesis is that the most accurate sea level height measurements are derived from the Synthetic Aperture Altimetry (SAR) mode. This study analyses the output of dedicated processing and assesses their impacts on the sea level change of the North-Eastern Atlantic. 

It will be shown that SAR altimetry reduces the minimum usable distance from five to three kilometres when the dedicated coastal retrackers SAMOSA+ and SAMOSA++ are applied to data processed in SAR mode. A similar performance is achieved with altimeter data processed in pseudo low resolution mode (PLRM) when the Spatio-Temporal Altimeter sub-waveform Retracker (STAR) is used. Instead the Adaptive Leading Edge Sub-waveform retracker (TALES) applied to PLRM is less performant. SAR processed altimetry can recover the sea level heights with 4 cm accuracy up to 3-4 km distance to coast. Thanks to the low noise of SAR mode data, the instantaneous SAR and in-situ data have the highest agreement, with the smallest standard deviation of differences and the highest correlation. A co-location of the altimeter data near the tide gauge is the best choice for merging in-situ and altimeter data. The r.m.s. (root mean squared) differences between altimetry and in-situ heights remain large in estuaries and in coastal zone with high tidal regimes, which are still challenging regions. The geophysical parameters derived from CryoSat-2 and Sentinel-3A measurements have similar accuracy, but the different repeat cycle of the two missions locally affects the constructed time-series.

The impact of these new SAR observations in climate change studies is assessed by evaluating regional and local time series of sea level. At distances to coast smaller than 10 Kilometers the sea level change derived from SAR and LRM data is in good agreement. The long-term sea level variability derived from monthly time-series of LRM altimetry and of land motion-corrected tide gauges agrees within 1 mm/yr for half of in-situ German stations. The long-term sea level variability derived from SAR data show a similar behaviour with increasing length of the time series.

 
Regional scale mapping of rockfall-protection forest efficiency
Authors: Sala Gianluca , Lanfranconi Camilla , Frattini Paolo , Crosta Giovanni B.
Published: March 2020

In mountainous areas, rockfall phenomena cause damages and safety problems in residential areas and along transportation facilities. Forests that lay upslope the elements at risk can mitigate rockfall hazard by reducing the kinetic energy of blocks and the probability of impact. Nevertheless, the effects of rockfall protection forests is usually quantified only at local scale.

In order to assess the forest efficiency for different combinations of forest (tree size, forest density, forest position, forest length), morphological (slope gradient) and lithological (expected block volume) conditions, we performed a large set of parametric simulations by using the HY-STONE rockfall simulator (Crosta et al, 2004) with a tree impact algorithm that allows calculating the probability of impact, the loss of energy and the lateral deviation of the trajectories based on forest density, tree size and block volume. For each simulation, we therefore quantified the forest efficiency by using a new energy-based efficiency index (EEI) that measure the reduction of rockfall kinetic energy along the forest.

The results of the parametric simulations show that the block volume, the slope inclination, the tree size, and the forest density are, in decreasing order of relevance, the most sensitive parameters for rockfall efficiency. Due to its importance, the volume of blocks associated to different lithologies found in Central Italian Alps have been analysed through a statistical analysis of talus deposits. This allowed to obtain volume frequency distributions for the different lithologies, and the associated percentiles of expected block volume.

Starting from the parametric simulations, we developed a multiple linear regression that allows to predict an EEI index value (efficiency of protection forest) as a function of forest, morphological and lithological parameters. This regression function has been eventually applied to all the protection forest of Central Italian Alps, providing regional scale maps of rockfall-protection forest efficiency for different block volume percentiles.

 

Crosta, G. B., and F. Agliardi. (2004) Parametric evaluation of 3D dispersion of rockfall trajectories.” Natural Hazards and Earth System Science 4.4: 583-598.
Study of the 2012-2020 pit crater evolution in the summit caldera of Nyamulagira volcano using multiple satellite sensors and UAS-based photogrammetry
Authors: Smets Benoît , Subira Josué , Dille Antoine , Theys Nicolas , Broekmans Fran , Nobile Adriano , d'Oreye Nicolas , Kervyn François
Published: March 2020

Since its last flank eruption in 2011-2012, the activity of Nyamulagira volcano (Virunga Volcanic Province, DR Congo) has been characterized by pit crater collapse, lava fountaining and intermittent lava lake activity. No more flank eruption occurred since this concentration of the eruptive activity at the summit. As Nyamulagira is located in a remote area of the Virunga National Park, field observations remain limited. As a consequence, observations of the ongoing changes at the summit of the volcano mostly rely on satellite observations. Time-series of very-high to high resolution optical and SAR amplitude images for instance provide the required information to follow the evolution of the pit crater, from the first signs of collapse to its filling by lava. Hotspot detection from the combination of MODIS and Landsat-type images (including Sentinel-2) allows detecting the first appearance of lava in the pit crater and describing the intermittence of the lava lake activity that has developed since 2014. The OMI and TROPOMI instruments allow measuring the evolution of SO2 emissions. Thanks to few aerial surveys and the use of Unoccupied Aerial Systems (UAS or “drone”), the volume of lava accumulated within the pit crater since 2014 was measured. All these satellite and drone-based observations were finally compared with the known historical eruptive activity, in terms of lava and gas discharge rates and type of summit eruptive activity. The presented work shows how combining various remote sensing techniques that make use of recent generations of satellite images and UAS acquisitions allow a detailed interpretation of the evolution of the volcano, even when field access is an issue.

 
Particle production in the upper troposphere over the Amazon Basin
Authors: Liu Lixia , Su Hang , Pöschl Ulrich , Cheng Yafang
Published: March 2020

Particle production in the upper troposphere has been reported as an important source of aerosol particles and cloud condensation nuclei in pristine environment and tropical regions and exerts significant climate effects. In this work, we develop a new organic nucleation scheme to the WRF-Chem model with extended particle size bins from 1nm to 10μm. We improve on previous coarse-resolution global simulations that approximate the highly oxygenated multifunctional organic compounds (HOMs) in a thermodynamic state by implementing kinetic calculation of HOMs and using fine-grid regional simulations. Sensitivity studies are conducted over the Amazon Basin during the dry season in 2014 to characterize the HOMs-induced new particle formation and identify its key controlling factors in Amazon. The model simulations are evaluated using aircraft observations of profiles of aerosol particles during the 2014 ACRIDICON-CHUVA campaign. We show that the new particle formation occurs mostly at the upper troposphere and modestly in the planetary boundary layer, driven by low temperature and high concentration of biogenic precursors, respectively. Including the HOMs-induced biogenic new particle formation mechanism decreases the model prediction bias of the particle number concentration in the upper troposphere by over 50%, suggesting an important role of the HOMs-induced biogenic new particle formation in the dry season over the Amazon region.
The Western Tibetan Vortex as an emergent feature of near-surface temperature variation?
Authors: Li Xiaofeng , Yu Jingjing
Published: March 2020

The Western Tibetan Vortex (WTV) was identified through research efforts to understand the causal mechanisms responsible for the ‘Karakoram Anomaly’. The WTV has been shown to be an important anomalous circulation system influencing near surface climate over the Tibetan Plateau (TP). Existing researches have characterised the dynamical characteristics and thermodynamic behaviours of the WTV in detail. Scientific consensus has not yet been established. However, regarding the physical mechanisms which produce the WTV itself, a recent argument has asserted that the WTV is the set of wind field anomalies resulting from changes in 2m near-surface air temperatures (T2m) over the western TP. This argument can spur constructive discussion for improving our understanding on the WTV. This paper examines whether a putative thermal-generating machanism for the WTV can explain the established defining features of the WTV. In particular we evaluate if warmer (colder) T2m over the western TP is sufficient to drive downward (upward) wind anomaly in the overlying air column. Detailed consideration is given to whether the supposedly thermally induced vortex does indeed have the expected baroclinic structure – i.e. cyclonic (anti-cyclonic) wind anomaly at the mid-lower (mid-higher) troposphere – rather than a quasi-barotropic structure – i.e. cyclonic or anti-cyclonic wind anomaly at both the mid-lower and mid-higher troposphere –  as the research first identifying the WTV reported. This work thus seeks to determine the ‘direction of causality’ of whether  the WTV drives T2m over the western TP or the thermal forcing of the western TP’s T2m is the mechanism generating the WTV. This work utilises ERA5 meteorological reanalysis data to assess how the WTV may impact the western TP’s T2m through modulating the cloud cover and hence net surface radiation. These analyses complement previously published evaluation of the prosoposed adiabatic heating mechimism through which the WTV impacts the mid-lower tropospheric and near surface air temperarure. It is important to note that further evaluations of the skill of the newly released ERA5 dataset in representing the atmospheric conditions accurately over the western TP are still needed.
Is hydraulic modelling parametrization the major source of variability in flood hazard assessment? Insight into hydrologic uncertainty and the role of design rainfall in probabilistic flood maps
Authors: Volpi Elena , Annis Antonio , Nardi Fernando , Fiori Aldo
Published: March 2020

In this work, a methodology for quantifying the relative impact of hydrological and hydraulic modelling parameterizations on uncertainty of inundation maps has been developed and applied in the Marta river basin, central Italy. A lumped rainfall-runoff forced by a synthetic hyetograph derived from regionalized IDF curves and a Quasi-2D hydraulic model were adopted to delineate the flood hazard maps related to different return periods. The uncertainty related to the design rainfall estimation method, given by the limited length of the time series from which the IDF curves fitted, was considered adopting a Monte Carlo approach.  On the other hand, the uncertainty related to floodplain roughness was considered adopting literature values. The above mentioned methodologies for representing both uncertainties were applied simultaneously and separately. Results, expressed in terms of variability of simulated flood extents and flow depths, suggest a significant predominance of the uncertainty related to hydrological modelling as respect to the hydraulic modelling.
Water budget estimation under parameter uncertainty using Stein Variational Gradient Descent
Authors: Ramgraber Maximilian , Weatherl Robin , Schirmer Mario
Published: March 2020

Increasingly intensive drought periods during the summer months put stresses even on traditionally water-rich regions such as Switzerland. In the particularly dry year of 2018, several Swiss municipalities were forced to place bans on agricultural irrigation, while others were forced to import water from neighbouring catchments to sustain water supply. The preparation for and management during such droughts demands sustainable management plans which are often informed by numerical models providing decision support.

Unfortunately, sustainable water resources management of alpine regions often demands a greater degree of system complexity than usual. This complexity must be reflected in the models used for decision-support: fixed head boundaries must be used cautiously, the aquifer’s depth and properties are often uncertain and highly heterogeneous, and inflow and recharge are similarly difficult to quantify. Considering these diverse sources of uncertainty renders the Bayesian parameter inference problem highly challenging.

Towards this end, we explore a technique known as Stein Variational Gradient Descent (SVGD). This variational method implements a series of smooth transformations resulting in a particle flow, incrementally transforming an ensemble of particles into samples of the posterior. The method has been shown to be able to reproduce non-Gaussian and even multi-modal distributions, provided the underlying posterior is sufficiently smooth.

In this study, we test this algorithm with a groundwater model of the catchment of Fehraltorf implemented in MODFLOW 6. We consider parameter uncertainty for the aquifer depth and topology, its hydraulic parameters, and control variables for recharge and inflow. We report the resulting water table and budget and discuss the optimization performance.
Stress-based tomography: potential, open-questions and future developments
Authors: Bayer Peter , Afshari Moein Mohammad Javad , Somogyvári Márk , Ringel Lisa , Jalali Mohammadreza
Published: March 2020

Fracture network characterization is critical for many subsurface engineering problems in petroleum, mining, nuclear waste disposal and Enhanced Geothermal Systems (EGS). Due to limited exposure, direct measurement of fracture network properties at great depth is not possible and geophysical imaging techniques cannot resolve the fractures. Therefore, tomographic imaging techniques have been proposed and applied to reconstruct the structural discontinuities of rock mass. Stress-based tomography is a novel concept aiming at probabilistic imaging of the fracture network using the stress perturbations along deep boreholes. Currently, this approach has only been successfully tested on two-dimensional fracture networks. However, its great potential to unravel the heterogeneous structure of fractured rocks at great depth motivates further scientific effort. Here, we present the potential, open questions, current challenges and necessary future developments in order to apply this methodology to image three-dimensional multiscale structure of the rock mass in the field. Other tomographic approaches such as tracer and hydraulic tomography invert tracer breakthrough curves (BTCs) and pressure response in an observational well. We suggest a joint and comparative tomographic analysis in a Bayesian inversion framework to reconstruct Discrete Fracture Networks (DFN). This is expected to provide a new view of the strengths of each tomographic variant.
Remote influences on the Indian monsoon Low-Level Jet intraseasonal variations
Authors: Izumo Takeshi , Swathi Maratt Satheesan , Lengaigne Matthieu , Vialard Jérôme , Ramesh Kumar Dr
Published: March 2020

A strong Low-Level Jet (LLJ), also known as the Findlater jet, develops over the Arabian Sea during the Indian summer monsoon. This jet is an essential source of moisture for monsoonal rainfall over the densely-populated Indian subcontinent and is a key contributor to the Indian Ocean oceanic productivity by sustaining the western Arabian Sea upwelling systems. The LLJ intensity fluctuates intraseasonally within the ~20- to 90-day band, in relation with the northward-propagating active and break phases of the Indian summer monsoon. Our observational analyses reveal that these large-scale regional convective perturbations  only explain about half of the intraseasonal LLJ variance, the other half being unrelated to large-scale convective perturbations over the Indian Ocean. We show that convective fluctuations in two regions outside the Indian Ocean can remotely force a LLJ intensification, four days later. Enhanced atmosphericdeep convection over the northwestern tropical Pacific yields westerly wind anomalies that propagate westward to the Arabian Sea as baroclinic atmospheric Rossby Waves. Suppressed convection over the eastern Pacific / North American monsoon region yields westerly wind anomalies that propagate eastward to the Indian Ocean as dry baroclinic equatorial Kelvin waves. Those largely independent remote influences jointly explain ~40% of the intraseasonal LLJ variance that is not related to convective perturbations over the Indian Ocean (i.e. ~20% of the total), with the northwestern Pacific contributing twice as much as the eastern Pacific. Taking into account these two remote influences should thus enhance the ability to predict the LLJ.

 

Related reference: Swathi M.S, Takeshi Izumo, Matthieu Lengaigne, Jérôme Vialard and M.R. Ramesh Kumar:Remote influences on the Indian monsoon Low-Level Jet intraseasonal variations, accepted in Climate Dynamics.
The remobilisation of seismically-sourced sediment by debris flows in Wenchuan: A grain size perspective
Authors: Harvey Erin , Fan Xuanmei , Hales Tristram , Hobley Daniel , Liu Jie , Xu Qiang , Huang Runqiu
Published: March 2020

Co-seismic landslides can mobilise up to 3 km3 of loose sediment within minutes. However, the export rate of this sediment is largely unconstrained. For example, it is estimated that a decade after the 2008 Wenchuan earthquake at least 90% of the co-seismic sediment remains stored on the hillslope. Post-earthquake debris flows are the main conduit by which such hillslope debris reaches the fluvial network but the mechanics that govern the triggering and runout of such flows remain unclear and as such they appear to behave largely unpredictably.  Material grain size is a key control on both triggering and runout, since it affects both hydrological (e.g. water loss during flow; saturation state before triggering) and frictional properties of the system. However, our understanding of the role of grain size in the genesis and evolution of debris flows remains poorly explored, largely due to limitations in real field data. Existing estimates for landslide and debris flow deposit grain size distributions (GSDs) are currently limited by 1. inconsistency of applied methods; 2. the very poor sorting of these sediments; 3. inaccessibility, and 4. inherent intra-deposit variability in GSD. 

Our research aims to better understand the role of grain size using an unprecedentedly detailed set of field-constrained GSDs across the post-seismic landslides and debris flows of the 2008 Wenchuan earthquake. Here we present data quantifying the grain size distribution across two debris flows using two different techniques. The two debris flows occurred in response to prolonged rainfall in August 2019 and mobilised co-seismic debris from the 2008 earthquake. In the field, we selected four to eight 1 m x 1 m x 0.5 m pits along the centre line of each debris flow at regular intervals and sieved the pit material into 8 cm, 4 cm, 2 cm and 1 cm fractions at 10 cm depth increments. Boulders >8 cm were measured and weighed individually. Smaller samples were then collected from the finer fraction (<1 cm) and sieved further in the laboratory. The coarse fraction was independently constrained from calibrated photogrammetry, and this was coupled to drone surveying to ensure the coarsest fraction (≥1 m) was correctly represented. This study presents a detailed estimate of post-earthquake debris flow GSDs with the overarching aim to better understand sediment transport and deposition from debris flows in the years following an earthquake.
Poro-visco-elasto-plastic seismo-hydro-thermomechanical geodynamic models for subduction zones and induced seismicity
Authors: Gerya Taras , Petrini Claudio , Yarushina Viktoriya
Published: March 2020

Natural and induced seismicity is widely investigated, and extensive knowledge has been acquired in the last years, but exact earthquake mechanisms remain elusive and poorly understood. The high impact of earthquakes on human society emphasizes that a deeper understanding of earthquake processes must be a priority in order to improve seismic hazard assessment and mitigate associated risks. Pervasive fluid flow is a key process significantly influencing rock physics and mechanics, and thus has a crucial impact on natural and induced earthquakes. Seismo-hydro-thermo-mechanical (SHTM) modelling is an important nascent branch of geodynamic modelling, which investigates evolution of coupled fluid-solid systems under conditions of both slow tectonic and fast seismic deformation rates. Here, we present a new fully coupled two-dimensional seismo-hydro-mechanical numerical code, with a poro-visco-elasto-plastic rheology, based on fully staggered finite differences with marker-in-cell technique, adaptive time stepping and global Picard iterations. The presented numerical code combines inertial mechanical deformation with pervasive fluid flow. The adaptive time stepping allows the resolution of co-seismic and interseismic phases with time steps ranging from milliseconds to years.

First, we demonstrate how fluid-bearing subducting rocks are intrinsically seismic and how seismic events in the form of highly localized ruptures spontaneously nucleate along the subduction interface. Nucleation and propagation of such events are driven by rapid fluid pressurization caused by visco-plastic compaction, counterbalanced by a nearly simultaneous and equivalent poroelastic decompaction inside the propagating and rupturing fault. Successive post and interseismic fluid pressure release, generated by poroelastic compaction along the fault, allows strength recovery of the megathrust. The model reproduces the broad range of seismic events present at the subduction interface, including slower events, regular earthquakes, and earthquakes that rupture the entire megathrust and reach velocities on the order of m/s, without employing slip rate dependent frictional properties.

Next, we show how our approach can be successfully adapted for fluid injection setups to model induced seismicity phenomena. The numerical code successfully modelled fluid induced seismic events and the resulting seismic wave propagation.  Preliminary results show that faults can form spontaneously and grow aseismically at the injection site thereby creating favorable conditions for the development of broad induced seismicity region where different faults can be activated seismically at different time.

Finally, we outline in short future SHTM modeling directions that should account for fracture-induced dilatation and dynamic permeability variations, thermal effects and three-dimensionality.
The urban wind island from a three-dimensional perspective
Authors: Droste Arjan , Steeneveld Gert-Jan , Holtslag Bert , Wouters Hendrik
Published: March 2020

The Urban Wind Island (UWI), a small but persistent positive wind anomaly over the city as a whole, has previously been revealed using a simplified conceptual model of the convective atmospheric boundary layer. However, the urban boundary layer is strongly heterogeneous and complex, and many interactions with surrounding land-use are not taken into account with the conceptual model used. Additionally, the transition to a stable or neutral nocturnal boundary layer substantially influences wind speed, for instance leading to nocturnal jets, which could also lead to UWI formation. This study extends the UWI research into less idealised cases by using the 3D WRF mesoscale model for Amsterdam (the Netherlands) and its surroundings, at 500m resolution. Two summers of forecast results for in total 173 days are used to identify whether the UWI persists in a 3-dimensional modelling environment, and which conditions are optimal for its formation and persistence. In order to focus only on wind modified by surface processes, large-scale influences which modify wind speed, such as frontal passages, are identified and eliminated from the dataset. We find that a positive UWI is present roughly half the time, with an order of magnitude that is similar to the previous work (~ 0.5 m/s). In addition we find an evening UWI that is caused by the delayed onset of the transition from an unstable to a stable or a neutral boundary layer in the urban area, while the rural area is already stable and calm.

 
Anaerobic Digestate Fraction and Nutrient Stoichiometry Significantly Influence the Carbon Cycle in Grassland Soils
Authors: Cattin Marta , Stutter Marc , Lag-Brotons Alfonso , Wadley Phil , Semple Kirk T. , Parry Chris , Surridge Ben W.J.
Published: March 2020

The application of digestate from anaerobic digestion to grassland soils is of growing interest as an agricultural practice. However, significant uncertainties surrounding the potential impacts of digestate application on processes associated with the soil microbial community remain, particularly for processes governing Carbon Use Efficiency (CUE) and the broader soil C cycle. In this research, we examined how the C:N stoichiometry of digestate and the nutrient status of soil influenced the impact of digestate application on the soil C cycle.  

Three fractions of digestate (whole [WD], solid [SD] and liquid [LD]), spanning a range of C:N, were each applied to two soils of contrasting starting nutrient status (high and low) and compared to unamended controls (Ctr). Two short-term incubations, each lasting seven days, were undertaken. In the first, applications of WD, SD and LD each achieved the same total N input to soils. In the second, digestate applications were adjusted to provide consistent total C input to soils. In each incubation, CO2-C efflux, microbial biomass C (Cmicro) and pH were determined.  

In each of the two incubations, the application of digestate significantly increased cumulative CO2-C efflux compared to control soils. However, the precise effect of digestate application varied between the two incubations and with both soil nutrient status and digestate fraction. Microbial biomass C was largely unchanged by the treatments in both incubations. During the first incubation, soil pH decreased substantially following each digestate treatment in both soil types. A similar pattern was observed within the second incubation in the high nutrient soil. However, in contrast, soil pH increased substantially following LD and WD application to the low nutrient soil in the second incubation. Varying CUE responses are likely to be observed following the application of digestate to agricultural soils, dependent on digestate fraction, C:N ratio of the digestate, and the initial soil nutrient status. Therefore, digestate application rates and soil management must be carefully planned in order to avoid adverse impacts of digestate application to land. 

 