bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling serpentinite dehydration on multiple scales constrained by field observations
Authors: Huber Konstantin , John Timm , Vrijmoed Johannes C.
Published: March 2020

Dehydration of serpentinites in subduction zones plays a major role in Earth's deep water cycle. The fact that there is still water present at the Earth's surface indicates an efficient fluid release mechanism that is able to keep up with transport of water into the mantle by subduction. Rock dehydration itself is a multi-scale process that spans several orders of magnitudes in both time and spatial scales. 
Plümper et al. (2016) showed that on small scales (µm-mm) dynamic porosity generation and fluid flow is mainly controlled by intrinsic chemical heterogeneities in the rock. However, field observations indicate that on larger scales the process might be mechanically dominated by the formation of a channelized system of hydraulic fractures that form during pulsed fluid release which occurs on much shorter time scales. To get a better understanding of the multi-scale formation of a channelized fluid network a mathematically and thermodynamically valid model is needed that describes the process of rock dehydration crossing a range of scales over several orders of magnitudes. The project is therefore in collaboration with mathematicians as part of the DFG funded CRC 1114. As a first step we want to extend the model of Plümper et al. (2016) by considering chemical transport during reactive fluid flow and upscale it by one order of magnitude, from the mm- to the cm-scale. 
In order to understand the chemical and structural heterogeneities in non-deformed serpentinites we mapped and sampled an outcrop in the Mirdita ophiolite in Albania. These serpentinites are still fully hydrated due to ocean floor serpentinization and show information about intrinsic heterogeneities of serpentinized mantle as it enters the subduction zone. We will use these data as input for the extended model that aims to simulate serpentinite dehydration in the downgoing slab.
We present the results of field work in the Mirdita ophiolite and the results of the preliminary extended and upscaled model. Geological mapping has been done on an outcrop scale as well as detailed mapping of representative units in order to get information about structural and lithological heterogeneities that might influence the formation of the dehydration vein network on large scales. The samples were then further studied by EDX mapping, XRF and detailed electron microscopy. Of special interest will be the coupling of the chemical and mechanical processes on different scales and what controls the transition from a chemically to a mechanically dominated system.

Reference

Plümper, Oliver et al. (Dec. 2016). "Fluid escape from subduction zones controlled by channel-forming reactive porosity".
In: Nature Geoscience 10.2, pp. 150-156. doi:10.1038/ngeo2865.
The structure of the Central-Eastern Rif (Morocco) and the disregarded subduction of the North-West African paleo-margin
Authors: Gimeno Oriol , Frizon de Lamotte Dominique , Leprêtre Rémi , Haissen Faouziya , Atouabat Achraf , Mohn Geoffroy
Published: March 2020

The Rif Belt (Northern Morocco) forms the western edge of the Alpine-Himalayan orogenic system developed during the convergence between the Africa and Eurasia plates. Compared to other mountains belts, the External Rif, which preserves remnants of the North African paleo-margin, presents two unusual features: (1) the presence of metamorphic massifs [External Metamorphic Massifs (EMMs)] and (2) the existence of large allochthonous thrust-sheets that travelled far away [the Higher Nappes]. In this contribution, we combined structural, stratigraphic and metamorphic data, complemented by new field observation and thermochronology results, to revisit the structure of the External Rif and to review its Cenozoic evolution. The External Rif was the site of a poly-phased tectonic evolution recorded before and after of a major unconformity: the so-called “Mesorif Unconformity” postdating an important Midde-Late Eocene deformation. This tectonic event is well-preserved in the North-African paleo-margin because of its under-thrusting (“subduction”) below the Maghrebian Tethys, the former oceanic domain separating Iberia from Africa. The MP-LT metamorphism, recorded in the EMMs (Temsamane Units in Morocco), is a direct vestige of this process.  By contrast, traces of this event are absent in the oceanic units of the Intrarif Domain, element of the Maghrebian Tethys. After the “Mesorif Unconformity”, i.e. during the Miocene, the regional geodynamics is dominated by the westward translation of the Alboran Domain and the coeval deformation of the Ketama Unit (Intrarif) in front of it. This process results directly from the subduction of the Maghrebian Tethys, which happened at that time. The docking of the Ketama Unit against the already exhumed EMMs allowed an uplift and the subsequent detachment of the top of its lithostratigraphic pile, individualizing the Higher Nappes. During their gravity-driven travel towards the foredeep basin, they dragged at their floor the already exhumed Senhadja Nappes, inherited from the distal-most part of the NW African margin. All these elements are integrated in a coherent model integrating the External Rif in the geodynamics of the West Mediterranean.
On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake
Authors: D'Acquisto Mario , Herman Matthew , Govers Rob
Published: March 2020

During and after a large megathrust earthquake, the overriding plate above the rupture zone moves oceanward. Enigmatically, the post-seismic motion of the overriding plate after several recent large earthquakes, further along strike from the rupture zone, was faster in the landward direction than before the event. Previous studies interpreted these changes as the result of increased mechanical coupling along the megathrust interface, transient slab acceleration, or bulk postseismic deformation with elastic bending mentioned as a possible underlying mechanism. Before invoking additional mechanisms, it is important to understand the contribution of postseismic deformation processes that are inherent features of megathrust earthquakes. We thus aim to quantify and analyse the deformation that produces landward motion during afterslip and viscous relaxation. 

We use velocity-driven 3D mechanical finite element models, in which large megathrust earthquakes occur periodically on the finite plate interface. The model geometry is similar to most present-day subduction zones, but does not exactly match any specific subduction zone. 

The results show increased post-seismic landward motion at (trench-parallel) distances greater than 450 km from the middle of the ruptured asperity. Similar patterns of landward motion are generated by viscous relaxation in the mantle wedge and by deep afterslip on the shear zone downdip of the brittle megathrust interface. Landward displacement due to postseismic relaxation largely accumulates at exponentially decaying rates until ~6 Maxwell relaxation times after the earthquake. The spatial distribution and magnitude of the velocity changes is broadly consistent with observations related to both the 2010 Maule and the 2011 Tohoku-oki earthquakes.  

Further model experiments show that patterns of landward motion due to afterslip and to viscous relaxation are insensitive to the locking pattern of the megathrust. However, the locking distribution does affect the magnitudes of the displacements and velocities. Results show that the increased landward displacement due to postseismic deformation scales directly proportionally to seismic moment. 

We conclude that the landward motion results from in-plane horizontal bending of the overriding plate and mantle. This bending is an elastic response to oceanward tractions near the base of the plate around the ruptured asperity, causing extension locally and compression further away along-trench. This elastic in-plate bending consistently contributes to earthquake-associated changes in surface velocities for the biggest megathrust earthquakes, producing landward motion along strike from the rupture zone.
On the energy balance behind frictional ruptures
Authors: Barras Fabian
Published: March 2020

Earthquake ruptures are driven by the dynamic weakening of frictional strength along faults. This drop of frictional stress toward a residual level is at the origin of the slip-weakening model, which became a well-established framework to study seismic ruptures and their energy budget. In this framework, the part of frictional energy associated to the rupture propagation (i.e. the fracture energy) corresponds to the excess of frictional dissipation on top of the residual stress, also referred as the breakdown work.

In this study, we test this energy partition for friction models that do not impose the magnitude of the residual stress. For example, rate-and-state models are a class of generic friction laws for which the residual stress after the rupture emerges from the interplay with the bulk elastodynamics. In this context, we simulate a frictional rupture at the interface between two linearly elastic solids and study the energy balance driving its propagation. Using dynamic fracture mechanics, we independently measure throughout the rupture the energy release rate from the bulk elastic fields and the frictional dissipation along the interface. From the comparison between these two quantities, we identify the part of interface dissipation corresponding to the fracture energy and show how the latter can be significantly smaller than the total breakdown work.

In a second phase, we test the generality of these results along another type of interface representative of mature fault zones filled with gouge.

This study shines new light on the energy budget of frictional ruptures and finds implications in the estimation of the fracture energy during earthquakes.
Can ocean deoxygenation accelerate global warming via enhanced marine N2O production?
Authors: Landolfi Angela , Koeve Wolfgang
Published: March 2020

Ocean warming is projected to cause marine deoxygenation, reduce solubility, affect ocean circulation and enhance metabolic rates over this century. These changes, affecting oceanic N2O production and emissions, have been suggested to potentially rise atmospheric N2O concentrations and increase the positive feedback to anthropogenic climate change.However, current global model projections all suggest a decline in marine N2O emissions under global warming but the processes leading to this decline are poorly constrained. Here, using an Earth system model of intermediate complexity, we disentangle the contribution of ocean deoxygenation and the direct and indirect warming effects on oceanic N2O production and emissions changes under RCP8.5 emission scenario. We find that ocean deoxygenation and warming-reduced N2O solubility do in fact increase oceanic N2O emissions, however this increase is overcompensated by ocean circulation slow-down and reduced export production, suggesting a neglectable N2O-emssion feedback to climate on centennial timescales.
Comparing Arctic Sea Ice Model Simulations to Satellite observations by Multiscale Directional Analysis of Sea Ice Deformation
Authors: Mohammadi Aragh Mahdi , Losch Martin , Goessling Helge
Published: March 2020

Sea ice models have become essential components of weather, climate and ocean models. The reliability of process studies, environmental forecasts and climate projections alike depend on a realistic representation of sea ice. Developing and evaluating sea ice models requires methods for both large scales and fine-scale geomorphological structures such as linear kinematic features (LKF). We introduce a Multiscale Directional Analysis (MDA) method that diagnoses distributions of LKF orientation and intersection angles. The MDA method is different from previous methods in that it (a)  takes into account the width of LKFs instead of estimating the orientation of centerlines; (b) separates curve-like features from point-like features providing the opportunity to reach a unified definition of LKF in both numerical and observational fields; (c) estimates scale-dependent intersection angles.
Impact of long-term experimental water level drawdown on vegetation and carbon gas dynamics of boreal mire ecosystems
Authors: Tuittila Eeva-Stiina , Korrensalo Aino , Laine Anna , Kokkonen Nicola , Mehtätalo Lauri , Laine Jukka
Published: March 2020

Recent paleoecological studies have demonstrated an ongoing drying trend in temperate and boreal peatlands in Europe and in Canada. This drying is likely to alter vegetation and carbon gas exchange with atmosphere. However, to revel the expected change in carbon gas dynamics associated with decrease in water level experimental studies and long-term monitoring are needed. In here we present results from long term experiment in Finland where the impact of water level drawdown (WLD) of ~10 cm on three different peatland sites, two fens and a bog, has been studied since year 2000.

 

Response to WLD differed between the three ecosystem types. In the nutrient rich fen WLD initiated rapid directional succession from sedge dominated system to the dominance of woody species. In the poor fen changes were less drastic: Initially WLD benefitted dwarf scrubs already present at the site, later they were overtaken by pines.  Sedges as a group hold their position but Carex species were replaced by Eriophorum. Similarly to sedges, in the moss layer proportions of different Sphagnum moss species changed. Bog vegetation was more stable than fen vegetation.

 

In all the ecosystems methane emissions decreased directly after WLD. In contrast, the response of CO2 dynamics was more complex. While long term net ecosystem exchange decreased to lower level than in controls in all studied ecosystems, the response of photosynthesis and respiration differed between the three ecosystems and between short term and long term. Results show how the response of peatlands to climate change is diverse and emphasize the need to understand what factors regulate the stability and resilience of peatland functioning.
Modelling soil carbon stocks in semi-natural and agro-ecosystems – quantifying national scale impacts of the Anthropocene
Authors: Janes-Bassett Victoria , Davies Jessica , Bassett Richard , Yumashev Dmitry , Rowe Ed , Tipping Edward
Published: March 2020

Throughout the Anthropocene, the conversion of land to agriculture and atmospheric deposition of nitrogen have resulted in significant changes to biogeochemical cycling, including soil carbon stocks. Quantifying these changes is complex due to a number of influential factors (including climate, land use management, soil type) and their interactions. As the largest terrestrial store of carbon, soils are a key component in climate regulation. In addition, soil carbon storage contributes to numerous ecosystem services including food provision. It is therefore imperative that we understand changes to soil carbon stocks, and provide effective strategies for their future management.

Modelling soil systems provides a means to estimate changes to soil carbon stocks. Due to linkages between the carbon cycle and other major nutrient cycles (notably nitrogen and phosphorus which often limit the productivity of ecosystems), models of integrated nutrient cycling are required to understand the response of the carbon cycle to global pressures. Simulating the impacts of land use changes requires capacity to model both semi-natural and intensive agricultural systems.

In this study, we have developed an integrated carbon-nitrogen-phosphorus model of semi-natural systems to include representation of both arable and grassland systems, and a range of agricultural management practices. The model is applicable to large spatial scales, as it uses readily available input data and does not require site-specific calibration.  After being validated both spatially and temporally using data from long-term experimental sites across Northern-Europe, the model was applied at a national scale throughout the United Kingdom to assess the impacts of land use change and management practices during the last two centuries. Results indicate a decrease in soil carbon in areas of agricultural expansion, yet in areas of semi-natural land use, atmospheric deposition of nitrogen has resulted in increased net primary productivity and subsequently soil carbon. The results demonstrate anthropogenic impacts on long-term nutrient cycling and soil carbon storage, and the importance of integrated nutrient cycling within models.
Global ocean surface stratifications due to rain based on ERA5
Authors: Bellenger Hugo , Perrot Xavier , Guez Lionel , Duvel Jean-Philippe , Supply Alexandre , Boutin Jacqueline , Reverdin Gilles
Published: March 2020

Temperature and Salinity at the ocean interface can be substantially different than their bulk values in the ocean mixed layer at 5-10 meters depth. The main phenomena that account for these differences are (i) the interfacial millimeter scale diffusive microlayer usually cooler and saltier than below due to surface fluxes and (ii) diurnal warm layers of few tens of centimeters to few meters that form under weak wind condition due to solar absorption. Although characterized by small vertical scales, these tightly wind-related phenomena corresponds to coherent structures up to the large-scale where they can impact air-sea exchanges of heat, water and chemical species. Another phenomenon that can impact global air-sea exchanges is the freshwater lenses produced by rain. Rain freshens and cools the ocean surface, as raindrops temperature is usually lower than surface temperature. The induced negative salinity anomaly enables surface cold anomalies to be sustained and further cooled down by surface fluxes after rain has ceased. This study presents a first global estimate of basic statistics rain-induced ocean surface freshening and temperature changes and of their variations with seasons.
Importance of the non-linearity of the convective response to surface temperature for eastern Pacific El Niños
Authors: Gangiredla Srinivas , Vialard Jerome , Izumo Takeshi , Lengaigne Matthieu , Guilyardi Eric
Published: March 2020

 Understanding the key physical processes involved in the development and diversity of El Niño events is essential to anticipate their multiple impacts. Current El Niño theories generally assume that wind stress responds linearly to El Niño Sea Surface Temperature (SST) anomalies. Yet, the deep atmospheric convection that energizes this wind stress response has obvious nonlinear features. Observations indeed indicate that rainfall (a proxy of the tropospheric heating) increases slowly with SST up to 26.5OC, followed by a sharp increase of rainfall at higher SSTs. In this study, we use that mean observed relation to derive a nonlinear relation between SST and rainfall anomalies, that depends on the background climatological SST. This relation performs much better to explain rainfall anomalies in the eastern Pacific (Niño3 region) than a linear relation, which underestimates rainfall during most extreme El Niños events. On the other hand, it underestimates rainfall anomalies in the western Pacific (Nino4), because it only considers the local SST forcing and neglects the atmospheric convergence feedback. Our observational results are in line with previous modeling studies, who have also underlined the importance of the nonlinearity of the convective response to SST anomalies for large El Niño events in coupled models. We end by discussing other possible sources of nonlinearity in the wind stress and heat flux responses to SST, which play a strong role in the most essential El Niño feedbacks.
Progress towards atmospheric isotope ratio carbon dioxide and nitrous oxide reference materials that meet the WMO-GAW data quality objectives for compatibility
Authors: Hill-Pearce Ruth , Mussell Webber Eric , Hillier Aimee , Moossen Heiko , Worton David , Brewer Paul
Published: March 2020

Widely available reference materials that are traceable and consistent with international stable isotope scales are necessary in order to create a robust and sustainable global measurement infrastructure for isotope ratio of CO2 and N2O.

We report on progress towards the production and certification of atmospheric amount fraction greenhouse gas reference materials with isotope ratios spanning the full atmospheric range. Reference materials are produced with a chosen delta value with uncertainties aiming to achieve the WMO GAW data quality objectives for extended compatibility of delta value of of ∂13C-CO2 and ∂18O-CO2 of 0.1‰ (northern hemisphere) and amount fraction of 0.2 µmolmol-1 for CO2 and 0.3 nmolmol-1 for N2O at atmospheric amount fraction ranges.

To illustrate the work towards these challenging goals we present studies of sampling technique and isotope ratio stability with storage, pressure and cylinder passivation. The precision of blending and dilution of source gases is presented alongside studies of measurement instrument precision and drift. Contributing factors from matrix gases are also discussed. 
Investigate the softening properties of weak interlayers in slope failure process using nanoindentation test and simulation
Authors: Xu Jingjing , Feng Yufei , Tang Xuhai
Published: March 2020

This work proposed an available approach to analyze the property evolution of weak interlayers during immersion softening at micro and macro scales, which combining the advantages of nanoindentation tests and numerical modelling. The weak interlayers has significant impact on the failure process of natural slopes, however, their properties are difficult to be obtained using traditional triaxial compression tests. Because these weak interlayers are consist of clay and rock fragments which leads to the difficult to prepare intact samples. Additionally, the softening properties of these weak interlayers are strongly related to their fillings at micro scale. In this work, the weak interlayers is investigated using nano-scale micromechanical tests and upscaling methodologies, so only small rock fragments are required (see Fig.1). 
In northwestern Hubei China, the mountains often developed several layers of weak interlayers with major lithology as shale which is sedimentary rock with low strength and dense clay particles. We investigated these shale fragments in weak interlayers, which is prone to decrease in strength induced by precipitation erosion. The Gaussian mixture model was used to analyze a large amount of data obtained by statistical grid nanoindentation method. Then the Mori-Tanaka scheme was used to homogenize the elastic properties of the samples and upscale the nanoindentation data to the macroscale. The hardness values which obtain by Berkovich and Cube corner indenter were able to assess the cohesion and friction angle of shale. Finally, these achieved parameters were applied in numerical model, in order to analyze the slope failure caused by the softening of weak interlayers (see Fig. 2).
The results show that: (1) the chlorite and muscovite minerals, which are major proportion of shale, soften or dissolve with the increasing saturation time. The fine mineral particles are gradually stripped from micro structure. As a result, at microscale the compact shale samples sale became loose. The strength of these shale samples are also decrease because water seeped through pores and micro cracks. (2) After water immersion, the friction angle is almost constant, while the elastic modulus and cohesion decrease significantly with increasing saturation time. (3) The shear strength decrease so that the shearing creep occurs along the weak interlayers surface, then bottom sliding surface is cut, which leads to landslide.
Differences in the ERA5-Land reanalysis and real observation datasets for calculation of drought indices from two distinct points
Authors: Babre Alise , Bikse Janis , Popovs Konrads , Kalvans Andis , Delina Aija
Published: March 2020

Even though, droughts usually correspond to smaller latitudes, during the last decade Latvia has faced several long-term drought events. This have caused awareness of more frequent drought episodes in future due to climate change. Accurate and complete meteorological data are required to calculate realistic drought indices and to estimate drought probability in the future.

In places were direct meteorological observation data are absent or dataset is incomplete and not sufficient, data from numerical weather forecasting reanalysis such as ERA5 can be used instead or along with direct observations. Reanalysis provide comprehensive snapshots of conditions at regular intervals over long time periods — often years or decades. The European Center for Medium-Range Weather Forecasts (ECMWF) has released its latest reanalysis product, the ERA5-Land dataset (C3S, 2019).

The goal of this study is to evaluate the ERA5-Land reanalysis product as a substitute for observations in meteorological stations for calculation of drought related indices for time period from 1981 to 2018.  Two meteorological stations more than 200 km apart in Latvia - Riga and Rezekne - were considered. 

Meteoric and agricultural drought indices were calculated with freely available software DrinC (Tigkas et.al., 2013) as well as R – packages spei and pdsi - using monthly mean reanalysis as well as observed meteorological data as input. It is found that meteorological parameters as well as drought indices have high consistency between two data sources. 

References:

Copernicus Climate Change Service (C3S) (2019): C3S ERA5-Land reanalysis. Copernicus Climate Change Service, 12.12.2019.

Tigkas, Dimitris & Vangelis, Harris & Tsakiris, George. (2013). The Drought Indices Calculator (DrinC).

The study is supported by fundamental and applied science research programme, project No.: lzp-2019/1-0165 “Spatial and temporal prediction of groundwater drought with mixed models for multilayer sedimentary basin under climate change”.
The transdisciplinary approach on coastal hydrogeosystems: tracing back socioenvironmental trajectories and water policies evolution to improve their management and adaptability
Authors: Erostate Melanie , Ghiotti Stephane , Huneau Frederic , Garel Emilie , Pasqualini Vanina
Published: March 2020

The Mediterranean coasts are subject to multiple environmental risks (erosion of the coastline, marine submersion, flooding, degradation of water quality) and overdeveloped anthropogenic pressures (urbanization, tourism, agriculture, industry, etc.). These natural and anthropogenic pressures already affect water resources and dependent coastal wetlands. For these coastlines, which are particularly rich in biodiversity, the consequences could get worse in the coming years as a result of climate change. In this context of increasing pressures, understanding the dynamics/trajectories of coastal hydrosystems appears to be the only robust approach allowing the establishment of integrated water resource management and territorial sustainability.  

To this end, this study proposes to demonstrate how the transdisciplinary approach between environmental sciences (hydrology, hydrogeology, hydroecology and geosciences) and human sciences (geography, cartography, history, anthropology) allows the production of a particularly rich common knowledge, which makes it possible to accurately analyze the dynamics and trajectories of coastal hydrosystems. Two coastal hydrosystems have been studied: the Biguglia lagoon (Corsica, France) and l’Etang de l’Or (Hérault, France), through a detailed analysis of (i) the uses, practices, behavior and state of the coastal hydrosystems (surface and ground waters, lagoon and associated wetlands), (ii) planning and development policies and issues, and (iii) the governance of these spaces. Thanks to this information, it is thus possible to describe and to analyze the evolution of coastal hydrosystems over time. The correlation between the understanding of the hydrodynamic behavior of systems and socio-economic dynamics of land use planning allows the identification of causal links between anthropogenic development and the status of resources. Thanks to this collaborative work, the chronology and identification of resource degradation processes could be traced. By understanding the contemporary issues, the transdisciplinary approach provides new basis for thinking about the anticipation, the adaptation and the sustainable management of coastal hydrosystems.
A simulator for the CLARA-A2 cloud climate data record and its application to assess EC-Earth polar cloudiness
Authors: Eliasson Salomon , Karlsson Karl Göran , Willén Ulrika
Published: March 2020

One of the primary purposes of satellite simulators is to emulate the inability of retrievals, based on visible and infrared sensors, to detect subvisible clouds from space by removing them from the model. The current simulators in the COSP rely on a single visible cloud optical depth (τ)-threshold (τ=0.3) applied globally to delineate cloudy and cloud-free conditions. However, in reality, the cloud sensitivity of a retrieval varies regionally.

This presentation describes the satellite simulator for the CLARA-A2 climate data record (CDR). The CLARA simulator takes into account the variable
skill in cloud detection of the CLARA-A2 CDR using long/lat-gridded values separated by daytime and nighttime, which enable it to filter out clouds from
climate models that would be undetectable by observations. We introduce two methods of cloud mask simulation, one that depends on a spatially variable
τ-threshold and one that uses the cloud probability of detection (POD) as a function of the model τ and long/lat. The gridded POD values are from the
CLARA-A2 validation study by Karlsson and Hakansson (2018).

Both methods replicate the relative ease or difficulty for cloud retrievals, depending on the region and illumination. They increase the cloud sensitivity where the cloud retrievals are relatively straightforward, such as over mid-latitude oceans, and they decrease the sensitivity where cloud retrievals are
notoriously tricky, such as where thick clouds may be inseparable from cold, snow-covered surfaces, as well as in areas with an abundance of broken and
small-scale cumulus clouds such as the atmospheric subsidence regions over the ocean.

The CLARA simulator, together with the International Satellite Cloud Climatology Project (ISCCP) simulator of the COSP, is used to assess Arctic clouds in the EC-Earth climate model compared to the CLARA-A2 and ISCCP H-Series CDRs. Compared to CLARA-A2, EC-Earth generally underestimates cloudiness in the Arctic. However, compared to ISCCP and its simulator, the opposite conclusion is reached. Based on EC-Earth, this paper shows that the simulated cloud mask of CLARA-A2 is more representative of the CDR than using a global optical depth threshold, such as used by the ISCCP simulator.
The simulator substantially improves the simulation of the CLARA-A2-detected clouds compared to a global optical depth threshold, especially in the polar regions, by accounting for the variable cloud detection skill over the year.
High frequency radio emissions as a manifestation of physical processes in the auroral plasma
Authors: Rothkaehl Hanna , Matyjasiak Barbara , Chuchra Agata , Schreiber Roman , Marek Michał , Przepiórka Dorota
Published: March 2020

The Earth’s auroral region and its close neighbourhood is the origin of strong radio emissions caused by complex physical plasma processes. Among them we can list auroral hiss, auroral roar, auroral medium frequency (MF) burst, and auroral kilometric radiation (AKR).  Analysis of such emissions can provide information about magnetospheric structure and dynamics. 

In this work we present selected cases of Earth’s AKR-like radio emissions observed by RELEC  and mission at the top side ionosphere leyers. The emissions are seen at frequencies of the order of hundreds of kHz in the ionosphere, just below the auroral oval and  can be observed not only in disturbed geomagnetic conditions, but also during quiet periods. The maximum occurrence is at ∼ 75 ◦ invariant latitude and can have extent up to ∼ 11 ◦ in invariant latitude.

 
Extensional tectonics during the Tyrrhenian back-arc basin formation synthetized in a new morpho-tectonic map
Authors: Loreto Maria Filomena , Zitellini Nevio , Ranero César Rodriguez , Palmiotto Camilla , Prada Manel
Published: March 2020

A new tectonic map is presented focused upon the extensional style accompanying the formation of the Tyrrhenian back-arc basin. Our basin-wide analysis synthetizes the interpretation of vintage multichannel and single channel seismic profiles integrated with modern seismic images and P-wave velocity models, and with a new morpho-tectonic map of the Tyrrhenian (Palmiotto & Loreto, 2019). Four distinct evolutionary opening stages have been constrained: 1) the initial Langhian(?)/Serravallian opening phase actives offshore central/southern Sardinia and offshore western Calabria; 2) the Tortonian/Messinian phase dominated by extension offshore North Sardinia-Corsica, and by oceanic accretion in the Cornaglia and Campania Terraces; 3) the Pliocene phase, dominated by mantle exhumation which was active mainly in the central Tyrrhenian and led to the full opening of Vavilov Basin; and 4) the Quaternary phase characterized by the opening of the Marsili back-arc basin. Listric and planar normal faults and their conjugates bound a series of horst and graben, half-graben and triangular basins. Distribution of extensional faults, active since Middle Miocene, throughout the basin allowed us to define a faults arrangement in the northern / central Tyrrhenian mainly related to in a pure shear which evolved a simple shear opening of continental margins. At depth, faults accommodate over a Ductile-Brittle Transitional zone cut by a low-angle detachment fault possibly responsible for mantle exhumation in the Vavilov and Magnaghi abyssal plains. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variationthroughout the back-arc basin combined with wide-angle seismic velocity models, from Prada et al. (2014; 2015), allow to explore the relationship between shallow deformation, represented by faults distribution throughout the basin, and crustal-scale processes, subduction of Ionian slab and exhumation.

 

REFERENCES

Palmiotto, C., & Loreto, M. F., (2019). Regional scale morphological pattern of the Tyrrhenian Sea: New insights from EMODnet bathymetry. Geomorphology, 332, 88-99.

Prada, M., Sallarès, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. & De Franco, R., 2014. Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains. J. Geophys. Res.: Solid Earth, 119(1), 52-70.

Prada, M., Sallarès, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. & De Franco, R., 2015. The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin. Geophys. J. Int., 203(1), 63-78.
Evaluating key aspects of large-scale circulation for Europe in a coupled PPE
Authors: McSweeney Carol , Sexton David , Bett Philip , Thornton Hazel , McDonald Ruth , Drouard Marie , Woollings Tim , Rostron John , Yamazaki Kuniko , Murphy James
Published: March 2020

European climate is influenced by a number of large-scale phenomena which are typically poorly represented by global climate models.  A key motivation in generating a coupled perturbed parameter ensemble (PPE) for use in the latest UK climate projections (UKCP18) was to exploit the significant improvements in regional dynamics that have been demonstrated at higher vertical and horizontal resolutions.

The UKCP18 package includes a number of products, including a set of 28 global model ‘realizations’ comprising a 15-member PPE and a filtered sub-set of 13 CMIP5 members. These physically coherent, spatially and temporally complete scenarios of future change provide a flexible tool for exploring plausible future changes and their likely impacts.

We present an assessment of the PPE’s ability to represent key aspects of the regional large-scale circulation and its implications for the realistic simulation of UK and European climate and its variability. These include the large-scale circulation climatology, frequencies of weather types determined by clustering of north Atlantic MSLP anomalies, latitude and strength of the north Atlantic jet, location and frequency of north Atlantic and European storms and the frequency of blocking events. We show that the PPE members perform at least at as well as, or better than, the filtered 13-member CMIP5 subset with respect to these circulation characteristics.  This realistic behaviour offers a good basis for UK and European climate impacts studies, as well as the further development of ‘storylines’ approaches.
Middle atmosphere ionization from auroral particle precipitation as observed by the SSUSI satellite instruments
Authors: Bender Stefan , Espy Patrick , Paxton Larry
Published: March 2020

Solar, auroral, and radiation belt electrons enter the atmosphere at polar regions leading to ionization and affecting its chemistry. Climate models usually parametrize this ionization and the related changes in chemistry based on satellite particle measurements. Precise measurements of the particle and energy influx into the upper atmosphere are difficult because they vary substantially in location and time. Widely used particle data are derived from the POES and GOES satellite measurements which provide electron and proton spectra.

We present electron energy and flux measurements from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) satellite instruments on board the Defense Meteorological Satellite Program (DMSP) satellites. This formation of now four satellites observes the auroral zone in the UV from which electron energies and fluxes are inferred in the range from 2 keV to 20 keV. We use these observed electron energies and fluxes to calculate ionization rates and electron densities in the upper mesosphere and lower thermosphere (≈ 70–200 km). We present an initial comparison of these rates to other models and compare the electron densities to those measured by the EISCAT radar. This comparison shows that with the current standard parametrizations, the SSUSI inferred auroral (90–120 km) electron densities are larger than the ground-based measured ones by a factor of 2–5. It is still under investigation if this difference is due to collocation (in space and time) and EISCAT mode characteristics or caused by incompletely modelling the ionization and recombination in that energy range.
Dissecting the Barotropic Transport in a High-resolution ocean model
Authors: Claus Martin , Wang Yuan , Greatbatch Richard , Sheng Jinyu
Published: March 2020

We present a method to decompose the time mean vertically averaged transport, as simulated by an high-resolution ocean model, into its four dominant components. These components are driven by the gradient of potential energy per unit area (PE), the divergence of the flux of time mean momentum (MMF) and eddy momentum (EMF), and the wind stress. Since the local vorticity budget and the bathymetry are noisy and dominated by small spatial scales, a barotropic shallow water model is used as a filter to diagnose the respective transports instead of integrating along lines of constant f/H.
Applying this method to the output of a high-resolution model of the North Atlantic we find that PE is the most important driver, including the northwest corner. MMF is an important driver of transport around the Labrador Sea continental slope and, together with the EMF, it drives significant transport along the path of the Gulf Stream and North Atlantic current. Additionally, the circulation patterns driven by the EMF compares well with an estimate based on a satellite product. Hence, the presented method provides insights into the relative importance of the different dynamical processes that may drive barotropic transport in an ocean model. But it may also be used to isolate potential issues if a model misrepresents the barotropic transport.
Determining the global coherence of plasmaspheric hiss waves in the magnetosphere
Authors: Zhang Shuai , Rae Jonathan , Watt Clare , Degeling Alexander , Tian Anmin , Shi Quanqi
Published: March 2020

Plasmaspheric hiss waves is important in the radiation belt. Previous papers have shown that considering the variability of wave parameters will improve the effectiveness of modeling wave-particle interactions in the Radiation Belt, but less is known about how rapidly (and by how much) wave characteristics vary. We use measurements from the Van Allen Probe mission to study the correlation and ratio of wave amplitudes over a range of frequencies covering the plasmaspheric hiss band as a function of separation and time delay between two satellites. A total of 1851 events with small separation (<1RE) were found. The statistical results show that, as separation between spacecraft increase, the characteristics of hiss change in both correlation of the wavepacket and amplitude. Moreover, we find that the coherence between spacecraft is strong at low-L, and decreases strongly with increasing L. We investigate the coherence of plasmaspheric hiss on geomagnetic indices and solar wind driving. We discuss the ramifications of our results with relevance to understanding the global characteristics of plasmaspheric hiss waves.
Acidification in the Mediterranean Sea following a transient climate change scenario simulated with a high-resolution regional model
Authors: Dutay Jean-Claude , orr James , le-vu briac , palmieri julien , richon camille , somot samuel
Published: March 2020

Oceans contribute to the removal of 25%-30% of the atmospheric anthropogenic CO2, which increase sea water CO2 concentration and acidity, and decrease the Aragonite saturation state that may cause problems for calcium carbonate skeletons of marine species. The Mediterranean Sea is a specific environment with a higher alkalinity and a fast ventilation that is in favor of a more important uptake of  anthropogenic CO2 relatively to global ocean, and an acidification process impacting the whole water. The future acidification of the Mediterranean Sea has not been investigated by regional model yet.

In this study, we used an eddy-permitting regional model of the Mediterranean Sea (NEMO_MED8) coupled to an oceanic biogeochemical model (PISCES) to evaluate how climate and anthropogenic CO2 changes will modify the acidification and its annual cycle from the 1850 period to the end of the 21st century according to the future IPCC SRES-A2.  Evolution of boundary conditions from Rivers and exchange at the Gibraltar strait are considered. We analyse the relative influence of temperature, salinity, DIC and alkalinity on the mean and the seasonal amplitude of acidity (H+) and aragonite saturation sate (ΩA) and their evolution following a changing climate scenario SRES-A2.
Small-scale Spatial Variability of Hydro-physical Properties of Differently Degraded Peat
Authors: Wang Miaorun , Liu Haojie , Lennartz Bernd
Published: March 2020

Spatial variability of soil properties is important for hydrological studies. However, little information is available on the spatial variability of hydro-physical properties of peat soils. Three study sites: natural, degraded and extremely degraded peatland were selected for this study. At each site, 72 undisturbed soil cores were collected from 5m by 5m grid cells in an area of 40m by 45m. The saturated hydraulic conductivity (Ks), soil water retention curves, total porosity, macroporosity, bulk density and soil organic matter (OM) content were determined for all sampling locations. The van Genuchten model parameters (θs, α, n) were optimized using the RETC software package. A strong positive correlation between macroporosity and Ks was observed irrespective of the degradation stage of the peat. However, the relationships between macroporosity and Ks differed for the different sites. The soil physical properties (e.g. OM content and bulk density) exhibited different levels of spatial autocorrelation depending on the soil degradation stage. The cross-semivariograms showed a strong or moderate spatial dependency between soil physical properties and van Genuchten model parameters. The more a peat soil is degraded, the more likely it is that soil physical properties are spatially dependent. In conclusion, degradation stage plays an important role and should be considered more often in spatial analysis. The obtained cross-semivariogram may serve as a basis for 2D and 3D hydrological modelling. 
Taking advantage of satellite clock stability for Galileo orbit model performance assessment.
Authors: Sidorov Dmitry , Dach Rolf , Jäggi Adrian
Published: March 2020

Over the course of 2016 and 2017 the European GNSS Agency (GSA) made the Galileo satellite meta information publicly available. This long-awaited metadata package included details on satellite mass, dimensions, surface optical properties, attitude law as well as the antenna phase center corrections. As a result of this undertaking, the GNSS community initiated numerous studies to advance orbit models for these spacecrafts. In particular, the Center for Orbit Determination in Europe (CODE) refined the Empirical CODE Orbit Model (ECOM2) to adopt it to these lightweight satellites. This extended ECOM2 is currently used for computation of the CODE precise products involving Galileo (the Ultra-Rapid, Rapid and Multi-GNSS Extension (MGEX) products) in the frame of the International GNSS Service (IGS) activities.

The Galileo satellites carry state-of-the-art passive hydrogen maser (PHM) clocks that have been marked by high stability by many research groups. The commonly adopted procedure for the satellite clock corrections computation includes introduction of orbits estimated beforehand. This is served to fix the geometry between satellites and ground stations with a disadvantage that the estimated satellite clock corrections to a large degree depend on the quality of the introduced orbits. As a consequence, the estimated satellite clock corrections may suffer from potential radial orbital errors.

In this study we make an attempt to assess empirical orbit models used for Galileo satellites by introducing clock modelling in our precise orbit determination (POD) procedure. Thus, we take advantage of the stability of the PHM clocks operated by the Galileo satellites to introduce additional constraints to the radial orbital component already during the dynamic POD step. The obtained results suggest that introducing a satellite clock model to POD leads to improvements in solutions if the employed dynamic orbit model is correct. Also, in view of increasing number of GNSS satellites using well-performing clocks, the POD employing clock modelling appears to have high potential in further refining of orbit models.