bluuebunny/crossref_metadata_2025 huggingface dataset:
Cooling of the Northern Hemisphere triggered by Northeast Atlantic opening at the Eocene – Oligocene Transition 
Authors: Straume Eivind , Nummelin Aleksi , Gaina Carmen , Nisancioglu Kerim
Published: March 2021

The Eocene – Oligocene Transition (~33.7 million years ago), marks the largest step transformation within the Cenozoic cooling trend, and is characterized by a sudden growth of the Antarctic ice sheets. The role of changes in oceanic basin configuration and the evolution of key oceanic gateways in triggering these climatic variations remains disputed. Here we implement a new state-of-the-art paleogeography model in the Norwegian Earth System Model (NorESM-F) to investigate the effect of oceanic gateway changes on the Eocene – Oligocene climate. We run different cases using realistic max/min depth configurations of the Atlantic – Arctic oceanic gateways, the Tethys Seaway, and the Southern Ocean gateways, and investigate the ocean and climate sensitivity to these changes. In addition, we run separate simulations investigating the impact on the carbon cycle. The models show that changes in the Atlantic – Arctic gateways (i.e. Greenland – Scotland Ridge and the Fram Strait) cause the most significant changes in ocean circulation and climate compared to the Southern Ocean gateways or the Tehthys Seaway. The Iceland mantle plume caused depth variations on the Greenland – Scotland Ridge at this time, and our model result indicate that variations in dynamic support from the Iceland plume could have played a key role in the Eocene – Oligocene climate transition. Essentially, reduced dynamic support from the plume deepen the Greenland – Scotland Ridge and cause freshwater leakage from the Arctic Ocean which inhibits deep water formation in the North Atlantic, reducing the AMOC and ultimately cool the Northern Hemisphere.
Space-borne terrain deformation monitoring for large infrastructure projects
Authors: Frauenfelder Regula , Vöge Malte , Salazar Sean E. , Hauser Carsten
Published: March 2021

Ground settlement and associated deformation of existing infrastructure is a major risk in urban development projects. Project owners have a responsibility to document and manage settlement records before, during and after construction works. Traditionally, land surveying (e.g. leveling and total station) techniques have been the state-of-practice to provide settlement monitoring data. However, in big infrastructure projects, conventional geodetic data acquisition is a major cost driver. Modern space-borne radar interferometry (InSAR) provides the opportunity to drastically increase the number of monitored locations, while at the same time reducing expenses for traditional geodetic survey work. Furthermore, the method allows for highly effective monitoring during all phases of a project.

The application of InSAR technology is demonstrated for three large development projects near Oslo, the capital of Norway. Showcase examples include a new highway development project and two railway line upgrade projects. In two of the cases, InSAR monitoring was performed by exploiting very high resolution TerraSAR-X data (ca. 1.5 x 1.5 m spatial ground resolution), and in one case, using high resolution Radarsat-2 data (ca. 7 x 7 m spatial ground resolution). A combined area of 127 km2 was monitored for all three projects, yielding a total of roughly 800,000 measurement points on the ground. Achieved measurement point density based on the TerraSAR-X data was around 37,000 points per km2, while density based on the Radarsat-2 data resulted in approximately 6,000 points per km2 in built-up areas. Both data resolutions offer millimetric deformation precision, with surfaces of buildings and infrastructure providing the best signal reflection and phase coherence, resulting in high-quality results. In all cases, the interferometric time series analyses were communicated to the end users through a web-based map portal, enabling simple visual interpretation of the results, as well as integration with the settlement records of the project.
Decadal predictability in the North Atlantic as seen by EC-Earth3.
Authors: Christiansen Bo , Yang Shuting , Matte Dominic
Published: March 2021

We study the decadal predictability in the North Atlantic region using  ensembles of historical and decadal prediction experiments with EC-Earth3  and other CMIP models. In particular, the focus is on the NAO and the sub-polar gyre region. In general the impact of initialization is weak  for lead-times larger than one to two years and we investigate different ways to isolate and estimate the statistical significance of this impact. For the sub-polar gyre region the prediction skill is found to be mainly due to an abrupt change in the late 90ies and models disagree on whether this skill is due to forcing or initial conditions. Also the predictability of the NAO is weak and varies with lead-time and length of the predicted period. We only see weak evidence of the 'signal-to-noise paradox'. The importance of the ensemble size is also studied.                                                              
Tectonic evolution of the Paleo-Tethys Ocean in Southwest Guangxi: evidence from acidic magmatic rocks in the Pingxiang area, SW China
Authors: Huang Wenmin , Liu Xijun , Li Zhenglin , Zhao Bing , Han Yiying
Published: March 2021

Early Mesozoic development of Southeast Asia involved oceanic subduction, closure, accretion and collision of discrete terranes rifted from Gondwana. South China, as an important continental terrane, is bound to the north by the Qinling-Dabie collisional orogenic belt, to the south by the Indochina Block, and to the east by the Pacific Plate. The role of continental collision and subduction during the Early Mesozoic development of South China has sparked the interest of geologists worldwide and stimulated considerable research. The Triassic tectonic history of the southwestern South China Block is marked by the Indosinian orogeny that records amalgamation of the Indochina and South China blocks during the late Permian to Triassic as a result of closure of the eastern branch of the Paleo-Tethys Ocean. In South China, there is widespread granitic magmatism, metamorphism and deformation. The closure of eastern Paleo-Tethys Ocean and subsequent collision between the South China block and Indochina Block has caused the collision zone metamorphism and formation of granites during the Permo-Triassic, with the Song Ma fault zone as the collision boundary. The Indosinian magmatism in the Pingxiang region was the magmatic products in this period. We report the new results of bulk-rock major and trace element, Nd, Hf isotopic compositions and zircon U–Pb dating of granites and rhyolites in the Pingxiang region in Guangxi Province, Southwest China, to decipher their petrogenesis and tectonic settings. The granites and rhyolitics in the Pingxiang area have low Mg# values (11.1–36.7), low Nb/Ta ratios (9.26–13.74) exhibiting a both affinity from S-type to I-type granaite. The isotopic features of these rocks show negative εHf(t) with the values ranging from -9.89 to -6.09, negative εNd(t) values ranging from -12.89 to -12.02 and T2DM values of 1.8–3.3 Ga, suggesting that the Pingxiang granites and rhyolites was derived from partial melting of paleoproterozoic crust rocks. The granites yielded 206Pb/238U ages ranging from 243 to 241 Ma, and the rhyolites yielded 206Pb/238U ages ranging from 247 to 245 Ma, which are both within the age range of the subduction to collision. Combine the regional geology, we suggest these granitoids and rhyolites were formed by the partial melting of crustal rocks during a transition from subduction to post-collisional environment with closure of Paleo-Tethys Ocean between the South China block and Indochina Block.

This study was financially supported by Guangxi Natural Science Foundation for Distinguished Young Scholars (2018GXNSFFA281009) and the Fifth Bagui Scholar Innovation Project of Guangxi Province (to XU Ji-feng).
Downscaling of a seasonal ensemble forecast at the convection-permitting resolution over the Horn of Africa using the WRF model
Authors: Mori Paolo , Schwitalla Thomas , Ware Markos , Warrach-Sagi Kirsten , Wulfmeyer Volker
Published: March 2021

Studies have shown the benefits of convection-permitting downscaling at the seasonal scale using limited-area models. To evaluate the performance with real forecasts as boundary conditions, four members of the SEAS5 global ensemble were dynamically downscaled over Ethiopia during June, July, and August 2018 at a 3-km resolution. We used a multi‐physics ensemble based on the WRF model to compare the effects of boundary conditions and physics parametrization producing 16 ensemble members. With ECMWF analyses as a reference, SEAS5 averaged to a +0.17°C bias over Ethiopia whereas WRF resulted in +1.14°C. With respect to precipitation, the WRF model simulated 264 mm compared to 248 mm for SEAS5 and 236 mm for GPM-IMERG. The maximum northward extension of the tropical rain belt decreased by about 2° in both models. Downscaling enhanced the ensemble spread in precipitation by 60% on average, correcting the SEAS5 underdispersion. The WRF ensemble spread over Ethiopia was mostly generated by the perturbed boundary conditions, as their effect is often 50% larger than the physics‐induced variability. The results indicate that boundary condition perturbations are necessary, although not always sufficient, to generate the right amount of ensemble spread in a limited-area model with complex topography. The next step is to use specific methods to calculate the added value provided by the downscaling.
Investigation of Land Subsidence Phenomena in the wider Tirana (Albania) Region by applying Persistent Scatterer Interferometry Techniques
Authors: Skenderas Doris , Loupasakis Constantinos , Papoutsis Ioannis , Alatza Stavroula , Kontoes Charalampos (Haris)
Published: March 2021

The occurrence of land subsidence phenomenon has been investigated for the wider area of the city of Tirana, Albania.  A set of Ninety-four SAR images acquired between January 2015 and 23 of November 2019 by the European Space Agency (ESA) Sentinel1, have been processed by applying the Persistent Scatterer Interferometry (PSI).

Interpretation of PSI analysis output results, revealed subsidence deformations at the northwest and near the center of Tirana, mainly due to natural land compaction. The deformation rates reach up to 9.6 mm/yr.

The most intensive phenomena have been identified at the Laknas and Breg Shkoze- Rinas regions. In particular at the ``Mother Tereza`` National Airport of Tirana, located at the Rinas area, land subsidence ranges between 2.3mm/yr and 4.5mm/yr.  Whereas in Tirana e Re, close to the city center, less intensive subsiding movements have been identified, ranging from 1.5 to a maximum of  5.2 mm/yr.    

By evaluating geological, geotechnical, and hydrological data it was determined that except for Laknas, in all other areas, land subsidence is caused by natural compression of alluvial deposits of the Ishmi River. At the Laknas zone, besides natural compression, water withdrawal due to over pumping of ground water can be identified as well. This was proved by the piezometric surface monitoring data referring to the period 2015-2019.

Besides the interesting findings about the deformation pattern at the wider area of Tirana, the current study highlights the potential of PSI as a suitable, accurate, and cost-efficient technique for the study of land subsidence phenomena.
A data-driven generative model for sea surface temperature fields in the tropical Pacific
Authors: Schlör Jakob , Goswami Bedartha
Published: March 2021

The most dominant mode of oceanic climate variability on an interannual scale is the El Niño-Southern Oscillation (ENSO), which is characterized by anomalous sea surface temperatures (SSTs) in the equatorial Pacific. The SST fields associated with ENSO show strong variability between different events, also known as ENSO diversity. While the diversity of SST patterns have a strong impact on local climate, ecosystem and society, the spatial differences between ENSO events are not yet fully understood.

In this work, we present a data-driven approach to model SST anomaly patterns in the Pacific using a deep generative model. In particular, we use a variational autoencoder (VAE) to nonlinearly decompose the monthly SST anomalies into a low dimensional ‘latent’ space. VAEs are probabilistic models with neural network transition functions which allow us to model nonlinear features, quantify uncertainty, and include prior knowledge. In our approach, we use mutual information to favor a disentangled latent space with respect to a ground truth derived from correlation-based spatial SST clustering. The VAE-based approach improves upon earlier non-linear dimensionality reduction methods like kernel PCA which only optimize for statistical properties.

Our results indicate that the anomalous SST field diversity can be explained primarily by 1) an eastern equatorial Pacific component, 2) a central equatorial Pacific component and 3) a transequatorial component. The components capture underlying spatial correlations to regions in the Northern Pacific and to the basin wide horseshoe pattern. We also observe an asymmetry between the warm and cool phases of the components.
Finite-frequency effects for imaging underground cavities
Authors: Schneider Felix M. , Kolínský Petr , Bokelmann Götz
Published: March 2021

We study finite-frequency effects that arise in cavity detection. The task comes along with the Onsite-Inspection part for the Comprehensive Nuclear Test Ban Treaty (CTBT), where the remnants of a potential nuclear test need to be identified. In such nuclear tests, there is preexisting knowledge about the depths at which nuclear tests may take place, and also about sizes that such cavities can attain. The task of cavity detection has consistently been a difficult one in the past, which is surprising, since a cavity represents one of the strongest seismic anomalies one can ever have in the subsurface. A conclusion of this study is that considering finite-frequency effects are rather promising for cavity detection, and that it is worthwhile to take them into account. We utilize an analytical approach for the forward problem of the a seismic wave interacting with a underground cavity in order to develop an inversion routine that finds and detects an underground cavity utilizing the transmitted wave-field.

 
A new VLF radio receiver in Greece for the detection of lower ionosphere anomalies before strong seismic events and the preliminary results for a strong (6.7 Mw) earthquake that occurred in Samos (Greece) on 30/10/2020.
Authors: Politis Dimitrios , Potirakis Stelios , Biswas Sagardweep , Sasmal Sudipta , Hayakawa Masashi
Published: March 2021

A new VLF/LF (10 - 47.5 kHz) radio receiver has recently been installed in the University of West Attica, in Athens (Greece), and has been operating in trial mode since April 2020 for the study of sub-ionospheric propagation variations, mainly aiming at the identification of possible earthquake (EQ) precursors or signatures of other extreme geophysical phenomena. The receiver is monitoring signals from a number of transmitters. Most of them are located in Europe, while some are located in Asia, Australia and North America. The recorded data (amplitude and phase) from this receiver are sampled at a rate of 1 sample per second. In this paper we present information about the new VLF/LF receiver as well as preliminary results concerning a very recent, strong (Mw = 6.7), shallow (focal depth = 12 km), EQ that occurred in Greece (epicenter located in the Aegean Sea, off-coast of the Samos island, close to the Greece-Turkey borders) on 30/10/2020, hereafter referred to as Samos’ EQ. The subionospheric propagation data associated with two specific transmitters were analyzed. Τhe first transmitter, with call sign TBB, is located in Denizköy (Turkey) and the location of Samos’ EQ epicenter is within of 5th Fresnel zone of the corresponding propagation path. The second transmitter, with call sign ISR, is located in Negev (Israel) and the location of Samos’ EQ epicenter is in close distance to the borders of the 5th Fresnel zone, so that, considering the magnitude of the specific EQ, the corresponding propagation path could possibly be disturbed. In this paper we present the analysis of the receiver’s amplitude data by means of the Terminator Time Method (TTM) in order to reveal any possible pre-seismic anomaly in the lower ionosphere. Our preliminary results show that there are indications for disturbance of the lower ionosphere a few days before the EQ occurrence.
Salt thickness and heterogeneity control the degree of coupling between sub- and supra-salt structure during salt-detached translation: evidence from physical models
Authors: Evans Sian , Jackson Christopher , Schueller Sylvie , Mengus Jean-Marie
Published: March 2021

Salt flows like a fluid over geological timescales and introduces significant structural complexity to the basins in which it is deposited. Salt typically flows seaward due to tilting of the basin margins, and is therefore influenced by the geometry of the surface that it flows across (e.g. fault scarps or folds on the base-salt surface). This can lead to coupling of sub- and supra-salt structures, with the orientation and distribution of base-salt structures reflected in the structure of the overburden. However, precisely what controls the degree of strain coupling during salt-detached translation is still poorly understood, in particular the role played by salt thickness and lithological heterogeneity. This partly reflects the fact that it can be difficult to deconvolve the relative contributions of natural variables such as the magnitude of relief, sediment supply, and regional tectonic regime. In addition, seismic data provide only the present structural configuration of salt basins, from which their formative kinematics must be inferred. If we can develop a better understanding of how sub-salt structure controls the types and patterns of supra-salt deformation, we can produce better kinematic (structural) restorations of salt basins and, therefore, have a better understanding of the related mechanics.

In order to isolate the influence of salt thickness and heterogeneity on sub- to supra-salt strain coupling during salt-detached horizontal translation, we present a series of physical analogue models with controlled boundary conditions. We use a simple base-salt geometry comprising three oblique base-salt steps, and vary the thickness and composition of the ductile salt analogue in each experiment. X-ray tomography allows us to image the internal structure during model evolution and therefore gain a 4D picture of its structural development.

Results show that thicker and more homogeneous salt units experience more vertical movement (i.e. minibasin subsidence and diapiric rise) and the overburden structure is less explicitly coupled with the underlying base-salt relief. Conversely, thinner and more heterogeneous salt units restrict vertical movement, and therefore the resulting overburden structure is dominated by lateral movement and more closely coupled to the geometry of the base-salt surface. These results highlight the important role of base-salt relief in the subsequent structural evolution of salt basins and why, despite broad similarities between different salt basins, there is significant variability in their structural styles.
Submarine landslide tsunamis in SW Iberia Margin: Sensitivity of tsunamigenic potential and hazard extent to physical properties of marine sediments
Authors: Ramalho Inês , Omira Rachid , Piedade Aldina , Gamboa Davide , Grazina José , Lemos Luís
Published: March 2021

Slope instability is probably the most eﬀective process shaping the seaﬂoor of continental margins. This process often leads to the occurrence of submarine mass failures that, if large enough, can cause potential tsunamis. Yet, the dynamics of the landslide evacuated material and their induced tsunamigenic potential remain largely uncharacterized in most continental margins. This applies to the SW Iberia Margin, where large underwater landslide episodes have been evidenced.

In this work, we investigate the sensitivity of landslide-generated tsunami to the physical properties of marine sediments involved in the slope failures in the SW Iberia Margin. This includes the landslide dynamics, the tsunamigenic potential and the tsunami hazard extent. Based upon the MAGICLAND (Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin) project database, we select promising sizable submarine landslide scenarios. We then use an in-house developed two-layer numerical code (based on a Bingham visco-plastic model for the landslide and a non-linear shallow water model for the tsunami) to simulate both the landslide dynamics and the induced tsunami generation and propagation.

In a first stage, the numerical simulations are done considering uncertain sediments properties deduced from the literature. Next, we perform numerical simulations of the selected landslide scenarios using accurate geotechnical properties (mainly the in-situ shear strength obtained from undisturbed samples) determined by laboratory tests conducted on from the analysis of available marine gravity cores in the SW Iberian Margin. Results show that the geotechnical parameters significatively influence the simulation results of both the landslide dynamics and induced tsunami. Particularly, we noticed major effects on the landslide downslope deformation, failure speed, deposited thickness and run-out, which considerably control the momentum transferred to the generated tsunami wave. This demonstrates that the use of inappropriate material properties leads to a misquantification of landslide tsunamigenesis and hazard extent.

This work was financed by national funds through FCT—Portuguese Foundation for Science and Technology, I.P., under the framework of the project MAGICLAND – Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin (PTDC/ CTA-GEO/30381/2017).
Effects of simulated nitrogen deposition increase on plant nutritional status and physiological responses at two contrasting Beech forest sites in Italy
Authors: Teglia Alessandra , Di Baccio Daniela , Magnani Federico , Giorgio Matteucci , Scartazza Andrea , De Cinti Bruno , Mazzenga Francesco , Muzzi Enrico , Ravaioli Dario , Marcolini Graziella
Published: March 2021

Anthropogenic activities resulted in a significant increase in nitrogen (N) compounds in the atmosphere and their deposition back to the biosphere, with important implications on both carbon (C) and N cycles. Indeed, an increase in N deposition can increase forest productivity in N limited forest ecosystems. In addition, it can also increase N loss pathways, leading to soil acidification and nutrient imbalance. Several N manipulation experiments have been carried out for decades till now, though most of them focused on conifer forests. We consider two manipulation experiments established in 2015 on two beech (Fagus sylvatica L.) forests in Italy, Cansiglio and Collelongo sites, located on the Eastern Alps and Central Apennines, respectively. The two forests were chosen along a climate and N deposition gradient. Thus, our goal was to assess the effects of simulated N deposition increase on nutritional, physiological status and growth of beech forests from two contrasting climatic conditions. At both sites, N was added directly to the soil as NH4NO3 in two doses: 30 kg N ha-1 yr-1 and 60 kg N ha-1 yr-1. Moreover, in Cansiglio we also included a canopy N fertilization adding 30 kg N ha-1 yr-1. Leaves were collected in 2016 and 2018 for the analyses of nutrients, stable C and N isotopes, and photosynthetic pigments. The aboveground production was periodically monitored with girth band and litterfall collectors. The nutrient stoichiometry analysis showed elevated N concentrations and high N:P in both forests, even in the control plots. N addition significantly increased N:P and N:S ratios in the treated plots. Changes in chlorophyll concentration were mainly related to differences between the two sites, while carotenoids were also influenced by N fertilization. After four years, we did not find an effect of the treatment (regardless of the doses) on both tree growth and leaf biomass. Altogether, our results suggest that both forests were not N limited. Finally, difference between the two manipulation approaches will be discussed in terms of leaf nutrients and C and N stable isotopes in the case of Cansiglio site.
Reactive Transport Modelling applied to Ni laterite ore deposits in New Caledonia : Impact of discrete fractures on Ni mineralization
Authors: Favier Sylvain , Teitler Yoram , Golfier Fabrice , Cathelineau Michel
Published: March 2021

Laterite nickel-ore formation in New Caledonia is classically assumed to be governed by supergene processes, and downward migration of waters with Ni-enrichment at the basis of the laterite profile. However, Ni-ore distribution's heterogeneity seems to have been favoured by secondary processes controlled by the combined effects of inherited tectonics, geomorphological evolution and hydrologic systems since the primary laterite formation. Fluid flow and mass transfer processes are not purely downward at low-temperature conditions, but can also be related to lateral fluid circulations, and local drainage along damaged zones in the vicinity of faults (Cathelineau et al., 2016a; 2016b; Myagkiy et al., 2019). This study aims to investigate through reactive transport modelling the impact of discrete fracture on the Ni distribution.

We simulate the dissolution of olivine profile where fractures are the main channels of the fluid-flow. Olivine dissolution is assumed to be kinetically controlled whereas the precipitation of secondary weathering products is considered to occur according to local equilibrium. Results from two different numerical approaches are presented and discussed. The first one is based on a 1D dual-porosity model of a vertically oriented column of serpentinized olivine using PhreeqC associated with the llnl.dat thermodynamic database. The second one is a 2D modelling of hydro-chemical processes in fractured porous media based on the coupling of PhreeqC and Comsol Multiphysics through ICP. While the 1D model aims to describe the general trend of the progression of the weathering front and the global mineral redistribution, the 2D model focuses on particular fracture geometry and hotspot moments of the dissolution process to highlight crucial transition and redistribution of the different mineral phases in relation with the spatial distribution of fractures.

In the 1D dual-porosity model, the fractures are modelled as advective cells connected to a diffusive cell containing the main part of olivine. Two different geochemical models are thus designed. The first one describes the fracture and the advective area's geochemical behaviour, while the second one focuses on the matrix in the diffusive area. The 2D model extends the work initiated by Myagkiy et al. (2019) on simple configurations. The fractures are modelled herein as 1D discrete surfaces interacting with a porous matrix of olivine. Different fracture configurations are studied to assess their impact on mineral redistribution.

Results from both modellings are then compared with observed field data from New Caledonia and previous modelling of an olivine profile without fractures (Myagkiy et al., 2017) to validate the models and highlight the differences induced by the fracture network.
Estimates of future flood risk in Western Europe and its potential impact on insured losses.
Authors: Meynadier Remi , Rakotoarimanga Hugo , Deroche Madeleine-Sophie , Buisine Sylvain
Published: March 2021

The large-scale and complex nature of climate change makes it difficult to assess and quantify the impact on insurance activities. Climate change is likely affecting the probability of natural hazard occurrence in terms of severity and/or frequency.

Natural catastrophe risk is a function of hazard, exposure and vulnerability. As a (re)-insurer it is seen that changes in year-on-year losses are a function of all these components and not just the hazard.

The present study focuses, in a first step, on assessing impacts of climate change on fluvial flood risks in Europe solely due to changes in hazard itself. A stochastic catalogue of future flood risk events is derived from Pan-European data sets of river flood probability of occurrence produced within EU FP7 RAIN project. The loss modelling framework internally developed at AXA is then used to provide a geographical view of changes in future flood risks.

 
Automatic detection of magnetopause and bow shock crossing signatures in MESSENGER magnetometer data using Convolutional Neural Networks.
Authors: Lavrukhin Alexander , Parunakian David , Nevskiy Dmitry , Julka Sahib , Granitzer Michael , Windisch Andreas , Möstl Christian , Reiss Martin A. , Bailey Rachel L. , Amerstorfer Ute
Published: March 2021

During its 2011-2015 lifetime the MESSENGER spacecraft completed more than 4000 orbits around Mercury, producing vast amounts of information regarding the planetary magnetic field and magnetospheric processes. During each orbit the spacecraft left and re-entered the Hermean magnetosphere, giving us information about more than 8000 crossings of the bow shock and the magnetopause of Mercury's magnetosphere. The information obtained from the magnetometer data offers the possibility to study in depth the structures of the bow shock and magnetopause current sheets and their shapes. In this work, we take a step in this direction by automatically detecting the crossings of bow-shock and magnetopause. To this end, we propose a five-class problem and train a Convolutional Neural Network based classifier using the magnetometer data. Our key experimental results indicate that an average precision and recall of at least 87% and 96% can be achieved on the bow hock and magnetopause crossings by using only a small subset of the data. We also model the average three-dimensional shape of these boundaries depending on the external interplanetary magnetic field . Furthermore, we attempt to clarify the dependence of the two boundary locations on the heliocentric distance of Mercury and on the solar activity cycle phase. This work may be of particular interest for future Mercury research related to the BepiColombo spacecraft mission, which will enter Mercury’s orbit around December 2025.
Observations of CO2 clouds on Mars from TIRVIM and NIR solar occultation measurements onboard TGO
Authors: Luginin Mikhail , Ignatiev Nikolay , Fedorova Anna , Trokhimovskiy Alexander , Grigoriev Alexey , Shakun Alexey , Montmessin Franck , Korablev Oleg
Published: March 2021

Carbon dioxide is the major constituent of the Martian atmosphere. Its seasonal cycle plays an important role in atmospheric dynamics and climate. Formation of the polar CO2 frost deposits results in up to 30% of atmospheric pressure variations as well as in dramatic change in surface reflectance and emissivity. Another case of carbon dioxide condensation is formation of a CO2 clouds that are still poorly studied, despite the fact that they have been observed by a number of instruments [1−6] on the orbit of Mars.

In this work, we will present first results of CO2 clouds observations from a combination of thermal-infrared (1.7−17 µm) and near-infrared (0.7-1.6 µm) spectra measured by TIRVIM and NIR instruments onboard the ExoMars Trace Gas Orbiter (TGO) in solar occultation geometry. These instruments are part of the Atmospheric Chemistry Suite (ACS), a set of three spectrometers (NIR, MIR, and TIRVIM) that is conducting scientific measurements on the orbit of Mars since the spring of 2018 [7].

This work was funded by Russian Science Foundation, grant number 20-42-09035.

References

[1] Montmessin et al. (2006). Subvisible CO2 ice clouds detected in the mesosphere of Mars. Icarus, 183, 403–410. https://doi.org/10.1016/j.icarus.2006.03.015

[2] Montmessin et al. (2007). Hyperspectral imaging of convective CO2 ice clouds in the equatorial mesosphere of Mars. Journal of Geophysical Research, 112, E11S90. https://doi.org/10.1029/2007JE002944

[3] Määttänen et al. (2010). Mapping the mesospheric CO2 clouds on Mars: MEx/OMEGA and MEx/HRSC observations and challenges for atmospheric models. Icarus, 209, 452–469. https://doi.org/10.1016/j.icarus.2010.05.017

[4] McConnochie et al. (2010). THEMIS-VIS observations of clouds in the Martian mesosphere: Altitudes, wind speeds, and decameter-scale morphology. Icarus, 210, 545–565. https://doi.org/10.1016/j.icarus.2010.07.021

[5] Vincendon et al. (2011). New near-IR observations of mesospheric CO2 and H2O clouds on Mars. Journal of Geophysical Research, 116, E00J02. https://doi.org/10.1029/2011JE003827

[6] Jiang et al., (2019). Detection of Mesospheric CO 2 Ice Clouds on Mars in Southern Summer. Geophysical Research Letters, 46(14), 7962–7971. https://doi.org/10.1029/2019GL082029

[7] Korablev et al., (2018). The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev. 214, 7. doi:10.1007/s11214-017-0437-6
Open Polar: a new freely search service of publications and research data of Polar Regions
Authors: Abu-Alam Tamer , Nilsen Karl Magnus , Odu Obiajulu , Longva Leif , Aspaas Per Pippin
Published: March 2021

Research data plays a key role in monitoring and predicting any natural phenomena, including changes in the Polar Regions. The limited access to data restricts the ability of researchers to monitor, predict and model environmental changes and their socio-economic repercussions. In a recent survey of 113 major polar research institutions, we found out that an estimated 60% of the existing polar research data is unfindable through common search engines and can only be accessed through institutional webpages. In social science and indigenous knowledge, this findability gap is even higher, approximately 84% of the total existing data. This raises an awareness sign and the call for the need of the scientific community to collect information on the global output of research data and publications related to the Polar Regions and present it in a homogenous, seamless database.

In this contribution, we present a new, open access discovery service, Open Polar, with the purpose of rendering polar research more visible and retrievable to the research community as well as to the interested public, teachers, students and decision-makers. The new service is currently under construction and will be hosted by UiT The Arctic University of Norway in close collaboration with the Norwegian Polar Institute and other international partners. The beta version of the Open Polar was made available in February 2021. We welcome comments and suggestions from the scientific community to the beta version, while we plan to launch the stable production version of the service by summer 2021. The beta version of the service can already be tested at the URL: www.openpolar.no
Structural, Hydrologic, and Sediment Connectivity in a Shrub-Encroached and Restored Semiarid Grassland
Authors: Johnson Justin , Williams Jason , Guertin Phillip , Archer Steven , Heilman Philip , Pierson Frederick , Wei Haiyan
Published: March 2021

Shrub encroachment of semiarid grasslands is influenced by connected runoff and erosion patterns that preferentially accumulate resources under vegetated patches (canopy microsites) and deplete interspaces. Soil loss from dryland hillslopes results when areas of bare ground become structurally and functionally connected through overland flow. Although these patterns have been well-described, uncertainty remains regarding how these feedbacks respond to restoration practices. This study compared the structure and hydrologic function of a shrub-encroached semiarid grassland treated five years prior with the herbicide, tebuthiuron, to that of an adjacent untreated grassland. Through a series of hydrologic experiments conducted at increasing spatial scales, vegetation and soil structural patterns were related to runoff and erosion responses. At a fine scale (0.5 m2), rainfall simulations (120 mm·h-1 rainfall intensity; 45 min) showed herbicided shrub canopy microsites had greater infiltration capacities (105 and 71 mm·h-1 terminal infiltration rates) and were less susceptible to splash-sheet erosion (3 and 26 g sediment yield) than untreated shrub canopy microsites, while interspaces were statistically comparable between study sites. Concentrated flow simulations at a coarse scale (~9 m2) revealed that gaps between the bases of vegetation (i.e. basal gaps) > 2 mwere positively related to both concentrated flow runoff (r = 0.72, p = 0.008) and sediment yield (r = 0.70, p = 0.012). Modeled hillslope-scale (50 m2) runoff and erosion (120 mm·h-1 rainfall intensity; 45 min) indicated less soil loss in the tebuthiuron-treated site (1.78 Mg·ha-1 tebuthiuron; 3.19 Mg·ha-1 untreated), even though runoff was similar between sites. Our results suggest interspaces in shrub-encroached grasslands continue to be runoff sources following herbicide-induced shrub mortality and may be indicators of runoff responses at larger spatial scales. In contrast, sediment sources are limited post-treatment due to lesser sediment detachment from sheet-splash and concentrated flow processes. Reduced sediment supplies provide evidence that connectivity feedbacks that sustain a shrub-dominant ecological state may have been dampened post-treatment. Our study also highlights the utility of simple measures of structural connectivity, such as basal gaps, as an indicator of hillslope susceptibility to increased runoff and erosion.
The timing of fjord formation and early glaciations in North and Northeast Greenland
Authors: Pedersen Vivi Kathrine , Larsen Nicolaj Krog , Egholm David Lundbek
Published: March 2021

The timing and extent of early glaciations in Greenland, and their co-evolution with the underlying landscape remain elusive. In this study, we explore the timing of fjord formation in Northeast and North Greenland, between Scoresby Sund (70°N) and Independence Fjord (82°N). By determining the timing of fjord formation, we can improve our understanding of the early history of the Greenland Ice Sheet in these regions. We use the concept of geophysical relief to estimate fjord erosion volumes and calculate the subsequent flexural isostatic response to erosional unloading. The timing of erosion and isostatic uplift is constrained by marine sediments of late Pliocene-early Pleistocene age that are now exposed on land between ~24 and 230 m a.s.l. The late Pliocene-early Pleistocene sediments themselves attest to a time of limited ice cover in Greenland, with temperatures as much as 6-8 °C higher than present (e.g. Bennike et al., 2010).

We find that the northern Independence Fjord system must have formed by glacial erosion since the deposition of the marine late Pliocene-early Pleistocene sediments at ~2.5 Ma, in order to explain the current elevation of the sediments by erosion-induced isostatic uplift. In contrast, fjord formation in the outer parts of southward Scoresby Sund commenced prior to the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene with fjord formation progressing inland. Our results suggest that the inception of the Greenland Ice Sheet began in the central parts of Northeast Greenland before the Pleistocene and spread to North Greenland only at the onset of the Pleistocene. 

References:

Bennike, O., Knudsen, K.L., Abrahamsen, N., Böcher, J., Cremer, H., and Wagner, B., 2010, Early Pleistocene sediments on Store Koldewey, north­east Greenland: Boreas v. 39, p. 603–619, https://doi.org /10.1111/j.1502-3885.2010.00147.x.
From weekly to seasonal variability of the North Brazil - Equatorial Undercurrent retroflection
Authors: Vallès Casanova Ignasi , Pelegrí Josep Lluís , Martín Rey Marta , van Sebille Erik , Olivé Abelló Anna
Published: March 2021

The northward flow in the western tropical Atlantic Ocean is carried mainly by North Brazil Current (NBC), hence playing a major role in the cross-equatorial exchange of properties. As thermocline waters reach the equator, they largely retroflect to feed the Equatorial Undercurrent (EUC), a quasi-permanent zonal current that brings salty and highly-oxygenated waters to the eastern side of the basin. This retroflection system is governed by the zonal pressure gradient, which is driven by the trade winds. Hence, the wind fluctuations represent the major source of variability at seasonal and interannual scales. However, at shorter time scales, the variability of the retroflection system may be associated with both interior and coastal waves. In the present study we describe the water mass balance at the NBC-EUC retroflection area using a combination of shipboard observations and numerical reanalysis. The observations, from an oceanographic campaign in April 2010, provide a synoptic view of the retroflection region and allow assessing the goodness of the numerical data. We then use the ocean reanalysis GLORYS2v4 to analyse the temporal variability of this region, from intra-seasonal to seasonal scales, and use Lagrangian simulations to identify the principal water mass pathways feeding the retroflection. We find a substantial seasonal cycle in the boundary and interior (southern and northern) origins of those waters that feed the EUC. Our results also show the propagation of high-frequency waves (16-30 days) along the coast from the south, probably as coastal trapped waves, while waves with 30-60 days period come from the northern hemisphere, probably as westward Rossby waves reach the coast of America and follow south as Kelvin waves. These short-term fluctuations have a high impact on the water mass pathways that feed the EUC and the retroflection structure itself.
Artificial neural networks in the problem of determining the position and size of the solar disk in wide-angle photographs of the sky
Authors: Borisov Mikhail , Krinitskiy Mikhail
Published: March 2021

Total cloud score is a characteristic of weather conditions. At the moment, there are algorithms that automatically calculate cloudiness based on a photograph of the sky These algorithms do not know how to find the solar disk, so their work is not absolutely accurate.

To create an algorithm that solves this data, the data used, obtained as a result of sea research voyages, is used, which is marked up for training the neural network.

As a result of the work, an algorithm was obtained based on neural networks, based on a photograph of the sky, in order to determine the size and position of the solar disk, other algorithms can be used to work with images of the visible hemisphere of the sky.
Hybrid-Vlasov modelling of three-dimensional dayside magnetopause reconnection
Authors: Pfau-Kempf Yann , Palmroth Minna , Johlander Andreas , Turc Lucile , Alho Markku , Battarbee Markus , Grandin Maxime , Dubart Maxime , Ganse Urs
Published: March 2021

Dayside magnetic reconnection at the magnetopause, which is a major driver of space weather, is studied for the first time in a three-dimensional (3D) realistic setup using the Vlasiator hybrid-Vlasov kinetic model. A noon–midnight meridional plane simulation is extended in the dawn–dusk direction to cover 7 Earth radii. The southward interplanetary magnetic field causes magnetic reconnection to occur at the subsolar magnetopause. Perturbations arising from kinetic instabilities in the magnetosheath appear to modulate the reconnection. Its characteristics are consistent with multiple, bursty, and patchy magnetopause reconnection. It is shown that the kinetic behavior of the plasma, as simulated by the model, has consequences on the applicability of methods such as the four-field junction to identify and analyse magnetic reconnection in 3D kinetic simulations.
Advances and challenges in the past decade: from univariate to multivariate bias adjustment of climate models for impact studies
Authors: Tootoonchi Faranak , Haerter Jan Olaf , Raty Olle , Grabs Thomas , Teutschbein Claudia
Published: March 2021

Climate models are primary tools to reconstruct past and predict future climates. It is common procedure to use general circulation models (GCMs) for large scale studies and regional climate models (RCMs), for impact studies at a finer spatial resolution. However, climate models face biases compared to observation. To overcome these biases, different statistical methods have been suggested in the scientific literature that employ a transformation algorithm to re-scale (or bias-correct) RCM outputs. Some of these methods (e.g. univariate methods that adjust only one RCM-simulated variable at a time) are comparatively easy to implement while others (e.g., multi-variate correction that guarantees consistency in spatiotemporal fields and different climate variables) that have been introduced lately to the field, are more complex and require advanced statistical knowledge and more computing power. Therefore, the need to further investigate the performance of the latest more complex bias-adjustment methods under different climatic conditions still exists and their added value still needs to be evaluated from different aspects.

Thus, we assessed the skill of two commonly used multivariate methods, namely copula based bias adjustment methods and non-parametric n-dimensional multivariate bias correction (MBCn). We further compared them with widely used univariate methods, i.e. the parametric distribution mapping (DS) and the non-parametric quantile delta mapping (QDM), to adjust RCM-simulated temperature and precipitation. We evaluated these methods over 55 Swedish catchments varying in size and climatic features using an ensemble of 10 different RCMs under varying climate conditions to check multiple features that represent both probabilistic and temporal behavior. To evaluate how these methods, perform in nonstationary climate conditions, we performed the assessment over two periods of 22 years each, where the period 1961-1982 is used for calibration and 1983-2004 for validation. The adequacy of each bias adjustment method in reducing the biases varies depending on several factors such as the studied watershed, the applied RCM model, utilized climate variable and the statistical feature that is subjected to adjustment. We further discuss potential issues and trade-offs of each of the applied methods and present an evaluation of each bias-corrected climate variable in terms of its (1) statistical properties, (2) temporal behavior utilizing cross correlation and autocorrelation measures, and (3) dependence structure to the other variable with help of copula-based dependence measures. Finally, we also examined how the four bias-adjustment methods influence the Clausius Clapeyron relation, which serves as an important climatic illustration of the relationship between extreme precipitation and temperature.