bluuebunny/crossref_metadata_2025 huggingface dataset:
Semi-brittle transient creep in Carrara marble: Hardening and Twinning-induced Plasticity
Authors: Rybacki Erik , Niu Lu , Evans Brian
Published: March 2020

Abundant observations of field- and micro-structures in marble rocks in both natural and laboratory settings indicate that these rocks have deformed by various combinations of mechanical twinning, dislocation motion, and dilatant fracturing. To better constrain the systematics of this semi-brittle flow, we performed a set of about 80 experiments at eight different temperatures (20°C<T<800°C). At each T, deformation conditions included different confining pressures (50 < PC <300 MPa) and strain rates (10-6 < ε’ <10-4 s-1). Under almost all these conditions, both the strength (σ) and the hardening coefficient (Θ=∂σ/∂ε) are affected by changes in PC and ε’, but the functional relationships of σ(PC, ε’) and Θ(PC, ε’) are unique. For example, at 20°C, σ is a non-linear function of both PC and ε’, while Θ depends on PC alone. In contrast, at 600°C, the dependence of σ on PC is very weak, and Θ depends on ε’ alone.

At T<650°C (less than half the absolute melting point of calcite), and PC greater than 50 MPa, the hardening coefficients are substantial (1% or more of the shear modulus), similar to steels and hexagonal metals that deform in a regime called twinning induced plasticity (TWIP). During TWIP, deformation proceeds with “easy” mechanical twinning, combined with dislocation glide on several slip systems whose glide planes are at high angles to the twin plane. In the calcite rocks, depending on conditions, the hardening resulting from twinning may be reduced by dilation and failure owing to brittle processes (at low pressures and temperatures), or by recovery and recrystallization (at higher temperatures or slower strain rates). Thus, both microstructural observations and mechanical deformation data are consistent with the interpretation that the hardening coefficient and strength are determined by the relative partitioning of inelastic strain amongst mechanical twinning, dislocation mechanisms, and dilatant fracturing. One important aspect is the nature of the mechanism that accommodates of discontinuous inelastic strain at the termination of twins at grain boundaries.
Azimuthally anisotropic ambient-noise tomography using the AlpArray seismic network
Authors: Kästle Emanuel , Molinari Irene , Boschi Lapo , Working Group AlpArray
Published: March 2020

We make use of the AlpArray Seismic Network to study the properties of the ambient-noise field and create a new 3D shear-velocity model of the Alpine crust. The latter will be used to improve our understanding of the tectonic processes that formed the Alps.

From two years of data, more than 150,000 station-station cross-correlations are extracted and used to evaluate strength and directivity of the noise field and its seasonal variations. Phase-velocity measurements for both Love and Rayleigh waves are obtained and the anisotropic phase-velocity structure is imaged. At mid-crustal levels, the strongest azimuthal anisotropy is found underneath the northern Italian Po plain and in the northern Dinarides, with strengths of 10-20% and a fast axis direction pointing NNE in Italy and NE in the Dinarides. In the western and central Alps we find an approximately NE direction and a strength of 5%; the eastern Alpine fast axis point toward the north with strengths of 2-5%.

We apply a probabilistic inversion to resolve the 3D shear-velocity structure of the crust. The homogeneous and dense station setup results in a shear-velocity model of unprecedented resolution for the uppermost 60 km of the crust underneath the entire orogen. By using data in the period range between 2 and 100s, we are able to better constrain shallow structures, such as the sedimentary basins, and to link surface-geological features to velocity variations observed at depth.
A Model interface for ERA5
Authors: Pelupessy Inti , Chertova Maria , van den Oord Gijs , van Werkhoven Ben
Published: March 2020

The ERA5 dataset provides a comprehensive view on recent climate data by assimilating vast amounts of historical observations into the ECMWF integrated forecast system, and as such establishing a reference point in the field of weather and climate modelling. The successor of ERA-interim is ubiquitous in the earth sciences, with applications such as boundary conditions for regional simulations, atmospheric forcings to ocean or land surface models, initial conditions to climate prediction experiments, etc.. The conventional workflow for such applications is to download the data, extract the necessary variables, optionally regrid or resample and save it in a model specific format. This procedure is time consuming, difficult to document properly and generates a lot of intermediate data of low reuse value. Here, we provide an alternative to this by wrapping access to the ERA5 dataset in a standardized OMUSE model interface. OMUSE is a Python framework for Earth System modelling, developed to simplify the use of simulation codes and enable new model couplings. Within OMUSE the ERA5 dataset is transparently accessed using the CDSAPI and the resulting interface is very much like an OMUSE interface for a simulation code. Data is pulled from the online climate data store only when needed and cached for later reuse. This approach simplifies the access and coupling of the ERA5 dataset with OMUSE model components and makes it trivially easy to repeat a model run with a different dataset or even replace it with a life model.
Mass-based mixing state of black carbon measured by a tandem CPMA-SP2 system in wintertime in the North China Plain
Authors: Zhu Shaowen , Ma Nan , Pan Xihao , Dong Wenlin , Tao Jiangchuan , Hong Juan , Zhang Yuxuan , Li Guo , Ditas Jeannine , Su Hang , Cheng Yafang
Published: March 2020

Black carbon (BC) is the most important light absorbing component in the atmosphere and has significant impacts on the climate, environment and public health. Its effects depend not only on its spatial-temporal distribution, but also on its physico-chemical characteristics. Mixing state is one of the most important properties of BC and strongly determines its hygroscopicity and radiative properties. During an intensive field campaign conducted in the North China Plain in winter 2018, mass-based mixing state of BC-containing particles were online measured with a Centrifugal Particle Mass Analyzer and Single Particle Soot Photometer (CPMA-SP2) tandem system. This technique directly provides the mass ratio of non-refractory coating matter to BC core (MR) in individual particles and does not require to assume the density, morphology and refractive index of BC core and coating in data retrieval, therefore has lower uncertainly compared with leading-edge fit technique. In our measurement, the mean number fraction of uncoated (MR=0), thin coated (0<MR<3) and thick coated (MR≥3) BC-containing particle during the campaign were respectively ~10%, ~35% and ~55%, indicating the strong aging process of BC-containing particle in the North China Plain. The median value of MR was much higher in polluted days than clean days, for example, the median value of MR with a particle mass of 8.56 fg (~220 nm in diameter) for polluted and clean days were ~3.2 and ~1.6, respectively. The mixing state of BC-containing particles obtained by different methods were also compared and evaluated.
Operation Plan of Geostationary Environmental Monitoring Spectrometer (GEMS)
Authors: Jeong Jaehoon , Kim Goo , Moon Kyung-Jung , Nam Minseok , Kim Deokrae , Lee Dongwon
Published: March 2020

The Geostationary Environmental Monitoring Spectrometer (GEMS), which is the world's first geostationary environmental satellite, is scheduled to be launched in February of this year. Observing more than 8 times a day (up to 10 times), GEMS is expected to play an important role for regional and periodic monitoring of air quality and pollution in East Asia. In this study, we report the status of GEMS operation readiness and the overall operation plan after launch. The design and development of a ground station system for GEMS operation and utilisation are now completed. The GEMS ground system will generate level 1B (L1B) data through radiometric and geometric correction after receiving the signal and produce a level 2 (L2) product by using L1B as input data. In the case of L2 data, it will produce 20 kinds of output, including ozone, aerosol, volatile organic compounds (VOCs) such as formaldehyde and glyoxal, gas products such as nitrogen dioxide and sulphur dioxide, surface information, and more. All algorithms for L2 product generation have been developed and verified. Currently, we are continuing to work toward stabilisation and speed improvement and plan to produce L2 products within one hour of observation. All processing must be completed within one hour before the next observation begins, specifically 30 minutes for L1B generation and the remaining 30 minutes for L2 generation. GEMS L2 processing is scheduled day and night. In the daytime, the goal is to produce L2 products within one hour for real-time distribution. In the night operation, on the other hand, the goal is to produce L2 products with a main purpose of improving the quality of L2 products through the use of additional information. GEMS will have an in-orbit test (IOT) period of approximately eight months following launch for radiometric and geometric calibration. During this period, many efforts will be made to ensure the quality of GEMS data, including comparative verification with reference data obtained from various observation methods and cross-calibration and -validation with the organisations that have made an agreement in advance. Suggestions from institutions interested in mutual collaboration for GEMS calibration are still welcome (note that proposals for mutual collaboration remain open). We also plan to verify the effectiveness of the night-time operation during the IOT period. The products will be distributed in stages after IOT according to the internally established distribution regulations. In this study, the overall operation of GEMS and the data distribution plan are presented. Although the schedule may change slightly depending on various situations after launch, this information is expected to be useful for many institutions and researchers in related fields who are very interested in GEMS data.
A novel application of Unmanned Aerial Systems (UASs) in alpine environment for monitoring gravity-driven natural hazards: BLUESLEMON project
Authors: Bojeri Alex , Giannotta Giovanni , Kofler Christian , Mai Erika , Mayrguendter Sebastian , Scarton Gabriele , Seppi Stefano , Steger Stefan , Quagliotti Fulvia
Published: March 2020

The Project “BLUESLEMON – BT Beacon and Unmanned Aerial System technologies for Landslide Monitoring” is funded by provincial funds of South Tirol Italian Autonomous Province and it is developed with the support of Beacon Südtirol-Alto Adige project (funded by the south tyrolean European Regional Development Fund – www.beacon.bz.it) under the supervision of the NOI Techpark Südtirol/Alto Adige as support for consultancy, networking and R&D project backing for the use of UAS in alpine environments.

The project “BLUESLEMON” aims to develop a low-cost automatic system for monitoring landslide surface displacement through the integration of Bluetooth (BT) Beacons localization and UAS also named Remotely Piloted Aircraft System (RPAS) technologies. Two subsystems will assemble the final setup: the ground sensors technology and the periodic localization system composed by UAV and beacon reader. These are designed as an inseparable integrated architecture and each individual subsystem cannot operate on the supposed landslide areas without the cooperation of the other one. Thus, a main challenge consists in the identification of low-power-consumption and high-precision Bluetooth devices, as well as in the development of a UAV platform capable to work even at a limit of feasibility considered for an Alpine scenario (e.g. -20 °C at 2500 m asl). To prevent undesirable collisions with surrounding structures (e.g. trees, powerlines and funicular railways), the UAV platform will be equipped with obstacle-detection sensors and collision-avoidance algorithms.

The proposed architecture aims to exceed the state-of-the-art methodologies by obtaining a single low-cost system adaptable for the inspection of movements related to different types of gravity-driven natural hazards (e.g. slow-moving earth flows, discontinuities in rock walls). In addition, the expected autonomy of the system will allow to avoid the risky operations in-situ. Nowadays, the current methodologies (with or without UAS) are characterized by a high level of criticality in extreme environments such as the alpine surroundings. The solutions of the project’s requirements are of great interest for future reconfigurations of the developed system, in order to extend its use for search and rescue operations in dangerous conditions. Therefore, the suggested method will represent a strong novelty in the reference sector and lead to further application developments with considerable added value elements.
Comparison of the surface mass and energy balance of CESM and MAR forced by CESM over Greenland: present and future
Authors: Lang Charlotte , Amory Charles , Delhasse Alison , Hofer Stefan , Kittel Christoph , van Kampenhout Leo , Lipscomb William , Fettweis Xavier
Published: March 2020

We have compared the surface mass (SMB) and energy balance of the Earth System model (ESM) CESM (Community Earth System Model) with those of the regional climate model (RCM) MAR (Modèle Atmosphérique Régional) forced by CESM over the present era (1981 — 2010) and the future (2011 — 2100 with SSP585 scenario).

Until now, global climate models (GCM) and ESMs forcing RCMs such as MAR didn’t include a module able to simulate snow and energy balance at the surface of a snow pack like the SISVAT module of MAR and were therefore not able to simulate the SMB of an ice sheet. Evaluating the added value of an RCM compared to a GCM could only be done by comparing atmospheric outputs (temperature, wind, precipitation …) in both models. CESM is the first ESM including a land model capable of simulating the surface of an ice sheet and thus to directly compare the SMB of an RCM and an ESM the first time.

Our results show that, if the SMB and is components are very similar in CESM and MAR over the present era, they quickly start to diverge in our future projection, the SMB of MAR decreasing more than that of CESM. This difference in SMB evolution is almost exclusively explained by a much larger increase of the melter runoff in MAR compared to CESM whereas the temporal evolution of snowfall, rainfall and sublimation is comparable in both runs.
Humidity calibration of relative humidity devices in Martian conditions
Authors: Hieta Maria , Genzer Maria , Polkko Jouni , Jaakonaho Iina , Lorek Andreas , Garland Stephen , de Vera Jean-Pierre , Martinez German , Fischer Erik
Published: March 2020

Finnish Meteorological Institute (FMI) has developed relative humidity measurement devices for past and future Mars lander missions: REMS-H for Curiosity, MEDA HS for Mars 2020 and METEO-H for ExoMars 2020. The sensors used in these devices are HUMICAP® capacitive thin-film polymer sensors by Vaisala Inc. New calibration measurements are performed with ground reference models of these devices in the Mars Simulation Facility (MSF) and Planetary Analog Simulation Laboratory (PASLAB) at the German Aerospace Center (DLR) in spring 2020. The preliminary results will be given at the EGU 2020.

Calibration of relative humidity devices requires in minimum two humidity points over the expected operational temperature and pressure range of the device. With two-point calibration the relative humidity devices can be used for scientific measurements with satisfactory quality but the uncertainty is notable. Stable humidity conditions between dry and saturation humidity in Martian conditions can be achieved reliably in very few laboratories in the whole world and humidity measurements in Martian conditions have been previously performed for the same devices in FMI laboratory and in Michigan Mars Environmental Chamber (MMEC) at the University of Michigan.

The new measurement campaign will consist of stable humidity point measurements in multiple temperatures between +10°C to -70°C in CO2 gas and Martian pressure of approximately 7 hPa. The measurements are performed simultaneously for multiple devices in a small pressure vessel with continuous humidified carbon dioxide flow.

The new measurement campaign will improve the characterization of the existing relative humidity devices in Mars lander missions and define in more detail the measurement uncertainties.
High resolution soil moisture estimation and evaluation from Earth observation
Authors: Peng Jian , Quaife Tristan , Pinnington Ewan , Evans Jonathan , Harris Phil , Robinson Emma , Blyth Eleanor , Dadson Simon
Published: March 2020

Soil moisture is an important component of the Earth system and plays an important role in land-atmosphere interactions. Remote sensing of soil moisture is of great scientific interest and the scientific community has made significant progress in soil moisture estimation using Earth observations. Currently, several operational coarse spatial resolution soil moisture datasets have been produced and widely used for various applications such as climate, hydrology, ecosystem and agriculture. Due to the strong demand for high spatial resolution soil moisture in regional applications, much effort has been recently devoted to the generation of high spatial resolution soil moisture from either Sentinel-1 observations or downscaling of existing coarse resolution soil moisture datasets. The aim of this study is to evaluate high spatial resolution soil moisture products derived from multisource satellite observations. First, the COSMOS-UK measured soil moisture was used to validate existing satellite-based soil moisture datasets including SMAP_9km, SMOS_1km, Sentinel-1, and Sentinel-1/SMAP combined products. Second, an approach based on triple collocation was applied to inter compare these satellite products in the absence of a reference dataset. Third, two merging schemes including a simple average and a triple collocation method were used to develop a combined satellite soil moisture product based on existing satellite soil moisture datasets. From the above analysis, it is found that merging all the above soil moisture data provides a better estimate of soil moisture than any of them alone. Therefore, we conclude that combining existing satellite-based soil moisture products has the potential to provide the best estimate of high spatial resolution soil moisture in the UK.
Mapping Forest Degradation with ALOS PALSAR: Case studies from Mexico and Ghana
Authors: Wheeler Charlotte , Mitchard Edward , Nolasco Rayes Hugo , Mohammed Yakubu
Published: March 2020

Forest degradation is one of the least understood processes in the terrestrial biome. Information about both the extent and rate of degradation is limited; meaning that estimation of subsequent carbon emissions are poorly quantified. Countries are required to report emissions from forest degradation to the UNFCCC, therefore, increased efforts to improve mapping and monitoring of forest degradation are essential for national reporting. As forest degradation is related to more subtle changes within a forest, resulting from loss of trees, then earth observation technologies, which can quantify changes in Aboveground Biomass (AGB) offer great opportunities in mapping forest degradation.

 

We test a methodology for monitoring forest degradation, which combines time-series forest plot data with L-band Synthetic Aperture Radar (SAR) data (ALOS/ ALOS-2) to map changes in AGB over time. We test this method in two countries (Mexico and Ghana), to determine if a single methodology can be used to map forest degradation across the tropics. Our study-sites span two tropical continents, covering a range of precipitation, AGB values, forest types, and modes of degradation, from seasonally dry pine forests in Mexico to humid lowland forests in Ghana,

 

In lower biomass forest, we could map changes in AGB over time, including small AGB losses, associated with minor degradation events (<20% loss of AGB). These minor degradation events are far more widespread than major degradation events (>50% loss of AGB) and therefore are an important source of emissions from degradation. However, in high biomass forest there was some saturation of the radar backscatter signal (>200 Mg ha-1).

 

The use of ground-based AGB change data is essential for calibration of SAR data, therefore well managed national forest plot networks, which include degraded forest, are essential for accurate monitoring of degradation. Additionally, using longer wavelength P-Band SAR data, alongside L-Band SAR, could help overcome some issues related to saturation in high biomass forest. If this method were adopted at the regional or national level, it would allow countries, particularly those with lower biomass forest, to quantify emissions from degradation more accurately.
The challenge of estimating high return levels with short records under large internal variability
Authors: Zeder Joel , Fischer Erich M.
Published: March 2020

The scientific understanding of changes in climate extremes is mostly limited to moderate definitions of extreme events occurring every few years, due to a lack of long-term observational daily data sets. In order to estimate return levels beyond observed time periods and event magnitudes, extreme events are typically modelled statistically based on extreme value theory. This is challenging since the short observational record may be affected by low-frequency natural internal variability and limits the block size that can be used.

Here we test some common assumptions in the statistical modelling of extremes based on indices of climatic extremes (Tx7d, Rx1d, Rx5d) using long pre-industrial control runs and initial-condition large ensembles with thousands of years of model data.

The tail of a distribution fitted to temperature and precipitation maxima is known to be highly sensitive to the compliance with statistical assumptions and choices such as the block size. Typically, 1-year block maxima are extracted from observational time series due to short record length. It is unclear whether these maxima are already in the domain of true extremes suitable for an extreme value analysis. Furthermore, the observational record is too short to sample low-frequency regional variability and potential transient changes in the mean climate. Standard uncertainty estimates (confidence intervals and hypothesis tests) are generally not accounting for potential biases introduced by a dominant mode of climate variability or violated modelling assumptions.

Based on a 4700-year pre-industrial control simulation and an 84-member ensemble performed with CESM 1.2.2 model, we systematically extend the statistical modelling of temperature and precipitation extremes to larger block-sizes and longer synthetic observational periods. This analysis reveals a considerable influence of climate variability on tail estimates. Furthermore, the use of too small block sizes can induce substantial random as well as systematic biases. Statistical model complexity and thus uncertainty further increases for extremes retrieved from transient large-ensemble members, as non-stationarity has to be accounted for in the model formulation. Thus, the potential of spatial pooling or conditioning on further climatic variables as proxies for a specific climatic mode to derive more robust tail estimates is also evaluated. Findings based on the CESM ensemble are compared with pre-industrial control runs performed with other models in CMIP6 and other initial-condition large ensembles of the CLIVAR large ensemble working group.
Significant changes in the magma dynamics of Stromboli steady-state volcano recorded by clinopyroxene crystals.
Authors: Petrone Chiara Maria , Di Stefano Flavio , Gertisser Ralf , Mollo Silvio , Tommasini Simone , Del Bello Elisabetta , Andronico Daniele , Scarlato Piergiorgio , Giacomoni Pierpaolo , Coltorti Massimo
Published: March 2020

Steady-state volcanic activity implies equilibrium between the rate of magma replenishment and eruption of compositionally homogeneous magmas, lasting for tens to thousands of years in an open conduit system. The Present-day activity of Stromboli volcano (Aeolian Islands, Southern Italy) has long been recognised as typical of a steady-state volcano, with a shallow magmatic reservoir (highly porphyritic or hp-magma) continuously refilled by more mafic magma (with low phenocryst content or lp-magma) at a constant rate and accompanied by mixing, crystallisation and eruption. The lp-magma is erupted only during more violent explosive events (paroxysms), which usually occur at intervals of a few years. However, the two most recent paroxysms occurred at very short timescales on 3 July and 28 August 2019 offering the unique opportunity of obtaining crucial information on the current magma dynamics of Stromboli.

Albeit the plumbing system shows such uniformity, clinopyroxene phenocrysts exhibit marked chemical heterogeneities and complex textures caused by continuous lp-hp magma mixing as well as antecryst recycling from different mush portions. The compositional zoning in clinopyroxene provides essential information on pre-eruptive magma dynamics, indicating multi-stage crystallization across the lp-hp-reservoirs, where diopsidic compositions are markers of more primitive, high-T magmas injecting into shallow, low-T domains of the plumbing system. By comparing clinopyroxene texture, chemistry and residence times from the Present-day eruptions with the previous Post-Pizzo activity, we conclude that a distinct phase in the life of Stromboli volcano commenced after the violent 2003 paroxysm. Our observations suggest there are more efficient mechanisms of mush disruption and cannibalization, in which old diopsidic antecrysts are continuously remobilized and transported by the lp-magmas permeating the mush. The disappearance of diopsidic recharge bands within augitic overgrowths indicates that over time, magmatic injections feeding the persistent Present-day activity are more intensively mixed and homogenized prior to eruption.
A geodetic exploration of the behavior of aseismic slip along the central section of the North Anatolian fault
Authors: Jara Jorge , Ozdemir Alpay , Benoit Angelique , Jolivet Romain , Çakir Ziyadin , Ergintav Semih , Dogan Ugur
Published: March 2020

Many geodetic evidence suggest aseismic slip along active faults is more common than previously thought. Furthermore, aseismic slip during the interseismic period seems to be made of intermittent slow slip events, corresponding to episodes of loading and releasing of tectonic stress over time. However, although our capabilities of detection and location of aseismic deformation have significantly increased together with the growth in available geodetic data, the physical mechanisms governing slow slip remain unknown.

We explore the spatial and temporal behavior of aseismic deformation in the vicinity of the small town of Ismetpasa, located along the central section of the North Anatolian Fault (Turkey). We combine InSAR and GNSS data acquired over the last 10 years to locate and quantify aseismic slip in the subsurface. We process SAR images (ALOS and Sentinel-1) acquired from 2007 to 2018 to build time series of ground deformation and maps of ground velocity. We confirm the presence of a 100 km-long creeping section, at rates of 10-20 mm/yr. Along this section, slip is not constant and decreases over time as formerly observed over the last 60 years. Furthermore, via a detailed analysis of our geodetic time series, we detect 3 major episodes of aseismic slip between 2015 and 2018, with durations ranging from 6 months to 1 year and magnitudes between 4.6 - 5.2. These results are compared with time series obtained from a network of GNSS permanent stations we have installed in the region (17 stations, period 2016 - 2019). As a conclusion, aseismic slip along this section of the North Anatolian Fault is characterized by slow slip events rather than by a constant, steady-state aseismic slip rate. We discuss the potential implications in terms of mechanics of slow slip along the NAF.
Ground movements associated with thermal water production from the Buda Thermal Karst (Hungary) by PS-InSAR
Authors: Békési Eszter , Grenérczy Gyula , Frey Sándor , Farkas Péter , van Wees Jan-Diederik , Fokker Peter
Published: March 2020

Interferometric Synthetic Aperture Radar has been used worldwide for investigating ground deformation due to subsurface extraction processes. However, in the Central and Eastern European region, no such studies are available so far. We present a case study for the Buda Thermal Karst demonstrating the effectiveness of satellite-based monitoring of the region. Budapest (and the whole territory of Hungary) is well-known from balneology for centuries. Thermal bathes in Budapest mainly utilize water discharging from carbonate reservoirs. Hot springs in the area are commonly located along fault zones controlling the groundwater flow systems. We investigate ground deformation in the vicinity of the Buda Thermal Karst by Persistent Scatterer time series analysis based on Sentinel-1 data for the period of 2014-2018. Results show that surface movements associated with the extraction of thermal water and groundwater recharge and discharge exist. Inverse geodetic modeling based on various deformation sources embedded in an elastic half-space is applied to infer for reservoir processes and properties and fault structures controlling fluid pathways. The modeling results are jointly interpreted with geological and hydrogeological models of the area. The satellite-based monitoring together with the modeling results allow a better understanding of the characteristics of fluid flow systems in the area and the dynamics of geothermal reservoirs under production. Such information can be of high importance for the sustainable production of thermal water in the future.
On the loading conditions for pore fluid stabilization of failure in crustal rock
Authors: Aben Franciscus , Brantut Nicolas
Published: March 2020

During shear failure in rock, fracture damage created within the failure zone causes localized dilation, which, under partially drained conditions, results in a localized pore fluid pressure drop. The effective normal stress within the failure zone therefore increases, and with it the fracture and frictional strengths. This effect is known as dilatancy hardening. Dilatancy hardening may suppress rupture propagation and slip rates sufficiently to stabilize the rupture and postpone or prevent dynamic failure. Here, we study the loading conditions at which the rate of dilatancy hardening is sufficiently high to stabilize failure. We do so by measuring the local pore fluid pressure during failure and the rate of dilatancy with slip at a range of confining and pore fluid pressures.

We performed shear failure experiments on thermally treated intact Westerly granite under triaxial loading conditions. The samples were saturated with water and contained notches to force the location of the shear failure zone. For each experiment, we imposed a different combination of confining pressure and pore fluid pressure, so that the overall effective pressure was either 40 MPa or 80 MPa prior to axial deformation at 10-6 s-1 strain rate. Dynamic shear failure was recognized by a sudden audible stress drop, whereas the stress drop during stabilized shear failure took longer and was inaudible. Local pore fluid pressure was measured with in-house developed pressure transducers placed on the trajectory of the prospective failure.

At effective pressures of 40 MPa and 80 MPa, we observe stabilized failure for a ratio λ (imposed pore fluid pressure over confining pressure) > 0.5. For λ < 0.5, we observe dynamic failure. Of two experiments performed at λ = 0.5 and 80 MPa effective pressure, one showed stabilized failure and one failed dynamically. For λ > 0.5, we observe pore fluid pressure drops in the failure zone of 30-45 MPa for 40 MPa effective pressure, and 60 MPa for 80 MPa confining pressure. The local pore fluid pressure during dynamic failure (λ < 0.5) is 0 MPa, strongly suggesting local fluid vaporization. Of the two experiments at λ = 0.5, the dilation rate with slip is higher for the dynamic failure relative to the stabilized failure.

We show that with increasing effective pressure, dilatancy hardening increases as the local pore fluid pressure drop during failure becomes larger. For λ < 0.5, dilatancy hardening is insufficient to stabilize failure because the local pore fluid pressure drop is larger than the absolute imposed pore fluid pressure. Near λ = 0.5, small variations in dilatancy control rupture stability. For λ > 0.5, dilatancy hardening is sufficient to suppress dynamic failure.
Using CryoSat-2 estimates to analyse sub-grid scale sea ice thickness distribution in HadGEM3 simulations for CMIP6
Authors: Schroeder David , Feltham Danny , Tsamados Michel
Published: March 2020

A sub-grid scale sea ice thickness distribution (ITD) is a key parameterization to enable a large-scale sea ice model to simulate winter ice growth and sea ice ridging processes realistically. Recent sophisticated developments, e.g. a melt pond model, a form drag parameterization, a floe-size distribution model, fundamentally depend on the ITD. In spite of its importance, knowledge is poor about the accuracy of the simulated ITD. Here, we derive the ITD from individual Arctic sea ice thickness estimates available from the CryoSat-2 (CS2) radar altimetry mission during ice growth seasons since 2010. We bin the CS2 data into 5 ice thickness categories used by the sea ice component CICE of HadGEM3 climate simulations: (1) ice thickness h < 60 cm, (2) 60 cm < h < 1.4 m, (3) 1.4 m < h < 2.4 m, (4) 2.4 m < h < 3.6 m, (5) h > 3.6 m. Our analysis includes historical simulations and future projections with the HadGEM3-GC31 model as well as forced ocean-ice and standalone ice simulations with the same model components NEMO v3.6 and CICE v5.1.2. The most striking difference occurs regarding the annual cycle of area fraction of ice in the thickest category (> 3.6 m). According to CS2, in the Central Arctic the fraction is below 2% in October and increases to 15-40% in April. In contrast the annual cycle is weak in all simulations. The magnitude of the area fraction differs between the simulations. For simulations which agree best with CS2 for grid cell mean ice thickness, the area fraction of thick ice is around 5% constantly throughout the whole year. Potential reasons for the discrepancy are discussed and sensitivity experiments presented to study the impact of sea ice settings on the simulated ITD, e.g. ice strength parameter, parameter for participating in ridging, heat transfer coefficients.
Characterizing denitrification in the aquifer and transit times based on spatially-distributed measurements in streams
Authors: Vautier Camille , Petton Christophe , Abhervé Ronan , Pinay Gilles , Lavermann Anniet , de Dreuzy Jean-Raynald
Published: March 2020

Human activity has more than doubled reactive nitrogen delivery to Earth’s ecosystems. In the past several decades, efforts have been made to reduce agricultural inputs of nitrogen, but the decrease of the nitrate concentration in rivers is also controlled by natural processes, especially by flow and denitrification in the aquifer. Yet, with current knowledge, it remains difficult to characterize transit times and groundwater denitrification rates at scales relevant for mitigation actions (catchment scale to regional scale).

Data directly obtained in piezometers generally display large variabilities without any obvious correlation to any landscape, geological or geomorphological characteristics. Here we propose an alternative method based on in-stream measurements to get a representative view of the role of the aquifer in the temporary storage and degradation of nitrates. We performed spatially-distributed measurements in low-order streams within a 35 km2 agricultural catchment underlain by a crystalline, fractured bedrock aquifer. Measurements were performed during low-flow. Stream discharge and radon activity were used to determine the groundwater discharge into the streams. Silica was used as an age-tracer [1]. Nitrate concentrations and isotopic ratios allowed to characterize the denitrification in the aquifer.

Results show that in-stream measurements provide a representative view of transport and denitrification in the aquifer. They highlight that the scale of homogenization is larger than the studied catchment, and reveal an unexpected correlation between the mean residence time and the characteristic denitrification time. This allows to hypothesize a common control on residence time and denitrification in the aquifer, that could be exercised by the depth of the weathered zone. Unraveling such a correlation could be a first step towards a global characterization of aquifer processes through geophysical imagery methods.

 

[1] Marcais, J., et al. 2018. Dating groundwater with dissolved silica and CFC concentrations in crystalline aquifers. STOTEN.
CODE IGS reference products including Galileo
Authors: Prange Lars , Villiger Arturo , Schaer Stefan , Dach Rolf , Sidorov Dmitry , Jäggi Adrian , Beutler Gerhard
Published: March 2020

The International GNSS service (IGS) has been providing precise reference products for the Global Navigation Satellite Systems (GNSS) GPS and (starting later) GLONASS since more than 25 years. These orbit, clock correction, coordinate reference frame, troposphere, ionosphere, and bias products are freely distributed and widely used by scientific, administrative, and commercial users from all over the world. The IGS facilities needed for data collection, product generation, product combination, as well as data and product dissemination, are well established. The Center for Orbit Determination in Europe (CODE) is one of the Analysis Centers (AC) contributing to the IGS from the beginning. It generates IGS products using the Bernese GNSS Software.

 

In the last decade new GNSS (European Galileo and Chinese BeiDou) and regional complementary systems to GPS (Japanese QZSS and Indian IRNSS/NAVIC) were deployed. The existing GNSS are constantly modernized, offering - among others - more stable satellite clocks and new signals. The exploitation of the new data and their integration into the existing IGS infrastructure was the goal of the Multi-GNSS EXtension (MGEX) when it was initiated in 2012. CODE has been participating in the MGEX with its own orbit and clock solution from the beginning. Since 2014 CODE’s MGEX (COM) contribution considers five GNSS, namely GPS, GLONASS, Galileo, BeiDou2 (BDS2), and QZSS. We provide an overview of the latest developments of the COM solution with respect to processing strategy, orbit modelling, attitude modelling, antenna calibrations, handling of code and phase biases, and ambiguity resolution. The impact of these changes on the COM products will be discussed.

 

Recent assessment showed that especially the Galileo analysis within the MGEX has reached a state of maturity, which is almost comparable to GPS and GLONASS. Based on this finding the IGS decided to consider Galileo in its third reprocessing campaign, which will contribute to the next ITRF. Recognizing the demands expressed by the GNSS community, CODE decided in 2019 to go a step further and consider Galileo also in its IGS RAPID and ULTRA-RAPID reference products. We summarize our experiences from the first months of triple-system (ULTRA)-RAPID analysis including GPS, GLONASS, and Galileo. Finally we provide an outlook of CODE’s IGS analysis with the focus on the new GNSS.
Cultural heritage monument complex monitoring data analyses using machine learning algorithms
Authors: Kvavadze David , Basilaia Giorgi , Munchava Tea , Laluashvili Giorgi , Elashvili Mikheil
Published: March 2020

Cultural heritage monuments, that were created by mankind for centuries are scattered throughout the world. Most of them are experiencing impacts coming from nature and humans each year that result in damage and changing their common state. Many of the monuments are facing critical conditions and require diagnostics, study and planning and management of conservation/rehabilitation works. Due to the impact of environmental factors such as temperature, humidity, precipitation, the existence of complex structure of cracks, infiltrated water and runoff water streams, together with active tectonics in the region, Uplistsikhe and Vardzia rock-cut city monuments located in Georgia face problems and permanent destruction.

We have developed continuous monitoring systems that are installed in Vardzia and Uplistsikhe.

These systems are generating large amounts of data and it is almost impossible to analyze this data using conventional methods. In parallel with technological development, it is now possible to analyze big data using machine learning. We decided to use machine learning to address our problem. This approach gave us some interesting results. We were able to detect correlations between different sensors, see anomalies in data that gave us some clues about hazard zones. Additionally  models and predictions about the monument's condition were made.

Our work shows that machine learning could be used to estimate conditions make predictions about monuments state.

This work was supported by Shota Rustaveli National Science Foundation of Georgia (SRNS) [Grant Number fr17_90]
Maximum river runoff regime in The North Caucasus under the influence of recent climate change
Authors: Durmanov Ivan , Rets Ekaterina , Kireeva Maria
Published: March 2020

Difficult climatic conditions characterized The North Caucasus and high flood hazard in this region. Over the past decades, significant climate changes have occurred, which has influenced the flow of mountain rivers, including the maximum flow. Since the end of the last century, there has been an increase in the number of dangerous floods in the basins of North Caucasus rivers, which led to significant material damage and deaths. In the flood zone were several tens of thousands of houses. In addition, infrastructure facilities were destroyed and hydraulic structures damaged. In this regard, there is an urgent task of analyzing the spatio-temporal changes in the characteristics of the maximum runoff and the factors that determine them.

In the course of the study, methods of statistical analysis, geoinformation methods, graphoanalytic, and the method of geographical generalization were used. Calculation of statistical parameters and visualization were carried out using the programming languages R and FORTRAN.

The spatial variability of the maximum runoff of the rivers of the North Caucasus over the past 70-80 years was analyzed. The results indicate a predominantly negative trend of maximum water discharge in the highlands of the North Caucasus and a positive in the middle reaches of the Kuban. This is consistent with data on the absence of a positive trend in average annual temperatures in the highlands due to lower temperatures in the winter, as well as with an increase in the number of days with heavy rainfall. The latter factor determined the almost universal increase in interannual variability of maximum expenditures, which indicates an increase in flood hazard throughout the region.

An analysis of the characteristics of the flood flow showed that the dependence of floods on precipitation in the mountains manifests itself at extreme values, while for all the main factor is air temperature. The maximum discharge of rain floods tends to increase in foothill areas, while no changes have been detected in the mountains.

The results can give a clearer view of the processes of changing the maximum flow, and become the basis for the development of measures to minimize the damage from such natural disasters.

This work was financial supported by RFBR (Project 20-35-70024)
Assessing and valuing ecosystem services for managing hydropower constructed rivers systems
Authors: Marttila Hannu , Ashraf Faisal , Haghighi Ali Torabi , Hellsten Seppo , Kopsakangas-Savolainen Maria , Ruokamo Enni , Huuki Hannu , Karhinen Santtu , Romakkaniemi Atso , Pongraczs Eva , Juutinen Artti
Published: March 2020

Rivers developed for hydropower production are important electricity generators with an increasing role as a balancing power source in new wind-power dominated energy systems. However, hydropower constructed rivers also provide many ecosystem services, such as habitats for migratory fish species and opportunities for recreational activities. Currently, we see drastic changes in needs from society to use regulated river corridors for multiple purposes, and therefore, new approaches are needed to support the sustainable management of river resources. In our new EcoRiver-project we develop an integrated assessment framework and examine cost and benefits provided by hydropower constructed rivers. We use hydrodynamic modelling to quantify the ecosystem services and variability during short-term regulation practices (hydropeaking). Hydropower and energy markets modelling is used to examine the impacts of increasing demand flexibility on hydropower. Environmental valuation methods are applied to evaluate the ecosystem services monetarily. Finally, we integrate these methods for cost-benefit analysis in order to support well-informed decision making for river management.
Validation of year-round Stepped Frequency Microwave Radiometer (SFMR) measurement of sea surface wind speed around the Korean Peninsula during 2018-2019
Authors: Kim Ji-Hyoung , Lee Chulkyu , Yang Hyojin , Jung Suengpil , Ko Heejong , Yun Jonghwan , Hong Seongeun , Kim Seungbum , Joo Sangwon
Published: March 2020

Korea Meteorological Administration/National Institute of Meteorological Sciences (KMA/NIMS) has adopted KMA/NIMS Atmospheric Research Aircraft (NARA) since the beginning of 2018. NARA has performed year-round airborne measurement of Sea surface Wind Speed (SWS) using Stepped Frequency Microwave Radiometer (SFMR) during 2018-2019. Total 84 flights of SFMR SWS measurements during this period were analyzed by comparing to concurrent measurements of KMA marine buoy. SFMR SWS around the Korean peninsula during the same period was 6.34±4.95 m s-1. SFMR SWS was appeared to be 12.3% larger than those of KMA marine buoy and mean Bias Difference (BD) was 0.69 m s-1. However, SFMR SWS and KMA marine buoy were correlated well to each other (R2~0.80). The BD was decreased with increasing SWS, this agreed well with results of previous studies (Klotz et al., 2014), however, SFMR SWS measurement showed still reliable even in low SWS environment (< 15 m s-1). For more accurate measurement of SFMR SWS, parameters such as the flight altitude (swath area) and pre-input values (sea surface temperature, salinity) should also be considered. Also, this result can be a comparison reference for those of satellite-borne sensors, as well.