bluuebunny/crossref_metadata_2025 huggingface dataset:
Geology, mineralization, and alteration of B prospect of the epithermal Au-Ag deposit in central Thailand: A study on Chatree’s peripheral deposit for further gold exploration.
Authors: Kaewpaluk Sirawit , Salam Abhisit , Assawincharoenkij Thitiphan , Manaka Takayuki , Poompuang Sopit , Munsamai Surachat
Published: March 2022

The B prospect is located at the southeast of the Chatree gold-silver deposit. The mineralization is hosted in the Late Permian-Early Triassic Chatree volcanic sequence consisting of volcaniclastic and volcanogenic-sedimentary rocks ranging in composition from basaltic andesite to rhyolite. At the study area, the total thickness of volcanic succession is about 300 meters, and the succession can be divided into three main stratigraphic units from bottom to top, namely, 1) porphyritic andesite unit (Unit 3), 2) polymictic intermediate breccia unit (Unit 2), and 3) volcanogenic sedimentary unit (Unit 1). The ore zones are mainly confined to polymictic intermediate breccia and volcanogenic sedimentary units (Units 1 and 2). At least three stages of mineralization have been identified, namely 1) quartz -pyrite (Stage 1), 2) quartz-chlorite-calcite-sulfides-electrum (Stage 2) and 3) quartz-calcite (stage 3) veins/veinlets. Gold occurs chiefly in Stage 2 mineralization which is characterized by typical vein textures of low sulfidation epithermal deposit (e.g., crustiform, colloform banding, comb textures). Pyrite is a primary sulfide mineral with minor sphalerite, chalcopyrite, and galena. Gold occurs as electrum with fineness ranging from 506 to 632 ppm. The hydrothermal alteration at B prospect is composed of two main types: 1) quartz-adularia (silicic alteration) assemblage close to ore zone, and 2) adularia-quartz-illite-calcite-chlorite (phyllic alteration) assemblage distal to ore zone. Based on characteristics of mineral assemblages, textures, and alterations the mineralization at B prospect can be classified as a low sulfidation epithermal gold-silver style deposit. 
Experimenting with automatized numerical methods
Authors: Schneider Naomi , Michel Volker
Published: March 2022

The approximation of the gravitational potential is still of interest in geodesy as it is utilized, e.g., for the mass transport of the Earth. The Inverse Problem Matching Pursuits (IPMPs) were proposed as alternative solvers for these kind of problems. They were successfully tested on diverse applications, including the downward continuation of the gravitational potential.

It is well-known that, for such linear inverse problems on the sphere, there exist a variety of global as well as local basis systems, e.g. spherical harmonics, Slepian functions as well as radial basis functions and wavelets. Each type has its specific pros and cons. Nonetheless, approximations are often represented in only one of them. On the contrary, the IPMPs enable an approximation as a mixture of diverse trial functions. They are chosen iteratively from an intentionally overcomplete dictionary such that the Tikhonov functional is reduced. However, an a-priori defined, finite dictionary has its own drawbacks, in particular with respect to efficiency.

Thus, we developed a learning add-on which uses an infinite dictionary instead while simultaneously reducing the computational cost. The add-on is implemented as constrained non-linear optimization problems with respect to the characteristic parameters of the different basis systems. In this talk, we give details on the matching pursuits and, in particular, the learning add-on and show recent numerical results with respect to the downward continuation of the gravitational potential.
ArchPy, automated hierarchical modelling of Quaternary aquifers: an example from the Upper Aare Valley, Switzerland
Authors: Schorpp Ludovic , Straubhaar Julien , Renard Philippe
Published: March 2022

When modelling groundwater systems in Quaternary formation, one of the first steps is to construct a geological and petrophysical model. This  is often  repetitive because it relies on multiple manual steps which include geophysical interpretation, construction of a structural model, identification of geostatistical model parameters, facies and property simulations. Those steps are often carried out in different softwares, which makes the automation intractable or very difficult. A non automated approach requires a lot of time and is critical to update the model for integrating new available data or when some geological interpretations are modified, and to conduct a cross-validation procedure to assess the overall quality of the models. Moreover, it renders the quantification of the joint structural and parametric uncertainty tedious. 

 

To address these issues, we propose a new approach and a Python module to automatically generate realistics geological and parameter models. One of its main features is that the modelling operates in a hierarchical manner. The input data consists of a set of borehole data, surface geology, and a stratigraphic pile. The stratigraphic pile describes formally and in a compact manner how the model should be constructed. It contains the list of the different stratigraphic units and their order in the pile, their conformability (eroded or onlap), the surface interpolation method (e.g. kriging, SGS, MPS, etc.) or also the filling method (e.g. MPS, SIS, etc.). Then, the procedure is automatic. In a first step the stratigraphic unit boundaries are simulated. Secondly, they are filled with lithologies and finally the petrophysical property models are simulated inside the lithologies. All these steps are straightforward and automated once the stratigraphical pile and its related parameters have been defined. Hence, this approach is extremely flexible. It is illustrated using data from an alpine quaternary aquifer in the Upper Aare plain (south-east of Bern, Switzerland).
Eddies, Winds, and Carbon in coupled ocean-circulation biogeochemical models: from the Baltic Sea to the Southern Ocean
Authors: Dietze Heiner , Löptien Ulrike
Published: March 2022

Recent advances in the development of hardware have pushed the explicit resolution of mesoscale (and, using nesting approaches, even sub-mesoscale) processes in global coupled ocean-circulation biogeochemical models within reach. This adds realism to the models in that previously-parameterized processes can now be explicitly resolved. Showcasing examples of our modeling work in the Baltic Sea, the subtropical North Atlantic and the Southern Ocean we will put the relevance of this paradigm to the test. We report on surprisingly small effects of explicitly-resolved mesoscale and even submesoscale features on a variety of domain-averaged entities such as air-sea and carbon cluxes in Boussinesq-approximated general ocean circulation models.
Temporal Variations of Shallow Material Properties During the Kumamoto Earthquake Sequence
Authors: D. D. Esfahani Reza , Cotton Fabrice , Bonilla Fabian
Published: March 2022

 Strong ground motion can generate a large dynamic strain in shallow materials, lead to a nonlinear response, and cause permanent damage in near-surface materials. The nonlinear behavior of soils subjected to strong vibrations leads to an increase in wave attenuation and a decrease in shear modulus. These effects lead to a decrease in the resonance frequency of the soil and a decrease in the propagation speed of S-waves. This work investigates, using deconvolution and autocorrelation methods, “in situ” seismic velocity changes and predominant ground-motion frequency evolution during the 2016 Kumamoto earthquake sequence. The Kumamoto sequence contains two major foreshocks (Mw6, Mw6.2) and a mainshock (Mw7.2) that occurred 24 hours after the last foreshock. We present results of the seismic velocity evolution during this sequence for seismological records collected by Kik-Net and K-Net stations between 2002 to 2020. The results indicate that nonlinearity response is profoundly occurring in the damaged material close to the surface. We quantify these velocity reductions occurring during the mainshock and show that the healing process lasted about three months after the mainshock. We finally quantify the relationships between velocity changes, ground-motion predominant frequency variations, and site condition characteristics (Vs30).  
Study of common aperiodic displacements at ITRF co-location sites
Authors: de La Serve Maylis , Rebischung Paul , Altamimi Zuheir , Collilieux Xavier , Métivier Laurent
Published: March 2022

In historical versions of the International Terrestrial Reference Frame (ITRF), the time evolution of station positions was described by piece-wise linear models. These kinematic models have been extended with exponential and logarithmic functions in ITRF2014 to account for post-seismic displacements, then with annual and semi-annual sine waves in ITRF2020 to account for the seasonal deformation of the Earth. However, part of the Earth’s surface deformation, such as inter-annual hydrological loading deformation, or high-frequency atmospheric loading deformation, is still not captured by such deterministic functions.

A reference frame in the form of a time series could allow such aperiodic displacements to be taken into account. This would require the aperiodic motions sensed by the different space geodetic techniques to be tied in a common frame by means of co-motion constraints. However, common aperiodic displacements between co-located space geodetic stations have not been evidenced at a global scale so far, and the relevance of such constraints is thus debatable. In this study, in order to investigate the possible existence of common aperiodic displacements at ITRF co-location sites, we use the solutions provided by the technique services for ITRF2014. Those solutions are first carefully aligned to a common reference frame in order to minimize differential network effects and obtain comparable position time series across techniques. The obtained position time series are then cleaned from linear, post-seismic and periodic signals (including seasonal deformation and technique systematic errors). The remaining aperiodic displacements are finally inter-compared at co-location sites.

Modest correlations are thus evidenced between the GNSS residual position time series and the other space geodetic techniques, mostly in the vertical component. The magnitude of the common aperiodic displacements evidenced in this study is finally discussed.
A proxy compatible model for the YD and the subsequent greening of the Sahara
Authors: Velay-Vitow Jesse , Chandan Deepak , Peltier Richard
Published: March 2022

Throughout the Quaternary, northern Africa has experienced recurring periods of intensified precipitation, known as African Humid Periods. The most recent such period began after the termination of the Younger Dryas (YD), which was a dramatic reversion to ice-age temperatures during the deglaciation. One intriguing explanation for the timing of this most recent greening of the Sahara is that the rapid recovery of the Atlantic Meridional Overturning Circulation (AMOC) after the YD caused a northward shift of the Inter-Tropical Convergence Zone (ITCZ), resulting in increased precipitation in Northern Africa. In previous attempts to model the YD (Peltier et al., 2006; Peltier, 2007), and the subsequent transition to a Green Sahara, (Menviel et al. 2021, 2011), the total volume of freshwater forcing applied to the Arctic Ocean was quite large. The Eustatic Sea Level (ESL) increase associated with the freshwater influx in these studies is not compatible with proxy inferred ESL constraints. Furthermore, the increase in precipitation at the end of the YD was not nearly as abrupt as that which was simulated for the Green Sahara period at the end of the penultimate deglaciation, a fact that the authors attributed to the misalignment of the timing of AMOC maximum and the maximum in insolation forcing at the YD.

Here we present a model of the YD, in which only 0.15 Sv forcing for 100 years, applied to the Beaufort Gyre, was needed to collapse the AMOC and keep it in a collapsed state for nearly 1000 additional years. As the YD is approximately 1000 years long, we are able to achieve this interval of AMOC shutdown without continuously hosing the model with freshwater. As a result, the ESL rise in our model is physically plausible. Furthermore, unlike the results of Menviel et al. (2021, 2011), the simulated precipitation over North Africa in our model increases abruptly, in step with the abrupt resumption of the AMOC. The AMOC itself recovers due to a reinvigorated ocean-atmosphere flux exchange that occurs following the opening of a polynya in the Irminger Sea.
Building a climate change impacts portal for Senegal to promote decision making
Authors: Sultan Benjamin , Sane Youssouph
Published: March 2022

In recent decades, West Africa has experienced some of the most extreme rainfall variability anywhere in the world with adverse impacts on different sectors such as food security or water resources. Climate projections for the 21st century tend to show that the future could be even worse. Better access to reliable climate information underpins effective climate change adaptation in a variety of sectors. However the data needed are often hard to find and there are major obstacles which limit the confidence and use of this information in decision-making processes: climate data use requires very good IT skills and climate knowledge. Effective and easy to use climate tools require a clear need for interactive climate portals that allow data visualization and download for further analysis. Although, some climate portals already exist in West Africa, most of them suffer from major flaws or were not designed based on user’s needs. To address this challenge, IRD together with ANACIM (Senegalese Meteorological Service) co-designed a Web-portal in Senegal with high quality simulations and following three steps to make it usable by stakeholders: (i) build a dialogue with relevant stakeholders, (ii) develop methodologies for using climate and impacts models and (iii) perform capacity building and training activities. This talk will illustrate those three steps of the design of the Web-portal.
Interpretable Solar Flare Prediction with Deep Learning
Authors: Jarolim Robert , Veronig Astrid , Podladchikova Tatiana , Thalmann Julia , Narnhofer Dominik , Hofinger Markus , Pock Thomas
Published: March 2022

Solar flares and coronal mass ejections (CMEs) are the main drivers for severe space weather disturbances on Earth and other planets. While the geo-effects of CMEs give us a lead time of about 1 to 4 days, the effects of flares and flare-accelerated solar energetic particles (SEPs) are very immediate, 8 minutes for the enhanced radiation and as short as about 20 minutes for the highest energy SEPs arriving at Earth. Thus, predictions of solar flare occurrence at least several hours ahead are of high importance for the mitigation of severe space weather effects.

Observations and simulations of solar flares suggest that the structure and evolution of the active region’s magnetic field is a key component for energetic eruptions. The recent advances in deep learning provide tools to directly learn complex relations from multi-dimensional data. Here, we present a novel deep learning method for short-term solar flare prediction. The algorithm is based on the HMI photospheric line-of-sight magnetic field and its temporal evolution together with the coronal evolution as observed by multi-wavelengths EUV filtergrams from the AIA instrument onboard the Solar Dynamics Observatory. We train a neural network to independently identify features in the imaging data based on the dynamic evolution of the coronal structure and the photospheric magnetic field evolution, which may hint at flare occurrence in the near future.

We show that our method  can reliably predict flares six hours ahead, with 73% correct flaring predictions (89% when considering only M- and X-class flares), and 83% correct quiet active region predictions.

In order to overcome the “black box problem” of machine-learning algorithms, and thus to allow for physical interpretation of the network findings, we employ a spatio-temporal attention mechanism. This allows us to extract the emphasized regions, which reveal the neural network interpretation of the flare onset conditions. Our comparison shows that predicted precursors are associated with the position of flare occurrence, respond to dynamic changes, and align with characteristics within the active region.
Shallow Fracture Buffers High Elevation Runoff in Northwest Greenland
Authors: Culberg Riley , Chu Winnie , Schroeder Dustin
Published: March 2022

The growth of shallow, low-permeability ice slabs in Greenland’s firn is known to increase surface meltwater runoff by hindering vertical percolation. However, the partitioning of meltwater between local impoundment, downslope runoff, and drainage to the ice sheet bed is still poorly constrained. Northwest Greenland is a particularly interesting study area for understanding the role of englacial hydrology because ice-penetrating radar surveys have identified coexisting ice slabs and firn aquifers in this region. These results suggest that ice slabs may not necessarily preclude local firn water storage. However, the mechanism that would allow these two distinct facies to develop together is unclear.

               To examine the relationship between firn aquifers and ice slabs in Northwest Greenland, we analyzed six-years of NASA Operation IceBridge radar data between 2011 and 2017. These observations show that isolated, short-lived water pockets frequently develop beneath the ice slabs and over time refreeze to form kilometer-scale ellipsoidal buried ice masses. These ice blobs covered ~14% of the 1176 radar line-kms flown in 2017 and analysis of Landsat imagery between 2000 and 2016 shows they are spatially correlated with visible runoff in supraglacial lakes, streams, or massive slush swamps. High-resolution optical satellite imagery also shows that surface crevassing is widespread in this region and that many of the ice blobs are associated with moulins or lake drainage events in the 2012 melt season. This suggests that ice blobs form where fractures create high permeability pathways through the ice slab through which surface meltwater can drain into the relict firn. In the short term, this process impounds water and heat in the upper 30 meters of the ice column, reducing surface runoff and limiting the immediate impact of surface melt on local ice dynamics. However, on longer timescales, this efficient filling of pore space beneath supraglacial flow paths may lead to more efficient surface hydrology and full ice thickness hydrofracture at high elevations. 
Extracellular enzyme stoichiometry reflects the C-and P- microbial metabolic limitations along a grassland succession on the Loess Plateau in China.
Authors: Xue Zhijing , Liu Chunhui , Wolfgang Wanek
Published: March 2022

Soil extracellular enzyme stoichiometry (EES) reflects the biogeochemical balance between microbial metabolic requirements and environmental nutrient availability. Previous studies have focused on the perspective of nutrient acquisition, while soil microbial metabolic limitations (SMML) were minor in the focus of those studies. Therefore, how grassland succession drives SMML has mainly been under explored. Here, we used EES models to identify the response of SMML during grassland restoration while also investigating potential implications of microbial nutritional limitations across the time series (herbaceous succession) and with space (transformation interface soil and underlying topsoil layer) in a grassland restoration series. The results showed that soil microorganisms were generally limited by C, both in the transformation interface soil (TIS) and the underlying topsoil layer (UTS). During herbaceous succession, microbial P-limitation was more substantial than that by N-limitation. Microbial C-limitation displayed a uni-modal direction, peaking in intermediate successional stages. However, microbial P-limitation presented the opposite trend. In the TIS layer, SMML gradually transferred from P- to N- and back to P-limitation at later successional stages. Biotic factors, together with soil basic index, and soil nutrients, explained 92.2% of the variation in microbial C-limitation and 84.4% of the variation in microbial P-limitation. Multi-interaction factors show the most significant relative influences of 65.11% (TIS) and 43% (UTS) of the SMML, respectively. Microbial C-limitation was induced by the imbalance between C supply and microbial C demand, while the changes in microbial P-limitation were due to changes in the competition for P between plants and microorganisms. Therefore, the impacts of long-term grassland succession on SMML resulted from the concerted changes in vegetation composition, soil properties, and the nutritional demands of the soil microorganisms.
Arctic Sea-Ice Permittivity Derived from GNSS Reflectometry Data of the MOSAiC Expedition 
Authors: Semmling Maximilian , Wickert Jens , Kreß Frederik , Hoque Mainul , Divine Dmitry , Gerland Sebastian , Spreen Gunnar
Published: March 2022

Sea ice is a crucial parameter of the Earth’s climate system. Its high albedo compared to water and its insulating effect between ocean and atmosphere influences the oceans’ radiation budget significantly. The importance of monitoring sea-ice properties arises from the high variability of sea ice induced by seasonal change and global warming. GNSS reflectometry can contribute to global monitoring of sea ice with high potential to extend the spatio-temporal coverage of today’s observation techniques. Properties like ice salinity, temperature, thickness and snow cover can affect the signal reflection. The MOSAiC expedition (Multidisciplinary drifting Observatory for the Study of Arctic Climate) gave us the opportunity to conduct reflectometry measurements under different sea-ice conditions in the central Arctic. A dedicated setup was mounted, in close cooperation with the Alfred-Wegener-Institute (AWI), on the German research icebreaker Polarstern that drifted for one year with the Arctic sea ice.

We present results from data recorded between autumn 2019 and spring 2020. The ship drifted in this period from the Siberian Sector of the Arctic (October 2019), over the central Arctic (November 2019 until May 2020) towards Fram Strait and Svalbard (reached in June 2020). Profiles of sea-ice reflectivity over elevation angle (range: 1° to 45°) are derived with daily resolution considering reflection data recorded at left-handed (LH) and right-handed (RH) circular polarization. Respective predictions of reflectivity are based on reflection models of bulk sea ice or a sea-ice slab. The latter allows to include the effect of signal penetration down to the underlying water. Results of comparison between LH profiles and bulk model confirm a reflectivity decrease (about 10 dB) when surrounding open water areas is reduced (by freezing) and the ship drifts in compact sea ice.

Further results comprise estimates of sea-ice permittivity from mid-elevation range reflectivity (10° to 30°). The median of estimated permittivity 2.4 (period of compact sea ice) lies in the expected range of reported old ice type (mostly second-year ice). The retrieved reflectivity in the low-elevation range (1° to 10°) give strong indication of signal penetration into the dominating second-year ice with influence of sea ice temperature and thickness. We conclude that sea-ice characterization in future can profit form GNSS reflectometry observations. The on-going study is currently extended to the further evolution of Arctic sea ice during winter and spring period of the MOSAiC expedition.
Imaging TGFs and GRBs from the earth rim mounting of the ASIM/MXGS imager-spectrometer on the ISS
Authors: Connell Paul , Reglero Victor , Navarro Javier , Eyles Christopher
Published: March 2022

On January 10th 2022 the ASIM mission to the ISS was moved to the SDN mount point on the Columbus module for observations towards the earth rim and the cosmos. This enabled the ASIM/MXGS imager spectrometer to observe TGFs in a small ISS nadir FOV covering 35-65 degrees off-axis, and GRBs in the cosmos which covers most of its FOV. We present here initial results of imaging locations for off-axis TGFs with a low spectral hardness ratio and a much larger event count due to the reduction in the "flux cosine effect", and how this might facilitate estimates of mean TGF altitude. We also present the first MXGS location images of second long GRBs and their associated lightcurves and spectra.
Determining optimal scale of water infrastructure considering economical aspects with stochastic evaluation – Case study at the Municipality of Western Mani
Authors: Markantonis David , Siganou Aimilia , Moraiti Konstantina , Nikolinakou Maria , Sargentis G.-Fivos , Dimitriadis Panayiotis , Chiotinis Michalis , Iliopoulou Theano , Mamassis Nikolaos , Koutsoyiannis Demetris
Published: March 2022

Infrastructures for the supply of water are one of the most necessary facilities in modern life. The optimal design of such infrastructures (for example, dams or even small-size tanks) is often a great challenge in civil engineering, given the large number of factors required for their design (e.g., feasibility, reliability, cost effectiveness, resilience). One of the most critical decisions that may have a great impact on the optimization procedure is the determination of the scale of the proposed system.

During a study of such a design of a water supply infrastructure in the Municipality of Western Mani, it became clear that several solutions of different scales coexisted. Ultimately, the cost-benefit factors were the most heavily considered ones, provided that the required reliability was met. Stochastic methods have been proven to be appropriate tools for studying such highly complex and uncertain puzzles. The current study intends to approach this problem by considering solutions of different scales, and to establish the long-term cost effectiveness as the main criterion to evaluate the different solutions.
Dynamic Water-Energy-Food nexus management in transboundary river basins incorporating water infrastructure operation and demand control
Authors: Yang Guang , Giuliani Matteo , Matta Elena , Piuri Veronica , Castelletti Andrea
Published: March 2022

Water resources infrastructure plays an important role in energy and food security by providing water storage for hydropower generation and food production. Yet, Water, Energy, and Food (WEF) often interplay and evolve dynamically over time with social-economic development and water system expansions. Understanding the WEF Nexus is particularly challenging in transboundary contexts, where interdependencies also develop across multiple riparian countries. In this work, we investigate how to address the WEF Nexus in transboundary river basins to discover innovative solutions mitigating existing tradeoffs and facilitating international agreements. Our approach is demonstrated on the Nile River basin, where we explore tradeoffs between power generation and irrigation water supply across Ethiopia, Sudan, and Egypt. In particular, we analyze innovative portfolios of interventions that combine the coordinated operation of large water reservoirs (i.e., the Grand Ethiopian Renaissance Dam, Merowe Dam, and High Aswan Dam) and the main irrigation diversions, with water demand management options (e.g., aquaponics systems, new desalination plants) for reducing the water demand in the Nile Delta. Our results show that the Nile River basin features both strong tradeoffs and notable synergies across the WEF Nexus and across countries. For example, our analysis shows a clear tradeoff between hydropower generation in Egypt and irrigation water supply in Sudan. In contrast, the hydropower generation in Sudan and Egypt are positively correlated. Additional challenges will be generated by the projected decrease in water availability as suggested by most climate change scenarios. Finally, the potential reduction of the irrigation demands in the Nile Delta can contribute in mitigating existing tradeoffs and represents an additional option in the current international negotiations between Ethiopia, Sudan, and Egypt.
Sensitivity of the relationship between Antarctic ice shelves and iron supply to projected changes in the atmospheric forcing
Authors: Dinniman Mike , St-Laurent Pierre , Arrigo Kevin , Hofmann Eileen , van Dijken Gert
Published: March 2022

Previous studies showed that correlations of satellite-derived estimates of chlorophyll a in coastal polynyas over the Antarctic continental shelf with the basal melt rate of adjacent ice shelves are a result of upward advection or mixing of iron-rich deep waters due to circulation changes driven by ice shelf melt, rather than a direct influence of iron released from melting ice shelves.  In this study, the effects of projected changes in winds, precipitation, and atmospheric temperatures on this relationship were examined with a 5-km resolution ocean/sea ice/ice shelf model of the Southern Ocean.  The atmospheric changes are added as idealized increments to the forcing.  Inclusion of a poleward shift and strengthening of the winds, increased precipitation, and warmer atmospheric temperatures resulted in an 83% increase in the total Antarctic ice shelf basal melt, with changes being heterogeneously distributed around the continent.  The total dissolved iron supply to the surface waters over the continental shelf increased by 62%, while the surface iron supply due just to basal melt driven overturning increased by 48%.  However, even though the total increase in iron supply is greater than the increase due to changes in the ice shelf melt, the ice shelf driven supply becomes relatively even more important in some locations, such as the Amundsen and Bellingshausen Seas.  The modified atmospheric conditions also produced a reduction in summer sea ice extent and a shoaling of the summer mixed layers.  These simulated responses to projected changes suggest relief of light and nutrient limitation for phytoplankton blooms over the Antarctic continental shelf and perhaps an increase in annual production in years to come.
Satellite detection of firn aquifers in the Antarctic Peninsula
Authors: Buth Lena , Veldhuijsen Sanne , Wouters Bert , Lhermitte Stef , van den Broeke Michiel
Published: March 2022

In recent years, the existence of firn aquifers in the Antarctic Peninsula (AP) has been confirmed by in situ observations. Due to their importance for understanding the hydrology of the Antarctic ice sheet, a more spatially comprehensive assessment of AP firn aquifers is desirable. The purpose of this study is to map firn aquifers in the AP from space using C-band Synthetic Aperture Radar imagery from ESA's Sentinel-1 mission. This product enables the detection of firn aquifers at 1 km2 resolution for the period 2017 to 2020. The method is based on quantifying the characteristic shape of the backscatter curve over time during the (partial) refreezing of the liquid water in the firn layer after each peak melt season. In this context, both seasonal aquifers and perennial aquifers are detected together, acknowledging that their backscatter signature in any given year is indistinguishable with the given method. With the new method, seasonal firn aquifers are being detected in the north and northwest of the AP, as well as on the Wilkins Ice Shelf and the George VI Ice Shelf. Imposing the aquifers to occur during all available years, as a proxy for perennial firn aquifers, limits their extent to the north and northwest AP. Both distributions agree well with model simulations. Further in situ and modelling studies and longer time series of satellite observations are needed to validate the results of this study.
Turbulence Metrics from Surface Image Velocimetry
Authors: Zandonadi Moura Leonardo , Ferreira Rui , Aleixo Rui
Published: March 2022

Image-based monitoring of rivers is a growing field of research and is being popularized as a technical alternative for discharge, erosion and flood risk estimation applications. Surface velocimetry can also be a way to characterize the turbulence structure of shallow flows, making possible the remote determination of quantities of interest such as dissipation and integral length scales. To evaluate velocimetry methods and data processing workflows, a laboratory facility emulating a river reach was assembled at IST, and monitored using commercial grade cameras, in field-like conditions. In this work the results of estimates of turbulent dissipation and integral length scales using multiple methods are provided, along with a discussion on the differences among methods and possible applications of the derived data in hydrodynamic model parameter calibration and data assimilation. LSPIV and PTV display similar results with regard to velocity estimation and vortex detection. In the estimation of integral lengths, the longitudinal scales are most affected by limitations in the measurement setup, whereas for the dissipation and turbulent viscosity estimates, spectrum methods seem to be less reliable than simpler methods based on dimensional analysis and integral length scales.
Changing extreme sea levels in the Ganges-Brahmaputra-Meghna delta
Authors: Mussa Alexandre , Becker Mélanie , Karpytchev Mikhail
Published: March 2022

Low-standing deltas are a home for half a billion of people that are extremely vulnerable to sea level variations. Justly only in the Ganges-Brahmaputra-Meghna (GBM) delta, over 100 million people suffer every year from floods due to storm surges and monsoons exacerbated by the ongoing sea level rise. The aim of our study is to re-assess the variations of extreme sea levels (ESL), as well as the interactions between the relative sea level rise and the ESL in the GBM delta. A set of hourly tide gauge records from the Bay of Bengal, especially from the low-lying Bangladesh's coastal area, has been used to evaluate ESL changes over the past decades. We focus on the variations of extreme high waters and their components (surge and tide), and on the interaction between them by applying advanced methods of statistical extreme values analysis. An assessment of temporal changes in storm surge duration and their intensity was obtained in the framework of a rigorous re-analysis of the past storm surge events.
Optimizing water infrastructure solutions for small-scale distributed settlements – Case study at the Municipality of Western Mani.
Authors: Moraiti Konstantina , Markantonis David , Nikolinakou Maria , Siganou Aimilia , Sargentis G.-Fivos , Iliopoulou Theano , Dimitriadis Panayiotis , Meletopoulos Ilias Taygetos , Mamassis Nikos , Koutsoyiannis Demetris
Published: March 2022

Water infrastructure is an indicator of human civilization and its evolution. The sustainable water management and distribution to local communities remains a critical engineering priority so that the most efficient usage is achieved. In this analysis the design of water-infrastructure establishments is studied for the community of the Municipality of Western Mani (western Peloponnese, Greece).

One of the main issues that arise is the presence of karstic-limestone geological structure at the study area with no permanent watercourses. Furthermore, the lack of data about the current quantity of surface water makes it difficult to formulate trustworthy conclusions on the availability of water resources. Additionally, the notable growth of the tourist sector during the summer months in the past few years exacerbates this issue. Due to the above reasons, the available water is not enough to cover the needs of the Municipality, especially during the summer.

After examining all the possible options that have been proposed to increase the water availability (e.g., through dams, wells, desalination, water ponds etc.), we investigate an optimal solution that aims to achieve a more efficient water management and distribution to the communities of Western Mani. To this aim, we apply a multi-criteria decision-making approach by also considering local traditional water harvesting systems to increase water resilience.
Forest damage caused by the impact of strong wind during extra-tropical cyclones – modelling and prediction
Authors: Pawlik Lukasz , Harrison Sandy , Godziek Janusz , Zawolik Lukasz
Published: March 2022

Climate change will potentially modify wind characteristics related to the passage of extra-tropical cyclones over Europe, and the increasing frequency of strong winds will increase forest damage. Negative impacts will be significantly higher in managed forests. Analyzing data about past forest damage can provide a better understanding of the complex relationship between tree/forest features, wind climate properties, and the rate of forest damage. We present results of forest damage modelling and prediction using machine learning techniques. We applied five machine learning methods to data on the volume (m3) of damaged trees between 2007-2010. In a second step, logistic regression was applied to these data expressed as a rate of damaged forest area. We focus on two case studies: the Sudety Mountains region in SW Poland and the catastrophic damage caused by windstorm Klaus in SW France in 2009. We found that the best predictors of tree damage were tree age and volume, the distance from the windstorm track, the normalised difference vegetation index (NDVI) and wind exposure. For the second case study, we tested several combinations of data splitting cut-off levels and various definitions of the damage class during the training stage of the modeling. We obtained models' good predictive power (accuracy and AUC > 0.7) for training and test sets in both cases.

 

The study has been supported by the Polish National Science Centre (project no 2018/28/U/ST10/00075 and 2019/35/O/ST10/00032) and the ERC Advanced Grant (project no 694481).
High off-season nitrous oxide emissions negate potential soil C-gain from cover crops in boreal cereal cropping
Authors: Dörsch Peter , Sturite Ievina , Trier Kjær Sigrid
Published: March 2022

Enhancing carbon storage in managed soils through increased use of cover and catch crops in cereal cropping is at the heart of a carbon-negative agriculture. However, increased C storage by additional biomass production has a nitrogen cost, both in form of increased N fertilizer use and by potentially increasing nitrous oxide (N2O) emissions when cover crops decay. Frost-sensitive, N-rich aboveground biomass may be a particular problem during wintertime, as it may fuel off season N2O emissions during freezing-thawing cycles, which have been shown to dominate the annual N2O budget of many temperate and boreal sites. Here we report growing season and winter N2O emissions in a plot experiment in SE Norway, testing a barley production system with seven different catch and cover crops (perennial and Italian ryegrass, oilseed radish, summer and winter vetch, phacelia​ and an herb mixture) against a control without cover crops. Cover crops where either undersown in spring or established after harvesting barley. While ryegrass undersown to barley marginally reduced N2O emissions during the growing season, freeze-thaw cycles in winter resulted in significantly larger N2O emissions in treatments with N-rich cover crops (oilseed reddish, vetch) and Italian ryegrass. N2O budgets will be presented relative to aboveground yield and quality of cover crops and compared to potential souil organic carbon gains. 
Formation of dense water over the North Atlantic subpolar gyre in a hierarchy of climate models
Authors: Petit Tillys , Robson Jon , Ferreira David
Published: March 2022

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate. Recent observations have highlighted the dominant role of the buoyancy forcing in the transformation of surface waters to the AMOC lower limb at subpolar latitudes. The short (4 years) length of the OSNAP timeseries, however, limits conclusions over longer time scales. To investigate a wide range of temporal scales, we use three 100-years long coupled simulations of HadGEM3-GC3.1, at resolutions ranging from ~130 km atmosphere and 1° ocean to 25 km atmosphere and 1/12° ocean. In line with observations, the models show that the mean overturning and buoyancy-induced transformation are concentrated in the eastern subpolar gyre rather than in the Labrador Sea.

However, the horizontal resolution of the models impacts the formation of dense water over the subpolar gyre. An unrealistically large sea ice extent induces a weak buoyancy-induced transformation over the western subpolar gyre at low resolution, while a bias in surface density produces too dense water at high resolution. These biases are associated with a shift in the location of dense water formation. The transformation is mainly localized in the interior of the Irminger and Labrador seas at low resolution, and over the boundary current at high resolution. The interannual variability of the transformation is thus driven by different mechanisms between the simulations. In contrast with observations, the interannual variance in air-sea fluxes plays a more prominent role in the variance of transformation along the boundary current at high resolution.
Atlantic Water properties, transport, and water mass transformation from mooring observations north of Svalbard 
Authors: Koenig Zoé , Kalhagen Kjersti , Kolås Eivind , Fer Ilker , Nilsen Frank , Cottier Finlo
Published: March 2022

The Atlantic Water inflow to the Arctic Ocean is transformed and modified in the ocean areas north of Svalbard, and influences the Arctic Ocean heat and salt budget. As the Atlantic Water layer advances into the Arctic, its core deepens from about 250 m depth around the Yermak Plateau to 350 m in the Laptev Sea, and gets colder and less saline due to mixing with surrounding waters. The complex topography in the region facilitates vertical and horizontal exchanges between the water masses and, together with strong shear and tidal forcing driving increased mixing rates, impacts the heat and salt content of the Atlantic Water layer that will circulate around the Arctic Ocean.

In September 2018, 6 moorings organized in 2 arrays were deployed across the Atlantic Water Boundary current for more than one year (until November 2019), within the framework of the Nansen Legacy project to investigate the seasonal variations of this current and the transformation of the Atlantic Water North of Svalbard. The Atlantic Water inflow exhibits a large seasonal signal, with maxima in core temperature and along-isobath velocities in fall and minima in spring. Volume transport of the Atlantic Water inflow varies from 0.7 Sv in spring to 3 Sv in fall. An empirical orthogonal function analysis of the daily cross-isobath temperature sections reveals that the first mode of variation (explained variance ~80%) is the seasonal cycle with an on/off mode in the temperature core. This first mode of variation is linked to the first mode of variation of the current. The second mode (explained variance ~ 15%) corresponds to a shorter time scale (6-7 days) variability in the onshore/offshore displacement of the temperature core linked to the mesoscale variability. On the shelf, a counter-current flowing westward is observed in spring, which transports colder (~ 1°C) and fresher (~ 34.85 g kg-1) water than Atlantic Water (θ > 2°C and SA > 34.9 g kg-1). This counter-current is driven by Ekman dynamics. At greater depth (~1000 m) on the offshore part of the slope, a bottom-intensified current is detected, partly correlated with the wind stress curl. Heat loss of the Atlantic Water between the two mooring arrays is maximum in winter, estimated to 300-400 W m-2 when the current speed and the heat loss to the atmosphere are the largest.

 
A global scale assessment of the intensification of rainfall extremes
Authors: Paschalis Athanasios , Moustakis Yiannis , Chen Yuting
Published: March 2022

Intensification of precipitation extremes under a changing climate is expected to severely impact societies due to increased flooding, and its impacts on infrastructure, agriculture, and ecosystems. Extensive research in the last decades has identified multiple facets of precipitation changes, from super Clausius – Clapeyron scaling of precipitation extremes with temperature increase, to the change of the intensity and spatial extent of mesoscale convective systems.

In this study we attempt to compile state of the art data and simulations to understand the multiple facets of the changes in precipitation extremes across the world. To do that we combined data from thousands of weather stations globally, reanalysis datasets, and general circulation and convection permitting model simulations. Our results show that:

Hourly precipitation extremes scale with temperature at a rate of ~7%/K globally, albeit very large spatial heterogeneities were found, linked to topography, large-scale weather dynamics and local features of atmospheric convection

Precipitation extremes change beyond this thermodynamic basis, with increases in the heaviness of the tails of precipitation distribution at fine scales

The spatial extent of convective systems is expected to increase

Precipitation extremes with shorter spell duration that are distributed more uniformly throughout the year are expected
Stochastic modeling of CO2 fluctuations and Snowball transitions on Earth and other planets
Authors: Wordsworth Robin , Knoll Andrew
Published: March 2022

The question of what causes global glaciations to occur on Earth-like planets is of great importance to habitability and climate evolution. Earth itself has a complex climate history consisting of long stretches of apparently clement conditions in the Archean, a stable Proterozoic climate punctuated by major intervals of glaciation at the beginning and end, and fluctuation between warm and cool climates in the Phanerozoic without any further global glaciation events. Deterministic models of the carbonate-silicate cycle on Earth-like planets do not predict such a sequence of transitions, instead yielding either permanently clement conditions, or limit-cycle behavior only for planets receiving low stellar fluxes.

In this work, we take a stochastic approach to modeling atmospheric CO2 evolution. We present a simple model that assumes an imperfect CO2 thermostat, such that pCO2 follows a bounded random walk around a mean value that alone would maintain clement climate conditions. Because less CO2 is required to keep the planet warm as solar luminosity increases, the model predicts an increase in climate variability with time. This implies that unless some mechanism is present to decrease CO2 variance as stellar luminosity increases, the climates of Earth-like planets should become increasingly unstable as they approach the inner edge of their systems’ habitable zones. Implications for exoplanets are discussed, and the model is then applied to the specific problem of Earth’s climate history. In particular, the potential role of the biosphere in forcing and/or inhibiting Snowball transitions both in the Phanerozoic and earlier in Earth history is discussed.