bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismogenic potential of the Main Himalayan Thrust constrained by coupling segmentation and earthquake scaling
Authors: Michel Sylvain , Jolivet Romain , Rollins Chris , Jara Jorge , Dal Zilio Luca
Published: March 2021

Recent studies have shown that the Himalayan region is under the threat of earthquakes of magnitude 9 or larger. These estimates are based on comparisons of the geodetically inferred moment deficit rate with the seismicity of the region. However, these studies do not account for the physics of fault slip, specifically the influence of frictional barriers on earthquake rupture dynamics, which controls the extent and therefore the magnitude of large earthquakes. Here, we propose a methodology for incorporating outcomes of physics-based earthquake cycle models into hazard estimates. The methodology takes also into account the moment deficit rate, the magnitude-frequency of the current and historical catalogs, and the moment-area earthquake scaling law.

For the Himalaya setting, we estimate an improved probabilistic estimate moment deficit rate using coupling estimates inferred using a Bayesian framework. The locking distribution of the fault suggests an along-strike segmentation of the MHT with three segments that may act as aseismic barriers. The effect of the barriers on rupture propagation is assessed using results from dynamic models of the earthquake cycle. We show that, accounting for measurement and methodological uncertainties, the MHT is prone to rupturing in M8.7 earthquakes every T>200 yr, with M>9.5 events being greatly improbable. The methodology also allows to estimate the probability of the position of earthquakes on the fault based on the effect of the seismic barriers and their magnitude. This study provides a straightforward and computationally efficient method for estimating regional seismic hazard accounting for the full physics of fault slip.
Simulations of electric field at the initiation altitudes of sprites and halos generated by the thundercloud charge structure and lightning channels of causative return strokes
Authors: Kaspar Petr , Kolmasova Ivana , Santolik Ondrej , Popek Martin , Spurny Pavel , Borovicka Jiri
Published: March 2021

Sprites and halos are transient luminous events occurring above thunderclouds. They can be observed simultaneously or they can also appear individually. Circumstances leading to initiation of these events are still not completely understood. In order to clarify the role of lightning channels of causative lightning return strokes and the corresponding thundercloud charge structure, we have developed a new model of electric field amplitudes at halo/sprite altitudes. It consists of electrostatic and inductive components of the electromagnetic field generated by the lightning channel in free space at a height of 15 km. Above this altitude we solve Maxwell’s equations self-consistently including the nonlinear effects of heating and ionization/attachment of the electrons. At the same time, we investigate the role of a development of the thundercloud charge structure and related induced charges above the thundercloud. We show how these charges lead to the different distributions of the electric field at the initiation heights of the halos and sprites. We adjust free parameters of the model using observations of halos and sprites at the Nydek TLE observatory and using measurements of luminosity curves of the corresponding return strokes measured by an array of fast photometers. The latter measurements are also used to set the boundary conditions of the model.
Spatial permeability variations of aquifers in North China Plain derived from large magnitude earthquake signals
Authors: Gu Hongbiao , Xu Yirong , Wang Mingyuan , Su Zhandong , Lan Shuangshuang , Woo Nam Chil , Sauter Martin
Published: March 2021

Permeability changes induced by earthquakes have been widely studied. The question remains of how multiple large earthquakes influence permeability at different depths in the far-field and permeability changes could possibly be employed for hydraulic characterization of the aquifers has not yet been investigated. We study the change in permeability in fractured aquifers of the North China Paraplatform based on 11 years of groundwater hydrographs of 7 wells and 62 earthquakes. From 2008 to 2018, the permeability changes varied from well to well, all aquifers showed a consistent and distinct magnitude of change in permeability (decrease, increase and no change) following each earthquake. From the perspective of a single well to multiple shocks, the permeability variation of the JN well is the most sensitive to seismic events. From the perspective of multiple wells to one single earthquake, there were no cases of simultaneous permeability changes in all 7 wells induced by a single earthquake. Permeabilities varying within a wide range at a given depth implies that it could be considered as a dynamically self-regulating value, while permeability changes indicate great differences at varying depths. We found that the correlations between permeability changes and seismic energy density or depth are weak, however, the azimuths of seismic waves could greatly impact the changes in permeability, i.e., from 25° to 295°, and the most significant span is 250° to 295°, and fault distribution around the monitoring wells may also contribute to this result. Employing a seismic waves-pressure amplitude model, the mobilization of colloids driven by the oscillation of pressure head as a possible mechanism of permeability change. Distant, large magnitude earthquakes can alter the permeability, also can accelerate or slow down the rate of permeability change of the aquifer material.
Classification and transformation of aerosols over selected Indian cities during reduced emissions under COVID-19 lockdown
Authors: Attri Pradeep , Sarkar Siddhartha , Mani Devleena
Published: March 2021

An improved air quality around the globe and over India has been witnessed during the Covid-19 pandemic lockdown. Using surface observations of particulate matter and chemical species data and products from the MERRA-2 reanalysis Ångstrom exponent (α) and aerosol optical depth (AOD), this study documents the changes in atmospheric chemistry over the Indian subcontinent as a result of nationwide lockdown. Two major cities are selected in five Indian regions to cover a large spatial domain. A general shift from fine to coarse particle size, predominantly of dust type, in all regions is observed, which implies a lowered residence time of aerosol in the atmosphere during decreased anthropogenic emissions. For the studied period, Thiruvananthapuram is the cleanest city with marine origin aerosols and an average PM2.5 concentration of 7.69±2.40µg/m3 in the last phase of nationwide lockdown. Over Delhi and Ahmedabad, industrial and vehicular emission play important role in influencing the air quality. The diurnal variation of O3 and NO2 and their interdependency on each other vary over space and time, with the sharp nighttime O3 peak observed in the southern region for each lockdown phase. Biomass burning type aerosols decrease over the eastern region. In lockdown, NO2 also shows a significant correlation with population density (R2 = 0.75; p < 0.05), suggesting human mobility (and accordingly vehicular emissions) as the major contributor to NO2 concentration in the atmosphere. The results of present study did not find any relationship between the ambient concentrations of pollutants to the cumulative increase in COVID-19 cases. However, there is a significant relationship with O3 concentrations, and in turn with NO2, which can be associated with respiratory ailments.
On the depth-dependent stress accumulation for earthquake generation process
Authors: Aochi Hideo , Tsuda Kenichi
Published: March 2021

Dynamic rupture simulation of an earthquake mostly aims at a characteristic event, which may rupture the entire seismogenic zone of a fault system, perhaps reaching the ground surface. However, hazardous earthquakes sometimes occur along a part of the depths of a fault. Many questions arise why only this particular depth does rupture and whether the surrounding part remains hazardous. Previously, Aochi (GJI, 2018) has considered a depth-dependent stress accumulation for emphasizing the difference of reverse and normal faults under the hypothesis that stress is sufficiently and uniformly charged at all depths. We probably need to revise this hypothesis and the partially charged fault along depth would be more suitable for explaining the given question. By developing the previous simulations by Aochi (GJI, 2018), we carry out numerical simulations for demonstrating the importance of the depth-dependent stress accumulation.  
Eastern Alpine summit mass balances as complementary indicators of local climate change 
Authors: Fischer Andrea , Bohleber Pascal , Stocker-Waldhuber Martin
Published: March 2021

Eastern Alpine Mountain Glaciers are threatened by current climate change, for which they are visible and prominent indicators. This makes them an important part of climate communication pushing our commitment for mitigation efforts. At the same time, this requires the scientific community to thoroughly understand and communicate the ongoing processes.

From a scientific viewpoint, the link between classical in-situ mass balance data and the climate and environmental records potentially preserved in the so-called cold “miniature ice caps” sparks novel research perspectives. Summit stake measurements and ice core drillings are both rare, although the comparison of today’s stake mass balance records with the variance of annual accumulation preserved in ice cores offers an intriguing hub to unravelling past processes.

We implemented summit stake mass balance measurements on two summits in the Austrian Alps, Weißseespitze (3500 m) in Ötztal Alps and Großvenediger (3600 m) in Hohe Tauern National Park. At Weißseespitze summit ice cap, two ice cores were drilled recently to bedrock and subsequently micro-radiocarbon dated. A stake network is complemented by a continuous monitoring of point thickness changes and a time lapse cam to monitor patterns of snow cover distribution. An energy balance station offers information on wind, air and ice temperatures and radiation.

The results from the first two years of monitoring at Weißseespitze indicate that the remaining ice cap of about 10 m thickness will be gone within two decades even under current conditions. In view of present melt rates of about 0.6 m/year, a dated ice core record could eventually shed light on the question if similar conditions as today have occurred earlier in the past 6000 years of glacier cover at the summit. Learning more about (sub)seasonal patterns of accumulation is extremely import for the interpretation of these ice cores, as main accumulation takes place during early and late accumulation season, whereas the accumulation during colder periods is lost by wind erosion. The so far rarely studied miniature ice caps therefore open windows to complementary climate information, different from summer temperatures and winter precipitation which are widely accepted to be represented in total glacier mass balances.
Polymer type and UV-treatment influence the first week of biofilm development in Caribbean sublittoral waters 
Authors: Goudriaan Maaike , Witte Harry , Vreugdenhil Sanne , Brouwer Maartje , Niemann Helge
Published: March 2021

Marine plastic pollution has increased exponentially since the start of mass production in the 1950´s and the negative impacts of marine plastic debris (MPD) on marine life are general acknowledged. Typically, MPD is overgrown by diverse biofilms comprised of prokaryote and eukaryotes, but it is mostly unresolved whether polymers are colonized by opportunist that attach to any hard surface, or if different polymers attract specific communities. This question is further complicated by the fact that floating MPD is subjected to UV-induced photo-oxidation, which results in polymer degradation, i.e. the release of smaller and more bioavailable daughter products, and also causes changes in the polymer’s surface properties. If weathered surfaces are more prone to colonization than pristine ones and whether communities on these surfaces are different is unknown. In consonance, whether colonizers interact with the different polymers, e.g. degrade it, or are just ‘hitching a ride’ is ambiguous. To solve this complex problem we investigated the initial colonization of pristine plastics and the influence of photo-oxidation on community succession. We incubated five different polymer types (PE, PP, PET, PS and Nylon; one set UV pre-treated, one set pristine), in shallow coastal waters of the Caribbean island St. Eustatius at a depth of 5m. Multivariant-analyses to compare day 1 and day 6 revealed that the microbial community changed over time, which is a typical feature during colonisation. Communities of day 1 and day 6 were also analysed separately to assess the influences of UV pre-treatment and polymer type during separate stages of biofilm development. On day 1, UV pre-treated foils attracted a different community than non-pre-treated foils, while there was no statistical difference in community composition between the five polymer types. In contrast, on day 6, the influence of UV treatment on community composition was no longer significant, while different polymer types supported different communities. These results show that the community is dynamic in the initial stage of colonization of polymers. The effects of UV pre-treatment and polymer type indicate that colonizers are not purely opportunistic. With more in-depth analysis on OTU and/or order level, we aim to answer the following questions: 1) What is the main driver for community succession 2) Are there polymer-specific members of the community 3) Do the different polymer types select for communities that might utilise the polymer or its UV-degradation products for energy gain and/or growth.
Study of thermodynamic properties of trade-wind cumulus clouds with Remotely Piloted Aircrafts during the EUREC4A field campaign
Authors: Maury Nicolas , Roberts Gregory , Couvreux Fleur , Verdu Titouan , Narvor Pierre , Seguin Florian , Lacroix Simon , Hattenberger Gautier , Cayez Gregoire
Published: March 2021

Trade wind cumulus clouds have a significant impact on the earth's radiative balance, due to their extensive coverage in subtropical regions but due to their characteristic size are still parameterized.
The feedback of low clouds on the climate system as well as biases still existing in their representation of Global Climate Models (GCMs) results in a climatic response with relatively large uncertainty and induce a significant divergence in GCMs. Many studies and campaigns have focused on a better understanding of the thermodynamic and macroscopic properties of cumulus clouds with ground-based and satellite-based remote sensing
and also in-situ observations from aircraft flights, but few provide information on the three-dimensional properties of individual cumulus clouds. Our understanding of cumulus clouds is also based on high-resolution numerical simulations (LES: 25m, 5m of resolution) that reproduce the
average characteristics of cumulus clouds fairly reliably, yet these simulations still depend on parametrizations (turbulence and microphysics).
The development of a fleet the sampling of RPAs (Remotely Piloted Aircraft) contributes to the increase in the resolution of the sampling of the evolution of cloud microphysical properties. Recent studies have permitted to have an autonomous adaptive sampling and a mapping using Gaussian
Process Regression to interpolate missed values during exploration.
An experimental strategy has been developed and tested in a cumulus cloud field simulated in a LES simulation with the Meso-NH model by implementing a simulator of RPA flights. During the EUREC4A field campaign in Barbados in January-February, more than forty RPAs flights have been conducted and thermodynamic properties of cumulus clouds were studied in three dimensions using miniaturized instruments installed on-board (PTU probe, cloud sensor). We validate first the results of cloud sensor with an other microphysics instrument. Several clouds were followed for about ten minutes and their thermodynamic evolution have been compared to cumulus clouds simulated in the LES.
Magnetic fabric of Devonian and Precambrian dikes from the northeastern Kola Peninsula, Russia
Authors: Fursova Sofya , Veselovskiy Roman
Published: March 2021

Nowadays, anisotropy of magnetic susceptibility (AMS) is a very widespread method to investigate the magnetic fabric of the rocks. AMS studies provide the information on the magma flow during formation of intrusives (dikes and sills) based on the orientation of the AMS ellipsoid. In this work we present the results of the AMS measurements of Devonian, Paleoproterozoic and Neoarchean dikes, which are located on the northeastern part of the Kola Peninsula. We use these data to reconstruct the direction of magma flow with the final aim to reconstruct the spatial distribution of the magma sources.

Laboratory studies of AMS were carried out on 1282 samples representing 102 dikes. At this stage, all studied dikes were typified based on their geological age and type of AMS (normal, reversed, intermediate). It is shown that not all the studied intrusive bodies retained the primary magnetic fabric and only a few of them can be used to reconstruct the position of magmatic centers and are promising for obtaining reliable paleomagnetic data. We also present the first results of interpretation of the direction of the magma flow during dike swarms forming.

The study is supported by the grant of RSF #16-17-10260.
Utilising Citizen Science Rain Data for Improved Rainfall Estimation in Urban Pluvial Flooding
Authors: O'Hara Tess , Parkin Geoff , Fowler Hayley , Lewis Elizabeth , McClean Fergus , Brown Jake
Published: March 2021

Did you know there are millions of rain observations from thousands of privately owned automated weather stations located throughout Britain (and beyond) held in a freely accessible online archive? Citizen Scientists are sharing detailed sub-daily weather observations, including from locations where other gauge data is not available, often in close to real-time. There is distinct clustering of rain gauges in British urban areas, and with an anticipated increase in convective storms resulting in localised pluvial flooding, such high-resolution data should not be ignored. The aims of this research are to assess data quality, investigate how access to the data can be made easier, and to explore how the data can be used to support improved flood risk assessment.

British rain observations are presented, spanning 10 years from more than 3000 unique citizen science weather stations via the Met Office WOW archive. These citizen science observations have the potential to fill gaps in the official monitoring network run by the Met Office and agencies responsible for flooding in Britain. Analysis indicates that if the official ground based rain gauge network was interpolated on a 5km grid there would be coverage for 36% of Britain, but if citizen science weather stations were included that figure increases to over 50%. A methodology to identify poor quality observations has been developed; the preliminary findings show that even where absolute values may be inaccurate, citizen science gauges can capture the pattern of extreme rainfall. Examples are shown from work in progress showing how combining citizen science observations with official rain data (radar and ground based gauges) can improve delineation of specific events that resulted in pluvial flooding.
Low-likelihood high-warming storylines for extremes 
Authors: Fischer Erich , Schwingshackl Clemens , Sillmann Jana
Published: March 2021

Recent IPCC focused their assessment of changes in climate extremes primarily on the likely range and on mapping them as multi-model means. Recently, it has been argued that focusing primarily on the likely range potentially ignores changes in the physical climate system that are unlikely to occur but are associated with the highest risks for human and ecological systems. This is particularly the case for extremes where impacts often non-linearly depend on changes in hazards and where uncertainties are typically large both due to model response uncertainty and internal variability. Low-likelihood high-warming storylines have been proposed as a powerful tool to assess and communicate the risk associated with such future climates. However, storylines that are consistent across variables and spatial patterns is challenging.

Here, we introduce and compare different approaches for creating low-likelihood high-warming storylines for extremes based on CMIP6 models, and discuss their strengths and limitations for temperature extremes, heavy rainfall and droughts. We demonstrate that all approaches yield storylines in which changes in hot extremes, extreme rainfall and droughts strongly exceed the multi-model mean over large parts of the globe. This suggests that a focus on the likely range may indeed substantially underestimate the risk associated with changes in extremes.

We further demonstrate that the choice of the storyline approach needs to be informed by the purpose of the assessment. Pattern-scaling based storyline approaches are simple and easy to communicate and provide a reasonable first guess for extremes that are closely related to temperature changes. However, they often lead to implausible global patterns and violate physical consistency across regions and different variables. Particularly for wet and dry extremes, the models showing the largest global warming often do not show the greatest changes in extremes. Other more complex approaches have the advantage of generating storylines of globally coherent patterns of changes in extremes. Such approaches allow assessing physically consistent and spatially coherent global low-likelihood high-warming storylines of regional extremes that are suited for global risk assessment and resilience building across different sectors.
Reconstructing provenance changes in sediments supplying the South East African margin
Authors: Pryor Ellie , Hall Ian , Andersen Morten , Babin Daniel , Cai Yue (Merry) , Goldstein Steven , Hemming Sidney , van der Lubbe Jeroen , Simon Margit
Published: March 2021

Sediment provenance is of key importance for understanding transport history and characterising sediment source regions in the marine and terrestrial environment. Radiogenic isotopes are widely used to identify inland and coastal sediment origins. They document changes in detrital terrigenous sediment fluxes which can be related to continental hydrological variability. Understanding sediment sources to the ocean is a pre-requisite before interpreting past climate archives in marine sediment cores.

South African coastal drainage basins are composed of various geological units, each reflected by different radiogenic isotope signals in the sediment. In addition to the age and nature of their source rocks, the sediment type influences this radiogenic signature.

Here, we present a review of the present-day radiogenic isotopic fingerprints of South African river catchments signals from new river sediment samples with the aim to gain a broad spatial coverage of the source rocks in the region and their relative contributions of terrigenous sediment delivered to the ocean. This information will be applied to marine sediment core MD20-3591 (36° 43.707 S; 22° 9.151 E, water depth 2464m), located offshore South Africa which has the potential to record both Agulhas Current and terrestrial variability. The core site receives a significant amount of terrigenous material from the African continents via riverine input. During the last glacial period, these rivers flowed across the continental shelf within a subdued incised valley. The Gourritz River catchment drains the Cape Supergroup and Karoo Supergroup, typical of these southern drainage basins, whereas the eastern Cape rivers drain the Karoo Supergroup geological unit which is capped by the Drakensberg basalts.

We are using the knowledge gained from these new South African terrestrial river sediment samples to identify the sources and transport pathways of the terrigenous sediments in MD20-3591. Of particular interest is the sensitivity of the radiogenic isotopic signatures to grain size variabilities and how this relationship can help to define local or distal sediments. These records will allow us to explore variability in regional hydroclimate in relation to the abundant archaeological evidence of cultural and technological innovations of Middle Stone Age humans in southern Africa.
Temporal Variability in Interior Dissolved Inorganic Carbon
Authors: Keppler Lydia , Landschützer Peter , Gruber Nicolas , Lauvset Siv K.
Published: March 2021

Air-sea CO2 fluxes display large temporal fluctuations on seasonal to interannual timescales, both at global and regional scales. These fluctuations in the oceanic carbon uptake suggest that the interior dissolved inorganic carbon (DIC) is equally highly variable, driven by changes in this uptake, but also by changes in circulation and biological activity. In turn, fluctuations in DIC affect the air-sea CO2 exchange, thus altering the amount of CO2 in the atmosphere. However, most studies at global scale have focused on the anthropogenic increase in oceanic carbon and have done so at decadal mean time scales. Consequently, to date, the seasonal and interannual variability (IAV) of the contemporary DIC (natural + anthropogenic) in the water column has not been quantitatively mapped from observations at a global scale. Here, we fill this gap by using our newly developed global ocean DIC map product “Mapped Observation-Based Oceanic DIC” (MOBO-DIC) which is based on DIC measurements from GLODAPv2.2019 and a 2-step neural network method to gap-fill and map the measurements globally until 2000 m. Its seasonal climatology (Keppler et al., 2020a) reveals that the seasonal surface DIC amplitudes range from 0 to more than 50 μmol kg−1. The seasonal variations mostly stem from high DIC concentrations in winter, when mixed layers are deep, and low DIC concentrations in summer, when enhanced net community production (NCP) removes large amounts of DIC. We estimate a spring-to-fall NCP in the euphotic zone of the mid-latitudes of 3.9±2.7 Pg C yr-1, which corresponds to 8.2±5.6 Pg C yr-1 when upscaling globally (Keppler et al., 2020b). The monthly fields of MOBO-DIC from 2004 through 2018 reveals that the largest interannual variability of DIC is found in the tropical Pacific, strongly driven by the El Niño Southern Oscillation. The DIC trend suggests that in the upper 500 m, the DIC concentration has increased by ~21 Pg C from 2004 through 2018 (i.e., ~14 Pg C decade-1) in our study domain.

References

Keppler, L., Landschützer, P., Gruber, N., Lauvset, S. K. & Stemmler, I. (2020a). Mapped Observation-Based Oceanic Dissolved Inorganic Carbon (DIC), monthly climatology from January to December (based on observations between 2004 and 2017), from the Max-Planck-Institute for Meteorology (MOBO-DIC_MPIM) (NCEI Accession 0221526). NOAA National Centers for Environmental Information. Dataset. https://doi.org/10.25921/yvzj-zx46.

Keppler, L., Landschützer, P., Gruber, N., Lauvset, S. K., & Stemmler, I. (2020b). Seasonal carbon dynamics in the near-global ocean. Global Biogeochemical Cycles, 34, e2020GB006571. https://doi.org/10.1029/2020GB006571.
Internal Atlantic Multidecadal Variability mechanism at two model resolutions 
Authors: Lai Michael , Robson Jon , Wilcox Laura , Dunstone Nick
Published: March 2021

The Atlantic Multidecadal Variability (AMV) is a key factor in modulating climate change and its impacts around the world. Therefore, understanding of its physical mechanism will be crucial to achieving predictability on decadal timescales. However, details of the mechanism are not fully understood. This is evident in the wide range of simulated AMV timescales and spatial patterns exhibited by climate models in both pre-industrial and historical simulations.

In this study, we assess the impact of model resolution on the internal AMV mechanism by taking advantage of the close physical similarities between the medium- and low-resolution versions of the HadGEM3 models. Here, we present results from analysing the N96ORCA1 (~135km atmosphere, 1° ocean) and N216ORCA025 (~60km, 0.25°) pre-industrial simulations.

At both resolutions, we found that the internal AMV has a timescale of 70-100 years, comparable to the observed record. The processes driving decadal SST variability varies by latitude. Ocean heat transport changes associated with the AMOC drive subpolar variability, while surface fluxes associated with cloud and wind changes are more important in the subtropics. The AMOC strengthening is induced by density forcing from two sources. First, a Labrador Sea surface cooling driven by low-frequency positive NAO leads the AMOC by 5 years. Second, a source of anomalously saline Arctic water flowing into the subpolar North Atlantic also leads the AMOC by 5 years. Interestingly, the two resolutions disagree on the relative importance of these AMOC drivers. In the lower resolution model, the Arctic contribution is more important. However, the NAO dominates in the medium resolution model, and decadal NAO variability is more strongly associated with the AMV. Differences between the models are likely due to mean state differences including the strength and position of ocean currents such as the Gulf Stream, and their impacts on upper ocean properties.

 
Remote sensing of atmospheric winds using an infrared all-sky imager
Authors: Kurzrock Frederik , Boudreault Louis-Etienne , Reinhardt Maria , Schoger Sybille Y. , Potthast Roland , Millerioux Quentin , Schmutz Nicolas
Published: March 2021

The motion of clouds at a given location can be detected using ground-based all-sky imagers that frequently acquire images of the sky dome. Motion flow is used for minute-scale forecasting of cloud cover and solar irradiance, for example in the case of forecasting photovoltaic power production. While visible-range sky cameras are often applied for this purpose, they neither allow to detect the altitude of clouds, nor accurately detect clouds at night time. However, thermal-infrared all-sky imagers, such as Reuniwatt’s Sky InSight, retrieve brightness temperatures with constant accuracy at day and night time. This allows for the retrieval of diverse cloud parameters such as cloud base height. Atmospheric wind vectors can be derived and geolocalised by combining cloud motion detection and cloud-base height retrieval. In this study, we evaluate the accuracy of atmospheric wind vector retrievals by the means of the Sky InSight. Radiosoundings and wind profiler observations are used as a reference.
Characterizing Dam Induced Flood at Downstream of a Hydel Project 
Authors: Devi Dipsikha , Baruah Anupal , Sarma Arup Kumar
Published: March 2021

Flooding due to sudden release from a hydropower dam during monsoon is becoming a serious concern for downstream locality, especially when there is lack of coordination between the dam authority and the Disaster Management Authority (DMA) at downstream. For hilly river, a disastrous flash flood is generally caused by short duration high intensity precipitation and a pondage hydropower project cannot attenuate such flood. Generally, reservoir simulation/optimization for a hydropower project is carried out on monthly, ten-daily or at best on daily basis to determine the best operating policy and to analyze impact of such operation on the flow scenario and therefore, in conventional analysis such flash flood event goes un-noticed. A detailed investigation of the downstream flooding is required before the construction of any hydropower project with at least on hourly basis to get insight into the impact of such inflow at downstream. Non-availability of short duration precipitation/flow data in interior project area, particularly in developing country hinder such analysis. Need and scope of such analysis is demonstrated by using a typical flow hydrograph of 48 hours, having two flood peaks, as inflow to the Lower Subansiri Hydroelectric Project (LSHP). The project is located in the Subansiri River, the largest tributary of the Brahmaputra River in India. Two operating policies; i) Standard Operating Policy (SOP) and ii) Dynamic Programming (DP) generated operating policy have been tested and both the polices have generated similar hourly flow time series of total reservoir outflow (spill + Release). These reservoir operation models have been coupled with the hydrodynamic model to route the hourly reservoir outflow from LSHP to a flood prone area located 13Km downstream of it. Post dam flood scenario thus generated is compared with the pre dam flood scenario by routing the same inflow hydrograph without considering the dam. As the river has an embankment, and flooding occurs only when the embankment fails, a specified water level at the downstream section has been considered as critical for flooding for the purpose of a comparative study.  For the considered inflow hydrograph, it is observed that the flood magnitude is not increased by the action of dam operation rather peaks get slightly attenuated. However, in natural condition without dam, flood rises gradually providing prior information to the locality and providing sufficient time for completing pre-disaster actions based on experience. With inclusion of dam, peak flow rises vary rapidly from a very low flow without showing any indication of flood beforehand and thus flood becomes more disastrous. Sudden fluctuation of water level can also cause failure of river bank and progressive bank failure can eventually cause the embankment to fail. The analysis has shown the possible impact of hydel project with more clarity to help disaster manager prepare mitigation measures in an informed way.
A framework for the Integrated Assessment of SDG trade-offs in the Sundarbans Biosphere Reserve.
Authors: Marcinko Charlotte , Nicholls Robert , Daw Tim , Hazra Sugata , Hutton Craig , Hill Chris , Clarke Derek , Harfoot Andy , Basu Oindrila , Das Isha , Giri Sandip , Pal Sudipa , Mondal Partho
Published: March 2021

The United Nations Sustainable Development Goals (SDGs) and their corresponding targets are significantly interconnected, with many interactions, synergies and trade-offs between individual goals across multiple temporal and spatial scales.  We propose a framework for the Integrated Assessment Modelling (IAM) of a complex deltaic socio-ecological system in order to analyse such SDG interactions. We focus on the Sundarbans Biosphere Reserve (SBR), India within the Ganges-Brahmaputra-Meghna Delta. It is densely populated with 4.4 million people (2011), high levels of poverty and a strong dependence on rural livelihoods. It is only 50 km from the growing megacity of Kolkata (about 15 million people in 2020). The area also includes the Indian portion of the world’s largest mangrove forest – the Sundarbans – hosting the iconic Bengal Tiger. Like all deltaic systems, this area is subject to multiple drivers of environmental change operating across different scales. The IAM framework is designed to investigate current and future trends in socio-environmental change and explore associated policy impacts, considering a broad range of sub-thematic SDG indicators. Integration is achieved through the soft coupling of multiple sub-models, knowledge and data of relevant environmental and socio-economic processes.  The following elements are explicitly considered: (1) agriculture; (2) aquaculture; (3) mangroves; (4) fisheries; and (5) multidimensional poverty. Key questions that can be addressed include the implications of changing monsoon patterns, trade-offs between agriculture and aquaculture, or the future of the Sundarbans mangroves under sea-level rise and different management strategies, including trade-offs with land use to the north.  The novel high-resolution analysis of SDG interactions allowed by the IAM will provide stakeholders and policy makers the opportunity to prioritize and explore the SDG targets that are most relevant to the SBR and provide a foundation for further integrated analysis.
Adaptive Localization for Tropical Cyclones With Satellite Radiances in an Ensemble Kalman Filter
Authors: Wang Chen , Lei Lili , Tan Zhe-Min , Chu Kekuan
Published: March 2021

One important aspect of successfully implementing an ensemble Kalman filter (EnKF) in a high dimensional geophysical application is covariance localization. But for satellite radiances whose vertical locations are not well defined, covariance localization is not straightforward. The global group filter (GGF) is an adaptive localization algorithm, which can provide adaptively estimated localization parameters including the localization width and vertical location of observations for each channel and every satellite platform of radiance data, and for different regions and times. This adaptive method is based on sample correlations between ensemble priors of observations and state variables, aiming to minimize sampling errors of estimated sample correlations. The adaptively estimated localization parameters are examined here for typhoon Yutu (2018), using the regional model WRF and a cycling EnKF system. The benefits of differentiating the localization parameters for TC and non-TC regions and varying the localization parameters with time are investigated. Results from the 6-h priors verified relative to the conventional and radiance observations show that the adaptively estimated localization parameters generally produce smaller errors than the default Gaspari and Cohn (GC) localization. The adaptively estimated localization parameters better capture the onset of RI and yield improved intensity and structure forecasts for typhoon Yutu (2018) compared to the default GC localization. The time-varying localization parameters have slightly advantages over the time-constant localization parameters. Further improvements are achieved by differentiating the localization parameters for TC and non-TC regions.
Soil structural development in a rehabilitated open-cast mine site in south-east Australia
Authors: Haberstok Tiia , Pihlap Evelin , Bucka Franziska , Klör Tabea , Baumgartl Thomas , Kögel-Knabner Ingrid
Published: March 2021

Rehabilitated soils from post mining fields are considered to have poor soil structure, low nutrient content and microbial activity. Soil development during rehabilitation is a complex biogeochemical process influenced by the inherent properties of the substrate used for the rehabilitation. Besides disturbed soil properties, in Australia soil rehabilitation success is also influenced by climatic conditions like high evaporation rate which affects rebuilding of soil system functions. There are several studies looking into the development of soil properties post rehabilitation in temperate climates, however, the intertwined development of soil structure, quality and quantity of soil organic matter (SOM) after the rehabilitation under water stressed environment is not clear until now.

In this study, we used a space-for-time chronosequence approach in the rehabilitated open-cast mine site at Yallourn (Victoria, Australia) to elucidate the development of soil structure and soil organic matter after rehabilitation. We selected five different fields with increasing rehabilitation ages (2, 3, 10, 21 and 39 years) and two mature soils that are used as grazing land. In each field, we sampled 6 independent locations with stainless steel cylinders (100 cm3) at two depths of 0-4 cm and 10-14 cm.  All samples were analysed for bulk density, organic carbon (OC) and total nitrogen (TN) concentration. Selected samples were wet sieved into four aggregate size classes of <63 µm, 63-200 µm, 200-630 µm and >630 µm. Each aggregate size class was characterized by OC and TN concentration. The chemical composition of the SOM of selected samples was characterized using solid-state 13C NMR spectroscopy.

The studied soils have a strong temporal dynamic and variability as determined for the soil properties bulk density and SOM stocks. Aggregate fractionation showed that large macroaggregates (>630 µm) were the most abundant size class fractions in each rehabilitation field, representing 95-75% of the total soil mass. SOM played an important role in the formation of large macroaggregates, where the highest contribution to total OC content was observed. It became evident that plant derived carbon had a decisive role in the structural formation, because O/N-alkyl-C and alkyl-C chemical shift regions represented the highest relative intensities throughout the chronosequence.
Differential absorption lidar for water vapor isotopologues in the 1.98 µm spectral region: sensitivity analysis with respect to regional atmospheric variability
Authors: Hamperl Jonas , Raybaut Myriam , Dherbecourt Jean-Baptiste , Chazette Patrick , Totems Julien , Flamant Cyrille
Published: March 2021

Improved understanding of the variability underlying the distribution of stable water isotopologues in the troposphere, using both observations and modelling, has proven to be invaluable to study processes related to the hydrological cycle on a local as well as global scale. To date though, existing observation means (CRDS from ground-based or airborne platforms, passive remote sensing from space) only provide a partial picture of the complexity of the process at play due to their limited spatial or temporal coverage. On the other hand, laser active remote sensing, and in particular differential absorption lidars (DIAL) can deliver reliable, continuous, highly resolved (150 m, 10 min) profiles of H216O and HD16O in the lower troposphere, thereby providing observational insights into small scale processes such as evapotranspiration above continental surfaces and mixing in the planetary boundary layer.

Such a lidar system is currently in development (WaVIL project funded by ANR) that will operate at 1.98 µm where water isotopologues exhibit close but distinct absorption features, sensitive photodetectors are commercially available, and where pulsed laser emission over 10 mJ can be achieved using for instance parametric conversion.

In order to assess the expected instrument performances and to evaluate the potential of a ground-based system for simultaneous measurement of H216O and HD16O, we performed an error budget based on an end-to-end simulator. Lidar backscatter signals were simulated for different instrument-specific and atmospheric parameters. On the instrument side, calculations were performed for a commercial InGaAs PIN photodiode and for a state of the art low-noise HgCdTe avalanche photodiode. The sensitivity to environmental factors was investigated exemplarily for mid-latitude, arctic, and tropical environments where both vertical water vapor and aerosol variability were accounted for. Vertical profiles of aerosol extinction and backscatter coefficients were derived from the AERONET database (https://aeronet.gsfc.nasa.gov/) and extrapolated to the 2 µm spectral region, taking statistical seasonality into account. Performance simulations have been also conducted using vertical profiles derived from a field campaign where water vapor isotopologue concentrations and aerosol extinction were measured. We will outline the majority biases for such a lidar system and how statistical errors can be mitigated in a view of a forthcoming airborne DIAL instrument.
Spatio-temporal variation of Anaelastic and Scattering Seismic Attenuation during the 2016-2017 Central Italy Seismic Sequence
Authors: Gabrielli Simona , Akinci Aybige , Napolitano Ferdinando , De Siena Luca , Del Pezzo Edoardo , Ventura Guido
Published: March 2021

Between August and October 2016, the Central Apennines in Italy have been struck by a long-lasting seismic sequence, known as the Amatrice (Mw 6.0) - Visso (Mw 5.9) - Norcia (Mw 6.5) sequence. The cascading ruptures occurred in this sequence have been considered connected to the fluid migration in the fault network, as suggested by previous studies. The behaviour of fluids in the crust is crucial to understand earthquakes occurrence and stress changes since fluids reduce fault stability. It has long been understood that the seismic attenuation is strongly controlled by the structural irregularity and heterogeneities; micro-cracks and cavities, either fluid-filled or dry, temperature and pressure variations cause a decrease in seismic wave amplitude and pulse broadening. Hence seismic attenuation imagining is a powerful tool to be a relevant provenance of information about the influence and abundance of fluids in a seismic sequence.

The aim of this work is to separate scattering and absorption contributions to the total attenuation of coda waves and to provide their spatial and temporal variations at different frequency bands of these quantities using two datasets: the first one comprising 592 earthquakes occurred before the sequence (March 2013-August 2016) and the second one comprising 763 events (ML > 2.8) from the Amatrice-Visso-Norcia sequence. Scattering and absorption have been measured through peak-delay and coda-wave attenuation parameters (the latter inverted using frequency-dependent sensitivity kernels).

The preliminary results show a clear difference between the pre-sequence and sequence images, mainly at low frequencies (1.5 Hz), where we can define a spatial increase of scattering with time attributed to rock fracturing and fluid circulation. The coda attenuation tomography also demonstrates a clear variation between the pre-sequence and the sequence over series of time windows being before and after the largest main shocks of the seismic sequence, with an increase of the attenuation in space with decreasing time. The peak delay indicates a high scattering area corresponding to the Gran Sasso massif and L’Aquila zone, where an important seismic sequence (Mw 6.3) occurred in 2009.
The CMEMS In Situ TAC multi-year and multi-variate products to monitor and understand the ocean variability
Authors: Szekely Tanguy , Juza Mélanie , Gourrion Jérôme , Rotllán-García Paz , Pouliquen Sylvie , Tarot Stephane , Tintoré Joaquin
Published: March 2021

The CMEMS In Situ TAC (INSTAC) integrates in situ observations from various platforms, (e.g. profiling floats, gliders, drifters, saildrones, research vessels, ferryboxes, fixed stations, tides gauges, sea mammals, high-frequency radar), providing physical and biogeochemical ocean data at local, regional and global scales, with an increasing data integration from the polar and coastal regions.

 

The INSTAC quality-controlled data in both delayed mode and near-real time are contributing to support the operational oceanography (e.g. model forecasting, analysis and reanalysis, satellite calibration, downstream services) and to monitor the 4-dimensional ocean at various spatial and temporal scales. The INSTAC multi-year products provide an essential information on the ocean state, variability and changes and allow addressing long-term variations (climate) analysis as well as detecting remarkable events. Hence, the INSTAC group has contributed substantially to the elaboration of the annual CMEMS Ocean State Report (OSR, Von Schuckmann et al., 2016, 2018, 2019, 2020, 2021).

 

A general overview of the INSTAC contributions to the CMEMS OSR is presented, highlighting its capacity to describe, analyze and understand the ocean state and variability of both physical and biogeochemical components from the sea surface to the deep ocean, from the coastal to open sea waters, from tropical to polar regions, from semi-enclosed seas to the global ocean, from short-term to long-term temporal scales. The INSTAC team contributes to the CMEMS Ocean Monitoring Indicators reporting, investigates the ocean circulation variability, analyses the impact of climate change on marine ecosystem and ocean circulation, and develops operational applications and services.

 

Maintaining the current observational network, integrating new platforms, enhancing the spatial and temporal resolutions, improving methodologies and developing new metrics (e.g. quality control, data assimilation), developing new products, INSTAC will continue to serve the overall need to understand and predict the ocean state and variability, in line with the present and future scientific, societal and environmental challenges.