bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigating the drought-prone biological interplay of soil microbial communities and Scots pine trees 
Authors: Jäger Astrid , Hartmann Martin , Hagedorn Frank , Six Johan , Solly Emily
Published: March 2021

In forest ecosystems, microorganisms hold key functions as nutrient cyclers, decomposers, plant symbionts or pathogens and thereby regulate biogeochemical processes and forest health. These microbial dynamics are controlled by water availability in three fundamental ways: as resource, as solvent, and as transport medium. For one of the dominant tree species in Swiss forests - Scots pine (Pinus sylvestris L.) - high mortality rates have been observed in recent decades. In the Rhone valley of Switzerland, forest dieback appears to be primarily caused by direct effects of drought and an increasing susceptibility of trees to further constraints, such as pathogen attacks. Nonetheless, water limitation does not affect soil microbes and trees separately but rather induces a series of interconnected effects between trees and the associated soil microbiome, which could strongly alter carbon and nutrient cycling in forests. We conduct a study to investigate the effects of drought on the biological interplay between Scots pine trees and soil microbial communities. We aim to estimate how shifts in microbial community composition and functional capacity under drought may affect nutrient cycling and tree vitality potentially contributing to tree mortality. In order to understand these mechanisms, we perform greenhouse experiments with tree-soil mesocosms under controlled conditions. State-of-the art molecular methods such as metabarcoding of ribosomal markers, shotgun metagenome sequencing, and qPCR of key functional genes are used to unravel alterations in the soil microbiome and in the underlying functional metabolic potential related to drought and associated tree-mortality. Furthermore, to elucidate the impact of drought on microbial carbon dynamics, stable isotope labelling techniques have been applied to trace 13C labeled plant photosynthates into the soil microbial communities by analyzing 13C signatures of phospholipid fatty acids. Investigation of soil physicochemical properties and tree-vitality is done in parallel with the microbial assessments to understand the feedbacks on nutrient-cycling and the soil-tree continuum. The overarching aim of this study is to gain new insights into the complex relationships between soil, trees and microbes under drought.
A methodology for a participatory approach to the elaboration of drought risk management plans in small and medium towns
Authors: De Stefano Lucia , Vargas Jesús , Hernández-Mora Nuria , Ballester Alba , Herrera Tony , Lacalle Abel , Paneque Pilar
Published: March 2021

Droughts are recurrent phenomena that are intrinsic to any climate. In Spain, as in many countries in the Mediterranean region, forecasts derived from climate change models predict an increase in the frequency and intensity of this type of phenomena. This makes even more necessary to focus efforts on strengthening social and institutional capacities through prevention, mitigation and adaptation strategies to mitigate the possible impacts of drought on the society and the environment. Despite the progress achieved at the scale of river basin districts and large municipalities, small and medium-sized towns often do not have drought risk management tools adapted to their specific needs. This study developed a participatory methodology for the elaboration of drought risk management plans in small and medium-sized towns. The methodology was tested and validated in three pilot municipalities: Madridejos (Toledo), Puente Genil (Córdoba) and Xàbia (Alicante). As a result, a methodological guide was developed to facilitate the preparation and adaptation of these plans to the different contexts, realities and needs of each municipality. The communication presents the key elements of this participatory methodology and the lessons learnt from the experience in the three pilot sites.

 
Long-term ice loss from Greenland mediated by ice-load bedrock uplift feedback
Authors: Zeitz Maria , Haacker Jan , Donges Jonathan , Winkelmann Ricarda
Published: March 2021

Mass loss from the Greenland Ice Sheet has significantly accelerated over the past decades, both through enhanced melting as well as the acceleration of outlet glaciers. Positive feedback mechanisms, including the melt-elevation feedback and the ice-albedo feedback, introduce a non- linear evolution and may further accelerate mass loss. Negative feedbacks, such as the feedback between receding ice load and subsequent bedrock uplift, might counteract these accelerating positive feedbacks on long timescales. Bedrock uplift can amount to roughly one third of the change in the ice sheet thickness on a timescale of millennia. Here we explore the interplay of both positive and negative feedbacks, using simulations of the Greenland Ice Sheet with the Parallel Ice Sheet Model (PISM) including an Elastic Lithosphere Relaxing Asthenosphere (ELRA) model in an idealized warming scenario. In particular, we find that depending on the temperature anomaly (and thus the ice retreat rate) and the asthenosphere viscosity, distinct responses of the ice sheet are possible, ranging from the full or partial retreat of the ice sheet to the full or partial recovery of the ice sheet after an initial retreat, and potential large-scale self-sustained oscillations of ice volume on multi- millennial timescales.
Dynamic fracture mechanics in dry snow slab avalanche release
Authors: McClung David
Published: March 2021

Field observations and measurements show that dry snow slab avalanches initiate by propagating shear fractures within a relatively thin weak layer sandwiched between a planar, stronger, thicker slab above and stronger material below. After initiation, the weak layer fracture can propagate up and down slope for distances which range from about 10 to 100’s of meters to cause tensile fracture through the body of the slab which results in avalanche release.  In this paper, dynamic fracture mechanics is applied to slab tensile fracture after which avalanche release is imminent. Two mechanisms for production of tensile stress are explored employing field measurements of slab properties and lab measurements. The first considers inertial effects related to quasi-brittle fracture near the tip of a propagating weak layer shear fracture. The second is concerned with the tensile stress generation from the stress drop behind the crack front as the fracture propagates in the weak layer. Analysis suggest that both mechanisms can contribute to produce the tensile fracture line which precedes avalanche release. Even though both mechanisms may operate together, they are analyzed separately in this paper. 
Ground deformation related to slip and afterslip of the 29 December 2020 Mw 6.4 Petrijna earthquake (Croatia) imaged by InSAR
Authors: Ganas Athanassios , Valkaniotis Sotiris , Elias Panagiotis , Tsironi Varvara , Karasante Ilektra , Briole Pierre , Sansosti Eugenio , De Novallis Vincenzo
Published: March 2021

On December 29, 2020, at 11:19 UTC, a strong (M6.4), shallow earthquake occurred in the central region of Croatia. The epicentre was located near the town of Petrinja, about 40 km to the south of the capital, Zagreb. Here we present a preliminary analysis of the geodetic data (differential InSAR & GNSS) and preliminary estimates of the slip that occurred on the fault during the earthquake and subsequent aftershocks. We picked InSAR data to invert for the seismic fault assuming linear rheology and Okada-type dislocation (rectangular) source with non-uniform slip. The interferograms show an asymmetric, four‐lobed pattern, centered on a NW‐SE oriented discontinuity that is in agreement with the right-lateral plane of the moment tensor solutions for the mainshock. We found that the Petrijna earthquake ruptured a segment of a strike-slip fault zone that is shorter (8 km) than average and with larger slip (~ 3 m). All parameters of the seismic fault are well constrained by InSAR modeling due to the full azimuthal coverage with both ascending and descending data of good quality. The fit to the fringes is better with a steep dip angle (76°) than with a purely vertical fault. The upper edge of the modeled fault is at a depth of ~1 km, this means that the slip drop from 3 to 0 m in the uppermost kilometer and our geodetic analysis cannot assess whether the fault reached the surface in some sections of the fault, however should this be the case, we expect ruptures at the surface in the range of 0.1 to 0 m for consistency with our model and the structure of the fringes pattern. In particular, preliminary modelling results with distributed fault-slip show that the slip reached a peak of more than 2.5 m at a depth of about 2 km. We also found that, differently from what reported in the European database of seismogenic sources (EDSF), the seismic fault dips westward instead of eastward. Additionally, the 2020 rupture and the InSAR mapped trace do not match the EDSF composite seismogenic fault surface trace. Kinematic analysis of GNSS waveforms at station BJEL (about 70-km east of the epicentre) revealed that horizontal ground motion reached 7-cm (peak-to-peak). The InSAR data revealed a 7 km of right-lateral afterslip on the NW-edge of the rupture, and 5 km to the south of the main fault rupture. In particular, the afterslip data on the NW edge of the rupture document the curved shape of the post-seismic deformation, that highlights the non-planarity of faults in nature and possibly indicating the existence of a ramp structure connecting to the neighboring segment towards north.
First results from temporary deployment of small seismic network following the Mw=6.4 Petrinja earthquake
Authors: Stipčević Josip , Poggi Valerio , Herak Marijan , Parolai Stefano , Herak Davorka , Dasović Iva , Bertoni Michele , Barnaba Carla , Pesaresi Damiano
Published: March 2021

The Department of Geophysics, University of Zagreb and the Italian National Institute of Oceanography and Applied Geophysics (OGS) installed on January 4th 2021, five temporary seismic stations near the town of Petrinja, Croatia, in the aftermath of  the 29 Decembre 2020 Mw 6.4 earthquake. The stations equipped with a seismometer and a strong motion sensor, recorded the aftershock sequence beginning six days after the mainshock allowing to augment the permanent seismic network in the area improving the azimuthal coverage and providing additional near‐field observations.

In this presentation we summarize the motivation and goals of the deployment; details regarding the station installation, instrumentation, and configurations and observations from the network. The collected data set will be useful for carrying out several seismological studies including the analysis of variability of strong ground motions in near field, the determination of the aftershocks source parameters,  the estimation (if any) of rupture directivity of small events, the clustering of events in space and time, the better imaging of the fault zone, the evolution of crustal properties within and outside of the fault zone.
Three-dimensional modelling of Uttarakhand slides using smoothed particle hydrodynamics (SPH)
Authors: Li Shuai , Tang Hui , Peng Chong , An Hui-Cong
Published: March 2021

On 7 February 2021, a massive flood occurred in the river Dhauliganga that damaged two hydroelectric stations, five bridges and trapped 100 to 150 casualties who are feared dead. Some evidence has been indicated that caused by a landslide, an avalanche, or a portion of the Nanda Devi glacier that broke off early in Uttarakhand's Joshimath area Chamoli district. The magnitude of the flood caused by the collapse was so large that it far exceeds the collapse itself. Two potential explanations were proposed to explain: the frictional heating of the avalanche may result in high temperatures in the sliding face, which is sufficient for ice and frozen sediments melting to occur in the path. The high-water content generated debris flows that enhanced the mobility of flowing. Another explanation is that it could be related to a glacial lake outburst flood or a temporary lake that eventually broke through its debris dam and poured down the valley. In any case, the collapse materials hold very high moisture content and fast mobility. In this study, a three-dimensional Smoothed Particle Hydrodynamics (SPH) method is adopted to model the flow-like Uttarakhand slides and to explore the physical processes during this event. The SPH is an adaptive, mesh-free, Lagrangian method that simulates free surfaces, moving interfaces, and large flow deformations. A non-Newtonian debris flow model, the Bingham rheological relationship, was incorporated into the SPH framework to describe source materials' characteristics. Besides, the whole flow processes of the flow-like Uttarakhand slides across the 3D terrain are represented. The time history of the velocity, acceleration, and forces were obtained from modelling to analyze the landslide dynamics.
Liquefaction field reconnaissance following the 29th December 2020 Mw 6.4 Petrinja earthquake (Croatia)
Authors: Amoroso Sara , Barbača Josip , Belić Nikola , Kordić Branko , Brčić Vlatko , Budić Marko , Civico Riccardo , De Martini Paolo Marco , Hećej Nina , Kurečić Tomislav , Minarelli Luca , Novosel Tomislav , Palenik Damir , Pantosti Daniela , Pucci Stefano , Filjak Radovan , Ricci Tullio , Špelić Marko , Vukovski Matija
Published: March 2021

Earthquakes and related coseismic effects at the surface, both primary and secondary, such as liquefaction and lateral spreading, can impact humans due to induced economic or social disruptions (e.g. slope, bridge and building foundation failures, flotation of buried structures). In this respect, it results of primary interest to map liquefaction induced evidences soon after an earthquake. On the 29th December 2020, a major earthquake (Mw 6.4) occurred in Croatia, close to Petrinja, 45 km south of Zagreb, generating widespread liquefaction and lateral spreading phenomena in a radius of approximately 20 km from the epicentre. A European team of researchers (geologists and engineers), in strict collaboration with the Croatian Geological Survey, performed field reconnaissance campaigns with the aim to provide a detailed identification and characterization of the primary and secondary geological and geotechnical coseismic effects induced by the Croatian earthquakes. Specifically with reference to the liquefaction phenomena, the Working Group integrated the data collected directly in the field with those from remote survey by drone aerial photos acquired in the post-event immediate. The adopted process allowed the collection of the liquefaction record with the highest possible completeness both in terms of pattern and distribution of the phenomena. The database includes several detailed case studies typified by the following characteristics: (1) liquefaction occurring on alluvial plain sites (Kupa river, Sava river and Glina river); (2) blows made by sand and/or gravel with local presence of shells and armored mud balls; (3) lateral spreading phenomena along road and river embankments; (4) sand ejecta of different grain size and matrix, even at the same site; (5) sand and/or gravel ejecta along fault traces. The characteristics of these features are discussed with reference to the alluvial setting and tectonic context. All together, the detailed survey of these recent liquefaction features will assist to build new empirical relations, to update the existing ones and to mitigate the effects of future earthquakes recognizing liquefaction prone areas for a correct land use planning, as for seismic microzonation studies.
Tracking the sediment plume from the 7th February 2021 Chamoli (Uttarakhand, India) hazard cascade
Authors: Dunning Stuart , Gascoin Simon , Shugar Dan , Schwanghart Wolfgang
Published: March 2021

The 7th February Chamoli hazard cascade originated from a 25 million m³ rock/ice avalanche slope failure that transformed into a destructive, far travelled debris flow / debris flood. There has a been necessarily a significant science focus on the proximal and immediate part of the hazard cascade. Here we report on the larger spatial and temporal scale: the sediment plume that progressed over the following days and weeks along the Ganga (Ganges) River. At the time of submission this was still recognisable over 900 km from the landslide site and had passed through hydro and nuclear power schemes. Beyond the initial plume, which has implications for rapid sedimentation in hydropower schemes and water / aquatic habitat quality, the subsequent (or not) mobilisation of event sediments over future years is a possible medium term chronic-threat to some hydropower projects. We show spectral ‘recipes’ and semi-automated methods for tracking the mass movement sediment plume and quantifying celerity using Sentinel 2 imagery, infilled using high-temporal repeat optical imagery from Planet Labs. data. The plume averaged ~60 km/day and, as expected has begun to slow as the river gradient decreases, as well as becoming less distinctive as some sediment is deposited, and as other sediment-rich water joins the Ganga.

The tracking of sediment plumes from these hazard cascades can be extended over inventories of similar events using both Sentinel 2 and Landsat archives. Such approaches allow us to provide insight into the possibilities of automated detection of hazard cascade sediment plumes to identify previously unknown events from remote source regions, as plumes have a far larger spatial-temporal footprint than the initial event.
Geodetic benchmark displacement measurements following the 2020 Petrinja earthquake in Croatia
Authors: Kordić Branko , Vukovski Matija , Budić Marko , Špelić Marko , Barbača Josip , Belić Nikola , Brčić Vlatko , Filjak Radovan , Kurečić Tomislav , Palenik Damir , Bočić Neven , Atanackov Jure , Bavec Miloš , Brajkovič Rok , Celarc Bogomir , Novak Ana , Novak Matevž , Jamšek Rupnik Petra , Amoroso Sara , Civico Ricccardo , Pucci Stefano , Ricci Tullio , Bonico Paolo , Iezzi Francesco , Pace Bruno , Testa Alessio , Benedetti Lucilla , Henriquet Maxime , Moulin Adrien , Baize Stéphane , Métois Marianne , Markusic Snjezana
Published: March 2021

The earthquake with magnitude ML=6.2 that occurred on 29th December 2020 has caused significant material damage to objects and infrastructure in the towns of Petrinja, Sisak,Glina and the surrounding area. According to the satellite interferometry data, the coseismic and postseismic deformation area covers around 500 square kilometers. The existing geodetic benchmarks have been set in the affected towns, and their coordinates have been determined based on previous GPS campaigns. The GPS network was set up and adjusted at the State Geodetic Administration's request for geodetic monitoring of infrastructure and cadastral projects. These points are not primarily intended for high accuracy measurements at the level of a few millimeters, so their accuracy and the absolute shift concerning geodynamic processes in the region should be taken into account. Nevertheless, the data obtained by their observation after the earthquake can provide valuable information about the horizontal and vertical displacements with a certain level of confidence. The field survey has detected disappearance of a large number of benchmarks and some valuable information has been lost. Still, 58 points were found and observed and it has been concluded that 52 points are reliable and can be used for future research. Because the network of benchmarks is not developed in rural areas, there is a gap in the distribution of benchmarks in affected area. Therefore, the additional data was collected using the benchmarks established for the engineering and cadastral projects and studies. From a total of 67 points that have been found and observed, 42 points will be used. Along with the data collected in urban areas, there will be a total of 94 benchmarks. The accuracy of the geodetic benchmark measurements is at the centimeter level, while the values of deformation are at the level of a few decimeters. Therefore, the obtained data can be used to better assess the displacement recorded during the 29 December 2020 event. In the future, field research will focus on finding additional benchmarks to reach a better spatial distribution.
Aggregate stability of cultivated vineyard soils with high rock fragment content in the Mosel area, Germany
Authors: Benzing Teresa , Hauter Paula , Iserloh Thomas , Seeger Manuel
Published: March 2021

Within the European project Diverfarming (Horizon 2020, no 728003), which investigates crop diversification and low-input farming across Europe, we study the aggregate stability variability of soils with high rock fragment content on steep sloping vineyards in the upper Saar valley of the Mosel area (Wawern, Rhineland-Palatinate, Germany).

In the framework of the case study researched by Trier University and their partners, aromatic herbs (Oregano and Thyme) are planted in rows underneath the grapevines to minimize soil erosion, suppress unwanted weeds and to be harvested for further use. Additionally, this cultivation affects different soil characteristics such as aggregate stability.

We analyse the aggregate stability using and comparing three different methods:

wet sieving which is executed in two different ways – slaked and rewetted treatment,

percolation method and

single drop technique.

Aim of the study is to understand the effect of soil treatments underneath the grapevines, and to identify the method(s) being able to quantify the differences best.

Regarding the different methods, first results indicate that the quantified aggregate stabilities of each method are comparable. With this, we could identify differences between uncultivated rows (control areas), and the rows intercropped with aromatic herbs. In the latter ones, the aggregate stability underneath the grapevines is affected positively. Furthermore, there is a clear difference between slaked and rewetted treatment within the wet sieving method, where less stable aggregates are isolated.

The results indicate that the accomplished management (vine intercropped with Oregano and Thyme) improves the aggregate stability and therefore it improves the soil quality in general.
Ground motions induced by pore pressure changes at the Szentes geothermal area, SE Hungary
Authors: Békési Eszter , Fokker Peter , Candela Thibault , Szanyi János , van Wees Jan-Diederik
Published: March 2021

The long-term sustainable exploitation of geothermal resources requires cautious planning and regulation. Exploitation in excess of natural recharge can result in reservoir pressure decline, causing a decrease in production rates. Furthermore, such “overexploitation” of geothermal reservoirs may lead to compaction and land subsidence. Understanding of such phenomena is critical for the assessment of societal-environmental risks, but can also be used for optimization by constraining reservoir processes and properties.

Excessive thermal water volumes have been extracted from porous sedimentary rocks in the Hungarian part of the Pannonian Basin. Thermal water production in Hungary increased significantly from the early 70’s. Regional-scale overexploitation of geothermal reservoirs resulted in basin-scale pressure drop in the Upper Pannonian sediments, leading to compaction and ground subsidence.

We investigated surface deformation at the Szentes geothermal filed, SE Hungary, where the largest pressure decline occurred. We obtained data from the European Space Agency’s ERS and Envisat satellites to estimate the ground motions for the periods of 1992-2000 and 2002-2010. We applied inverse geomechanical modelling to understand the compaction behaviour of the reservoir system and to estimate the subsurface properties. We constrained the model parameters using the Ensemble Smoother with Multiple Data Assimilation, which allowed us to incorporate large amounts of surface movement observations in a computationally efficient way. The model requires pressure time series as input parameters, therefore, the lack of regular pressure measurements in geothermal wells of Szentes resulted in significant uncertainties. Still, we managed to identify a potential delay in pressure drop and subsidence, implying a time-decay compaction behaviour of the reservoir system,  and we arrived at realistic estimates for the compaction coefficient of the reservoir. The improved parametrization enables better forecasting of the reservoir behaviour and facilitates the assessment of future subsidence scenarios. This study thus demonstrates the effectiveness of InSAR-based ground motion data and inverse geomechanical modelling for the monitoring of geothermal reservoirs and the establishment of a sustainable production scheme.
Drivers for micrometer-scale deformation and progressive rock mass damage in a deglaciating rock slope – insights from subsurface in-situ monitoring
Authors: Hugentobler Marc , Aaron Jordan , Loew Simon
Published: March 2021

Large rock slopes instabilities form over long timescales through progressive rock mass strength weakening of initially stable slopes. Progressive rock mass damage is driven by environmental loads and is thus strongly dependent on the local setting and environmental conditions of the rock slope, which can vary over time. It is often assumed that the strong variations of the thermal and hydraulic boundary conditions during deglaciation in combination with unloading due to ice downwasting cause enhanced rates of rock mass damage. However, in-situ observations to quantify deformation, damage and the relevance of different drivers in such environments are rare. This presentation is related to the contribution of Oestreicher et al., presenting in the same session, addressing similar questions, but at different scales and based on different field data and analysis.

In this contribution we analyze continuous pore pressure, temperature and micrometer-scale deformation time series from a subsurface monitoring system comprised of three, 50 m deep, highly instrumented boreholes in a crystalline rock slope which is located beside the rapidly retreating glacier tongue of the Great Aletsch Glacier (Switzerland). We compare high-resolution reversible and irreversible deformation signals with potential drivers, including locally measured pore pressure fluctuation, rock temperature variations, and nearby earthquakes. We show that shallow (10 - 15 m deep) deformations in our rock slope are dominated by thermo-mechanical forcing, whereas deformation measured below this depth is mainly driven by hydro-mechanical effects related to pore pressure fluctuations. Both reversible deformation and irreversible damage events occur more frequently during the snow-free summer season, when we observe higher dynamics in thermal and hydraulic boundary conditions. In our 2.5 years long time series, we do not find any significant deformation event coinciding with a nearby earthquake. Additionally, we discuss differences in the deformation signal with respect to the stability state and the rock mass quality at the different monitoring locations. Also, we assess longer term impacts of glacier retreat and ice downwasting on rock slope deformation and damage. Such information is critical for an improved understanding and quantification of factors contributing to the formation of paraglacial rock slope instabilities.
The Gravel Parameterization Schemes on Tibetan Plateau and Its Assessment Using RegCM4
Authors: Liu Yigang , Lyu Shihua , Ma Cuili , Xu Yue , Luo Jiangxin
Published: March 2021

In this paper, the impact of gravel is taken into account in regional simulations on the Tibetan Plateau (TP). The differences of ground surface and soil hydrological processes in the TP are compared when the gravel parameterization schemes and the original soil hydrothermal parameterization schemes are respectively adopted in the regional climate model version 4.7 (RegCM4.7), which is driven by the EIN15. Moreover, the performances in simulating the liquid soil moisture (LSM) by using the two schemes are also assessed. When the impact of gravel is considered, the changes of ground hydrological processes are consistent with those of liquid precipitation and snow meltwater except the infiltration, indicating the dominance of liquid precipitation and snow meltwater in ground hydrological processes. The lower gravel content will facilitate the downward transportation of LSM. However, in the case of high gravel content, the roles of gravel content are completely opposite in the western and central TP. The most obvious change is that the simulated LSM by the gravel schemes is lower at most soil depths compared with that by the original schemes, which is beneficial in most cases. For instance, the mean absolute errors of the reference data with the simulations by the gravel schemes and original schemes at the soil depth of 0.1 m in the southeastern TP are 0.026 and 0.101, respectively. Besides the southeastern TP, the performance in simulating the temporal variation of the LSM below the middle soil layers still needs to be improved.
Climatic effects of mesoscale sea frontal structures in the Mediterranean Sea
Authors: Desbiolles Fabien , Meroni Agostino , Alberi Maria , Hamouda Mostafa E. , Giurato Michele , Ragone Francesco , Pasquero Claudia
Published: March 2021

Sea Surface Temperature (SST) is known to affect the marine atmospheric boundary layer (MABL) at scales smaller than O(1000 km) via different mechanisms. In particular, the oceanic thermal forcing induces modification in the wind speed, its divergence and its curl by the action of the Downward Momentum Mixing (DMM) mechanism and the Pressure Adjustment (PA) one. 

By analyzing 25 years of observations of surface wind speed and SST in the Mediterranean, it is found that the probability of observing surface wind convergence is significantly higher over a thermal oceanic front crossed from the warm to the cold side, in agreement with the DMM mechanism. Physically, this is due to a deceleration of the surface wind over the cold side of the SST front because of the increased atmospheric stability over the cold water. The strongest response in terms of surface convergence is found when atmospheric fronts (already characterized by strong surface convergence) cross SST gradients from the warm to the cold side.

Using 25 years of ERA5 reanalysis data, it is also found that the wind divergence variability within the MABL (until about 925 hPa) is partially driven by mesoscale SST patterns via their effect on the boundary layer stability. This results in a cloud cover and rainfall response: when a wind blows from warm-to-cold (cold-to-warm) ocean patterns, a converging (diverging) cell is enhanced, increasing (decreasing) low-cloud cover and favouring rainfall. Specifically, strong warm-to-cold fronts (the upper 25th percentile) are associated with a mean increase of cloud cover of 10±5% and a mean increase in the probability of a rain event of 15±6%, with respect to the average values. 

The cloud and rainfall dependence on SST fronts is more pronounced in fall than in the rest of the year, probably due to the stronger SST gradients present at the end of the summer season. The effects on cloud cover, in particular, are a preferential way through which mesoscale SST structures can impact the radiation budget and, thus, the Earth climate.
Opening and closure of Iranian back-arc basins: A seismic tomography view
Authors: Lom Nalan , Qayyum Abdul , Gürer Derya , van der Meer Douwe G. , Spakman Wim , van Hinsbergen Douwe J.J.
Published: March 2021

Iran is a mosaic of continental blocks that are surrounded by Tethyan oceanic relics. Remnants of these oceanic rock assemblages are exposed around the Central Iranian Microcontinent (CIM), discretely along the Sanandaj-Sirjan Zone and in Jaz-Murian. The ophiolite belts surrounding the CIM are mainly assumed to represent narrow back-arc basins that opened in Cretaceous and closed before the Eocene. Although these ophiolites are exposed as small pieces on continental crust today, they represent oceans wide enough to form supra-subduction ophiolites and arc-related magmatic rocks which suggest that their palaeogeographic width was at least some hundreds of kilometers. Current models for the palaeogeographic dimension, opening and closure of these basins are highly schematic. They usually seem plausible in two-dimensional reconstructions, however a single three-dimensional model explaining whole Iran and its surrounding regions has not been fully accomplished.  This is mostly because while the geological record provides constraints on the origin and ages of the subducted ocean floor, it provides limited information about onset and cessation of the subduction and almost no constraints on the dimension of these oceans and the subduction zones that consumed them.

In this study, we follow a novel approach in estimating the dimension and evolution of these back-arc basin by using seismic tomography. Seismic tomography has revealed that we can image and trace subducted lithosphere relics. Imaged mantle structure is now being used to link sinking slabs with sutures and to define shape of a slab. Systematic comparison of regions where the timing of subduction is reasonably well constrained by geological data showed that slabs sink gradually through the mantle at rates more or less the same. This perspective enabled us to study slab shape as a function of absolute trench motion. While mantle stationary trenches tend to create steep slabs or slab walls, the flat-lying segments are formed where the overlying trenches are mobile relative to the mantle, normal facing during roll-back, overturned during slab advance.  Under the assumption of vertical sinking after break-off, it is also possible to locate the palaeo-trenches.  When combined with absolute plate motion reconstructions, tomographically determined volume and size of the subducted lithosphere can also be used to estimate the size/width of the prehistoric oceans. To this end, we build on and further develop concepts that relate absolute trench motion during subduction to modern slab geometry to evaluate the possible range of dimensions associated with opening and closure of the Iranian back-arc basins.
Effect of Macroporosity on Physical Property Estimates for Peat Soils
Authors: Wang Miaorun , Liu Haojie , Lennartz Bernd
Published: March 2021

Hydrophysical soil properties play an important role in regulating the water balance of peatlands and are known to be a function of the status of peat degradation. The objective of this study was to revise multiple regression models (pedotransfer functions, PTFs) for the assessment of hydrophysical properties from readily available soil properties. We selected three study sites, each representing a different state of peat degradation (natural, degraded and extremely degraded). At each site, 72 undisturbed soil cores were collected. The saturated hydraulic conductivity (Ks), soil water retention curves, total porosity, macroporosity, bulk density (BD) and soil organic matter (SOM) content were determined for all sampling locations. The van Genuchten (VG) model parameters (θs, α, n) were optimized using the RETC software package. Macroporosity and the Ks were found to be highly correlated, but the obtained functions differ for differently degraded peatlands. The introduction of macroporosity into existing PTFs substantially improved the derivation of hydrophysical parameter values as compared to functions based on BD and SOM content alone. The obtained PTFs can be applied to a wide range of natural and degraded peat soils. We assume that the incorporation of macroposity helps to overcome effects possibly resulting from soil management. Our results suggest that the extra effort required to determine macroporosity is worth it, considering the quality of parameter estimates for hydraulic conductivity as well as the soil hydraulic VG model.
The Arctic lapse rate feedback: An energy budget analysis of CMIP6 models
Authors: Linke Olivia , Quaas Johannes
Published: March 2021

The strong warming trend in the Arctic is mostly confined at the surface, and particularly evident during the cold season. The lapse rate feedback (LRF) stands out as one of the dominant causes of the Arctic amplification (besides the surface albedo feedback) given its differing response between high and lower latitudes. The LRF is the deviation from the uniform temperature change throughout the troposphere, and can thereby be quantified as the difference of tropospheric warming and surface warming. In the Arctic, it enforces a positive radiative feedback as the bottom-heavy warming is increasingly muted at higher altitudes, which has been suggested to relate to the lack of vertical mixing. In fact, climate model studies have recently identified more negative lapse rates for models with stronger inversions over large parts of the Arctic ocean, and snow-free land during winter.

Here we quantify individual components of the atmospheric energy balance to better understand the determination of the temperature lapse rate in the Arctic, which does not only interact with the surface albedo feedback, but also changes in atmospheric transport. A decomposition of the atmospheric energy budget is derived from the 6th phase of the Coupled Model Intercomparison Project (CMIP6), and concerns the radiation budgets, the transport divergence of heat and moisture, and the surface turbulent heat fluxes. Alterations of the budget components are obtained through pairs of model scenarios to simulate the impact of increasing atmospheric CO2 levels in an idealized setup.

The most notable features are the strongly opposing winter changes of the surface heat fluxes over regions of sea ice retreat and open Arctic ocean, and the interplay with the compensating energy transport divergence which can be linked to the near-surface air moist static energy in an energetic-diffusive perspective. We further aim to relate the changes of individual energetics to the temperature lapse rate in the Arctic to better understand and quantify the factors contributing to its evolution.
Copernicus POD Service - Orbit reprocessing for Copernicus Sentinel-1 satellites
Authors: Peter Heike , Fernández Marc , Arnold Daniel , Duan Bingbing , Simons Wim , Gini Francesco , Wermuth Martin , Hackel Stefan , Fernández Jaime , Jäggi Adrian , Hugentobler Urs , Visser Pieter , Zandbergen René , Féménias Pierre
Published: March 2021

The Copernicus Sentinel-1 SAR (Synthetic Aperture Radar) mission consists of two satellites A and B launched in April 2014 and April 2016, respectively. The Copernicus POD (Precise Orbit Determination) Service is responsible for the generation of precise orbital products of the mission requiring a high orbit accuracy of 5 cm in 3D RMS in the comparison to external processing facilities.

The operational POD setup at the Copernicus POD Service has passed through several updates during the last years. For instance the ITRF update from ITRF08 to ITRF14 at the end of January 2017, the fundamental background model update in May 2020, and the switch to updated GPS antenna reference point coordinates together with the introduction of carrier phase ambiguity fixing at the end of July 2020 have been done to mention just the major changes in the processing. To provide a homogeneous and up-to-date orbit time series for the two satellites a reprocessing of the full mission period is done.  

The quality control of the reprocessed Copernicus Sentinel-1 orbits is done by analysing processing metrics and by comparing the results to orbits, which were independently reprocessed by members of the Copernicus POD Quality Working Group (QWG).

Results from the full Copernicus Sentinel-1 POD reprocessing campaign are presented together with the accuracy and quality assessment of the orbits.
Glacier melt contribution to streamflow during extremely dry summers
Authors: Van Tiel Marit , Freudiger Daphné , Kohn Irene , Weiler Markus , Seibert Jan , Stahl Kerstin
Published: March 2021

Extreme dry (and hot) summers, such as observed in Europe in the years 2003, 2015, 2018 and 2019, cause meteorological, hydrological and soil moisture droughts. These different types of droughts can have a range of negative impacts on, for instance, agricultural yield, water supply and hydropower production. The European Alps, also known as Europe’s water tower, potentially play an important role during such extreme summers by providing (extra) water from the melt of snow and ice. In this research study, we analyzed the streamflow conditions from a large sample of glacierized headwater catchments in the Swiss Alps during low flow years (1976, 1985, 1991, 2003, 2011, 2015, 2018 and 2019) observed downstream. Streamflow and its components (snow, ice and rain) were modelled with the HBV-light model for the period 1973-2020. These simulated streamflow components, together with observed total streamflow records, were compared between different catchments and different drought years. For each drought year, the winter conditions were examined, and the development of the drought situation over the summer was evaluated. To estimate the streamflow contribution of headwaters in the European Alps in such drought years in a situation without any glaciers, we also performed a model simulation where glaciers were assumed to have disappeared entirely. The results showed that glacier- and snowmelt contributed substantially to streamflow during these extreme years in the glacierized headwater catchments. In some cases, glacier ice provided up to three times as much melt than usually during summer. Catchments with a high glacier cover fraction usually showed a positive streamflow anomaly during these years. In 1991 and 2003, all catchments had an increased ice melt contribution, while in the other extreme years some catchments provided less ice melt contribution than average. Overall, this study shows that glaciers play an important role during low flow years and that a reduced glacier cover, or even completely retreated glaciers, will substantially reduce the buffer capacity of Europe’s water tower in the situation of meteorological drought.
Vortex streets to the lee of Madeira in a km-resolution regional climate model
Authors: Gao Qinggang , Zeman Christian , Vergara Temprado Jesus , Molnar Peter , Schär Christoph
Published: March 2021

Atmospheric vortex streets are one of the widely studied dynamical effects of isolated islands. However, the study of vortex shedding is still limited by the availability of observational wind ﬁelds of high spatial and temporal resolutions. Although the geometry, kinematics, and dynamics of vortex streets have been intensively investigated in numerous theoretical, numerical, and observational studies, our understanding of vortex shedding in the real atmosphere and atmospheric models is still insufficient.

Using the non-hydrostatic limited-area COSMO model driven by the ERA-Interim reanalysis, we simulated a mesoscale domain in high spatial (grid spacing 1 km) and temporal resolutions over one decade. This enabled us to investigate vortex streets within the planetary boundary layer despite limited observations. The basic properties of vortex streets are analyzed and validated through a 6-day-long case study in the lee of the Madeira island. The simulation compares well with satellite and aerial observations, and with the existing literature on idealized simulations.

Our results show a strong dependency of vortex shedding on local and synoptic flow conditions, which are to a large extent governed by the location, shape, and magnitude of the Azores high, which represents one pole of the North Atlantic Oscillation. As part of the case study, we have developed a vortex identification algorithm, consisting of a wavelet analysis using a set of objective criteria. The algorithm shows good performance in terms of false-positive rate and enables us to develop a climatology of vortex shedding in this region for the 10-year simulation period. Based on the long term analysis, we can identify an increasing vortex shedding rate from April to August and a sudden decrease in September, which can be well explained by the large-scale wind conditions.
Deriving the full turbulent stress tensor from paired ADCP measurements: application to under-ice convection
Authors: Kirillin Georgiy , Bogdanov Sergey , Volkov Sergey
Published: March 2021

The Reynolds stress tensor (RST) is the key characteristic of turbulence describing the paths of turbulent kinetic energy transfer and its anisotropy. Despite recent technical advances in application of multi-beam acoustic Doppler current profilers (ADCPs) to in situ acquiring of the RST components, derivation of the full Reynolds tensor from raw flow measurements remains a challenging problem. We present a method for derivation of the full set of turbulent stresses, based on combined use of two ADCPs with two beams from adjacent devices crossing at some point.  In the proposed framework, two 3-beam ADCPs with vertically aligned axes constitute the minimum configuration sufficient to derive 6 equations for all 6 RST components. 
The method was applied to studying turbulence in a convectively mixed layer in ice-covered Lake Kilpisjärvi. The calculated dynamics of all six stress components revealed diurnal periodicity along with the variations with the periods of a few hours. The pulsations intensities (diagonal components of RST) remained positive except short outliers; less than 5% of cases did not meet the so-called realizability requirements (positive definiteness of the stress matrix). The off-diagonal stresses demonstrated sign-changing dynamics, mirroring the inter-component energy transfer.
The ratio of pulsation intensities along vertical and horizontal axes varied in the range from 0.02 to 0.25. The r.m.s. values of horizontal and vertical pulsations reached diurnal maximums of 4 and 1 mm/s correspondingly, the latter being close to 1/3 of the convective velocity w*, in accordance with the previous studies on free convection. 
The new approach provides an immediate insight into the internal structure of the turbulent boundary mixing, especially relevant to anisotropic non-stationary flows, like buoyancy-driven convection. The preliminary results on under-ice convection elucidate strong anisotropy of the convective flow — a key to understanding the heat and mass transport in ice-covered waters.
X-ray fluorescence spectrometry for rapid screening of particle size in soils
Authors: Croffie Maame , Williams Paul N. , Fenton Owen , Fenelon Anna , Daly Karen
Published: March 2021

Soil texture is an essential factor for effective land management in agricultural production. Knowledge of soil texture and particle size at field scale can aid with on-going soil management decisions. Standard soil physical and gravimetric methods for particle size analysis are time-consuming and X-ray fluorescence spectrometry (XRF) provides a rapid and cost-effective alternative. The objective of this study was to explore the use of XRF as a predictor for particle size. An extensive archive of Irish soils with particle size and soil texture data was used to select samples for XRF analysis. Regression and correlation analyses on XRF determined results showed that the relationship between Rb and % clay varied with soil type and was dependent on the parent material. There was a strong relationship (R > 0.62, R2>0.30, p<0.05) between Rb and clay for soils originating from bedrock such as limestones and slate. Contrastingly, no significant relationship (R<0.03, R2=0.00, p>0.05) exists between Rb and % clay for soils originating from granite and gneiss. Furthermore, there was a significant negative correlation (p<0.05) between Rb and % sand. The XRF is a useful technique for rough screening of particle size distribution in soils originating from certain parent materials. Thus, this may contribute to the rapid prediction of soil texture based on knowledge of the particle size distribution.

 