bluuebunny/crossref_metadata_2025 huggingface dataset:
Joint analysis of remotely sensed soil moisture and water storage variations from satellite gravimetry
Authors: Blank Daniel , Eicker Annette , Jensen Laura , Güntner Andreas
Published: March 2021

Information on water storage changes in the soil can be obtained on a global scale from different types of satellite observations. While active or passive microwave remote sensing is limited to investigating the upper few centimeters of the soil, satellite gravimetry is sensitive to variations in the full column of terrestrial water storage (TWS) but cannot distinguish between storage variations occurring in different soil depths. Jointly analyzing both data types promises interesting insights into the underlying hydrological dynamics and may enable a better process understanding of water storage change in the subsurface.

In this study, we aim at investigating the global relationship of (1) several satellite soil moisture (SM) products and (2) non-standard daily TWS data from the GRACE and GRACE-FO satellite gravimetry missions on different time scales. We decompose the data sets into different temporal frequencies from seasonal to sub-monthly signals and carry out the comparison with respect to spatial patterns and temporal variability. Level-3 (Surface SM up to 5 cm depth) and Level-4 (Root-Zone SM up to 1 m depth) data sets of the SMOS and SMAP missions as well as the ESA CCI data set are used in this investigation.
Since a direct comparison of the absolute values is not possible due to the different integration depths of the two data sets (SM and TWS), we will analyze their relationship using Pearson’s pairwise correlation coefficient. Furthermore, a time-shift analysis is carried out by means of cross-correlation to identify time lags between SM and TWS data sets that indicate differences in the temporal dynamics of SM storage change in varying depth layers.
Better Than Just Average: The Many Faces of Bayesian Model Weighting Methods and What They Tell Us about Multi-Model Use
Authors: Höge Marvin , Guthke Anneli , Nowak Wolfgang
Published: March 2021

In environmental modelling it is usually the case that multiple models are plausible, e.g. for predicting a certain quantity of interest. Using model rating methods, we typically want to elicit a single best one or the optimal average of these models. However, often, such methods are not properly applied which can lead to false conclusions.

At the examples of three different Bayesian approaches to model selection or averaging (namely 1. Bayesian Model Selection and Averaging (BMS/BMA), 2. Pseudo-BMS/BMA and 3. Bayesian Stacking), we show how very similarly looking methods pursue vastly different goals and lead to deviating results for model selection or averaging.

All three yield a weighted average of predictive distributions. Yet, only Bayesian Stacking has the goal of averaging for improved predictions in the sense of an actual (optimal) model combination. The other approaches pursue the quest of finding a single best model as the ultimate goal - yet, on different premises - and use model averaging only as a preliminary stage to prevent rash model choice.

We want to foster their proper use by, first, clarifying their theoretical background and, second, contrasting their behaviors in an applied groundwater modelling task. Third, we show how the insights gained from these Bayesian methods are transferrable to other (also non-Bayesian) model rating methods and we pose general conclusions about multi-model usage based on model weighting.

 

 
The sensitivity of cloud radiative forcing with respect to the macrophysical properties and organization of the trade-wind cloud field during EUREC4A
Authors: Luebke Anna , Ehrlich André , Schäfer Michael , Wolf Kevin , Wendisch Manfred
Published: March 2021

The clouds in the Atlantic trade-wind region are known to have an important role in the global climate system, but the interactions between the microphysical, macrophysical and radiative properties of these clouds are complex. This work seeks to understand how the macrophysical properties and organization of the cloud field impact the large-scale cloud radiative forcing in order to provide the necessary information for the evaluation of the representation of these clouds in models. During the 2020 EUREC4A campaign, the German HALO aircraft was equipped for the first time with two instruments - the BACARDI instrument, a broadband radiometer that encompasses a set of pyrgeometers and pyranometers to measure the upward and downward solar and terrestrial radiation at flight level, and the VELOX Thermal IR imager. Simultaneously, one-minute resolution observations of the flight domain were obtained by the GOES-E satellite, thus providing information about the properties of the clouds on a spatial scale compatible with the large footprint of the BACARDI instrument. Using the products of these three instruments, we observe how the changing cloud field (e.g. cloud fraction, mean liquid water path (LWP), cloud top height, degree of clustering) in the EUREC4A domain impacts the radiation measured at flight level. We see that although cloud fraction plays a significant role as expected, it is not sufficient to parameterize the cloud radiative effects. Furthermore, the results indicate that the general organization of the cloud field as well as other properties describing the cloud population are necessary, but their relative importance varies between different cloud scenes.
Interpretation of volcanic surface deformation using a 3D multi-source approach
Authors: Fernandez Jose , Camacho Antonio G. , Samsonov Sergey V. , Tiampo Kristy F. , Palano Mimmo
Published: March 2021

Volcano geodetic observation is a valuable tool to infer location, strength and geometry of magmatic plumbing systems. The availability of high precision and spatial resolution, spanning decades, deformation data from satellite radar observation and Global Navigation Satellite Systems (GNSS) can give us important information for detecting and characterizing their temporal variations as well as other possible geodynamic sources acting in the volcanic area. For this objective inversion techniques are necessary which help us to obtain the maximum of information from these new datasets. We present a new, original methodology to carry out a multi-source inversion of ground deformation data to better understand the subsurface causative processes (Camacho et al., 2020). The methodology uses a nonlinear approach which permits the determination of location, size and three-dimensional configuration, without any a priori assumption as to the number, nature or shape of the potential sources. The proposed method identifies a combination of pressure bodies and different types of dislocation sources (dip-slip, strike-slip and tensile) representing magmatic sources and other processes such as earthquakes, landslides or groundwater-induced subsidence through the aggregation of elemental cells. This approach carries out a simultaneous inversion of the deformation components and/or line-of-sight (LOS) data; and a simultaneous determination of diverse structures such as pressure bodies or dislocation sources, representing local and regional effects. Both things are done in a fully 3D context and without any initial hypothesis about the number, geometry or types of the causative sources is necessary. We show results from the application of this new methodology to synthetic and real test cases (e.g., Mt. Etna).

This research has been primarily supported by the Spanish Ministerio de Ciencia, Innovación and Universidades research project DEEP-MAPS (RTI2018-093874-B-I00) and is part of the CSIC-PTIs TELEDETEC and POLARCSIC activities.

References
Camacho, A.G., Fernández, J., Samsonov, S.V., Tiampo K.F., Palano, M., 2020. Multisource 3D modelling of elastic volcanic ground deformations. Earth and Planetary Science Letters, 547C, 116445. https://doi.org/10.1016/j.epsl.2020.116445.
Evaluating climate effects over long-term salts accumulation in hyperarid soils using stochastic modeling
Authors: Siman-Tov Lior , Crouvi Onn , Morin Efrat , Amit Rivka , Enzel Yehouda , Marra Francesco , J. Reznik Itay , Rosenzweig Ravid
Published: March 2021

Hyperarid (< 80 mm yr-1) soils in hot deserts are characterized by accumulations of soluble salts (gypsum and halite) in diagnostic horizons as a result of limited moisture availability. In most desert terrains, the source for pedogenic gypsum and halite is atmospheric dust and rainwater. The interplay between climatic properties such as frequency and intensity of rain events, rainfall composition, dust flux, and evaporation rates, govern the depth and concentration of these salts. Better understanding of these relationships can improve our estimation of regional paleoenvironmental and paleoclimate conditions. Up to date, only empirical correlations between annual rainfall and pedogenic salt horizons are available.

The goals of this study are to: 1) quantify rates of pedogenic gypsum accumulation with time and the role of controlling climatic conditions that govern its accumulation, 2) estimate the most likely climatic scenarios that led to the formation of the diagnostic gypsic horizon developed in late Pleistocene (~ 60 ka) abandoned alluvial fan surfaces in the hyperarid Negev desert,  southern Israel. To achieve these goals, we constructed a compartment model that simulates gypsum accumulation in soil and tests its sensitivity to various changes in the long-term climate properties. The model predicts gypsum content and depth of accumulation in the soil profile over thousands of years and more. The input parameters are stochastically simulated rainstorms, evaporation, dust flux, and sulfate concentration in rainwater, at daily time steps. The model was tested and calibrated using data of Holocene (< 11 ka) soil profiles developed on stable alluvial fans in the hyperarid Negev. With the assumption that the climate during the Holocene was not much different than today (i.e., mean annual rainfall < 50 mm). Sensitivity analyses indicate that gypsum accumulation is highly sensitive to mean annual rainfall and sulfate concentration in rainwater. Synthetic gypsum profiles were calculated using different climate scenarios and compared to late Pleistocene soils. Our results suggest that: (a) gypsum accumulation in late Pleistocene soils cannot occur simply by extending current climate conditions for a much longer duration. (b) The plausible climate scenarios for the late Pleistocene must include additional rain input (1.5 – 2.0 times than mean annual rainfall today) and increased sulfate concentration in rainwater (2.0 – 2.5 times than today) to successfully reconstruct the observed accumulated gypsum in mature (60 – 12 Ka) soil profiles.
Exploring the influence of frontal ablation on global glacier mass change projections
Authors: Malles Jan-Hendrik , Maussion Fabien , Marzeion Ben
Published: March 2021

Mountain glaciers across the world are contributing around one-third to the recent barystatic global mean sea-level rise, and relevant for regional hydrological changes. Although the majority of Earth’s glaciers is land-terminating, roughly one-third of the glaciated area drains into an ocean or a lake. Due to the interrelation of surface and frontal mass budget, marine-terminating glaciers are subject to different dynamics than land-terminating ones, which are only forced by the atmosphere. This means that mass changes of marine-terminating glaciers cannot only be explained by changes in the atmospheric forcing. Thus, if ice-ocean interaction is not explicitly treated in a mass-balance model, calibration using, e.g., geodetic mass balances will lead to an overestimation of these glaciers’ sensitivity to changes in atmospheric temperatures. However, most large-scale glacier models are not yet able to account for this process and frontal ablation remains an elusive feature of glacier dynamics, because direct observations are sparse. We explore this issue by implementing a simple frontal ablation parameterization in the Open Global Glacier Model (OGGM). One of the major changes this entails is the lowering of marine-terminating glaciers’ sensitivities to atmospheric temperatures in the model’s surface mass-balance calibration. We then use this model, forced with an ensemble of atmospheric temperature and precipitation projections from climate models taking part in the Climate Model Intercomparison Project’s sixth phase (CMIP6), to project global glacier mass change until 2100. The main aim of this work is to investigate  the influence of the frontal ablation parameterization on those projections. We find that introducing the parameterization of frontal ablation, but ignoring changes in ocean climate, reduces the spread between different emission scenarios in 2100.
The spacecraft wake as a tool to detect cold ions: Turning a problem into a feature
Authors: André Mats , Eriksson Anders I. , Khotyaintsev Yuri V. , Toledo-Redondo Sergio
Published: March 2021

Wakes behind scientific spacecraft caused by supersonic drifting ions is common in collisionless plasmas. Such wakes change the local plasma conditions and disturb in situ observations of the geophysical plasma parameters. We concentrate on observations of the electric field with double-probe instruments. Sometimes the wake effects are caused by the spacecraft body, are minor and easy to detect, and can be compensated for in a reasonable way. We show an example from the Cluster spacecraft in the solar wind. Sometimes the effects are caused by an electrostatic structure around a positively charged spacecraft causing an enhanced wake and major effects on the local plasma. Here observations of the geophysical electric field with the double-probe technique becomes impossible. Rather, the wake can be used to detect the presence of cold positive ions. Together with other instruments, also the cold ion flux can be estimated. We discuss such examples from the Cluster spacecraft in the magnetospheric lobes. For an intermediate range of parameters, when the drift energy of the ions is comparable to the equivalent charge of the spacecraft, also the charged wire booms of a double-probe instrument must be taken into account to extract useful information from the observations. We show an example from the MMS spacecraft near the magnetopause. With understanding of the physics causing wakes behind spacecraft, the local effects can sometimes be compensated for. When this is not possible, sometimes entirely new geophysical parameters can be estimated. An example is the flux of cold positive ions, constituting a major part of the mass outflow from planet Earth, using electric and magnetic field instruments on a spacecraft charged due to photoionization

 
Tropical Climate Variability and Coral Reefs - A Past to Future Perspective on Current Rates of Change at Ultra-High Resolution
Authors: Felis Thomas , Pfeiffer Miriam
Published: March 2021

Climate change, in particular the rise in tropical sea surface temperatures, is the greatest threat to coral reef ecosystems today and causes climatic extremes affecting the livelihood of tropical societies. The combination of long-term global warming and interannual El Niño-related warm events has severely affected corals and coral reefs throughout the tropical ocean basins. Mass coral bleaching, a result of large-scale temperature stress, was first observed during the 1982/83 El Niño, and was followed by much more severe, global scale bleaching events during the El Niño years of 1997/98 and 2010, culminating in the most wide-spread and most destructive global bleaching episode to date, which lasted from 2014-2017. The interval between recurrent mass coral bleaching events driven by anomalously high sea surface temperatures is becoming too short for a full recovery of mature coral reef assemblages and will have dramatic effects on future coral reef growth. Assessing how future warming will change coral reef ecosystems and tropical climate variability is therefore of extreme urgency.

The recently established Priority Programme „Tropical Climate Variability and Coral Reefs – A Past to Future Perspective on Current Rates of Change at Ultra-High Resolution“ (SPP 2299; https://www.spp2299.tropicalclimatecorals.de/) of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) aims to enhance our current understanding of tropical marine climate variability and its impact on coral reef ecosystems in a warming world, by quantifying climatic and environmental changes during both the ongoing warming and past warm periods on timescales relevant for society. Ultra-high resolution coral geochemistry provides a tool to understand the temporal response of corals and coral reefs to ongoing climate and environmental change, to reconstruct past tropical climate and environmental variability and to use these data in conjunction with advanced statistical methods, earth system modelling and observed ecosystem responses for improved projections of future changes in tropical climate and coral reef ecosystems.

The Priority Programme is organised around three major research topics in order to fuel interdisciplinary collaboration among various disciplines: (a) Large-scale ocean, climate & environment reconstructions, (b) Coral & reef-scale response to current environmental stress, and (c) Climate, reef & proxy modelling – Climate & proxy advanced statistics. The strongly interdisciplinary Priority Programme will bring together expertise in the fields of climate, environmental and ecosytem research in a sustainable manner, and aims to provide an ultra-high resolution past to future perspective on current rates of change to project how tropical marine climate variability and coral reef ecosystems will change in a warming world.
Human induced changes in the carbon cycle over the last 60 years
Authors: Friedlingstein Pierre
Published: March 2021

Human activities have an unprecedented impact on the global carbon cycle.  Atmospheric CO2 concentrations have been continuously monitored since 1958, and show a 30% increase, from 315 ppm in 1958 to 412 ppm in 2020. Anthropogenic emissions, primarily from fossil fuel combustion, but also from land-use changes, are the drivers of these changes, with global emissions almost tripling over that period, from 4GtC per year in 1958 to almost 12 GtC per year at present. Although fossil fuel emission declined by about 7% in 2020 due to response to the COVID-19 pandemic, there are no long-term sign of global emissions declining yet, despite climate policies being put in places in many countries.

The atmospheric CO2 increase induces land and ocean carbon uptake, respectively driven by enhanced photosynthesis, leading to larger land biomass and soil carbon; and by enhanced air-sea CO2 exchange, leading to larger carbon content in the surface ocean and export to the deep ocean. These mechanisms are negative feedbacks in the Earth system and are removing about 50% of the CO2 emitted in the atmosphere. Without these land and ocean carbon sinks, current atmospheric CO2 would already be around 600 ppm.

However, modelling studies show that climate change reduces land and ocean carbon sinks, hence amplifying the warming. Although there is agreement that such positive feedback will develop over the course of the century, there are not yet clear evidence of a major climate driven reduction of the carbon sinks.  So far, observations and modelling studies of the historical carbon cycle do not show any sign of a tipping point in the global carbon cycle.
Stochastic modelling of stratospheric temperature
Authors: Eggen Mari , Rognlien Dahl Kristina , Näsholm Sven Peter , Mæland Steffen
Published: March 2021

A stochastic model for daily-spatial mean stratospheric temperature over a given area is suggested. The model is a sum of a deterministic seasonality function and a Lévy driven vectorial Ornstein-Uhlenbeck process, which is a mean-reverting stochastic process. More specifically, the model is an order 4 continuous-time autoregressive (CAR(4)) process, derived from data analysis suggesting an order 4 autoregressive (AR(4)) process to model the deseasonalized stochastic temperature data empirically. In this analysis, temperature data as represented in ECMWF re-analysis model products are considered. The residuals of the AR(4) process turn out to be normal inverse Gaussian distributed random variables scaled with a time dependent volatility function. In general, it is possible to show that the discrete time AR(p) process is closely related to CAR(p) processes, its continuous counterpart. An equivalent effort is made in deriving a dual stochastic model for stratospheric temperature, in the sense that the year is divided into summer and winter seasons. However, this seems to further complicate the modelling, rather than obtaining a simplified analytic framework. A stochastic characterization of the stratospheric temperature representation in model products, such as the model proposed in this paper, can be used in geophysical analyses to improve our understanding of stratospheric dynamics. In particular, such characterizations of stratospheric temperature may be a step towards greater insight in modelling and prediction of large-scale middle atmospheric events like sudden stratospheric warmings. Through stratosphere-troposphere coupling, this is important in the work towards an extended predictability of long-term tropospheric weather forecasting.
The new CYCOFOS forecasting at coastal, sub-regional and regional scales in the Mediterranean and the Black Sea
Authors: Zodiatis George , Lardner Robin , Nikolaidis Marios , Sofianos Sarantis , Vervantis Vasilis , Zhuk Elena , Spanoudaki Katerina , Kampanis Nikolaos , Kallos George , Sylaios George
Published: March 2021

The Cyprus coastal ocean forecasting system, known as CYCOFOS has been providing operational hydrodynamical and sea state forecasts in the Eastern Mediterranean since early 2002. Recently, it has been improved with the implementation of new hydrodynamic and new wave modeling systems with the objective of targeting higher resolution domains, at coastal, sub-regional and regional scales in the Mediterranean and the Black Sea. For the new CYCOFOS hydrodynamic modeling system a novel parallel version of the well established POM has been implemented. The new CYCOFOS hydrodynamical models covers the entire Eastern Mediterranean with a resolution of 2 km and the Levantine Basin with a resolution of ~600 m, both nested in the Copernicus Marine Environmental Monitoring Service of the Mediterranean Forecasting Center-CMEMS Med MFC. For sea waves forecasting, CYCOFOS has implemented  the new ECMWF wave model WAM CY46R1 in the Mediterranean and the Black seas at a higher resolution of 5 km. The CYCOFOS hydrodynamical models received an extended cal/val against the parent model, Argo profiles and satellite SST time series, while in-situ wave data gathered by the HERMES buoy monitoring network in the Eastern Mediterranean and the Black Sea were used for statistical validation of the new CYCOFOS wave forecasts. The new CYCOFOS validated modeling systems,  provide higher resolution quality controlled forecasting data suiting the needs for : a) down-streaming applications supporting risk assessment for offshore platforms in the Levantine Basin and studies concerning the coastal erosion in the Eastern Mediterranean (Albania, Cyprus, Greece) and the Black Sea (Bulgaria) in the framework of the HERMES project, and b) further hierarchical downscaling applications for the development of the COASTAL CRETE operation forecasting system at a higher resolution in the Eastern Mediterranean (Crete, Greece).
Seismogenic fault system of the Mw 6.4 November 2019 Albania earthquake: new insights into the structural architecture and active tectonic setting of the outer Albanides
Authors: Teloni Simone , Invernizzi Chiara , Mazzoli Stefano , Pierantoni Pietro Paolo , Spina Vincenzo
Published: March 2021

Fault geometries are usually reconstructed through seismic data, which can provide a very good image of the subsurface. However, the recognition of deep structures is often difficult for the shallow depth of these data and their low resolution in depth. On the contrary, recent earthquakes and their parameters (e.g. hypocentre, focal mechanism, magnitude, etc.) may have an important role in better understanding deep features, outlining the active crustal structures.

November 26th 2019 a 6.4 Mw Durres earthquake struck the Albanian coastal area, claiming 51 victims and hundreds of injured people. This seismic sequence sheds new light into the structural architecture and active tectonic setting of the northern outer Albanides. Stress field analysis performed through local mechanisms of the main seismic events of the sequence and those recorded since 1997 by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) confirm that the area is dominated by ENE trending, horizontal maximum compression, with a ENE dipping thrust faults roughly parallel to the coastline. Further analysis to investigate the structural architecture of this area was conducted plotting hypocentre distribution which show that shallower hypocentres tend to cluster around the deeper portion of projected fault segment proposed by the DISS ‘composite seismogenic source’ labelled ALCS002, whereas most of the seismic events including the Mw = 6.4 main shock are nucleated within the crystalline basement. This result unravels for the first time the fundamental role of deeply rooted, crustal ramp-dominated thrusting in seismogenesis, implying a profound reconsideration of the seismotectonic setting of the region.

The outcomes of this study show here that the recent earthquakes are pivotal in outlining the active crustal frontal structure of the thrust belt, providing new fundamental constraints, not only on the active tectonic setting of the region, but also on the crustal architecture of the outer Albanides. In this regard, the identification of such deep seismogenic sources and the definition of their dimensional parameters may have major implications on the correct assessment of the seismic hazard, especially for this large and densely populated area of Albania. Furthermore, the evidence provided in this study for a deep seismogenic thrust system in a foreland basin setting may be of general interest in similar tectonic contexts worldwide, where deep structures are possibly unidentified, and may represent a weakness in seismic hazard assessment.
Brittle deformation during eclogitization: a perspective from a cold, early Paleozoic subduction zone
Authors: Bukała Michał , Barnes Christopher , Klonowska Iwona , Hidas Károly , Fassmer Kathrin , Majka Jarosław
Published: March 2021

The Tsäkkok Lens (northern Scandinavian Caledonides) represents the outermost part of the rifted passive Baltica margin and consists of sediments and pillow basalts of MORB affinity that were metamorphosed under eclogite facies conditions. Fieldwork and further multidisciplinary analytical approach (including e.g. X-ray and EBSD mapping, and μ-CT imaging) revealed that eclogites record brittle deformation on the μm-to-m scale. This deformation is expressed as a set of microfractures (single-grain rupture) and mesofractures (sealed by garnet- and omphacite-veins). Phase equilibrium thermodynamic modeling of phengite-bearing and phengite-free eclogites performed in NCKFMMnASHT and NCFMMnASHT systems predict profuse dehydration related to lawsonite and amphibole breakdown at ~2.35 GPa and ~600°C, close to the peak conditions of ~2.55 GPa and ~640°C. These estimates are in line with conventional thermobarometry and Zr-in-rutile thermometry results. The evidence for dehydration is also provided by the  occurrence of relic glaucophane in matrix and polyphase inclusions in garnet consisting of clinozoisite + quartz ± kyanite ± paragonite that are interpreted as pseudomorphs after lawsonite. Dehydration reactions were responsible for producing fluid, which facilitated brittle fracturing of the eclogites at HP conditions due to increased pore-fluid pressure (also promoted by the volume changes during eclogitization) on the microscale. Altogether, micro- and mesofracturing acted as migration pathways for released fluid, whereas the microfractures are likely precursors of the mesoscale fractures. Garnet-WR Lu-Hf geochronology provided ages of 487.7 ± 4.6, 486.2 ± 3.2, and 484.6 ± 4.5 Ma. LA-ICP-MS trace element profiles of garnet revealed a well-pronounced peak of Lu content in the garnet cores that decreased towards the rims, indicating these dates represent the age of prograde metamorphism. Therefore, the early Paleozoic Tsäkkok Lens eclogites constitute the oldest documented natural example of HP brittle deformation during eclogitization of blueschist.

Research funded by NCN project no. 2019/33/N/ST10/01479 (M. Bukała) and no. 2014/14/E/ST10/00321 (J. Majka), as well as the Polish National Agency for the Academic Exchange scholarship no. PPN/IWA/2018/1/00046/U/0001 given to M. Bukała.
Mechanisms of decadal North Atlantic climate variability and implications for the recent cold anomaly
Authors: Årthun Marius , Wills Robert C. J. , Johnson Helen L. , Chafik Léon , Langehaug Helene R.
Published: March 2021

There has recently been a large focus on identifying the mechanisms responsible for Atlantic multidecadal variability (AMV). However, decadal-scale variability embedded within the AMV has received less attention, despite being a prominent feature of observed North Atlantic sea surface temperature (SST) and important for the climate of adjacent continents. These decadal fluctuations in the North Atlantic Ocean are also a key source of skill in decadal climate predictions. However, the mechanisms underlying decadal SST variability remain to be fully understood. This study isolates the mechanisms driving North Atlantic SST variability on decadal time scales using low-frequency component analysis, which identifies the spatial and temporal structure of low-frequency variability. Based on observations, large ensemble historical simulations and pre-industrial control simulations, we identify a decadal mode of atmosphere-ocean variability in the North Atlantic with a dominant time scale of 13-18 years. Large-scale atmospheric circulation anomalies drive SST anomalies both through contemporaneous air-sea heat fluxes and through delayed ocean circulation changes, the latter involving both the meridional overturning circulation and the horizontal gyre circulation. The decadal SST anomalies alter the atmospheric meridional temperature gradient, leading to a reversal of the initial atmospheric circulation anomaly. The time scale of variability is consistent with westward propagation of baroclinic Rossby waves across the subtropical North Atlantic. The temporal development and spatial pattern of observed decadal SST variability are consistent with the recent observed cooling in the subpolar North Atlantic. This strongly suggests that the recent cold anomaly in the subpolar North Atlantic is, in part, a result of decadal SST variability, and that we might expect it to become less pronounced over the next few years.
Upscaling transport of Bacillus subtilis endospores and phiX174 coliphages in heterogeneous porous media from the column to the field scale
Authors: Oudega Thomas , Lindner Gerhard , Derx Julia , Farnleitner Andreas , Sommer Regina , Blaschke Alfred , Stevenson Margaret
Published: March 2021

Groundwater contamination and subsequent transport of viruses and bacteria are a major concern in aquifers worldwide. To ascertain the ability of these aquifers to remove pathogens, tracer tests with microbial indicators are carried out. But because these tests are laborious and require special permission, column tests are often done instead. Unfortunately, results from column tests tend to grossly overestimate removal rates λ when compared to the field scale, which can lead to underestimations of groundwater contamination risks. Scale is an important consideration when examining pathogen transport through porous media, as pathogen removal rarely happens by linear processes. Field tests were carried out with Bacillus subtilis endospores and phiX174 coliphages over a distance of 25 m in an alluvial gravel aquifer in Vienna, Austria. The sandy gravel material from the field site was also used in column tests with the same tracers. Both attachment-detachment and Colloid Filtration Theory were used to model these tests. The results show a big difference in removal between the two scales. A comparison with the literature showed a correlation between the heterogeneity (or preferential flow) of the porous media and the difference in removal rates between the column and field scale.
A formula for downscaling extreme sub-daily rainfall intensities
Authors: Benestad Rasmus
Published: March 2021

Global warming is associated with an increased rate of evaporation due to higher surface temperatures which also implies a higher hydrological cycle turn-around in a steady-state atmosphere with respect to the water budget. The latter is accompanied with increased atmospheric overturning and more convective activity. In addition, there have been indications of a decreasing area of 24-hr rainfall on a global scale over the last decades, suggesting that rainfall is becoming concentrated over smaller regions. There have also been indications of higher cloud tops. In sum, a consequence of an increased greenhouse effect and modified hydrological cycle is an increased probability for heavy rainfall on local scales and a greater risk of flooding. Changes in risks connected to meteorological and hydrological challenges make it necessary to adapt to new weather statistics. For instance, there is a need to estimate the frequency of heavy downpour and their return levels, both for 24-hr amounts and sub-daily timescales. It is common to account for extreme rainfall by designing infrastructure with the help of intensity-duration-frequency (IDF) curves. One problem is that the IDF curves are based on long records of hourly rainfall measurements that are not widely available. Traditional IDF curves have also been fitted assuming stationary statistics, while climate change implies non-stationary weather statistics. We propose a formula for downscaling sub-daily rainfall intensity based on 24-hr rainfall statistics that is not as limited by data availability nor assumes stationarity. This formula provides a crude and approximate and rule-of-thumb for sites with 24-hr rain gauge data and can be used in connection with downscaling of climate model results. It also represents a way of downscaling rainfall statistics in terms of the time dimension.
Deriving CME volume and density from remote sensing data
Authors: Temmer Manuela , Holzknecht Lukas , Dumbovic Mateja , Vrsnak Bojan , Sachdeva Nishtha , Heinemann Stephan G. , Dissauer Karin , Scolini Camilla , Asvestari Eleanna , Veronig Astrid M. , Hofmeister Stefan
Published: March 2021

Using combined STEREO-SOHO white-light data, we present a method to determine the volume and density of a coronal mass ejection (CME) by applying the graduated cylindrical shell model (GCS) and deprojected mass derivation. Under the assumption that the CME  mass is roughly equally distributed within a specific volume, we expand the CME self-similarly and calculate the CME density for distances close to the Sun (15–30 Rs) and at 1 AU. The procedure is applied on a sample of 29 well-observed CMEs and compared to their interplanetary counterparts (ICMEs). Specific trends are derived comparing calculated and in-situ measured proton densities at 1 AU, though large uncertainties are revealed due to the unknown mass and geometry evolution: i) a moderate correlation for the magnetic structure having a mass that stays rather constant and ii) a weak correlation for the sheath density by assuming the sheath region is an extra mass - as expected for a mass pile-up process - that is in its amount comparable to the initial CME deprojected mass. High correlations are derived between in-situ measured sheath density and the solar wind density and solar wind speed as measured 24 hours ahead of the arrival of the disturbance. This gives additional confirmation that the sheath-plasma indeed stems from piled-up solar wind material. While the CME interplanetary propagation speed is not related to the sheath density, the size of the CME may play some role in how much material is piled up.
Water balance in the Antarctic lakes
Authors: Shevnina Elena
Published: March 2021

Antarctica keeps great volume of water on Earth. Its cold, dry and windy climate leads peculiar balance of water in various phases (solid, liquid and gas), and it is sensitive to warming. Increase of near surface temperature enhances water transition from solid to liquid phase (melting) as well as to gas (evaporation). The melted water is accumulated in a population of glacial lakes. These water bodies are located inside glaciers (subglacial type), over their surface (supraglacial type) or contacted glaciers (proglacial or epiglacial type). The glacial lakes are connected by a network of ephemeral streams. This hydrological network is typical in a lowest zone of Antarctic ice sheet, where the melting is substantial in the continental mass balance.

Water cycle in the glacial lakes differs with their type, and various processes drive water transport in the glacial lakes. In this study, the water balance equation method was applied to evaluate the volume of water accumulated in the glacial lakes. The water balance equation was written separately for the lakes of the epiglacial and supraglacial types. We used the observations by the long-term monitoring network, the data collected by the remote sensing, and the in-situ measurements gathered in field campaigns in the evaluations of the volume of lakes, the evaporation over a lake surface, and the inflow/outflow runoff. The components were evaluated for the epiglacial lakes located in the the Shirmacher, the Larsemann Hills and the Thala Hills oases (East Antarctica). 

The lake volume was evaluated from the lake surface area and depth measured withing last 10 years. The results show that since late 1980s, the lake volume has increased on many epiglacial lakes located not only in the coastal oases but also in the continental interior. The results suggest that the evaporation in among a key components of the water balance of the glacial lakes located in the Antarctica. In the polar region, the role of the evaporation is traditionally underestimated due to lack of the observations with precise measuring techniques. The results of the study contribute with the QAntarctica with the dataset on the actual physiography of the glacial lakes in Antarctica. This study is supported by the Academy of Finland (contract number 304345) with the logistic support of the national programs on the Antarctic research. 
The influence of Antarctic and Greenland ice loss on polar motion: an assessment based on GRACE and multi-mission satellite altimetry
Authors: Göttl Franziska , Groh Andreas , Kappelsberger Maria , Strößenreuther Undine , Schröder Ludwig , Helm Veit , Schmidt Michael , Seitz Florian
Published: March 2021

Increasing ice loss of the Antarctic and Greenland Ice Sheets (AIS, GrIS) due to global climate change affects the orientation of the Earth’s spin axis with respect to an Earth-fixed reference system (polar motion). Ice mass changes in Antarctica and Greenland are observed by the Gravity Recovery and Climate Experiment (GRACE) in terms of time variable gravity field changes and derived from surface elevation changes measured by satellite radar and laser altimeter missions such as ENVISAT, CryoSat-2 and ICESat. Beside the limited spatial resolution, the accuracy of GRACE ice mass change estimates is limited by signal noise (meridional error stripes), leakage effects and uncertainties of the glacial isostatic adjustment (GIA) models, whereas the accuracy of satellite altimetry derived ice mass changes is limited by waveform retracking, slope related relocation errors, firn compaction and the density assumption used in the volume-to-mass conversion.

 

In this study we use different GRACE gravity field models (CSR RL06M, JPL RL06M, ITSG-Grace2018) and satellite altimetry data (from TU Dresden, University of Leeds, Alfred Wegener Institute) to assess the accuracy of the gravimetry and altimetry derived polar motion excitation functions. We show that due to the combination of individual solutions, systematic and random errors of the data processing can be reduced and the robustness of the geodetic derived AIS and GrIS polar motion excitation functions can be increased. Based on these investigations we found that AIS mass changes induce the pole position vector to drift along the 60° East meridian by 2 mas/yr during the study period 2003-2015, whereas GrIS mass changes cause the pole vector to drift along the 45° West meridian by 3 mas/yr.
Sea ice and atmospheric potential predictability in coupled GCMs
Authors: Flocco Daniela , Hawkins Ed , Ponsoni Leandro , Massonnett François , Feltham Daniel , Fichefet Thierry
Published: March 2021

Assimilation of sea ice concentration satellite products has successfully been used to initialize sea ice models and coupled NWP systems. Sea-ice thickness observations, being much less mature, are typically not assimilated. However, many studies suggest that initialization of winter sea-ice thickness could lead to improved prediction of Arctic summer sea ice. We have examined the potential for sea ice thickness observations to improve forecast skill on timescales from days to a year ahead in two state-of-the-art coupled GCMs.

Here we examine the influence of Arctic sea-ice thickness observations on the potential predictability of the sea-ice and atmospheric circulation using idealised ‘data denial’ experiments. We perform paired sets of ensembles with the HadGEM3 and EC-Earth GCMs using different initial conditions retrieved from present-day control runs.

One set of ensembles start with complete information about the sea-ice conditions and is treated as “truth”, and one set has degraded sea ice information. We investigate how the pairs of ensembles, all started in January, predict the subsequent evolution of the sea-ice state, sea level pressure and circulation within the Arctic with the aim of quantifying the value of sea-ice observations for improving predictions.

We show that accurate initialization of sea ice thickness improves the model prediction skill during the first month of simulation and that several sea ice state and atmospheric variables present a re-emergence of skill in September. Prediction skill of several oceanic variables is also observed. The two models present a good agreement in terms of the regions where they show either a skill gain or loss.
Daily variability of upwellings ? The case study of South Vietnam upwelling (South China Sea)
Authors: Duy To Thai , Herrmann Marine , Estournel Claude , Marsaleix Patrick , Duhaut Thomas , Trinh Bich Ngoc , Ulses Caroline , Hong Bui Long
Published: March 2021

The South Vietnam upwelling (SVU) is one of the major processes involved in the South China Sea (SCS) ocean dynamics and planktonic ecosystem. Several numerical modelling studies examined its variability, revealing the leading role of wind and ENSO, but also, more recently, of ocean intrinsic variability (OIV) related to chaotic eddies. However, the spatial resolution of the models used in these studies did not allow to fully consider and understand the role of small scale dynamics. Our objective is therefore to implement a very high resolution model over the SCS in order to investigate the contribution of fine scale dynamics to the daily to interannual variability of the SVU.

We developed a configuration of the SYMPHONIE regional ocean model, using a curvilinear orthogonal grid over most of the SCS with a horizontal resolution increasing linearly from ~1.0 km along the Vietnamese coast to ~4.5 km offshore, and 50 layers. The surface forcing is prescribed using the 3-hourly output of the ECMWF, tidal forcing by FES2014, the initial and lateral ocean boundary conditions by the daily outputs of the global ocean 1/12° COPERNICUS analysis; monthly climatology and daily of freshwater river runoff are used for the 35 main rivers of the modeled domain.

We first evaluate the realism of the model by comparing a simulation performed over the period 2008-19 with in-situ measurements and satellite data. This multiannual simulation moreover confirms the leading role of wind on the daily to interannual variability of upwelling that develops in the coastal and offshore region. It also suggests, as already demonstrated by Da et al. (2019) at the interannual scale, that other processes are involved in this development. We thus explore the impact of ocean intrinsic variability, tides and rivers at the daily scale on the upwelling development by studying in details the intense upwelling that develops during summer 2018. For that, we perform several sensitivity experiments including ensemble simulations with perturbated initial conditions. We will present a synthesis of the results that reveal the strong impact of ocean background mesoscale circulation on the upwelling intensity at the daily scale, and its evolution during the summer.
Using clustering techniques for magnetic reconnection detection
Authors: Sisti Manuela , Finelli Francesco , Pedrazzi Giorgio , Faganello Matteo , Califano Francesco , Delli Ponti Francesca , Zalizniak Valeriia
Published: March 2021

The formation of coherent current structures in turbulent collisionless magnetized plasmas and their disruption through magnetic reconnection has been extensively studied in past years via in situ observations, numerical simulations, and theoretical models. Presently there is no automatic verified way to detect reconnection events so that only an accurate human analysis can be performed. We set-up a machine learning unsupervised technique aimed at automatically detecting the presence of current sheet (CS) magnetic structures where reconnection is occurring. We make use of clustering techniques as KMeans and DBscan, and compare their efficiency to that of simpler methods which do not use machine learning but are only based on thresholds on important physical quantities. The unsupervised machine learning method turns out to be the one with the best performance. We applied these techniques to 2D kinetic HVM (Hybrid Vlasov Maxwell) plasma turbulence simulations, where ions evolve by solving the Vlasov equation while the electrons are treated as a fluid. Electron inertia is included. We are presently working on adapting our techniques to 1D time series extracted from our simulations aiming at reproducing typical data measured by satellites. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 776262 (AIDA, www.aida-space.eu).
10 years of matching pursuits for inverse problems: what’s been done and what’s to come
Authors: Schneider Naomi , Michel Volker
Published: March 2021

In the light of significant challenges like the climate change, the visualization of the gravitational potential remains a priority in geodesy. A decade ago, the Geomathematics Group Siegen proposed alternative representations for such problems.

The respective methods are based on matching pursuits: hence, they build a representation in a so-called best basis. However, they include additional aspects which occur, for instance, when the downward continuation of the gravitational potential is approximated.

In this talk, we summarize the different developmental stages from 2011 up to now which started with a basic implementation and then included aspects of orthogonality, weakness and dictionary learning, respectively. Further, we give an outlook on our next steps with these methods. For the current status-quo, we show numerical results with respect to the downward continuation of the gravitational potential.