bluuebunny/crossref_metadata_2025 huggingface dataset:
The Splash without a Merger
Authors: Amarante João A. S. , Beraldo e Silva Leandro , Debattista Victor P. , Smith Martin C.
Published: March 2020

The Milky Way’s progenitor experienced several merger events that left their imprints on the stellar halo, including the Gaia-Sausage/Enceladus. Recently, it has been proposed that this event perturbed the proto-disk and gave rise to a metal-rich ([Fe/H] > −1), low angular momentum (v

ϕ
 < 100 km s−1) stellar population. These stars have dynamical and chemical properties different from the accreted stellar halo, but are continuous with the canonical thick disk. In this Letter, we use a hydrodynamical simulation of an isolated galaxy that develops clumps that produce a bimodal thin+thick disk chemistry to explore whether it forms such a population. We demonstrate that clump scattering forms a metal-rich, low angular momentum population, without the need for a major merger. We show that, in the simulation, these stars have chemistry, kinematics, and density distribution in good agreement with those in the Milky Way.
THE POLICY OF WORKERS RELOCATION TO REMOTE AREAS IN THE USSR IN THE 1920S AND EARLY 1930S
Authors: Moiseenko V.
Published: March 2020

After 1917, under the influence of new social conditions, the beginning of industrialization in the USSR and the policy of development of the outskirts, a new type of migration emerged, entitled in official documents of that time as “relocating workers to remote areas”. The systematization of legislative regulation of this type of migration in the absence of well-established statistical accounting is the purpose of the study, the results of which are presented in this article. The 1920s became a noticeable frontier in the long history of Russia’s settlement of the eastern regions, but the costly practice of attracting specialists, developed in the mid-1920s in the framework of the departmental approach, cannot be considered effective from the point of view of the formation of a stable population in these areas.
A cryptic new species of Chlidonoptera Karsch, 1892 from the south west protected zone of the Central African Republic (Insecta, Mantodea, Hymenopodidae)
Authors: Moulin Nicolas
Published: March 2020

Between 1998 and 2012, several scientific expeditions in Dzanga-Sangha Special Reserve and Dzanga-Ndoki National Park led to the collection of many Mantodea specimens from Central African Republic (CAR). Among these specimens, several males of an undescribed species were discovered. Morphologically, this species most closely resembles to Chlidonoptera vexillum Karsch, 1892 and Chlidonoptera lestoni Roy, 1975. A new lineage was revealed by DNA barcoding. Therefore, a new species is described, Chlidonoptera roxanaesp. nov. Habitus images, genitalia illustrations and descriptions, measurement data, a key to species, natural history information, and locality data are provided. These results add to the evidence that cryptic species can be found in tropical regions, a critical issue in efforts to document global species richness. They also illustrate the value of DNA barcoding, especially when coupled with traditional taxonomic tools, in disclosing hidden diversity.
Removal of sodium compounds from Co/SBA-15 catalysts for Fischer-Tropsch Synthesis
Authors: Silva Lidiane Sabino da , Cher Gabriela Gonzaga , Baldanza Maria Auxiliadora Scaramelo , Silva Victor Luis dos Santos Teixeira da , Arroyo Pedro Augusto
Published: March 2020

In the present work, the synthesis of Co/SBA-15 catalysts intended for Fischer-Tropsch (FT) synthesis was performed. During the synthesis of catalysts there was contamination of samples with sodium nitrate due to the nature of the reducing agent used for the synthesis of metallic phase. This kind of impurity is not advantageous for the FT reaction. Attempts at removal of sodium compounds were carried out by means of simple leaching treatments, using ethanol and acid ethylenediaminetetraacetic (EDTA) as solvent and complexing agent, respectively, followed by heat treatment at temperatures of 150 or 300°C. It was possible to conclude that the treatment using EDTA was more effective in removing almost all the alkaline phase of samples, despite the occurrence of oxidation, agglomeration, and removal of the metal nanoparticles in this process. In addition, there were no significant differences in the product selectivity of FT synthesis of the catalysts after sodium removal, although the nanoparticles were larger than 10 nm.
Cellular disruption and its influence over the drying kinetics of brewer’s spent yeast biomass
Authors: Biz Ana Paula , Rigo Elisandra , Bertolo Angélica Patrícia , Cavalheiro Darlene
Published: March 2020

Spent yeast biomass is one of the residues of brewing. It is specifically the second-largest residue from brewing industry. Most of the spent yeast is sold at low prices, or disposed as waste or used as animal feed. Spent yeast biomass is predominantly composed of proteins, and it has a high biological value, being an excellent source of high-quality protein, comparable in value with soy protein. Therefore, spent yeast biomass has great potential for use in foodstuffs for human consumption. The objective of this work was to evaluate the influence of cell rupture over the drying kinetics of spent yeast biomass using mathematical models (Lewis and Page). Also, to verify the influence of cell rupture method over the amount of protein. The cellular rupture was performed by two methods (chemical method and physical method: ultrasound). The drying process was performed by freeze-drying, and the parameters of the models were obtained using the non-linear regression (Generalized Reduced Gradient Nonlinear Optimization Code). Mathematical models of drying kinetics showed a strong correlation with the experimental data, R² > 0.96. The disruption process did not significantly affect the drying time and protein content. But the cellular autolysis improves the protein digestibility since the proteins will be totally available to the digestive enzymes and also increase the bioavailability of nutrients.
On the complexity of the cogrowth sequence
Authors: Bell Jason , Mishna Marni
Published: March 2020

Given a finitely generated group with generating set

S

, we study the
cogrowth
sequence, which is the number of words of length

n

over the alphabet

S

that are equal to one. This is related to the probability of return for walks in a Cayley graph with steps from

S

. We prove that the cogrowth sequence is not

P

-recursive when

G

is an amenable group of superpolynomial growth, answering a question of Garrabrant and Pak.
Enhanced Scheduling Support to Improve Continuity of Care in a Resident Training Clinic
Authors: LaVine Nancy A. , Coletti Daniel J. , Verbsky Jennifer , Block Lauren
Published: March 2020

Background

Clinical continuity is recognized as a driver of satisfaction for patients and physicians. Greater continuity may positively affect trainee decisions to enter primary care. Maintaining clinical continuity remains a challenge in residency clinics.

Objective

We determined whether enhanced scheduling support was associated with improvement in internal medicine resident continuity with patients.

Methods

This study was conducted from June 2017 to December 2018. In the intervention clinic, a single scheduling staff member (ratio of 10 residents to 1 scheduler) was colocated within the clinical space, allowing the scheduler to participate in clinical discussions and direct communication with physicians regarding future appointments. In the comparison clinic, scheduling staff (19:1 ratio) were located at a remote front desk area and relied on patient reports or electronic health record orders to identify appointment needs and arrange follow-up appointments. The main outcome of the intervention was resident continuity, calculated using the continuity for physician formula.

Results

During the study period, mean resident continuity was 23% (range 13%–37%) in the comparison clinic (57 residents) and 54% (range 38%–66%) in the intervention clinic (10 residents). Resident continuity was significantly higher in the intervention clinic compared with the traditional control clinic for every quarter measured (P < .001 for all comparisons).

Conclusions

Enhancing scheduling support through colocation and a lower resident to scheduler ratios was associated with significantly higher rates of resident continuity compared with a traditional front desk model, with results sustained over 18 months.
H-1B Visa Sponsorship and Physician Trainee Retention: A Single Institution Experience
Authors: Abdel-Aziz Yousef , Khan Zubair , Barnett William R. , Altorok Nezam , Assaly Ragheb
Published: March 2020

Background

International medical graduates (IMGs) form a significant portion of the physician workforce in the United States and are vital in filling training slots due to a shortage of American medical graduates. Most often, IMGs require visa sponsorship, which must be solidified before applying for a residency or fellowship.

Objective

We examined the association of H-1B visa sponsorship on retention of physician trainees within the state of Ohio.

Methods

This was a single institutional study that examined all visa-sponsored residency and fellowship graduates who entered fully licensed clinical practice between 2006 and 2015. Practice location was ascertained immediately upon completion of training and at follow-up to determine which visa group (H-1B or J-1) were more likely to initially practice in Ohio after graduation and remain within the state.

Results

Of 103 visa-sponsored residency and fellowship graduates, 42 were H-1B sponsored and 61 were J-1-sponsored. Fifty-two percent (22) of H-1B visa-sponsored trainees and 31% (19) of J-1 visa-sponsored trainees were retained in Ohio after graduation. At follow-up, 40% (17) of H-1B and 26% (16) of J-1 visa holders remained in the state.

Conclusions

H-1B visa–sponsored trainees were more likely than those with J-1 visas to practice in the state of Ohio after graduation. Regardless of visa status, graduates tended not to change their geographical location over time.
Constraining Ammonia Emissions in Vehicle Plumes Utilizing Nitrogen Stable Isotopes
Authors: Walters Wendell W. , Song Linlin , Chai Jiajue , Fang Yunting , Colombi Nadia , Hastings Meredith G.
Published: March 2020

Abstract. Vehicle emissions have been identified as an important urban source of ammonia (NH3). However, there are large uncertainties regarding the contribution of vehicle emissions to urban NH3 budgets, as well as its role in spatiotemporal fine particulate matter (PM2.5) formation and nitrogen (N) deposition patterns. The N stable isotopic composition (δ15N) may be a useful observational constraint to track NH3 emission sources and chemical processing, but previously reported vehicle δ15N(NH3) emission signatures have reported a wide range of values, indicating the need for further refinement. Here we have characterized δ15N(NH3) spatiotemporal variabilities from vehicle plumes in stationary and on-road measurements in the US and China using a laboratory- and field-verified NH3 collection technique shown to be accurate for characterizing δ15N(NH3) on the order of hourly time resolution. Significant spatial and temporal δ15N(NH3) variabilities were observed and suggested to be driven by vehicle fleet composition and influences from NH3 dry deposition on tunnel surfaces. The reactive NH3 sink associated with particulate ammonium (pNH4+) formation was found to have a minimal impact on the vehicle plume δ15N(NH3) measurements due to the vast majority of NHx (= NH3 + pNH4+) residing as NH3. Overall, a consistent δ15N(NH3) signature of 6.6 ± 2.1 ‰ (x ± 1σ; n = 80) was found in vehicle plumes with fleet compositions typical of urban regions. Overall, these measurements constrain the δ15N(NH3) urban traffic plume signature, which has important implications for tracking vehicle NH3 in urban-affected areas.
Influence of mid-latitude oceanic fronts on the atmospheric water cycle
Authors: Ogawa Fumiaki , Spengler Thomas
Published: March 2020

      Midlatitude oceanic fronts play an important role in the air-sea coupled weather and climate system. Created by the confluence of warm and cool oceanic western boundary currents, the strong sea-surface temperature (SST) gradient is maintained throughout the year. The climatological mean turbulent air-sea heat exchange maximizes along these SST fronts and collocates with the major atmospheric storm tracks. A recent study identified that the air-sea heat exchange along the SST front mainly occurs on sub-weekly time scales, associated with synoptic atmospheric disturbances. This implies a crucial role of air-sea moisture exchange along the SST fronts on the atmospheric water cycle through the intensification of atmospheric cyclones and the associated precipitation.  

      In this study, we investigate this influence of the SST front on the atmospheric water cycle by analyzing the atmospheric response to different prescribed SST in the Atmospheric general circulation model For the Earth Simulator (AFES). Changing the latitude of the prescribed zonally symmetric SST in aqua-planet configuration, we find a distinctive response in convective and large-scale precipitation, surface latent and sensible heat fluxes, as well as diabatic heating and moistening with respect to the latitude of SST front. Upward surface latent heat flux and convective precipitation always maximize along the equatorward flank of SST front. On the other hand, large-scale precipitation is always located on the poleward flank of the SST front, in correspondence with the maximum atmospheric moisture flux convergence. The moisture flux convergence is mainly associated with midlatitude eddies and not with the time mean transport. This highlights the influence of mid-latitude SST fronts on the atmospheric water cycle through the organization of atmospheric storm track.
Improving the robustness of flood catastrophe models in insurance through academia-industry collaboration
Authors: Noacco Valentina , Pianosi Francesca , Wagener Thorsten , Styles Kirsty , Hutchings Stephen
Published: March 2020

To quantify risk from natural hazards and ensure a robust decision-making process in the insurance industry, uncertainties in the mathematical models that underpin decisions need to be efficiently and robustly captured. The complexity and sheer scale of the mathematical modelling often makes a comprehensive, transparent and easily communicable understanding of the uncertainties very difficult.  Models predicting flood hazard and risk have shown high levels of uncertainty in their predictions due to data limitations and model structural uncertainty. Moreover, uncertainties are estimated to increase with climate change, especially for higher warming levels.

Global Sensitivity Analysis (GSA) provides a structured approach to quantify and compare the relative importance of parameter, data and structural uncertainty. GSA has been implemented successfully in tools such as the Sensitivity Analysis For Everybody (SAFE) toolbox, which is currently used by more than 2000 researchers worldwide. However, tailored tools, workflows and case studies are needed to demonstrate GSA benefits to practitioners and accelerate its uptake by the insurance industry.

One such case study has been the collaboration between the University of Bristol and JBA Risk Management on JBA’s new Global Flood Model, whose technology and flexibility has allowed to test a catastrophe model in ways not possible in the past. JBA has gained great insight into the sensitivity of modelled losses to uncertainties in the model datasets and analysis options. This has helped to explore the key sensitivities of the results to the assumptions made, for example to visualise how the distribution of modelled losses varies by return period and explore which parameters have the biggest impact on loss for the part of the Exceedance-Probability curve of interest. This information is essential for insurance companies to form their view of risk and to empower model users to adequately communicate uncertainties to decision-makers.
Upstream versus downstream changes in a natural sediment routing system from source to sink
Authors: Sharma Nikhil , Vérité Jean , Watkins Stephen , Valero Luis , Whittaker Alex , Garcès Miguel , Puigdefabregas Cai , Guillocheau François , Adatte Thierry , Castelltort Sébastien
Published: March 2020

The Middle Eocene Climatic Optimum (MECO) represents an episode of widespread warming occurring ~40 million years ago. It is characterized by gradual warming over a period of 500,000 years, leading to a rise in ocean temperatures of about 5° C in the mid and high-latitudes (Sluijs et al., 2013). Contrary to the traditional understanding and consensus that accommodation space or downstream factors control stratigraphic architecture in fluvial successions, we test the hypothesis that upstream factors, rather than downstream factors, control fluvial architecture through changes in the median grain size, sediment supply and water discharge with paleoslope being a measurable proxy to quantify these changes. We test our hypothesis utilizing the natural system of the Escanilla sediment routing system, encompassing the Middle Eocene Climatic Optimum. The Escanilla system is an overall prograding system, consisting of 1000 m thick alluvial and fluvial deposits at the southern-margin of the Tremp-Graus Basin in the south/central Pyrenees, Spain. Multiple lateral measurements for grain size distributions and cross-set measurements, flow direction and channel geometry are taken close to the source (Coll de Vent), at an intermediate location (Lascuarre), and at a distal part (Olson) of the system for paleohydraulic reconstructions. Drone flight missions are also undertaken to capture aerial photographs of the field area, which are required for the construction of 3D photogrammetric models. At Olson, alternating sequences of laterally continuous amalgamated channel bodies and several small sequences of vertically stacked isolated channel bodies have been identified. Preliminary results show distinct values of median grain size, dune height, flow depth and paleoslope for the amalgamated and vertically stacked isolated channel sequences across the MECO; the addition of our 3D models provide further insight into the lateral connectivity of the amalgamated units. Our results suggest different paleohydraulic conditions during the deposition of amalgamated and nonamalgamated units. This data will also be supported by numerical simulations carried out to better understand the response of fluvial systems to changes in upstream factors.
Impact of parametric uncertainty on simulated climate extremes and attribution studies
Authors: Timmermans Ben , Collins William , O'Brien Travis , Stone Dáithí , Risser Mark
Published: March 2020

The attribution of extreme weather events, such as heavy rainfall, to anthropogenic influence typically involves the analysis of their probability in simulations of climate, such as those conducted in the C20C+ Detection and Attribution Project. The climate models used however, such as the Community Atmosphere Model (CAM), employ approximate physics that gives rise to “parameter uncertainty”—uncertainty about the most accurate or optimal values of numerical parameters within the model. Parameterisations for convective processes, for example, are well known to be influential in the simulation of precipitation extremes.

In the context of extreme event attribution, we investigate the importance of components of parameterisations—through their associated tuning parameters—relating to deep and shallow convection, and cloud and aerosol microphysics in CAM. We present results from the analysis of a large perturbed physics ensemble experiment (~12,000 years of simulation, ~1 degree horizontal resolution) designed to explore extremes in both the observed world and pre-industrial conditions. Using surrogate models based upon Gaussian processes fitted marginally to both regional and grid cell output, we have computed sensitivity measures associated with the physics parameters, for precipitation and temperature extremes and their respective “risk ratios”.

Our results reveal the high geospatial variability in averages and extremes of output variables arising from physics perturbations, and how this contrasts with low variability in estimates of risk ratios based upon the same variables. We conclude that for CAM, variability induced by perturbed physics is typically consistent across warming scenarios, and unlikely to be a significant source of uncertainty in extreme event attribution studies. However, we caution that this may not be the case in regions where relevant parameterisations are strongly active.
The active North Ligurian domain: new geophysical insight from the SEFASILS cruise
Authors: Dessa Jean-Xavier , Beslier Marie-Odile , Schenini Laure , Sambolian Serge , Canva Albane , Ribodetti Alessandra , Operto Stéphane , Bachir Miguil Mohamed , Chamot-Rooke Nicolas , Corradi Nicola , Delescluse Matthias , Déverchère Jacques , Larroque Christophe
Published: March 2020

The first leg of the SEFASILS cruise took place in November 2018 onboard the RV Pourquoi-Pas ? Up-to-date multichannel and wide-angle seismic data were acquired offshore Monaco, from margin to basin, aiming at providing a renewed vision of the complex North Ligurian backarc system. The compressive and extensive tectonic phases that have closely alternated in time and space over the last 45 My have yielded fairly contrasting structures, whose understanding is rendered even more challenging by the strong overprint of the Messinian salt tectonics. There is ample evidence of a compressive reactivation of the North Ligurian margin since 5 Ma at least, especially to the East, along the Gulf of Genoa. Such deformation is associated with some notable seismicity originating from faults and mechanisms that remain poorly apprehended. Yet, this seismicity peaked at one historical Mw ~6.6-6.9 destructive event (1887 Ligurian earthquake). The main objective of the SEAFASILS effort is a better characterization of the crustal structures, and chiefly, of the active crustal faults and their potential interplay with salt tectonics beneath the margin and the northernmost part of the basin, both featuring seismicity. Linking these aspects with broader-scale lithospheric processes within the Southern Alps/Northern Apennines, addressed in the AlpArray initiative, is also of great importance. Here we present preliminary results of these seismic investigations, with time and prestack depth migrated MCS data. Emphasis was put on the construction of some suitable velocity models to get optimal focusing of structures from surface to depth. Some active crustal tomographic velocities derived from the dense OBS deployment providing complementary insight will also be presented.
Modeling spatial and temporal hydrologic variability of karst vulnerability at a large Slovenian karst aquifer
Authors: Scheller Mirjam , Blatnik Matej , Kogovšek Blaž , Liu Yan , Mayaud Cyril , Petrič Metka , Ravbar Nataša , Hartmann Andreas
Published: March 2020

About 50% of the Slovene drinking water demand are covered by karst aquifers. Consequently, appropriate protection and sustainable management of these aquifers are essential. Due to the hydrologic complexity and variability of karst systems, predicting potential contaminations and aquifers’ responses to changes in climate conditions, remains a challenge for karst research. In this study, the dynamics of potential solute contaminant transport in the Unica springs catchment, located in the southwest of Slovenia, are characterized and simulated with a semi-distributed karst model. The catchment encompasses autogenic and allogenic recharge across an area of about 820 km². The autogenic karst massive hosts one of Europe’s largest confluences of subterranean river branches and is strongly karstified. To take into account the temporal and spatial characteristics of the catchment, the model is linked with a GIS-based approach to assess spatiotemporal karst vulnerability. The validation of the model is performed by discharge observations and tracer experiments. The resulting simulations enable us to identify hot spots and hot moments of high contamination risks. By simulating solute contaminant transport during extremely dry and extremely wet years, we show that contaminant transport slows down under dry conditions. This can be explained by fast flow pathways not being activated or hydraulically connected under low flow conditions, which results in a retention and dilution of the contaminant in the aquifer. Our new approach improves the understanding of potential contaminants' transport behavior in a large complex karst system and justifies the consideration of spatiotemporal hydrologic variability in solute transport forecasting. It proposes a good basis for a better evaluation, management and protection of water resources in karst areas.
"Anti-squeeze" for Mantle Convection Simulations in Two-Dimensional Spherical Geometry
Authors: Tackley Paul
Published: March 2020

It is common to perform 2-dimensional simulations of mantle convection in spherical geometry, either with (r, theta) axisymmetry or the (r, phi) spherical annulus geometry (Hernlund and Tackley, PEPI 2008). 

A problem with both of these is that the geometrical restriction forces deformation that is not present in 3 dimensions. Specifically, in a 2-D spherical approximation, a downwelling is forced to contract in the plane-perpendicular direction, requiring it to extend in the 2 in-plane directions. In other words, it is "squeezed" in the plane-perpendicular direction.  If the downwelling has a high viscosity, as a cold slab does, then it resists this forced deformation, sinking much more slowly than in three dimensions, in which it could sink with no deformation. This can cause unrealistic behaviour and scaling relationships for high viscosity contrasts. 

This problem can be solved by subtracting the geometrically-forced deformation ("squeezing") from the strain-rate tensor when calculating the stress tensor. Specifically, components of in-plane and plane-normal strain rate that are required by and proportional to the vertical (radial) velocity are subtracted, a procedure that is here termed "anti-squeeze". It is demonstrated here that this "anti-squeeze" correction results in sinking rates and scaling relationships that are similar to those in 3-D geometry whereas without it, abnormal and physically unrealistic results can be obtained for high viscosity contrasts. This correction has been used for 2-D geometries in the code StagYY (Tackley, PEPI 2008; Hernlund and Tackley, PEPI 2008) since 2010.
Recent advances and new features in the operational cloud products of Sentinel-5 Precursor and prospects for Sentinel-4
Authors: Lutz Ronny , Argyrouli Athina , Romahn Fabian , Loyola Diego , Siddans Richard
Published: March 2020

The measurement of atmospheric composition from space requires also a precise knowledge regarding the appearance of clouds within the observed scene, and if present, a quantification of cloud properties such as cloud fraction, cloud height and cloud optical thickness/cloud albedo. The Copernicus mission Sentinel-5 Precursor, being operational since 2 years, covers the UV/VIS/NIR/SWIR spectral region. By covering the spectral region of the Oxygen A-band in the NIR, it provides an excellent prerequisite to retrieve the cloud parameters mentioned above. The same holds true for the anticipated Sentinel-4 mission (foreseen launch in 2023). In this contribution we present the most recent advances in the algorithms for retrieving the operational cloud products from TROPOMI onboard Sentinel-5 Precursor and from the future Sentinel-4/UVN onboard MTG-S. The applied cloud retrieval algorithms OCRA (Optical Cloud Recognition Algorithm) and ROCINN (Retrieval of Cloud Information using Neural Networks) have their heritage with GOME/ERS-2 and GOME-2 on MetOp-A/B/C, where they have already been successfully implemented in an operational environment. OCRA uses a broad band color space approach in the UV/VIS in combination with a set of cloud-free reflectance background composite maps to determine a radiometric cloud fraction while the ROCINN algorithm retrieves the cloud top height, cloud optical thickness and cloud albedo from NIR measurements in and around the oxygen A-band, taking as a priori input the cloud fraction computed by OCRA. ROCINN includes two different cloud models. One which treats clouds more realistically as layers of scattering water droplets (clouds-as-layers, CAL) and another one which treats clouds as simple Lambertian reflectors (clouds-as-reflecting boundaries, CRB). Substantial improvements to the algorithms have been implemented recently, some of which will be presented here, e.g. improved background maps, inclusion of cloud phase, retrieval of surface properties using machine learning. Further validation efforts via satellite-to-satellite comparisons with VIIRS on Suomi-NPP have been carried out and consolidate the product quality.
Wind estimates in the mesosphere - lower thermosphere retrieved from infrasound data
Authors: Vorobeva Ekaterina , Näsholm Sven Peter , Espy Patrick , Orsolini Yvan , Hibbins Robert
Published: March 2020

We analyze dataset of infrasound observations from surface military explosions in northern Finland which occur yearly in August and September since 1988. The transient nature of these events allows for identification of returns reflected (or scattered) both from stratospheric and from mesospheric - lower thermospheric (MLT) altitudes. The  infrasound data were recorded at Norwegian infrasound-array station around 200 km north of the explosion site. In this study, we use the measured travel-time and backazimuth deviation of the arriving infrasound wavefronts to estimate snapshots of the MLT cross-wind averaged along the propagation path. The spatial extent of that averaging process is explored, and the MLT wind estimates retrieved from infrasound data are presented and compared against high-top atmospheric model winds.
Arctic Ocean near-surface circulation: altimetry and in situ observations along the Transpolar Drift.
Authors: Doglioni Francesca , Ricker Robert , Rabe Benjamin , Kanzow Torsten
Published: March 2020

Recent decades have seen a strong intensification of major circulation systems in the Arctic Ocean, namely the Beaufort Gyre and Transpolar Drift. Observing and studying seasonal, interannual and decadal variability of large-scale Arctic Ocean surface circulation is a key element to understand changes in climate-relevant export of both sea ice and fresh surface water from the Arctic. However, lack of in-situ ocean surface velocity observations have prevented further investigation until recently.

In the past decade, charts of the Arctic geostrophic surface flow field have been derived from new satellite altimetry missions over the ice-covered oceans, such as CryoSat-2, which was launched in 2010. The altimetric measurements allow the detection of leads and therefore to retrieve sea surface height (SSH) across the ice-covered Arctic Ocean. Aiming to characterize the seasonal to interannual variability of geostrophic surface currents in the Transpolar Drift, we use SSH observations from the Cryosat-2 mission between 2011 and 2018.

Here we present an evaluation of optimally interpolated altimetric SSH anomalies against in situ ocean observations of both bottom pressure and dynamic Height in Fram Strait and north of Arctic Cape, in the years between 2016 and 2018. Following the assessment of the quality of altimetry-based SSH, we discuss the timescales of SSH variability in seasonally ice-covered regions. Moreover, from the comparison with ocean bottom pressure and dynamic height we will attribute the relative importance of mass and steric contributions to the variability of SSH along the two transects. From first preliminary results in a test year (2011), SSH at a meridional transect in central Fram Strait between 78°N and 80°N shows a seasonal cycle with minimum in the months of March and April, enhanced at the most southern mooring. 
What happens when the ice is gone? A hydrological journey into the glacier forefield subsurface
Authors: Müller Tom , Schaefli Bettina , Lane Stuart N.
Published: March 2020

Rapid glacier recession related to recent climate change in Alpine regions is exposing large areas of previously ice-covered till and bedrock. These newly created proglacial areas are composed of poorly sorted sediments and debris of mixed subglacial (till), englacial and supraglacial origin. They are subject to rapid geomorphological and ecological modifications. They also constitute potential new groundwater reservoirs for rain, snowmelt and ice melt. The hydrology of such glaciated catchments is therefore evolving, but the connectivity between glacier meltwater and other paraglacial structures such as talus slopes, outwash plains or small lakes to these areas remains unclear. We propose a conceptual model of water connectivity and storage based on the Otemma glacier, one of the largest Swiss glaciers, which summarizes the key geomorphological structures and their hydrological functions. In particular, we combine multiple field data such as water table fluctuations, river discharge, isotopic analysis and geophysical studies from the proglacial area of the Otemma glacier to show the growing importance of the outwash plain for storing water and maintaining baseflow in these headwater catchments. We show that the accumulation of reworked subglacial till and exported sediments from the glacier create new reservoirs for the storage and release of water which may become larger in regions where the subglacial bedrock has a low slope and where ice is rapidly retreating. These fluvioglacial aquifers are mainly recharged by ice-melt at present but could store more snowmelt and precipitation in the future. The processes influencing sediment export and aggradation combined with future snow and ice melt dynamics are therefore key to understanding the future hydrological functioning of these catchments. River and groundwater dynamics will eventually shape the biodiversity and vegetation succession of these areas that are hotspots for many endemic species and where soil stabilization and development will create a clear feedback on the future sediment and water budget of high Alpine environments.
Late Holocene fire history documented at Lake Khamra, SW Yakutia (Eastern Siberia)
Authors: Glückler Ramesh , Herzschuh Ulrike , Pestryakova Luidmila , Kruse Stefan , Vyse Stuart , Andreev Andrei , Dietze Elisabeth
Published: March 2020

Recent large-scale fire events in Siberia have drawn increased attention to boreal forest fire history. Boreal forests contain about 25% of all global biomass and act as an enormous carbon storage. Fire events are important ecological disturbances connected to the overarching environmental changes that face the Arctic and Subarctic, like vegetation dynamics, permafrost degradation, changes in soil nutrient cycling and global warming, and act as the dominant driver behind boreal forest’s landscape carbon balance. By looking into past fire regimes we can learn about fire frequency and potential linkages to other environmental factors, e.g. fuel types, reconstructed temperature/humidity or geomorphologic landscape dynamics. Unfortunately, fire history data is still very sparse in large parts of Siberia, a region strongly influenced by climate change. The Global Charcoal Database (www.paleofire.org) lists only a handful of continuous charcoal records for all of Siberia, with only three of those featuring published data from macroscopic charcoal as opposed to microscopic charcoal from pollen slides.

We aim to reconstruct the late Holocene fire history using lacustrine sediments of Lake Khamra (SW Yakutia at N 59.99°, E 112.98°). It covers an area of c. 4.6 km² with about 22 m maximum water depth, located within the zone of transition from summer-green and larch-dominated to evergreen boreal forest. We present the first continuous, high-resolution (c. 10 years/sample) macroscopic charcoal record (> 150 μm) including information on particle size and morphology for the past c. 2200 years. We compare this to complementary information from microscopic charcoal in pollen slides, a pollen and non-pollen palynomorph record as well as μXRF data. This multi-proxy approach adds valuable data about fire activity in the region and allows a comparison of different prevalent fire reconstruction methods. As the first record of its kind from Siberia, it provides a long-term context for current fire activity in central Siberian boreal forests and enables a better understanding of the environmental interactions occurring in the changing subarctic landscape.
Measuring and modelling thermal erosion patterns of peat plateaus in northern Norway
Authors: Westermann Sebastian , Martin Leo , Nitzbon Jan , Aas Kjetil , Scheer Johanna , Eiken Trond , Etzelmüller Bernd
Published: March 2020

Peat plateaus are a major type of permafrost landscape in Arctic and Siberian lowlands. They represent a substantial pool of several hundreds of petagrams of organic carbon that has the potential to contribute to the Permafrost Carbon Feedback. The thermal response of these soils to the climate signal is complex and implies the interaction of various surface and subsurface processes operating at a very small spatial scale involving water, snow and heat fluxes and surface subsidence. As these processes have the ability to generate feedbacks between each other and trigger non-linear evolutions of the landscape, they challenge our abilities to measure and model them.

Peat plateaus in Northern Norway have been actively degrading over at least the last 60 years. They thus offer a precious opportunity to measure and model the degradation patterns they exhibit. We present new topographical observations derived from drone-based photogrammetry that we acquired for one site in Northern Norway. Over a period of 3 years, these Digital Elevation Models allows quantifying precisely the surface subsidence and resulting lateral degradation of the peat plateaus. In a second time, we use the land surface model CryoGrid to model the observed patterns. The model is able to (i) simulate the snow fluxes and the water and heat sub-surface fluxes within the plateau and between the plateau and the surrounding wet mire and to (ii) represent the soil surface subsidence due to excess ice melt in the soil. We implement a set up that discretize the interface between the peat plateaus and the wet mire and force the Surface Energy Balance module of the model with climatic data derived from regional atmospheric modelling.

Our simulations manage to reproduce the degradation speed we observe in our topographical data. We also present a sensitivity analysis of the degradation speed to snow cover and to the geometry of the peat plateaus and show how the feedbacks between the dynamical topography and the lateral fluxes of snow and water can trigger rapid permafrost thawing and fast degradation of permafrost landscapes.
On the Nature of Fault Slip: From the Field to the Lab
Authors: Passelegue Francois , Almakari Michelle , Dublanchet Pierre , Barras Fabian , Violay Marie
Published: March 2020

Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. Despite geodetical, seismological, experimental and field observations, the origin of this variation of the rupture velocity in nature, as well as the physics behind it, is still debated. Here, we first discuss the scaling relationships existing for the different types of fault slip observed in nature and we highlight how they appear to stem from the same physical mechanism. Second, we reproduce at the scale of the laboratory the complete spectrum of rupture velocities observed in nature. Our results show that when the nucleation length is within the fault length, the rupture velocity can range from a few millimetres to kilometres per second, depending on the available energy at the onset of slip. Our results are analysed in the framework of linear elastic fracture mechanics and highlight that the nature of seismicity is governed mostly by the initial stress level along the faults. Our results reveal that faults presenting similar frictional properties can rupture at both slow and fast rupture velocities. This combined set of field and experimental observations bring a new explanation of the dominance of slow rupture fronts in the shallow part of the crust and in areas presenting large fluid pressure, where initial stresses are expected to remain relatively low during the seismic cycle.
Exploring the impact of aerosol radiative forcing uncertainty on shifts in ITCZ position and tropical rainfall in the near-term future
Authors: Peace Amy , Booth Ben , Carslaw Ken , Regayre Leighton , Lee Lindsay , Sexton David , Rostron John
Published: March 2020

Anthropogenic aerosol emissions over the industrial period have caused a negative but highly uncertain radiative forcing. This negative radiative forcing has had a cooling effect mainly over the northern hemisphere, affecting the atmospheric interhemispheric energy balance. Consequently aerosols have been linked to observed dynamical responses over the industrial period that depend on the atmospheric interhemispheric energy balance, such as changes in the position of the Intertropical Convergence Zone (ITCZ) and resultant tropical precipitation shifts. However, over the course of the 21st century anthropogenic aerosol emissions are predicted to decline. The reduction in anthropogenic aerosol emissions will cause a positive radiative forcing relative to present day, creating a warming effect in the northern hemisphere. Hence, if the strength of aerosol radiative forcing modulates the magnitude of shifts in the ITCZ, then the large uncertainty in aerosol radiative forcing will limit our understanding of how tropical precipitation will shift in the near-term future.

We use a perturbed parameter ensemble (PPE) of a global coupled climate model to investigate the link between aerosol radiative forcing and ITCZ and tropical rainfall shifts in the near-term future. The PPE consists of 20 simulations of the UK Met Office’s GC3.05 model with parameters perturbed from a range of model schemes. The ensemble was designed to sample uncertainties in future changes, and as a result spans a range of aerosol radiative forcings.

The PPE reveals both northward and southwards shifts in the ITCZ position across the ensemble in the latter half of the 20th century and first half of the 21st century, as well as changes in width and intensity of the ITCZ. We find a correlation between the shift in the ITCZ position and the magnitude of aerosol radiative forcing and AOD trends. However, the correlations in our ensemble are not as strong as those cited in previous studies that use multi-model ensembles. The potential causes of this difference are investigated. We also compare our model output to aerosol, cloud and radiation observations in attempt to identify the most plausible future aerosol-driven climate responses.
Opportunities and challenges in Teaching Structural Geology and Tectonics
Authors: Fusseis Florian , de Bresser Hans , Grasemann Bernhard , Urai Janos , Ustaszewski Kamil , Rogowitz Anna , Anderson Mark
Published: March 2020

In most university geosciences curricula, structural geology and tectonics (SGT) form a core part of teaching. While only a small percentage of Earth science graduates will become structural geologists, many will someday use structural concepts and techniques to solve problems in fields such as nuclear waste storage, the geology of growing urban environments,  geohazards, unconventional reservoirs, geothermal energy, CO2 sequestration, energy storage and more. A basic understanding of structural geology is thus part of a critical knowledge foundation in Earth sciences and many related disciplines. In addition, new tools and data are becoming available at a rapid pace, and enable more integrated, multi-dimensional assessments of the geosphere and our societal interfaces with it. All of this provides new opportunities and challenges for STG courses.

In April 2019, a pre-EGU two-day workshop (TeachSGT21) was organized during which strengths and weaknesses of, and threats to current SGT curricula were analyzed. Participants of the workshop covered 11 European and 2 overseas countries, and came from academia as well as industry. On the basis of the workshop, we now outline educational demands from industry and research and discuss the role and significance of field training. Further, we review initiatives that use innovative tools and techniques in teaching. While not claiming to represent all aspects of modern SGT teaching, we expect that our observations can stimulate reflection on degrees and approach and may help making choices in curriculum renewal.
Data-driven reduced order modelling of tide-induced sand bars in confined channels
Authors: Hepkema Tjebbe , de Swart Huib , Schuttelaars Henk
Published: March 2020

Tidal bars are bed forms in tidal channels that have a wave-like structure in both the along-channel and cross-channel direction. They are found in tidal channels all around the globe, for example, in the Western Scheldt in the Netherlands, the Exe Estuary in England, the Ord River Estuary in Australia and the Venice Lagoon in Italy. Typically, tidal bars are several meters high, have wavelengths of 1-15 km and migration speeds of meters per day. Understanding their dynamics is important as they are invaluable for many living organisms (e.g., migrating birds) but they hamper marine traffic.

 

It has been shown, by means of a linear stability analysis, that these bars emerge due to inherent feedbacks between the tidal currents and the erodible bed. When the bars mature, their dynamics becomes nonlinear. Schramkowski et al. (2004) applied a bifurcation analysis to analyse the bar dynamics, but their method was limited to small bottom friction. Here, we developed a numerical (time integration) model that simulates the nonlinear dynamics and the corresponding (stable) equilibrium patterns for realistic parameter values.

 

Using the output of the numerical model we derive a reduced order model with a method called SINDy (Brunton et al., 2016). Loiseau and Brunton (2018) showed that from output of complex numerical models simulating fully nonlinear fluid flows, SINDy can identify small systems of equations which govern the complex flows. Here we show that, for parameters regimes where the dynamics is weakly nonlinear, SINDy finds a Landau type equation that reproduces the tidal bar dynamics well. The Landau equation is a nonlinear ordinary differential equation in terms of the Fourier amplitude of the pattern that initially has the largest growth rate. The form of this equation corresponds with the one that is expected from the symmetry of the patterns. Also, the application of SINDy to the fully nonlinear dynamics of tidal bars will be discussed.

 

 

Brunton, S.L., Proctor, J.L., and Kutz, J.N. (2016). Discovering governing equations from data by sparse identification of nonlinear dynamical systems. Proceedings of the National Academy of Sciences, 113(15):3932-3937.

Loiseau, J.-C. and Brunton, S.L. (2018). Constrained sparse Galerkin regression. Journal of Fluid Mechanics, 838:42-67.

Schramkowski, G.P., Schuttelaars, H.M., and de Swart, H.E. (2004). Nonlinear channel-shoal dynamics in long tidal embayments. Ocean Dynamics, 54(3):399-407.