bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal variations of mode-1 M2 internal tides observed by satellite altimetry
Authors: Zhao Zhongxiang
Published: March 2021

The seasonal variations of M2 internal tides is investigated using 25 years of satellite altimetric sea surface height measurements from 1992--2017. The satellite data are divided into four seasonal subsets, from which four seasonal M2 internal tide models are constructed. This study employs a new mapping technique that combines along-track spatial filtering, harmonic analysis, plane wave analysis, and two-dimensional spatial filtering. The vector mean of the four seasonal models yields the seasonal-mean model, which is equivalent to the 25-year-coherent model constructed directly using all the data. The seasonal models have larger errors than the seasonal-mean model, because the seasonally-subsetted data sets are short. Two seasonally-variable models are derived: The first model is a step function of the four seasonal models (phase-variable, amplitude-variable); The second model is same as the first one but that the amplitude is from the seasonal-mean model (phase-variable, amplitude-invariable). All these models are evaluated using independent CryoSat-2 data. Each seasonal model reduces most variance in its own season and least variance in its opposite season. Based on globally-integrated variance reductions, the two seasonally-variable models reduce 13% and 23% more variance than the seasonal models, respectively. The seasonal-mean model can reduce 27% more variance, thanks to its small model errors. However, the seasonally-variable models are better than the seasonal-mean model in the tropical zone, where the seasonal signals are larger than model errors. The satellite results reveal that M2 internal tides are subject to seasonal variation in varying degrees and that the seasonal variation is a function of location. Large variations in amplitude and phase mainly occur in the tropical zone. The seasonal phase variations are mainly caused by the seasonal variations of ocean stratification and internal tide speed. Significant amplitude variations are usually associated with strong internal tides such as from the Luzon and Lombok Straits, and in the Amazon River plume, the western Pacific and the Arabian Sea. At higher latitudes such as the North Pacific and North Atlantic Oceans, the seasonal variations are weak but detectable. The seasonally-variable models can partly account for the seasonal variations of internal tides, in particular, in the tropical zone.  A major challenge is the large model errors, which will be further reduced with the accumulation of new altimeter missions and data (e.g., SWOT).
Expanse of greater india in the cretaceous
Authors: Meng Jun , Gilder Stuart , Li Yalin , Wang Chengshan
Published: March 2021

Knowing the original size of Greater India is a fundamental parameter to quantify the amount of continental lithosphere that was subducted to help form the Tibetan Plateau and to constrain the tectonic evolution of the India-Asia collision. Here, we report Early Cretaceous paleomagnetic data from the central and eastern Tethyan Himalaya that yield paleolatitudes consistent with previous Early Cretaceous paleogeographic reconstructions. These data suggest Greater India extended at least 2,675 ± 720 and 1,950 ± 970 km farther north from the present northern margin of India at 83.6°E and 92.4°E, respectively. The paleomagnetic data from Upper Cretaceous rocks of the western Tethyan Himalaya that are consistent with a model that Greater India extended ~2700 km farther north from its present northern margin at the longitude of 79.6°E before collision with Asia. Our result further suggests that the Indian plate, together with Greater India, acted as a single entity since at least the Early Cretaceous. An area of lithosphere ≥4.7 × 106 km2 was consumed through subduction, thereby placing a strict limit on the minimum amount of Indian lithosphere consumed since the breakup of Gondwanaland. The pre-collision geometry of Greater India’s leading margin helped shape the India-Asia plate boundary. The proposed configuration produced right lateral shear east of the indenter, thereby accounting for the clockwise vertical axis block rotations observed there.
Heavy winter precipitation events with extratropical cyclone diagnosed by GPM products and trajectory analysis
Authors: Ueno Kenichi , Sawada Morihiro
Published: March 2021

In Japan, Extratropical cyclone sometimes causes sporadic heavy snow in the coastal cites or heavy rains on snow covers in mountainous areas. Ando and Ueno (2015) identified that heavy precipitation events tend to occur with occluding cyclones. However, three-dimensional structure of precipitation system embedded in the cyclone system are difficult to capture by surface observation network over Japanese archipelago that are composed of complex coastal lines and mountains. This study identified heavy precipitation events during the cold seasons of 2014-2019 by two-day accumulated precipitation data at 137 stations of the Japan Meteorological Agency. The mechanisms for producing heavy precipitation in relation to the structure of an occluding extratropical cyclone were analyzed with the aid of the products of the Dual-frequency Precipitation Radar onboard the Global Precipitation Measurement (GPM) core satellite and trajectory analysis on European Centre for Medium-range Weather Forecasts atmospheric reanalysis data. Upper-ranked events with heavy precipitation were mostly due to extratropical cyclones, and many of them were in mature stages. In the top 50 ranked events, three south-coast cyclones were nominated, and relationships between the development of the mesoscale precipitation system and airstreams were intensively diagnosed. Hourly precipitation changes at stations that recorded heavy precipitation were primary affected by a combination of the warm conveyor belt (WCB), the cold conveyor belt (CCB) and the dry intrusion (DI). Wide-ranging stratiform precipitation in the east of cyclone center was composed of low-level WCB over the CCB and the upper WCB, and convective clouds around the cyclone center was associated with the upper DI over the WCB that provided an extreme precipitation rate at the surface, including formation of a band-shaped precipitation system. The convective cloud activities also contributed to moist air advection over the stationary stratiform precipitation areas recognized as the upper WCB. DPR products also identified deep stratiform precipitation in the cloud-head area behind the cyclone center with mid-level (near-surface) latent heat release (absorption) with increased potential vorticity along the CCB that was made feed-back intensification of the cyclone possible. (This study will be published in GPM special issue of JMSJ)　
Correcting sea surface temperature spurious effects in salinity retrieved from spaceborne L-band Radiometer measurements
Authors: Boutin Jacqueline , Vergely Jean-Luc , Dinnat Emmanuel , Waldteufel Philippe , D'Amico Francesco , Reul Nicolas , Supply Alexandre , Thouvenin-Masson Clovis
Published: March 2021

We derived a new parametrisation for the dielectric constant of the ocean (Boutin et al. 2020). Earlier studies have pointed out systematic differences between Sea Surface Salinity retrieved from L-band radiometric measurements and measured in situ, that depend on Sea Surface Temperature (SST). We investigate how to cope with these differences given existing physically based radiative transfer models. In order to study differences coming from seawater dielectric constant parametrization, we consider the model of Somaraju and Trumpf (2006) (ST) which is built on sound physical bases and close to a single relaxation term Debye equation. While ST model uses fewer empirically adjusted parameters than other dielectric constant models currently used in salinity retrievals, ST dielectric constants are found close to those obtained using the Meissner and Wentz (2012) (MW) model. The ST parametrization is then slightly modified in order to achieve a better fit with seawater dielectric constant inferred from SMOS data. Upgraded dielectric constant model is intermediate between KS and MW models. Systematic differences between SMOS and in situ salinity are reduced to less than +/-0.2 above 0°C and within +/-0.05 between 7 and 28°C. Aquarius salinity becomes closer to in situ salinity, and within +/-0.1. The order of magnitude of remaining differences is very similar to the one achieved with the Aquarius version 5 empirical adjustment of wind model SST dependency. The upgraded parametrization is recommended for use in processing the SMOS data. 

The rationale for this new parametrisation, results obtained with this new parametrisation in recent SMOS reprocessings and comparisons with other parametrisations will be discussed.

Reference:

Boutin, J.,et al. (2020), Correcting Sea Surface Temperature Spurious Effects in Salinity Retrieved From Spaceborne L-Band Radiometer Measurements, IEEE TGRSS, doi:10.1109/tgrs.2020.3030488.
Hunting for reconnection and energy exchange sites in 3D turbulent outflows
Authors: Lapenta Giovanni
Published: March 2021

Plasma turbulence is typically characterized by a preferred directon, that of teh magnetic field. Most plasmas have a coherent average field component and turbulence develop over it. Tokamaks are teh archetypical case with their strong toroidal field. But also solar arcades, solr wind, magnetospheres and ionospheres have that same property. We consider here turbulence in 3D reconnection outflows. Reconnection often has a gudie field to begin with, but even without it, in the outflow there is a significant field residual from the process of reconnection. This macroscopic field organizes the plasma turbulence to form a very anistotropic state. We recenlty, investigted the properties of turbulence at different locations [1]. We deploy now innovative machine learning tools to investigate the outflows and detect the presence of secondary reconnection sites and regions of energy exchange.

[1] Lapenta, G., et al. "Local regimes of turbulence in 3D magnetic reconnection." The Astrophysical Journal 888.2 (2020): 104.

Work supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 776262 (AIDA, www.aida-space.eu).
Push-pull flows reveal the scalar signature of chaos in porous media
Authors: Heyman Joris , Lester Daniel R. , Le Borgne Tanguy
Published: March 2021

Recent works have shown that laminar flows through porous media generate Lagrangian chaos at pore scale, with strong implications for a range of transport, reactive, and biological processes in the subsurface. The characterization and understanding of mixing dynamics in these opaque environments remains an outstanding challenge. We present a novel experimental technique based upon high-resolution imaging of the scalar signature produced by push-pull flows through various porous materials (beads, gravels, sandstones) at high Péclet number. We show that this method provides a direct image (see below) of the invariant unstable manifold of the chaotic flow, while allowing a precise quantification of the incompleteness of mixing at pore scale. In the limit of large Péclet numbers, we demonstrate that the decay rate of the scalar variance is directly related to the Lyapunov exponent of the chaotic flow. Thus, this new push-pull method has the potential to provide a complete characterization of chaotic mixing dynamics in a large class of opaque porous materials.

 
Interfacial generation of internal waves and turbulent heat flux due to enhanced inertial motion for deformed sea-ice floe: Preliminary results from MOSAiC expedition
Authors: Kawaguchi Yusuke , Koenig Zoe , Hoppman Mario , Nomura Daiki , Granskog Mats , Inoue Jun , Katlein Christian , Nicolaus Marcel ,   MOSAiC OCEAN Team
Published: March 2021

Sea-ice drift becomes most energetic at last moment in summer when refreezing is about to onset. Perennial ice floes, surviving over all seasons, tend to experience a number of deformation events over yearlong drift, with uneven distribution in thickness. Deformed ice floes protrude tall keels into water of ice-ocean boundary, and then stir it up. Consequently, combination of fast ice drift and deformation-experienced perennial ice could be a primary source of momentum/thermal energy for upper waters through propagation of internal waves. In this study, during MOSAiC expedition, we attempted to perform direct observation of wave generation in ice-ocean boundary layer underneath a drifting ice floe in the central Arctic Ocean. Time series of turbulent signals, represented by Reynolds stress  and eddy heat flux , were obtained by an eddy covariance system (ECS), coupling a high-frequency (34 Hz) single-point current meter and a temperature sensor. Vertical/temporal properties of near-inertial waves were obtained by a downward-looking ADCP, collocated with ECS on the same ice floe. At same time, a triangle of high-precision GPS systems tracked ice movement to represent mean drift speed, rotation and deformation about the same floe seamlessly in time. Preliminary analyses of those combined data suggested that pronounced signals of inertial motion occurred in early September of 2020 as sheer ice keels dragged underlying waters, stratified by accumulation of melt water. It then allowed occurrence of near-inertial internal waves that tend to be trapped within the interfacial boundary layer, located within top 20 m. At the conference, we will present latest and quantitative knowledges from the MOSAiC expedition.
Decoupled changes in upwelling and acidity in the eastern equatorial Pacific during the Pliocene
Authors: Shankle Madison , Burls Natalie , Fedorov Alexey , Thomas Matthew , Penman Donald , Ford Heather , Jacobs Peter , Planavsky Noah , Hull Pincelli
Published: March 2021

The Pliocene epoch (5.3-2.6 million years ago) is the last time Earth experienced atmospheric carbon dioxide levels comparable to present day anthropogenic levels. As such, this time interval is a potential analogue for future, warmer Earth system states. One enigmatic feature of Pliocene climate is a reduced east-west sea surface temperature gradient in the equatorial Pacific (indicative of reduced equatorial upwelling) coinciding with enhanced biological productivity in the eastern equatorial Pacific (indicative of enhanced equatorial upwelling).  Here we use boron isotopes to investigate these dynamics and to reconstruct the zonal surface pH gradient across the Pliocene equatorial Pacific. We find a strengthened pH gradient relative to modern (with more acidic conditions in the east than the west) despite a reduced temperature gradient at this time. These findings are in contrast to modern-day dynamics in which temperature and acidity co-vary, such that the reduction of the zonal temperature gradient during an El Niño event is accompanied by reduced acidity (as well as reduced upwelling and productivity) in the eastern equatorial Pacific. We show that this decoupling between changes in the pH and temperature gradients is consistent with biogeochemically enabled model simulations of Pliocene climate containing an active Pacific meridional overturning circulation and a weakly stratified equatorial thermocline. This reorganization of Pacific circulation and the onset of north Pacific deep water formation allows old, acidic, more nutrient-rich waters to reach the eastern equatorial Pacific despite weak wind-driven upwelling rates, accounting for the low pH values we observe there as well as previous evidence of enhanced productivity.
A local climate perspective from Arctic towns
Authors: Esau Igor ,   SERUS team
Published: March 2021

Across the Arctic, human settlements are challenged by rapid climate change and a broad range of environmental transformations. Some of them, such as Barrow (Utqiagvik, Alaska), must relocate; others, such as Norilsk (Russia), must restructure and rebuild. This presentation reports on local climate anomalies in 118 circum-Arctic cities and towns. For several key towns, a nexus review of the environmental consequences of the local warm anomalies is detailed. Longyearbyen (Svalbard), Apatity and Nadym (Russia) are in focus. For instance, Longyearbyen – the European “gate” to the Arctic – experiences one of the stongest climate change. The surface air temperature here has increased by almost 10oC over the last 100 years with more than 100 consecutive months being warmer than normal. Snowfall increases threatening with hazardous slab snow avalanches. The last extreme heat wave (July, 2020) showed temperatures up to +21oC and massive flooding in the coal mine.  This study synthesizes observational evidence of the climate change in the town from a local perspective. We relate meteorological conditions with sustainability issues. The study looks at local climate diversity and its role for society and economy of the settlement.
 The 2019 Eruption Dynamics and Morphology at Ebeko Volcano Monitored by geophysical instrument networks and Unoccupied Aircraft Systems (UAS)
Authors: Walter Thomas R. , Belousov Alexander and Marina
Published: March 2021

Vulcanian explosions are hazardous and are often spontaneous and direct observations are therefore challenging. Ebeko is an active volcano on Paramushir Island, northern Kuril Islands, showing characteristic Vulcanian-type activity. In 2019, we started a comprehensive survey using a combination of geophysical field station records and repeated unoccupied aircraft system (UAS) surveys to describe the geomorphological features of the edifice and its evolution during ongoing activity. Seismic data revealed the activity of the volcano and were complemented by monitoring cameras, showing a mean explosion interval of 34 min. Digital terrain data generated from UAS quadcopter photographs allowed for the identification of the dimensions of the craters, a structural architecture and the tephra deposition at cm-scale resolution. The UAS was equipped with a thermal camera, which in combination with the terrain data, allowed it to identify fumaroles, volcano-tectonic structures and vents and generate a catalog of 282 thermal spots. The data provide details on a nested crater complex, aligned NNE-SSW, erupting on the northern rim of the former North Crater. Our catalog of thermal spots also follows a similar alignment on the edifice-scale and is also affected by topography on a local scale. New analysis are included in this presentation as well as a long term change analysis based on remote sensing data.
Towards a potential vorticity based mesoscale closure scheme
Authors: Uchida Takaya , Jamet Quentin , Dewar William , Balwada Dhruv , Le Sommer Julien , Penduff Thierry
Published: March 2021

With the advent of high-performance computing, we are now capable of simulating the ocean and climate system on decadal to centennial timescales. However, global and basin-scale simulations still lack the spatial resolution necessary to resolve the mesoscales (hereon referred to as mesoscale-permitting simulations), a scale roughly on the order of O(100 km). Here, we provide a first step towards a potential vorticity (PV) based mesoscale closure scheme in order to improve the representation of mesoscale eddies in such simulations by taking advantage of the thickness-weighted averaged (TWA) framework. In the TWA framework the total eddy feedback can be encapsulated in the Eliassen-Palm (E-P) flux divergence. This implies that mesoscale closure schemes aimed at representing the total eddy feedback should therefore be representing the E-P flux divergence. The TWA framework further elucidates that its divergence is equivalent to the eddy Ertel PV flux. In other words, if one is to parametrize the eddy Ertel PV flux, one has parametrized the total eddy feedback onto the mean flow. Using a 1/12° North Atlantic ensemble simulation with 24 members, which allows us to decompose the mesoscale variability from the forced dynamics, we show that the eddy Ertel PV flux can be related to the local-gradient of mean Ertel PV as an active tracer via an anisotropic eddy diffusivity tensor. What follows is that not only does the tensor bring together the isopycnal thickness skew diffusivity and isopycnic tracer diffusivity, the former known as the Gent-McWilliams (GM) parametrization and latter the Redi parametrization, but also incorporates the eddy momentum fluxes. Although the Redi parametrization has existed longer than GM, there has been much more development in the latter, leaving the Redi diffusivity poorly constrained. Being able to treat GM and Redi simultaneously is another strength of our framework.
Sustainable Product-Service Systems: A different approach to secure smallholder production?
Authors: Intriago Zambrano Juan Carlo , Diehl Jan Carel , Ertsen Maurits W.
Published: March 2021

Smallholder farming is the cornerstone of the agricultural sector in the Global South. It produces 80% of the food in Sub-Saharan Africa and Asia, though it accounts for barely 12% of the global farmland. Its sustainable intensification is therefore paramount in the accomplishment of Sustainable Development Goal 2: Zero Hunger. In this respect, adoption of sustainable water pumping technologies is key to ensure access to irrigation water, thus to secure smallholder production. Sustained uptake of agricultural technologies, however, is a complex process whose attainment is far beyond the sole technology itself. It encompasses a number of intertwined variables of all kinds related to the adopter and the use context: biophysical, financial, institutional, social, cultural, etc.

We argue that innovative business models—like sustainable product-service system (SPSS)—have the potential to ease the adoption process by overcoming many of its constraints (e.g. unaffordable upfront costs, lack of adequate servicing). These business models, unlike traditional linear approaches of technology transfer, have to take into account a broader network of stakeholders. In this way, the technology becomes an agent of interaction between involved parties. It turns into a dynamic element, connected to other products and well-developed services, that caters multiple farming needs. In our paper, we discuss enablers and barriers for the implementation of an SPSS in smallholder contexts under different scenarios. We analyze them based on evidence from Nepali and Indonesian smallholder communities where a novel hydro-powered pumping technology, known commercially as the Barsha pump, has been deployed. The insights gathered reveal many leverage points to create synergies between farmers, entrepreneurs, financial institutions, non-profit organizations and governmental agencies. They also denote the persistent challenges in the required shift of mindset for such an innovative system to come into full operation.
Wavelet Entropy Energy Measure (WEEM): A multiscale measure to grade a geophysical system's predictability
Authors: Guntu Ravi Kumar , Agarwal Ankit
Published: March 2021

Model-free gradation of predictability of a geophysical system is essential to quantify how much inherent information is contained within the system and evaluate different forecasting methods' performance to get the best possible prediction. We conjecture that Multiscale Information enclosed in a given geophysical time series is the only input source for any forecast model. In the literature, established entropic measures dealing with grading the predictability of a time series at multiple time scales are limited. Therefore, we need an additional measure to quantify the information at multiple time scales, thereby grading the predictability level. This study introduces a novel measure, Wavelet Entropy Energy Measure (WEEM), based on Wavelet entropy to investigate a time series's energy distribution. From the WEEM analysis, predictability can be graded low to high. The difference between the entropy of a wavelet energy distribution of a time series and entropy of wavelet energy of white noise is the basis for gradation. The metric quantifies the proportion of the deterministic component of a time series in terms of energy concentration, and its range varies from zero to one. One corresponds to high predictable due to its high energy concentration and zero representing a process similar to the white noise process having scattered energy distribution. The proposed metric is normalized, handles non-stationarity, independent of the length of the data. Therefore, it can explain the evolution of predictability for any geophysical time series (ex: precipitation, streamflow, paleoclimate series) from past to the present. WEEM metric's performance can guide the forecasting models in getting the best possible prediction of a geophysical system by comparing different methods. 
Changing low flow seasonality in Central European headwaters
Authors: Vlach Vojtech , Ledvinka Ondrej , Matouskova Milada
Published: March 2021

In the environment of the changing climate in Central Europe, the seasonality and magnitude of low flow events and hydrological droughts are projected to change in the near future. Ongoing increases in the air temperature, rates of evaporation and decreasing snow cover will significantly affect the summer deficit volumes even in the rivers of humid montane and highland areas in mid-latitudes. However, what if the significant changes have already been happening during the last decades? Therefore, this research is focused on analysis of the variability and seasonality of low flow events and hydrological drought events in fifteen near-natural catchments along the Czech–German and Czech–Polish national borders. To quantify the low flow regime changes of the study regions in the last 52 years (1968–2019), we applied tools from the R package lfstat. The 30-year moving averages of seasonality ratio (SR) and the seasonality index (SI) were derived to address the degree of change in each catchment. Moreover, the 7-day and 30-day mean summer minimum discharges were computed, as well as the streamflow deficit volumes for every episode of hydrological drought. The results showed a continual increase in the proportion of summer low flow and drought events during the study period along with a significant shift in the average date of low flow occurrence towards the beginning of the year. The most marked shifts in low flow seasonality were found mainly in catchments with the average altitude 800–1000 m a. s. l. Conversely, the low flow regime in catchments above 1000 m a. s. l. and also in the catchments below 800 m a. s. l. remained nearly stable throughout the 1968–2019 period. Moreover, the analysis of 7- and 30-day mean summer minimum discharges indicated a much-diversified pattern in the behavior of long-term trends than it was expected.
Exploring the in situ high temperature emissivity of 2014–2015 Bardarbunga magmas
Authors: Biren Jonas , Cosson Lionel , del Campo Leire , Genevois Cécile , Veron Emmanuel , Ory Sandra , Li Hao , Slodczyk Aneta , Andújar Joan
Published: March 2021

Abstract: Temperature is a key parameter controlling the rheology of lava flows. Unfortunately, the hazardous behavior of eruptions prevents direct measurements of hot magmatic bodies. Hence, the temperature of magma is mostly retrieved by using remote sensing methods (ground-based or satellite-based detectors) build on measuring the infrared (IR) radiance of the body [1]. These well-established techniques are however subjected to important errors related to, among others, the poor knowledge of the spectral emissivity (ε), which is one of the most critical parameters in IR radiance measurement [2, 3]. In this study, we performed in situ optical measurements at relevant magmatic temperatures of basaltic magma from the 2014–2015 Holuhraun eruption (Bardarbunga volcano, Iceland). Spectral emissivity has been systematically determined over a wide spectral range (400–15000 cm−1) covering TIR, MIR and SWIR regions, from room temperature up to 1473 K using a non-contact in situ IR emissivity apparatus [4]. SEM, EMPA, Raman spectroscopy, DSC, XRD and TEM techniques helped characterize and understand the complex radiative behavior of this natural magmatic composition. The results show not only that spectral emissivity varies accordingly with temperature and wavenumber but also that small changes in bulk rock composition or texture produce drastic changes in emissivity at given temperature, with iron content and its oxidation state being the main agents controlling this parameter. Appropriate emissivity values can then be used to refine current radiative data from IR remote sensing and to implement the thermo-rheological models of lava flows [5] as to support hazard assessment and risk mitigation.

References: [1] Kolzenburg et al. 2017. Bull. Volc. 79:45. [2] Harris, A. 2013: Cambridge University press. 728. [3] Rogic et al. 2019 Remote Sens., 11, 662 [4] De Sousa Meneses et al. 2015. Infrared Physics & Technology 69. [5] Ramsey et al. 2019. Annals of Geophysics, 62, 2.

Keywords: Spectral emissivity, temperature, IR spectroscopy, remote sensing, basalt
Terrestrial water storage under changing climate and implications on future droughts
Authors: Pokhrel Yadu ,   Co-authors
Published: March 2021

Terrestrial water storage (TWS) strongly modulates the hydrological cycle, and is a key determinant of water resource availability, and an indicator of drought. While historical TWS variations have been extensively studied, the impacts of future climate change on TWS and the linkages to droughts remain unexamined. In this study, we quantify the impacts of climate change on TWS using an ensemble of hydrological simulations and examine the implications on droughts using the TWS drought severity index. Results indicate that climate change is projected to reduce TWS in two-third of global land area; TWS declines are especially severe in the southern hemisphere, leading to clear north-south contrast. Strong agreement across 27 ensemble simulations suggests high confidence in these projections. The declines in TWS translate to substantial increase in the occurrence and frequency of drought by mid- and late-21st century. By the late-21st century global land area and population in extreme-to-exceptional TWS drought could more than double, each increasing from 3% during 1976-2005 to 7% and 8%, respectively. Our findings underscore the need for stringent climate adaptation measures to avoid adverse effects on water resources due to declining TWS and increased droughts.
GuMNet – The Guadarrama Monitoring Network initiative (Spain)
Authors: González-Rouco Fidel ,   The GuMNet Consortium Team
Published: March 2021

GuMNet is a facility that operates continuous observation of the atmosphere, surface and subsurface at the Sierra de Guadarrama, located 50 km north-northwest of Madrid. It is composed of 10 real–time automatic stations and attempts to promote research on weather, soil thermodynamics, boundary layer physics, impacts of climate change on climate and ecosystems and air pollution in Sierra de Guadarrama. This infrastructure represents a first step into providing a unique observational network in a high protected environment that can serve a wide range of scientific and educational interests and also management.

The stations are located at heights ranging from 900 m.a.s.l. to 2225 m.a.s.l. Every station has been settled in open areas, except for one that can be found in a forested zone. High altitude sites are focused on periglacial areas, while low elevation sites are placed in pasture environments. The atmospheric instrumentation includes sensors used for the measurement of air temperature, air humidity, 4-component radiation, solid and liquid precipitation, snow depth, wind speed and wind direction. For the subsurface measurements, soil temperature and humidity sensors have been placed in 9 trenches up to 1 m depth and 12 boreholes up to 2 m and 20 m depth. One of the lowest stations has been equipped with a 3D sonic anemometer that includes a CO2/H2O analyzer. Wind profiles and eddy-covariance will be sampled, which is important for energy and water vapor exchanges. A portable station has also been equipped with a 3D sonic anemometer, which will enable the comparison between measurements at both sites. The entire network is connected via general packet radio service (GPRS) to the management software at the central laboratory located at the Campus of Excellence of Moncloa (Madrid, Spain).

The database generated by GuMNet is accessible through request and allows for developing studies concerning environmental and climate change in middle and high mountain areas. This valuable source of data aims at generating a space for scientific collaboration with other national and international institutions. The diversity of potential uses of the GuMNet observational network will be very useful in education at every level.

Website and contact: http://www.ucm.es/gumnet/
Active subaquatic fault segments in Lake Iznik along the middle strand of the North Anatolian Fault, NW Turkey
Authors: Gastineau Renaldo , De Sigoyer Julia , Sabatier Pierre , Fabbri Stefano C. , Anselmetti Flavio S. , Develle Anne-Lise , Şahin Mustafa , Gündüz Serkan , Niessen Frank , Gebhardt A. Catalina
Published: March 2021

Lake Iznik (NW Turkey), is bordered by the middle strand of the North Anatolian Fault (MNAF), whose seismic activity is debated because of its quiescence during the instrumental period. In contrast, significant historical activity is documented by several chronicles over the last two millennia.

This study aims to get a new insight into its long-term seismicity and its tectonic setting. Lacustrine sediment cores reveal fourteen earthquake-induced turbidites since their ages correspond to seismic events during the past two millennia. Bathymetry and high-resolution seismic reflection data allow describing two hitherto unknown subaquatic active fault structures (the South Boyalica and Iznik faults), belonging to the MNAF system. Sediment cores sampled on both sides of the Iznik Fault document an event deposit and a sedimentary unit vertically offset of ∼ 40 cm interpreted as the last rupture during the 1065 CE destructive earthquake. Older events are supposed on this fault more than a thousand years ago. Further studies will help to estimate the horizontal coseismic offset of this oblique-slip fault and the calendar of older ruptures. The current seismic gap of thousand years on this segment greatly increases the seismic hazard in this region and must be considered in the seismic risk assessment of the NAF system.
Modelling calving at Kronebreen, Svalbard using Elmer/Ice
Authors: Holmes Felicity , van Dongen Eef , Kirchner Nina
Published: March 2021

Understanding how tidewater glaciers are responding to climatic and oceanographic changes is vital in order to reduce uncertainty in sea level rise estimates. In this project, we are using the 3D calving model in Elmer/Ice to simulate how Kronebreen responds over short time scales to various forcing scenarios. Specifically, a variety of frontal melt scenarios are being implemented to understand how calving and glacier dynamics respond to changing inputs. Both the magnitude and spatial distribution of frontal melt will be varied, with these scenarios being informed by a dataset of glacier proximal water temperatures (spanning Aug 2016 –  Aug 2017) as well as by plume locations as identified from satellite imagery.  The model output will be compared to observational data (frontal position, velocities) collected for the period 2016 – 2017 with the aim of running longer simulations using a ’best fit’ model set up. Details of the experimental set up, as well as some preliminary results, are presented here. 
Metrology for radiation protection:  A new European network in the foundation phase
Authors: Röttger Annette , Veres Attila , Sochor Vladimir , Pinto Massimo , Derlacinski Michal , Ioan Mihail-Razvan , Sabeta Amra , Bernat Robert , Adam-Guillermin Christelle , Gracia Alves João Henrique , Glavič-Cindro Denis , Bell Steven , Wens Britt , Persson Linda , Živanović Miloš , Nylund Reetta
Published: March 2021

More than 23 million workers worldwide are exposed occupationally to ionizing radiation in the workplace and all people in the world are exposed to environmental radiation. Due to developments in healthcare and changes in living conditions, radiation exposure from artificial and natural sources has been increasing for years. Accurate measurement of radiation dose is key to ensuring safety, but there are two challenges to address. First, new standards and reference fields are needed due to the rapid developments in medical imaging, radiotherapy and industrial applications. Second, communication channels are needed to ensure that information on best practice in measurements reaches the people concerned effectively and quickly.

It is therefore necessary to provide access to identified problems and solutions on an international level. A European Metrology Network (EMN) under the roof of EURAMET is in the foundation phase prepared by the project supportBSS[1]. This project will prepare this future EMN by addressing this issue through the identification of stakeholder research needs and implementing a long-term ongoing dialogue between them and the metrology community. The EMN will serve as a single point of contact to address all metrological needs related to radiation protection and will relate to all environment processes in which ionising radiation and radionuclides are involved.

A Strategic Research Agenda and two roadmaps are under development, covering the metrology needs of both the Euratom Treaty and the EU Council Directive 2013/59/EURATOM (laying down basic safety standards for protection against the dangers arising from exposure to ionizing radiation). Furthermore, long-term knowledge-sharing and capacity building will be supported and a proposal for a joint and sustainable European metrology infrastructure is in the development. This will significantly strengthen radiation protection metrology and support radiation protection measures. The final goal of the network project is a harmonised, sustainable, coordinated, and smart specialised infrastructure to underpin the needs expressed in the European regulation for radiation protection.

[1] This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. 19NET03 supportBSS denotes the EMPIR project reference.

 
Higher-Order Ionospheric Corrections derived from realistic electron density fields
Authors: Zus Florian , Wickert Jens
Published: March 2021

We developed a rapid and precise algorithm to compute Higher-Order Ionospheric Corrections (HOIC) utilizing realistic electron density fields. The electron density field is derived from the International Reference Ionosphere (IRI) and the required magnetic field is the International Geomagnetic Reference Field (IGRF). Direct application of such HOICs is regarded impractical due to the large data volume to be handled. Therefore, we developed a parameterized version; for any location near the Earth's surface (grid with a resolution of 2.5° times 5°) a set of HOICs are computed (various elevation and azimuth angles) and the coefficients of a polynomial expansion (Zernike polynomials) are stored in a look-up-table. These look-up-tables cover the time period 1990-2019 and are available via FTP (ftp://ftp.gfz-potsdam.de/pub/home/GNSS/products/gfz-hoic/). We call this parameterized version GFZ-HOIC. A scalable version utilizing GNSS Total Electron Content (TEC) maps is under construction. A version available for real time applications is foreseen. With such accurate and easy-to-use HOICs available we performed extensive impact studies. For example, we examine how HOIC leak into estimated station coordinates, clocks, zenith delays and tropospheric gradients in Precise Point Positioning (PPP). The study includes a few hundred globally distributed stations and covers the time period 1990-2019. The PPP simulation shows the known significant systematic impact of HOICs on the estimated station y-coordinates and the estimated north-gradient components. In addition, the PPP simulation reveals the significant systematic impact of HOICs on the estimated zenith delays. This impact is not caused by higher-order terms in the formula for the refractive index of the ionosphere. This impact is caused by the ray-path bending effects. These ray-path bending effects are automatically taken into account thanks to the ray-tracing algorithm that is used in the derivation of the HOICs. In conclusion, GFZ-HOICs are both highly accurate and easy-to-use so that we can recommend them for practical applications.
Monitoring of Ionospheric D-Region Behavior Utilizing the Dual VLF Experiment
Authors: Danielides Michael , Skripachev Vladimir O.
Published: March 2021

Studying Earth's ionosphere applying very low radio frequency (VLF) ground-based networks or only single station instrumentation provides spatially and temporal limited information. The majority of the VLF experiments utilize strong naval communication transmitters as their signal sources. In most of those cases, the signal is relatively unknown, except perhaps for its frequency and field strength. Other than ionosondes (vertical ionospheric sounder), VLF radio transmitters are usually located at different locations than their receiver stations. This results in very different radio wave propagation paths and because of different ionospheric regimes (longitudinal, latitudinal, or seasonal variations).

Because VLF radio transmission can be influenced by regular natural sources, e.g. sunrise or sunset, or irregular natural sources, e.g. solar X-ray flare or earthquake, it is non-trivial to provide accurate ionospheric weather forecasts or detect precursors for possible hazards. For natural hazards, such as earthquakes, ionospheric disturbances are often found only after the occurrence of the hazard. Therefore, it is essential to experiment with modified approaches, other than the common ionospheric investigation methods.

The aim of this study is a case-based analysis of the two VLF transmissions from Iceland at 37.5 kHz and 57.4 kHz originating from the Naval Radio Transmitter Facility at Grindavik. Utilizing passive broadband VLF ground-based measurements, we compare observed delay times of the signal behaviors at sunrise and sunset, as well as sudden ionospheric disturbances (SID). Other than the zenith angle dependence, which causes changes of the photoionization at the ionospheric D-region, SID is caused by solar X-ray flare radiation. The solar X-ray flare flux data are provided by NOAA's GOES satellite. The temporal difference in the VLF signal level is of the order of minutes for dusk and dawn. The difference between the two VLF signal levels can not be caused by significant differences in their propagation paths. However, it is assumed that this temporal delay reflects vertical ionospheric composition changes.

Usually, VLF monitoring networks are used for comparing an observed SID event at various VLF frequencies and recorded from various VLF monitoring stations. The D-region enhancement during daytime is stronger during solar flare events. Especially, by comparing the VLF signal levels the spatial effects of solar flares are studied. However, the present study focuses mainly on temporal variation of the signal levels during dusk, dawn, and during SID events, which again could be caused by vertical ionospheric composition changes.
A new mode of decadal variability in the Tropical Indian Ocean subsurface temperature and its association with heat redistribution
Authors: Mohapatra Sandeep , Gnanaseelan Chellappan
Published: March 2021

Similar to the Pacific and Atlantic, Tropical Indian Ocean (TIO) has its own internal climate mode of variabilities such as Indian Ocean Dipole (IOD) and subsurface mode (SSM). A typical interannual SSM is characterized by the meridional gradient in opposing subsurface temperature anomalies in the eastern equatorial IO and in the southwestern IO. Here in the present study, we have explored the structure and the underlying dynamics for the SSM in decadal time scale which has not been reported before. By analyzing different reanalysis products we observe that decadal SSM is characterized by a pure north-south pattern with the northern mode covering the entire equatorial belt which is different from interannual SSM. A north-south SSM is the leading mode of decadal variability in the thermocline and subsurface temperature over the TIO. Our preliminary analysis suggests that the decadal variability in the surface winds along the equatorial IO and the associated wind stress curl are found to be the primary forcing mechanisms for the decadal evolution of the north-south mode. Positive wind stress curl anomalies south of 8oS intensify the downwelling Rossby waves in the south during the positive phase of the decadal SSM. On the other hand, the northern cooling is driven mostly by the equatorial upwelling Kelvin waves and the Ekman divergence. Further, the phase transition in the SSM is primarily determined by the strength of the surface wind and the associated Ekman transport. The equatorial easterlies (westerlies) diverge (converge) the meridional Ekman transport, transporting heat towards the off-equatorial (equatorial) region during the positive (negative) phase. Consistently with SSM, upper 500m oceanic heat content reveals a conventional north-south dipole highlighting the importance of SSM on the TIO heat redistribution. This is further supported by the modulation of meridional overturning circulation and the meridional heat balance across the southern Indian Ocean (SIO). Overall the present study explores the underlying mechanism responsible for decadal SSM and its association with the heat distribution across the SIO.
Interhemispheric asymmetry of surface mean and extreme wind projections in CanESM5 climate change simulations
Authors: Yu Bin , Zhang Xuebin , Li Guilong , Yu Wei
Published: March 2021

The internal climate variability contributes to various aspects of climate change projections. This presentation will report results of the ensemble mean and spread of future projections of globally surface mean and extreme winds in boreal winter, based on single model initial-condition simulations forced by the SSP5-8.5 high-emissions scenario from a 50-member ensemble of CanESM5 models. Over the next half century, surface wind is projected to increase in the Northern Hemisphere mid-latitudes and increase in the Southern Hemisphere low-latitudes, an interhemispheric asymmetry feature relevant to large-scale changes in surface temperature and atmospheric circulation. Decreases in the surface extreme wind are clearer than the mean wind in the northern mid-latitudes. Large ensemble spreads are apparent in the mean and extreme wind changes, including spatial pattern and magnitude of the projected trends over the next half century. The internal climate variability generated components of the mean and extreme wind trends exhibit large-scale spatial coherences, and are comparable to the externally anthropogenic forced components of the trends.