bluuebunny/crossref_metadata_2025 huggingface dataset:
Micromechanical testing of olivine grain boundaries
Authors: Avadanii Diana , Hansen Lars , Darnbrough Ed , Marquardt Katharina , Armstrong David , Wilkinson Angus
Published: March 2021

The mechanics of olivine deformation play a key role in large-scale, long-term planetary processes, such as the response of the lithosphere to tectonic loading or the response of the solid Earth to tidal forces, and in short-term processes, such as the evolution of roughness on oceanic fault surfaces or postseismic creep within the upper mantle. Many previous studies have emphasized the importance of grain-size effects in the deformation of olivine. However, most of our understanding of the role of grain boundaries in deformation of olivine is inferred from comparison of experiments on single crystals to experiments on polycrystalline samples.

To directly observe and quantify the mechanical properties of olivine grain boundaries, we use high-precision mechanical testing of synthetic forsterite bicrystals with well characterised interfaces. We conduct nanoindentation tests at room temperature on low-angle (13o tilt about [100] on (015)) and high-angle (60o tilt about [100] on (011)) grain boundaries. We observe that plasticity is easier to initiate if the grain boundary is within the volume tested. This observation agrees with the interpretation that certain grain-boundary configurations can act as sites for initiating microplasticity.

As part of continuing efforts, we are also conducting in-situ micropillar compression tests at high-temperature (above 600o C) within similar bicrystals. In these experiments, the boundary is contained within the micropillar and oriented at 45o to the loading direction to promote shear along the boundary. In these in-situ tests, our hypothesis is that the low-angle grain boundary displays a higher viscosity relative to the high-angle interface. Key advantages of performing in-situ experiments are the direct observation of grain-boundary migration or sliding, simplified kinematics of a single boundary segment, and  potentially changes in style of deformation with different grain-boundary character.

These small deformation volume experiments allow us to qualitatively explore the differences between the crystal interior and regions containing grain boundaries. Overall, the variation in strain and temperature in our small scale experiments allows the fundamental investigation of the response of well characterised forsterite grain boundaries to deformation. 
Carbon monoxide variability in the atmosphere of Moscow region.
Authors: Kirillova Natalia , Rakitin Vadim , Skorokhod Andrey , Rakitina Alexandra , Shilkin Arseny
Published: March 2021

  Complex analysis of CO total content measurements in Moscow (site OIAP, city center) and Moscow province (site ZSS, Zvenigorod Scientific Station) using OIAP RAS spectroscopic data, MosEcoMonitoring automatic network station (MEM) data and satellite monitoring results. Analysis of meteorological information on parameters of atmospheric boundary layer (ABL) in Moscow and surrounding regions is performed. Long-term variability and trends of CO total column (TC) and meteorological parameters was explored, pollutant accumulation characteristics of carbon monoxide in calm days in ABL were obtained. ZSS data as regional background characteristics were used. It was revealed that transports from Moscow don’t lead to a significant increase in CO TC in the ZSS. The decrease of CO TC averaged annual values for 2000−2018 in Moscow (-2.56±0.52%/yr) and ZSS (-1.15±0.37%/yr) is established. After approximately 2007−2008 the rate of CO TC decrease declined at both sites. In the summer and autumn months of 2008-2018 CO TC increase with the rate of about 0.7%/yr is found at the ZSS. Increase of wind velocity in Moscow ABL in different periods of 2000-2018 (0.4-1.6%/yr) is established. In contrast with Moscow, statistically significant changes of wind velocity in Kaluga province were not detected. Repeatability of calm days in Moscow for 2006−2017 time-period was decreased (-7.06±3.96%/yr) with the diminution of anthropogenic part of the CO content in the same period (-6.72±3.48%/yr). Obtained results indicate not only urban anthropogenic emissions reduction but also the influence of climatic (meteorological) factor on Moscow air quality.
Adjusting spatial dependence of climate model outputs with Cycle-Consistent Adversarial Networks 
Authors: François Bastien , Thao Soulivanh , Vrac Mathieu
Published: March 2021

Climate model outputs are commonly corrected using statistical univariate bias correction methods. Most of the time, those 1d-corrections do not modify the ranks of the time series to be corrected. This implies that biases in the spatial or inter-variable dependences of the simulated variables are not adjusted. Hence, over the last few years, some multivariate bias correction (MBC) methods have been developed to account for inter-variable structures, inter-site ones, or both. As proof-of-concept, we propose to adapt  a computer vision technique used for Image-to-Image translation tasks (CycleGAN) for the adjustment of spatial dependence structures of climate model projections. The proposed algorithm, named MBC-CycleGAN, aims to transfer simulated maps (seen as images) with inappropriate spatial dependence structure from climate model outputs to more realistic images with spatial properties similar to the observed ones. For evaluation purposes, the method is applied to adjust maps of temperature and precipitation from climate simulations through two cross-validation approaches. The first one is designed to assess two different post-processing schemes (Perfect Prognosis and Model Output Statistics). The second one assesses the influence of non-stationary properties of climate simulations on the performance of MBC-CycleGAN to adjust spatial dependences. Results are compared against a popular univariate bias correction method, a "quantile-mapping" method, which ignores inter-site dependencies in the correction procedure, and two state-of-the-art multivariate bias correction algorithms aiming to adjust spatial correlation structure. In comparison with these alternatives, the MBC-CycleGAN algorithm reasonably corrects spatial correlations of climate simulations for both temperature and precipitation, encouraging further research on the improvement of this approach for multivariate bias correction of climate model projections.
Strongly Coupled Assimilation of a Hypothetical Ocean Current Observing Network within a Regional Ocean-Atmosphere Coupled Model: An OSSE Case Study of Typhoon Hato
Authors: Phillipson Luke , Li Yi , Toumi Ralf
Published: March 2021

The forecast of tropical cyclone (TC) intensity is a significant challenge.  In this study, we showcase the impact of strongly coupled data assimilation with hypothetical ocean currents on analyses and forecasts of Typhoon Hato (2017). 

Several observation simulation system experiments were undertaken with a regional coupled ocean-atmosphere model. We assimilated combinations of (or individually) a hypothetical coastal current HF radar network, a dense array of drifter floats and minimum sea-level pressure. During the assimilation, instant updates of many important atmospheric variables (winds and pressure) are achieved from the assimilation of ocean current observations using the cross-domain error covariance, significantly improving the track and intensity analysis of Typhoon Hato. As compared to a control experiment (with no assimilation), the error of minimum pressure decreased by up to 13 hPa (4 hPa / 57 % on average). The maximum wind speed error decreased by up to 18 knots (5 knots / 41 % on average). 

By contrast, weakly coupled implementations cannot match these reductions (10% on average). Although traditional atmospheric observations were not assimilated, such improvements indicate there is considerable potential in assimilating ocean currents from coastal HF radar, and surface drifters within a strongly coupled framework for intense landfalling TCs.
A Kinematic Reconstruction of Jurassic ocean spreading from the ophiolites of California, the western U.S. using structural geology and paleomagnetism.
Authors: Arkula Cemil , Lom Nalan , Wakabayashi John , Rea-Downing Grant , Dekkers Mark , van Hinsbergen Douwe
Published: March 2021

The western edge of the North America plate contains geological records that formed during the long-lived convergence between plates of the Panthalassa Ocean and North America. The geology of different segments along western North America indicates different polarities (eastward and westward) for subducted slabs and thereby various tectonic histories and settings. The western United States (together with Mexico) plays a key role in this debate, many geologic interpretations assume continuous eastward subduction in contrast to observations within proximal geologic segments and tomographic images of the lower mantle below North America and the eastern Pacific Ocean which suggest a more complex subduction history. In this study, we aim to evaluate the plate tectonic setting in which the Jurassic ophiolites of California formed. Geochemical data from these ophiolites suggest that they formed above a nascent intra-oceanic or continental margin subduction zone. We first developed a kinematic reconstruction of the western US geology back to the Jurassic based on published structural geological data. Importantly, we update the reconstruction of the various branches of the San Andreas fault system to determine the relative position of the ophiolite fragments and adopt a previous restoration of Basin and Range extension which we expand northward towards Washington state. We then reconstruct North American margin deformation associated with Cretaceous to Paleogene shortening and strike-slip faulting. We find no clear candidates in the geological record that may have accommodated major subduction between the Jurassic ophiolite belt and the North American margin and consequently concur with the school of thought that considers that the ophiolite belt, as well as the underlying subduction-accretionary Franciscan Complex, likely formed in the North American fore-arc. We collected paleomagnetic data to reconstruct the spreading direction of the Jurassic Californian ophiolites, by providing new paleomagnetic data from sheeted dykes of the Josephine and Mt. Diablo Ophiolites. These suggest a NE-SW paleo-ridge orientation, oblique to the North American margin which may be explained by partitioning of a dextral component of subduction obliquity relative to North America. We used this spreading direction in combination with published ages of the ophiolites and our restoration of the relative position of these ophiolites prior to post-Jurassic deformation to construct a ridge-transform system at which the Jurassic ophiolites accreted. The results will be used to evaluate which parts of the subduction systems that existed in the eastern Panthalassa Ocean may reside in the western US, and which parts may be better sought in the northern Canadian Segment or/and in the southern Caribbean region.
Increased winter warm events in Iceland drive enhanced glacier velocity and melting
Authors: Hart Jane , Martinez Kirk , Baurley Nathaniel , Robson Benjamin
Published: March 2021

A key element in the comprehension of the response of glaciers to climate change is an understanding of the bed conditions, and these are a vital component of ice sheet models. The West Antarctic ice streams are potentially highly unstable, with implications for rapid sea level rise. These are underlain by unconsolidated sediments (soft-bed), which have a distinct but rarely studied subglacial hydrology. We present a detailed data set from Skálafellsjökull, a soft-bedded glacier in Iceland, as an analogue for other soft-bedded glaciers. These data include wireless in situ till water pressure, meteorological, surface melt, discharge and glacier surface velocity from GPS as well as remote sensing imagery. We show how short-term warm events during winter can effect annual velocity, and how the number of warm events has increased over the last 10 years. We argue this was because water was stored in a soft-bed subglacial reservoir where it could be rapidly released during winter, with the resultant storage levels effecting the following summer dynamics.  To test whether warm winter events are unique to Iceland, we analyzed the daily air temperatures record of 18 World Glacier Monitoring Service ‘reference’ glaciers (1979-2018). We were able to show that periods of warm temperatures during winter were present in maritime locations, and the number of these events had increased in locations where winter temperatures had also increased. We propose that winter events are an important component of glacier retreat and sea level rise that have hitherto not been examined in detail.
Major element geochemistry of European agricultural soil: weathering processes of silicate parent materials
Authors: Negrel Philippe , Ladenberger Anna , Reimann Clemens , Demetriades Alecos , Birke Manfred , Sadeghi Martiya
Published: March 2021

Collection of agricultural soil samples in Europe (0–20 cm, 33 countries, 5.6 million km2) during the GEMAS (GEochemical Mapping of Agricultural and grazing land Soil) continental-scale project allowed the study of geochemical behaviour of major elements during weathering (SiO2, TiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, P2O5) using their total concentrations (XRF data). The chemical composition of soil represents to a large extent the primary mineralogy of the source bedrock, the effects of pre- and post-depositional weathering and element mobility, either by leaching or mineral sorting with the addition of formation of secondary products such as clays.

Bulk geochemistry is used to calculate a set of weathering indices such as chemical index of alteration CIA, reductive and oxidative mafic index of alteration MIA, the change in mass balance t (calculation relative to immobile Nb) for soil derived from silicate parent materials defined as granite, gneiss and schist at the European continental-scale. Silicate minerals of soil parent materials can be either very resistant to weathering or very soluble and export of elements in dissolved form and precipitation of secondary phases can occur at a large scale. Either way, they leave a strong chemical signature in derived soil, which can be quantified and classified with help of geochemical indices that are useful tools to evaluate chemical weathering trends. Weathering indices and gain-loss mass transfer coefficients were applied to agricultural soil to provide an insight into the weathering processes affecting three silicate parent rocks and their impact on soil development at the European scale. Distinct chemical composition and weathering patterns has been evidenced in silicate derived soil. The interpretation of geographical distribution of soil types with silicate substrate allows better understanding of soil nutritional status, metal enrichments, degradation mechanisms under various climate conditions.
Monitoring zero water level in a drought-affected headwater stream network
Authors: Herzog Amelie , Stahl Kerstin , Weiler Markus , Blauhut Veit
Published: March 2021

Even largely perennial rivers can fall dry during drought events. A resulting partial or full drying-up of streambeds is difficult to monitor with conventional gauging stations, but important as it heavily impacts water availability, quality and aquatic ecosystems. With a predicted tendency towards more extreme droughts, event-based intermittency is likely to increase requiring a better longitudinal quantification of water level and streamflow conditions. The Dreisam River in the south-west of Germany is a stream with a highly dynamic hydrology. In the recent extreme drought years of 2015, 2018 and 2019 the main stream and tributaries partly fell dry; whereas the main gauging station still recorded flow. Furthermore, several tributaries fell dry in 2016, 2017 and 2019.To improve the understanding of the interaction between streamflow, groundwater and water usages in low flow and zero-flow situations, a flexible longitudinal water quality and quantity monitoring network was developed. Different techniques such as QR-code-reading camera systems and ultrasound devices to log water levels as well as water temperature and electrical conductivity sensors were used. The set-up was additionally equipped with conventional capacitive water level loggers. Here, we present a comparison of the different water level monitoring techniques in order to a) evaluate the advantages and limits of the novel techniques and b) investigate any added value of longitudinal, catchment wide zero level monitoring. The results show that the choice of the measurement sites' environment, including shading of QR-codes, light reflections of the water surface and streambed topography, is crucial for a successful application of the used techniques. The distributed gauges reveal a highly variable longitudinal drying pattern within the river network that appears to be event-specific and may not be explained without consideration of all natural and altered system fluxes.
Observing Earth space environment with LEO multi-mission data
Authors: Stolle Claudia , Xiong Chao , Michaelis Ingo
Published: March 2021

In situ data from satellites in Low Earth Orbit (LEO) has become indispensable to monitor and explore near-Earth space. In contrast to ground-based observations they provide global coverage, and they sense parameters at altitudes that often remain hidden when applying remote sensing techniques either ground- or space-based. 

In recent years, data derived from instruments onboard LEO missions, which were not primarily dedicated for space science application, have proven added value in deriving the spatial and temporal variations of the magnetosphere, ionosphere and thermosphere.

This presentation will discuss the benefit of calibrated data from platform magnetometers that are originally designed for spacecraft attitude control. We will put focus on the dual-satellite GRACE-FO mission, that is suitable to derive scale-lengths, e.g., for auroral field-aligned currents, and in constellation with data from other platform magnetometers to resolve the local time dependence of the magnetospheric ring current signal. We further introduce new data sets of electron density and GPS-derived topside electron content from the GRACE and GRACE-FO missions.
The Met Office operational global ocean forecast system FOAM-ORCA12
Authors: Barbosa Aguiar Ana , Waters Jennifer , Price Martin , Inverarity Gordon , Pequignet Christine , Maksymczuk Jan , Smout-Day Kerry , Martin Matthew , Bell Mike , While James , King Robert , Lea Daniel , Siddorn John
Published: March 2021

The importance of oceans for atmospheric forecasts as well as climate simulations is being increasingly recognised with the advent of coupled ocean / atmosphere forecast models. Having comparable resolutions in both domains maximises the benefits for a given computational cost. The Met Office has recently upgraded its operational global ocean-only model from an eddy permitting 1/4 degree tripolar grid (ORCA025) to the eddy resolving 1/12 degree ORCA12 configuration while retaining 1/4 degree data assimilation. 

We will present a description of the ocean-only ORCA12 system, FOAM-ORCA12, alongside some initial results. Qualitatively, FOAM-ORCA12 seems to represent better (than FOAM-ORCA025) the details of mesoscale features in SST and surface currents. Overall, traditional statistical results suggest that the new FOAM-ORCA12 system performs similarly or slightly worse than the pre-existing FOAM-ORCA025. However, it is known that comparisons of models running at different resolutions suffer from a double penalty effect, whereby higher-resolution models are penalised more than lower-resolution models for features that are offset in time and space. Neighbourhood verification methods seek to make a fairer comparison using a common spatial scale for both models and it can be seen that, as neighbourhood sizes increase, ORCA12 consistently has lower continuous ranked probability scores (CRPS) than ORCA025. CRPS measures the accuracy of the pseudo-ensemble created by the neighbourhood method and generalises the mean absolute error measure for deterministic forecasts. 

The focus over the next year will be on diagnosing the performance of both the model and assimilation. A planned development that is expected to enhance the system is the update of the background-error covariances used for data assimilation. 
Testing PFAS Immobilization
Authors: Bierbaum Thomas , Braun Juergen , Klaas Norbert , Haslauer Claus , Lange Frank Thomas , Nuerenberg Gudrun , Scheurer Marco
Published: March 2021

In the region Rastatt/Baden-Baden in the Upper Rhine Valley, Germany, approximately 1000 ha of predominantly agricultural land has been contaminated with per- and polyfluoroalkyl substances (PFASs) about one decade ago when paper-fiber biosolids mixed with compost was applied. These substances affect various land uses (agriculture, open pit gravel quarries, and urban planning) and the underlying aquifer as the main drinking water resource for surrounding cities and municipalities.

Remediation attempts have been limited to date, particularly due to the large spatial extent of the contamination and the related high costs. One strategy currently being investigated is to immobilize the PFASs in the soil in-situ. Substances with a high sorption capacity would be applied on the ground surface and mixed with the soil. The then altered soil should still fulfill its original purpose (e.g., for agriculture). Another strategy could be to remove the contaminated soil and use it for construction (e.g., noise protection embankment) after treatment with the immobilization agents.

The purpose of this research is to develop a test strategy to evaluate the long-term leaching characteristics of soil treated with substances to increase its sorption capacity. Treated soil is tested on three different scales (batch experiments, column experiments, lysimeters) and under different saturation conditions (saturated, variably saturated). Effluent concentrations are monitored over time with different analytical methods (target analysis, determination of sum parameters (EOF/AOF), Total Oxidizable Precursor Assay (TOP)). Mathematical models are employed to evaluate the appropriateness of various processes (e.g., equilibrium sorption) and the leaching behavior for time scales larger than possible in laboratory experiments.

A special challenge for both the analytical strategy and the numerical modeling poses the fact that PFASs consist of a more than 4700 compounds (according to OECD), from which currently only about 20 usually are quantified in routine analysis. A number of these analytical targets are breakdown products, derived from larger precursors by microbial activity, which makes the source term undefined.

The current data illustrate significant reductions in PFAS desorption rates in some of the treated soils. In comparison to the control material (N-1), eluate concentrations in a treated soil (R-1) are found to be lowered by a factor of 1000. The desorbed PFAS mass in the column experiment with R-1 is less than 4%, relative to N-1. In the lysimeter experiments (variably saturated), delayed increasing eluate concentrations indicate additional processes (source term).

The measured and modelled time-series of effluent concentrations serve as the basis for a simple and cost-effective method for the experimental testing of immobilization measures for PFASs.
Towards a continuous NASA cloud climate data record from MODIS to VIIRS
Authors: Meyer Kerry , Platnick Steven , Holz Robert , Ackerman Steven , Heidinger Andrew , Amarasinghe Nandana , Wind Galina , Frey Richard , Dutcher Steve
Published: March 2021

The Suomi NPP and JPSS series VIIRS imagers provide an opportunity to extend the NASA EOS Terra (20+ year) and Aqua (18+ year) MODIS cloud climate data record into the new generation NOAA operational weather satellite era. However, while building a consistent, long-term cloud data record has proven challenging for the two MODIS sensors alone, the transition to VIIRS presents additional challenges due to its lack of key water vapor and CO2 absorbing channels available on MODIS that are used for high cloud detection and cloud-top property retrievals, and a mismatch in the spectral location of the 2.2µm shortwave infrared channels on MODIS and VIIRS that has important implications on inter-sensor consistency of cloud optical/microphysical property retrievals and cloud thermodynamic phase. Moreover, sampling differences between MODIS and VIIRS, including spatial resolution and local observation time, and inter-sensor relative radiometric calibration pose additional challenges. To create a continuous, long-term cloud climate data record that merges the observational records of MODIS and VIIRS while mitigating the impacts of these sensor differences, a common algorithm approach was pursued that utilizes a subset of spectral channels available on each imager. The resulting NASA CLDMSK (cloud mask) and CLDPROP (cloud-top and optical/microphysical properties) products were publicly released for Aqua MODIS and SNPP VIIRS in early 2020, with NOAA-20 (JPSS-1) VIIRS following in early 2021. Here, we present an overview of the MODIS-VIIRS CLDMSK and CLDPROP common algorithm approach, discuss efforts to monitor and address relative radiometric calibration differences, and highlight early analysis of inter-sensor cloud product dataset continuity.
Approach for analyzing landslide and torrential flow hazard conditions in relation to landscape evolution in the northern Colombian Andes 
Authors: Naranjo Bedoya Karolina , Aristizábal Edier , Hölbling Daniel , García John , Aguilar Asaf , Ortiz David
Published: March 2021

Colombia is an equatorial country located in the northwestern corner of South America with characteristic and complex climatic and geologic settings, which contribute to a great diversity of landforms in the Colombian Andes. 65% of the Colombian population is concentrated in this mountainous terrain, where landslides and torrential flows are common. These natural hazards led to several tragic events over time. Their occurrence is favored by a very dynamic landscape made up of weak and highly weathered materials and affected by tectonic stress. In this study, we aim to gain a better understanding of morphometric control on the occurrence of landslides and torrential flows through process geomorphology and information derived from Digital Elevation Models (DEMs). Several morphometric indices related to drainage network, basin geometry, drainage texture, relief characteristics, asymmetry factor and others were calculated over 168 drainage basins in the northern Colombian Andes. We used quantitative geomorphology to find patterns of anomalies associated with landscape evolution and the occurrence of landslides and torrential flows. Understanding morphodynamics from morphogenesis is important to assess landslide and torrential flow hazard conditions in relation to landscape characteristics and evolution, to support hazard assessment, and consequently to reduce human and economic losses.
Keywords: Landslide, torrential flow, morphometric indices, mountainous terrains.
Regime Behaviour in the Upper Stratosphere as a Precursor of Stratosphere- Troposphere Coupling of the Northern Hemisphere
Authors: Lu Hua , Gray Lesley , Martineau Patrick , King John , Bracegirlde Thomas
Published: March 2021

A flow regime index is constructed based on the November-December standard deviation of the Ertel’s potential vorticity (EPV) in the northern upper stratosphere at 1500 K (~40 km). The index reveals two flow regimes in both the stratosphere and the troposphere. In the stratosphere, the two flow regimes involve zonally asymmetric variability that is manifested by a modulation of the Aleutian High and distinct early-to-late winter development of the polar vortex. During the wide-jet regime, an anomalously strengthened, upright polar vortex is found in middle winter, which involves an equatorward shift of the surf zone in the middle to upper stratosphere, a poleward movement of the polar vortex axis, and a sharpening of the polar vortex edge, suggesting a dominant effect of Rossby wave breaking. During the narrow-jet regime, the vortex weakens at least a month earlier in association with enhanced large-scale PV mixing.

The upper stratospheric flow regimes also have detectable signal in the vicinity of the tropospheric westerly jets in middle winter. The tropospheric responses are also zonally asymmetric. During the wide-jet regime, the largest response is found over the North Pacific with a weakened, poleward shifted westerly jet over north America.  The circulation anomalies during the narrow-jet regime are most strong over the North Atlantic with a weakened, and equatorward shifted westerly jet there. The flow regimes also differ distinctively in their impacts on high-frequency variability downstream of the westerly jets and associated temperature variability. Given the flow regimes in the upper stratosphere leads the tropospheric response by one to two months, improved representation of upper stratospheric variability in climate models may offer more skillful prediction of long-range surface weather forecasts.
Isolation and characterization of calcifying bacteria from “living rocks”: a possible carbon sink
Authors: del Gallo Maddalena , Mignini Amedeo , Moretti Giulio , Pellegrini Marika , Cacchio Paola
Published: March 2021

CO2 emissions triggered by anthropogenic and natural activities contribute to climate change, one of the current environmental threats of public and scientific concern. At present, microbially-induced biomineralization of CO2 by calcium carbonate (CaCO3) is one of the highly topical study subjects as carbon stabilization process. In the present study we focused our attention on the calcifying bacteria of “living rocks”. The origin of these concretions, composed by a silicate skeleton of quartz and feldspars, merged by massive carbonate concrete, has so far been recognized as abiotic. Within this study we investigated the role of calcifying bacteria in their formation of these concretions and we isolated and characterized the species with CaCO3 precipitation abilities. Concretions were sampled in Romania (Trovant) and Italy (Sibari and Rome). Samples were first analyzed for their culturable microflora (i.e. isolation, CaCO3 precipitation capability and molecular characterization). Then, in vitro regeneration tests were carried out to confirm the contribution of bacteria in the formation of these erratic masses. Moreover, natural samples and bioliths regenerated in vitro were (i) observed and analyzed by scanning electron microscopy (SEM-EDS) and (ii) characterized at molecular level by DNA extraction and 16S rRNA analysis (V3-V4 regions). By isolating and characterizing the culturable microflora, we obtained 19 calcifying isolates, with different morphological, bacteriological and mineral precipitation properties. These evidences have given a first relevant contribution for the definition of the biotic role to the formation of these concretions. These evidences were confirmed by the efficient in vitro regeneration and SEM-EDS analysis. The molecular identification of the isolates and the comparison of the data obtained from the Illumina sequencing with those present in the literature, allowed us to hypothesize the genera that most likely contributed to the formation of these concretions. The results obtained provide a good scientific basis for further studies, which should be directed towards the use of isolates in studies of environmental and socio-economic relevance. Several studies demonstrate that microbially mediated biomineralization has the potential to capture and sequester carbon. Calcium carbonate, is a stable pool of carbon and is an effective sealant to prevent CO2 release back into the atmosphere.
Energy transport during 3D small-scale reconnection driven by anisotropic turbulence using PIC simulations
Authors: Agudelo Rueda Jeffersson Andres , Verscharen Daniel , Wicks Robert T , Owen Christopher J , Nicolaou Georgios , Walsh Andrew P , Zouganelis Yannis , Germaschewski Kai , Vargas-Dominguez Santiago
Published: March 2021

Heating and energy dissipation in the solar wind remain important open questions. Turbulence and reconnection are two candidate processes to account for the energy transport to subproton scales at which, in collisionless plasmas, the energy ultimately dissipates. Understanding the effects of small-scale reconnection events in the energy cascade requires the identification of these events in observational data as well as in 3D simulations. We use an explicit fully kinetic particle-in-cell code to simulate 3D small scale magnetic reconnection events forming in anisotropic and Alfvénic decaying turbulence. We define a set of indicators to find reconnection sites in our simulation based on intensity thresholds.  According to the application of these indicators, we identify the occurrence of reconnection events in the simulation domain and analyse one of these events in detail. The event is highly dynamic and asymmetric. We study the profiles of plasma and magnetic-field fluctuations recorded along artificial-spacecraft trajectories passing near and through the reconnection region as well as the energy exchange between particles and fields during this event. Our results suggest the presence of particle heating and acceleration related to asymmetric small-scale reconnection of magnetic flux tubes produced by the anisotropic Alfvénic turbulent cascade in the solar wind. These events are related to current structures of order a few ion inertial lengths in size.
A kinetic formation model of foreshock transients
Authors: Liu Terry Zixu , An Xin , Zhang Hui , Turner Drew
Published: March 2021

Foreshock transients are ion kinetic structures in the ion foreshock. Due to their dynamic pressure perturbations, they can disturb the bow shock, magnetosheath, magnetopause, and magnetosphere-ionosphere system. Recent studies found that they can also accelerate particles through shock drift acceleration, Fermi acceleration, betatron acceleration, and magnetic reconnection. Although foreshock transients are important, how they form is still not fully understood. Using particle-in-cell simulations and MMS observations, we propose a physical formation process that the positive feedback of demagnetized foreshock ions on the varying magnetic field caused by the foreshock ion Hall current enables an “instability” and the growth of the structure.      
Intensity-Duration-Frequency (IDF) Curves Under Changing Climate – A Non-Stationary Modelling Approach
Authors: Sojan Jency Maria , Srivastav Roshan
Published: March 2021

Anthropogenic activities have accelerated the global warming phenomena, causing a rapid change in the weather patterns, especially the extremes. Intensification of magnitude and frequency of extreme events have increased the stress on water infrastructures. Hence design methods have to be updated to build climate-resilient infrastructures. Intensity-Duration-Frequency (IDF) curves play a vital role in flood risk assessment and impact the region's socio-economic structure. In this study, a non-stationary modelling approach is proposed to develop IDF curves under changing climate using Global Climate Models (GCMs). Non-Stationary Generalized Extreme Value Distribution (NS-GEVD) location parameter is modelled as a linear function of GCM outputs.  Data used for analysis is the annual maximum daily precipitation generated at a Hyderabad city station, India using 27 GCMs of Coupled Model Intercomparison Project Phase-5 (CMIP-5).  The analysis is carried out for the baseline period of 1971 to 2005 and the future time-period of 2006 to 2100. Corrected Akaike Information Criterion test statistic is used to identify the best NS-GEVD model. The results indicate that NS-GEVD model could capture the non-stationary behaviour and predicted an average increase of 7% in extreme rainfall intensity for the future. Besides, it is observed that six GCM covariates outperform other GCMs. The outcomes of this study will benefit the city municipality, practitioners and decision-makers in identifying future risk for water infrastructures. 
The MOSAiC sea ice albedo record: its context and role for informing improved surface radiative budgets in a climate model 
Authors: Light Bonnie , Holland Marika , Smith Madison , Perovich Donald , Webster Melinda , Clemens-Sewell David , Linhardt Felix , Raphael Ian , Bailey David
Published: March 2021

Sea ice albedo is both a driver and a consequence of summer melt evolution. The ability to collect comprehensive observations and develop accurate, general, and consistent physics-based models is central to our quantitative understanding of sea ice mass and heat budgets and a variety of associated feedback processes. Sea ice albedos recorded during the MOSAiC field campaign have extended our knowledge of the optical properties of specific ice types as well as their seasonal evolution. This new dataset complements and extends observations made during the Surface Heat Budget of the Arctic Ocean (SHEBA) campaign in the Beaufort Sea in 1998. It also presents an opportunity to improve numerical treatment of shortwave radiation partitioning by sea ice covers in climate models. Specifically, the observations include spectral and broadband albedo measurements made by observers on the surface for two classes of measurement: 1) individual ice types including snow covered ice (prior to and during melt), bare melting ice, ponded ice, and sediment-laden ice, and 2) time series measured over the full seasonal cycles. The MOSAiC and SHEBA data sets show remarkable similarity with respect to the steady spectral albedo of bare, melting summer ice and the seasonal evolution measured over representative survey lines. Both data sets include coordinated physical property characterization, which is key to the development and refinement of radiative transfer treatment in climate modeling.

In this work, we compare the observational record with results generated from runs of the CESM2 model. The Community Earth System Model (CESM2) is a coupled climate model that includes a physics-based radiative transfer treatment for sea ice. This model relies on a 2-stream delta-Eddington solution with prescribed ice-type-specific inherent optical properties. Specifically, we consider newly available sub-gridscale diagnostics in the model that detail the radiative partitioning for individual surface types and thickness categories. Comparisons between observed and modeled values are considered for the albedo of individual surface types, aggregate albedo estimates, and their seasonal progression. In particular, we use these comparisons to derive a quantitative picture of the overall partitioning of shortwave radiation by the ice cover, and how it has changed over past decades. These results can help pinpoint where the most substantial model upgrades can be accomplished as well as where the best observational investments should be made.
Linking the optically bright Gaia frame to the third International Celestial Reference Frame
Authors: Lunz Susanne , Anderson James , Xu Ming H. , Heinkelmann Robert , Titov Oleg , Johnson Megan , Schuh Harald
Published: March 2021

The new data release of the Gaia satellite operated by the European Space Agency recently published its 3rd data release (Early Data Release 3, EDR3). The dataset contains astrometric data of about 1.8 billion objects detected at optical frequencies and therefore it outperforms any catalog of astrometric information up to date. The reference frame defined by Gaia EDR3 is aligned to the International Celestial Reference System by referring to counterparts in its realization, the third International Celestial Reference Frame (ICRF3), which is calculated from very long baseline interferometry (VLBI) observations of extragalactic objects at radio frequencies.
The Gaia dataset is known to be magnitude-dependent in terms of astrometric calibration. As the objects in ICRF3, although bright at radio frequencies, are mostly faint at optical frequencies, the optically bright Gaia frame has to be linked to ICRF3 by additional counterparts besides objects in ICRF3. The non-rotation of the optically bright Gaia frame is especially important as optically bright objects can, besides astrophysical studies, be used for navigation in space, where other geodetic systems like global navigation satellite systems are out of reach. Suitable additional counterparts are radio stars which are observed by VLBI relative to extragalactic objects in ICRF3. We discuss the orientation and spin differences between the optically bright Gaia EDR3 and VLBI data of radio stars and their impact on the Gaia data usage.
Exploring deep learning approaches to predict hourly evolution of surge levels
Authors: Tiggeloven Timothy , Couasnon Anaïs , van Straaten Chiem , Muis Sanne , Ward Philip
Published: March 2021

In order to better understand current coastal flood risk, it is critical to be able to predict the characteristics of non-tidal residuals (from here on referred to as surges), such as their temporal variation and the influence of coastal complexities on the magnitude of storm surge levels. In this study, we use an ensemble of Deep Learning (DL) models to predict hourly surge levels using four different types of neural networks and evaluate their performance. Among deep learning models, artificial neural networks (ANN) have been popular neural network models for surge level prediction, but other DL model types have not been investigated yet. In this contribution, we use three DL approaches - CNN, LSTM, and a combined CNN-LSTM model- , to capture temporal dependencies, spatial dependencies and spatio-temporal dependencies between atmospheric conditions and surges for 736 tide gauge locations. Using the high temporal and spatial resolution atmospheric reanalysis datasets ERA5 from ECMWF as predictors, we train, validate and test surge based on observed hourly surge levels derived from the GESLA-2 dataset. We benchmark our results obtained with DL to those provided by a simple probabilistic reference model based on climatology. This study shows promising results for predicting the temporal evolution of surges with DL approaches, and gives insight into the capability to gain skill using DL approaches with different Architectures for surge prediction. We therefore foresee a wide range of advantages in using DL models for coastal applications: probabilistic coastal flood hazard assessment, rapid prediction of storm surge estimates, future predictions of surge levels.
Large-scale connections between Fram Strait recirculation and warm water pathways towards Greenland fjords
Authors: McPherson Rebecca , Kanzow Torsten , Wekerle Claudia
Published: March 2021

In the last two decades, rising ocean temperatures have significantly contributed to the increased melting and retreat of marine-terminating glaciers along the coast of Greenland. Warming subsurface waters have also been shown to interact with the glaciers in Northeast Greenland, which until recently were considered stable, and caused their rapid retreat. The main source of these waters is the westward recirculation of subducted Atlantic Water (AW) in Fram Strait, which has shown a warming of up to 1° C over the past few decades.

In this study, the connection between the subsurface warm Atlantic Intermediate Water (AIW) found on the wide continental shelf of Northeast Greenland and in the fjords, and AW within the West Spitsbergen Current (WSC) is investigated using historical hydrographic observations and high-resolution numerical simulations with the Finite-Element Sea-ice Ocean Model (FESOM). We find that AW from the WSC takes between 10 – 14 months to recirculate across Fram Strait and reach the shelf break where it moves southwards. The pronounced inter-annual variability in the WSC is preserved as the water recirculates. However, the variability of temperature and AIW layer thickness on the shelf at seasonal or inter-annual time scales is at best weakly controlled by the AW temperature in the WSC. There is no significant correlation between AIW and the WSC anywhere on the shelf, suggesting advection from the WSC alone does not control AIW signals. The role of wind-driven, episodic upwelling is then investigated as a driver of transport of AIW from Fram Strait onto the shelf (following an approach by Münchow et al., 2020) where it then may follow the deep trough system towards the glaciers.
Hydrological consistency between the upstream and downstream estimates of Q1000 flood on the upper Rhine River, using historical series in Basel (1808-2017) and Maxau (1815-2018)
Authors: Lang Michel , Renard Benjamin , Le Coz Jérôme
Published: March 2021

Estimation of extreme design floods with a short series of a few decades remains challenging because the statistical extrapolation of observed floods to extreme floods induces great uncertainties. Several alternative methods take advantage of the use of additional information: regional methods (e.g. the index flood method), Monte Carlo rainfall-runoff simulation methods, or specific statistical methods adapted to historical series. Here we present a flood frequency analysis on the upper Rhine River, using long historical series in Basel (1808-2017) and Maxau (1815-2018). We used a Bayesian framework to fit the parameters of the GEV distribution. Each value of the annual maximum discharge has uncertainties, which vary from ± 5-7% for the last decades to ± 22-42% for the oldest period depending on the station. At the local scale, without prior assumption on the three parameters of a GEV distribution, we found that the credibility intervals of the Basel and Maxau flood distributions are consistent. However, beyond a 1000-year return period, flood quantiles are incoherent with Q(Maxau) < Q(Basel) although Maxau (50 000 km2) is located downstream of Basel (36 000 km2). The floods at Basel are almost Gumbel distributed (shape parameter k = 0.066), whereas the floods at Maxau are Weibull distributed (shape parameter k = 0.219) with an asymptotic maximum value. Assuming that the shape parameter k has a certain regional consistency, we have performed a second iteration, with a prior interval [-0.1; +0.4] on k. The width of this interval corresponds to the union of the posterior distribution of k parameter of each local distribution: [-0.1; +0.2] at Basel and [0.0; +0.4] at Maxau. The second version of each distribution is almost the same up to a return period of 100 years, but there is no more crossing for extreme values. Using the predictive distribution with a regional prior on the shape parameter of the GEV distribution, the result is hydrologically consistent from upstream to downstream.