bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic reanalysis of storm surge extremes in Europe
Authors: Mir Calafat Francisco , Marcos Marta
Published: March 2020

Extreme sea levels are a significant threat to life, property, and the environment. These threats are managed by coastal planers through the implementation of risk mitigation strategies. Central to such strategies is knowledge of extreme event probabilities. Typically, these probabilities are estimated by fitting a suitable distribution to the observed extreme data. Estimates, however, are often uncertain due to the small number of extreme events in the tide gauge record and are only available at gauged locations. This restricts our ability to implement cost-effective mitigation. A remarkable fact about sea-level extremes is the existence of spatial dependences, yet the vast majority of studies to date have analyzed extremes on a site-by-site basis. Here we demonstrate that spatial dependences can be exploited to address the limitations posed by the spatiotemporal sparseness of the observational record. We achieve this by pooling all the tide gauge data together through a Bayesian hierarchical model that describes how the distribution of surge extremes varies in time and space. Our new approach has two highly desirable advantages: 1) it enables sharing of information across data sites, with a consequent drastic reduction in estimation uncertainty; 2) it permits interpolation of both the extreme values and the extreme distribution parameters at any arbitrary ungauged location. Using our model, we produce the first, to our knowledge, observation-based probabilistic reanalysis of surge extremes covering the entire Atlantic and North Sea coasts of Europe for the period 1960-2013.
ENSO teleconnection over the Euro-Mediterranean sector: the role of extratropical Pacific modulation
Authors: Benassi Marianna , Conti Giovanni , Gualdi Silvio , Ruggeri Paolo , Garcia–Serrano Javier , Palmeiro Froila , Battè Lauriane , Ardilouze Constantin
Published: March 2020

El Nino Southern Oscillation (ENSO) represents the major driver of interannual climate variability at the global scale. Observational and model-based studies have fostered a long-standing debate on the shape and the intensity of ENSO influence over the Euro-Mediterranean sector. Indeed, the detection of this signal is strongly affected by the large variability which characterizes the atmospheric circulation in the North Atlantic and European sector.

Different mechanisms have been proposed as involved in the propagation of ENSO signal from low to mid latitude, and we want to investigate if and how the low frequency variability of North Pacific sea-surface temperature (SST) may affect their efficacy. In this work, we study how the different phases of the extratropical SST pattern linked to the Pacific Decadal Oscillation (PDO) modulates the ENSO fingerprint over the Euro-Mediterranean region.

A set of idealized sensitivity experiments designed in the framework of the MEDSCOPE project has permitted to identify the ENSO teleconnection over the Euro-Mediterranean domain and to reveal the potential modulating role of the different phases of the extratropical PDO SST forcing.

In order to place this process in a dynamical framework, a tropospheric pathway has been proposed. The propagation of planetary waves from low to mid latitude has been investigated, by looking at the sensitivity of this mechanism to different underlying mean state.

These results allow to gain a deeper understanding of the links between mid-latitude climate variability and tropical forcing and of the processes ruling the low-mid latitude teleconnection in the Northern Hemisphere. Moreover, a clearer insight of these processes may lead to a new comprehension of possible sources of predictability for the Euro-Mediterranean domain over different time scales.

 
Storyline approach to extreme event characterization
Authors: Shepherd Theodore
Published: March 2020

Extreme climate events are invariably highly nonlinear, complex events, resulting from the confluence of multiple causal factors, and often quite singular. In any complex system there is a tension between analysis methods that respect the singularity of the extreme events at the price of statistical repeatability, and those that emphasize statistical repeatability at the price of nonlinearity and complexity; this dichotomy is found across all areas of science. In the climate context, the ‘storyline’ approach has emerged in recent years as a way of following the first of these two pathways. I will discuss how the storyline approach can be cast within the mathematical framework of causal networks, which provides a way to bridge between the storyline and probabilistic approaches. This also provides a way to interpret data in an appropriately conditional manner, thereby aiding model-measurement comparison.
Moving Average Convergence/Divergence analysis of geophysical and geochemical time series: application to the 2011-2012 El Hierro eruption
Authors: Salehiozoumchelouei Robabeh , Rajaeitabrizi Yousef , Sánchez de la Rosa José Luis , D'Auria Luca , Pérez Nemesio M.
Published: March 2020

Financial markets specialists often use multiscale analysis on different kind of time series. Many tools have been developed for these tasks. Two of them, widely used, are: candlestick charts and technical indicators. Our approach consists in using both tools to analyze geophysical and geochemical time series.

In this work we represent signals using candlesticks at user selected time scales. In our case we use four summary quantities of the signal: the amplitude of the first sample, the maximum amplitude within the candle, the minimum amplitude and the amplitude of the last sample used in the candle. We show how the graphical candlestick representation alone is able to emphasize representative changes within the time-series in a multiscale fashion.

On the other hand, many technical indicators have been defined to extract further information from such type of charts. Among the most commonly used technical indicators are: Simple Moving Average (SMA), Exponential Moving Average (EMA) and Moving Average Convergence/Divergence (MACD). EMA is a temporal smoothing with an exponential weighting determined by a time scale factor. MACD is the difference between EMA realized at a short scale with another EMA at a larger scale. For instance, a commonly used MACD in financial markets is computed using scales of 12 and 26 days. In the case of actual geophysical and geochemical datasets, such scales should be selected on the basis of the time scales of interest.

Using tests realized on synthetic datasets we demonstrate that MACD is a proxy for the derivative of time-series, event with a very high noise level. This is of course of great interest when analyzing geophysical and geochemical time series, with the aim of detecting changes in their trends. We applied candlestick analysis to various seismological and geochemical datasets, in particular we show an example application to recent 2011-2012 eruption of the island of El Hierro in the Canary Islands, highlighting the capability of this method to detect changes in the trend of time-series earlier and better that other simpler techniques.
Methane uptake by various forest soils with and without litter
Authors: Walkiewicz Anna , Bulak Piotr , Osborne Bruce , Khalil Mohammad Ibrahim , Islam Syed Faiz-ul , Kruijt Bart , Hutjes Ronald , Spengler Daniel , Gottschalk Pia , Sachs Torsten , Klumpp Katja , Vigan Aurore , Hassouna Mélynda , Henessy Donagh , Shalloo Laurence
Published: March 2020

Forest soils are often a sink for atmospheric methane (CH4) and are thus worth special attention in the context of mitigation of greenhouse gases (GHGs) and offset of agricultural GHG emissions at farm to national levels. The litter layer influences the exchange of GHGs between soil and atmosphere; however, most studies focus on the contribution of only soil to the CH4 cycle. In order to improve the inventory of this gas, it is worth investigating how litter influences the exchange of GHGs. Its effect on CH4 uptake may vary in deciduous and coniferous sites due to the different properties of litter. Field experiments were carried out to assess the CH4 uptake capability in 5 different soil types (with and without litter) under different forest types (deciduous, coniferous, and mixed) in Poland. During summer 2019, the highest CH4 uptake (about 2 mg C m-2 day-1) in a variant without litter on the ground was detected in Dystric Cambisol (with the highest C/N ratio) under a 100-year-old coniferous forest and in Albic Luvisol under a 58-year-old mixed forest. The presence of the litter level reduced the CH4 flux in the range of 6-27% in these locations. Methane consumption was the lowest in silty soils (~ 0.4 – 1 mg C m-2 day-1) in the mixed forest and decreased by 13-29% when covered with the litter layer. The negative effect of the litter layer on CH4 absorption was the lowest (~ 3-4%) in sandy Eutric Gleysol under a 75-year-old deciduous forest with 90% of oak and 10% of European hornbeam. The dry conditions in the summer 2019 (with total rainfall 163 mm during the tested months in the studied region) resulted in low moisture in both the litter and soil. However, even low-humidity litter (below 10%) reduced CH4 consumption rates in the measured sites.

Research was partially conducted under the project financed by Polish National Centre for Research and Development within of ERA-NET CO-FUND ERA-GAS Programme (ERA-GAS/I/GHG-MANAGE/01/2018).
Covariates selection assessment for field scale digital soil mapping in the context of precision fertilization management
Authors: Mzid Nada , Pignatti Stefano , Veretelnikova Irina , Casa Raffaele
Published: March 2020

The application of digital soil mapping in precision agriculture is extremely important, since an assessment of the spatial variability of soil properties within cultivated fields is essential in order to optimize agronomic practices such as fertilization, sowing, irrigation and tillage. In this context, it is necessary to develop methods which rely on information that can be obtained rapidly and at low cost. In the present work, an assessment is carried out of what are the most useful covariates to include in the digital soil mapping of field-scale properties of agronomic interest such as texture (clay, sand, silt), soil organic matter and pH in different farms of the Umbria Region in Central Italy. In each farm a proximal sensing-based mapping of the apparent soil electrical resistivity was carried out using the EMAS (Electro-Magnetic Agro Scanner) sensor. Soil sampling and subsequent analysis in the laboratory were carried out in each field. Different covariates were then used in the development of digital soil maps: apparent resistivity, high resolution Digital Elevation Model (DEM) from Lidar data, and bare soil and/or vegetation indices derived from Sentinel-2 images of the experimental fields. The approach followed two steps: (i) estimation of the variables using a Multiple Linear Regression (MLR) model, (ii) spatial interpolation via prediction models (including regression kriging and block kriging). The validity of the digital soil maps results was assessed both in terms of the accuracy in the estimation of soil properties and in terms of their impact on the fertilization prescription maps for nitrogen (N), phosphorus (P) and potassium (K).
Aerosol layering in free troposphere, its impact on modification of the UV irradiation over industrial site in southern Poland
Authors: Pietruczuk Aleksander , Krzyscin Janusz , Szkop Artur , Fernandes Alnilam
Published: March 2020

Ceilometers are effective instruments to study atmospheric profiles. They are primarily designed to study cloud base height however are widely used to study aerosol optical properties profiles, aerosol backscatter or extinction coefficients or just atmospheric layering. In this work we utilized statistics of aerosol layers in free troposphere to explain differences between measured and modelled UV radiation at Raciborz station in southern Poland.

Raciborz is a town in southern Poland, close to the Czech Republic border. This area is affected by local urban and industrial pollutions from urban area of Silesia in South Western Poland and North Eastern Czech Republic. Remote locations of aerosols may also play important role in UV radiation modification. The observatory in Raciborz is equipped with CHM-15k Nimbus ceilometer, triple Sun-Sky-Lunar CIMEL ceilometer, and Kipp & Zonen UVS-E-T biometer.

Series of erythema dose rates were compared to that modelled by Tropospheric Ultraviolet-Visible (TUV) radiation transfer model. We used satellite (OMI) ozone, aerosol columnar properties (optical thickness at 340 nm, Angstrom exponent for 340-440nm range as well as single scattering albedo and asymmetry parameter at 440 nm) measured by CIMEL photometer as model input values. The model/observations differences are within +/- 5% range for 90% of measured doses during cloud free conditions. The median of model/observations ratio differences is 0.994. To explain revealed ratio variability a statistical, regression model was developed. A random forest approach applied to normalized erythema doses explained about 52% of model/observations ratio differences by aerosol characteristics in free troposphere.

Aerosol characteristics provided as statistical model input are: mean altitude of aerosol’s layer base and top, geometrical thickness of all layers and sum of aerosol layer backscatter intensity (in arbitral units) normalized by layer geometrical thickness. Aerosol layers are found throughout the year with the highest frequency in August (about 80%  days with at least one layer) and the lowest in November (about 10% days). For days with layers, the mean number of  the layers per day is less variable usually 2-3 layers in one day. The mean depth of the layer  is  larger in summer (1.3 km) than in winter (0.8 km) but the life time of the layer is similar of about 7-8 hours in both periods.

Acknowledgements

This work was supported by Polish National Science Center under grant no. 2017/25/B/ST10/01650.
Source Spectral studies using Lg wave in western Tibet
Authors: Sarkar Sukanta , Jaiswal Namrata , Singh Chandrani , Dubey Arun Kumar , Singh Arun
Published: March 2020

The tectonic structure of western Tibet is complex and formed of several blocks, which are separated by distinct suture zones. This complexity makes the region very crucial for understanding the local tectonic settings. Here, we investigate the spectral characteristics of Lg wave from 420 waveforms recorded at 26 seismic stations located across Karakoram Fault (KKF) in western Tibet. We subdivide the study region into two parts across KKF. A frequency  dependent QLg is observed in both sides of KKF with strong attenuation in the crust. The moment magnitude of each earthquake is computed using displacement spectra and subsequently compared with the reported local magnitude. Variations of the corner frequency with magnitude and distance
are also studied, which show a decreasing nature due to the path dependency.
Cold seep hibernation in the Arctic sediments during cold bottom water conditions
Authors: Ferré Bénédicte , Jansson Pär G. , Mosser Manuel , Serov Pavel , Portnov Alexey , Graves Carolyn , Panieri Giuliana , Gründger Friederike , Berndt Christian , Lehmann Moritz , Niemann Helge
Published: March 2020

Large amounts of methane are trapped within gas hydrate in sub-seabed sediments in the Arctic Ocean, and bottom-water warming may induce the release of methane from the seafloor. Yet, the effect of seasonal temperature variations on methane seepage activity remains unknown, as surveys in Arctic seas are mainly conducted in summer. Here, we compare the activity of cold seeps along the gas hydrate stability limit offshore Svalbard during cold (May 2016) and warm (August 2012) seasons. Hydro-acoustic surveys revealed a substantially decreased seepage activity during cold bottom-water conditions, corresponding to a 43 % reduction of total cold seeps and methane release rates compared to warmer conditions. We demonstrate that cold seeps hibernate during cold seasons, when more methane gas becomes trapped in the sub-seabed sediments. Such a greenhouse gas capacitor increases the potential for methane release during summer months. Seasonal bottom-water temperature variations are common on the Arctic continental shelves. We infer that methane-seep hibernation is a widespread phenomenon that is underappreciated in global methane budgets, leading to overestimates in current calculations.

This research is part of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) and is supported by the Research Council of Norway through its Centres of Excellence funding scheme grant No. 223259 and UiT.
Using a nested single-model large ensemble to assess the internal variability of the North Atlantic Oscillation and its climatic implications for Central Europe
Authors: Böhnisch Andrea , Ludwig Ralf , Leduc Martin
Published: March 2020

The ClimEx-project ("Climate change and hydrological extreme events"; www.climex-project.org) provides a single-model initial-condition ensemble that is unprecedented in terms of size, resolution and domain coverage: 50 members of the Canadian Earth System Model version 2 (CanESM2 Large Ensemble, 2.8° spatial resolution) are downscaled using the Canadian Regional Climate Model version 5 (CRCM5 Large Ensemble, 0.11° spatial and up to hourly temporal resolution) over two domains, Europe and northeastern North America. The high-resolution climate information serves as input for hydrological simulations to investigate the impact of internal variability and climate change on hydrometeorological extremes.

This study evaluates the downscaling of a teleconnection which affects northern hemisphere climate variability, the North Atlantic Oscillation (NAO), within the nested single-model large ensemble of the ClimEx project. The overall goal of this study is to assess whether the range of NAO internal variability is represented consistently between the driving global climate model (GCM, i.e., the CanESM2) and the nested regional climate model (RCM, i.e., the CRCM5).

The NAO pressure dipole is quantified in the CanESM2-LE; responses of mean surface air temperature and total precipitation sum to changes in the NAO index are evaluated within a Central European domain in both the CanESM2-LE and the CRCM5-LE. NAO–response relationships are expressed via Pearson correlation coefficients and the change per unit index change for historical (1981–2010) and future (2070–2099) winters.

Results show that statistically robust NAO patterns are found in the CanESM2-LE under current forcing conditions, and reproductions of the NAO flow pattern present in the CanESM2-LE produce plausible temperature and precipitation responses in the high-resolution CRCM5-LE. The NAO–response relationship is more strongly evolved in the CRCM5-LE than in the CanESM2-LE, but the inter-member spread shows no significant differences: thus internal variability expressed as inter-member spread can be seen as being represented consistently between the GCM and RCM. NAO–response relationships weaken in the future period in both the CanESM2-LE and CRCM5-LE, suggesting that the NAO influence on Central European temperature and precipitation decreases.

The results stress the advantages of a single-model ensemble regarding the evaluation of internal variability. They also strengthen the validity of the nested ensemble for further impact modelling using RCM data only, since important large-scale teleconnections present in the driving GCM propagate properly to the fine scale dynamics in the RCM.
Alpine glaciers disappearance tipping point: results from EURO-CORDEX models
Authors: Scoccimarro Enrico , Peano Danile
Published: March 2020

The front variations of Alpine glaciers show a general retreat over the past 150 years. This glacier retreat, then, has a large impact on many regional sectors, such as hydroelectricity production, river runoff, and touristic sector. In the last decades, glacier retreat in the Alps has been extremely evident due to the pronounced temperature increase affecting these mountains.

Moreover, numerous model studies exhibit a high probability of occurrence of Alpine glacier disappearance by the end of the current century, especially under extreme future climate change conditions.

The Alpine glaciers disappearance is expected to largely influence the Alpine glaciers regions climate, especially in terms of water availability. For this reason, the occurrence of the Alpine glaciers disappearance is enumerated among the climate tipping point.

Given the reduced average glaciers dimension, high-resolution data are needed to investigate the occurrence and the potential impacts of this tipping point. Thus, the EURO-CORDEX dataset over the EUR-11 domain are analyzed in this study.

Alpine glaciers differ under many characteristics, such as elevation, mean aspect, length, and shape. Consequently, a minimal glacier model, which takes into account few glacier features, is used in detecting the occurrence of the Alpine glaciers disappearance. Besides, a simplified surface mass balance model contributes to generalize the tipping point detection and assess the expected water budget changes.

This effort is part of the EU-funded COACCH project.   

 

Keywords

 

Alpine Glaciers, tipping point, water cycle, EURO-CORDEX
Validation of Aeolus winds using atmospheric radars in Arctic Sweden and in Antarctica and NWP modelling
Authors: Lindskog Magnus , Belova Evgenia , Voelger Peter , Kirkwood Sheila , Körnich Heiner , Hagelin Susanna , Chatterjee Sourav , Satheesan Karathazhiyath
Published: March 2020

ESRAD and MARA, , respectivelyThe Aeolus HLOS wind component (L2B) is also compared to the corresponding component of winds derived from the HARMONIE model for the ESRAD collocations and from the ECMWF ERA5 re-analysis for the MARA collocations. We estimate bias, root-mean-squared error and correlation for the Aeolus winds the radar and model data.

 

 
Evaluation of various setups of hydraulic structures in wild creek by River Flow2D
Authors: Tu Chin-Hsiang , Huang Hung-Pin
Published: March 2020

In Taiwan, the hydraulic structures of groundsill, check dam and embankment are frequently used in wild creek in order to prevent longitudinal and lateral scour. The benefit of these structures could not be numerically evaluated before construction without movable bed computational software. In recent years, the downstream scour-and-fill of hydraulic structures in wild creek could be carried out by software of River Flow 2D. This study used this software to evaluate the various setups of hydraulic structures in Jianshi, Hsinchu. Before carrying out software, the unmanned aerial vehicle (UAV) was operated to capture aerial photos of watershed. Then, the digital surface model (DSM) and orthomosaic photos were produced by Pix4Dmapper. Because most of wild creeks have no vegetation on their own creek bed, the DTM could be replaced by DSM. Associated with the various setups of hydraulic structures, Global mapper, QGIS and designed rainfall data, the software of River Flow 2D could give the downstream scour-and-fill of various setups of hydraulic structures. And, the convenient setup could be selected after evaluating the various setups of hydraulic structures.
Contrasting the skills and biases of deterministic predictions for the two types of El Niño
Authors: Zheng Fei , Yu Jin-Yi , Zhu Jiang
Published: March 2020

The tropical Pacific has experienced a new type of El Niño, which has occurred particularly frequently during the last decade and is referred to as the central Pacific (CP) El Niño. Various coupled models with different degrees of complexities have been used to make real-time El Niño predictions, but large uncertainties still exist in the forecasts. It is still not yet known how much of the uncertainty is specifically related to the new CP type of El Niño and how much is common to both this type and the conventional Eastern Pacific (EP) type of El Niño. In this study, the deterministic performance of an El Niño-Southern Oscillation (ENSO) ensemble prediction system (EPS) is examined for these two types of El Niño. Ensemble hindcasts are performed for the nine EP El Niño events and twelve CP El Niño events that have occurred since 1950. The results show that (1) the skill scores for the EP events are significantly better than those for the CP events at all lead times; (2) the systematic forecast biases come mostly from the prediction of the CP events; and (3) the systematic error is characterized by an overly warm eastern Pacific during the spring season, indicating a stronger spring prediction barrier for the CP El Niño. Further improvements of coupled atmosphere-ocean models in CP El Niño prediction should be recognized as a major challenge and high-priority task for the climate prediction community.
Comparing the effect of shortwave penetration and mixing induced by non-breaking surface waves in an ocean climate model
Authors: Wang Shizhu , Wang Qiang , Shu Qi , Scholz Patrick , Lohmann Gerrit , Qiao Fangli
Published: March 2020

Numerical models have been widely utilized to simulate the ocean and climate system. Parameterizations of some important processes, however, including the vertical mixing induced by surface waves, are still missing in many ocean models. In this work we incorporate the vertical mixing induced by non-breaking surface waves derived from a wave model into the multi-resolution Finite Element Sea ice-Ocean Model (FESOM), and compare its effect with that of shortwave penetration, another key process to vertically redistribute the heat in the upper ocean. Numerical experiments reveal that both processes ameliorate the simulation of upper-ocean temperature in mid and low latitudes mainly on the summer hemisphere. The regions where nonbreaking wave generates stronger improvement are where large temperature bias exists. The non-breaking surface waves plays a more significant role in decreasing the mean cold biases at 50 m (by 1.0 °C, in comparison to 0.5 °C achieved by applying shortwave penetration). We conclude that the incorporation of mixing induced by non-breaking surface waves into FESOM is practically very helpful, and suggest that it needs to be considered in other ocean climate models as well.
Understanding and quantifying carbon cycling in managed grasslands through model-data fusion
Authors: Myrgiotis Vasileios , Clement Rob , Jones Stephanie K. , Keane Ben , Lee Mark , Levy Peter E. , Rees Robert M. , Skiba Ute M. , Smallman Luke T. , Toet Sylvia , Williams Mathew , Blei Emanuel
Published: March 2020

Managed grasslands are extensive terrestrial ecosystems that provide a range of services. In addition to supporting the world’s various livestock production systems they contain climatically significant amounts of carbon (C). Understanding and quantifying the C dynamics of managed grasslands is complicated yet crucial.This presentation describes a process-model of C dynamics in managed grasslands (DALEC-Grass). DALEC-Grass is a model of intermediate complexity, which calculates primary productivity, dynamicallyallocates C to biomass tissues and describes the impacts of grazing/harvesting activities. The model is integrated into a Bayesian model-data fusion framework (CARDAMOM). CARDAMOM uses observations of ecosystem functioning (e.g. leaf area, biomass, C fluxes) to optimise the model’s parameters while respecting a set of biogeochemical and physiological rules. The model evaluation results presented demonstrate the model’s skill in predicting primary productivity and C allocation patterns in UK grasslands using both ground and satellite based leaf area index (LAI) time series as observational constraints.
A new method for the detection of incompressible turbulence as a deviation from the hydrostatic balance assumption
Authors: Šácha Petr , Pišoft Petr
Published: March 2020

This study aims at introducing a simple and physically consistent method for identification and analysis of turbulent layers in the free atmosphere that can supplement the traditional methods (Richardson number criterion, Thorpe scale). The method is based on differences between the observed and hydrostatically derived (with floating level of initialization) pressure. In the paper we derive the method analytically from the Navier Stokes equations and propose a methodology how to isolate information on turbulence from an internal gravity wave and atmospheric structure signal in the pressure differences. Finally we apply the methodology on high vertical-resolution radiosonde data to demonstrate the utility of the novel method by contrasting the results with traditional diagnostics. 
Unravelling rift development: a key study from the Northern Volcanic Zone of Iceland
Authors: Russo Elena , Tibaldi Alessandro , Bonali Fabio Luca , Pasquarè Mariotto Federico , Einarsson Páll , Hjartardóttir Ásta Rut
Published: March 2020

Unravelling the kinematics, development and origin of the structures along a volcano-tectonic rift is of paramount importance for understanding plate separation, seismicity, volcanic activity and the associated hazards. Here, we focus on an extremely detailed survey of the Holocene deformation field along the Northern Volcanic Zone of Iceland, the northernmost point of emergence of the Mid-Atlantic Ridge. The study of this extremely dynamic rift is also useful for a better comprehension of how mid-oceanic ridges work. The study is based on extensive field and unmanned aerial vehicle surveys performed over the last four years, completed by about 6000 measures collected at 1633 sites on fault strike, dip and offset, and fracture strike, dip, dilation direction and dilation amount. The rift, named Theistareykir Fissure Swarm, is composed of N-S to NNE-SSW-striking normal faults and extension fractures affecting an area 8 km-wide and 34 km-long. The computed overall spreading direction is N111° averaged during Holocene times, with values of N125° to the north and N106° to the south. The kinematics is characterised by the presence of complex components of right-lateral and left-lateral strike-slip motions, with a strong predominance of right-lateral components along structures parallel and coeval to the rift zone. The surveyed 33 Holocene faults (696 sites of measurement) along the central part of the rift show two opposite directions of fault/rift propagation, based on fault slip profile analyses. We discuss the possible causes of these characteristics and analyse in detail the interaction of both faults and extension fractures with the WNW-ESE transform Tjornes Fracture Zone, and in particular with the parallel right-lateral Husavik-Flatey Fault in the central part of the rift, and the Grimsey Lineament to the north. We also assess the role of: i) repeated dyke intrusions from the magma chamber outward along the plate margin, ii) regional tectonic stresses, iii) mechanical interaction of faults, and iv) changes in the rheological characteristics of rocks.
4D imaging of the seismic energy release before the 2011 El Hierro eruption (Canary Islands)
Authors: García-Hernández Rubén , D'Auria Luca , Barrancos José , Padilla Germán D.
Published: March 2020

The estimation of the spatial and temporal variations of the b-value of the Gutenberg-Richter law is of great importance in different seismological applications. However, its estimate is strongly dependent upon the selected spatial and/or temporal scale due to the heterogeneous distribution of the seismicity. This is especially relevant in volcanic and geothermal areas where dense clusters of earthquakes often overlap to the background seismicity.

For this reason, we propose a novel multiscale approach allowing a consistent estimation of the b-value regardless of the considered spatial and/or temporal scales. Our method, named MUST-B (MUltiscale Spatial and Temporal estimation of the B-value), basically consists in computing estimates of the b-value at multiple temporal and spatial scales, extracting for a given spatio-temporal point a statistical estimator of its value, as well as an indication of the characteristic spatio-temporal scale. This approach includes also a consistent estimation of the completeness magnitude (Mc) and of the uncertainties over both b and Mc, as well as, estimates of the seismic energy release rates.

We applied this method to the seismic datasets of El Hierro submarine eruption, started on October 2011 and linked to a precursor seismic unrest episode that initiated on July 2011. The seismicity showed a very complex spatial distribution, which also changed over time, showing a migration from the north of the island to the south. Results show that the high resolution 4D mapping is of great importance to understand the distribution of the seismic energy release in volcanic islands, which is possibly correlated to a variable geothermal fluid flow paths and/or magmatic sources. What is also remarkable is that even in highly heterogeneous catalogues, as for the 2011 El Hierro dataset, the MUST-B method could provide reliable estimates.
Mapping surface rock exposures to enhance geohazard susceptibility assessment: a random forest approach
Authors: Williams Chris , Finlayson Andrew , Palamakumbura Romesh , Kearsey Tim , Cornillon Severine , Whitbread Katie
Published: March 2020

We present the approach taken to map surface rock exposures in upland areas of Scotland. This has been carried out as a means of enhancing the mapping of superficial sediment thickness which has important applications including the assessment of potential geohazard susceptibility. The presented study includes selected test cases that have been constructed prior to scaling up the approach to upland areas across Great Britain (GB).

The presence of rock at surface acts as a marker of locations with minimal superficial sediment cover (essentially a zero depth). The thickness of superficial sediments across GB are currently estimated based on borehole records which range in both quality and coverage, with limited data particularly for upland regions. Superficial sediment thickness is an integral factor for assessing geohazard processes including landslides. Therefore, by improving datasets detailing rock at surface, we can enhance superficial sediment thickness estimates and enhance the variable inputs to the models used to assess geohazard susceptibility.

The GB landscape has been subject to a range of different environmental processes through time with its current topography being the subject of glacial erosion through to marine incursions. However, these patterns are not uniform and this results in a range of landscapes. The resulting domains are an important consideration when attempting to model the relationship between the presence and absence of natural rock exposures.  With a wealth of information available across GB including high resolution topography, the resulting (often scale-dependent) geomorphometric derivatives, geological datasets as well as satellite imagery, we are able to consider a range of possible relationships that might exist. We combine these datasets coupled with field validation of rock absence/presence to train a random forest classifier for specific domains with the aim being to identify a way of modelling rock exposure in areas of limited data availability as is the case for many upland areas.

The methodology and results of the approach for specific process domains will be presented with a specific focus on the Glen Gyle catchment, at the head of Loch Katrine (the primary water reservoir for the city of Glasgow) in the Trossachs National Park, Scotland. This is an area that has been subject to recent landslides which have affected local properties and infrastructure.
Weakly and strongly coupled data assimilation with the coupled ocean-atmosphere model AWI-CM
Authors: Tang Qi , Mu Longjiang , Sidorenko Dmitry , Nerger Lars
Published: March 2020

In this study we compare the results of strongly coupled data assimilation (SCDA) and weakly coupled data assimilation (WCDA), and among the different WCDAs by analyzing the assimilation effect on the prediction of the ocean as well as the atmosphere variables. We have implemented the parallel data assimilation framework (PDAF, http://pdaf.awi.de) with the AWI climate model (AWI-CM), which couples the ocean model FESOM and the atmospheric model ECHAM. In the WCDA, the assimilation acts separately on each component in the coupled model and observations of one component only directly influence its own component. The other components can benefit from the DA through the model dynamics. The alternative to WCDA is SCDA, in which the atmosphere as well as the ocean variables are updated jointly using cross-covariances between the two components. Our current system allows both the SCDA and the WCDA. For the SCDA configuration, either the ocean observations (e.g., satellite sea surface temperature, profiles of temperature and salinity) or the atmosphere observations (e.g., air temperature, surface pressure) or both of them can be assimilated to update the ocean as well as the atmosphere variables. For the WCDA, it allows 1) assimilating only the ocean observations into the ocean state; 2) assimilating only the atmosphere observations into the atmosphere state; 3) assimilating both types of observations into the corresponding component models. The results are evaluated by comparing the estimated ocean and atmosphere variables with the observational data.
On the scale sizes of magnetosheath jets
Authors: Plaschke Ferdinand , Hietala Heli
Published: March 2020

The subsolar magnetosheath is oftentimes permeated by jets. These are localized entities of enhanced dynamic pressure with respect to the ambient plasma. Magnetosheath jets are thought to arise from bow shock ripples and/or foreshock structures. They can easily propagate through the entire magnetosheath and impact on the magnetopause, where they can cause large amplitude indentations, launch magnetopause surface waves, or modulate magnetopause reconnection. The scale size distributions of magnetosheath jets observed by single spacecraft are relatively well modeled by exponential functions with characteristic scales of 0.71 Earth radii (RE) and 1.34 RE in the directions parallel and perpendicular to the jet propagation direction, respectively. However, these functions do not represent the actual, true jet scale size distributions, because of two reasons: (1) Spacecraft are much more likely to observe large scale jets rather than small scale jets. Hence, the observed scale size distributions are biased towards larger scales. (2) The distributions modeled by exponential functions highly overestimate observation probabilities of jets of smallest scales (on the order of 0.1 RE). We overcome both shortcomings by replacing the exponential functions by log-normal functions, which can be corrected for the bias. By re-analyzing THEMIS multi-spacecraft data, we obtain, for the first time, unbiased, i.e., actual jet scale size distributions. Our results reveal a large population of jets of smallest scales that have not been accounted for, so far. Consequently, we find median scale sizes of jets to be about an order of magnitude smaller than previously thought: 0.15 and 0.12 RE in the parallel and perpendicular directions, respectively.
Modeling methane from the North Sea region with ICON-ART
Authors: Scharun Christian , Ruhnke Roland , Schröter Jennifer , Weimer Michael , Braesicke Peter
Published: March 2020

Methane (CH4) is the second most important greenhouse gas after CO2 affecting global warming. Various sources (e.g. fossil fuel production, agriculture and waste, biomass burning and natural wetlands) and sinks (the reaction with the OH-radical as the main sink contributes to tropospheric ozone production) determine the methane budget. Due to its long lifetime in the atmosphere methane can be transported over long distances.

Disused and active offshore platforms can emit methane, the amount being difficult to quantify. In addition, explorations of the sea floor in the North Sea showed a release of methane near the boreholes of both, oil and gas producing platforms. The basis of this study is the established emission data base EDGAR (Emission Database for Global Atmospheric Research), an inventory that includes methane emission fluxes in the North Sea region. While methane emission fluxes in the EDGAR inventory and platform locations are matching for most of the oil platforms almost all of the gas platform sources are missing in the database. We develop a method for estimating the missing sources based on the EDGAR emission inventory.

In this study the global model ICON-ART (ICOsahedral Nonhydrostatic model - Aerosols and Reactive Trace gases) will be used. ART is an online-coupled model extension for ICON that includes chemical gases and aerosols. One aim of the model is the simulation of interactions between the trace substances and the state of the atmosphere by coupling the spatiotemporal evolution of tracers with atmospheric processes. ICON-ART sensitivity simulations are performed with inserted and adjusted sources to access their influence on the methane and OH-radical distribution on regional (North Sea) and global scales.
High magma flux beneath Corbetti caldera (Ethiopia) accommodated by a ductile and compressible reservoir
Authors: Gottsmann Joachim , Biggs Juliet , Lloyd Ryan , Biranhu Yelebe , Lewi Elias
Published: March 2020

Large silicic magma reservoirs preferentially form in the upper crust of 

extensional continental environments. However, our quantitative understanding of the link between mantle magmatism, silicic reservoirs and surface deformation during rifting is very limited. Here, we focus on Corbetti, a peralkaline caldera in the densely-populated Main Ethiopian Rift, which lies above a focused zone of upper mantle partial melt and has been steadily uplifting at ≤6.6±1.2 cm yr−1 for more than ten years. We show that a concomitant residual gravity increase of ≤9±3 μGal yr−1 by the intrusion of mafic magma at ∼7 km depth into a compressible and inelastic crystal mush best explains the uplift. The derived magma mass flux of ∼10^11 kg yr−1 is anomalously high

and at least one order of magnitude greater than the mean long-term mass

eruption rate. We demonstrate that periodic and high-rate magmatic rejuvenation of upper-crustal mush is a significant and rapid contributor to mature continental rifting.
Sensitivity of Summertime Heatwaves to Vegetation Cover in the Northern Hemisphere
Authors: Li Jing , Tam Chi-Yung , Tai Amos P. K. , Lau Ngar-Cheung
Published: March 2020

Heatwaves are a serious threat to society and can lead to grave consequences. It is well known that persistent large-scale circulation anomalies are the key to generating heatwaves. Vegetation plays a vital role in energy and water exchange between land and atmosphere, through its responses to incoming radiation and emission of longwave radiation, its imposition of surface friction and transpiration. However, its impact on surface energy exchange during heatwaves is largely unknown. In this study, we first analyzed the relationship between summer heatwaves and vegetation cover, based on the Global Heatwave and Warm-spell Record (GHWR) and leaf area index (LAI) products from satellites during 1982-2011. Our results revealed differences in the correlation between heatwave characteristics and summertime LAI in different regions. In particular, lower LAI over Central Europe is associated with more frequent heatwaves locally. Over the south to the southeastern part of North America, a similar negative correlation is found. However, in the northeastern part of the continent, the reverse tends to be true, with higher-than-normal LAI associated with an increase of heatwave occurrence. These findings are in general supported by composite analyses of extreme LAI years in these regions and heatwave characteristics therein.

We speculate that the difference between surface heat flux responses for different vegetation types during heatwaves may explain the results. Focusing on North America, and using various datasets including those generated by the Global Land Data Assimilation System (GLDAS) with three different land surface models (CLM, MOS, NOAH), three reanalysis datasets (MERRA-2, NOAA-CIRES-DOS, NCEP/NCAR), and also observations from an extensive network of flux towers, it was found that over coniferous forests (both boreal and temperate), the sensible heat anomalies increase significantly during heatwaves in high-LAI years. Also, during high-LAI years, over boreal evergreen forests (BEF), changes of latent heat anomalies are much smaller than positive sensible heat anomalies, so that BEF can prolong and amplify heatwaves significantly. On the other hand, for temperate deciduous forests (TDF) and grassland (GSL), both negative sensible heat anomalies and positive latent heat anomalies during heatwaves are found in all datasets; these response act to weaken the heatwave amplitudes. Model experiments were further carried out, in order to test the sensitivity of heatwaves to LAI forcings. It was found that heatwaves are most sensitive to BEF LAI variations, but the response of heatwaves are opposite between middle and high latitudes when BEF LAI increased. For TDF and GSL, heatwaves shortened slightly when LAI increased.
The continental shelf and rifted continental margins of offshore Newfoundland revisited using constrained 3-D gravity inversions: tracking inheritance trends and rift scars
Authors: Welford J. Kim , Geng Meixia
Published: March 2020

The rifted continental margins of Newfoundland represent one of the best-studied examples of non-volcanic/magma-poor margins in the world. In addition to hosting proven prolific resources within the rift basins on the continental shelf, the rifted margins also host many promising frontier regions for oil and gas exploration in both the Flemish Cap and Orphan basins. Prior to rifting and opening of the North Atlantic Ocean during the breakup of Pangaea, the Newfoundland margins lay conjugate to the Iberian margin to the southeast and the Irish Atlantic margin to the northeast. Rifting and breakup evolved from south to north during three rift phases of varying orientation: NW-SE oriented Late Triassic-Early Jurassic rifting between Iberia/Eurasia and North America, W-E oriented Late Jurassic to Early Cretaceous rifting between Eurasia (Ireland) and North America, and SW-NE oriented Late Cretaceous rifting in the Labrador Sea. While the first phase of rifting exploited pre-existing Caledonian-Appalachian basement structures and tectonic fabrics, later rifting reactivated and crosscut these same inherited structures.

While multichannel seismic reflection imaging has been extensively undertaken across the Newfoundland shelf and rifted margins, deep crustal structure from seismic refraction profiling has been more sparsely constrained. To interpolate between existing crustal-scale seismic refraction profiles, constrained 3-D gravity inversion has previously been undertaken, providing regional constraints on Moho depth, crustal thickness, and beta factors. However, these early inversion attempts suffered from coarse parameterizations of densities within the sedimentary column and an inability to incorporate sparse deep seismic constraints. In this work, we present 3-D density anomaly models for the crust and upper mantle across the Newfoundland margin using constrained 3-D gravity inversions performed using two independent inversion methodologies (minimum structure and probabilistic). Common features to both inversions are deemed robust and provide an improved regional view of the crustal architecture of the offshore margins. In particular, crustal thinning is observed to align with earlier projections of ancient terrane boundaries such as the boundary between the Avalonian terrane and the Meguma terrane at the southeastern limit of the Grand Banks. Furthermore, the derived crustal thicknesses also provide a clear means of delimiting rafted continental fragments, revealing rift trends and the resulting crustal scars. This is particularly evident for the Orphan Basin where the southeastward rotation and displacement of the Flemish Cap has left a trail of orphaned continental pieces. These form crucial components for future deformable plate reconstructions in GPlates and, until then, provide a detailed regional view of the segmentation of the margin during rifting.