bluuebunny/crossref_metadata_2025 huggingface dataset:
Process-based GCMs evaluation over South Tropical South America during the dry-to-wet transition season following a weather typing approach
Authors: Olmo Matias , Espinoza Jhan Carlo , Bettolli Maria Laura , Sierra Juan Pablo , Junquas Clementine , Arias Paola
Published: March 2022

The representation of the South American Monsoon System (SAMS) by global climate models (GCMs) is of key relevance for a better comprehension of the physical mechanisms behind the recent and future climate changes over South Tropical South America (STSA) in a global warming scenario. During the last four decades STSA experimented a lengthening of the dry season related to diverse forcings, leading to an increase in fire activity and severe socio-environmental impacts. In the present study, a set of 16 GCMs simulations from the CMIP6 experiment were evaluated during the historical period 1979-2014 in terms of how well they reproduced the atmospheric circulation over STSA through a weather-typing (WTs) approach. 9 WTs were first identified based on low-level wind anomalies from the ERA5 reanalysis, which summarized the atmospheric variations over STSA throughout the year. Focus was put on the representation of WTs during the SAMS initiation and the dry-to-wet transition season (from July to October). Model performance depended on the seasonal cycle and spatial structure of the WTs. Some of the GCMs adequately reproduced the different WTs and their spatio-temporal configurations, with lower skills in the transition seasons. Furthermore, GCMs tended to go from dry to wet conditions too quickly, evidencing deficiencies in the representation of the SAMS onset. This was particularly associated with a poor representation of the southerly wind intrusions to STSA and the intra-seasonal variability of the South American low-level jet. In terms of the relationship between WTs and rainfall on interannual time-scales, a selection of GCMs was able to associate the occurrence of anomalous wet and dry years with specific WTs, indicating well-represented physical processes modulating precipitation variability. Overall, this study could identify few GCMs that managed to simulate the main atmospheric circulation features in STSA (among them, the CESM2, CMCC-CM2-HR4 and MPI-ESM1-2-HR models), which is particularly important for driving high-resolution modelling experiments as well as for the analysis of future projections.
Effect of Channel Bed Slope on Shannon Entropy-Based Velocity Distribution in Open Channel Flow
Authors: Singh Gurpinder , Khosa Rakesh
Published: March 2022

Streamflow measurement is essential in hydraulic engineering to develop and manage water resources and ensure they are managed correctly and adequately. Two primary parameters for discharge measurements in natural rivers, namely, the mean flow velocity and cross-sectional flow area at the measurement site, are requisites. The cross-sectional area of the section could be measured using river bathymetric surveys or by using advanced and modern methods such as Acoustic Doppler Current Profiler (ADCP). For mean velocity, numerous ways and tools are available depending on the fact, whether the measurements are taken from a distance (non-contact) or using a contact method (traditional approach). Nowadays, non-contact velocity measurement approaches are becoming more popular as they are less time-consuming and user‑friendly to deal with high flows and rough weather. In contrast, the entropy-based concepts (such as Shannon entropy, Tsallis entropy and Renyi entropy) are utilized to obtain the discharge from the non-contact measurements, which gives better results than the traditional approaches such as the velocity area method. Entropy-based velocity distribution depends on the crucial parameter called entropy parameter (a function of the mean and maximum velocity), which is linked to the channel characteristics such as channel roughness and bed slope. Due to a lack of concrete evidence regarding its variation with the channel characteristics, the entropy parameter was surmised as constant. In this study, the experimental velocity data was collected from a rectangular flume fitted with a mechanical apparatus to change the bed slope. The obtained velocity data was employed to comment on the actual variation of the Shannon entropy parameter for the one such channel characteristic, i.e., channel bed slope. The velocity data analysis depict only a slight variation in entropy parameter. In addition, the discharge error analysis provided a substantial justification for using a unique constant value of the entropy parameter for the whole cross-section can be utilized instead of individual values for each channel bed slope condition.
Prediction of north Indian Ocean Tropical Cyclones  using  WRF model:  Sensitivity for perturbation and filtering on the initial condition
Authors: Tiwari Gaurav , Kumar Pankaj , Bobde Vishal , Mishra Alok Kumar
Published: March 2022

The northern Indian Ocean (NIO) is known for tropical cyclones (TCs), likely to increase in the future. It occurs mainly in April-June (pre-monsoon) and October-December (post-monsoon) seasons, destructive for the coastal regions of India, Bangladesh, Pakistan, Oman. To provide reliable alerts and disaster warnings ahead of time, better forecasting of TC aspects (such as track, landfall, strength, rainfall, and so on) is a primary focus. The Weather Research and Forecasting (WRF) model is a mesoscale numerical weather prediction system used to forecast short and medium-range weather phenomena. The reliability of the skill of WRF prediction has been qualitatively enhanced with the successful implementation of some advanced methods and subjected to various constraints i.e. initial conditions, domain, parameterization, etc. In this study, the sensitivity of the initialization is accessed by deploying the digital filter initialization (DFI), and a stochastically perturbed physics-tendency (SPPT) based ensemble-mean techniques to anticipate the two NIO TCs, Tauktae (May 2021) and Nivar (November 2020). Compared to control simulations, the adoption of both DFI and SPPT-based ensemble-mean approaches in the model setup yields considerable gains, replicating closer to the observations, albeit with some deviations. The DFI technique significantly improved the TC's track prediction, while the SPPT-based ensemble-mean forecast approach increased the model's efficiency in predicting the TC's intensity.
Statistical bounds on how induced seismicity stops
Authors: Schultz Ryan , Ellsworth William , Beroza Gregory
Published: March 2022

Earthquakes caused by human activities receive scrutiny due to the risks and hazards they pose.  Seismicity that occurs after the causative anthropogenic operation stops has been particularly problematic – both because of high-profile cases of damage caused by this trailing seismicity and due to the loss of control for risk management.  With this motivation, we undertake a statistical examination of how induced seismicity stops.  We borrow the concept of Båth’s law from tectonic aftershock sequences.  Båth’s law anticipates the difference between magnitudes in two subsets of seismicity as dependent on their population count ratio.  We test this concept for its applicability to induced seismicity, including ~80 cases of earthquakes caused by hydraulic fracturing, enhanced geothermal systems, and other fluid-injections with clear operational end points.  We find that induced seismicity obeys Båth’s law: both in terms of the magnitude-count-ratio relationship and the power law distribution of residuals.  Furthermore, the distribution of count ratios is skewed and heavy-tailed, with most earthquakes occur during stimulation/injection.  We discuss potential models to improve the characterization of these count ratios and propose a Seismogenic Fault Injection Test to measure their parameters in situ.  We conclude that Båth’s law quantifies the occurrence of earthquake magnitudes trailing anthropogenic operations.
Speleothem deformation due to the 2017 Mw 6.6 Bodrum–Kos earthquake in a cave on Pserimos (Dodecanese, Greece)
Authors: Grasemann Bernhard , Plan Lukas , Baron Ivo , Scholz Denis
Published: March 2022

Although damaged speleothems have been widely investigated to study paleo-earthquake records in caves, only few reports could directly link damages to specific recent earthquakes. We mapped before the 2017 Mw 6.6 Bodrum–Kos earthquake the so-far unexplored Korakia Cave on Pserimos island in the Dodecanese (Greece), which is located at the transition between the Aegean and Anatolian region and is known for its strong seismicity. The cave formed along an active normal fault and records numerous broken columns and flowstones sealed by younger speleothems. New 230Th/U-ages show that paleoseismic events occurred since the formation of the cave, which is older than the limit of the dating method. During a cave visit 2 months after the 2017 Mw 6.6 Bodrum–Kos earthquake we noted that c. 10 cm small stalactites, which were actively growing along fractures in the cave ceiling, have been chipped off by movements along the fractures and were lying on flowstones covered by greenish biofilms. Removal of the broken fragments demonstrated that the chlorophyll pigment below the position of the fragments did not show a colour difference to the surrounding area, which is exposed to the daylight of the cave entrance. The preservation of the photoautotrophic biofilm, which can survive only a few months without daylight, suggests that the stalactites have been broken by the 2017 Mw 6.6 Bodrum–Kos earthquake, which also caused the collapse of several buildings on the island of Kos only 4 km S of Pserimos. We conclude that earthquake capable of causing small shear displacements on fractures can damage speleothems. However, other delicate speleothems including long and slim stalactites remained undamaged.
The 1983 and 1993 tsunamis on the coast of the Sea of Japan: observations and numerical modelling
Authors: Tsukanova Elizaveta
Published: March 2022

The last major events in the Sea of Japan were in 1983 and 1993. There were the 1983 Nihonkai-Chubu Earthquake (Mw 7.8) and the 1993 Hokkaido Nansei-Oki Earthquake (Mw 7.7). These earthquakes caused tsunamis, which we are studying in this research. I use numerical modelling to reproduce and study effects for the Russian coast. The tsunami waves were stimulated by the TUNAMI numerical model. The bottom topography was created using GEBCO database (30 arc seconds), SRTM data, digitized Russian navigational charts and NOAA Center data. The tsunami source was calculated using Okada's formulas. To better resolve local resonant properties arising from local topography and tsunami run-up, calculations were carried out with nested grids. Using nested grids made it possible to obtain significant agreement with the observational data. Since the seismic source of the 1993 earthquake has a complex structure, three different models were analyzed: USGS, Harvard-model and Takahashi et al. 1995. This study focuses on an examination of the Russian coast. Vladivostok, Posyet and Nakhodka were considered in the most detail. Comparison of the model with the observations was done for both the tsunami waveforms and their spectra. Also, a tsunami wave height map was built for the entire Russian coast of the Sea of Japan. The maximum tsunami wave height on the Russian coast in 1993 was more than 5 m.
Characteristics of groundwater quality and its non-carcinogenic health risk assessment through monsoon inputs in Wanaparthy watershed, Telangana, India
Authors: Vaiphei S. Paolalsiam , Mohan K. Rama
Published: March 2022

Human modernizations and achievements are at peak but in contrary we ignore facts about the tremendous amount of anthropogenic waste that are exposed directly to atmosphere which later reach groundwater aquifer and contaminate through natural water cycle. So, to limelight man-made sources, Wanaparthy watershed is chosen as it is densely agriculture urban area covering about 1600 km2 were peoples solely get their daily wages from farming. Samples were collected systematically for pre (march-may) and post monsoon (september-december) through gird preparation (5*6 sq.km) to determine the hydrogeochemical characteristics of physicochemical parameters and major analytes concentration to preside the types, quality, permissibility, facies and nitrate health risk of different age groups in groundwater. In short findings are as follows: Major analytes concentration for pre-monsoon, Cl- (8.02%) >HCO3- (3.27%) >SO42-(2.75%) >NO3-(1.09%) >F-(0.02%); Na+(4.08%) >Ca+2(1.71%) >Mg+2 (0.45%) >K+ (0.26%)while post-monsoon, HCO3-(8.94%) >Cl- (6.9%) >SO42- (2.46%) >NO3- (2.42%) >F-(0.02%); Na+(3.28%) >Mg+2(2.14%) >Ca+2(0.75%) >K+(0.28%) respectively. Piper diagram explains the major water types for pre- and post-monsoon as Na-Cl type and Ca-Mg-Cl type. Gibb’s plot shows that in both seasons the dominant environmental facies are influence by rock and evaporation conditions. Water quality index shows deterioration increase at most twice from “poor to unfit class” (36.21% - 60.34%) during pre to post season. Health Quotient evaluation for nitrate indicates “children group” as most effected where HQ value range from 5.40E-03 to 1.23E+01 (72.4 pc) followed by infant group, 5.80E-03 to 1.31E+01 (68.97 pc) and adult 2.10E-03 to 4.68E+00 (32.7pc). And, from spatial distribution maps it is observed that slope and structure have direct response to recharge/discharge as well as aquifer properties.
REE fluorocarbonates within rocks and emerald-bearing veins in eastern emerald belt, Colombia
Authors: Garcia Toloza Javier , González Andrés , Day James , Ramirez Juya Valeria , Betancur Camilo , Angarita Luis
Published: March 2022

In Colombia, emerald deposits are sediment-hosted in two parallel belts (Western and Eastern Emerald Belt). Host rocks are calcareous mudstones and limestones of Lower Cretaceous age. The emerald genesis is associated to the flow and mixing of basinal and evaporate derived fluids; a process that took place in organic-rich beds, the leached and released elements like beryllium, chromium, vanadium essentials for emerald formation were present there. The mineralization is found in veins and hydrothermal breccias, frequently includes carbonates, pyrite, albite; less common minerals as: emerald, parisite, apatite, fluorite. In the host rocks is common to find trace minerals such as pyrite, rutile, and, remarkably, the REE carrier monazite.  Parisite —Ca(Ce,La)(CO)F— was first and only described in Colombian emerald mines associated with sedimentary rocks. The Western Emerald Belt is the one where parisite and emerald have been found together. Nevertheless, we report the occurrence of parisite-(Ce) and synchysite-(Ce) —Ca(Ce,La)(CO)F—  in Eastern Emerald Belt. Both minerals have similar Ce/La ratios. Chondrite normalized REE patterns show a relative enrichment in the light-REE and a subtle negative europium anomaly; no significant difference with authigenic monazite REE patterns was observed, thus suggesting a genetic link. The fluorocarbonates were found in emerald-bearing veins consisting of albite, dolomite, pyrite, and apatite. The mineral assemblage suggests that fluorocarbonates were formed under similar P-T conditions ≈ 250-350ºC and 0.8-1.2 kbar (Giuliani et al 1993; Cheilletz et al 1994; Romero et al 1999; García-Toloza et al 2017) of emerald-bearing fluids with approx. composition: Na-Ca-K-Fe-Be-Cl-F-CO-N-CH (Banks et al 2000).  It is proposed that monazite-bearing black shales are the likely source for the REE, and the interaction with F-CO -rich saline hydrothermal fluids led to the dissolution of monazite and eventual precipitation of REE as fluorocarbonates in veins.
Modelling human-water systems experiencing drought-to-flood events: is there one model that fits all?
Authors: Barendrecht Marlies H , Matanò Alessia , Mendoza Heidi D , Weesie Ruben V , van Loon Anne F
Published: March 2022

According to future climate projections both droughts and floods are expected to increase in severity and frequency. A lot of research has been done on the adaptation of society and the feedbacks between hazard and society for these individual hazards, while the feedbacks between hazards and society in a system that experiences drought followed by flooding are less well known. In this study we aim to identify common variables and characteristics of different human-water systems that experience drought-to-flood events and use this to inform model development. Through a literature study of a variety of case studies across the world we investigate the hydrological and socio-economic settings and characteristics of each system as well as the underlying processes and adaptation measures that played a role in the events. Drought-to-flood events can have very different drivers and impacts. In some cases the main driver is human adaptation, such as in the case of the Millennium Drought in Australia where flood prevention reservoirs were already full because they were being used to store water to cope with the drought (Van Dijk et al. 2013). In other cases the combination of hydrological drivers plays a more important role, such as in the case of Peru where a drought followed by extreme rainfall resulted in mud-slides (Fraser 2017). The comparison across cases provides an overview of common variables as well as differences between case studies and is used to inform the construction of one socio-hydrological model that fits all or multiple models that capture the specifics of each case. In future work the model(s) will be used for a more in-depth investigation of the behaviour of a selection of human-water systems, using qualitative and quantitative data in combination with the models to investigate possible future pathways and policy interventions.

References

Fraser, B. (2017). Peru’s floods teach tough lessons. Nature, 544(7651), 405-406.

Van Dijk, A. I., Beck, H. E., Crosbie, R. S., de Jeu, R. A., Liu, Y. Y., Podger, G. M., ... & Viney, N. R. (2013). The Millennium Drought in southeast Australia (2001–2009): Natural and human causes and implications for water resources, ecosystems, economy, and society. Water Resources Research, 49(2), 1040-1057.
Sensitivity study of C/O logging measurements by the Monte Carlo method
Authors: Szucs Jozsef Gabor , Balazs Laszlo
Published: March 2022

Carbon oxygen ratio (C/O) logging is an important method for the accurate determination of hydrocarbon saturation in the reservoir region. One of the advantages of the measurement, that it is independent of Cl content. Furthermore, the insensitivity of high energy neutrons to the casing, makes it possible to use it in cased boreholes too. In addition to the application in the oil industry, monitoring of CO2 reservoirs is also possible. In our study, the modeling of the time-dependent coupled neutron-gamma field produced by the tool was carried out, using MCNP, a general-purpose Monte Carlo radiation transport code. The energy spectrum of gammas reaching the scintillation detector crystal were simulated in different detector positions, and different tool environments: reservoir rock, reservoir porosity, hydrocarbon saturation, and well status (cased or open). The effect of the parameters above are illustrated by vertical cross sections of the particle fluxes around the tool, and shown by the changes of the interpretation charts. By the introduction of a “goodness” factor, derived from the interpretation chart, the potential, and the limitations of C/O logging are investigated.
Effect of N fertilizer amount and water management on CO2 exchange and net ecosystem C balance of rice cultivation in Southern Benin
Authors: Sossa Leonce Geoffroy , Naab Jesse , Augustin Jürgen , Sintondji Luc , Sanogo Souleymane , Hoffmann Mathias
Published: March 2022

Application of mineral nitrogen (N) fertilizer and water management are two very essential farming practices, used to optimize potential yields in sub-Sahara African rice cultivation. Differences in both practices, however, might affect the patterns of climate relevant gaseous carbon (C) emissions (CO2 and CH4) and soil C losses, thus contributing to global climate change. To date, knowledge about the combined effects of different N fertilizer rates together with different water management practices on the gaseous C emissions and soil C losses are very limited. This is even more the case for arable lands in sub-Sahara Africa. Our study aims to identify the best combination of water management and N fertilizer amount to reduce gaseous C emissions and limit soil C losses for an irrigated rice production in Benin. We hypothesize that especially a combination of alternate wetting and drying (AWD) as water management and an optimum amount of N fertilizer reduce gaseous C emissions and might help to enhance C sequestration by reducing soil C losses from irrigated rice production in Benin. To test this hypothesis, a field experiment was established at Koussin lélé, Cove district, southern Benin using a full factorial, split-plot experimental design. Within the experiment the combination of three levels of water management and two levels of N fertilizer amount are tested. The water management technologies include continuous flooding (CF) and two alternate wetting and drying (AWD) methods (AWD15 and AWD25) of irrigation. Nitrogen fertilizer levels is 90 kg/ha (farmer’s practice) and 120 kg/ha (high amount of fertilizer). To measure gaseous C emissions (CO2 and CH4) and estimate dynamics in soil C losses, an innovative, customized low cost dynamic NFT-NSS closed chamber system is used. The system consists of CO2/CH4 NDIR sensors connected to a microcontroller for data storage and transparent (NEE measurements) polycarbonate chambers (40 cm x 40 cm x 100 cm). To measure Reco, transparent chambers where covered with an opaque hood. Chamber measurements for diurnal variability in CH4 and CO2 fluxes are performed biweekly at all plots. In addition, agronomy and crop growth indices such as the Normalized difference vegetation index (NDVI) are measured weekly. Here we present CO2 and NECB balances for the first crop growth period.

Key words: Water management, N fertilizer, CO2 emission, net ecosystem carbon balance (NECB), rice
Effects of different tropospheric mapping functions on GPS positioning
Authors: Sezer Gizem , Erdogan Bahattin
Published: March 2022

Global Navigation Satellite Systems (GNSS) can be operated 24 hours in all weather conditions; thus, it is widely preferred in many geodetic studies. With GNSS, position information can be obtained with high accuracy. However, in order to achieve precise position, GNSS error sources such as atmospheric effects should be eliminated. Since ionospheric delay depends on the frequency of the transmitted signal, it can be eliminated with dual-frequency receivers. But, the tropospheric delay does not depend on the signal frequency. Therefore, it can not be eliminated by signal combinations. The effect of tropospheric delay depends on various factors such as station’s altitude, signal direction, cut off angle, atmospheric pressure, temperature and relative humidity. Although tropospheric delays occur along the signal path, these delays are estimated in zenith direction. Tropospheric mapping functions (MFs) are used to project slant to zenith delay. In this study, the effects of most preferred MFs in the literature, which are Global Mapping Function (GMF), Niell Mapping Function (NMF) and Vienna Mapping Function 1 (VMF1), on position accuracy was investigated. For this aim, three networks with different baseline lengths, (1) less than 100 km, (2) between 100 km and 500 km and (3) more than 500 km, were designed including 10 stations. In addition, to examine the seasonal effect of the MFs, four month dataset (January – April – July – October) were selected. These dataset were processed with the Bernese software implementing relative point positioning method by fixing 3 stations. Moreover, the dataset were subdivided into different session durations (2-3-4-6-8-12 and 24 hours) and the effect of session duration on position accuracy was analysed. According to the initial results, it can be concluded that the position accuracy on short session duration depends on the baseline length and more accurate results were obtained in the shortest network. In addition, more accurate results were obtained by VMF1 for the up component; however, for the horizontal components, there were no significant differences between the MFs.

 

Keywords: GPS, Accuracy, Troposphere, Mapping Functions, Bernese
Understanding the Differences in the Sub-seasonal Predictability of Stratospheric Extreme Events
Authors: Wu Rachel Wai-Ying , Wu Zheng , Domeisen Daniela I.V.
Published: March 2022

In subseasonal-to-seasonal (S2S) prediction systems, strong vortex events are found to be more predictable than sudden stratospheric warming (SSW) events. The reason for this difference in predictability between different types of events is however not resolved. To investigate this question using a larger sample size, we extend the definition of strong vortex and SSW events to wind acceleration and deceleration events due to their similar dynamics. Specifically, we use the zonal mean zonal wind at 60°N, 10hPa from ERA-interim reanalysis for the winters of 1998/99 to 2017/18 to identify wind acceleration and deceleration events, which are defined as a wind change over a 10-day window. We then assess the predictability of the identified events using the ECMWF S2S hindcasts. It is found that wind acceleration events are more predictable than deceleration events. However, when expressing the predictability of deceleration and acceleration events as a function of event magnitude, they qualitatively exhibit the same predictability behaviour; that is, events of stronger magnitude are less predictable. We explain the observed predictability dependence from two perspectives: 1) In a statistical sense, strong magnitude events lie within the tails of the climatological distribution and thus are penalised more heavily than weak magnitude events, and 2) from a dynamical perspective, extreme stratospheric events are associated with strong anomalies in precursors such as wave activity and vortex background state, and are  therefore often associated with large ensemble spread and large uncertainties. In particular, the magnitude of extremely strong wave activity is underestimated in the model for strong deceleration events. Therefore, we suggest the observed predictability difference between event types can to a large extent be explained by the difference in event magnitude between event types, i.e. the fact that wind deceleration events are associated with greater magnitudes than wind acceleration events, and that SSW events are stronger in magnitude than strong vortex events. We also suggest that a better representation of extremely strong wave activity in the prediction system can enhance the predictability of stratospheric extreme events, and by extension their impacts on surface weather and climate.
Assessing the habitat suitability of the Ganga River under anthropogenic influence
Authors: Sonkar Gaurav Kailash , Gaurav Dr. Kumar
Published: March 2022

The Ganga River ecosystem in the Indo-gangetic plains is under severe anthropogenic stress. Flow regulation and habitat fragmentation caused due to structural barriers are responsible for the degradation of biodiversity in a river system. Determining the suitability of river habitats under contemporary modification is detrimental for river health management. Habitat suitability of several reaches of the Ganga River is impacted by the barriers through hydrological alteration leading to poor hydraulic condition and loss of lateral connectivity.

We study the hydrological, hydraulic, and geomorphic suitability of the Ganga River between Bijnor and Narora barrage for the Ganga river dolphin (Platanista gangetica), an indicator species of the Ganga, Brahmaputra- Meghna River system. The discharge data measured downstream of the Bijnor barrage shows that the minimum flow required for the biodiversity and the fluvial process is available only during the Indian summer monsoon period (June- September). While the river reaches upstream of the Narora barrage has maintained the required flow for biodiversity throughout the year. The channel hydraulics influences the habitat selectivity in a river system. The minimum preferred depth for navigation and foraging activity of the Ganga river dolphin is 1-2 m. We calculate the reach averaged hydraulic parameters of the Ganga River at the upstream of Narora barrage using the Geomorphic instream flow tool (GIFT) and altimeter derived water level for different flow conditions. The minimum required depth is available only when the water level is >178.95 m. This only suggests the reach averaged condition and does not reflect the cross-section level depth. The channel geometry analysis of several cross-sections shows that the mean depth of the reach upstream of Narora barrage is 2 m (range 1-2.8 m, SD= 0.8 m) in the low flow season (March)  and the maximum depth ranged from 2.4 to 12 m (SD= 2.8 m). During the high flow season (September), the mean depth is 2.8 m (range 2.2-4 m, SD= 0.53) and the maximum depth ranges from 4.4 to 14.4 m (SD= 2.8 m). This suggests that the reach upstream of the Narora barrage has adequate depth during the low and high flow seasons.  
Analysis of the polar motion excitation function based on ITSG daily models
Authors: Partyka Aleksander , Nastula Jolanta , Śliwińska Justyna , Kur Tomasz , Wińska Małgorzata
Published: March 2022

Understanding the polar motion (PM) changes is one of the major tasks in geodesy. In order to understand this changes cause by internal forces, it is necessary to analyse the so called PM excitation functions of geophysical fluids layers, namely atmosphere, ocean, and land hydrology with cryosphere. The impact of atmosphere and oceans is pretty well understood, but the impact of land hydrology is not well known and the study of the Hydrological Angular Momentum (HAM) is still the main research topic in finding the agreement between observed geodetic changes in PM and geophysical ones. The study of different HAM excitations are possible, among other things, through the use and analysis of temporal gravity models, which are constantly being developed by numerous research centres around the world.

The main aim of this study is to compare the equatorial components of the PM excitation (χ1 and χ2) calculated using the ITSG (The Institute of Geodesy at Graz University of Technology) daily gravity field models (ITSG-Grace2014, ITSG-Grace2016, ITSG-Grace2018) with other daily models and reference data, in order to assess their accuracy. The comparison of successive versions of ITSG solutions (2014, 2016, 2018) will allow for the assessment of the improvement in the accuracy of the excitation functions determined on their basis. Their potential for use in future research will be evaluated. These models are an object of study due to the fact that they have a daily temporal resolution, unlike most models that offer a monthly resolution.

The ITSG-Grace models used in the study were created by researchers at Technische Universität Graz using data obtained from the GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Gravity Recovery And Climate Experiment-Follow-On) missions. The equatorial components of the PM excitation were calculated from the relationship between χ1, χ2 and degree-2, order-1 Stokes coefficients (∆C21, ∆S21) available in the ITSG-Grace models. In this study, HAM series from the LSDM (Hydrological Land Surface Discharge Model) delivered by GFZ (GeoForschungsZentrum in Potsdam) and GAO geodetic residuals, being a differences between geodetic angular momentum (GAM) and a sum of atmospheric and oceanic excitaions, provided by Observatoire de Paris were used for comparison with PM excitation series determined from ITSG-Grace models.

In order to compare the PM excitation determined from ITSG-Grace models with series obtained using other models, trends as well as seasonal and non-seasonal variations were determined. Correlations between the series, amplitude agreement and root mean square errors were calculated, on the basis of which their accuracy and relations with other models were assessed.
Imprints of Crust- and Mantle-Scale Deformation in Central Anatolide-Tauride Region: Exploiting Receiver Functions
Authors: Keleş Derya , Eken Tuna , Licciardi Andrea , Schiffer Christian , Taymaz Tuncay
Published: March 2022

Central Anatolia is a seismically active region with complex tectonic provinces and represents one of the significant regions experiencing active deformation in Turkey. It involves the Anatolide-Tauride Block settled in southern Anatolia that is separated from the Pontides by the İzmir-Ankara-Erzincan Suture Zone (IAESZ). In central Anatolia, the Kırşehir Massif mainly comprises complex crystalline metamorphic and plutonic rocks with obducted ophiolitic fragments. It is detached from the Anatolide-Tauride Block by the Intra-Tauride Suture (ITS). The ITS is thought to represent the footprint of subducted Neo-Tethyan ocean. This region further includes a number of active tectonic features, i.e., the Central Anatolian Fault Zone (CAFZ), the Tuz Gölü Fault (TGZ), the East Anatolian Fault zone (EAFZ), the Dead Sea Fault (DSF), and the Bitlis-Zagros Suture. In order to investigate the style of deformation of the region and its influence on the crustal and lithospheric structure and to better understand the relationship between tectonic features and regional deformation at different depth and tectonic features, we quantify the strength and orientation of seismic anisotropy. To achieve this, we focus on the directional dependence of P-to-S converted teleseismic waves (i.e., receiver functions) through the harmonic decomposition analysis. Our findings indicate that seismic anisotropy is mostly localized in the mid-crust (15-25 km) with an overall NE-SW and NNW-SSE orientation in the west and east portions of the study area which is present in the mid-crust (15-25 km). In the uppermost mantle, we observed NE-SW oriented and relatively strong anisotropy. This is compatible with fast shear wave azimuths inferred from SKS splitting measurements reported in previous studies and likely be associated with a sub-lithospheric origin. Anisotropic orientations found at crustal and upper mantle depths are consistent with a model of the ITS reaching to great depths suggest anisotropic fabrics in frozen related to past deformation events. We further perform a joint inversion of receiver functions with apparent S wave velocities to better constrain crustal thickness estimates derived from the harmonic decomposition analysis. The resulting crustal thicknesses vary from about 25-28 km nearby the EAFZ and DSF, and to ~35 and 40 km beneath the Kırşehir block and the Eastern Tauride Mountains.
Spatial analysis of hydrogen and oxygen stable isotopes (“isoscapes”) in Himalayan basins: improved prediction using Geographically Weighted Regression (GWR) models
Authors: Dar Tanveer , Jahan Akhtar , Rai Nachiketa , Bhat Mohd Aadil , Kumar Sudhir
Published: March 2022

Isotopic landscapes or “Isoscapes” are a valuable tool for studying hydro-climatic processes and their impact on water supplies at various spatial scales. These isoscapes are extremely useful because they enable the documentation and visualization of large-scale hydrological processes occurring on a regional, continental, or global scale. This study focuses on surface water isotope data (present study and published data) to interpolate, develop isoscapes of Himalayan basins (Indus, Ganga, and Brahmaputra), and analyze spatial variability from regional to local scale. We use physically based information of three basins from hydro-climatic variables such as actual evapotranspiration (AET), mean annual precipitation (MAP), mean annual runoff (MAR), and runoff coefficient, as well as basin variables such as elevation, slope, aspect, size, and land-use/land-cover (LULC), to develop geographically weighted regression (GWR) models. We identified a systematic spatial pattern in the stable isotopes (δ18O, δ2H, d-excess) of surface water that can be predicted using a GWR model. In the absence of long-term precipitation isotope records, an increased spatial and temporal sampling of surface water for isotopic isoscapes would significantly aid our understanding of hydrological processes, providing that catchment characteristics are taken into consideration. The GWR models used in this study demonstrated the ability to predict isotopic changes in the context of future climate and land-use change in these three major basins.

Keywords: Stable isotopes, Geographically Weighted Regression (GWR), Isoscapes, Himalayan basins.
Assessment of global and regional ionospheric maps over Brazil using simulated kinematic precise point positioning. 
Authors: Siqueira Loram , Francisco Galera Monico Joao , Rodrigues de Aguiar Claudinei
Published: March 2022

Precise point positioning (PPP) is an available solution for one-frequency receivers if the ionosphere delay is informed during the data processing. Such information may be retrieved from the ionospheric maps, which can have a global or regional coverage. IGS has traditionally being providing them globally, throughout different analyses centers. On the other hand, regional products have been increasingly catching the interest of the scientific community.  Regional Ionosphere Maps (RIM) will use local active GNSS networks with multi-frequency receivers to model and represent the ionospheric delays. Because of the larger amount of information from a specific region, which may lack in the global products, the representation can be better and show improvements for areas where the ionosphere is more active. For the South American area, studies have been conducted using active networks. GIB (Brazilian Ionospheric Grid) was developed in 2010 and computes regional maps using GPS data from the Brazilian Continuous Monitoring Stations (RBMC). More recently (2018) the Meteorología espacial, Atmosfera terrestre, Geodesia, Geodinámica, diseño Instrumental y Astrometría (MAGGIA) made available its regional product covering the same area using GNSS data from Brazil, Uruguay and Argentina. Presently we are verging to the beginning of the next solar cycle and understanding the availability of global and regional products for ionosphere correction, and its level of accuracy will be a crucial information to be hold. In this contribution, an evaluation of four products was performed using kinematic PPP for the day 80 of 2021, of course with a reduced amount of data. The global products (CODE and GFZ) used the IGS network on its construction. A reference station from RBMC, with known coordinates was used as the ground truth to determine the accuracy of each product using a simulated PPP kinematics. with residuals and needed system transformation the accuracy and precision for each product was acquired. Overall results show that the MAGGIA product presents the best accuracy, followed by the GFZ, IGS and GIB. For this analysis it was possible to conclude that two elements play an important role when creating ionosphere maps: not only the regional characterization but also using multi constellation GNSS data will play a key role in the products quality. MAGGIA and GIB, both regional products, obtained the best and the worse results, respectively and the major difference being the use of only one GNSS constellation (GIB) and multiple GNSS constellations (MAGGIA) for its calculation.
Joint Instabilities of Sheared Flows and Magnetic Fields
Authors: Lewis Patrick , Hughes David , Kersale Evy
Published: March 2022

Shear flows and magnetic fields are ubiquitous in astrophysical bodies such as stars and accretion discs. Furthermore,
the interaction between flows and magnetic field plays a key role in the dynamics of plasma fusion devices. Typically,
the flows and magnetic field are both sheared, and it is therefore a problem of fundamental importance to understand
the instabilities that may occur in such a system.

In the absence of magnetic field, the linear stability of a viscous sheared flow is governed by the Orr-Sommerfeld
equation; this is one of the classic problems of hydrodynamics. At the other limit, there are somewhat analogous
instabilities of a fluid of finite electrical conductivity containing a static sheared magnetic field. These are related to
the classical tearing modes that have received considerable attention in both the astrophysical and plasma physics
literature.

In general though, the fluid flow and the magnetic field will both be important players. Previous studies have investigated
configurations which have served as models for systems such as the magnetotail and solar surges. While these
investigations have been fruitful, the prescription of the basic field and flow, while physically motivated, have been
chosen somewhat arbitrarily. It is therefore of interest to consider the instability problem within this more general
framework.

Motivated astrophysically, such as by the dynamics in the solar tachocline, here we consider a self-consistent problem
in which both instabilities can occur. In particular, we consider the stability of equilibrium states arising from the
shearing of a uniform magnetic field by a forced transverse flow. The problem is governed by three non-dimensional
parameters: the Chandrasekhar number, and the flow and magnetic Reynolds numbers. In opposite limits of parameter
space, we recover the predictions of the aforementioned classical problems. As we move through this three-dimensional
parameter space, a range of interactions are possible: We demonstrate the stabilisation of a purely hydrodynamic
instability through the magnetic field, show the existence of a joint instability outlining the physical mechanisms at
play, and demonstrate that under certain conditions, hydrodynamically-stable parallel shear flows lead to instability
growth rates that exceed those of static tearing modes. To conclude, we elucidate the consequences of considering
the linear stability of an evolving background state and show that a quasi-static approach may not be meaningful. In
these circumstances, it therefore becomes essential to perform a stability analysis of a time-varying basic state.

 

 
Estimating Head Induced by Moving Bedforms Using Dye Tracer Tests and Modeling
Authors: Teitelbaum Yoni , Shimony Tomer , Saavedra Cifuentes Edwin , Packman Aaron , Arnon Shai , Hansen Scott
Published: March 2022

Under moving bedform conditions, the shape of the sediment-water interface (SWI) is known to evolve over time. However, existing mathematical models of bedform-induced hyporheic exchange flux (HEF) assume a fixed bedform shape in determining the pressure boundary condition at the SWI. This simplifying assumption is adopted because there is no established method for prescribing head along an arbitrary, changing sediment-water interface (SWI). This gap has prevented most flow modeling efforts from accounting for the dynamics of bedform sizes and shapes, and it is currently not well understood how such dynamics are expected to affect transport and biogeochemical processes in streams. Previously, measurements of head along the SWI have been taken under stationary bed conditions using pressure sensors installed within bedforms, but installing sensors to take the same measurements under moving-bedform conditions is impractical. We propose a method to quantify the dynamics of hydraulic head at the SWI using timelapse photos of dye tracer tests, without installing any sensors in the flume. For every photo, an initial guess of head along the SWI is generated using established methods from the literature. Flow paths in the bed are calculated using the steady-state groundwater flow equation and Darcy’s Law. The predicted evolution of the dye plumes in the photo is compared against the dye plumes from the subsequent photo. This comparison is used as the objective criterion in an optimization procedure, which is run until the estimate of head at the SWI converges. Preliminary results show agreement with experimental observations from dye penetration tests. In providing a new way to estimate head under moving-bed conditions, this work is an important advance in realistic modeling of bedform-induced HEF and its effect on flow, transport, and biogeochemical processes in streams.
Different drivers of Sea Level Variability at the North – Baltic Sea transition
Authors: Ek David , Poropat Lea , Heuzé Céline
Published: March 2022

Global mean sea level is rising, however not uniformly. Regional deviations of sea surface height (SSH) are common due to local drivers, including surface winds, ocean density stratifications, vertical land- & crustal movements and more. The contribution of each background driver needs to be better understood to create reliable sea level rise projections, enable effective local policymaking and aid in urban planning decisions.

In this study, we assess region-specific historic sea levels along the western Swedish coastline (Kattegat, Skagerrak & South Baltic Sea).

We use monthly satellite altimetry observations spanning 26 years and daily observations spanning 6 years, as well as in situ tide gauge measurements to identify SSH covariance between sub-regions. We employed a number of manual statistical methods and found that SSH variability in the Skagerrak and Kattegat Seas behaves differently than areas south of the Danish Straits. While typically the correlation between SSH time series from different locations declines with distance, this is not seen at the entrance to the Baltic Sea due to the complexity of the region. To investigate this further and identify underlying primary forcings, we introduced re-analyzed ERA5 estimates of climatic drivers such as 10m-winds, sea surface temperature and sea level pressure, and tested these against principle components of the SSH variability signal within these regions. Zonal winds are most important for determining short-term sea level variability in areas north of the Danish Straits, while neither of these drivers successfully explain observed sea level variability south of them. As freshwater discharge from rivers and tributaries to the Baltic Sea is large, pressure- & density gradients may be more important as SSH regulators in this area.

Additionally, we used neural networks to try to capture non-linear dependencies between the sea level drivers and sea level that are not apparent from statistical analyses. By predicting sea level at selected locations from different combination of drivers, we can determine which drivers have the highest influence. While feedforward neural networks did successfully predict some variability, they prove rather limited as delays between signals are present. Future tests using recurrent neural networks with a long short-term memory architecture might prove more successful.