bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of Suitability of Global Reanalysis for Hydrological Applications by Coupling Performance Statistics and Sensitivity Analysis in Kenya
Authors: Wanzala Maureen , Ficchi Andrea , Cloke Hannah , Stephens Elizabeth
Published: March 2021

Information about monitoring of hydrological extremes, agricultural yields and irrigation may be informed by early warning, forecasts and flood management advice through appropriate modelling skills. However hydrological modelling is a challenging task in poorly gauged catchments, especially in developing countries like Kenya. Open access global precipitation and temperature reanalysis datasets with different spatial and temporal resolutions provide alternative sources in data-scarce regions but, individual reanalysis precipitation datasets have significant uncertainties. Inspired by data scarcity issues, significant spatial and temporal gaps in gauge observations, and poor performance of individual reanalysis in hydrological models, this study assess the performance of five new-era reanalysis datasets (ERA5, ERA-Interim, Modern Era Retrospective Analysis for Research and Applications version 2 (MERRA2), Climate Forecast System Reanalysis (CFSR) and Japanese 55-year Reanalysis Project(JRA55)) to simulate daily streamflow using the GR4J model across the 20 catchments in Kenya. Deviating from the modelling normality of calculating the model performance statistics for the calibration and validation periods to investigate whether a model serves as satisfactory representations of the natural hydrologic phenomenon, we couple with sensitivity analysis (SA) to unveil model structural uncertainty and suitability when forced with the different reanalysis products. In this study we use the reanalysis precipitation, maximum (T max) and minimum (T min) temperatures against the observations from the Climate Hazards group Precipitation (CHIRPS) for 1981–2016 to calculate performance statistics, streamflow simulations and sensitivity analysis. In addition, we develop model suitability index (MSI) by coupling the performance statistics with the sensitivity results across the different reanalysis products for our study catchments. Our results show that ERA5 performs better than other reanalysis products in terms of performance statistics and streamflow simulations at catchments scale. MSI results were suitable with ERA5 and lower in JRA55 across most of the Kenyan catchments, with 0.8 and 0.4 MSI respectively. MSI developed in this study is a quantitative measure that can be used for the comparison of reanalysis products for different catchments, thus useful for application to modelling to assess the suitability of both the modelling tools and catchment response to alternative forcings for early warning and inform early action.
Effect of clay content on Acoustic Doppler Velocimeter backscatter for suspended sediment concentration measurements
Authors: Aras Akın , Sahin Cihan
Published: March 2021

The capability of ADVs (Acoustic Doppler Velocimeters) to estimate suspended sediment concentration (SSC) has been widely investigated using commercial glass microspheres of the same size or well-sorted fractions in experimental studies. In the natural environment, sediment samples may be composed of different types of sediments having various types of grain size distribution.

This study aims to analyze experimentally the effect of clay ratio in sediment content on acoustic response. Modification of scattering and attenuation characteristics for different clay ratios is evaluated theoretically. In laboratory experiments, four different sediment mixtures constituting non-cohesive sand and cohesive clay materials were prepared with clay ratios of 0, 5, 10 and 15% by dry mass. A-10 MHz acoustic Doppler velocity profiler (ADVP, The Nortek Vectrino Profiler) was used in controlled laboratory environments under a wide range of concentration conditions up to 10 g/L. Acoustic backscatter measurements were made by immersing the ADVP in a well-mixed circulation tank filled with mixtures with known concentration and sediment composition. The backscattered signals were recorded at 100 Hz, from which 1.5-min ensemble averages were obtained. For each sediment mixture, calibration curves representing the relationship between SSC and acoustic backscatter were obtained based on the sonar equation. Acoustic estimates of suspended sediment parameters obtained for mixtures with different clay contents are compared to identify the effect of increasing clay content on the acoustic signal.

The experimental results showed that the slope of the calibration curve decreases with increasing validity range as the clay ratio of the mixture increases. Under the fixed SSC condition, the backscatter strength is greater for the mixture with a lower clay ratio. The theoretical analysis indicated that changing clay content modifies the scattering and attenuation properties compared to the mono-size suspension with the same mean size. Introducing clay material in a mixture affects the scattering properties more significantly than the attenuation properties. Therefore, information on the form of the sediment distribution and the sorting of sediments in suspension is crucial for acoustic estimates of suspended sediment parameters.

Acknowledgments

This research is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) with project number 218M428.
Assessment of geodetic products from Multi-GNSS analyses at the Onsala site
Authors: Diamantidis Periklis-Konstantinos , Kłopotek Grzegorz , Haas Rüdiger , Johansson Jan
Published: March 2021

The dawn of Beidou and Galileo as operational Global Navigation Satellite Systems (GNSS) alongside Global Positioning System (GPS) and GLONASS as well as new features that are now present in all GNSS, such as a triple-frequency setup, create new possibilities concerning improved estimation and assessment of various geodetic products. In particular, the multi-GNSS analysis gives an access to a better sky coverage allowing for improved estimation of zenith wet delays (ZWD) and tropospheric gradients (GRD), and can be used to determine integer phase ambiguities. The Multi-GNSS Experiment (MGEX), as realised by the International GNSS Service (IGS), provides orbit, clock and observation data for all operational GNSS. To take advantage of the new capabilities that these constellations bring, space-geodetic software packages have been retrofitted with Multi-GNSS-compliant modules. Based on this, two software packages, namely GipsyX and c5++, are utilised by way of the static Precise Point Positioning (PPP) approach using six months of data, and an assessment of the derived geodetic products is carried out for several GNSS receivers located at the Onsala core site. More specifically, we perform both single-constellation and multi-GNSS data analysis using Kalman filter and least-squares methods and assess the quality of the derived station positions, ZWD and GRD. A combined solution using all GNSS constellations is carried out and the improvement with respect to station position repeatabilities is assessed for each station. Results from the two software packages are compared with respect to each other and the discrepancies are discussed. Inter-system biases, which homogenise the different time scale that each GNSS operates in, and are necessary for the multi-GNSS combination, are estimated and presented. Finally, the applied inter-system weighting and its impact on the derived geodetic products are discussed.
Development of earth observation data cubes for monitoring land degradation processes in South Africa
Authors: Otte Insa , Mashiyi Nosiseko , Kluter Pawel , Hill Steven , Hirner Andreas , Eberle Jonas , Urban Marcel , Mlisa Andiswa , Kganyago Mahlatse , Schwinger Maximilian , Gessner Ursula , Schmullius Christiane , Baade Jussi
Published: March 2021

Global biodiversity and ecosystem services are under high pressure of human impact. Although avoiding, reducing and reversing the impacts of human activities on ecosystems should be an urgent priority, the loss of biodiversity continues. One of the main drivers of biodiversity loss is land use change and land degradation. In South Africa land degradation has a long history and is of great concern. The SPACES II project SALDi (South African Land Degradation Monitor) aims for developing new, adaptive and sustainable tools for assessing land degradation by addressing the dynamics and functioning of multi-use landscapes with respect to land use change and ecosystem services. SPACES II is a German-South African “Science Partnerships for the Adaptation to Complex Earth System Processes”. Within SALDi ready-to-use earth observation (EO) data cubes are developed. EO data cubes are useful and effective tools using earth observations to deliver decision-ready products. By accessing, storing and processing of remote sensing products and time-series in data cubes, the efficient monitoring of land degradation can therefore be enabled. The SALDi data cubes from optical and radar satellite data include all necessary pre-processing steps and are generated to monitor vegetation dynamics of five years for six focus areas. Intra- and interannual variability in both, a high spatial and temporal resolution will be accounted to monitor land degradation. Therefore, spatial high resolution earth observation data from 2016 to 2021 from Sentinel-1 (C-Band radar) and Sentinel-2 (multispectral) will be integrated in the SALDi data cube for six research areas of 100 x 100 km. Additionally, a number of vegetation indices will be implemented to account for explicit land degradation and vegetation monitoring. Spatially explicit query tools will enable users of the system to focus on specific areas, like hydrological catchments or blocks of fields.
Characterizing plastic debris accumulating in the North Pacific Garbage Patch
Authors: Egger Matthias , Strietman Wouter Jan , Thoden van Velzen Ulphard , Smeding-Zuurendonk Ingeborg , Lebreton Laurent
Published: March 2021

Citizen science programs and tracking applications have been used in the collection of data on plastic debris in marine environments to determine its composition and sources. These programs, however, are mostly focused on debris collected from beach cleanups and coastal environments. Large plastic debris currently afloat at sea, which is a significant contributor to marine plastic pollution and a major source of beach litter, is less well-characterized.

Transported by currents, wind and waves, positively buoyant plastic objects eventually accumulate at the sea surface of subtropical oceanic gyres, forming the so-called ocean garbage patches. It is important to know where the debris that persists in the offshore gyres is entering the ocean, where it is produced and what practices (commercial, cultural, industrial) are contributing to the accumulation of these debris into the ocean garbage patches. This information coupled to data on how long and well the plastics persevere at the sea surface is necessary for creating effective and efficient mitigation strategies.

Here we provide a comprehensive assessment of plastic debris afloat in the North Pacific Garbage Patch (NPGP). Offshore debris collected by The Ocean Cleanup’s System 001b from the NPGP in 2019 was analyzed using the Litter-ID method, which applies an adapted and expended version of the OSPAR guideline for monitoring beach litter. Our results reveal new insights into the composition, origin and age of plastic debris accumulating at the ocean surface in the NPGP. The standardized methodology applied here further enables a first thorough comparison of plastic debris accumulating in offshore waters and coastal environments.
Aeolus aerosol and cloud product
Authors: Flament Thomas , Dabas Alain , Trapon Dimitri , Lacour Adrien , Ehlers Frithjof , Baars Holger , Huber Dorit
Published: March 2021

The European Satellite has the first space-borne high-spectral resolution UV lidar onboard called ALADIN. Two detection channels, a broadband (Rayleigh channel) and a narrowband (Mie channel), are implemented. Carefully calibrated, this combination offers the possibility to derive independent estimates of the backscatter and extinction coefficients of clouds andaerosols, leading to a direct estimation of the lidar ratio, useful for aerosol classification.

The presentation will show how the official processor of the mission works for the retrieval of optical properties of cloud and aerosol particles, with a focus on the currently available products (called L2A). The potential of the L2A processor will be illustrated by results obtained on data acquired since Aeolus launch and by comparisons to ground based lidars in the frame of Cal/Val activities.

The L2A product will become publicly available during Spring 2021. Thus, this is also an opportunity to introduce a few practical aspects about its usage.
Nocturnal surface fluxes of N2O and CH4 determined from atmospheric measurements at the Cabauw tall tower
Authors: Tong Xin , Bosveld Fred , Hensen Arjan , Scheeren Bert , Frumau Arnoud , Chen Huilin
Published: March 2021

The agricultural emissions are the dominant sources of N2O and CH4 in the Netherlands. In this study, we have estimated nocturnal surface fluxes of both N2O and CH4 using atmospheric measurements at the Cabauw tall tower (4.927◦ E, 51.971◦ N, - 0.7 m a.s.l.). The nocturnal N2O and CH4 surface fluxes were derived using two different methods, the vertical gradient method (VGM), i.e. the sum of the storage flux and the turbulent flux, and the radon-tracer method (RTM), for the period of March 2017-December 2018 and 2016-2018, respectively. For N2O, we show that a few events occurring between May 30 and June 4 in 2018 dominated the monthly means. Using the VGM, we have estimated the annual mean nocturnal surface flux to be 0.59 ± 0.38 g/m2/yr (1 σ, the same as below) and 0.53 ± 0.19 g/m2/yr with and without events, respectively. The fluxes are high in the summer and low in the winter, with a seasonal amplitude of around 1.0 g/m2/yr and 0.5 g/m2/yr, with and without events, respectively, which is likely caused by the seasonality of agricultural activities. For CH4, the annual mean nocturnal surface flux is 12.1 ± 3.3 g/m2/yr and the amplitude is around 9.9 g/m2/yr. Using the RTM, the mean fluxes of the whole period for N2O and CH4 are estimated to be 1.18 ± 2.25 (1.08 ± 1.29, without the events) g/m2/yr and 26.9 ± 24.8 g/m2/yr, respectively; in contrast to the VGM, no apparent seasonal pattern has been found. However, there is a good linear correlation between the estimated N2O fluxes from the two methods and the monthly means show a similar pattern when the same nights are considered; the R-squared value is around 0.9 with events and 0.6 without events, and the slope varies from 1.9 to 0.8 when different estimates of radon fluxes are used. Furthermore, we found that large N2O fluxes are related to the amount of rainfall occurring days before, with the correlation coefficient of around 0.6 (p value<0.01). For CH4, there is no correlation between the estimated CH4 fluxes from the two methods. Our findings demonstrate that nocturnal N2O and CH4 fluxes in the Cabauw area are highly variable and vary over different seasons, and that both VGM and RTM are useful to quantify regional N2O and CH4 fluxes.
Statistical calculation of thrust curve of a wind turbine based on available power curve and general specifications data
Authors: Atlaskin Evgeny , Suomi Irene , Lindfors Anders
Published: March 2021

Power curves for a substantial number of wind turbine generators (WTG) became available in a number of public sources during the recent years. They can be used to estimate the power production of a wind farm fleet with uncertainty determined by the accuracy and consistency of the power curve data. However, in order to estimate power losses inside a wind farm due to wind speed reduction caused by the wake effect, information on the thrust force, or widely used thrust coefficient (Ct), is required. Unlike power curves, Ct curves for the whole range of operating wind speeds of a WTG are still scarcely available in open sources. Typically, power and Ct curves are requested from a WTG manufacturer or wind farm owner under a non-disclosure agreement. However, in a research study or in calculations over a multitude of wind farms with a variety of wind turbine models, collecting this information from owners may be hardly possible. This study represents a simple method to define Ct curve statistically using power curve and general specifications of WTGs available in open sources. Preliminary results demonstrate reasonable correspondence between simulated and given data. The estimations are done in the context of aggregated wind power calculations based on reanalysis or forecast data, so that the uncertainty of wake wind speed caused by the uncertainty of predicted Ct is comparable, or do not exceed, the uncertainty of given wind speed. Although the method may not provide accurate fits at low wind speeds, it represents an essential alternative to using physical Computational Fluid Dynamics (CFD) models that are both more demanding to computer resources and require detailed information on the geometry of the rotor blades and physical properties of the rotor, which are even more unavailable in open sources than power curves.
On self-similarity of waves in tropical cyclones
Authors: Yurovskaya Maria , Kudryavtrsev Vladimir , Chapron Bertrand
Published: March 2021

Wave fields generated by tropical cyclones (TC) are of strong interest for marine engineering, navigation safety, determination of coastal sea levels and coastal erosion. Considerable efforts have been made to improve knowledge about the surface waves in TC, both from measurements and numerical experiments. Full sophisticated spectral wave models certainly have the capability to provide detailed wave information, but they require large computer power, precise well-resolved surface winds and/or needs to consider large ensembles of solutions. In this context, more simplified but robust solutions are demanded.

This work is based on 2D-parametric model of waves evolution forced by wind field varying in space and time, non-linear wave interactions and wave breaking dissipation [submitted to J. Geoph. Res., see also preprint DOI: https://doi.org/10.1002/essoar.10504620.1]. Numerical solutions of model provide efficient visualization on how waves develop under TC and leave it as swell. Superposition of wave-rays exhibits coherent spatial patterns of wave parameters depending on TC characteristics, - maximal wind speed (um), radius (Rm), and translation velocity (V).

In this presentation we demonstrate how solutions of 2D-parametric model can be described analytically through self-similar functionsusing proper scaling involving the main TC parameters: um, Rm, and V. These self-similar solutions can be treated as TC-wave Geophysical Model Function (TC-wave GMF), to help analytically derive azimuthal-radial distributions of the primary wave system parameters (SWH, wavelength, direction) under TC characterized by arbitrary sets of um, Rm and V conditions. Self-similar solutions describe the main properties of wave field under TC, in particular: right-to-left half asymmetry of wave field under TC; strong dependence of wave energy and wavelength on V, um and Rm caused by group velocity resonance; division of TCs on “slow” and “fast” when TC-induced waves outrun TC and form wake of swell trailing TC.

Comparisons between self-similar solutions and measurements of TC-generated waves reported in the literature, demonstrate excellent agreement to warrant their use for research and practical applications.

The core support for this work was provided by the Russian Science Foundation through the Project №21-47-00038 at RSHU. The support of the Ministry of Science and Education of the Russian Federation under State Assignment No. 0555-2021-0004 at MHI RAS, and State Assignment No. 0736-2020-0005 at RSHU are gratefully acknowledged.
Episodic earthquake mechanisms and intervening seismicity during the 2018 summit collapse at Kilauea caldera 
Authors: Alvizuri Celso , Matoza Robin , Okubo Paul
Published: March 2021

The 2018 rift zone eruption of Kilauea volcano was accompanied by a remarkable and episodic collapse of its summit. Between May-August the eruption and collapse sequence included over 70,000 earthquakes (M≥0) and 54 major earthquakes (M≥5). We analyzed the seismicity in the Kilauea summit region and estimated seismic full moment tensors with their uncertainties for the 54 M≥5 events. These events occurred at almost daily intervals and were accompanied by intense seismicity which was concentrated between 0-3 km depths beneath the Halema‘uma‘u pit crater. The hypocenters reveal partial elliptical patterns (map view) that migrated downward by ∼200 m. The moment tensors reveal remarkably consistent mechanisms, with negative isotropic source types and localized uncertainties, and vertical P-axis orientations. From the moment tensors we derived Poisson’s ratios which are variable (ν = 0.1 − 0.3) for the first half of the collapse events and converged to ν ∼ 0.28 from June 26 onward.
Seasonal variations in the Andaman Sea’s internal tides
Authors: Yadidya Badarvada , Rao Ambarukhana Devendra , Latha Ganesan
Published: March 2021

The presence of large-amplitude internal waves in the Andaman Sea have been observed since 1965 but their temporal variability is yet to be understood. Therefore, in-situ observations from March 2017 to February 2018 are used to study the temporal variability and vertical structure of internal tides. The kinetic energy of semidiurnal internal tides dominates that of diurnal internal tides by a factor of 4. The internal tides at semidiurnal frequency are relatively stronger in summer and autumn, whereas at the diurnal frequency they are stronger during summer and winter. Density stratification seems to be playing a more significant role in controlling the temporal variability of internal tides when compared with the astronomical tides. Moreover, the stratification near the surface is controlled by salinity variations, whereas the temperature variations control the sub-surface stratification. This leads to the occurrence of a strong double pycnocline during autumn and winter. The first-mode semidiurnal internal tides are more significant in all the seasons except during autumn. The semidiurnal internal tides are more coherent than the diurnal internal tides. Strong background currents due to mesoscale eddies are observed during periods of high incoherent internal tides. Therefore, the variations in background stratification and currents due to the presence of mesoscale eddies could be causing incoherent internal tides in this region.
IWV observations from a network of ground-based GNSS receivers during EUREC4A
Authors: Bock Olivier , Bosser Pierre , Flamant Cyrille , Doerflinger Erik , Jansen Friedhelm , Fages Romain , Bony Sandrine , Schnitt Sabrina
Published: March 2021

IWV data were retrieved from a network of nearly fifty Global Navigation Satellite System (GNSS) stations distributed over the Caribbean arc for the period 1 January-29 February 2020 encompassing the EUREC4A field campaign. Two of the stations had been installed at the Barbados Cloud Observatory (BCO) during fall 2019 in the framework of the project and are still running. All other stations are permanent stations operated routinely from various geodetic and geophysical organisations in the region. High spatial and temporal Integrated Water Vapour (IWV) observations will be used to investigate the atmospheric environment during the life cycle of convection and its feedback on the large-scale circulation and energy budget.

This paper describes the ground-based GNSS data processing details and assesses the quality of the GNSS IWV retrievals as well as the IWV estimates from radiosoundings, microwave radiometer measurements and ERA5 reanalysis.

The GNSS results from five different processing streams run by IGN and ENSTA-B/IPGP are first intercompared. Four of the streams were run operationally, among one was in near-real time, and one was run after the campaign in a reprocessing mode. The uncertainties associated with each of the data sets, including the zenith tropospheric delay to IWV conversion methods and auxiliary data, are quantified and discussed. The IWV estimates from the reprocessed data set are compared to the Vaisala RS41 radiosonde measurements operated from the BCO and to the measurements from the operational radiosonde station at Grantley Adams international airport (GAIA). A significant dry bias is found in the GAIA humidity observations with respect to the BCO sondes (-2.9 kg/m2) and the GNSS results (-1.2 kg/m2). A systematic bias between the BCO sondes and GNSS is also observed (1.7 kg/m2) where the Vaisala RS41 measurements are moister than the GNSS retrievals. The HATPRO IWV estimates agree with the BCO soundings after an instrumental update on 27 January, while they exhibit a dry bias compared to GNSS and BCO sondes before that date. ERA5 IWV estimates are overall close to the GAIA observations, probably due to the assimilation of these observations in the reanalysis. However, during several events where strong peaks in IWV occurred, ERA5 is shown to significantly underestimate the IWV peaks. Two successive peaks are observed on 22 January and 23/24 January which were associated with heavy rain and deep moist layers extending from the surface up to altitudes of 3.5 and 5 km, respectively. ERA5 significantly underestimates the moisture content in the upper part of these layers. The origins of the various moisture biases are currently being investigated.
What it takes to increase Europe’s resilience to drought – Insights from a pan European survey on recent drought perception, impacts and management
Authors: Blauhut Veit , Stoelzle Michael , Ahopelto Lauri , Brunner Manuela , Wendt Doris , Teutschbein Claudia
Published: March 2021

In recent years, drought impacts have been more severe and frequent than past impacts throughout Europe. Due to the heterogeneity of Europe’s hydro- climatological situation as well as the multiple nations on the continent, drought events and their impacts vary with respect to location, sector, extent, duration and scale. In order to understand recent effects of drought and their possible drivers, national representatives distributed a uniform questionnaire to water management stakeholders of 28 contributing countries. Here, we focus on obtaining information on stakeholders’ drought perception,impacts, and current management strategies on a national and sub-national scale. With the survey, we analyse how strong the relationship between perceptions and actual hazard information is. Actual drought hazard information from the European Drought Observatory for the years 2018 and 2019 is compared with the questionnaire’s results. The results of the study highlight the diversity among national drought perceptions and the value of  already existing drought management strategies. An absence of coordinated drought management is mostly attributed to a lack of resources and macro- governmental guidance. Supported by the national perspectives, possible macro-governmental pathways to increase national and sub-national awareness and resilience are discussed. The results support the need for national  drought policies, which could be pushed forward with international drought management directives.
Building Performance Simulations coupled to Borehole Heat Exchanger Simulations: a tool for realistic monitoring and forecast
Authors: Niederau Jan , Fink Johanna , Lauster Moritz
Published: March 2021

The actual heat demand of a building depends on various building-specific parameters, such as building age, insulation type, housing volume, but also external parameters, e.g. outdoor temperature. Being able to dynamically model the thermal power demand of a specific building can increase the robustness of coupled borehole heat exchanger simulations (BHE-simulations), as the transient heat demand models of a building / consumer can be used to simulate the thermal response of the subsurface to the prescribed consumer demand.

We present results of coupling results of Building Performance Simulation (BPS) with simulations of Borehole Heat Exchangers. BPS are carried out using TEASER (Tool for Energy Analysis and Simulation for Efficient Retrofit) which models the thermal power demand of a building based on parameters, such as year of construction, net-lease area, and outdoor-temperature.

Using annual temperature curves, we model the thermal power demand of buildings from the 1950s, once in original state and in retrofitted state. The thermal response of a connected BHE-field is simulated using SHEMAT-Suite, an open-source simulator for heat- and mass-transfer in porous media. In our BHE simulations, thermal plumes develop as a result of heat-extraction and regional groundwater flow.

To improve the forecast of, e.g. the magnitude of these plumes, realistic knowledge of the heat demand is important, which can be achieved by the presented coupling of BPS- and BHE-modelling.

 
Propagation characteristics of hot flow anomalies
Authors: Zhu Xiaoqiong , Wang Mengmeng , Shi Quanqi , Zhang Hui , Tian Anmin , Yao Shutao , Guo Ruilong , Liu Ji , Bai Shichen , Zhang Shuai , Shang Wensai , Niu Zhe
Published: March 2021

Hot flow anomalies (HFAs), characterized by heated plasma and flow deflection, are frequently observed near Earth’s and other planetary bow shocks. There are two kinds of HFAs, classic HFAs formed by the interaction of tangential discontinuities (TD) and the bow shock, and spontaneous HFAs (SHFAs) which are not associated with discontinuties. A statistical study of the propagation characteristics of HFA edges has been performed base on 19 classic HFAs and 23 SHFAs with one-dimensional edges observed by Cluster from 2001 to 2010. The propagation velocity and normal direction of each edge are calculated using the timing method, the minimum directional difference (MDD) method, and the spatial-temporal difference (STD) method. The angle between the leading edge normal and the corresponding TD normal is less than 30 degrees for 93% of the classic HFAs. The angle between the edge normal and background magnetic field is near 90 degrees for 74% of the SHFAs. Observations indicate that the leading edge of the classic HFAs propagates along the same direction as the driving TD and the SHFAs propagate perpendicular to the background magnetic field. Furthermore, we find that all 42 HFAs propagate toward the Earth in the spacecraft frame as expected. However, in the solar wind frame HFAs have different propagation directions (i.e., toward the Earth, the Sun or be stationary in the solar wind frame).
Multifluid modelling of cometary coma for diverse range of parent volatile compositions
Authors: Ahmed Sana , Acharyya Kinsuk
Published: March 2021

Comets show a general diversity in their parent volatile composition, but in most cases H2O is observed to be the dominant volatile in terms of abundance. This is followed by CO and CO2, and trace amounts of other species such as CH4, CH3OH, O2, and NH3 are also present. However, the observed ratio of n_x/H2O varies considerably from one comet to another (n_x represents any parent species other than water).

We aim to study how the chemistry and dynamics of the cometary coma changes for varying abundances of the major parent volatiles. We have constructed a fluid model, using the principles of conservation of mass, momentum and energy, for our study. Parent volatiles sublimating from the nucleus undergo photolytic reactions due to the solar UV radiation field, resulting in the formation of secondary neutral and ionic species and photoelectrons. Active chemistry occurs in the coma, and some of the chemical reactions taking place are ion-neutral rearrangement, charge exchange, dissociative recombination, electron impact dissociation and radiative de-excitation. The energy that is released due to these chemical reactions is non-uniformly distributed amongst all the species, resulting in different temperatures. Hence,  for a complete description of the coma, we have used a multifluid model whereby the neutrals, ions and electrons are considered as three separate fluids. Apart from chemical reactions, we have also considered the exchange of energy between the three fluids due to elastic and inelastic collisions.

We consider different initial compositions of the comet, and then use our model to generate the temperature and velocity profiles of the coma, for varying cometocentric distances. We also obtain the number density profiles of the different ionic and neutral species that are created in the coma. We see that changes in the initial parent volatile abundance will modify the temperature profile, and there are significant changes in the ionic abundances. Hence, the parent volatile composition of the comet drives the physico-chemical attributes of the coma.
3D structure of detachment faulting and related tectono-sedimentary processes in the SE South China Sea
Authors: Legeay Etienne , Mohn Geoffroy , Ringenbach Jean-Claude , Vetel William
Published: March 2021

Before Break-Up, the opening of the South China Sea Passive Margin (SCS) was characterized by a wide rift mode during Cenozoic rifting. Such wide extensional margin (>600 km wide) is controlled by a set of hyper-extended sub-basins separated by basement highs.

These basins infill recorded a polyphased extensional deformation hence resulting in complex 3D sedimentary evolution. Based on a recent industrial 3D seismic reflection survey along the Sabah area (southern margin of the SCS), this contribution aims to investigate the detailed 3D geometries of extensional structures as well as their control on the overlying successive sedimentary sequences and relation to crustal deformation.

We mapped and analyzed several crustal-scale rolling hinge structures controlled by a series of low-angle normal faults. Deeper crustal levels are likely exhumed along the core of these rolling hinge structures, separated by extensional allochthones blocs of upper continental crust. Our structural analysis enables us to identify three main extensional phases corresponding to distinct sedimentary packages: (1) a synrift sequence 1 controlled by small offset normal faults formed during incipient rifting; (2) an intermediate synrift sequence 2 recording the development of extensional detachment faults. (3) a thick syn-rift sequence 3 recording a continuation of extension along the detachment faults resulting in the dismembering of the syn-
rift sequence 2. Intra-basement seismic reflectors dipping towards the north-west are observed, onto which extensional structures often seem to root. Some of these reflectors are interpreted as interleaved thrust sheets from a dismantled accretionary wedge of the former Mesozoic active margin (Yenshanian magmatic Arc).

Our results provide new key observations on the 3D mechanisms of detachment faulting and its control on sedimentary evolution as well as coeval crustal deformation. 3D approach throw some light on the detailed geometries of a metamorphic core-complex in relation with crustal boudinage, shear zones and lower/middle crust exhumation below the syn- rift sediments. These geometries can be compared to those described in the Basin and Range province or the Aegean Sea. Consequently, our results have implications for our understanding of rift and breakup mechanisms of marginal basins as a whole.
Additional carbon stabilization in temperate subsoils impeded by biogeochemical and hydraulic constraints
Authors: Guggenberger Georg , Liebmann Patrick , Mikutta Robert , Kalbitz Karsten , Wordell-Dietrich Patrick , Leinemann Timo , Preusser Sebastian , Bachmann Jörg , Don Axel , Kandeler Ellen , Marschner Bernd , Schaarschmidt Frank
Published: March 2021

Formation of mineral-associated organic matter (MAOM) is a decisive process in the stabilization of OM against rapid microbial decomposition and thus in the soils’ role as global carbon (C) sink. Sorption experiments of dissolved OM (DOM) repeatedly showed that particularly mineral subsoils have a large sorption capacity to retain more C. However, there is also an increasing body of literature, revealing an increasing output of dissolved organic C (DOC) from soils. Here, we investigated into this paradox in forest soil under beech by a combination of a field labelling experiment with 13C-enriched litter with a unique DO13C and 13CO2 monitoring, an in-situ C exchange experiment with 13C-coated minerals, and batch sorption experiments.

Within two years of 13C monitoring, only 0.5% of litter-derived DO13C entered the subsoil, where it was only short-term stabilized by formation of MAOM but prone to fast microbial mineralization. The 13C monitoring, sorption/desorption experiments in the laboratory, and also the in-situ C exchange on buried soil minerals revealed that there is a frequent exchange of DOM with native OM and a preferential desorption of recently retained OM. Hence, there appeared to be a steady-state equilibrium between C input and output, facilitated by exchange and microbial mineralization of an adopted microbial community. The remobilized OM was also richer in less sorptive carbohydrates. Along with transport of most of DOM along preferential paths, this further increased the discrepancy between laboratory-measured sorption capacities of subsoil and the actual C loading of minerals. Finally, the 13C labeling experiments revealed that input of fresh litter-derived OM into subsoil may even mobilize old-soil derived OM. Hence, in the field different biogeochemical constraints are acting that prevent that the laboratory-based C sink can be reached in the field.  We conclude, that forest subsoils can hardly be considered as additional C sink, even at management options that increase DOC input to subsoil.
Statistical Differences of Magnetic Field Kinks Observed by PSP and WIND
Authors: Hou Chuanpeng , Zhu Xingyu , Zhuo Rui , He Jiansen
Published: March 2021

Parker Solar Probe’s (PSP) observations near the sun show the extensive presence of magnetic field kinks (switchback for large kinks) in the slow solar wind. These kinks are usually accompanied by the enhancement of radial solar wind velocity and ion temperature, increasing or decreasing of number density. The magnetic field kinks have also been observed by WIND and Ulysses to exist near and beyond 1 AU, respectively. In this study, we statistically analyze the property difference of magnetic field kinks observed by PSP and WIND. We obtain the following four points of results. (1) Inside the PSP-kinks, the radial velocity and protons’ temperature increase while density shows enhancement or descent. However, inside the WIND-kinks, besides the slight enhancement of radial velocity, the density and temperature show no obvious change compared with the outside plasma. (2) By employing the Walen-test of kinks, we find that, R components of some PSP-kinks but not all satisfy the rotational discontinuity (RD) features, while the three components of most WIND-kinks well match the RD features. (3) The correlation between magnetic field and velocity inside the PSP-kinks and WIND-kinks does not show significant differences. (4) Both the PSP-kinks and WIND-kinks can be divided into two groups based on the histograms of θBn, where B is the background magnetic field, and n is the normal direction of kink. The first group (group-I) has θBn concentrating around 20° for PSP-kinks and 30° for WIND-kinks, indicating that the satellites were crossing the same kinked interplanetary magnetic field (IMF) from the upstream to the downstream. The second group (group-II) has θBn concentrating around 90° for PSP-kinks and WIND-kinks, suggesting that the satellites were crossing an interface between the unkinked and kinked IMF regions. Our findings help better understanding the nature of kinks and provide the observational basis for testifying models about radial propagation and evolution of magnetic field kinks.
Early Eocene simulations with three different palaeogeographic conditions
Authors: Zhang Zijian , Zhang Zhongshi , Guo Zhengtang
Published: March 2021

The early Eocene is a warm period with a very high atmosphere CO2 level in the Cenozoic. It  provides a good reference for our future climate under the Representative Concentration Pathway 8.5 scenario. Therefore, the early Eocene climate has received many attentions in  modeling studies, for example, the Deep-Time Model Intercomparison Project (DeepMIP). However, the early Eocene palaeogeographic conditions show remarkable contrasts to the present conditions. Meanwhile, there are a few different reconstructions for the early Eocene palaeogeography, which may cause further model spreads in simulating the early Eocene warm climate. Here, we present a series of experiments carried out with the NorESM1-F, under the framework of DeepMIP. In these experiments, we consider three different palaeogeographic reconstructions for the early Eocene. We also compare our simulations with climate proxy records, to validate which palaeogeographic reconstructions can reproduce simulations that agree better with the climate proxy records.
Pajala Fireball
Authors: Vierinen Juha , Aslaksen Torsten , Chau Jorge , Gritsevich Maria , Gustavsson Björn , Kastinen Daniel , Kero Johan , Kozlovsky Alexandre , McKay Derek , Midtskogen Steinar , Ulich Thomas , Vegum Ketil
Published: March 2021

Meteoroids entering the Earth's atmosphere are associated with a number of phenomena including ablation, ambipolar diffusion, plasma transport, chemical reactions, shock waves, and plasma turbulence. A bright daylight fireball observed on 2020-12-04 13:30 UTC with two meteor cameras located in Skibotn and Sørreisa allowed the precise entry trajectory of the fireball to be determined. The path of the entering object is approximately between Angeli Finland and Pajala Sweden. Based on the brightness and entry trajectory, it is possible to estimate the approximate mass of the object, and associate it with a meteor shower (Northern Taurids). The effects of the fireball on the atmosphere were detected with a number of radar and radio instruments within the region, including ionosondes, meteor radars, an all-sky VHF imaging system, and an infrasound sensor. These observations allow a detailed study of the atmospheric interaction of a large meteoric body with the Earth's atmosphere to be made. In this talk, we will describe the observations of this fireball and discuss preliminary findings.
SPH model for the simulation of lava-buildings interactions
Authors: Zago Vito , Bilotta Giuseppe , Cappello Annalisa , Dalrymple Robert , Fortuna Luigi , Ganci Gaetana , Herault Alexis , Del Negro Ciro
Published: March 2021

Numerical simulation is a fundamental aspect of modern volcanology, providing tools for the forecasting of lava flows behavior, so as to assist in the design of mitigation actions for volcanic risk. In addition to the prediction of the emplacement topology, numerical simulation can be useful to study the possible outcomes of the interaction between a lava flow and a building. This kind of information can help to estimate the vulnerability of buildings so as to produce more accurate risk evaluations. Smoothed Particle Hydrodynamics (SPH) is a particle-based numerical method, particularly suited for the simulation of fluids with a high level of complexity, that can intrinsically deal with all of the physical properties of lava. GPUSPH is a simulation engine based on the SPH method that has been developed in order to take into account the challenging aspects of lava simulations and has been successfully applied to the simulation of lava-related benchmark tests. Here we use the SPH method, coupled within the framework of GPUSPH with a rigid body mechanics solver provided by the Project Chrono engine, for the realistic study of lava-buildings interaction. The resulting coupled model is able to simulate masonry with a brick-level accurate description, providing insights on any damages happening to the structure. We will show the simulation of a lava flow interacting with an elementary masonry piece, where a total collapse of the structure is induced by the action of the lava.
Linkage between Arctic Sea Ice Area and Atmospheric Blocking Probability over Europe using Logistic Regression Models
Authors: Richling Andy , Ulbrich Uwe , Rust Henning , Riebold Johannes , Handorf Dörthe
Published: March 2021

Over the last decades the Arctic climate change has been observed with a much faster warming of the Arctic compared to the global average (Arctic amplification) and related sea-ice retreat. These changes in sea ice can affect the large-scale atmospheric circulation over the mid-latitudes, in particular atmospheric blocking, and thus the frequency and severity of extreme events. As a step towards a better understanding of changes in weather and climate extremes over Central Europe associated with Arctic climate change, we first analyze the linkage between recent Arctic sea ice loss and blocking variability using logistic regression models. ERA5 reanalysis data are used on a monthly and seasonal time scale, and specific regional sea ice variabilities are explored. First results indicate an increased occurrence-probability in terms of blocking frequency over Greenland in summer as well as over Scandinavia/Ural in winter during low sea ice conditions. 
Probabilistic Machine Learning for improved Decision-making with 3-D Geological Models
Authors: Wellmann Florian , de la Varga Miguel , Güdük Nilgün , von Harten Jan , Stamm Fabian , Liang Zhouji , Moulaeifard s.Mohammad
Published: March 2021

Geological models, as 3-D representations of subsurface structures and property distributions, are used in many economic, scientific, and societal decision processes. These models are built on prior assumptions and imperfect information, and they often result from an integration of geological and geophysical data types with varying quality. These aspects result in uncertainties about the predicted subsurface structures and property distributions, which will affect the subsequent decision process.

We discuss approaches to evaluate uncertainties in geological models and to integrate geological and geophysical information in combined workflows. A first step is the consideration of uncertainties in prior model parameters on the basis of uncertainty propagation (forward uncertainty quantification). When applied to structural geological models with discrete classes, these methods result in a class probability for each point in space, often represented in tessellated grid cells. These results can then be visualized or forwarded to process simulations. Another option is to add risk functions for subsequent decision analyses. In recent work, these geological uncertainty fields have also been used as an input to subsequent geophysical inversions.

A logical extension to these existing approaches is the integration of geological forward operators into inverse frameworks, to enable a full flow of inference for a wider range of relevant parameters. We investigate here specifically the use of probabilistic machine learning tools in combination with geological and geophysical modeling. Challenges exist due to the hierarchical nature of the probabilistic models, but modern sampling strategies allow for efficient sampling in these complex settings. We showcase the application with examples combining geological modeling and geophysical potential field measurements in an integrated model for improved decision making.