bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the discharge simulation of a conceptual hydrological model by introducing Cosmic Ray Neutron Sensor Based Soil Moisture Data
Authors: Akyurek Zuhal , Duygu Mustafa Berk
Published: March 2021

Conceptual models are the most frequently used hydrological models in practical hydrological studies. These models are developed by considering the rainfall-runoff relation specific to the area of interest through a set of parameter values, which are calibrated by using the observed discharges, groundwater levels, etc. Although, it is a common practice to calibrate conceptual models by using observed run-off data, considering the direct relation of the other elements of the hydrological cycle with each other, it is expected that using as many elements as possible will enhance the capacity of the models. Cosmic Ray Neutron Sensing (CRNS) is one of the most promising soil moisture observation methods and it has a very good potential to be used in hydrological studies due to its relatively larger horizontal footprint thus better representation of the study area. In this study, benefits of introducing CRNS based soil moisture values in the calibration of NAM model has been discussed for semi-arid basin located in Turkey. NAM model has been studied for the entire basin (421 km2) and one of its sub-basins (121 km2) by introducing the soil moisture data. Objective functions for model calibration has been defined for three cases: Discharge, soil moisture and the combination of discharge and soil moisture. The results have been discussed by using several statistical measures such as NSE, logNSE and KGE. According to the comparisons between models with different calibration properties, utilizing CRNP soil moisture reduces the difference between observation and simulation for both basins. Peak discharge values are better simulated and volume errors are significantly reduced when the combined objective function is used. For both basins, basin water storage values are well correlated with the observed and simulated soil moisture values even in the validation period. This is an indication of the closed coupling between volume storage in the root zone and measured soil moisture by CRNS in the study area.
Flash Drought Research: Growth, Challenges and Future Perspectives 
Authors: Rahim Akif , Markonis Yannis
Published: March 2021

Over the past decades, the evolution of the “flash drought” concept has offered new insights in the analysis of extreme climate. Rapid development and devastating effects on the ecosystem have made flash droughts different from the traditional drought. For example, the flash drought event of 2012 across the Great Plains in the USA caused an agricultural loss of $30 billion. In this study, we reviewed the progress and determined the growth rate of flash drought research over the past decades. Furthermore, we compiled the challenges addressed by the researchers and then presented the future perspectives to cope with these challenges. We used the Scopus database as a search engine to track articles published from 2000 to 2020. The association technique of clustering s applied to the author’s keywords and research titles to identify the hot spots of flash drought research. The results show that the literature on flash droughts has grown rapidly over the past decade. The main identified challenges are the appropriate definition and identification of flash drought, the development of an effective early warning system, the determination of the ecosystem response time to flash droughts, and the data scarcity in both spatial and temporal scales. Future research should establish a detailed framework to integrate each of the challenges and provide mitigation suggestions to the effects of flash drought.

 
Detection of an unknown emission source in the Baltic Sea using the new oceanographic tracer U-233/U-236
Authors: Hain Karin , Aldahan Ala , Eriksson Mats , Golser Robin , Henderson Gideon M. , Hou Xiaolin , Qiao Jixin , Possnert Göran , Steier Peter , Vartti Vesa-Pekka , Zhang Haitao
Published: March 2021

By analysing the two long-lived anthropogenic Uranium (U) isotopes U-233 and U-236 in different compartments of the environment affected by releases of nuclear power production or by global fallout from nuclear weapons tests, we showed that the corresponding isotopic ratios U-233/U-236 differ by one order of magnitude. Based on these experimental results which were obtained with the ultra-sensitive detection method Accelerator Mass Spectrometry, we suggested a representative ratio for nuclear weapons fallout of U-233/U-236 = (1.40 ± 0.15) ·10-2 and (0.12 ± 0.01) ·10-2 for releases from nuclear power production. Consequently, the U-233/U-236 ratio not only has the potential to become a novel sensitive fingerprint for releases from nuclear industry, but could also serve as a powerful oceanographic tracer due to the conservative behaviour of U in ocean water which does not suffer from chemical fractionation.

As a first application of this paired tracer, we studied the distribution of U-233 and U-236 concentrations in addition to I-129 in the Baltic Sea which is known to have received inputs of radionuclides from various contamination sources including the two European reprocessing plants, global fallout from weapons testings and fallout from the Chernobyl accident. Our data indicate an additional unidentified source of reactor U-236 in the Baltic Sea demonstrating the high sensitivity of the U-233/U-236 ratio to distinguish different emission sources in water mixing processes.
Analysis of the effects of increased river runoff on the Arctic Ocean hydrology using numerical modeling
Authors: Tarkhanova Marina , Golubeva Elena
Published: March 2021

The report discusses issues related to the influence of the increased discharge of Arctic rivers on the thermohaline structure of waters outside the Arctic shelf and, in particular, on the variability of Arctic Ocean heat content. The three-dimensional numerical model of the ocean and sea ice SibCIOM (Siberian Coupled Ice-Ocean Model), developed at the Institute of Computational Mathematics and Mathematical Geophysics SB RAS to study the climatic variability of the Arctic Ocean, and the NCEP/NCAR atmospheric reanalysis data are used.

To reveal the sensitivity of the model fields to the intensity of river runoff, numerical experiments assume the inclusion of variations in river discharge with unchanged remaining conditions, starting from 2000. The deviations of the monthly average values in a numerical experiment with increased discharge of individual Arctic rivers from the basic situation based on the monthly average climatic runoff assignment are considered.

An analysis of the numerical results obtained with increased discharge of the major Siberian rivers (Ob, Yenisei, Lena) by 1.3 times showed an increase in the Kara Sea's bottom temperature. This was followed by the warming of the subsurface layer of the waters propagating along the continental slope and increasing the heat content of the upper 200-meter layer of the Eastern Eurasian Basin. The heat preservation entering the deep-water part through the Kara Sea straits was facilitated by an increase in stratification's stability and a decrease of the mixed layer depth by 5-10 m on the continental slope of the Eurasian Basin. A similar process with a time delay (6-7 years) and on a smaller scale is developing on the Amerasian basin's continental slope and the Chukchi Sea shelf.

In the numerical experiment with an increased discharge of the Mackenzie River, deviations in the Beaufort Sea heat and freshwater content appear during the first two years. Still, their values are too small under the river's small discharge compared to the Siberian rivers' discharge.

The study is supported by the Russian Foundation for Basic Research, Grant No. 20-05-00536 A.
Real-time source apportionment of local vs regional dust in a semi-arid urban environment of the Eastern Mediterranean Middle East (EMME) region
Authors: Sciare Jean , Sarda-Estève Roland , Oikonomou Konstantina , Bimenyimana Elie , Pikridas Michael , Unga Florin , Christodoulou Aliki
Published: March 2021

Major efforts are currently put to reduce drastically PM emissions at the exhaust of the most recent vehicles, however, little is done to mitigate non-tail-pipe emissions and resuspended road dust, in particular. Such traffic-related resuspension of dust may become a major source of PM10 at a time our cars are becoming cleaner. This may be particularly true in (semi-)arid urban environments which are characterized by high deposition rates of desert dust and low rain wash-out rates of roads.

Near-real-time (10-min time resolution) on-line measurement of selected cations (Na+, Mg2+, Ca2+) in PM10 were performed using a Particle-into-liquid-sampler (PILS) coupled with an Ion Chromatograph (IC). Such high temporal resolution of these species has been rarely reported in literature and to the best of our knowledge, it is the first time that such dense observations are reported in PM10 for urban environment. These measurements were performed during a 3-month transition period between (from wet winter to dry summer) at an urban background site of Nicosia (Cyprus) a central location of the Eastern Mediterranean Middle East (EMME) region.

The consistency of these measurements was successfully assessed against 24-h integrated filter-based measurements while hypotheses related to the use of Calcium as a tracer of dust particles further verified against trace metal analysis. A comprehensive suite of co-located ancillary data (Aethalometer, Lidar, ACSM, SMPS, OPC) were used to further support the daily/weekly/monthly variability of Calcium concentration in PM10.

Diurnal variability of dust concentration in PM10 at our background urban site displayed a strong and intense traffic-related source at rush hours together with a maximum observed in the afternoon in phase with the development of the Planetary Boundary Layer and intrusion of desert dust from aloft. Interestingly, this pattern is amplified when moving from wet to dry months and encompassing the Spring dust season.

The contribution of the two dust sources in PM10 (traffic-related dust resuspension and intrusion of long-range transported desert dust) is provided here for different temporal scales (day, week, month). Estimate of traffic-related (non-)tail-pipe emissions (ie. combustion carbonaceous vs resuspended dust) is also provided here highlighting the dominant role of dust in PM10 emissions from road transport sector.
Impact of intra-seasonal coastal Kelvin waves on SST in the Canary upwelling system: composite analysis in Spring
Authors: Sané Badara , Lazar Alban , Wade Malick
Published: March 2021

The impact of intra-seasonal coastally trapped waves on SST in the Canary upwelling system is studied in satellite estimates of sea surface height, wind, and temperature, using a composite analysis of propagating upwelling and downwelling events. We focus on Spring, the season of strongest SST variability at this frequency. The results obtained show that the average wave reaches an amplitude at sea level of +/- 2 cm and is associated with an SST signal of +/-0.4 °C in the vicinity of the upwelling front, located off Senegal. Strikingly, this composite wave is reinforced by a constructive meridional wind anomaly when it reaches the upwelling front, the wind signal is likely as important as the wave in terms of SST impacts. We discuss the possible cause of this synchronicity in terms of basin-scale atmosphere and ocean waves.
Keywords:
- Impact
- Coastal Kelvin waves
- Intra-seasonal
- Boundary upwelling systems
- Composite analysis of spring
- Tropical Atlantic
Estimating Land Surface Temperature from AMSR-E and AMSR2 Data with Convolutional Neural Network
Authors: Wang Shaofei , Zhou Ji , Zhang Xiaodong , Jin Zichun
Published: March 2021

Land surface temperature (LST) is a key factor in earth–atmosphere interactions and an important indicator for monitoring environmental changes and energy balance on Earth's surface. Thermal infrared (TIR) remote sensing can only obtain valid observations under clear-sky conditions, which results in the discontinuities of the LST time series. In contrast, passive microwave (PMW) remote sensing can help estimate the LST under cloudy conditions and the LST generated by PMW observations is an important input parameter for generating medium-resolution (e.g., 1km) all-weather LST. Neural networks, especially the latest deep learning, have exhibited good ability in estimating surface parameters from satellite remote sensing. However, thorough examinations of neural networks in the estimation of LST from satellite PMW observations are still lacking. In this study, we examined the performances of the traditional neural network (NN), deep belief network (DBN), and convolutional neural network (CNN) in estimating LST from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) and Advanced Microwave Scanning Radiometer 2 (AMSR2) data over the Chinese landmass. The examination results show that CNN is better than NN and DBN by 0.1–0.4 K. Different combinations of input parameters were examined to get the best combinations for the daytime and nighttime conditions. The best combinations are the brightness temperatures (BTs), NDVI, air temperature, and day of the year (DOY) for the daytime and BTs and air temperature for the nighttime. Compared with the MODIS LST, the CNN LST estimates yielded root-mean-square differences (RMSDs) of 2.19–3.58 K for the daytime and 1.43–2.14 K for the nighttime for diverse land cover types for AMSR-E. Validation based on the in-situ LST demonstrates that the CNN LST yielded root-mean-square errors of 2.10–5.34 K and the error analysis confirms that the main reason for the errors is the scale mismatching between the ground stations and the MW pixels. This study helps better the understanding of the use of neural networks for estimating LST from satellite MW observations.
How can stratigraphy contribute to conservation paleobiology? Insights from a mid-Holocene to present-day transitional system of the Po coastal plain (N Italy)
Authors: Barbieri Giulia , Rossi Veronica , Armynot du Châtelet Éric , Da Prato Simone , Mazzini Ilaria , Vaiani Stefano Claudio , Frontalini Fabrizio
Published: March 2021

The definition of reference conditions has a major role for the understanding of the present-day and paleoecological quality status on transitional environments. The estuarine quality paradox and the paucity of unimpacted sites make the definition of reference conditions a challenging task. In this context, the integration of biological indicators with stratigraphic data is essential, as the vertical stacking pattern of facies composing the shallow subsurface of modern coastal plains reflects changes in physical-chemical parameters which, in turn, affect (paleo-)biotic communities.

In the Po coastal plain (N Italy), the mid to late Holocene back-barrier succession of the Mezzano Lowland and the adjacent present-day Bellocchio Lagoon offer a unique example of pristine paralic system for comparing reference conditions defined in fossil and modern settings, respectively. Benthic foraminifers and ostracods from the Mezzano succession allowed us to investigate vertical (i.e., temporal) and lateral (i.e., spatial) changes in (paleo-)environmental conditions, in analogy to the lateral variations recorded at the Bellocchio Lagoon.

Both sites present subtidal channel sands almost barren in autochthonous meiofauna and fine-grained lagoon sediments with abundant benthic foraminifers and ostracods mostly represented by euryhaline taxa recording the highest diversity. Intertidal muddy deposits are also recorded, including mud flat clays with abundant oligotypic assemblages dominated by highly-confined benthic foraminifers. In the present study, we demonstrate that changes in modern benthic foraminifer assemblages diversity and composition often interpreted as perturbations of ecological conditions in response to anthropogenic pressures also occur under natural state, as confirmed by paleoenvironmental conditions recorded by ostracods. This reflects the effects of authogenic processes at short time and geographic scales.
Evidence of in Situ Cirrus Formation in the Tropical Tropopause Layer over the Southwestern Indian Ocean 
Authors: Evan Stephanie , Reinares Martinez Irene , Wienhold Frank G. , Brioude Jerome , Jensen Eric J. , Thornberry Troy D. , Heron Damien , Verreyken Bert , Korner Susanne , Vomel Holger , Metzger Jean-Marc , Posny Françoise
Published: March 2021

A nascent in situ cirrus was observed on 11 January 2019 in the tropical tropopause layer (TTL) over the southwestern Indian Ocean, with the use of balloon-borne instruments. Data from CFH (Cryogenic Frost Point Hygrometer) and COBALD (Compact Optical Backscatter and AerosoL Detector) instruments were used to characterize the cirrus and its environment. Optical modeling was employed to estimate the cirrus microphysical
properties from the COBALD backscatter measurements. Newly-formed ice crystals with radius <1 μm and concentration ∼500 L −1 were reported at the tropopause. The relatively low concentration and CFH ice supersaturation (1.5) suggests a homogeneous freezing event stalled by a high-frequency gravity wave. The observed vertical wind speed and temperature anomalies that triggered the cirrus formation were due to a 1.5-km vertical-
scale wave, as shown by a spectral analysis. This cirrus observation shortly after nucleation is beyond remote sensing capabilities and presents a type of cirrus never reported before.
Modeling of convective heat-mass transfer in permeable parts of seismic focal zones of the Kamchatka region and associated volcanic arcs
Authors: Perepechko Yuri , Sorokin Konstantin , Mikheeva Anna , Sharapov Viktor , Imomnazarov Sherzad
Published: March 2021

The paper presents a non-isothermal model of hydrodynamic heating of lithospheric rocks above magma chambers in application to the seismic focal zone of the Kamchatka region and associated volcanic arcs. The effect of convective heating of mantle and crustal rocks on dynamics of metasomatic changes and convective melting was studied. In the existing models of ore-forming systems, fluid mass transfer is determined mainly by the retrograde boiling of magmas in meso-abyssal intrusive chambers. Analysis of the manifestations of deposits of the porphyry formation of the Pacific Ocean active margins shows the decisive participation in their formation of mantle-crust ore-igneous systems. The model of convective heat-mass transfer in fluid mantle-crust systems coupled with magma chambers is designed with the consideration of effects of interphase interaction in rocks of permeable zones above igneous fluid sources. Numerical simulation of the dynamics of fluid systems under the volcanoes of the frontal zone of Kamchatka shows altered ultramafic rocks in metasomatic zoning and the presence of facial changes in the mineral composition of wehrlitized rocks. In the mantle wedge of the northwestern margin of the Pacific Ocean, over which epicontinental volcanic arcs developed in the post-Miocene stage, there is possible combination of the products of different-time and different-level igneous systems in the same permeable "earth's crust-lithospheric mantle" transition zones. Assuming that the "cratonization" of volcanic sections of the continental Earth's crust follows the "metasomatic granitization" pattern, the initial element of which is the wehrlitization of mantle wedge ultramafic rocks, the processes of metasomatic fertilization of mantle wedge rocks were investigated using a flow-through multiple-reservoir reactor. In the seismically active regions of the Pacific transition lithosphere, specific conditions for heating of areas of increased permeability above mantle fluid sources should be recorded. Metasomatic columns in such fluid systems can describe the formation of at least three levels of convective melting of metasomatized mantle wedge substrates, as well as the formation of a region of high-temperature fluid change of mafic intrusion rocks in the Earth's crust. The work was financially supported by the Russian Foundation for Basic Research, grants No. 19-05-00788.
Near-inertial waves modulated by background flow in realistic global ocean simulations
Authors: Raja Keshav , Buijsman Maarten , Siyanbola Oladeji , Solano Miguel , Shriver Jay , Arbic Brian
Published: March 2021

Wind generated near-inertial waves (NIWs) are a major source of energy for deep-ocean mixing by transmitting wind energy from the ocean surface into the interior. Recently, it has been established that the NIW energy transmission to ocean depths is significantly modulated by background mesoscale vorticity. Thus, understanding NIW energetics in the presence of mesoscale eddies on a global scale is crucial.

We study the generation, propagation and dissipation of NIWs in global 1/25o Hybrid Coordinate Ocean Model (HYCOM) simulations with realistic tidal forcing. The model has 41 layers with uniform vertical coordinates in the mixed layer and isopycnal coordinates in the ocean interior. The model is forced by 1/3hr wind from the NAVGEM atmospheric model. We analyze one month of model data for May-June 2019. The 3D HYCOM fields are projected on vertical normal modes to compute the wind input, wave kinetic energy (KE), flux divergence and dissipation per mode.

We find that the globally integrated wind input in surface near-inertial motions is 0.21 TW for the 30-day period and is consistent with previous studies. The sum of the wind input to the first 5 modes accounts to only 31% of the total wind input while the sum of the NIW kinetic energy in the first 5 modes adds up to 60% of the total NIW KE. The difference in the fraction of the total between the wind input and NIW KE (31% and 60%) suggests that a significant portion of wind-induced near-inertial motions is dissipated close to the surface without being projected onto modes. We also find that NIW horizontal fluxes diverge from areas with cyclonic vorticity and converge in areas with anticyclonic vorticity, i.e., anticyclonic eddies are a sink for NIW energy in the global ocean.

The residual NIW KE that does not project onto modes is found to be largely trapped in anticyclonic eddies. In a next step, we will study the fate of this energy, which most likely propagate downward as beam-like features with large wave numbers. We will compute the near-inertial wave energy balance for fixed subsurface layers and consider the energy exchange between these layers to understand the vertical structure of NIW energy dissipation. We find that the downward NIW radiation to the ocean interior at 500 m depth is 19% of the surface near-inertial wind input for the 30-day period.
Effects of forest invasion and retreat on tundra biodiversity inferred from sedimentary ancient DNA of lake Levinson Lessing, Taymyr Peninsula, Russia
Authors: Courtin Jérémy , Schulte Luise , Andreev Andrei , Stoof-Leichsenring Kathleen , Lenz Matthias , Melles Martin , Herzschuh Ulrike
Published: March 2021

One of the consequences of the amplified warming of the arctic ecosystems is tundra “greening” and northward expansion of Siberian boreal forests. However, it is still challenging to predict how northern tundra biodiversity will change with the ongoing climate warming as models usually overestimate forest invasion. The investigation of Quaternary records spanning different Pleistocene glacial and interglacial cycles can provide unique insights on past diversity dynamics following forest invasion and retreat events. Therefore, by “looking backward to look forward“, reconstruction of past vegetation can help to forecast the effects of global warming on northern biodiversity.

In 2017, a 46 m core was recovered from the Lake Levinson Lessing located in the tundra of the far north Taymyr Peninsula (northern Central Siberia), the upper 38 m of which span the last 62ka continuously and with a rather constant sedimentation rate. A high resolution of 84 subsamples were collected from the lake sediment core with the aim to characterise biodiversity changes between glacials and interglacials in Russian Arctic during Late Quaternary. We studied pollen and non-pollen-palynomorphs and extracted the ancient DNA (sedaDNA), from the same sediment core samples. We also investigated past vegetation composition changes by a plant metabarcoding approach (chloroplast trnL P6 loop). We compared both pollen and sedaDNA signals to reconstruct changes in biodiversity in the Taymyr Peninsula emphasizing changes in diversity during forest invasion and retreat events.
Ensemble-Based Data Assimilation of volcanic ash clouds from satellite observations: application to the 24 December 2018 Mt.Etna explosive eruption.
Authors: Pardini Federica , Corradini Stefano , Costa Antonio , Guerrieri Lorenzo , Esposti Ongaro Tomaso , Merucci Luca , Neri Augusto , Stelitano Dario , de' Michieli Vitturi Mattia
Published: March 2021

Explosive volcanic eruptions release high amounts of ash into the atmosphere. Accurate tracking and forecasting of ash dispersal into the atmosphere and quantification of its uncertainty is of fundamental importance for volcanic hazard mitigation. Numerical models represent a powerful tool to monitor ash clouds in real-time, but limits and uncertainties affect numerical results. A way to improve numerical forecasts is by assimilating satellite observations of ash clouds through Data Assimilation algorithms, such as Ensemble-based Kalman Filters. In this study, we present the implementation of the so-called Local Ensemble Transform Kalman Filters inside a numerical procedure which simulates the release and transport of volcanic ash during explosive eruptions. The numerical procedure consists of the eruptive column model PLUME-MoM coupled with the tephra transport and dispersal model HYSPLIT. When satellite observations are available, ash maps supplied by PLUME-MoM/HYSPLIT are sequentially corrected/modified using ash column loading as retrieved from space. The new volcanic ash state represents the optimal solution with minimized uncertainties with respect to numerical estimates and observations. To test the Data Assimilation procedure, we used satellite observations of the volcanic cloud released during the explosive eruption that occurred at Mt. Etna (Italy) on 24 December 2018. Satellite observations have been carried out by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instrument, on board the Meteosat Second Generation (MSG) geostationary satellite. Results show that the assimilation procedure significantly improves the current ash state and the forecast. In addition, numerical tests show that the use of sequential Kalman Filters does not require a precise initialization of the numerical model, being able to improve the forecasts as the assimilation cycles are performed.
Data-Driven Inference of the Mechanics of Slip Along Glacier Beds Using Physics-Informed Neural Networks
Authors: Riel Bryan , Minchew Brent , Bischoff Tobias
Published: March 2021

Reliable projections of sea level rise depend on accurate representations of how fast-flowing glaciers slip along their beds. Specifically, ice sheet models require a quantitative sliding law that relates basal drag to sliding velocity and glacier geometry, yet the proper form of the law remains uncertain. Here, we present a novel deep learning-based framework for learning the time evolution of basal drag from time-dependent ice surface velocity and elevation observations. We train a pair of probabilistic neural networks through a combination of time-dependent surface observations, governing equations for ice flow, and known physical constraints. Neural network outputs are stochastic predictions of time-varying basal drag that do not require any prior assumptions on the form of the sliding law. This training strategy is well-suited to large volumes of remote sensing data while providing a natural way to integrate our existing understanding of the physics of ice flow into the learning process.

We test this framework on 1D and 2D ice flow simulations and demonstrate that, under certain stress conditions, recovery of the underlying sliding law parameters and their uncertainties can be derived from the stochastic predictions of time-varying basal drag. We also apply these methods to Rutford Ice Stream and Pine Island Glacier in Antarctica to investigate subglacial hydrological effects for the former and evidence for regularized Coulomb sliding for the latter.
Atmospheric drivers of a 4-month drift of an ice buoy in the Antarctic marginal ice zone
Authors: Womack Ashleigh , Vichi Marcello
Published: March 2021

Sea-ice drift in the Antarctic marginal ice zone (MIZ) was investigated by using an ice buoy (buoy U1), deployed during the winter sea-ice expansion in July 2017, and drifted for approximately four months from the South Atlantic sector to the Indian Ocean sector of the Southern Ocean. The analysis of this buoy revealed that it remained within the MIZ even during the winter ice expansion, as the mixed pancake-frazil field was maintained. This allowed for a continued assumption of free drift conditions for buoy U1’s full drift, where it continued to respond linearly to the momentum transfer from surface winds. The analysis of buoy U1 also indicated a strong inertial signature at a period of 13.47 hours however, the wavelet analysis indicated majority of the power remained within the lower frequencies. This strong influence at the lower (multi-day) frequencies has therefore been identified as the primary effect of atmospheric forcing. When these lower frequencies were filtered out using the Butterworth high-pass filter it allowed the inertial oscillations to become more significant within the wavelet power spectrum, where it can be seen that these inertial oscillations were often triggered by the passage of cyclones. The initiation of inertial oscillations of sea ice has therefore been identified as the secondary effect of atmospheric forcing, which dominates ice drift at sub-daily timescales and results in the deviation of ice drift from a straight-line path. This comprehensive analysis suggests that the general concentration-based definition of the MIZ is not enough to describe the sea-ice cover, and that the MIZ, where sea ice is in free drift and under the influence of cyclone induced inertial motion, and presumably waves, extends up to »200 km.
Meteoroid trajectories from BRAMS data
Authors: Lamy Hervé
Published: March 2021

BRAMS (Belgian RAdio Meteor Stations) is a Belgian radio network using forward scatter observations to detect and characterize meteoroids. A dedicated transmitter located in south of Belgium emits a CW signal with no modulation at a frequency of 49.97 MHz and with a power of 130 W. The network comprises currently 35 similar receiving stations located in Belgium and neighboring countries. They use Yagi antennas with a wide sensitivity pattern which therefore provide no information about the directivity of the meteor echoes. One of these stations is however a radio interferometer using the classical Jones configuration and is able to retrieve the direction of the meteor echoes.

We discuss here a general method to retrieve meteoroid trajectories based solely on time delays measured between meteor echoes recorded at multiple receiving stations. It is based on solving at least 6 non-linear equations to solve for the position of one specular reflection point (3 unknowns) and the 3 components of the speed. This method has also been described recently in Mazur et al (2020) and applied to CMOR data. However, specificities of the CMOR configuration has allowed simplifications that cannot be made with the BRAMS network. In order to maximize the number of meteoroid trajectories with at least 6 stations detecting meteor echoes, a number of additional stations geographically close to each other have been installed in the Limburg province in 2020. Another method to retrieve meteoroid trajectories using data from the radio interferometer and from 3 other stations is also presented.

We show preliminary results from both methods using also complementary data from the optical CAMS Benelux network.  The CAMS trajectories are used to select specific meteor echoes in the BRAMS data. The time delays between them are computed and used to solve the set of non-linear equations to retrieve the meteoroid trajectory and speed, which are then compared to the CAMS values. This allows us to assess the accuracy of both methods.

Finally we simulate the impact of using additional information, not currently available but that might become in a near future. This includes data from a monostatic system (a radar nearby our BRAMS transmitter is currently built), from a second radio interferometer (to be located in Limburg and/or near the transmitter), or the total range traveled by the radio wave if a coded CW transmitter such as in Vierinen et al (2016) is used.
The electrodynamic influence of thermospheric winds in the daytime ionosphere.
Authors: Immel Thomas , Harding Brian , Heelis Roderick , Maute Astrid , Forbes Jeffrey , England Scott , Mende Stephen , Englert Christoph , Stoneback Russell , Marr Kenneth , Harlander John , Makela Jonathan , Triplett Colin
Published: March 2021

The electrodynamic influence of thermospheric winds is an effect thought to dominate the development of the daytime low-latitude ionosphere, through the generation of dynamo currents and associated vertical plasma drifts. Until recently, observations of the thermospheric and ionopsheric state variables have mainly been defined and compared on climatological time scales, due to their collection from separate observatories with disparate measurement capabilities.  These datasets are inadequate for investigation of the actual action of thermospheric drivers as they modify the ionospheric state, as the response clearly changes on 24-hour timescales, and shorter when viewed in the a constant-local-time frame of reference. New observatiions of thermospheric winds, uninterrupted over the 90-300 km altitude range, are now provided by the Ionospheric Connection Explorer along with simultaneous plasma velocity and density measurments. These observations are directly comparable to the wind measurements in crossings of the magnetic equator, where the winds are magnetically conjugate to the drift measurements. Investigation of the noon-sector drifts vs wind drivers is presented. We find that the local driver is clearly evident in the noon-time vertical plasma drifts under all conditions.

 
Improved throughput for δ18O and δD measurements of water with Cavity Ring-Down Spectroscopy
Authors: Hofmann Magdalena E. G. , Lin Zhiwei , Woźniak Jan , Drori Keren
Published: March 2021

Oxygen (18O/16O) and deuterium (D/H) isotopes are a widespread tool to trace physical and chemical processes in hydrology and biogeosciences. Precision and throughput are key parameters for water isotope analysis. Here, we will present two new methodologies for the Picarro L2130-i Cavity Ring-Down Spectroscopy (CRDS) water isotope analyzer that allow to increase the throughput with no compromise of data quality.

The Picarro Express Method now distinguishes between a memory reduction stage and a sample analysis stage and allows to measure up to 50 samples per day while maintaining the excellent precision of CRDS (i.e. 0.01‰ for δ18O and 0.05‰ for δD). This corresponds to doubling the throughput compared to the standard Picarro methodology. The Picarro Survey Method makes use of ultrafast injections and sorts the samples by their measured isotopic values, enabling a powerful new strategy to reduce memory effects.

We will discuss different measurement strategies to increase the throughput for routine water isotope analysis. The improved methodologies do not require any hardware changes and are solely based on modifications of the injection procedure. If you are interested in Picarro’s off-the-shelve solution for increasing productivity of your existing and future installations, please visit the Picarro vEGU 2021 booth for a free voucher.
Estimation of the seasonal input of freshwater in the Kara sea surface layer using hydrochemical proxies
Authors: Kazakova Uliana , Polukhin Alexander
Published: March 2021

The Kara Sea receives about 55 % of the total continental runoff to the Siberian Arctic. Water of the Yenisei and Ob Rivers with low salinity (mineralization), flowing into the sea, forms a surface desalinated layer. The desalinated layer spreads over the sea area under the influence of hydrological and meteorological factors. Meltwater generated by the melting of marine and riverine ice and precipitation contribute to the formation of a surface desalinated layer along with continental runoff.

Determining the amount of fresh water is not accurate enough if only the salinity of surface water is considered. It is possible to identify riverine water and meltwater using hydrochemical proxies. The ratio of the major ions in seawater differs from that in riverine and meltwater. River waters are characterized by an increased content of silicate and reduced values of total alkalinity. At the same time, it is possible to identify the waters of the Ob and Yenisei Rivers by the estimated values of the total alkalinity and dissolved inorganic carbon obtained during the research expeditions to the Kara sea from 1993 to 2020.

The calculation of the parts of waters of different origin is done as a result of solving a system of equations. It includes the salinity and alkalinity values of the observed surface waters and those presumably involved in the mixing process. The salinity and alkalinity values of meltwater are taken as 0 and 134 µM respectively.

The total contribution of the Ob and Yenisei runoff ranges from 20 to 90% as it approaches the estuarine areas. The correlation coefficient between the proportion of river water and the salinity of the surface layer is quite high, it is equal to -0.9. This characterizes the inverse linear relationship. The separate contribution of the waters of the Yenisei differs from the contribution of the waters of the Ob, which is related to the hydrological conditions of the rivers.

The contribution of meltwater to the formation of the surface layer of the Kara Sea did not exceed 20%, with the exception of the coastal zone of the Novaya Zemlya. In this coastal zone, meltwater provides the greatest contribution compared to the other sources, which is associated with glacial runoff.

The work is implemented in the framework of the state assignment of the Shirshov Institute of Oceanology RAS (theme No. 0149-2019-0008), with the support of the Russian Scientific Foundation (project № 19-17-00196) and the grant of President of Russian Federation № MK-860.2020.5.
Artificial neural networks for clustering sediment grains in microphotographs.
Authors: Golikov Viktor , Krinitskiy Mikhail , Borisov Dmitry
Published: March 2021

Paleoreconstruction is a group of methods for evaluating geophysical parameters based on indirect indicators, such as the chemical composition of foraminiferal shells, the concentration of various gases in sedimentary grains on the ocean floor, etc. For example, with the distribution of types and sizes of foraminifera or sizes and shapes of crystals of various minerals in sediment deposits, one may reconstruct the temperature and salinity of water and even the direction and speed of currents. A number of methods are used to explore sediment particle composition nowadays: examining color characteristics, physical properties of grains, their isotopic composition, etc. However, the visual examination of sedimentary particles under a microscope remains one of the most exploited methods. In our study, we consider sediments' fraction of size from 100 microns under an 80x microscope. Our study aims to infer the distribution of sizes and shapes of the grains in a sediments sample. However, the problem we face is that it takes a great time and effort of an expert to classify the particles. In our study, we propose to employ artificial intelligence methods for automating this task. We collect optical imagery of prepared sediment samples. Using the images, we collect visual representations of different grains of sediments. We propose using a version of convolutional variational autoencoder for reducing the dimensionality of the visual representations. Then we apply a clustering algorithm for splitting the grains into groups of similar ones. An expert examines the groups for further classification.

In this work, we will demonstrate the preliminary results of the clustering of sedimentary particles and outline further development of the presented method for their automated classification.

The work is supported by the Russian State assignment no. 0149-2019-0007
Short-baseline interferometry at Onsala Space Observatory
Authors: Varenius Eskil , Haas Rüdiger , Diamantidis Periklis , Nilsson Tobias
Published: March 2021

A growing number of geodetic VLBI stations participate in the VLBI Global Observing System (VGOS). Multiple sites operate both new VGOS telescopes and legacy S/X VLBI telescopes. At Onsala Space Observatory, Sweden, we operate two 13.2 m diameter VGOS radio telescopes, ONSA13NE (OE) and ONSA13SW (OW), as well as the 20~m legacy S/X telescope ONSALA60 (ON). Transitioning from the legacy system and providing continuity of the terrestrial and celestial reference frames necessitate establishing ties between S/X and VGOS telescopes. Since spring 2019, we have carried out more than 20 short-baseline (550 m) interferometric observations at X-band to establish local-tie vectors between ON, OE and OW. The obtained data were correlated at Onsala Space Observatory using DiFX, post-processed using HOPS and analysed with nuSolve and ASCOT. In this presentation we given an overview of the observations, analysis, and results of these local-tie experiments. We investigate the impact of modeling e.g. gravitational deformation, and the possibility of using phase-delays to improve the precision. Finally, we present a comparison with preliminary results from two other methods: global mixed-mode observations and classical local-tie measurements.
Mapping potential impacts of dams and reservoirs in South America
Authors: Paredes-Beltran Bolivar , Sordo-Ward Alvaro , Garrote Luis
Published: March 2021

We present a continental-scale evaluation of the distribution of dams and reservoirs in South America. This analysis is relevant to estimate potential impacts on water supply and flow alteration. A combined total of 808 of the largest dams across the continent, which can store about 1,003 cubic kilometres of water, were evaluated. We divided the area of study into 27 hydrological regions and for each region we determined necessary inputs to assess the potential impacts of dams and reservoirs such as: total area, mean annual runoff, total storage volume, population, or equipped area for irrigation. Although the storage capacity of the reservoirs represents around 10% of the region's total mean annual runoff, the potential impacts for flow alteration differ considerably between hydrological regions because dams and reservoirs are not evenly distributed in South America. Whilst in some hydrological regions in the north, including the Amazon river, water storage from reservoirs represents less than 5% of their mean annual runoff, some hydrological regions in the south of the continent can store the equivalent of 2 to 3 years of their mean annual runoff. The region with the highest potential for hydrological impacts is the Rio Colorado basin in Argentina, where storage from reservoirs can be almost 3.5 times the region’s mean annual runoff. The observed variations in water storage can be explained by the diversity in hydrology and water demands of the different hydrological regions of the continent. For example, water storage for hydropower purposes represents about 85% of the total water storage in the continent. Also, the highest number of dams exclusively allocated for hydropower production are located in the east of the continent in Argentina and Brazil. The hydrological region with the highest ratio of water storage is “La Plata” in the southeast of the continent with approximately 35% of the total water storage of the continent.  In addition, almost 70% of dams are located in humid or sub-humid areas. In average, the dams in the continent can store 9,700 m3 of water per person and 161,000 m3 of water per hectare equipped for irrigation. The regions with the highest concentration of dams are Venezuela and the eastern region of Brazil, while the regions with the least number of dams per area are found in the northeast of Brazil and the south of the continent. These ratios may be useful to understand the potential effects of dams and reservoirs on a regional and continental scale, considering that development plans in several countries include many new dams across the continent. With this study, we expect to provide valuable insights to researchers and water resource managers about the current and future potential impacts of dams and reservoirs in South America.
Experimental investigation of glaucophane rheology through shear and axial compression Griggs apparatus experiments on hot-pressed aggregates  
Authors: Hufford Lonnie , Tokle Leif , Behr Whitney
Published: March 2021

Constraining the rheological properties of glaucophane is critical to understanding subduction zone rheology. Based on the rock record, glaucophane is a major constituent mineral associated with subducted mafic oceanic crust at blueschist metamorphic facies. No flow law describing the crystal-plastic deformation of this mineral has been developed. Previous experimental work involving glaucophane focused on the deformation of natural polyphase rocks with an emphasis on seismic anisotropy. Here we focus on experiments intended to activate crystal-plastic deformation mechanisms in glaucophane using a monophase aggregate powder separated from natural samples from Syros Island, Greece. We are conducting general shear and axial compression experiments in a Griggs apparatus using temperatures of 600-800°C, pressures of 1 GPa and shear strain rates between 10-5-10-6. Our first experiment was in a general shear orientation at 700°C, 1 GPa, and a shear strain rate of 1.18x10-5. This experiment had a ~80% modal abundance of glaucophane and appears to have been dominated by brittle deformation. After the first experiment, we decided to produce a purer glaucophane aggregate powder containing ~95% glaucophane with ~5% other phases and are finishing mineral separation at the time of submission. We will present early mechanical and microstructural data from experiments with the aim of developing a glaucophane flow law. Our results will also be compared to ongoing experiments focused on the viscous properties of experimentally deformed natural aggregates (see abstract in this conference by Tokle et al.).