bluuebunny/crossref_metadata_2025 huggingface dataset:
Topographic disequilibrium, landscape dynamics and active tectonics: an example from the Bhutan Himalayas
Authors: Simoes Martine , Sassolas-Serrayet Timothée , Cattin Rodolphe , Le Roux-Mallouf Romain , Ferry Matthieu , Drukpa Dowchu
Published: March 2021

The quantification of active tectonics from geomorphological and morphometric approaches most often implies that erosion and tectonics have reached a certain balance. Such equilibrium conditions may however be seldom found in nature, in particular because drainage basins may be quite dynamic even though tectonic and climatic conditions remain constant. Here, we document this drainage dynamics from the particular case example of the Bhutan Himalayas. Evidence for out-of-equilibrium morphologies have for long been noticed in Bhutan, from major (> 1 km high) river knickpoints and from the existence of high-altitude low-relief regions within the mountain hinterland. These peculiar morphologies were generally interpreted as representing a recent change in climatic and/or tectonic conditions. To further characterize these morphologies and their dynamics, and from there discuss their origin and meaning, we perform field observations and a detailed quantitative morphometric analysis using Chi plots and Gilbert metrics of drainages over various spatial scales, from major Himalayan rivers to local streams draining the low-relief regions. We first find that the river network is highly dynamic and unstable. Our results emphasize that the morphology of Bhutan does not result from a general wave of incision propagating upstream, as expected from most previous interpretations. Also, the specific spatial organization in which all major knickpoints and low-relief regions are located along a longitudinal band in the Bhutan hinterland, whatever their spatial scale and the dimensions of the associated drainage basins, calls for a common local supporting mechanism most probably related to active tectonic uplift. Our results emphasize the need for a precise documentation of landscape dynamics and disequilibrium over various spatial scales as a first-order step in morpho-tectonic studies of active landscapes.
Automatic generation from MCM of reduced mechanisms to study the formation and evolution of SOA in 3D air quality models 
Authors: Wang Zhizhao , Couvidat Florian , Sartelet Karine
Published: March 2021

As secondary organic aerosols (SOA) largely contribute to the mass of particles and may strongly affect health, it is essential to represent them as accurately as possible in air quality models (AQM). Their formation and aging involve multi-generation oxidations of numerous volatile organic compounds (VOC) combined with gas-particle partitioning processes.
 
Tracking the non-linear relationship between VOC emissions and aerosol formation demands comprehensive chemical mechanisms, which take into account the whole complexity of the SOA precursor oxidation to simulate aerosols under various conditions.
However, the use of explicit gas-phase chemical mechanism (e.g., MCM, GECKO-A) or molecular structure-limited parameterization (e.g., VBS, SOM, FGOM) could be problematical in large-scale SOA modeling, as the former is overwhelmingly computational expensive while the latter loses tracks of VOC oxidation products after few generations and specific properties relying on aerosol formation.
 
Consequently, we have developed semi-explicit SOA chemical mechanisms designed to model the SOA formation and evolution in 3D AQM. These mechanisms are reduced based on simulations of the near-explicit master chemical mechanism (MCM) performed under various conditions representative of ambient conditions and different lumping strategies. The new mechanisms integrate the crucial SOA species/reactions with different mechanism complexities. The mechanisms, therefore, preserve the complexity of the oxidation chemistry (dependence on NOx of the SOA formation, the influence of radical concentrations, humidity, photolysis, etc..) as well as the molecular composition of the organic aerosol. The mechanisms are implemented in a novel 0D aerosol model SSH-aerosol, which can use the molecular structure of lumped compounds to estimate the influence of non-ideality on SOA formation.

The current application has been conducted on the MCM degradation scheme of beta-caryophyllene (C15H24), the most representative sesquiterpene. A reduction of the average 90% CPU time and up to 92% number of S/IVOCs species has been achieved compared to the original MCM mechanism.
Subseasonal Predictability of the North Atlantic Oscillation
Authors: Newman Matthew , Albers John
Published: March 2021

Skillfully predicting the North Atlantic Oscillation (NAO), and the closely related Northern Annular mode (NAM), on “subseasonal” (weeks to a few months) timescales is a high priority for operational forecasting centers, because of the NAO’s association with high-impact weather events. Unfortunately, the relatively fast, weather-related processes dominating overall NAO variability are unpredictable beyond about two weeks. On longer timescales, the tropical troposphere and the stratosphere provide some predictability, but they contribute relatively little to total NAO variance. Moreover, subseasonal forecasts are only sporadically skillful, suggesting the practical need to identify the fewer potentially predictable events at the time of forecast. Here we construct an observationally-based Linear Inverse Model (LIM) that predicts when, and diagnoses why, subseasonal NAO forecasts will be most skillful. We use the LIM to identify those dynamical modes that, despite capturing only a fraction of overall NAO variability, are largely responsible for extended-range NAO skill. Predictable NAO events stem from the linear superposition of these modes, which represent joint tropical sea-surface temperature-lower stratosphere variability plus a single mode capturing downward propagation from the upper stratosphere. Our method has broad applicability because both the LIM (run operationally at NOAA's Climate Prediction Center) and the state-of-the-art European Centre for Medium-Range Weather Forecasts Integrated Forecast System (IFS) have higher (and comparable) skill for the same set of high skill forecast events, suggesting that the low-dimensional predictable subspace identified by the LIM is relevant to real-world subseasonal NAO predictions.
The Sb-Au-district Brandholz/Goldkronach (Fichtelgebirge, Germany): mineralogical indications for the evolution of hydrothermal Sb-mineralization.
Authors: Fritzke Björn , Seifert Thomas , Linhardt Elmar , Kehrer Christin
Published: March 2021

The Brandholz/Goldkronach district is situated in the southeastern part of Germany in the Bavarian Fichtelgebirge. Previous literature of the mineralogy of the district is rather descriptive and modern geochemical analysis are entirely missing. In this contribution, we combine petrography, bulk rock-geochemical analysis, SEM-MLA as well as EPMA to infer on precipitation mechanism and ore-forming processes. The quartz-polymetallic-sulfide veins are hosted in Ordovician shists, called “Phycodenschiefer”, which were intruded by upper Devonian meta-basalts. Antimony-sulfides are the main ore mineralization inside of the quartz-veins, accompanied by minor auriferous arsenopyrite and pyrite. Petrographic observations suggest a precipitation of an early stibnite phase (stage I). Sb-Pb-sulfides/sulfosalts (stage II) precipitated in fractures and fissures of stage I stibnite with a slightly change to Pb-rich Sb-phases. The antimony-mineralization event evolved from stibnite (Sb2S3), over fülöppite (Pb3Sb8S15), zinkenite (Pb9Sb22S42), plagionite (Pb5Sb8S17) to boulangerite (Pb5Sb4S11). Chemical analyses corroborate the petrographic observations and indicate a change in the hydrothermal environment from a Sb- to Sb-Pb dominated system with a distinct geochemical change from Pb-free to Pb-containing Sb-phases. A characterization of the precipitation sequence can be used to improve the understanding of the hydrothermal evolution of the whole Sb-Au-ore system in Goldkronach.
Numerical study of sheared mobile polydisperse sediment beds with a coupled lattice Boltzmann - discrete element method
Authors: Rettinger Christoph , Eibl Sebastian , Rüde Ulrich , Vowinckel Bernhard
Published: March 2021

With the increasing computational power of today's supercomputers, geometrically fully resolved simulations of particle-laden flows are becoming a viable alternative to laboratory experiments. Such simulations enable detailed investigations of transport phenomena in various multiphysics scenarios, such as the coupled interaction of sediment beds with a shearing fluid flow. There, the majority of available simulations as well as experimental studies focuses on setups of monodisperse particles. In reality, however, polydisperse configurations are much more common and feature unique effects like vertical size segregation.

In this talk, we will present numerical studies of mobile polydisperse sediment beds in a laminar shear flow, with a ratio of maximum to minimum diameter up to 10. The lattice Boltzmann method is applied to represent the fluid dynamics through and above the sediment bed efficiently. We model particle interactions by a discrete element method and explicitly account for lubrication forces. The fluid-particle coupling mechanism is based on the geometrically fully resolved momentum transfer between the fluid and the particulate phase. We will highlight algorithmic aspects and communication schemes essential for massively parallel execution.

Utilizing these capabilities allows us to achieve large-scale simulations with more than 26.000 densely-packed polydisperse particles interacting with the fluid. With this, we are able to reproduce effects like size segregation and to study the rheological behavior of such systems in great detail. We will evaluate and discuss the influence of polydispersity on these processes. These insights will be used to improve and extend existing macroscopic models.
Mind the gap: extending the conceptual model of river island development to different environmental conditions and tree species
Authors: Bertoldi Walter , Gurnell Angela M.
Published: March 2021

We present recent results of field observations on an island braided reach of the middle Tagliamento River, Italy, where riparian vegetation survival and establishment depends on an unstable balance between vegetation growth and flood disturbance. We combined field observations and information extracted from aerial images, airborne lidar data, and river flow time series for the period 1986-2017 to investigate the changing spatial distribution of woody vegetation and the associated changes in river topography. We also explored the role of Alnus incana (a member of the Betulaceae family), in an environment dominated by the Salicaceae family (e.g. Populus nigra).

We observed that gaps between established islands and/or floodplain offer shelter to vegetation, supporting higher colonisation success and different vegetation-landform evolution pathways.

In particular, A. incana predominantly grows in lines along channel, island and floodplain edges, bordering wooded areas dominated by P. nigra. Given their association with floodplain and island edges and the relationship of taller (older) trees with more elevated surfaces, A. incana in the study reach appears to complement the physical engineering of the dominant species, P. nigra. This suggests that P. nigra may facilitate colonisation by alder but then both species trap sediments to aggrade channel edges and bar surfaces and build island and floodplain landforms.

Time sequences of aerial images in combination with the flood disturbance time series allowed us to interpret vegetation dynamics and to identify the fate of sexual and asexual reproduction strategies by observing vegetation expansion from lines of young plants and shrubs and from uprooted deposited trees and pioneer islands, respectively. Field observations are then generalized to extend a conceptual model of island development.

Growing conditions, disturbance energy, and time (window of opportunity) between major floods are the main controls on vegetation colonization. These vary among rivers, among reaches along the same river and locally, as in the investigated gaps, allowing different tree species with different life history traits (e.g. Populus nigra, Alnus incana) to engineer local river landforms in different and complementary ways.

Although the conceptual model is inspired by observations on the Tagliamento River, consideration of species life history traits and the joint influences of growing conditions, disturbance energy and windows of opportunity provide a framework that may be applied to other temperate rivers where trees drive landform development.
Spatial and temporal analysis of high-frequency internal gravity wave signatures in brightness temperature satellite images
Authors: Vicari Robert
Published: March 2021

Highly idealized model studies suggest that convectively generated internal gravity waves in the troposphere with horizontal wavelengths on the order of a few kilometers may affect the lifetime, spacing, and depth of clouds and convection. To answer whether such a convection-wave coupling occurs in the real atmosphere, one needs to find corresponding events in observations. In general, the study of high-frequency internal gravity wave-related phenomena in the troposphere is a challenging task because they are usually small-scale and intermittent. To overcome case-by-case studies, it is desirable to have an automatic method to analyze as much data as possible and provide enough independent and diverse evidence.
Here, we focus on brightness temperature satellite images, in particular so-called satellite water vapor channels. These channels measure the radiation at wavelengths corresponding to the energy emitted by water vapor and provide cloud-independent observations of internal gravity waves, in contrast to visible and other infrared satellite channels where one relies on the wave impacts on clouds. In addition, since these water vapor channels are sensitive to certain vertical layers in the troposphere, combining the images also reveals some vertical structure of the observed waves.
We propose an algorithm based on local Fourier analyses to extract information about high-frequency wave patterns in given brightness temperature images. This method allows automatic detection and analysis of many wave patterns in a given domain at once, resulting in a climatology that provides an initial observational basis for further research. Using data from the instrument ABI on board the satellite GOES-16 during the field campaign EUREC4A, we demonstrate the capabilities and limitations of the method. Furthermore, we present the respective climatology of the detected waves and discuss approaches based on this to address the initial question.
An approach to construct a Netherlands-wide ground-motion amplification model
Authors: van Ginkel Janneke , Ruigrok Elmer , Herber Rien
Published: March 2021

Local site conditions can strongly influence the level of amplification of ground-motion at the surface during an earthquake. Especially near-surface low velocity sediments overlying stiffer seismic bedrock modify earthquake ground motions in terms of amplitudes and frequency content, the so-called site response. Earthquake ground-motion site response is of great concern because it can lead to amplified surface shaking resulting in significant damage on structures despite small magnitude events. The Netherlands has tectonically related seismic activity in the southern region with magnitudes up to 5.8 measured so far. In addition, gas extraction in the Groningen field in the northern part of the Netherlands, is regularly causing shallow (3 km), low magnitude (Mw max= 3.6), induced earthquakes. The shallow geology of the Netherlands consists of a very heterogeneous soft sediment cover, which has a strong effect on seismic wave propagation and in particular on the amplitude of ground shaking.

 

The ambient seismic field and local earthquakes recorded over 69 borehole stations in Groningen are used to define relationships between the subsurface lithological composition, measured shear-wave velocity profiles, horizontal-to-vertical spectral ratios (HVSR) and empirical transfer functions (ETF). For the Groningen region we show that the HVSR matches the ETF well and conclude that the HVSR can be used as a first proxy for earthquake site-response. In addition, based on the ETFs we observe that most of the seismic wave amplification occurs in the top 50 m of the much thicker sediment layer. Here, a velocity contrast is present between the very soft Holocene clays and peat on top of the stiffer Pleistocene sands.

 

Based on the learnings from Groningen we first constructed sediment type classes for the Dutch subsurface, each class representing a level of expected amplification. Secondly, the HVSR curves are estimated for all surface seismometers in the Netherlands seismic network and a sediment class is assigned to each location. Highest HVSR peak amplitudes are measured at sites with the highest level of amplification of the sediment classification. Based on this correlation and the presence of a detailed shallow geological model at most sites in the Netherlands, a simplistic approach is presented to predict amplification at any location with sufficient lithologic information. With this approach based on the shallow sediment composition, we can obtain constraints on the seismic hazard in areas that have limited data availability but have potential risk of seismicity, for example due to geothermal energy extraction.
Gravity data collection with a CG5 gravitymeter for densification of the gravity data around the AUT1 IHRF station
Authors: Natsiopoulos Dimitrios A. , Mamagiannou Elisavet G. , Pitenis Eleftherios A. , Vergos Georgios S. , Tziavos Ilias N. , Grigoriadis Vassilios N.
Published: March 2021

Within the GeoGravGOCE project, funded by the Hellenic Foundation for Research Innovation, a main goal has been the densification of the available land gravity database around the eastern part of the city of Thessaloniki, Greece, where the core International Height Reference Frame (IHRF) station AUT1 is located in order to improve regional geoid and potential determination. Hence it was deemed necessary to densify the available gravity data within radiuses of 10 km, 20 km, 50 km and 100 km from the AUT1 core IHRF site. In that frame, and given the geological complexity of the region surrounding Thessaloniki and the significant variations of the terrain, gravity campaigns were appropriately designed and gravity measurements were carried out in order to densify the database and cover as much as possible traverses of varying altitude. The measurements have been carried out with the CG5 gravity meter of the GravLab group and dual-frequency GNSS receivers in RTK mode for orthometric height determination. In this  study we provide details of the gravity campaigns, the measurement principle and the finally derived gravity and free-air gravity anomalies. The mean measurement accuracy achieved was at the ~20 μGal level for the gravity measurements and ~3 cm for the orthometric heights. In all cases the final derived gravity value was based on the absolute point established by the GravLab team at the AUTH seismological station premises with the A10 (#027) absolute gravity meter.
How high to ultra-high temperature terranes form
Authors: Cenki-Tok Bénédicte , Rey Patrice F. , Arcay Diane
Published: March 2021

Long-lived high- to ultra-high temperature (HT-UHT) terranes formed mostly during the Paleo-Proterozoic and are often associated to supercontinent cycles. Yet the detailed processes and conditions involved in their formation remain largely unresolved. Here we highlight the importance of the specific geothermal conditions necessary to form migmatitic to granulitic crusts. An analytical resolution of the heat equation highlights the interdependency of the thermal parameters controlling the crustal geotherm, i.e. the Moho temperature, when deformation occurs at thermal equilibrium. We further perform thermo-mechanical experiments mimicking an orogenic cycle, from shortening to gravitational collapse, to study the effect of deformation velocity that affects the crustal thermal equilibrium. We show that the formation of HT-UHT terranes is promoted by an elevated radiogenic heat production in the crust. Finally, the interplay between the thermal parameters and the orogenic cycle duration explain the difference in orogenic style through time and why some terranes are preferentially granulitic or migmatitic.
Late evolution of the inner Northern Apennines from the structure of the Monti del Chianti-Monte Cetona Ridge (Tuscany, Italy)
Authors: Brogi Andrea
Published: March 2021

The Neogene and Quaternary tectonic evolution of the inner Northern Apennines (i.e southern Tuscany and northern Tyrrhenian Sea), as well as its crustal features (i.e. low crustal thickness, Neogene-Quaternary magmatism, widespread geothermal anomalies, lateral segmentation of the stacked tectonic units, extensive deep sedimentary basins), are framed in different geodynamic scenarios: compressional, extensional or both, pulsing. Consequently, the basin and range structure that characterises the northern Tyrrhenian Sea and southern Tuscany is considered as a consequence of (i) out-of-sequence thrusts and related thrust-top-basins, (ii) polyphased normal faulting that formed horst and graben structures or (iii) a combination of both. This paper provides a new dataset from a sector of the eastern inner Northern Apennines (i.e. Monti del Chianti - Monte Cetona ridge) contributing to this scientific debate. New fieldwork and structural analysis carried out in selected areas along the ridge allowed to define the chronology of the main tectonic events on the basis of their influence on the marine and continental sedimentation. The dataset supports for early Miocene - (?) Serravallian in-sequence and out-of-sequence thrusting. Thrusting produced complex staking patterns of Tuscan and Ligurian Units. Extensional detachments developed since later middle Miocene and controlled the Neogene sedimentation in bowl-shaped structural depressions, later dissected by normal faults enhancing the accommodation space for Pliocene marine deposits in broad NNW-trending basins (Siena-Radicofani and Valdichiana Basins). In this perspective, no data supports for active, continuous or pulsing, compressional tectonics after late Serravalian. As a result, in the whole inland inner Northern Apennines the extensional tectonics was continuously active at least since middle Miocene and controlled the basins development, magmatism and structure of the crust and lithosphere.
Uncertainty and sensitivity analysis for natural risk and adaptation appraisal modeling with CLIMADA
Authors: Kropf Chahan M. , Ciullo Alessio , Meiler Simona , Otth Laura , McCaughey Jamie W. , Bresch David N.
Published: March 2021

Modelling societal, ecological, and economic costs of natural hazards in the context of climate change is subject to both strong aleatoric and ethical uncertainty. Dealing with these is challenging on several levels – from the identification and the quantification of the sources of uncertainty to their proper inclusion in the modelling, and the communication of these in a tangible way to both experts and non-experts. One particularly useful approach is global uncertainty and sensitivity analysis, which can help to quantify the confidence in the output values and identify the main drivers of the uncertainty while considering potential correlations in the model. Here we present applications of global uncertainty analysis, robustness quantification, and sensitivity analysis in natural hazard modelling using the new uncertainty module of the CLIMADA (CLIMate ADAptation) platform.

CLIMADA is a fully open-source Python program that implements a probabilistic multi-hazard global natural catastrophe damage model, which also calculates averted damage (benefit) thanks to adaptation measures of any kind (from grey to green infrastructure, behavioral, etc.). With the new uncertainty module, one can directly and comprehensively inspect the uncertainty and sensitivity to input variables of various output metrics, such as the spatial distribution of risk exceedance probabilities, or the benefit-cost ratios of different adaptation measures. This global approach does reveal interesting parameter interplays and might provide valuable input for decision-makers. For instance, a study of the geospatial distribution of sensitivity indices for tropical cyclones damage indicated that the main driver of uncertainty in dense regions (e.g. cities) is the impact function (vulnerability), whereas in sparse regions it is the exposure (asset) layer. 

CLIMADA: https://github.com/CLIMADA-project/climada_python 

(1) Aznar-Siguan, G. et al., GEOSCI MODEL DEV. 12, 7 (2019) 3085–97
(2) Bresch, D. N. and Aznar-Siguan., G.,  GEOSCI MODEL DEV. (2020), 1–20.
The influence of biochar on nutrient leaching and hydraulic conductivity in two California soils
Authors: Gelardi Danielle L. , Rippner Devin R. , Ainuddin Irfan , McElrone Andrew J. , Abou Najm Majdi , Parikh Sanjai J.
Published: March 2021

The unique chemical and physical properties of biochars typically include low bulk density, high porosity, high surface area, reactive surface functional groups, and variable particle size distribution. These attributes make biochar a promising material for amendment to agricultural soils, as biochar may help improve soil water holding capacity, hydraulic conductivity (Ksat), and nutrient retention through chemical or physical means. Despite increased interest and investigation, there remains uncertainty regarding the ability of biochar to alter soils to deliver these agronomic benefits, due to differences in biochar feedstock, production method, production temperature and soil texture. In this project, a suite of experiments was carried out using biochars of diverse feedstocks and production temperature, in order to determine the biochar parameters which may optimize agricultural benefits. Sorption experiments [SJP1] were performed with seven distinct, commercially available biochars to determine sorption efficiencies for ammonium and nitrate. Only one biochar effectively retained nitrate, while all biochars bound ammonium. The three biochars with the highest nitrate and/or ammonium binding capacity (produced from almond shell at 500 and 800 °C (AS500 and AS800) and softwood at 500 °C (SW500)), were chosen for a series of column experiments. These biochars were amended to a sandy loam and a silt loam at 0 and 2% (w/w) and saturated hydraulic conductivity (Ksat) was measured. The biochars reduced Ksat in both soils by 64-80%, with the exception of AS800, which increased Ksat by 98% in the silt loam. Breakthrough curves for nitrate and ammonium, as well as concentrations of nutrients in the leachate, were also measured in the sandy loam columns.  Biochars significantly reduced the quantity of ammonium in the leachate, and significantly slowed its movement through the soil profile. Biochars had little to no effect on the timing and quantity of nitrate release. In this presentation, we present results from each experiment, and show images from our current work using x-ray micro-computed tomography on these soils and biochars to quantify porosity, pore size, and pore connectivity. Together, this work sheds new light on the chemical and physical means by which biochar alters soils to impact nutrient leaching and hydraulic conductivity.
Transient effects of a pre-existing lattice preferred orientation on the strength of foliated quartzite
Authors: Holyoke Caleb , Braccia Casey
Published: March 2021

Much of our understanding of the strength of the continental crust is based on flow laws derived from homogeneous mono-mineralic aggregates (quartzites).  However, crystal plastic deformation of rocks in the middle to lower continental crust during orogenic events forms foliations, lineations and lattice preferred orientations (LPOs) which produce physical and viscous anisotropies in rocks.  In some of these orogenic events, such as in the Appalachian mountains, multiple deformation events form different, cross-cutting foliations and overprint existing LPOs.  In order to determine the effects foliation/lineation and preexisting LPO have on the strength of rocks in the middle crust, we deformed a natural quartzite with a cross-girdle LPO from the Moine Thrust in Scotland with the compressive stress at six different primary orientations relative to the foliation and lineation. This quartzite has aligned but distributed fine-grained muscovite which defines a foliation and lineation.  The cores were deformed at the same temperature (800°C), pressure (1500 MPa) and strain rate (1.6*10-6/s) to similar strains (50-58%), leaving the foliation/lineation orientation as the only difference between experiments.  Peak stresses occur at strains of 10-20% and are lowest for the sample with foliation at 45o to the compression direction (400 MPa, the weak orientation).  All other cores (hard orientations) have peak strengths of 600 to 1100 MPa and highest for the cores with lineation perpendicular to the compression direction (1100 MPa). These cores in hard orientations all strain weaken to a similar stress (~500 MPa), but are still ~100 MPa stronger than the core with both foliation and lineation initially oriented at 45 degrees to the compression direction.  Optical microstructures include undulatory extinction, deformation lamellae, and at high strain (58%), the quartzite is more than 50% recrystallized. Scanning electron microscope electron backscatter diffraction analyses indicate that recrystallized grains in all cores reflect the deformation conditions of the experiment and original grains retain their initial LPO.  Strength anisotropy at low strains is due to placing the foliation and lineation at non-ideal (hard) orientations relative to the compression direction and is greatest in cores with the lineation perpendicular to the compression direction.  The evolution to a similar strength at high strains indicates that dynamic recrystallization creates new grains oriented for easy slip in the second (experimental) deformation event. These results suggest that differences in lineation and foliation orientations and a pre-existing LPO may cause strength anisotropy in rocks in the mid to lower continental crust, but this anisotropy may be transient and unlikely to exist to high strains.
Assessment of Community Internet Intensity (CII) in Sakhalin Island
Authors: Konovalov Alexey , Stepnova Yuliya , Stepnov Andrey
Published: March 2021

Sakhalin Island is a region with high rate of seismic activity. Tens of felt earthquakes occur within the studied area every year. Rapid macroseismic observation through the web questionaries, social networks etc. gives reliable information about ground shaking intensities and today is processed by major seismological agencies (Bossu et al., 2018; Quitoriano and Wald, 2020).

The recent development of the methodology began with the web-based macroseismic observations following Dengler and Deweey (1998) and Wald et al. (1999). Widespread global use of Community Internet Intensity (CII) was routinely applied by the U.S. Geological Survey (USGS) through the USGS DYFI questionaries. Over 5 millions felt reports were collected during last 15 years (Quitoriano and Wald, 2020).

During last 5 years the methodology was tested in Sakhalin Island (Konovalov et al., 2018). For the collection of felt reports we used regional internet resource (https://eqalert.ru/#/). The DYFI USGS questionnaires translated into Russian were used for processing the macroseismic information. The felt reports of the respondents from each settlement were transformed to the Community Weighted Sum (CWS) which takes into account various indicators of ground shaking: human sensations, position of objects, visible damages of the building. The CII was calculated using the equation (Wald et al., 1999):

CII = 3.4 ln (CWS) – 4.38.

The obtained values were rounded to the first number after the comma. In general CII should be similar to the MM intensity.

During the period from 2016 to 2020 we have got about 400 felt reports. Most of the responses came in the first minutes after the origin time of seismic event. Data with only one report or incorrectly submitted questionnaires were excluded in further calculations. The small number of the felt reports may be explained by low population density of the central and northern districts of Sakhalin Island. Finally we have found correlation between the CII and PGA (cm/s/s) which is given by the equation:

CII = 2.5 log (PGA) + 2.32.

It is suggested that given approach can be used as a robust tool for express analysis of ground shaking. It is also a good way to involve the population and bring them closer to understanding the scientific process in the era of the growth of computer technology and social networks.
An improved approach for testing gravitational redshift via spacecraft based three frequency links combination
Authors: Shen Ziyu , Shen Wen-Bin , He Lin , Zhang Tengxu , Cai Zhan
Published: March 2021

We propose a new approach for testing the gravitational redshift based on frequency signals transmission between a spacecraft and a ground station. By a combination of one uplink signal and two downlink signals, the gravitational redshift can be tested at about 6.5×10-6 level for a GNSS satellite (the signals’ frequencies are about 1.2~1.6 GHz), and about 2.2×10-6 level for the International Space Station (the signals’ frequencies are up to 14.7 GHz), under the assumption that the clock accuracy is about 10-17 level. For better desinged cases the accuracy of gravitational redshift test can be improved to several parts in 10-8 level (the signals’ frequencies are about 8~12 GHz). Compared to the scheme of Gravity Probe-A (GP-A) experiment conducted in1976, the new approach does not require any onboard signal transponders, and the frequency values of the three links can be quite arbitrarily given. As the hardware requirement is reduced, a number of spacecrafts could be chosen as candidates for a gravitational redshift experiment. This approach could also be used in gravitational potential determination, which has prospective applications in geodesy. This study is supported by National Natural Science Foundation of China (NSFC) (grant Nos. 42030105, 41721003, 41631072, 41874023, 41804012), Space Station Project (2020)228, and Natural Science Foundation of Hubei Province(grant No. 2019CFB611).
Estimating dissolved oxygen of Lake Huron at multiple spatiotemporal scales using remote sensing and machine learning
Authors: Guo Hongwei , Huang Jinhui , Zhu Xiaotong , Wang Bo , Tian Shang
Published: March 2021

Dissolved oxygen (DO) effectively indicates the health and self-purification capacity of waterbodies. However, since DO is a non-optically active parameter and has little impact on the spectrum captured by satellite sensors, research on estimating DO by remote sensing at multiple spatiotemporal scales are limited. In this study, the support vector regression models were developed and validated using the remote sensing reflectance derived from both Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) data and synchronous DO measurements, water temperature and sampling coordinates of Lake Huron (N = 206) and three other inland waterbodies (N = 282) covering different latitudes. Using the developed models, spatial distributions of the annual and monthly DO since 1984 and the annual monthly DO since 2000 in Lake Huron were reconstructed for the first time. The impacts of five climate factors on DO were analyzed. Results showed that the developed models had good robustness and generalization (average R2 = 0.91, root mean square percentage error = 2.65%, mean absolute percentage error = 4.21%), and performed better than random forest and multiple linear regression. The monthly DO estimation by Landsat and MODIS data were highly consistent (average R2 = 0.88). Note that the model performance was limited for samples beyond the range of the training set. From 1984 to 2019, the oxygen loss of Lake Huron was 6.56%. The DO of Lake Huron showed obvious seasonal regularity of decreasing from spring to summer and increasing from summer to autumn. Since 2000, DO of Lake Huron has shown a decreasing trend in the same month of different years. Air temperature, incident shortwave radiation flux density and precipitation were the main climate factors affecting annual DO of Lake Huron. This study demonstrated that Landsat and MODIS data could be used for long-term DO retrieval at multiple spatial and temporal scales. As data-driven models, adding variables related to the target parameter and extending the training set to cover more water quality conditions could effectively improve model performance.
Metamorphism and geochronology of garnet amphibolite from the Beishan Orogen, southern Central Asian Orogenic Belt: Constraints from P-T path and zircon U-Pb dating
Authors: Kang Wenbin , Li Wei
Published: March 2021

Numerous lenses of garnet amphibolite occur in the garnet-bearing biotite-plagioclase gneiss belt in the Baishan area of the Beishan Orogen, which connects the Tianshan Orogen to the west and the Mongolia-Xing’anling Orogen to the east. According to the microstructures, mineral relationships, and geothermobarometry, four stages of mineral assemblages have been identified as follows: (1) a pre-peak stage, which is recorded by the cores of garnet together with core-inclusions of plagioclase (Pl1); (2) a peak stage, which is recorded by the mantles of garnet together with mantle-inclusions of plagioclase (Pl2) + amphibole (Amp1) + Ilmenite (Ilm1) + biotite (Bt1), developed at temperature-pressure (P-T) conditions of 818.9–836.5 °C and 7.3–9.2 kbar; (3) a retrograde stage, which is recorded by garnet rims + plagioclase (Pl3) + amphibole (Amp2) + orthopyroxene (Opx1) + biotite (Bt2) + Ilmenite (Ilm2), developed at P-T conditions of 796.1–836.9 °C and 5.6–7.5 kbar; (4) a symplectitic stage, which is recorded by plagioclase (Pl4) + orthopyroxene (Opx2) + amphibole (Amp3) + biotite (Bt3) symplectites, developed at P-T conditions of 732 ± 59.6 °C and 6.1 ± 0.6 kbar. Moreover, the U-Pb dating of the Beishan garnet amphibolite indicates an age of 301.9 ± 4.7 Ma for the protolith and 281.4 ± 8.5 Ma for the peak metamorphic age. Therefore, the mineral assemblage, P-T conditions, and zircon U-Pb ages of the Beishan garnet amphibolite define a near-isothermal decompression of a clockwise P-T-t (Pressure-Temperature-time) path, indicating the presence of over thickened continental crust in the Huaniushan arc until the Early Permian, then the southern Beishan area underwent a continental crust tectonic thinning process.
Alpine drought impact chains for sector-based climate-risk assessments
Authors: Terzi Stefano , Erfurt Mathilde , Stephan Ruth , Stahl Kerstin , Zebisch Marc
Published: March 2021

Droughts are slow and silent natural hazards that can lead to long-lasting environmental, societal and economic impacts. Mountain regions are also experiencing drought conditions with climate change affecting their environments more rapidly than other places and reducing water availability well beyond their geographical locations. These conditions call for better understanding of drought events in mountains with innovative methodologies able to capture their complex interplays.

Within this context, the Alpine Drought Observatory (ADO) Interreg Project aims to further improve the understanding of drought conditions in the Alpine Space, with activities spanning from the characterization of drought types’ components in five heterogeneous case studies in Austria, France, Italy, Slovenia and Switzerland. For each case study, different sectors exposed to drought, ranging from hydropower, agriculture to tourism are considered. Moreover, specific socio-economic characteristics were collected for each sector in order to better understand the main drivers leading to drought impacts.

Starting from the risk concept in the IPCC AR5, the Impact Chains (IC) methodology has been applied to characterize the hazard, exposure and vulnerability components in the ADO case studies. IC allowed to pinpoint the main factors affecting drought risk and the relevant socio-economic sectors integrating a mixed-method approach. Quantitative data collection on the hazard and exposure components were coupled with local experts’ knowledge on the main vulnerability factors (e.g., through a questionnaire). Although validation represents a critical part of drought modelling, IC analysis and results were therefor compared with information from the European Drought Impact Inventory (EDII) on local drought impacts collected from scientific publications, unions press releases and newspaper articles over a long time period.

While drought risk assessment through IC can improve the understanding of the main drought events and their underlying factors, they also provide insights to improve planning and management of future drought events in the Alpine Space.
A global perspective on the sub-seasonal clustering of precipitation extremes
Authors: Tuel Alexandre , Romppainen-Martius Olivia
Published: March 2021

The occurrence of several precipitation extremes at short time intervals can have major impacts on human societies, leading for instance to persistent flood conditions. Although the sub-seasonal clustering of precipitation extremes has already attracted attention, most studies have focused on catchment or regional scales. Therefore, little is known about its spatial and seasonal distribution. Here, we apply simple statistical metrics based on Ripley’s K function, at a global scale and for each season separately, to identify regions where precipitation extremes to cluster in time over timescales of a few days to a few weeks. We analyze several observational and reanalysis datasets, and compare them to Global Climate Models (GCMs) from the CMIP6 archive. While sub-seasonal temporal clustering is largely concentrated to the tropical oceans, it is also significant seasonally outside the tropics in several regions, like eastern subtropical oceans, southwest Asia or Eastern Africa. We also find that CMIP6 models generally correctly reproduce clustering patterns, paving the way for an assessment of trends in sub-seasonal clustering under climate change.
Linkage of Arctic Sea Ice and Energy Transport
Authors: Höschel Ines , Handorf Dörthe , Jacobi Christoph , Quaas Johannes
Published: March 2021

The loss of Arctic sea ice as a consequence of global warming is changing the forcing of the atmospheric large-scale circulation.  Areas not covered with sea ice anymore may act as an additional heat source.  Associated changes in Rossby wave propagation can initiate tropospheric and stratospheric pathways of Arctic - Mid-latitude linkages.  These pathways have the potential to impact on the large-scale energy transport into the Arctic.  On the other hand, studies show that the large-scale circulation contributes to Arctic warming by poleward transport of moist static energy. This presentation shows results from research within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3” funded by the Deutsche Forschungsgemeinschaft.  Using the ERA interim and ERA5 reanalyses the meridional moist static energy transport during high ice and low ice periods is compared.  The investigation discriminates between contributions from planetary and synoptic scale.  Special emphasis is put on the seasonality of the modulations of the large-scale energy transport.
Spatial stochastic simulation to aid local extreme value analysis of cyclone-induced wave heights when numerical hydrodynamic simulations are scarce
Authors: Rohmer Jeremy , Pedreros Rodrigo , Krien Yann
Published: March 2021

To estimate return levels of wave heights (Hs) induced by tropical cyclones at the coast, a commonly-used approach is to (1) randomly generate a large number of synthetic cyclone events (typically >1,000); (2) numerically simulate the corresponding Hs over the whole domain of interest; (3) extract the Hs values at the desired location at the coast and (4) perform the local extreme value analysis (EVA) to derive the corresponding return level. Step 2 is however very constraining because it often involves a numerical hydrodynamic simulator that can be prohibitive to run: this might limit the number of results to perform the local EVA (typically to several hundreds). In this communication, we propose a spatial stochastic simulation procedure to increase the database size of numerical results with synthetic maps of Hs that are stochastically generated. To do so, we propose to rely on a data-driven dimensionality-reduction method, either unsupervised (Principal Component Analysis) or supervised (Partial Least Squares Regression), that is trained with a limited number of pre-existing numerically simulated Hs maps. The procedure is applied to the Guadeloupe island and results are compared to the commonly-used approach applied to a large database of Hs values computed for nearly 2,000 synthetic cyclones (representative of 3,200 years – Krien et al., NHESS, 2015). When using only a hundred of cyclones, we show that the estimates of the 100-year return levels can be achieved with a mean absolute percentage error (derived from a bootstrap-based procedure) ranging between 5 and 15% around the coasts while keeping the width of the 95% confidence interval of the same order of magnitude than the one using the full database. Without synthetic Hs maps augmentation, the error and confidence interval width are both increased by nearly 100%. A careful attention is paid to the tuning of the approach by testing the sensitivity to the spatial domain size, the information loss due to data compression, and the number of cyclones. This study has been carried within the Carib-Coast INTERREG project (https://www.interreg-caraibes.fr/carib-coast).