bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear forced change and nonergodicity: The case of ENSO-Indian monsoon and global precipitation teleconnections
Authors: Drotos Gabor , Bodai Tamas , Ha Kyung-Ja , Lee June-Yi , Chung Eui-Seok
Published: March 2021

We study the forced response of the teleconnection between the El Niño–Southern Oscillation (ENSO) and the Indian summer monsoon (IM) in the Max Planck Institute Grand Ensemble, a set of Earth system ensemble simulations under historical and RCP forcing. The forced response of the teleconnection, or a characteristic of it, is defined as the time dependence of a correlation coefficient evaluated over the ensemble. We consider the temporal variability of spatial averages and that with respect to dominant spatial modes in the sense of Maximal Covariance Analysis, Canonical Correlation Analysis and Empirical Orthogonal Function analysis across the ensemble. A further representation of the teleconnection that we define here takes the point of view of the predictability of the complete spatiotemporal variability of the Indian summer monsoon. We find that the strengthening of the ENSO-IM teleconnection is robustly or consistently featured in view of various teleconnection representations, whether sea surface temperature (SST) or sea level pressure (SLP) is used to characterise ENSO, and both in the historical period and under the RCP8.5 forcing scenario. It is found to be associated dominantly with the principal mode of ENSO variability. Concerning representations that involve an autonomous characterisation of the Pacific, in terms of a linear regression model, the main contributor to the strengthening} is the regression coefficient, which can outcompete even a declining ENSO variability when it is represented by SLP. We also find that the forced change of the teleconnection is typically nonlinear by (1) formally rejecting the hypothesis that ergodicity holds, i.e., that expected values of temporal correlation coefficients with respect to the ensemble equal the ensemble-wise correlation coefficient itself, and also showing that (2) the trivial contributions of the forced changes in means and standard deviations are insignificant here. We also provide, in terms of the test statistics, global maps of the degree of nonlinearity/nonergodicity of the forced change of the teleconnection between local precipitation and ENSO.
Evaluation of the new high resolution unstructured grid Marmara Sea model
Authors: Ilicak Mehmet , Federico Ivan , Barletta Ivano , Pinardi Nadia , Ciliberti Stefania Angela , Clementi Emanuela , Coppini Giovanni , Lecci Rita , Mutlu Sabri
Published: March 2021

Marmara Sea including Bosphorus and Dardanelles Straits (i.e. Turkish Strait Systems, TSS) is the connection between the Black Sea and the Mediterranean. The exchange flow that occurs in the Straits is crucial to set the deep water properties in the Black Sea and the surface water conditions in the Northern Aegean Sea. We have developed a new high-resolution unstructured grid model (U-TSS) for the Marmara Sea including the Bosporus and Dardanelles Straits using the System of HydrodYnamic Finite Element Modules (SHYFEM). Using an unstructured grid in the horizontal better resolves geometry of the Turkish Straits. The new model has a resolution between 500 meter in the deep to 50 meter in the shallow areas, and 93 geopotential coordinate levels in the vertical. We conducted a 4 year hindcast simulation between 2016 and 2019 using lateral boundary conditions from CMEMS (https://marine.copernicus.eu/) analysis, in particular Black Sea Forecasting System (BS-FS) for the northern boundary and Mediterranean Sea Forecasting System (MS-FS) for the southern boundary. Atmospheric boundary conditions fare from the ECMWF dataset.

Mean averaged surface circulation shows that there is a cyclonic gyre in the middle of the basin due to Bosphorus jet flowing to the south and turning to west after reaching the southern Marmara coast. The U-TSS model has been validated against the seasonal in situ observations obtained from four different cruises between 2017 and 2018. The maximum bias occurs at around halocline depth between 20 to 30 meters.  We also found that root mean square error field is higher in the mixed layer interface. We conclude that capturing shallow mixed layer depth is very in the Marmara Sea due to the interplay of air-sea fluxes and mixing parametrizations uncertainties. Maximum salinity bias and rms in the new U-TSS model are around 3 psu which is a significant improvement with respect to previous studies. This new model will be used as an operational forecasting system and will provide lateral boundary conditions for the BS-FS and MS-FS models in the future.
The Barents-Kara Ice Sheet response to the CMIP6-PMIP4 simulations for the LGM climate
Authors: van Aalderen Victor , Charbit Sylvie , Dumas Christophe , Kageyama Masa
Published: March 2021

Recent observations show an acceleration of the glacier outflow in the West Antarctic ice sheet (WAIS) since the mid-1990s and an increase in calving events. Compared to the 1979-1990 period, mass loss from WAIS has been increased by a factor six between 2009 and 2017. The reduced buttressing effect from ice-shelf breakup may favour the ice flow from outlet glaciers and in turn the sea-level rise with potential noticeable consequences on human societies. However, despite continuous model improvements, large uncertainties are still present on the representation future evolution of the WAIS. The large panel of different results in the projections of the future sea-level rise stands, in part, to our misunderstanding of the process responsible for the marine ice sheet evolution. A possible approach to better constrain these processes, is to investigate past marine ice sheets, such as the Barents-Kara ice sheet (BKIS) at the Last Glacial Maximum (LGM), which can be considered, to a certain extent, as an analogue of the WAIS. Our objective is to study the processes responsible for the collapse of the BKIS during the last deglaciation. To simulate the evolution of the BKIS, we use the GRISLI ice-sheet model (20 km x 20 km) forced by different CMIP5/PMIP3 and CMIP6/PMIP4 models. We will present the response of the ice sheet to different types of atmospheric and oceanic forcing at the LGM coming from the PMIP models. This study represents a first step before studying more in depth the respective role of each climatic field but also the role of sea level rise coming from other LGM ice sheets in triggering the retreat of the BKIS at the beginning of the last deglaciation and the impacts of the dynamical processes.
Tropical Peatland Water Balance under Land Cover Change in Padang Island, Indonesia
Authors: Asyhari Adibtya , Kurnianto Sofyan , Suardiwerianto Yogi , Tanjungsari Rahila Junika , Hidayat Muhammad Fikky , Harahap Muhammad Iman Faisal , Marpaung Sahat Manimbo , Salam Yuandanis Wahyu , Deshmukh Chandra Shekhar
Published: March 2021

Changes in hydrological regime associated with land cover change may result in crucial implications to tropical peatland landscape since hydrology strongly controls peatland geomorphology, ecology, and biogeochemical cycle. Therefore, improved understanding of the land cover change impacts to the water balance is of significant importance in order to formulate responsible peatland management strategies. In this study, we investigated the water balance under historical land cover change within Padang Island, Indonesia, an ombrotropic tropical peatland landscape with heterogeneous land covers. For this purpose, we established a model setup using a coupled MIKE SHE and MIKE Hydro River. The model was calibrated and validated against comprehensive data set from field measurements. Land cover change impacts were evaluated by comparing the water balance under current and past condition. The past land cover distribution was derived from historical satellite imagery analysis covering the period of 25 years before the current condition. Meanwhile, the past topography data was generated following long-term subsidence monitoring data. Here, we will present the impacts of land cover change to water balance at the landscape level and their implications for management of tropical peatlands.
Thermal structure of the Amery Ice Shelf from borehole observations and simulations
Authors: Wang Yu , Zhao Chen , Gladstone Rupert , Galton-Fenzi Ben
Published: March 2021

The Amery Ice Shelf (AIS), East Antarctica, has a layered structure, due to the presence of both meteoric and marine ice. In this study, the thermal structures of the AIS are evaluated from vertical temperature profiles, and its formation mechanism are demonstrated by numerical simulations. The temperature profiles, derived from borehole thermistor data at four different locations, indicate distinct temperature regimes in the areas with and without basal marine ice. The former shows a near-isothermal layer over 100 m at the bottom and stable internal temperature gradients, while the latter reveals a cold core ice resulting from upstream cold ice advection and large temperature gradients within 90 m at the bottom. The three-dimensional steady-state temperature fields are simulated by Elmer/Ice, a full-stokes ice sheet model, using three different basal mass balance datasets. We found the simulated temperature fields are highly sensitive to the choice of dynamic boundary conditions on both upper and lower surfaces. To better illustrate the formation of the vertical thermal regimes, we construct a one-dimensional temperature column model to simulate the process of ice columns moving on the flowlines with varying boundary conditions. The comparison of simulated and observed temperature profiles suggests that the basal mass balance and meteoric ice advection are both crucial factors determining the thermal structure of the ice shelf. The different basal mass balance datasets are indirectly evaluated as well. The improved understanding of the thermal structure of the AIS will assist with further studies on its thermodynamics and rheology.
Airborne water vapor isotope measurements over the Iceland Sea in winter conditions
Authors: Touzeau Alexandra , Steen-Larsen Hans-Christian , Renfrew Ian , Jónsson Þorsteinn , Elvidge Andrew , Lachlan-Cope Thomas , Weng Yongbiao , Sveinbjörnsdóttìr Árný , Midtgarden Golid Heidi , Duscha Christiane , Sodemann Harald
Published: March 2021

Improved understanding of evaporation and condensation processes is critical to improve the representation of the water cycle in atmospheric models. Thereby, in-situ measurements along the entire moisture transport pathway, covering evaporation, mixing between different air masses in the atmospheric boundary layer and the free troposphere, and resulting precipitation are highly valuable to obtain new insight. In particular, coherent measurements of the stable isotope composition in atmospheric vapour can provide additional constraints on phase change processes of water vapour from source to sink, enabling direct comparison within isotope-enabled models.

Here we present stable isotope measurements from the Iceland Greenland Seas Project field campaign that took place in February-March 2018. This unique dataset includes simultaneous measurements from a land-station in Husavik, Iceland, a ship and an air plane in the subpolar region. Alternation between cold-air outbreaks and mid-latitude airmasses characterized the measurement period. Here we focus on the stable water isotope composition in water vapour obtained from 10 research flights, covering a large geographic range (64 °N to 72 °N). Careful data treatment was applied to ensure the quality of isotope measurements in the predominant cold, dry conditions with large gradients in isotope composition and humidity.

From an intercomparison flight over the Husavik station, we find good agreement between ground and airborne measurements. Out of 7 flights dedicated to the study of atmosphere-ocean-ice interactions, with both low-levels legs and vertical sections in predominant Cold Air Outbreak (CAO) conditions, we focus on the marginal ice zone and regions covered by shallow cumulus clouds. For open water flights, we find the horizontal and vertical distribution of δ18O in the marine boundary layer to covary with cloud cover. Thereby, downdrafts bring dry and 18O-depleted air from the free troposphere towards the surface, corresponding to openings in cloud cover. For flights passing over sea ice edge, both δ18O and specific humidity show a clear east-west gradient, with increasing values towards the open sea reflecting ocean moisture availability. Additionally, open leads in the sea ice also have a visible impact on isotope values. Lastly, relatively low d-excess values are observed over the sea-ice, which could either be caused by local processes or advection.
A multi-scale ground and drone-borne magnetic survey approach for the detection and investigation of archaeological structures
Authors: Gavazzi Bruno , Reiller Hugo , Munschy Marc , Pierrevelcin Gilles , Basoge Florian , Mercier de Lépinay Jeanne , Fréville Tristan
Published: March 2021

Ground magnetic surveys are commonly used for imaging near-surface structures in archaeological studies. Usually, surveys are conducted using vertical component gradiometers or scalar gradiometers to produce a vertical pseudo-gradient map. Scalar magnetometers can also be used, albeit less frequently, to produce maps of the total magnetic anomaly. In all these cases, the equipment is pushed or pulled by an operator or carried behind a vehicle. Here we present a third approach made available by the use of three-component fluxgate magnetometers: fast surveys over large areas using a compact lightweight drone flying automatically 1 to 2 m above the ground and high precision surveys acquired by an operator 0,2 to 1 m above the ground. A case study on the gallo-roman site of Oedenburg, located along the Rhine River in its upper valley, illustrates the results that can be obtained with the approach. A comparison with previously acquired pseudo-gradient surveys shows that the presented method allows a faster coverage, a greater resolution for the imaging of short wavelength structures (such as walls) and a better capacity of imaging large wavelength structures (such as pathways, palaeochannels or soil composition variations). As the site is crossed by a high voltage electric power line, a method to suppress the high-amplitude 50 Hz frequency magnetic field is presented.
Measuring floating ice thickness with optical fibers and DAS, a test case study on a frozen moutain lake.
Authors: Coutant Olivier , Moreau Ludovic , Boué Pierre , Larose Eric , Cimolino Arnaud
Published: March 2021

Accurate monitoring of floating ice thickness is an important safety issue for northern countries where lakes, fjords, and coasts are covered with ice in winter, and used by people to travel. For example in Finland, 15-20 fatal accidents occur every year due to ice-related drowning. We have explored the potential of fiber optics to measure the propagation of seismic waves guided in the ice layer, in order to infer its thickness via the inversion of the dispersion curves. An optical fiber was deployed on a frozen lake at Lacs Roberts (2400m) above Grenoble and we measured with a DAS the signal generated by active sources (hammer) and ambient noise. We demonstrate that we can retrieve the ice thickness. This monitoring method could be of interest since the deployment of a fiber on ice is quite simple (e.g. using a drone) compared to other techniques for ice thickness estimation such as seismic survey or manual drilling.
Land users’ perceptions of land degradation and implications for sustainable land management and governance in Niger State, Nigeria 
Authors: Ademola Adenle , Boillat Sébastien , Ifejika Speranza Chinwe
Published: March 2021

Declining land productivity remains a challenge for agricultural-based livelihoods and for achieving food security. This is particularly the case in social-ecological contexts where people are largely dependent on local food production for their livelihoods and food security, such as among rural communities in the Nigeria Guinea Savannah. Yet how land users perceive the problem of land degradation and their capacity to manage land in an environmentally sustainable manner, can influence the measures they can initiate to address land degradation. Using a case study of Niger state, Nigeria, this study examines land users’ experiences and land management measures to address land degradation in the Nigeria Guinea Savannah. 30 communities were purposively selected based on the validated mapping of the hotspots of degraded areas. We adapted the World Overview of Conservation Approaches and Technologies Sustainable Land Management questionnaires to also capture perceptions and administered 225 questionnaires to land users. Through, key informant interviews further insights and data on perspectives and motivations of land users and communities were collected to understand the land degradation situation and interpret the questionnaire surveys. Through qualitative and statistical analysis of differences in perceptions between socio-cultural strata, we show the relations between socio-demographic, socio-economic factors, and land degradation. We discuss land governance and sustainable land management practices for improving land productivity in the region.

 

 
The Transient and Equilibrium Response of the AMOC to Arctic sea decline in a coupled model.
Authors: Simon Amelie , Ferster Brady , Fedorov Alexey , Mignot Juliette , Guilyardi Eric
Published: March 2021

Since the mid-20th century, the Arctic has experienced two major impacts of climate change: a warming at a faster rate than the global mean surface temperature and a reduction of both winter and summer sea ice cover. However, the impact of the Arctic sea ice loss on global climate remains under debate, in particular the impact on the Atlantic meridional overturning circulation (AMOC). Specifically, some studies find that in response to Arctic sea ice decline, the AMOC weakens on multi-decadal timescales, reaching a new equilibrium state with a significantly reduced AMOC, while others studies see a weak AMOC reduction followed by a partial or full recovery. To further investigate the impact of sea ice loss on the climate, ensemble simulations are performed with the coupled atmosphere-ocean general circulation model CM5A2 from the Insitut Pierre Simon Laplace (IPSL-CM5A2). To induce the change in sea ice, the Arctic sea ice albedo is reduced by about 23%, previously shown to be consistent with the sea ice changes expected to occur by approximately the year 2040. The experimental design compares the response to sea ice loss starting from AMOC minimum and neutral phases, respectively. The objective of our experiment is to further investigate the AMOC-sea ice relationship in the transient and equilibrium responses to decreased sea ice and the robustness within a coupled model. The initial 30-year response results in similar spatial patterns in sea ice volume and 500mb potential height responses (inducing a negative NAO-like pattern) for both types of initial conditions. In both cases, the AMOC reduces by 0.5 to 1.5Sv Sv (about 15% of the model mean AMOC) during the first ~100 years of the experiment. Yet, there are differences in the response depending on the AMOC initial state, for example, in the magnitude and timing of the AMOC reduction. The AMOC eventually recover towards years 151-200. Our results give insight into the importance of decadal variability for anticipating the response of the next decades to climate change, as well as improves the understanding of the long-term transient and equilibrium responses between AMOC and Arctic sea ice.
The quality of velocities from GNSS campaign measurements when gaps in data exist
Authors: Turen Yener , Sanli Dogan Ugur , Erol Tuna
Published: March 2021

In this study, we investigate the effect of gaps in data on the accuracy of deformation rates produced from GNSS campaign measurements. Our motivation in investigating gaps in data is that campaign GNSS time series might not be collected regularly due to various constraints in real life conditions. We used the baseline components produced from continuous GPS time series of JPL, NASA from a global network of the IGS to generate data gaps. The solutions of the IGS continuous GNSS time series were decimated to the solutions of the campaign data sampled one measurement per each month or three measurements per year. Furthermore, the effect of antenna set-up errors, which show Gaussian distribution, in campaign measurements was taken into account following the suggestions from the literature. The number of gaps in campaign GNSS time series was incremented plus one for each different trial until only one month is left within the specific year. Eventually, we tested whether the velocities obtained from GNSS campaign series containing data gaps differ signiﬁcantly from the velocities derived from continuous data which is taken as to be the “truth”. The initial efforts using the samples from a restricted amount of data reveal that the deformation rate produced from the east component is more sensitive to the gaps in data than that of the components north and vertical.

Keywords: GPS time series; GPS campaigns; Velocity estimation; Gaps in data; Deformation.
Spatial Trends in Mineral Abundances across Tyrrhena Terra on Mars derived from Geomorphological and Mineralogical Mapping
Authors: Tirsch Daniela , Voigt Joana R. C. , Viviano Christina E. , Bishop Janice L. , Lane Melissa D. , Tornabene Livio L. , Loizeau Damien
Published: March 2021

Tyrrhena Terra hosts an intriguing variety of aqueously altered materials accompanied by unaltered mafic rocks. Our study region extends from the southern rim of the Isidis impact basin, including the Libya Montes region, southward to the Hellas Basin rim (Fig. 1). The NW part is dominated by lava flows from Syrtis Major that grade southwards into the TT highlands, dissected by fluvial channels and overprinted by abundant impact craters. These landforms together with lobate and fan-shaped deposits within impact craters are evidence for a variable history of erosion and deposition. Ancient phyllosilicate-rich materials have been exposed and uplifted from the subsurface, as they often occur in crater ejecta and central crater uplifts.

Our previous studies used CRISM spectral data together with CTX, HiRISE, and HRSC images as well as their derived topography data to create geomorphological maps of the southern Isidis region and Tyrrhena Terra. These datasets were used to map and characterize the types and occurrences of phyllosilicates, chlorite, opal, zeolites, carbonates, olivines, and pyroxenes and to assess the relationships between selected aqueous outcrops and surface features.

In this work, we build on these results by seeking correlations between aqueous mineral detections with our geomorphological map to assess 1) whether or not there are relationships between specific units and mineral occurrences, and 2) if there are trends across the study region in terms of mineral occurrence and abundance.

The mineralogical map originates from a study that spans not only the inter-Isidis-Hellas region, but also extends northwards to Nili Fosse and westwards to Terra Sabea. The focus of that study was on the metamorphic- and hydrothermally-related alteration history using CRISM targeted and mapping data, including hundreds of calibrated MTRDR images. These mineral detections were available to us as a mapped shape file, enabling us to assess the minerals in context with the geomorphological map. We utilized ESRI’s ArcGIS system and conducted multiple statistical queries in terms of mineral occurrence/type versus map unit in order to reveal possible trends within and across the study region.

Fe/Mg-phyllosilicates are the dominant aqueous mineral type within the study region and are more abundant in the central region compared to the proximity of either the Isidis or Hellas impact basin. Chlorites increase in abundance with distance from both impact basins, which could be an indication of hydrothermal processes from geothermal flux. The large Hellas impact event appears to have produced more varied temperatures and water chemistries, resulting in increased mineral variability near its rim.
Simulation of Lithological Classification in Choshui river Alluvial Fan based on Muliple-point geostastics 
Authors: Lin Ting-An , Yu Hwa-Lung
Published: March 2021

In the applications and studies of subsurface flow, it is necessary to understand the geological lithological composition in the study area. So as to find out the lithological distribution in the study area, many geological spatial statistical methods used to analyze the lithological composition on unsampled points. One of the drawbacks in the traditional two-point based geostatistical methods(e.g., Kriging) is that they based on variogram, thus, inability to handle complex and heterogeneous spatial structures. Furthermore, they produce excessively smooth results. The goal of Multiple-point geostatistics is to overcome the limitations of the variogram. Multiple-point geostatistics is a general statistical framework to model spatial fields with complex structures. It uses training image(TI) instead of variogram to estimate the conditional probability at interpolation location by the observed data and the already interpolated data. Take advantage of TI helps extracting spatial structure information and precisely describing more complex structures. This study focuses on Choshui river alluvial fan, using multiple-point geostatistics method to do simulation of lithological classification.
Lagrangian review of the origin of the humidity for the case of two extreme precipitation events in the Mediterranean region 
Authors: Cloux Sara , Insua-Costa Damián , Miguez-Macho Gonzalo , Perez-Muñuzuri Vicente
Published: March 2021

Extreme precipitation events are atmospheric phenomena causing floods that generate great economic and social losses. The Mediterranean region is characterized by a strong variability in time and space that favors the appearance of this type of phenomena. Therefore, determining the origin of humidity must be done.     

The UTrack-atmospheric-moisture model [1] is a Lagrangian tool to track atmospheric moisture flows forward in time using ERA-5 reanalysis weather data. The labeled moisture is released into the atmosphere in the form of evaporation. After determine the allocated moisture precipitated at each time, this model allows us to know the percentage of relative humidity that has precipitated for each of the labeled sources.  Here we present a comparison of these results with previous results obtained by other Lagrangian methods. 

[1] Tuinenburg, Obbe A., and Arie Staal. Tracking the global flows of atmospheric moisture and associated uncertainties." Hydrology and Earth System Sciences 24.5 (2020): 2419-2435. 
THM analysIs of natural and engineered barriers for large excavations in deep nuclear waste repository
Authors: Alonso Matias , Vaunat Jean , Vu Minh-Ngoc , Gens Antonio
Published: March 2021

Argillaceous rocks have great potential as possible geological host medium to store radioactive waste.  Andra is leading the design of a deep geological nuclear waste repository to be located in the Callovo-Oxfordian formation. In the framework of this project, excavations of large diameter galleries are contemplated to access and to store intermediate-level long-lived nuclear waste at repository main level. The closure of the repository will be realized by building sealing structures of expansive material.

The response of such structures is affected by several thermo-hydro-mechanical coupled processes taking place in the near and far field of the argillaceous formations. They include the formation of an excavation induced damaged zone around the galleries, the impact of the thermal load on host rock pressures and deformations, the long-term interaction with support concrete structural elements and the hydration and swelling of sealing materials. As a result, the study of their performance requires to perform simulation works of increasing complexity in terms of coupling equations, problem geometry and material behaviour. As well, challenging computational aspects, as the ones related to fractures creation and propagation, have to be considered for a representative analysis of the problem.

This work presents advanced large scale THM numerical models to provide keys about the response of the host rock around large diameter galleries during excavation and further thermal load as well as to analyse the performance of large diameter sealing structures. Particular features of the models include on one hand advanced constitutive laws to capture the development of the fractured zone around excavations, the behaviour of host rock/gallery support interfaces and the multi-scale response of bentonitic backfill. On the other hand, simulations consider geometries including constructive details of interest at decimetre scale within large discretization domain covering the whole formation stratigraphic column.

These challenging simulations provided qualitative and quantitative results on key aspects for natural and engineered barrier integrity, like extension of the damaged zone, impact of the thermal load and water pressure variations in the surrounding geological layers, duration of natural hydration phase, swelling pressure development and seals global stability.
Climate effects of changing aerosol emissions over the coming decades
Authors: Samset Bjorn H. , Stjern Camilla W. , Lund Marianne T.
Published: March 2021

Emissions of anthropogenic aerosols strongly influence the climate, by modulating global and regional temperature, and by affecting precipitation, extremes, circulation patterns and other local-to-global scale features. This influence has been continually changing over previous decades, and will continue to change at least until 2050. It is also highly heterogeneous, in space and time. Hence, a deeper look at the potential role of anthropogenic aerosol emissions in shaping climate change over the coming decades is crucial for both adaptation and mitigation strategies. 

 

Here, we discuss three techniques to bound the potential near-term role of aerosols: (i) The influence on local and global rates of warming, relative to natural variability, using simplified models in combination with Large Ensembles, (ii) an overall constraint on the precipitation influence of absorbing aerosols, combining recent emission projections with results from several multi-model intercomparison projects, and (iii) changes to regional distributions of daily temperature and precipitation as function of the level of aerosol emissions and global warming, leveraging the statistics available through Large Ensembles. 

 

Overall, we find that while greenhouse gas emissions will continue to dominate the global mean climate evolution, by driving surface temperature change and its associated feedbacks, aerosol emissions may still hold a key - or even dominating - influence on changes to regional weather and climate. 
Turbidity sensor response to seasonal and spatial variability of suspended particle composition in open clear waters –(Portuguese continental shelf)
Authors: Oliveira Anabela , Santos Ana Isabel , Santos Rita , Zacarias Nuno
Published: March 2021

As part of AQUIMAR project (MAR2020 nº MAR-02.01.01-FEAMP-017 – AQUIMAR – Caraterização geral das áreas aquícolas para estabelecimento de culturas marinhas), intensive CTD surveys and turbidity/concentration data were collected in four cruises along the Portuguese continental shelf (30-200m depth), in 5 aquaculture areas from 2018 to 2020. In-situ calibration of the turbidity sensor (Seapoint Turbidity Meter) was done using the traditional gravimetric method of suspended sediments concentration (SSC) determination with water sampling and filtering. The obtained FTU/SSC relations resulted in correlations in the order of R2=70-80% for all considered surveys.

Measured turbidity and concentration values, were generally very low (<2 FTU and <2 mg/l) for all measuring periods, however variations of the FTU/SSC sensitivity between the different areas indicate that significant variations of suspended matter composition exist throughout the Portuguese continental shelf.

This study aims to understand the seasonal and spatial variations of the turbidity signal sensitivity to SSC. To this end, a closer look will be given to samples collected during two contrasting seasonal periods (spring and late autumn 2019), as well as to the general water column structure at the time of the sample collection. Additionally, results from X-Ray diffraction analysis performed in some of the filtered samples will be used to better understand the variations of the suspended sediment composition in open clear waters. The mineralogical signal shows a dominance of clay minerals in suspension (mean 83%) and calcite (mean 10%), reflecting the detritic and organic fraction of SSC, respectively.
Homogenisation of monthly temperatures of the Swedish observational network 1850-2020
Authors: Joelsson L. Magnus T. , Sturm Christophe , Södling Johan , Engtsröm Erik
Published: March 2021

Monthly averages of statistical temperature variables (i.e. monthly averages of daily maximum, minimum, and mean temperatures) are homogenised for a large part of the Swedish observational network dataset from 1850 to 2020. Data from 573–587 weather stations (depending on variable) are coupled into 299–303 time series. The coupling of time series is partly performed automatically following a set of criteria of geographical proximity, altitude, proximity to coast line, time series overlap, and correlation of the data series.

The homogenisation of the data set is performed with the recently developed homogenisation tool Bart. Bart is a fully automatic modification of the homogenisation tool HOMER. Bart uses a set of input parameters to accept or reject potential homogeneity break points suggested by the different functions of HOMER. Bart performs correction and gap filling of the data series according to the accepted homogeneity break points. A rudimentary sensitivity test is performed to examine how sensitive the homogenisation is to the selection of the input parameters assumed most important and to find a optimal set up of these parameters. Other features in Bart include a novel procedure for the selection of reference time series to account for uneven data coverage, and parallel computing to reduce the computational time.

An important application of the homogenised data set is the calculation of the climate indicator of temperature. The climate indicator of temperature is the average annual mean temperatures of thirty-nine weather stations, carefully selected to represent the climate in Sweden over the last 170 years. The use of homogenised data gives a 1.8 °C (10 a)-1 greater warming than if raw data is used from 1860 to present, the period for which data coverage is sufficient.
Ray paths of VLF/LF transmitter radio signals in the seismic Adriatic regions
Authors: Boudjada Mohammed  Y. , Eichelberger Hans Ulrich , Biagi Pier Francesco , Schwingenschuh Konrad , Nico Giovanni , Solovieva Maria , Ermini Anita , Moldovan Iren Adelina , Contadakis Michael E. , Nina Aleksandra , Katzis Konstantinos , Bezzeghoud Mourad , Lammer Helmut , Galopeau Patrick H.M. , Besser Bruno , Aydogar Özer
Published: March 2021

We analyze the radio wave propagations of VLF/LF transmitter signals along subionospheric paths using two different reception systems localized in the Graz seismo-electromagnetic facility (15.43E,47.06N). Those systems allow the simultaneous detection of more than fifteen transmitter signals emitting in the northern (i.e. France, Germany and United Kingdom) and southern (i.e. Italy and Turkey) parts of Europe. In this work, we investigate the transmitter radio wave propagations associated with two earthquakes (EQs) which occurred, at two occasions, in nearly the same Croatian regions (Geo. Long.=16°E; Geo. Lat.=45°N). The first and second EQs happened, respectively, on March 22 and December 29, 2020, with magnitudes Mw equal to 5.4 and 6.4. The use of two complementary reception systems, i.e. INFREP (Biagi et al., Open Journal of Earthquake Research, 8, 2019) and UltraMSK (Schwingenschuh et al., Nat. Hazards Earth Syst. Sci., 11, 2011), and the proximity to the epicenters lead us to characterize the behavior of the transmitter signal amplitudes particularly above the Croatian seismic regions. We analyze the amplitude variation for a given transmitter frequency starting few weeks before the earthquakes occurrences. We discuss the observed anomalies in the transmitter signals which may be considered as precursors due to the ionospheric disturbances of the transmitter ray paths above the earthquakes preparation zones. 
A physically-based robust definition of convectively generated density currents : detection and characterization in convection-permitting simulations
Authors: Rochetin Nicolas , Hohenegger Cathy , Touzé-Peiffer Ludovic , Villefranque Najda
Published: March 2021

In this paper, a conceptual model to dene density currents is proposed. Based on theory, observations and modelling studies, we dene convective density currents as 3D coherent structures with an anomalously cold core, an adjacent wind gust and two vertical layers: a well-mixed one near the surface and a stratied one above. With this definition, a methodology to identify and label individual density currents in convection permitting simulations is designed. The method is illustrated through its application to four distinct cloud scenes issued from a convetion-permitting simulation. From this methodology, new dynamic, thermodynamic and geometric features related to the density currents imprint on the Planetary Boundary Layer are revealed. The method is found to be i) robust in time, ii) relevant in distinct convective regimes, iii) relevant in land and oceanic situations and iv) adapted to both Cloud Resolving Models and Large Eddy Simulations. It also provides proxies such as the number, the spatial coverage, the mean radius and the mean velocity of density currents, from which a detailed analysis of their role in convection life-cycle and spatial organization could be performed in the near future.
Peculiarities of marine eddy manifestation in the structure of surfactant slick band
Authors: Shomina Olga , Tarasova Tatiana , Danilicheva Olga , Kapustin Ivan
Published: March 2021

Slick structures on the sea surface can mark processes occurring in upper ocean and atmosphere. Spiral shape of slicks observed in optical and radar images of water surface is traditionally interpreted through the manifestation of marine eddy which length scale is supposed to be equal to the scale of spiral. This assumption implies that wind has no effect on the kinematics of forming slick band, which, according to our estimation, is incorrect even at moderate wind velocities. This approach can cause misinterpretation of remote sensing data when estimating the characteristics of observed marine eddies. This study is devoted to the investigation of conditions necessary for the formation of slick spiral and to some peculiarities of its shape and scale.

The system of equations for the description of kinematics of Lagrangian particle (element of water surface covered with surface active substance) in the fields of axisymmetric eddy with non-zero radial velocity component and homogeneous wind was obtained. It is demonstrated that the spiral center is not collocated with the center of the eddy; the distance between them can achieve the eddy length scale. It is shown that the displacement of the spiral center and the direction of the main axis is quasi perpendicular to the wind direction when radial component of the eddy is small compared to the tangential component. The presence of the threshold wind velocity corresponding to the breakdown of the spiral structure is demonstrated analytically. The possibilities of correct retrieval of length scales and character velocities of observed sub mesoscale marine eddies are discussed.

The research was funded by the Russian Science Foundation (Project RSF 18-77-10066).
European Underground Laboratories Association EUL – An International Partner for Underground Research Opportunities
Authors: Mischo Helmut , Fuławka Krzysztof , Joutsenvaara Jari
Published: March 2021

Underground experimental sites and laboratories are rare and offer unique opportunities for research, development, innovation, education and training, among other usages due to their special boundary conditions. Each underground facility is highly unique in its geological and geophysical characteristics. These sites can be either dedicated infrastructures built for specific usage or mines and parts of mines freed from underground extraction. Since they are usually isolated from environmental influences and, conversely, shield experiments as far as possible from the environment, they offer unique research conditions and possibilities compared to surface laboratories.

However, the sustainable operation of such underground experimental sites is not an easy task. Hence, to foster and accommodate the use, scientific collaboration and interdisciplinary scientific research among European underground research facilities, a specialized association has been set up by a number of European partners under the name European Underground Laboratories Association EUL.

This association defines its purpose by forming a network between the underground laboratories and client organizations from business, science and administration sectors. The goal is to bundle and develop existing competencies, and thus providing a common platform for members and prospective researchers and costumers on order to share and exchange information and experience, and in turn to contribute to the development and implementation of new research projects. As an Europe-wide and internationally active association comprising EU members and non-members, EUL also supports and promotes European integration and international cooperation.

This paper provides an overview over the structure and the organisation of EUL, its member institutions and associated underground research laboratories as well as the possibilities the association may offer for its members and interested partners in the fields of:

providing a comprehensive overview of the research possibilities and conditions at the different underground sites to clients and the public

infrastructure development at the research locations and improvement of research conditions in each underground facility

execution of joint research proposals and respective project planning

setting up and extending the spread of advertising materials and publications

education and training of students, researchers and professionals,

enabling the exchange of researchers, professionals and/or students among partnering facilities
The generatin of extremely low-frequency chorus waves associated with plasma density enhancement
Authors: He Qian , Liu Si
Published: March 2021

Chorus waves with extremely low frequency (ELF) below 0.1 fce are proposed to be a potential mechanism of scattering losses of relativistic electrons in the radiation belt. However, the generation of ELF chorus is still an open question. Here we report three interesting events that the occurrence of ELF chorus waves shows evident correlation with the increase of background plasma density while the disturbance of ambient magnetic field is negligible. We calculate the growth rate of chorus waves by using the correlated data of waves and particles form the Van Allen Probes. The calculated growth rates agree well with the wave along the satellite orbit. The current study suggests that the plasma density may play an important role on controlling the wave frequency during the chorus generation process.
How does heat flux affect potential vorticity in the Southern Ocean?
Authors: Pimm Ciara , Williams Ric , Jones Dan , Meijers Andrew
Published: March 2021

Surface heat loss leads to thick winter mixed layers over the Southern Ocean, which feeds the formation of subsurface mode water pools through subduction. One such water class is Subantarctic Mode Water (SAMW), which is characterised by its low absolute potential vorticity. SAMW occurs in several regions of the Southern Ocean on the northern side of the Antarctic circumpolar current and it extends into the subtropics below the surface on different density surfaces. Using the ECCOv4 global ocean circulation model, we conduct a series of adjoint sensitivity experiments and forward perturbation experiments at key Southern Ocean SAMW formation sites, focusing on how different surface forcing affects potential vorticity. This adjoint approach produces time-evolving sensitivity maps that identify where and when surface heat loss potentially impacts the formation of mode waters. Over the first year in lead time, we find that greater surface heat loss leads to stronger convection and lower SAMW potential vorticity. On lead times longer than one year, in some regions of high sensitivity, the sensitivity reverses its sign, such that more surface heat loss ultimately leads to higher values of potential vorticity in the subduction regions. This reversal of sign of the sensitivity can be attributed to a shift from local convective forcing to upstream advective forcing and the associated redistribution of potential temperature and salinity. Surface adjustment also plays a role in the upstream sensitivities due to the tendency for temperature anomalies to be weakened through compensating salinity before reaching the subduction zone. We use the adjoint sensitivity fields to design a set of forward, non-linear perturbation experiments to provide physical insight into how ventilation affects the uptake of heat and carbon. This physical insight is important for identifying which physical mechanisms affect the subducted properties in the Southern Ocean, especially as the ocean warms through climate change.
Automated mapping of supraglacial hydrology using Machine Learning
Authors: Corr Diarmuid , Leeson Amber , McMillan Malcolm , Zhang Ce
Published: March 2021

Mass loss from Greenlandic and Antarctic ice sheets are predicted to be the dominant contribution to global sea level rise in coming years. Supraglacial lakes and channels are thought to play a significant role in ice sheet mass balance by causing the speed-up of grounded ice and weakening, floating ice shelves to the point of collapse. Identifying the location, distribution and life cycle of these hydrological features on both the Greenland and Antarctic ice sheets is therefore important in understanding their present and future contribution to global sea level rise. Supraglacial hydrological features can be easily identified by eye in optical satellite imagery. However, given that there are many thousands of these features, and they appear in many hundreds of satellite images, automated approaches to mapping these features in such images are urgently needed.

 

Current automated approaches in mapping supraglacial hydrology tend to have high false positive and false negative rates, which are often followed by manual corrections and quality control processes. Given the scale of the data however, methods such as those that require manual post-processing are not feasible for repeat monitoring of surface hydrology at continental scale. Here, we present initial results from our work conducted as part of the 4D Greenland and 4D Antarctica projects, which increases the accuracy of supraglacial lake and channel delineation using Sentinel-2 and Landsat-7/8 imagery, while reducing the need for manual intervention. We use Machine Learning approaches including a Random Forest algorithm trained to recognise water, ice, cloud, rock, shadow, blue-ice and crevassed regions. Both labelled optical imagery and auxiliary data (e.g. digital elevation models) are used in our approach. Our methods are trained and validated using data covering a range of glaciological and climatological conditions, including images of both ice sheets and those acquired at different points during the melt-season. The workflow, developed under Google Cloud Platform, which hosts the entire archive of Sentinel-2 and Landsat-8 data, allows for large-scale application over Greenlandic and Antarctic ice sheets, and is intended for repeated use throughout future melt-seasons.