bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of a hydraulic fracture with parallel pre-existing fractures
Authors: Wang Haijun , Yu Shuyang , Ren Xuhua , Tang Lei , Dyskin Arcady , Pasternak Elena
Published: March 2020

Formation and growth of hydraulic fractures can be strongly affected by pre-existing fractures in the rock mass. Until now the main attention was directed towards the investigation of the interaction between the hydraulic fracture and the pre-existing fractures intersecting its path, as they could significantly hamper its formation and growth, alter the geometry and produce additional leak-off. Less attention was paid to the interaction of the hydraulic fracture with parallel and coplanar pre-existing fractures, yet their interaction and coalescence can lead to unwelcome increase in the hydraulic fracture dimensions, change the direction of growth and in some cases result in undesirable effects such as environmental damage.  

 

In order to investigate the hydraulic fracture interaction with parallel pre-existing fractures we conducted a series of tests on transparent rectangular samples with two artificial cracks. One of the crack was loaded with pressurised fluid. The types of interaction were classified and the conditions of fracture coalescence formulated. The results will contribute to the understanding of hydraulic fracture propagation in fractured rock masses and mitigating environmental damage.

 

Acknowledgements. Wang acknowledge support from the Natural Scinece Foundation of Jiangsu (BK20171130). The AVD and EP acknowledge support from the Australian Research Council through project DP190103260. AVD acknowledges the support from the School of Civil and Transportation, Faculty of Engineering, Beijing University of Civil Engineering and Architecture. Wang acknowledge support from the National Natural Science Fund (51409170,U1765204)
Impacts of logging on soil organic carbon and heterotrophic respiration in tropical forests in Borneo
Authors: Vetter Sylvia H. , Teh Yit Arn , Martin Michael , Elias Dafydd M. O. , Riutta Terhi , Smith Pete
Published: March 2020

Selective logging is the practice of extracting selected commercial trees from natural production forests. The intensity of logging correlates with a reduction in biodiversity, wood production and biomass stocks. Less is known about the relationship of logging to soil organic carbon (SOC) and how it changes or recovers over time. Empirical measurements in Borneo provided SOC, soil respiration, aboveground and belowground net primary productivity (NPP) from intact old-growth forest (OGF) as well as from moderately to heavily logged (LOG) forest sites. Soil carbon (C) content and heterotrophic respiration (Rh) was higher in LOG sites than in OGF sites. Moderately logged forest (logged > 10 years ago) contained more SOC than heavily logged forest (logged approx. 7 years ago). NPP was used to estimate the C input to the soil. All these data were used to test the biochemical model ECOSSE (Estimating Carbon in Organic Soils – Sequestration and Emissions) to calculate SOC for the study sites. The model performed well in simulating the soil respiration of OGF and generated acceptable results for LOG sites in the validation process. The results for logged forests showed an increase in Rh over the first 15 years, with some sites showing either a further increase over the next 15 years or stabilizing at a higher level compared to pre-disturbance conditions for other sites. However, for all modelled cases, a break was observed after 30 years, when Rh decreased to a lower level (but not as low as for OGF) before reaching a new equilibrium. At the same time, SOC begins to increase. Spatial modelling showed the results for Borneo under logged conditions and the potential of storing C if logging was reduced. Only 22% of Borneo is under old-growth forest; the results show moderate to high C losses if this region is subjected to logging. Overall, the results show the disturbance of SOC and Rh through logging over periods longer than 30 years.
Simulation of long-term changes in soil organic carbon and nitrous oxide emissions from permanent grass silage using the DNDC model
Authors: Khalil Mohammad I. , Osborne Bruce A.
Published: March 2020

Quantification and reporting of soil organic carbon density (SOCρ) changes and greenhouse gases (GHGs), particularly nitrous oxide (N2O), emissions from agricultural soils using higher tiers remain a key challenge. Modelling approaches can provide largescale land use and management coverage whilst minimizing spatial and temporal variability. Identification of an advanced tool to simulate the net balance of SOC and GHG for mitigation, offsetting and policy formulation is a global concern. We tested the widely used latest version of Denitrification-Decomposition (DNDC95) model, a process-based one, to simulate both SOCρ and N2O emissions and their annual changes over 45 years. The moist temperate grass silage was managed with inorganic fertilizer as urea and organic ones as cattle and pig slurry applied at low, medium and high rates. The model performed well for urea, cattle slurry and pig slurry to predict both SOCρ and N2O emissions. The measured data for SOCρ at a 0-15 cm depth for unfertilized and urea-fertilized fields (73-77 t C ha-1) were significantly higher than the simulated ones (54-55). However, the model-estimates showed good agreement with the measured values (R2 = 0.66) and revealed increased C sequestration with increasing added-C (0.46±0.06 vs. 0.37±0.01 t C ha-1 yr-1). The model simulated N2O emissions well and the resulted emission factors (EFs) estimated on average to be 0.35 ± 0.02, 1.80 ± 0.28 and 1.53 ± 0.41%, respectively, which are close to national and IPCC estimates. Variations in the simulated-SOCρ and derived-EFs could be explained mainly by differences in nitrogen inputs (49%) and added-C (62%), respectively, where the impact of rainfall (15-16%) and temperature (10-11%) was identical. Generally, SOCρ and N2O EFs were sensitive to soil texture, pH, bulk density and organic carbon (R2 = 0.77-0.99) but annual changes in SOCρ decreased with the latter two (R2 = -0.99). Application of animal slurry during autumn demonstrated more C being sequestered in the clay loam soil (Dystric Gleysol) and strategic replacement of slurry either after the second or third silage cuts by urea decreased N2O EFs significantly. Results  imply that the updated DNDC95 could provide an accurate representation of the key drivers influencing both SOCρ and N2O fluxes in temperate grass silage.
Slow build-up of turbid currents triggered by a moderate earthquake in the Sea of Marmara
Authors: Henry Pierre , Özeren M Sinan , Yakupoğlu Nurettin , Çakir Ziyadin , de Saint-Léger Emmanuel , Desprez de Gésincourt Olivier , Tengberg Anders , Chevalier Cristèle , Papoutsellis Christos , Postacıoğlu Nazmi , Dogan Uğur , Çağatay M Namik
Published: March 2020

Earthquake-induced submarine slope destabilization is known to cause debris flows and turbidity currents. These also interact with currents caused by tsunami and seiches resulting in deposits with specific sedimentological characteristics, turbidite-homogenites being a common example. Data on the deep-sea hydrodynamic events following earthquakes are, however, limited. An instrumented frame deployed at the seafloor in the Sea of Marmara Central Basin recorded some of the consequences of a magnitude 5.8 earthquake that occurred Sept 26, 2019 at 10-12 km depth without causing any significant tsunami. The instrumentation comprises a Digiquartz® pressure sensor recording at 5 s interval and a 1.9-2 MHz Doppler recording current meter set 1.5 m above the seafloor and recording at 1-hour interval. The device was deployed at 1184 m depth on the floor of the basin near the outlet of a canyon, 5 km from the epicenter. Chirp sediment sounder profiles indicate a depositional fan or lobe is present at this location. The passing of the seismic wave was recorded by the pressure sensor, but little other perturbation is recorded until 25 minutes later when the instrument, probably hit by a mud flow, tilts by 65° in about 15 seconds. Over the following 10 hours the tilted instrument records bursts of current of variable directions. The last burst appears to be the strongest with velocities in the 20-50 cm/s range, causing enough erosion to free the device from the mud and allowing the buoyancy attached to the upper part of the frame to straighten it back to its normal operation position. Then, the current, flowing down along the canyon axis, progressively decays to background level (≈2 cm/s) in 8 hours. Doppler signal backscatter strength is a proxy for turbidity, sensitive to sand-size suspended particles. Signal strength increased to high values during the event (max -7.6 dB from a background value of -40dB) and decayed over the next three days. These observations show that even a moderate earthquake can trigger a complex response involving mud flows and turbidity currents. We infer simultaneous slope failures at various locations may produce complex current patterns and cause build-up of kinetic energy over several hours.
Biogeomorphology from Space: Using optical satellite imagery time series for analyzing the dynamic interaction of vegetation and hydromorphology along the Naryn River, Kyrgyzstan
Authors: Betz Florian , Lauermann Magdalena , Egger Gregory , Cyffka Bernd
Published: March 2020

Under natural conditions, the structure and development of river corridors is controlled by an interplay of hydrological, geomorphological and ecological processes. Over the past decade, the concept of biogeomorphology has become increasingly popular to describe and analyze the manifold feedback mechanisms within river systems leading to an increasing number of studies. However, the majority of this work focuses either on conceptual development or on investigations on the scales of single geomorphic units or study reaches. Only very few studies enlarge the spatial scale to entire river corridors or networks despite the fact that recent frameworks emphasize these scales to be relevant for river research and management. A recent trend in remote sensing of terrestrial ecosystem is the use of dense imagery time series to assess trends and disturbances of vegetation development. In this study, we transfer this idea to the analysis of biogeomorphological interactions within fluvial environments on large spatial scales. We take the Naryn River in Kyrgyzstan as an example for demonstrating our satellite time series approach to biogeomorphological analysis of river corridors. The Naryn is still in a natural state on an entire flow length of more than 600 km with full longitudinal and lateral connectivity. Along the central part of the catchment, the Naryn is a highly dynamic braided river system shaped by the annual summer floods of a glacial discharge regime. This makes this river ideal to study large scale biogeomorphological dynamics. In our study, we follow the well-established concept of biogeomorphological succession suggested by Dov Corenblit and his colleagues. We mapped the different succession phases in the field and used the results to derive spectral-temporal indices of the succession phases. These indices are on the one hand used for a supervised classification based on Sentinel-2 imagery. On the other hand, we use Sentinel-2 as well as the longer term Landsat imagery time series to analyze the data for statistical trends and changepoints and evaluate this regarding biogeomorphological succession and disturbance events. The results reveal that dense time series of optical satellite imagery are well suited data sources to derive indicators of biogeomorphological interactions on large spatial scales. Especially when using the recently available Sentinel-2 imagery, such indicators have the potential to analyze biogeomorphological dynamics of entire river corridors or networks in a spatially and temporally continuous way at a reasonable spatial resolution.
New BioGeoChemical products provided by the Copernicus Marine Service
Authors: Racapé Virginie , Lien Vidar , Jan Even Øie Nilsen , Vindenes Havard , Perivoliotis Leonidas , Kaitala Seppo
Published: March 2020

The Copernicus Marine service is a “one-stop-shop” providing freely available operational data on the state of the marine environment for use by marine managers, advisors, and scientists, as well as intermediate and end users in marine businesses and operations. The Copernicus Marine service offers operationally updated and state-of-the-art products that are well documented and transparent. The European Commission’s long-term commitment to the Copernicus program offers long-term visibility and stability of the Copernicus Marine products. Furthermore, Copernicus Marine offers a dedicated service desk, in addition to training sessions and workshops.

Here, we present the in situ biogeochemical data products distributed by the Copernicus Marine System since 2018. It offers available data of chlorophyll-a, oxygen, and nutrients collected across the globe. These products integrate observation aggregated from the Regional EuroGOOS consortium (Arctic-ROOS, BOOS, NOOS, IBI-ROOS, MONGOOS) and Black Sea GOOS as well as from SeaDataNet2 National Data Centers (NODCs) and JCOMM global systems (Argo, GOSUD, OceanSITES, GTSPP, DBCP) and the Global telecommunication system (GTS) used by the Met Offices.

The in situ Near Real Time biogeochemical product is updated every month whereas the reprocessed product is updated two times per year. Products are delivered on NetCDF4 format compliant with the CF1.7 standard and well-documented quality control procedures.
Investigating fault sinuosity using discrete element modelling in 3D
Authors: Aleksans Janis , Childs Conrad , Schöpfer Martin
Published: March 2020

Scaled numerical models of faults are useful complements to geological data and by providing insights into fault dynamics they can improve our understanding of the different stages of development of normal fault systems, from nucleation through to localisation and maturity.

In this work, we use Particle Flow Code in three dimensions, which implements the Distinct Element Method (DEM), to study the development of systems of normal faults. The modelling is based on spherical particles that interact via a linear force-displacement law. Cohesion is modelled by adding linear elastic bonds to particle-particle contacts. These bonds break if the critical normal or shear strength is exceeded, thus creating a fracture surface within the rock volume. Model boundaries are represented by rigid and frictionless walls enclosing the modelled volume vertically and at the ends, with periodic lateral boundaries. Extension is replicated by slowly moving the end walls away from the centre while maintaining a constant confining pressure.

The DEM models replicate many aspects of the geometry and dynamics of natural fault systems with stages of fault nucleation, propagation, interaction and linkage. Here we focus on the sinuosity of model fault map traces which show a similar variability to that seen in nature. In the models, fault trace sinuosity is negatively correlated with the Young’s modulus of the rock, so that faults become less sinuous as the stiffness of the solid medium increases. This relationship supports a model in which the lengths of fault segments formed at the early stages of extension are smaller in rocks with lower Young’s modulus than in rocks with higher Young’s modulus. Longer initial fault segments become connected as displacement increases, to give lower sinuosity faults.
Disentangling synchrony from serial dependency in complex climate networks: Comparing Event Synchronization and Event Coincidence Analysis
Authors: Odenweller Adrian , Donner Reik
Published: March 2020

The quantification of synchronization phenomena of extreme events has recently aroused a great deal of interest in various disciplines. Climatological studies therefore commonly draw on spatially embedded climate networks in conjunction with nonlinear time series analysis. Among the multitude of similarity measures available to construct climate networks, Event Synchronization and Event Coincidence Analysis (ECA) stand out as two conceptually and computationally simple nonlinear methods. While ES defines synchrony in a data adaptive local way that does not distinguish between different time scales, ECA requires the selection of a specific time scale for synchrony detection.

Herein, we provide evidence that, due to its parameter-free structure, ES has structural difficulties to disentangle synchrony from serial dependency, whereas ECA is less prone to such biases. We use coupled autoregressive processes to numerically study the sensitivity of results from both methods to changes of coupling and autoregressive parameters. This reveals that ES has difficulties to detect synchronies if events tend to occur temporally clustered, which can be expected from climate time series with extreme events exceeding certain percentiles.

These conceptual concerns are not only reproducible in numerical simulations, but also have implications for real world data. We construct a climate network from satellite-based precipitation data of the Tropical Rainfall Measuring Mission (TRMM) for the Indian Summer Monsoon, thereby reproducing results of previously published studies. We demonstrate that there is an undesirable link between the fraction of events on subsequent days and the degree density at each grid point of the climate network. This indicates that the explanatory power of ES climate networks might be hampered since trivial local properties of the underlying time series significantly predetermine the final network structure, which holds especially true for areas that had previously been reported as important for governing monsoon dynamics at large spatial scales. In contrast, ECA does not appear to be as vulnerable to these biases and additionally allows to trace the spatiotemporal propagation of synchrony in climate networks.

Our analysis rests on corrected versions of both methods that alleviate different normalization problems of the original definitions, which is especially important for short time series. Our finding suggest that careful event detection and diligent preprocessing is recommended when applying ES, while this is less crucial for ECA. Results obtained from ES climate networks therefore need to be interpreted with caution.
Coupling SKS and SWMM to solve the inverse problem based on artificial tracer tests data in karst aquifers
Authors: Sivelle Vianney , Renard Philippe , Labat David
Published: March 2020

Artificial tracer tests constitute one of the most powerful tools to investigate solute transport in conduit-dominated karst aquifers. One can retrieve information about the internal structure of the aquifer directly by a careful analysis of the residence time distribution (RTD). Moreover, recent studies have shown the strong dependence of solute transport in karst aquifers from boundary conditions. Then, results from artificial tracer tests contain information about the internal structure of the aquifers and about the effect of the boundary conditions (mainly high or low water level). So, a multi-tracer test calibration of the model appears to be more consistent in order to identify the effect of change in boundary conditions and to take into consideration their effects on solute transport. In this study, we propose to run the inverse problems based on artificial tracer tests with a numerical procedure composed by the following three main steps: [1] conduit geometry is simulated using a pseudo-genetic algorithm, [2] hypothesis about boundary conditions are imposed in the simulated conduit network and [3] flow and solute transport are simulated. Then, using a trial-and-error procedure, the simulated RTD is compared to the observed RTD on a large range of simulations allowing to identify the conduit geometry and boundary conditions that better reproduce the field data. This constitutes a new approach in order to better constrain inverse problem using a multi-tracer tests calibration including transient flow.
Satellite-based observations of ground-level fine particulate matter and comparison to a regional air quality model
Authors: Handschuh Jana , Baier Frank , Erbertseder Thilo , Schaap Martijn
Published: March 2020

Particulate matter and other air pollutants have become an increasing burden on the environment and human health. Especially in metropolitan and high-traffic areas, air quality is often remarkably reduced. For a better understanding of the air quality in specific areas, which is of great environment-political interest, data with high resolution in space and time is required. The combination of satellite observations and chemistry-transport-modelling has proven to give a good database for assessments and analyses of air pollution. In contrast to sample in-situ measurements, satellite observations provide area-wide coverage ​​of measurements and thus the possibility for an almost gapless mapping of actual air pollutants. For a high temporal resolution, chemistry-transport-models are needed, which calculate concentrations of specific pollutants in continuous time steps. Satellite observations can thus be used to improve model performances.

There are no direct satellite-measurements of fine particulate matter (PM2.5) but ground-level concentrations of PM2.5 can be derived from optical parameters such as aerosol optical depth (AOD). A wide range of methods for the determination of PM2.5 concentrations from AOD measurements has been developed so far, but it is still a big challenge. In this study a semi-empirical approach based on the physical relationships between meteorological and optical parameters was applied to determine a first-guess of ground-level PM2.5 concentrations for the year 2018 and the larger Germany region. Therefor AOD observations of MODIS (Moderate Resolution Imaging Spectroradiometer) aboard the NASA Aqua satellite were used in a spatial resolution of 3km. First results showed an overestimation of ground-level aerosols and quiet low correlations with in-situ station measurements from the European Environmental Agency (EEA). To improve the results, correction factors were calculated using the coefficients of linear regression between satellite-based and in-situ measured particulate matter concentrations. Spatial and seasonal dependencies were taken into account with it. Correlations between satellite and in-situ measurements could be improved applying this method.

The MODIS 3km AOD product was found to be a good base for area-wide calculations of ground-level PM2.5 concentrations. First comparisons to the calculated PM2.5 concentrations from chemistry-transport-model POLYPHEMUS/DLR showed significant differences though. Satellite observations will now be used to improve the general model performance, first by helping to find and understand regional and temporal dependencies in the differences. As part of the German project S-VELD funded by the Federal Ministry of Transport and Digital Infrastructure BMVI, it will help for example to adjust the derivation of particle emissions within the model.
New pathways of the reaction of OH radicals with dimethyl sulfide based on CH3SCH2O2 isomerization
Authors: Berndt Torsten , Scholz Wiebke , Mentler Bernhard , Fischer Lukas , Hoffmann Erik Hans , Tilgner Andreas , Hyttinen Noora , Prisle Nonne , Hansel Armin , Herrmann Hartmut
Published: March 2020

Dimethyl sulfide (DMS), produced by marine organisms, represents the most abundant, biogenic sulfur emission into the Earth´s atmosphere. The gas-phase degradation of DMS is mainly initiated by the reaction with the OH radical forming first CH3SCH2O2 radicals from the dominant H-abstraction channel. A fast CH3SCH2O2 isomerization process was proposed as a result of quantum chemical calculations. In the present study, experimental investigations on the product formation from OH + DMS have been conducted in a free-jet flow system at 295 ± 2 K and 1 bar air. Very efficient detection of CH3SCH2O2 isomerization products has been achieved by iodide-CI-APi-TOF measurements allowing to run the reaction for close to atmospheric conditions. It is experimentally shown that the CH3SCH2O2 radicals undergo a two-step isomerization process finally forming a product consistent with the formula HOOCH2SCHO. The isomerization process is accompanied by OH recycling. The rate-limiting first isomerization step, CH3SCH2O2 → CH2SCH2OOH proceeds with k = (0.23 ± 0.12) s-1 at 295 ± 2 K. Competing bimolecular CH3SCH2O2 reactions with NO, HO2 or RO2 radicals are less important for trace-gas conditions over the oceans.  Results of atmospheric chemistry simulations demonstrate the predominance (≥95%) of CH3SCH2O2 isomerization. The rapid peroxy radical isomerization, not yet considered in models, substantially changes the understanding of DMS´s degradation processes in the atmosphere.
Global maps of ecosystem functional properties with the SCOPE model on Google earth engine Sentinel-2 composites
Authors: Prikaziuk Egor , van der Tol Christiaan , Migliavacca Mirco
Published: March 2020

To monitor ecosystems at large spatial scale multiple data sources are needed. We developed a methodology to simulate ecosystem functional properties (EFPs): light use efficiency (LUE), water use efficiency (WUE), and evaporative fraction (EF) with Soil Canopy Observation, Photochemistry and Energy fluxes (SCOPE) model at global scale using weather and optical satellite data.

EFPs, metrics that integrate ecosystem processes and environmental conditions, are calculated from ecosystem fluxes: gross primary productivity (GPP), sensible (H) and latent (LE) heat flux. These fluxes were simulated by SCOPE from weather parameters and plant traits (leaf area index (LAI), leaf chlorophyll content (Cab)). The weather data was taken from ECMWF ERA5-Land dataset, the plant traits were retrieved with look-up table (LUT) from Sentinel-2 Level 2 composites, exported from Google Earth engine at 10 km resolution.

LUT retrieval was optimized on a synthetic dataset to reach acceptable quality for the key drivers of GPP flux: LAI (R2 = 0.75) and Cab (R2 = 0.62). The global retrieved LAI showed some discrepancies with MODIS LAI product MCD15, especially in forest regions (RMSE = 1.73 m2 m-2). As a consequence, SCOPE-simulated GPP was lower in those regions, compared to MODIS GPP product (MYD17) (RMSE = 0.81 kgC m-2 yr-1). SCOPE-simulated heat fluxes were compared to ECMWF energy flux from ERA5-Land dataset (RMSEH = 35.4 W m-2, RMSELE = 41.6 W m-2). EFPs validation is in progress.

The discrepancies in LAI can be explained by the fact that we did not use plant functional type information during LUT retrieval, in contrast to the MODIS algorithm. Significant overestimation of LE in dry areas is the consequence of the absence of water balance routine in SCOPE model. We consider SCOPE to be a promising tool for optical and weather data fusion.

The project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 721995.
Navigating through extreme flood simulations with intelligently chosen parameter sets
Authors: Sikorska-Senoner Anna E. , Schaefli Bettina , Seibert Jan
Published: March 2020

The quantification of extreme floods and associated return periods remains to be a challenge for flood hazard management and is particularly important for applications where the full hydrograph shape is required (e.g., for reservoir management). One way of deriving such estimates is by employing a comprehensive hydrological simulation framework, including a weather generator, to simulate a large set of flood hydrographs. In such a setting, the estimation uncertainties originate from the hydrological model, but also from the climate variability. While the uncertainty from the hydrological model can be described with common methods of uncertainty estimation in hydrology (in particular related to model parameters), the uncertainties from climate variability can only be represented with repeated realizations of meteorological scenarios. These scenarios can be generated with the help of the selected weather generator(s), which are capable of providing numerous and continuous long time series. Such generated meteorological scenarios are then used as input for a hydrological model to simulate a large sample of extreme floods, from which return periods can be computed based on ranking.

In such a simulation framework, many thousands of possible combinations of meteorological scenarios and of hydrological model parameter sets may be generated. However, these simulations are required at a high temporal resolution (hourly), needed for the simulation of extreme floods and for determining infrequent floods of a return period equal to or lower than 1000 years. Accordingly, due to computational constraints related to any hydrological model, one often needs to preselect meteorological scenarios and representative model parameter sets to be used within the simulation framework. Thus, some kind of an intelligent parameter selection for deriving the uncertainty ranges of extreme model simulations for such rare events would be very beneficial but is currently missing.

Here we present results from an experimental study where we tested three different methods of selecting a small number of representative parameter sets for a Swiss catchment. We used 100 realizations of 100 years of synthetic precipitation-streamflow data. We particularly explored the reliability of the extreme flood uncertainty intervals derived from the reduced parameter set ensemble (consisting of only three representative parameter sets) compared to the full range of 100 parameter sets available. Our results demonstrated that the proposed methods are efficient for deriving uncertainty intervals for extreme floods. These findings are promising for the simulation of extreme floods in comparable simulation frameworks for hydrological risk assessment.
3D gravity inversion across the area struck by the 2016-2017 seismic events in Central and Northern Apennines, Italy
Authors: Mancinelli Paolo , Pauselli Cristina , Fournier Dominique , Fedi Maurizio , Minelli Giorgio , Barchi Massimiliano
Published: March 2020

In this work, the crustal volume struck by the 2016-2017 seismic sequence in Central and Northern Apennines is investigated using constrained 3D inversion of the Bouguer anomaly. After a preliminary regional field removal the residual dataset is then inverted into a 3D density contrast model. With an increasing complexity in the reference geometries, we test different geological scenarios and software settings. Geometries used in the reference models were retrieved from the available geological and geophysical information in the area. Starting with a reference model encompassing turbidites, carbonates and evaporites, and basement we finally test the effects of a low-density layer at the top of the basement. The retrieved density distribution with depth is compatible with previous models. Moreover, results support the hypothesis based on borehole evidence, of a low-density upper basement across the entire area, possibly phyllitic in composition. Comparison of the resulting models with the spatial distribution at depth of M>3 seismic events between August and November 2016, allows to locate volumes with the higher concentration of seismic events. Both at shallow and deep locations, the majority of the events enucleated in volumes relatively denser while deeper events occur in a region of major density change corresponding to the top of the basement.
Assessment of Dangerous Permafrost Processes in Urban Settlements of the Russian Arctic
Authors: Streletskiy Dmitry , Grebenets Valery , Zamyatina Nadezhda
Published: March 2020

Russian Arctic is characterized by developed infrastructure and high percentage of urban population on permafrost. The settlements on permafrost represent hot spots of permafrost transformations as rapidly changing climatic conditions are exacerbated by various types of human activities. To evaluate the exposure and risks of settlements to permafrost related dangerous processes, we selected several criteria, including geographic extent, duration, probability of occurrence, and total risk of damages associated with each permafrost process in 37 settlements located in various parts of the Russian Arctic. The following six types of potentially dangerous permafrost processes were considered: a) thermokarst, b) thermal erosion and thermal abrasion, c) frost heave, d) frost cracking, e) formation of icings, f) human-induced slope processes on permafrost. While risk from particular process was rather location specific, the integral assessment of all selected categories allowed to classify the overall exposure of settlements to permafrost processes. Results show that cities of Anadyr, Nadym and Kharp have rather small risk exposure, while cities of Igarka and Vorkuta have relatively high exposure. Bilibino and Norislk were among the cities having the highest overall exposure and potential risk associated with permafrost related processes considered in this study.  The research is supported by Russian Foundation for Basic Research project 18-05-600888  “Urban Arctic resilience in the context of climate change and socio-economic transformations”.
New constraints on the tectonic activity of the “Tellian Domain” from Northern Tunisia: preliminary paleomagnetic results.
Authors: Robion Philippe , Arfaoui Marwen , Ahmadi Riadh , Derder Mohamed El Messaoud , Amena Mohamed , Maouche Said , Rekihiss Farhat
Published: March 2020

In this study, we present preliminary results on paleomagnetic data collected in the Tunisian Tellian domain in both magmatic and sedimentary rocks of middle to lat Miocene ages from the Nefza-Mogods province, North-West of Tunisia. About 320 cores distributed over twenty one sites were collected both in magmatic rocks (16 sites) and in sedimentary rocks (5 sites), in order to obtain geometric constraints to establish a kinematic model along the North-East African margin. The sampled rocks are distributed between basanites, rhyodacites and microgranites. Some samples were taken from host sedimentary rocks host rocks in lacustrine limestones and jaspilites. Demagnetization process and Rock-Magnetism studies revealed a diversified magnetic mineralogy. In basalts, magnetite with an unblocking temperature of 580 °C is identified. In rhyodacites, the mineralogy is mixed with three types of minerals: a mineral with an unblocking temperature around 350°-400°C attributed either to a sulfide or to titanomagnetite, magnetite with unblocking temperature at 580°C, and a high temperature mineral with unblocking temperature between 600°C and 680°C attributed to hematite or titanohematite. The limestones, having a low magnetization intensity, are characterized by the presence of magnetite and the jaspilites by hematite. Basalts, which have been mainly demagnetized by AF process , show a characteristic component demagnetized between 20mT and 100mT. For rhyodacites, some sites have a characteristic component demagnetized between 400°C and 580°C and others up to 670°C. Although their low magnetization intensity, the lacustrine limestones show a magnetic component between 20mT and 140 mT. The first result indicate that the mean directions associated to the younger magmatic (basalts and rhyodacite) rocks (8 Ma, Tortonian) and their sedimentary host deposits are very close to the expected magnetic field after tilting in paleogeographic coordinates. By contrast, the older microgranites and rhyodacites(-12 Ma) display a vertical axis clockwise rotation of about 30°. This result suggests a significant tectonic phase between 12 Ma and 8 Ma, linked to the implementation of the Tell nappes.
An index to quantifying the impacts of agricultural drought and its application in China
Authors: sun huaiwei , Chen Jianing
Published: March 2020

As one of the major weather-driven natural disasters, droughts exhibit as the most frequent and widespread natural disasters in China. It is reported that the agriculture losses show continuously grown by following the increasingly severe droughts for the whole country. In order to investigate the impacts of drought on agricultural, we rechecked the functional relationship between the crop yield and climatic variables. Based on the meta-analysis from previous literature, we found a more stable statistical relationship between the yield and the precipitation and evapotranspiration. These results introduce a new drought index, indicated as Crop Water-Related Index for Drought (CWRID), which can be used as a reference index to approximate the drought impact on the loss of yield. Based on the climatic data in China during 1982-2015, several other drought indices (SPI, SPEI, CI, and SEDI) were compared with CWRID to identify the most appropriate agricultural drought index. The data of historical drought damaged area and drought damaged crop yield reduction were used to validate the performances of different indices. The CWRID reasonably predicted the drought damaged area as well as the drought damaged yield reduction during the past 30 years in China. As a contrast, the SEDI is proved to be no suit for quantifying drought. Also, the calculated values are stored in the dataset and can be shared with researchers by request. As a simple index, results indicated that CWRID can be used to quantify the impacts of drought on agricultural as it can reflect the variation of crop yields.
Stochastic comparison of climate model outputs to observed temperature fields
Authors: Angelopoulos Georgios , Dimitriadis Panayiotis , Iliopoulou Theano , Koutsoyiannis Demetris
Published: March 2020

We compare the stochastic behaviour of temperature outputs of climate models for the 20th century
to the historical data (stations and reanalysis fields) at several temporal and spatial scales. In
particular we examine the marginal distributions and the dependence structure with emphasis on
the Hurst-Kolmogorov behaviour. The comparison aims to contribute to the quantification of
reliability and predictive uncertainty of temperature climate model outputs over different scales in a
framework of assessing their relevance for engineering planning and design.

(Acknowledgement: This research is conducted within the frame of the course "Stochastic Methods"
of the National Technical University of Athens (NTUA). The School of Civil Engineering of NTUA
provided moral support for the participation of the students in the Assembly.)
Decomposing terrestrial carbon ﬂux anomalies after El Niño: process-based predictability of land carbon sinks and sources
Authors: Dunkl István , Brovkin Victor
Published: March 2020

Anthropogenic fossil fuel emissions are increasing, and about a half of these emissions is absorbed by land and ocean. The CO2 fraction remaining in the atmosphere, the airborne fraction, is varying from year to year. Most of this variability can be explained by the land-atmosphere carbon fluxes. This variability is strongly affected by the El Niño – Southern Oscillation (ENSO); however, it is difficult to determine the cause of the flux anomalies due to the complex interactions between the climatic effects of the ENSO cycle. Here, we use MPI Earth System Model, MPI-ESM, to study the mechanisms of post El Niño carbon fluxes and assess their predictability. 10-member ensemble simulations with small perturbations are initialized at six El Niño events of a 1000-year control run. After removing the long-term mean from the ensemble simulations, a density-based clustering algorithm is applied to the carbon fluxes due to primary productivity, respiration and ﬁres. This allows to identify and delimit the individual hotspots of ENSO-related carbon flux anomalies that contribute most to the atmospheric CO2 change.
We found that the main carbon sources are due to a reduction of primary production in the tropics, while the carbon sinks are due to reduced respiration or increased primary production in the extratropics. The potential predictability of the carbon fluxes from these clusters was assessed by using the perfect model approach. In accordance with this method, the predictive horizon is estimated as the time, when the variability within the ensemble members exceeds the long-term variability. As climate change will likely modify the frequency of El Niño events, this decomposition of the ENSO carbon flux anomalies could be used to improve our understanding of the future trends of land carbon sinks.
Improving the accuracy of soil carbon models using a Rock-Eval-based initialization method
Authors: Kanari Eva , Cécillon Lauric , Baudin François , Clivot Hugues , Ferchaud Fabien , Mary Bruno , Soucémarianadin Laure , Chenu Claire , Barré Pierre
Published: March 2020

In most soil organic carbon (SOC) dynamics models, SOC is divided into pools to which different mineralization rates are ascribed. The lack of a reliable, operational and fully validated method to initialize the size of the different SOC kinetic pools is a limitation for the accuracy of predictions of SOC stocks evolution provided by these models. AMG is a simple, well established French model, successfully used to simulate the evolution of C stocks for a large network of long-term monitored sites with agricultural experiments (LTEs). Initial conditions, namely the size of the stable C pool (CS) at the onset of the simulation, have been shown to be important for the accuracy of the model. Recently, Rock-Eval 6® (RE) thermal analysis has been proposed as a new method for direct determination of SOM stability. Based on this technique, a random forests model (RE model) was developed, calibrated on Long Term Bare Fallow data, which allows the estimation of the size of the centennially persistent SOC fraction (CPSOC) in a sample. Here, we first aimed at evaluating the performance of the RE model on fully independent soil samples. For this purpose, we compared the CPSOC values of 73 samples from 7 LTEs calculated with the RE model with the corresponding CS values optimized from AMG ex-post simulations. Then, we used the CPSOC values given by the RE model to define the size of the stable C pool of the AMG model (CS) at the onset of AMG simulations for the 7 sites. We show that the CPSOC (RE model) and optimized CS (ex-post AMG simulations) fractions are in good agreement (slope b=1.01, intercept a=0.04 / spearman ρ=0.88). This observation serves as a successful independent validation of the RE model. Finally, we show that the use of the RE based model improves the accuracy of the AMG model compared to default initialization (mean RMSE decreased by 13.5%), especially for sites with complex land-use history and long-term organic matter amendment. Our study therefore provides an operational method suitable to initialize the AMG model that can be expanded to other SOC dynamics models.
Interactive Aerosol Feedbacks on Photolysis Rates in the GEM-MACH Air Quality Model for an Athabasca Oil-Sands Modelling Study
Authors: Majdzadeh Mahtab , Stroud Craig , Akingunola Ayodeji , Makar Paul , Sioris Christopher , McLinden Chris , Zhao Xiaoyi , Moran Michael , Abboud Ihab
Published: March 2020

The radiative transfer module of an on-line chemical transport models requires input data from aerosol extinction efficiency, single scatter albedo and asymmetry factor, in order to predict the radiative state of the atmosphere. These aerosol optical properties (aerosol optical depth, AOD), may be integrated vertically for comparison to satellite observations. These optical effects may also influence the shorter wavelengths associated with atmospheric gas photolysis, influencing atmospheric reactivity. These processes may be harmonized in an on-line reaction transport model, such as Environment and Climate Change Canada’s GEM-MACH (GEM: Global Environmental Multi-scale – MACH: Modelling Air quality and Chemistry). Previous photolysis routine in the radiative transfer module, MESSY-JVAL (Modular Earth Sub-Model System), in GEM-MACH, made use of a climatology of aerosol optical properties, and the previous on-line version made use of a homogeneous mixture Mie code for meteorological radiative transfer calculations.

We calculated a new lookup table for the extinction efficiency, absorption and scattering cross sections of each aerosol type. The new version of MESSY-JVAL uses GEM-MACH predicted aerosol size distributions, chemical composition and relative humidity in each vertical column at each time step as input, reads aerosol absorption and scattering cross section data from the new lookup table and calculates aerosol optical properties, that are then used to modify both photolysis and meteorological radiative transfer calculations.

In order to evaluate these modifications to the model, we performed a series of simulations with GEM-MACH with wildfire emissions inputs from the Canadian Forest Fire Emissions Prediction System (CFFEPS) and compared the model AOD output with satellite and AERONET (Aerosol Robotic Network) measurement data. Comparison of the hourly AERONET and monthly-averaged satellite AOD demonstrates major improvements in the revised model AOD predictions. The impact of the updated photolysis rates and meteorological radiative transfer calculations on predictions of oxidant mixing ratios and rates of pollutant oxidation (nitrogen dioxide conversion to nitric acid) will be assessed both within and below the forest fire plume.
Optical clocks for gravity field observation and further geodetic applications
Authors: Wu Hu , Müller Jürgen , Knabe Annike
Published: March 2020

In the past three decades, optical clocks and frequency transfer techniques have experienced a rapid development. They are approaching a fractional frequency uncertainty of 1.0x10-18, corresponding to about 1.0 cm in height. This makes them promising to realize “relativistic geodesy”, and it opens a new door to directly obtain gravity potential values by the comparison of clock frequencies. Clocks are thus considered as a novel candidate for determining the Earth’s gravity field. We propose to use a spaceborne clock to obtain gravity potential values along a satellite orbit through its comparison with reference clocks on ground or with a co-orbital clock. The sensitivity of clock measurements is mapped to gravity field coefficients through closed-loop simulations.

In addition, clocks are investigated for other geodetic applications. Since they are powerful in providing the height difference between distant sites, clocks can be applied for the unification of local/regional height systems, by estimating the offsets between different height datums and the systematic errors within levelling networks. In some regions like Greenland, clocks might be a complementary tool to GRACE(-FO) for detecting temporal gravity signals. They can be operated at locations of interest and continuously track changes w.r.t. reference clock stations. The resulting time-series of gravity potential values reveal the temporal gravity signals at these points. Moreover, as the equipotential surface at a high satellite altitude is more regular than that on the Earth’s surface, a couple of clocks in geostationary orbits can realize a space-based reference for the determination of physical heights at any point on the Earth through clock comparisons.

We gratefully acknowledge the financial support by the Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy EXC-2123/1 (Project-ID: 390837967).