bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Fluidized Backfill Materials for Optimized Bedding of Buried Power Cables
Authors: Eckhardt Maximilian , Pham Hung , Schedel Markus , Sass Ingo
Published: March 2021

The transition towards renewable energy systems leads to increased loads on the electrical power grid. As a result, many transmission lines have to be extended or newly built. According to a government resolution, in Germany the preferred implementation of new high-voltage, direct current (HVDC) electric power transmission systems should be buried power cables.

When operating buried power cables, the mechanical and thermal properties of the cable bedding need to meet certain requirements. On the one hand, accurate positioning and protection of the cable and protection pipe from mechanical stress demand mechanical stability. On the other hand, electric losses during transmission result in thermal energy that needs to be dissipated. Since the ampacity of the cable depends on the maximum permissible temperature of the conductor, the potential load of the power line is directly connected to the thermal properties of the bedding.

To ensure both of these technical requirements, the pre-existing soil mostly is disposed and replaced by sand or artificial fluidized backfill materials with well-known material properties, resulting in potentially high logistical effort, environmental impact and costs. One way to address these effects could be the reuse of the excavated soils as a basic material for the on-site production of a fluidized backfill material, allowing for the adjustment of soil properties (within limits) by adding cement and other additives. By enhancing the thermal properties of the cable bedding, the ampacity of the cable route can be increased, potentially reducing land use due to smaller dimensions of the cable trench. Reusing excavated soils further reduces potential land use, since less material needs to be disposed in landfill sites. 

Within the scope of our research, the technical and economical possibilities and limits of reusing excavated soils for the production of fluidized backfill materials are explored. In addition, the stability of fluidized backfill materials under cyclic load scenarios is investigated to assess possible alterations of such materials during cable operation, which may affect the long-term efficiency of the transmission system.
Coastal lows climatology along the Chilean coast using ERA5 reanalysis
Authors: Gómez Contreras Álvaro , Carrera Ávila Natalia , Rapanague María Jesús , Rondanelli Rojas Roberto
Published: March 2021

Coastal lows are prevalent along the coast of Chile. They are thermal lows that propagate poleward. The leading edge of the coastal low is associated with easterly winds, warm surface temperatures and clear skies. They are forced by the reversal of the typical meridional pressure gradient by the passage of synoptic scale high pressure systems embedded in the extratropical storm track. Coastal lows are an important feature of Southwestern South America, as they are involved in some of the major air pollution episodes in Central Chile, as well as are a factor in summertime bushfire events. Similar coastally trapped disturbances occur in Southeastern Australia, South Africa and the west coast of North America.

In this work, we characterize the climatology of coastal lows in Chile using surface pressure, wind and geopotential height at 500 hPa from the ERA5 reanalysis (1979 to 2018). These high resolution fields allow, for the first time, to characterize the behavior of coastal lows in the mesoscale, which were only coarsely represented in previous reanalyses. We identify the events using a method based on the drop of surface pressure and winds from the associated coastal low level jet. We found an average of 39 events per year, developing mostly during winter and spring. We found that the coastal low demise occurs typically at around 19:00 Local Time. We also characterize the propagation speed of the low along the coast finding a very striking change from about 40 m/s north of 30ºS to about 17 m/s south of 30ºS. We will discuss our findings in the light of dynamical theories proposed for the propagation of these disturbances.
The shifting of climate types: manifestation to phenology and ecosystems structure
Authors: Kalvāne Gunta , Kalvāns Andis , Briede Agrita , Krampis Ilmārs , Kaupe Dārta , Rūsiņa Solvita
Published: March 2021

According to the Köppen climate classification, almost the entire area of Latvia belongs to the same climate type, Dfb, which is characterized by humid continental climates with warm (sometimes hot) summers and cold winters.  In the last decades whether conditions on the western coast of Latvia more characterized by temperate maritime climates. In this area there has been a transition (and still ongoing) to the climate type Cfb.

Temporal and spatial changes of temperature and precipitation regime have been examined in whole territory to identify the breaking point of climate type shifts. We used two type of climatological data sets: gridded daily temperature from the E-OBS data set version 21.0e (Cornes et al., 2018) and direct observations from meteorological stations (data source: Latvian Environment, Geology and Meteorology Centre). The temperature and precipitation regime have changed significantly in the last century - seasonal and regional differences can be observed in the territory of Latvia.

We have digitized and analysed more than 47 thousand phenological records, fixed by volunteers in period 1970-2018. Study has shown that significant seasonal changes have taken place across the Latvian landscape due to climate change (Kalvāne and Kalvāns, 2021). The largest changes have been recorded for the unfolding (BBCH11) and flowering (BBCH61) phase of plants – almost 90% of the data included in the database demonstrate a negative trend. The winter of 1988/1989 may be considered as breaking point, it has been common that many phases have begun sooner (particularly spring phases), while abiotic autumn phases have been characterized by late years.

Study gives an overview aboutclimate change (also climate type shift) impacts on ecosystems in Latvia, particularly to forest and semi-natural grasslands and temporal and spatial changes of vegetation structure and distribution areas.

This study was carried out within the framework of the Impact of Climate Change on Phytophenological Phases and Related Risks in the Baltic Region (No. 1.1.1.2/VIAA/2/18/265) ERDF project and the Climate change and sustainable use of natural resources institutional research grant of the University of Latvia (No. AAP2016/B041//ZD2016/AZ03).

Cornes, R. C., van der Schrier, G., van den Besselaar, E. J. M. and Jones, P. D.: An Ensemble Version of the E-OBS Temperature and Precipitation Data Sets, J. Geophys. Res. Atmos., 123(17), 9391–9409, doi:10.1029/2017JD028200, 2018.

Kalvāne, G. and Kalvāns, A.(2021): Phenological trends of multi-taxonomic groups in Latvia, 1970-2018, Int. J. Biometeorol., doi:https://doi.org/10.1007/s00484-020-02068-8, 2021.
Plastic debris and plastic litter in the Kerch Strait of the Black Sea
Authors: Zavialov Peter
Published: March 2021

It is well-known that the shallow Sea of Azov can be thought of as a large estuary receiving discharges from the Don and the Kuban rivers, therefore, the flow through the Kerch Strait towards the Black Sea usually carries a variety of pollutants. However, the flux of plastic waste through the Strait has never been quantified. In situ measurements and sampling of microplastic debris and floating plastic litter in the Kerch Strait were conducted by a team from Shirshov Institute of Oceanology on July 16-18, 2020, along with CTD and ADCP profiling in the cross-section of the strait. The microplastic debris were sampled using a 0.3 mm mesh size Manta trawl net towed behind the R/V "Peleng" cruising at 4 kts and taking material from the upper 1 m of the water column. As a result, a large set of plastic particles, fibers and films were collected. All sampled items were measured, weighted, and sorted by composition using Micro NIR 1700 spectrometer instrument. The particle sizes ranged from 0.4 to 25.0 mm and weights varied between 0.05 and 7.72 mg. With respect to the chemical composition, about 63% of the collected particles were udentified as HDPE (high-densuty polyethylene), 21% as PP (polypropylene), 5% as PET (polyethylene terephthalate), 4% as PA (polyamide), 4% as PC (polycarbonate), and 3% as all other types of plastic. The content of visually identifiable plastic litter in the Kerch Strait varied between about 10 and 200 pieces per km2, with the average value close to 100 pieces/km2. However, the distribution was far from homogeneous – the litter was mainly concentrated in the western part of the Strait, where the principal stream carrying the Sea of Azov water into the Black Sea is usually localized. The newly obtained data of plastic litter concentration together with the current velocity data collected in ADCP profiling enabled us to estimate for the first time the flux of plastic through the Kerch Strait from the Sea of Azov into the Black Sea. This can be done by simply multiplying the plastic concentration by the velocity and then integrating it over the cross-section of the Strait. This procedure yields an estimate of 14,700 major pieces of plastic such as bottles, bags, etc., passing through the Strait per day. Assuming the average weight of a plastic litter piece 15 g , this leads to 220 kg/day, or about 9 kg/hour. This is quite a considerable mass of plastic, although it is about 20 times smaller than the amount brought to the Black Sea by the Danube according to [Lechner et al., 2014]. It must be kept in mind, however, that our estimate for the Kerch Strait is based on instantaneous one-time measurements, and may not represent long-term average values.

The studies described in this presentation represent the Russian contribution to the PLUMPLAS Project within STI BRICS cooperative initiative, implemented through the Russian Basic Research Foundation grant 19-55-80004.
Autonomous observations of sea ice mass balance during MOSAiC
Authors: Perovich Don , Raphael Ian , Moore Ryleigh , Clemens-Sewall David
Published: March 2021

Four seasonal ice mass balance buoys were deployed as part of the MOSAiC distributed network. These instruments measured vertical profiles of snow and ice temperature, as well as snow depth and ice thickness every six hours. Ice growth, surface melt, and bottom melt, as well as temporally averaged estimates of ocean heat fluxes, were calculated from these measurements. The buoys were installed in October 2019, with durations ranging from February 2020 to July 2020. Three of the buoys were destroyed in ridging events in February, March, and June 2020. The fourth buoy lasted until floe breakup in July 2020. The sites were separated by tens of kilometers, but had very similar air temperatures. While air temperatures were similar, snow – ice interface temperatures at different buoys varied by as much as 15 C due to differences in snow depth and ice thickness. Initial ice thicknesses ranged from 0.30 to 1.36 meters. During the growth season snow depths typically were around 0.1 to 0.2 meters, except for one case where the buoy was in a snow drift and the snow depth exceeded 0.5 meter. Peak growth rates of about 0.8 cm per day occurred in January. In mid-January there was a rapid increase in ice thickness associated with an aggregation of platelet ice. This aggregation only lasted for two weeks. In mid-April, air temperatures increased to nearly 0 C, almost ending the growth season.
Potential greenhouse gas production by organic matter decomposition in thawing subsea permafrost
Authors: Wild Birgit , Shakhova Natalia , Dudarev Oleg , Ruban Alexey , Kosmach Denis , Tumskoy Vladimir , Tesi Tommaso , Joß Hanna , Nybom Inna , Alexanderson Helena , Jakobsson Martin , Mazurov Alexey , Semiletov Igor , Gustafsson Örjan
Published: March 2021

Subsea permafrost extends over vast areas across the East Siberian Arctic Ocean shelves and might harbor a large and vulnerable organic matter pool. Field campaigns have observed strongly elevated concentrations of CH4 in seawater above subsea permafrost that might stem from microbial degradation of thawing subsea permafrost organic matter, from release of CH4 stored within subsea permafrost, from shallow CH4 hydrates or from deeper thermogenic/petrogenic CH4 pools. We here assess the potential production of CH4, as well as CO2 and N2O by organic matter degradation in subsea permafrost after thaw. To that end, we employ a set of subsea permafrost drill cores from the Buor-Khaya Bay in the south-eastern Laptev Sea where previous studies have observed a rapid deepening of the ice-bonded permafrost table. Preliminary data from an ongoing laboratory incubation experiment suggest the production of both CH4 and CO2 by decomposition of thawed subsea permafrost organic matter, while N2O production was negligible. These data will be combined with detailed biomarker analysis to constrain the vulnerability of subsea permafrost organic matter to degradation to greenhouse gases upon thaw.
A Deep Water Dispersion Experiment in the Gulf of Mexico
Authors: Meunier Thomas , Pérez Brunius Paula , Rodríguez Outerelo Javier , Furey Heather , Bower Amy , Ramsey Andrée , García Carrillo Paula , Ronquillo Argelia
Published: March 2021

The Deep Water Horizon oil spill has dramatically impacted the Gulf of Mexico from the seafloor to the surface. While dispersion of contaminants at the surface has been extensively studied, little is known about deep water dispersion properties. This study describes the results of the Deep Water Dispersion Experiment (DWDE), which consisted in the release of surface drifters and RAFOS floats drifting at 300 and 1500 dbar in the Gulf of Mexico. We show that surface diffusivity is elevated, and decreases with depth. The separation dependence of relative diffusivity follows a Richardson law at all depths. Time dependence of dispersion suggests a Richardson regime near the surface and a mixed Richardson/ballistic regime in depth at scales of [10-100 km]. Finite Scale Lyapunov Exponents and pair separation Kurtosis suggest the existence of a Lundgren regime at scales smaller than the Rossby radius near the surface, and at smaller scales in depth.
A mechanism of apparent inter-sonic propagation of shear fractures
Authors: Pasternak Elena , Dyskin Arcady
Published: March 2021

Inter-sonic (faster than the shear wave velocity) propagation of zones of shear over faults are observed both in the Earth’s crust and in specially designed laboratory experiments. This is usually interpreted as propagation of shear fractures caused by postulated special fracture mechanisms. This interpretation is however at variance with experimental facts that shear fractures in solids do not propagate in their own planes, kinking instead. Extensive (and fast) in-plane shear fracture propagation seems to only be possible over pre-existing planes considerably weaker than the surrounding material. A limiting case of fracture propagation over such a weak plane is the propagation of a sliding zone resisted by friction only. Another limiting case is shearing over a narrow elastic layer (shear Winkler layer) without rupture. The shear Winkler layer models both traditional elastic connections (positive stiffness) and rotation of non-spherical particles of the fault gouge (negative stiffness), e.g. [1, 2].

In both cases propagation of sliding/shear zone also involve longitudinal deformation in the surrounding material. Using a configuration different from [3, 4] we demonstrate that the presence of the longitudinal deformation makes the sliding/shear zone propagate with p-wave velocity. Propagation of such zones create seismic signals with power spectra resembling those observed in earthquakes.

Acknowledgement.   AVD and EP acknowledge support from the Australian Research Council through project DP190103260.
Effect of unsteady flows on the development and magnitude of bed forms
Authors: Wang Le , Cuthbertson Alan , Pender Gareth , Cao Zhixian
Published: March 2021

Sediment transport and associated morphological changes in alluvial rivers occur primarily under unsteady flow conditions that are manifested as well-defined flood hydrograph events. At present, typical bed forms generated by such unsteady flows is far less studied and, thus, more poorly understood, than equivalent bed forms generated under steady flow conditions. In view of this, the objective of this work is to investigate the development of morphological bed features, and specifically variability in the length, height and steepness of bed forms that develop in a mobile coarse-sand bed layer under unsteady flow hydrographs under zero sediment feed conditions. A series of laboratory flume experiments is conducted within which different flow hydrograph events are simulated physically by controlling their shape, unsteadiness and magnitude. Experimental results indicate that different categories of bed forms such as dunes, alternate bars or transitional dune-bar structures develop within the erodible bed layer when subject to varying hydrograph flow conditions. Examination of relative importance of three parameters used to describe the hydrograph characteristics (i.e. asymmetry, unsteadiness and total water work) on bed form dimensional descriptors (i.e. wavelength, height and steepness) reveals that hydrograph unsteadiness and total water work are the primary and second-order controls on bed deformations or corresponding bed form dimensions. By contrast, hydrograph asymmetry appears to have minimal or negligible influence on bed form development in terms of their type and magnitude. Based on these findings, a physical model was developed and tested to describe the effect of unsteady flow hydrographs with varying unsteadiness and total water work on the nature and size of resulting bed forms that are generated in sand-bed layers. 
A hydrogeomorphic perspective on emergent topographic properties at landscape equilibrium
Authors: Litwin David G. , Harman Ciaran J. , Tucker Gregory E. , Barnhart Katherine R.
Published: March 2021

Geomorphic properties of watersheds influence runoff generation, which drives landscape evolution over long timescales. Despite this strong process feedback, our understanding of how runoff generation affects long-term catchment evolution remains rudimentary. In most humid landscapes, storm runoff arises from shallow subsurface flow and from precipitation on saturated areas. Catchment geomorphology drives these runoff mechanisms, as landscape relief generates hydraulic gradients from hillslopes to streams, and regolith thickness and permeability affect flow partitioning and water storage capacity. However, there are few studies of how runoff coupled to dynamic shallow groundwater affects landscape form. In this study, we present a new groundwater-landscape evolution model and introduce a nondimensional framework to explore how subsurface-mediated runoff generation affects long-term catchment evolution. The model solves hydraulic groundwater equations to predict the water table location given prescribed recharge. Water in excess of the subsurface capacity for transport becomes overland flow, which may detach and transport sediment, affecting the landscape form that in turn affects runoff generation. We show that (1) two input parameters fully describe the possible steady state landscapes that coevolve under steady recharge, (2) subsurface flow capacity exerts a fundamental control on hillslope length and relief of these landscapes, and (3) three topographic metrics derived from the governing equations, steepness index, Laplacian curvature, and topographic wetness index, form a natural basis for evaluating the resulting coevolved landscapes. We derive a theoretical relationship using these metrics that allows us to recover the key model input parameters (including subsurface transmissivity) from topographic analysis of the landscape. These results open possibilities for topographic analysis of humid upland landscapes that could inform quantitative understanding of hydrological processes at the landscape scale.
Understanding of reservoirs in karst: the case of Vora Bosco cave (Salento, Italy)
Authors: Leins Tamara , Liso Isabella Serena , Parise Mario , Hartmann Andreas
Published: March 2021

Vora Bosco Cave is located in the Salento karst peninsula (Apulia, S Italy), surrounded by the Ionian and Adriatic Seas. In this part of Apulia, due to climate change, the typical Mediterranean climate is moving towards arid and semi-arid, with scarce or absent surface runoff. The Salento groundwater is a freshwater lens fluctuating on seawater, entering inland because of intrusion phenomena. The freshwater volume stored in the lens is subjected to both sea level rise and an increasing pressure caused by the high water demand, especially in summer time, for touristic purposes. Therefore, developing an understanding of the hydrogeological dynamics of the karst aquifer can be a useful tool for planning better protection and management actions on Apulian groundwater resources.

Vora Bosco cave was instrumented with a multi-parameter probe for groundwater level measurements from November 2017 to July 2018. Thereby, the system behaviour within the cave recharge area can be explored. To characterise and quantify the natural recharge and discharge behaviour of the system, a simple reservoir model was developed and calibrated with the measured data. The model consists of 4 reservoirs, which are filled and emptied using simple discharge equations. The model considers evapotranspiration from the soil, slow flow in the unsaturated and saturated zone, as well as fast flow in the karstic conduits. Daily data of precipitation and potential evapotranspiration are used as model inputs. The model simulates the water level at Vora Bosco and is calibrated by comparison of simulated and measured water level, using the Kling-Gupta-Efficiency as an objective function. Our results reveal that the model simulations show acceptable performance in reflecting the dynamics of the observed water level data. The calibration achieves reasonable results for the model parameters. In addition to the water level simulations, quantifying predictions uncertainty by Monte Carlo approach, it is shown that there is still potential to produce more reliable estimates of future groundwater dynamics, in order to better manage the precious regional groundwater resources.
A centennial-scale Arctic - North Atlantic recharge oscillator in a coupled climate model
Authors: Waldman Robin , Cassou Christophe , Voldoire Aurore
Published: March 2021

In global climate models, low-frequency natural variability related to the Atlantic Ocean overturning circulation is a common behaviour. Such intrinsic climate variability is a potential source of decadal climate predictability. However, over longer term scenario simulations, this natural variability becomes a major source of uncertainty. In this study, we document a large and sustained centennial variability in the 3500-year pre-industrial control run of the CNRM-CM6 coupled climate model which is driven by the North Atlantic ocean, and more specifically its meridional overturning circulation (AMOC). We propose a new AMOC dynamical decomposition highlighting the dominant role of mid-depth density anomalies at the western boundary as the driver of this centennial variability. We relate such density variability to deep convection and overflows in the western subpolar gyre, themselves controlled by and intense salinity variability of the upper layers. Finally, we show that such salinity variability is the result of periodic freshwater recharge and descharge events from the Arctic Ocean, themselves triggered by stochastic atmospheric forcing.
Solar Wind control of Auroral Kilometric Radiation as measured by the Wind Satellite
Authors: Fogg Alexandra R. , Jackman Caitríona M. , Waters James E. , Bonnin Xavier , Lamy Laurent , Cecconi Baptiste , Issautier Karine
Published: March 2021

Auroral Kilometric Radiation (AKR) emanates from acceleration regions from which escaping particles also excite a number of phenomenon in the terrestrial ionosphere, notably aurorae. As such, AKR emission is a barometer for particle precipitation, indicating activity in the magnetosphere. Observations suggest that the emission is mostly limited to the nightside, relating to bursty tail reconnection events. In this study we investigate the relationship between upstream interplanetary magnetic field and solar wind conditions, and the onset and morphology of corresponding AKR emission. Additionally, we explore the delay time between the arrival of solar wind phenomena at the magnetopause, and the onset of related AKR emission and morphology changes. Connections between AKR and solar wind observations allude to solar wind driving of energetic particle precipitation at different local times. The WAVES instrument on the Wind satellite has provided measurements of radio and plasma phenomenon at a range of locations for over two decades, and in this study a recently developed method is utilised to extract AKR bursts from WAVES data, enabling quantitative examination of AKR emission over statistical timescales.
3D overdeepened trough morphology revealed as a product of bedrock geology (northern Switzerland)
Authors: Gegg Lukas , Buechi Marius W. , Deplazes Gaudenz , Madritsch Herfried , Keller Lorenz , Spillmann Thomas , Anselmetti Flavio S.
Published: March 2021

Subglacial overdeepenings are a common element of once glaciated mountain forelands and have considerable implications for society, e.g. in construction projects, water production and radioactive waste disposal. Yet the processes of overdeepening erosion, especially the influence of bedrock lithology and structure, are poorly understood. We present a case study of the Gebenstorf-Stilli Trough in northern Switzerland, a unique overdeepening with complex underlying geology: In contrast to the Molasse-hosted majority of the Alpine foreland overdeepenings, it is to a large part incised into Upper Jurassic limestones and marls. In order to constrain its morphology in 3D, it was targeted with scientific boreholes as well as a seismic campaign based on analysis of surface waves. The results reveal unexpected trough morphology with two nested sub-basins that appear to be closely related to the bedrock geology. We suggest that this morphology is a product of low erosional efficiency in Jurassic limestones in comparison with both underlying marls and overlying Molasse deposits as well as secondary paleoglaciological effects. We further infer that the glacier’s basal drainage system was the main driver of subglacial erosion of the Gebenstorf-Stilli Trough.
How dry was the LGM? A Biosphere-Hydrosphere modelling approach for the paleo-lake Chew Bahir and Omo-River catchment in southern Ethiopia
Authors: Fischer Markus L. , Bachofer Felix , Trauth Martin H. , Junginger Annett
Published: March 2021

The formation of the East African Rift System led to the emergence of large topographical contrasts in southern Ethiopia. This extreme topography is in turn responsible for an extreme gradient in the distribution of precipitation between the dry lowlands (~500 mm a-1) in the surrounding of Lake Turkana and the moist western Ethiopian Highlands (~2,000 mm a-1). As a consequence, the prevailing vegetation is fractionated into a complex mosaic that includes desert scrubland along the Lake Turkana shore, woodlands and wooded grasslands in the Omo-River lowlands and the paleo-lake Chew Bahir catchment, afro-montane forests of the Ethiopian Highlands, and afro-alpine heath in most elevated parts. During the past 25 ka, southern Ethiopia has been exposed to significant climate changes, from a dry and cold Last Glacial Maximum (LGM, 25-18 ka BP) to the African Humid Period (AHP, 15-5 ka BP), and back to present-day dry conditions. These shifts in temperature and precipitation may have affected the vegetation pattern and landscape in the area, but environmental data especially from LGM times are rare. This is because in times of a dry climate the paleo-lake Chew Bahir was dried up and hence the climate record in lake sediments was interrupted.

In this study, we investigate the hydrological conditions during the LGM using a previously-developed lake balance model (LBM) for southern Ethiopia, which is now coupled with a new predictive vegetation model (PVM) to better understand the biosphere-hydrosphere interactions and thus possible precipitation thresholds. The PVM is based on the method of boosted regression trees using elevation and monthly precipitation as input to predict land-cover, tree-cover and vegetation greenness for a ~1 km grid covering the Omo-River, paleo-lake Chew Bahir, Lake Chamo and Lake Abaya catchments. We linked the PVM and the resulting land surface parameters with the LBM to model the impact of a changing land-cover to the actual evaporation. Furthermore, we used the glycerol dialkyl glycerol tetraethers (GDGT) based paleo-temperature and tropical lapse rate reconstructions from Mount Kenya to consider the orographic temperature distribution in southern Ethiopia during the LGM. Using both, we simulated different precipitation amounts from 100% to 50% compared to the modern-day multi-annual averages and their effect on vegetation and lake levels of paleo-lake Chew Bahir. Our biosphere-hydrosphere modelling approach suggests 25 to 30% lower moisture availability during the LGM compared to the modern conditions and provides a high-resolution spatial reconstruction of the potential prevailing vegetation in the southern Ethiopian region.
Tropospheric products as a signal of interest – overview of troposphere sensing techniques
Authors: Wilgan Karina , Rohm Witold , Bosy Jaroslaw , Geiger Alain , Siddique M. Adnan , Dick Galina , Wickert Jens
Published: March 2021

The microwave signals passing through the troposphere are delayed by refraction. Its high variations, both in time and space, are caused mainly by water vapor. The tropospheric delay used to be considered only as a source of error that needed to be removed. Nowadays, these delays are also a source of interest. The tropospheric delays or integrated water vapor are being assimilated into nowcasting or numerical weather prediction (NWP) models. Moreover, long time series of tropospheric observations have become an important source of information for climate studies. On the other hand, the meteorological data support the space-geodetic community by providing models that can be used to reduce the troposphere impact on the signal propagation. Furthermore, the delays calculated by one microwave technique can be used to mitigate the errors in others.

There are several ways of observing the troposphere, especially considering water vapor. The classical meteorological are: in-situ measurements, radiosondes or radiometers, which allow to sense the amount of water vapor directly. Another, indirect way of observing the water vapor distribution is by using the Global Navigation Satellite Systems (GNSS). This method is called GNSS meteorology. Other microwave techniques such as Very Long Baseline Interferometry (VLBI) or Interferometric Synthetic Aperture Radar (InSAR) are also capable to retrieve the atmospheric information from their signals.

This contribution shows an overview of the troposphere sensing techniques and their applications. We present multi-comparisons of the tropospheric parameters, i.e. refractivity, tropospheric delays in zenith and slant directions and integrated water vapor. The integration of the different data sources often leads to an improved accuracy of the tropospheric products but requires a careful preparation of data. The combination of the data sources allows for using the techniques of complementary properties, for example InSAR with very high spatial resolution with GNSS observations of high temporal resolution. With the emergence of new technologies, some traditional ways of tropospheric measurements can be augmented with the new methods. For example, we have tested meteo-drones as an alternative to radiosondes. The comparisons with GNSS data shows a good agreement of the drone and microwave data, even better than with radiosonde. Moreover, we present the results of the GNSS data assimilation into NWP models and the developments towards multi-GNSS, real-time assimilation of advanced products such as slant delays and horizontal tropospheric gradients.
A vertical fracture cluster embedded into thinly layered medium
Authors: Stovas Alexey , Shuai Da
Published: March 2021

The linear slip theory is gradually being used to characterize seismic anisotropy. If the transversely isotropic medium embeds vertical fractures (VFTI medium, according to Schoenberg and Helbig, 1997), the effective medium becomes orthorhombic.  The vertical fractures may exist in any azimuth angle which leads the effective medium to be monoclinic. We apply the linear slip theory to create a monoclinic medium by only introducing three more physical meaning parameters: the fracture preferred azimuth angle, the fracture azimuth angle and the angular standard deviation. First, we summarize the effective compliance of a rock as the sum of the background matrix compliance and the fracture excess compliance. Then, we apply the Bond transformation to rotate the fractures to be azimuth dependent, introduce a Gaussian function to describe the fractures’ azimuth distribution assuming that the fractures are statistically distributed around the preferred azimuth angle, and average each fracture excess compliance over azimuth. The numerical examples investigate the influence of the fracture azimuth distribution domain and angular standard deviation on the effective stiffness coefficients, elastic wave velocities, and anisotropy parameters. Our results show that the fracture cluster parameters have a significant influence on the elastic wave velocities. The fracture azimuth distribution domain and angular standard deviation have a bigger influence on the orthorhombic anisotropy parameters in the (x2; x3) plane than that in the (x1; x3) plane. The fracture azimuth distribution domain and angular standard deviation have little influence on the monoclinic anisotropy parameters responsible for the P-wave NMO ellipse and have a significant influence on the monoclinic anisotropy parameters responsible for the S1- and S2-wave NMO ellipse. The effective monoclinic can be degenerated into the VFTI medium. Assuming that the fracture cluster has a preferred azimuth angle and other fractures are statistically distributed around it, we define the effective compliance matrix by a Gaussian function,  the Bond transformation matrix and  the excess compliance matrix of the vertical fractures in the eigen-coordinate system. The resulting effective medium possess the monoclinic symmetry. The monoclinic anisotropy parameters (Stovas, 2021) can easily be defined from the effective stiffness coefficients.

 

Schoenberg, M. and Helbig K., 1997, Orthorhombic media: Modeling elastic wave behavior in a vertically fractured earth, Geophysics, 62(6), 1954-1974.

Stovas, A., 2021, On parameterization in monoclinic media with a horizontal symmetry plane, Geophysics (early online).
Parameter Estimation of a Decision-Support Seawater Intrusion Model Using Multiple Well and Geophysical Data
Authors: Coulon Cécile , Pryet Alexandre , Lemieux Jean-Michel
Published: March 2021

In coastal areas, seawater intrusion is a main driver of groundwater salinization and numerical models are widely used to support sustainable groundwater management. Sharp interface models, in which mixing between freshwater and seawater is not explicitly simulated, have fast run times which enable the implementation of parameter estimation and uncertainty analysis. These are essential steps for decision-support modeling, however their implementation in sharp interface models has remained limited. Few guidelines exist regarding which observations to use, and what processing and weighting strategies to employ. We developed a data assimilation framework for a regional, sharp interface model designed for management purposes. We built a sharp interface model for an island aquifer using the SWI2 package for MODFLOW. We then extracted freshwater head observations from shallow wells, pumping wells and deep open wells, and observations of the seawater-freshwater interface from deep open wells, time-domain electromagnetic (TDEM) and electrical resistivity tomography (ERT) surveys. After quantification of measurement uncertainties, parameter estimation was conducted with PEST and a data worth analysis was carried out using a linear approach. Model residuals provided insight on the potential of different observation groups to constrain parameter estimation. The data worth analysis provided insight on these groups’ importance in reducing the uncertainty of model forecasts. Overall a satisfying fit was obtained between simulated and observed data, but observations from deep open wells were biased. While observations from deep open wells and geophysical surveys had a low signal-to-noise ratio, parameter estimation effectively reduced predictive uncertainty. Interface observations, especially from geophysical surveys, were essential to reduce the uncertainty of model forecasts. The use of different types of observations is discussed and recommendations are provided for future data collection strategies in coastal aquifers. This framework was developed in the Magdalen Islands (Quebec, Canada) and could be carried out more systematically for sharp interface seawater intrusion modeling.
Isotopic characterization of coal mine methane in the Upper Silesian Coal Basin, Poland
Authors: Fiehn Alina , Kostinek Julian , Eckl Maximilian , Galkowski Michal , Gerbig Christoph , Röckmann Thomas , Menoud Malika , Maazallahi Hossein , Schmidt Martina , Korben Piotr , Necki Jaroslaw , Stanisavljevic Mila , Swolkien Justyna , Nickl Anna-Leah , Winterstein Franziska , Mertens Mariano , Jöckel Patrick , Fix Andreas , Roiger Anke
Published: March 2021

Emissions from fossil fuels are one of the primary sources of atmospheric methane (CH4) growth. However, estimates of anthropogenic CH4 emissions still show large uncertainties on global and regional scales. Differences in CH4 isotopic source signatures δ13C and δD can help to constrain different source contributions (e.g. fossil, thermogenic, or biogenic).

The Upper Silesian Coal Basin (USCB) represents one of the largest European CH4 emission source regions, with more than 500 Gg CH4 yr-1 released by more than 50 coal mine ventilation shafts. During the CoMet (Carbon Dioxide and Methane Mission) campaign in June 2018 methane observations were conducted from a variety of platforms including aircraft and cars. Beside the continuous sampling of atmospheric methane concentration, numerous air samples were taken from inside the ventilation shafts, around the ventilation shafts (1‑2 km distance) and aboard the DLR Cessna Caravan aircraft and analyzed in the laboratory for the isotopic composition of CH4.

The ground-based samples allowed determining the source signatures of individual ventilation shafts. These signatures displayed a considerable range between different shafts and also varied from day to day. The airborne samples contained a mixture of methane emissions from several mines and thus enabled accurately determining the signature of the entire region. The mean isotopic signature of methane emissions over the USCB derived from the aircraft samples was -51.9 ± 0.5 ‰ for δ13C and -233 ± 6 ‰ for δD. This is in between the range of other microbial and thermogenic coal reservoirs, but more depleted in δD than previous USCB studies reported based on samples taken within the mines. Signatures of methane enhancements sampled upwind of the mines and in the free troposphere clearly showed the presence of methane of biogenic origin (e.g. wetlands, waste, ruminants).

Furthermore, we simulated the methane isotopologues using the on-line three-times nested global regional chemistry climate model MECO(n). We implemented a submodel extension, which includes the kinetic fractionation and uses the isotopic source signatures determined by the ground-based observations. We compare the regional simulations to flask samples taken during CoMet.
He++  behavior on the an interplanetary shock wave 
Authors: Sapunova Olga , Borodkova Natalia , Yermolaev Yuri , Zastenker Georgii
Published: March 2021

In our study we analyzing the fine structure of interplanetary shock wave fronts recorded by the BMSW experiment, installed onboard the SPEKTR-R satellite. The high time resolution of the spectrometer (0.031 s for the plasma flux magnitude and direction and 1.5 s for velocity, temperature, and density) makes it possible to study the internal structure of the IPs front.

BMSW experiment registered 55 IPs waves from 2011 to 2019. For 21 events (where the temperature was not very high), the parameters of twice-ionized helium (He++ or α-particles) - density (absolute value and relative to protons content in the solar wind plasma), velocity, temperature. It is shown that the speed of He++ is slightly less (for about 5%) than the speed of protons, the relative density of He++ rarely exceeds 10%, and the temperature of He++ is about 2 times higher than the temperature of protons.

On the IPs front, short-term and significant (up to 20%) jumps in the relative density of He++ were detected in several events. No dependence was found between Mms/proton beta and He++ density changing after IPs front. However, we detected that the lower Qbn parameter is, the more the relative density of He++ falls behind the IPs front.
The influence of atmospheric rivers on winter melt and accumulation in the northeast of Greenland.
Authors: Turton Jenny , Mattingly Kyle , Mölg Thomas
Published: March 2021

The Greenland Ice Sheet (GrIS) has been losing mass at an accelerated rate in the last few decades, of which, approximately 50% is related to surface melting and runoff (Imbie Team, 2020). Since the mid 2010’s, the highest melt anomalies were found in the northeast of Greenland, where the North East Greenland Ice Stream drains 8 - 12 % of the GrIS. Unsurprisingly, the vast majority of melting occurs in the summer months, however the increasing trend in air temperatures is larger in winter. Similarly, very warm winter periods have been observed recently in the north of Greenland and Arctic Ocean. Due to our previous focus on summer melting, our understanding of glacial hydrology and surface mass balance in winter is still poor.

Here, we present the frequency and amount of surface melting and precipitation, as simulated by the Modèle Atmosphérique Régional (MAR) at 15 km spatial resolution (from 1980 to 2018) and the COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) at 1 km spatial resolution (from 2014 to 2018). Observations from two automatic weather stations are also used to analyse the meteorological setting. We find that both periods of winter melt and extreme precipitation are related to the presence of atmospheric rivers along the east coast of Greenland and in the Atlantic Ocean (specifically in the Greenland Sea and Fram Strait). On average, the detection of atmospheric rivers in the vicinity of the northeast of Greenland leads to a daily warming of +8°C and can raise temperatures to the melting point for a short period of time. We also present the changes in precipitation type (rainfall vs snowfall), from 1980 to 2018 from both MAR and the ERA5 reanalysis product, which are related to atmospheric rivers and passing storms.
Surface solar radiation trends under all-sky and clear-sky conditions over Europe
Authors: Ferreira Correa Lucas , Wild Martin , Folini Doris , Chtirkova Boriana
Published: March 2021

Solar radiation is the primary source of energy for the climate system and a variety of biological processes on the planet. In that sense, understanding the radiative processes in the atmosphere and identifying the governing factors of these processes is key for climate diagnosis and prognosis. In this work, we use daily in-situ observations from 528 stations over Europe from the World Radiation Data Centre (WRDC) database, to analyze Surface Solar Radiation (SSR) trends from 1964 until 2018 in all regions of the continent. Statistical methods were applied to quality-control the dataset: detecting and removing outliers, homogenization and gap-filling of the time series. Two different statistical approaches for identification of clear-sky conditions were applied and compared. Observations in most of the regions on the European continent agree with previously observed negative trends (diming) until the 80’s, followed by positive SSR trends (brightening) from then on, continuing until recent years. However, the regime shifts and the intensity of the trends are not homogeneous within the continent, indicating that regional aspects have non-negligible impacts on the SSR behavior. The comparison between all-sky and clear-sky SSR observations helps to identify to what extent the clouds were a relevant factor in the observed trends in every part of the continent. With this type of analysis we intend to not only present the SSR trends over Europe, but also to expand the comprehension of their spatial heterogeneity across the continent, as well as their causes.
Influence of oil field production life on optimal CO2 flooding strategies: Insight from the microscopic displacement efficiency
Authors: Chernova Anna , Afanasyev Andrey , Andreeva Anna
Published: March 2021

We investigate the influence of the microscopic displacement processes on optimal gas flooding strategies. We couple a 1-D compositional reservoir model with an economic model of the flooding to assess profitability of the strategies. In general, we aim at the net present value maximisation, although the oil recovery and CO2 storage efficiencies are also estimated. Under certain assumptions, we reduce the number of parameters controlling selection of optimal strategy to just a few dimensionless quantities characterising both physical and economic processes. We show that the production life of oil fields should not be fixed in optimisation studies, especially at low oil prices. A significantly larger net present value can be achieved by varying the reservoir lifetime in addition to the injection rates and volumes and other well controls. Herewith, the optimal strategy can differ from that in the case of a presumed production time. We conclude that waterflooding is the optimal recovery method if the injection rate is low, whereas gas (WAG) flooding applied as a primary method and followed by waterflooding is most optimal for large injection rates. Gas flooding applied as the tertiary recovery method is most optimal for an intermediate range of the rates. In the latter case, gas injection should begin much earlier than water breaks through to producing wells. Finally, we investigate how oil price influences the range of parameters suitable for gas injection.

The authors acknowledge funding from the Russian Foundation for Basic Research under grant # 20-31-80009.