bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical Ice Sheet-Climate System Response to Astronomical Forcing
Authors: Abe-Ouchi Ayako
Published: March 2021

Paleoclimate modelling using simple models, EMICs (Earth System Models of Intermediate Complexity) and GCMs (General Circulation Models) combined with ice sheet models has become a powerful tool for understanding how the long-term climate system with ice sheets responds to external forcings such as Milankovitch forcing. With the aid of supercomputers and advances in climate model development, it is now possible to perform a much larger number of snapshot experiments with fixed forcings as well as transient experiments with evolving forcings. This talk will review the models that simulate the Northern Hemisphere ice sheet change and climate during the ice age cycles and discuss upcoming challenges. The talk will also present recent works on simulating millennial scale climate changes and the link with the ice age cycle. The last termination of the ice age cycles as well as glacial periods were punctuated by abrupt millennial scale climate changes, such as the Bølling-Allerød interstadial, the Younger Dryas and Dansgaard-Oeschger events. Abrupt climate changes have been shown to be strongly linked to changes in the Atlantic Meridional Overturning Circulation (AMOC) and the shift between the (quasi) multiple equilibria of AMOC, but the mechanism behind these abrupt changes and the link to climate change in the orbital scale are not clear. Modelling the stability of AMOC under different climate conditions together with deglacial climate change using fully coupled ocean-atmosphere GCMs has been challenging. Here we present a series of long transient experiments of at least 10,000 years with forcings under different ice sheet sizes, greenhouse gas levels and orbital parameters, as well as deglacial experiments following PMIP4 protocols, using a coupled ocean-atmosphere model, MIROC4m AOGCM. When forcing under glacial condition is applied, even without freshwater perturbation, the climate-ocean system shows self-sustained oscillations within a “sweet spot.” We also see a bipolar seesaw pattern and switching between interstadials and stadials, whose return time ranges from 1,000 years to nearly 10,000 years depending on the background forcing during the ice age cycle. Our transient deglaciation experiment with a gradually changing insolation, greenhouse gas forcing and ice sheet with meltwater from the glacial period to the Holocene is analysed and compared with proxy data as well as with the series of experiments with self-sustained oscillations for a better interpretation. Implications on the role of abrupt climate changes in shaping the longer-term global ice age cycle are further discussed.
Petrinja Seismogenic Source and its 2020-2021 Earthquake Sequence (central Croatia)
Authors: Kastelic Vanja , Atzori Simone , Carafa Michele M. C. , Marin Govorčin Marin , Herak Davorka , Herak Marijan , Matoš Bojan , Stipčević Josip , Bruno Tomljenović Bruno
Published: March 2021

The ongoing Petrinja earthquake sequence interests a structurally complex area characterized by the transition between the Dinarides and the Pannonian Basin structural units. The sequence mainshock (December 29, 2020; Mw = 6.4) struck in the vicinity of the Petrinja town and caused significant damage in the human and in the natural environments. The preliminary seismological and geodetic analyses indicated a dextral strike-slip NW-SE oriented fault as the event source. Numerous geologic surface deformation patterns have been identified in the aftermath of the main event, including collapsed sinkholes, liquefaction, different forms of landslides, and surface fractures which nature and causative process require further detailed studies.
The aim of our contribution is to apply a multitude of different geophysical, geodetic and geologic methodologies to decipher the Petrinja seismogenic fault geometry in the light of its ongoing earthquake sequence. We will show how the different datasets converge in delineating the fault geometry and discuss their diverging aspects and implications. Our preliminary analyses on the geometric and kinematic characteristics of the mainshock (as well as those of the foreshocks and aftershocks) point to an important structural complexity. This aspect helps us to better understand the seismotectonic framework of the Petrinja seismogenic fault and other regional seismogenic faults of similar geologic and geodynamic setting.
Anatomy of a cascading hazard: the flood part of the 7 February Uttarakhand event
Authors: Dietze Michael , Paul Himangshu , Pandey Anand Kumar , Rekapalli Rajesh , Rao Puranchand , D. Srinagesh , Cook Kirsten L. , Pilz Marco , Hovius Niels , Tiwari Virendra Mani
Published: March 2021

The 7 February Chamoli, Uttarakhand singularity imposed a severe geomorphic crisis. While remote sensing imagery quickly identified a major rock avalanche as its origin, there is a fundamental lack in high precision temporal information on the kinetics of this event about when, how, and why it evolved from a slope failure into a channel-confined mass wasting process, and ultimately into a debris laden flood. Furthermore, while the initial rock slide could be detected and located by global seismic networks, it was the flood which caused most of the destruction and fatalities. Yet, that part of the process cascade remained elusive in global seismic data sets.

Here, we present a detailed anatomy of the hazard cascade, with emphasis on the flood part. Using information from a dense seismic network, we explore the limits of detection and constrain its propagation velocity. By jointly inverting two physical models that predict spectral signal properties of floods, we estimate important hydraulic and sediment transport metrics. These information are key for designing any future early warning infrastructure.
Accumulation patterns of soil organic matter in forests as a legacy of historical charcoal burning
Authors: Schneider Anna , Bonhage Alexander , Hirsch Florian , Raab Alexandra , Raab Thomas
Published: March 2021

Human land use and occupation often lead to a high heterogeneity of soil stratigraphy and properties in landscapes within small, clearly delimited areas. Legacy effects of past land use also are also abundant in recent forest areas. Although such land use legacies can occur on considerable fractions of the soil surface, they are hardly considered in soil mapping and inventories. The heterogenous spatial distribution of land use legacy soils challenges the quantification of their impacts on the landscape scale. Relict charcoal hearths (RCH) are a widespread example for the long-lasting effect of historical land use on soil landscapes in forests of many European countries and also northeastern USA. Soils on RCH clearly differ from surrounding forest soils in their stratigraphy and properties, and are most prominently characterized by a technogenic substrate layer with high contents of charcoal. The properties of RCH soils have recently been studied for several regions, but their relevance on the landscape scale has hardly been quantified.

We analyse and discuss the distribution and ecological relevance of land use legacy soils across scales for RCH in the state of Brandenburg, Germany, with a focus on soil organic matter (SOM) stocks. Our analysis is based on a large-scale mapping of RCH from digital elevation models (DEM), combined with modelled SOM stocks in RCH soils. The distribution of RCH soils in the study region shows heterogeneity at different scales. The large-scale variation is related to the concentration of charcoal production to specific forest areas and the small-scale accumulation pattern is related to the irregular distribution of single RCH within the charcoal production fields. Considerable fractions of the surface area are covered by RCH soils in the major charcoal production areas within the study region. The results also show that RCH can significantly contribute to the soil organic matter stocks of forests, even for areas where they cover only a small fraction of the soil surface. The study highlights that considering land use legacy effects can be relevant for the results of soil mapping and inventories; and that prospecting and mapping land use legacies from DEM can contribute to improving such approaches.
EMI characterization in mountain catchments: multi-frequency versus multi-coil inversion using EMagPy
Authors: Blanchy Guillaume , McLachlan Paul , Censini Matteo , Boaga Jacopo , Binley Andrew , Cassiani Giorgio
Published: March 2021

Advanced modeling of hydrological processes in mountain catchments requires accurate characterization of the shallow subsurface, and in particular the depth to the soil/bedrock interface. Frequency domain electromagnetic induction (EMI) methods are well suited to this challenge as they have short acquisition times and do not require direct coupling with the ground; consequently they can be highly productive. Moreover, although traditionally used for revealing lateral electrical conductivity changes, EMI inversion is increasingly used to quantitatively resolve both lateral and vertical changes. These quantitative models can then be used to inform several properties relevant for hydrological modelling (e.g. water content, permeability).

In this work the open-source software EMagPy is used to compare between EMI data collected with a multi-coil device (i.e. a single frequency device with multiple receiver coils) and a multi-frequency device (i.e. a single inter-coil distance and multiple frequencies). The latter instrument is easier to handle because of its shorter length and lower weight, and thus it is potentially more suitable for the rugged topography of mountain slopes. However it is important to compare the value of information (e.g. sensitivity patterns and data quality) obtained from both instruments.

To begin with, the performance of both devices is assessed using synthetic modeling. Following from this the analysis is focused on two mountainous catchments: one located in the Alpine region above 2000 m a.s.l., the other in a Mediterranean catchment in Southern Italy. Both sites have differing geological and hydrological conditions and provide a useful comparison to determine the suitability of multi-frequency and multi-coil devices, and highlight necessary considerations of EMI acquisition.
Neural networks, local minima and computational thermodynamics
Authors: Kaus Boris , Riel Nicolas
Published: March 2021

Thermodynamics plays an increasingly important role in computational geodynamics, as the community moves towards including chemical reactions in mechanical models of deformation. An example is mineral reactions that induce volume changes which affect the local state of stress that may trigger nonlinear feedbacks. Another example is numerical simulations of magmatic systems where the chemistry of melts changes dramatically as the melt differentiates on its way up through the lithosphere. In order to compare the results of numerical models with geochemical and petrological field data, it is crucial to predict the rock types and major element chemistry from numerical simulations of magmatic systems. Precomputing phase diagrams and including them as a lookup table, which is the current standard approach, works when the chemistry is more or less constant, but is nontrivial for magmatic systems where the chemistry changes drastically and involves a 13-dimensional system (11 oxides, plus pressure and temperature). Parameterizing the main reactions is a possibility, but this renders the comparison of simulation results with available data difficult.

In the context of magmatic systems, significant progress has been made in recent years and we now have thermodynamic melting models that are consistent with experiments and can simulate the full compositional range from mafic to felsic melt compositions. Yet, in order to be useful for geodynamic applications, we also need sufficiently fast Gibbs energy minimization software tools that can automatically determine the most stable assemblage for a given pressure, temperature and chemistry. This is a nonlinear constrained optimization problem, for which we have developed a new, parallel, solution approach. One novelty of our approach is that it can efficiently make use of good initial guesses, for example obtained from the previous timestep of a geodynamic simulation or from nearby points in pressure and temperature space. Yet, as with any gradient-based method, a risk remains to be trapped in a local minimum in the solution space that is not the overall most stable assemblage. It is thus important to explore a sufficiently broad range of starting parameters to ensure convergence toward the global minimum. Whereas this problem is well-known among users of existing thermodynamic software (such as THERMOCALC, where the starting values have to be adjusted manually), it is much less clear how nonlinear the parameter space actually is for real applications. Do we have thousands of local minima, or are there only a few (and if yes, can we precompute some of these)?

Here, we will discuss several examples of melting models and map out the nonlinearity of the parameter space for these cases to get better insights in how to further speed up such calculations. We also discuss how shallow and deep neural networks can be trained and implemented as part of the workflow.
All that is known about Mars discrete aurorae so far
Authors: Soret Lauriane , Milby Zachariah , Gérard Jean-Claude , Schneider Nick , Jain Sonal , Ritter Birgit
Published: March 2021

The discrete aurorae on Mars were discovered with the SPICAM spectrograph on board Mars Express. Now, they have been analyzed in detail using the much more sensitive MAVEN/IUVS imaging spectrograph.

This presentation gives a summary of the very latest results obtained by Schneider et al. and Soret et al. on this topic.

The main conclusions are the following:

the number of auroral event detections has considerably increased since the Mars Express observations;

many detections have been made outside of the Southern crustal magnetic field structures;

the MUV spectrum shows the same emissions as those observed in the dayglow, with similar intensity ratios;

the Vegard-Kaplan bands of N2 have been observed for the first time in the Martian aurora;

the CO Cameron and the CO2+ UVD emissions occur at the same altitude;

the OI emission at 297.2 nm has been analyzed;

the CO Cameron/CO2+ UVD ratio is quasi-constant;

intensities are higher in B-field regions;

auroral emissions are more frequent in the pre-midnight sector;

the altitude of the emission layer is independent of local time and presence or absence of a crustal magnetic field;

the altitude of the emission layer varies moderately with season (atmospheric effect);

the events are spatially correlated with an increase in the flux of energetic electrons simultaneously measured by the MAVEN/SWEA (Solar Wind Electron Analyzer) detectors;

the peak altitude of the emission is in good agreement with that expected from the average electron energy.
Coupled evolution of tectonic, ocean circulations, and depositional regime in the southeastern Amundsen Basin
Authors: Weigelt Estella , Gaedicke Christoph , Jokat Wilfried
Published: March 2021

The Lomonosov Ridge (LR) and Fram Strait (FR) represent prominent morphologic features in the Arctic Ocean. Their tectonic evolution control ocean circulation, sedimentation environment, glacial processes and ecosystem through time. We present findings of a 300 km long seismic transect from the Gakkel Deep through the southeastern Amundsen Basin (AB), and onto the LR. The data image an up to 3 km thick sedimentary sequence that can be subdivided into six major seismic units.

The two lower units AB-1 and AB-2 consist of syn-rift sediments of Paleocene to early Eocene age likely eroded off the Barents-Kara and Laptev Sea shelves, and the subsiding LR.

AB-2 includes the time interval of the “Azolla event,” which is regarded as an era of a warm Arctic Ocean punctuated by episodic incursions of fresh water. The connection to North Atlantic waters via the Fram Strait was not yet established, and anoxic conditions prevailed in the young, still isolated Eurasian Basin. Also, the LR still was above or close to sea level and posed an obstacle for water exchange between the Eurasian and Amerasian basins.

The top of AB-2 onlaps the acoustic basement at magnetic anomaly C21o (∼47.3 Ma). Its contact with unit AB-3 above is marked by a striking loss in reflection amplitudes. This prominent interface can be traced through the AB, indicating widespread changes in tectonic and deposition conditions in the Arctic Ocean since the middle Eocene. For younger crust the depth of acoustic basement rises significantly, as well as the deformation of the surface. Both are probably linked to a reorganization of tectonic plates accompanied by a significant decrease in spreading rates.

Units AB-3 and AB-4 indicate the accumulation of sediments between the middle Eocene and the earliest Miocene. Erosional, channel-like interruptions indicate these layers to reflect the stage when Fram Strait opened and continuously deepened. Incursions of water masses from the North Atlantic probably led to first bottom currents and produced erosion, slumping, and subsequent mixing of deposits.

The upper units AB-5 to AB-6 show reflection characteristics and thicknesses similar all over the Arctic Ocean indicating that basin-wide pelagic sedimentation prevailed at least since late Oligocene. Drift bodies, sediment waves, and erosional structures indicate the onset of a modern ocean circulation system and bottom current activity in the early Miocene in the Amundsen Basin. At that time, the FR was developed widely, and also the LR no longer posed an obstacle between the Amerasia and Eurasia Basins. Lastly, unit AB-6 indicates pronounced variations in the sedimentary layers, and is associated with the onset of glacio-marine deposition since the Pliocene (5.3 Ma).
Coastal zone dynamics - as a result of changes at the border of three environments
Authors: Batyrev Oleksii , Andrianova Olga , Belevich Radomir , Skipa Michael
Published: March 2021

Coastal zone research is becoming increasingly important because the impact of climate change is most significant here. The state of coastal regions is determined by the variability in three contact media (geological, water, and air). Evaluation of level changes on the coasts of various parts of the World Ocean (the Mediterranean, Black, Baltic and North Seas, and the Atlantic coasts in Brazil and France) over a long period of time shows various fluctuations with an upward trend in recent decades.

To highlight the factors that determine the seashores' level fluctuations, three contact media parameters were considered on the example of the western part of the Black Sea. Calculations, analysis, and comparison of trends in the variability of hydrometeorological characteristics (air and water temperatures, precipitation, and river discharge) and sea level over a period of more than 100 years have been carried out.

To assess the intensity of fluctuations of the coastal land along the western coast of the Black Sea, the series of level heights were considered at 6 Ukrainian stations: Vylkove, Chornomorsk (Ilyichevsk), Odesa-port, port Yuzhne, Ochakiv and Sevastopol (partially used as a benchmark), at 2 stations on the Romanian coast: Constanta and Sulina, and 2 stations on the Bulgarian coast: Burgas and Varna. Estimates of the dynamics of the land for the stations of this region's coastal zone for more than a 100-year period are calculated, and it is shown in which way changes in sea level are a consequence of the processes occurring in the coastal land and at the bottom.

Comparison of the years with extreme fluctuations in the sea level with the years of the global El Niño phenomenon showed that one of the causes of the observed disturbances in the water and air environments is the distant manifestations of this phenomenon.

Level fluctuations, both in the Black Sea and in the World Ocean, are synchronous at low-frequency scales (their period is more than 5 years) since global climatic processes on our planet influence them; short-term fluctuations are distinguished by regional features and are created under the influence of local factors (tectonic, geophysical, hydrostatic, etc.).

Modeling and predicting changes in the coastal zone of various parts of the World Ocean requires continuation of systematic observations of sea-level fluctuations, hydrometeorological characteristics, and seismic conditions in regions with the longest data series; it's crucial for the Black Sea as well for the Mediterranean, Baltic, North Seas, and Atlantic shores.
Delayed sedimentary grains
Authors: Carretier Sebastien , Guerit Laure , Harries Rebekah , Regard Vincent , Maffre Pierre , Bonnet Stéphane , Choy Sandrine , Farías Marcelo
Published: March 2021

River sediment grains are transported and stored episodically in different reservoirs (terraces, alluvial fans, foreland basin, etc.). The residence time of sediment grains in each reservoir has important implications for the paleo-environmental interpretation established from these grains, and their stratigraphic record, as well as for soil contamination, when these grains come from contaminated sources. The recycling of old sediments, via erosion of an old reservoir (e.g. foreland basin erosion), is a known problem. What is less well recognised is that the recycling of a minority of very old grains can strongly bias the average residence time of a grain population deposited in a stratum. In this case, the time-dependent paleo-environmental properties of a population of grains, such as the degree of weathering, or the concentration of cosmogenic isotopes, can then be biased. Several lines of evidence for this phenomenon, inherent to fluvial transport processes, have emerged, though reconstructing the residence time distribution of a grain population over long times (>>ka) remains a challenge. Using a landscape evolution model coupled with grain transport, we show that at the scale of a piedmont, grains can remain several hundred ka before being evacuated. At the scale of a river in Northern Chile, we used the concentration of 10Be in individual pebbles to show that some pebbles remain stored for several tens of ka before being evacuated to the river outlet. In addition, the distribution of residence times can also provide information on the nature of the diffusive processes that control the fluxes of exported sediment. These results suggest that the characterisation of grain-by-grain properties in a grain population can not only help to avoid possible interpretation biases but also provide constraints for models of long-term fluvial sediment outfluxes.  
Stable isotope composition of crocodilian teeth provides new information on climatic change in the East-African Rift along the Plio-Pleistocene period (Shungura Formation, Lower Omo Valley Ethiopia) 
Authors: Gardin Axelle , Pucéat Emmanuelle , Garcia Géraldine , Boisserie Jean-Renaud , Otero Olga
Published: March 2021

Isotopic fluctuation of certain stable isotopes, notably Oxygen, provide important information on paleoenvironmental change along geological times. However, interpreting isotopic change along continental series depends on our ability to understand its recording, for instance in soils or in mammal teeth. In the case of continental series yielding most of available information on hominid diversification and expansion within and beyond Africa, isotopic information even seems to show discrepancies depending on the archive. In our study, we use isotopic composition in crocodilian tooth enamel. We assume that, for these ectotherms that regulate their temperature, isotopic composition recorded in their teeth mainly depends on drinking water, itself depending on precipitation. Moreover, crocodilian fossil teeth are abundant and widely distributed within continental series, thus constituting an interesting archive. We sampled crocodilian teeth from the Shungura Formation (Lower Omo Valley, Ethiopia), which spans major steps of human evolution between 3.6 Ma and ~1.0 Ma, tentatively correlated with major environmental changes in eastern Africa (intensification of seasonal contrasts, increasing aridity and landscape opening). The analyses of δ18O of hundreds of crocodilian teeth have identified environmental changes. Whereas the isotopic composition of paedogenic carbonates displays a different trend over time, that of crocodilian teeth relates changes already observed in mammal teeth, notably a major shift between 2.6 Ma and 2.3 Ma toward more arid conditions. Our study indicates that crocodilian teeth are a relevant archive of environmental change in continental contexts, and calls for further study to strengthen interpretations of isotopic composition in fossil archives. 
Combining model-based quasi-Lagrange tracking of air mass intrusions into the Arctic with airborne observations 
Authors: Kirbus Benjamin , Schäfer Michael , Ehrlich André , Wendisch Manfred
Published: March 2021

Large-scale air mass exchanges between lower latitudes and the inner Arctic are one key aspect in understanding Arctic climate change. Of particular interest are Warm and Moist Air Intrusions (WMAI). These events, albeit covering only 10 % of the time, drive >60 % of the overall moisture flux into the Arctic. Conveyed by surging downward longwave radiation, WMAI can trigger pronounced sea-ice melt and alter local atmospheric conditions for weeks.

However, many models struggle with a correct representation of air mass transformations during these events. Thus, a Lagrangian approach is suggested to perform airborne measurement campaigns and to analyze numerical weather forecast and reanalysis data. Here, we present a combination of the Lagrangian analysis tool Lagranto with ECMWF forecast datasets and the atmospheric flight planning tool MSS. This approach was applied during the September 2020 MOSAiC airborne campaign. Additionally, five-day forward and backward trajectories were calculated to identify air masses linking the airborne observations with ground-based observations at the MOSAiC camp. A first analysis of the air mass characteristics and their change along the trajectories is presented.

Due to vertical wind shear, such an air mass analysis is not trivial. It requires a detailed flight planning in order to sample the temporal and spatial (horizontal and vertical) development of the air masses. As an outlook for the upcoming spring 2022 HALO-(AC)3 campaign, the potential of combining Lagranto with MSS in predicting the most effective flight track is therefore demonstrated.
Case study of integrating ecosystem managememnt into spatial planning in rural environment
Authors: Danacova Michaela , Vyleta Roman , Hlavcova Kamila , Kohnova Silvia , Szolgay Jan
Published: March 2021

The landscape is an open system driven by interactions between natural and anthropogenic elements. Their long-term impact is responsible for the current form and status of the landscape. Integrated landscape management enables to implement particular solutions to mitigate the effects of threats to the ecological stability of the environment, to preserve and support diversity of ecosystems, to improve ecologically less stable parts of landscape and their spatial spread, as well as the possibility to maintain important cultural heritage of the landscape. The aim of the study was to aid local and regional spatial planning in a headwater catchment by a complex quantitative assessment of risks of flash flooding, muddy floods and soil erosion caused by extreme rainfall.  The research on and the design of protection measures were realized in the cadaster of the village situated on the border to Moravia in Slovakia. Generally accepted robust quantitative methods for risk mitigation, which are simple enough, but are yielding reliable predictions, were integrated into complex mitigation measures in order to improve the ecological stability and recreational potential of the area. Present land management practices are increasing the risk of flash flooding and soil erosion, including rill erosion on the arable land in the region with prevailingly flysch geological structures. A set of flood detention storages, infiltration trenches and agrotechnical measures on the arable land were proposed for the reduction of the extreme runoff and erosion. The effectiveness of the proposed measures showed that we were able to reduce the amount of soil erosion to permissible values. The results were integrated into a spatial erosion and flood protection scheme which will be the bases of spatial planning on a local scale for sustainable agriculture and will enable recreational use of the riverine areas and of the hilly landscape.
The Efficiency of Upward Wave Propagation Near the Tropopause
Authors: Weinberger Israel , Garfinkel Chaim
Published: March 2021

Extreme states of the polar stratospheric vortex are typically followed by anomalous surface circulation. These extreme stratospheric vortex states are in turn often associated with extreme heat flux between the tropopause and 100 hPa. 

The goal of this work is to better understand upward wave propagation between the tropopause and the bottom of the vortex near 100 hPa using both theory and reanalysis data.

Following Charney and Drazin (1961) we analytically solve a quasi-geostrophic planetary-scale model with three different layers: troposphere, tropopause inversion layer (TIL) and stratosphere. We allow for different buoyancy frequencies in each layer and show the dependence of transmission and reflection coefficients on the buoyancy frequencies, TIL depth and mean-state zonal wind. The dependence of heat flux in the TIL and stratosphere, as well as phase-lines for the wave solution, are presented. This analysis highlights the key role that the TIL and jumps in buoyancy frequency play for upward wave propagation.

We then use reanalysis data to consider the importance of this effect in observations. Four different specifications of the index of refraction are compared: that derived by Charney and Drazin in 1961, that derived by Matsuno in 1970, and two that relax some of the assumptions used in the derivations of the first two. The Charney and Drazin index of refraction includes terms ignored by Matsuno that are critical for understanding upward wave propagation just above the tropopause in both the climatology and associated with extreme heat flux events. By adding these ignored terms to the Matsuno index of refraction, it is possible to construct a useful tool that describes wave flux immediately above the tropopause and at the same time also describes the role of meridional gradients within the stratosphere. Specifically, a stronger tropopause inversion layer (TIL) tends to restrict upward wave propagation. It is also shown that while only 38% of extreme wave-1 Eliassen-Palm flux vertical component (Fz) at 100hPa events are preceded by extreme Fz at 300hPa, there are almost no extreme events at 100hPa in which the anomaly at 300hPa is of opposite sign or very weak.  
The Combined Influence of the Stratospheric Polar Vortex and ENSO on Zonal Asymmetries in the Southern Hemisphere Upper Tropospheric Circulation during Austral Spring and Summer
Authors: Osman Marisol , Shepherd Theodore , Vera Carolina
Published: March 2021

The influence of El Niño Southern Oscillation (ENSO) and the Stratospheric Polar Vortex (SPV) on the zonal asymmetries in the Southern Hemisphere atmospheric circulation during spring and summer is examined. The main objective is to explore if the SPV can modulate the ENSO teleconnections in the extratropics. We use a large ensemble of seasonal hindcasts from the European Centre for Medium-Range Weather Forecasts Integrated Forecast System to provide a much larger sample size than is possible from the observations alone.

We find a small but statistically significant relationship between ENSO and the SPV, with El Niño events occurring with weak SPV and La Niña events occurring with strong SPV more often than expected by chance, in agreement with previous works. We show that the zonally asymmetric response to ENSO and SPV can be mainly explained by a linear combination of the response to both forcings, and that they can combine constructively or destructively. From this perspective, we find that the tropospheric asymmetries in response to ENSO are more intense when El Niño events occur with weak SPV and La Niña events occur with strong SPV, at least from September through December. In the stratosphere, the ENSO teleconnections are mostly confounded by the SPV signal. The analysis of Rossby Wave Source and of wave activity shows that both are stronger when El Niño events occur together with weak SPV, and when La Niña events occur together with strong SPV.
Meridional overturning circulation at 30ºS in the Pacific Ocean: 1992, 2003, 2009 and 2017.
Authors: Arumí-Planas Cristina , Casanova-Masjoan Maria , Caínzos Verónica , Santana-Toscano Daniel , Cubas Armas Melania , Pérez-Hernández M. Dolores , Hernández-Guerra Alonso
Published: March 2021

The meridional circulation and transports at 32oS in the Pacific Ocean in 1992 and 2017 are compared with analogous data from 2003 and 2009. The hydrographic data comes from the GO-SHIP database and an inverse box model has been applied with several constraints. In 1992, 2003 and 2017 the pattern of the overturning streamfunction is similar, but in 2009 the pattern of the circulation changes in the whole water column. The horizontal distribution of mass transports at all depths in 1992 and in 2017 changes notably from the “bowed gyre” found in 2009 and resembles that regular shape of 2003. The hydrographic data have also been compared with analogous data obtained from the numerical modelling output of GFDL, ECCO, and SOSE. Results show that the numerical modelling output in the upper layers (γn<27.58 kg/m3) have a roughly similar pattern as hydrographic data. This is not the case, however, for deep and bottom layers (γn>27.58 kg/m3), where noticeable differences are found. Furthermore, the temperature transport in 2009 (0.16 ± 0.12 PW) is significantly lower than in 1992 (0.42 ± 0.12 PW), 2003 (0.38 ± 0.12 PW) and 2017 (0.42 ± 0.12 PW). In addition, the freshwater transport result in 2009 (0.50 ± 0.03 Sv) is significantly higher than in 1992 (0.26 ± 0.08 Sv), 2003 (0.25 ± 0.02 Sv) and 2017 (0.34 ± 0.08 Sv). Westward Rossby waves are presumably the dynamical forcing that changes the circulation pattern in 2009.
Numerical modelling of igneous processes
Authors: Keller Tobias
Published: March 2021

Magma matters. From magmatic differentiation of terrestrial planets into core, mantle and crust, to magmatism modulating plate tectonics and deep volatile cycles that maintain a habitable Earth, and volcanism causing terrible hazards but also providing rich energy and mineral resources – igneous processes are integral to the evolution of Earth and other terrestrial planetary bodies. Our understanding of volcanoes and their deep magmatic roots derives from a range of disciplines including field geology, experimental petrology, geochemical analyses, geophysical imaging, and volcano monitoring. Observational and experimental studies, however, are hampered by incomplete access to processes that play out across scales ranging from sub-millimetre size to thousands of kilometres, and from seconds to billions of years. Computational modelling provides a tool kit for investigating igneous processes across these scales.

Over the past decade, my research has been focused on advancing the theoretical description and numerical application of multi-phase reaction-transport processes at the volcano to planetary scale. Mixture theory provides a framework to represent the spatially averaged behaviour of a large sample of microscopic phase constituents including mineral grains, melt films, fluid droplets, and vapour bubbles. The approach has been used successfully to model both porous flow of melt percolating through compacting rock, as well as suspension flow of crystals settling in convecting magma bodies. My recent work has introduced a new modelling framework that bridges the porous to mushy and suspension flow limits, and extends beyond solid-liquid systems to multi-phase systems including several solid, liquid, and vapour phases. Igneous process modelling can thus provide new insights into the generation and extraction of mantle melts, the dynamics of crustal magma processing, the outgassing and eruption of shallow magma reservoirs, and the generation of mineral resources by exsolution of enriched magmatic liquids.
From Mixing to the Large Scale Circulation: How the Inverse Cascade Is Involved in the Formation of the Subsurface Currents in the Gulf of Guinea.
Authors: Assene Fernand , Morel Yves , Delpech Audrey , Aguedjou Micael , Jouanno Julien , Cravatte Sophie , Marin Frédéric , Ménesguen Claire , Chaigneau Alexis , Dadou Isabelle , Alory Gael , Holmes Ryan , Bourlès Bernard , Koch-Larrouy Ariane
Published: March 2021

We analyse the results from a numerical model at high resolution. We focus on the formation and maintenance of subsurface equatorial currents in the Gulf of Guinea and we base our analysis on the evolution of potential vorticity (PV). We highlight the link between submesoscale processes (involving mixing, friction and filamentation), mesoscale vortices and the mean currents in the area. In the simulation, eastward currents, the South and North Equatorial Undercurrents (SEUC and NEUC respectively) and the Guinea Undercurrent (GUC), are shown to be linked to the westward currents located equatorward. We show that east of 20◦W, both westward and eastward currents are associated with the spreading of PV tongues by mesoscale vortices. The Equatorial Undercurrent (EUC) brings salty waters into the Gulf of Guinea. Mixing diffuses the salty anomaly downward. Meridional advection, mixing and friction are involved in the formation of fluid parcel swith PV anomalies in the lower part and below the pycnocline, north and south of the EUC, in the Gulf of Guinea. These parcels gradually merge and vertically align, forming nonlinear anticyclonic vortices that propagate westward, spreading and horizontally mixing their PV content by stirring filamentation and diffusion, up to 20◦W. When averaged over time, this creates regions of nearly homogeneous PV within zonal bands between 1.5◦ and 5◦S or N. This mean PV field is associated with westward and eastward zonal jets flanking the EUC with the homogeneous PV tongues corresponding to the westward currents, and the strong PV gradient regions at their edges corresponding to the eastward currents. Mesoscale vortices strongly modulate the mean fields explaining the high spatial and temporal variability of the jets.
DORIS results on Precise Orbit Determination and on geocenter and scale solutions from CNES/CLS IDS Analysis Center contribution to the ITRF2020 
Authors: Capdeville Hugues , Mezerette Adrien , Lemoine Jean-Michel
Published: March 2021

The processing configuration for our IDS contribution to the International Terrestrial Reference Frame (ITRF2020) realization was defined. We adopted the last standards and models recommended by IERS. We took into account the IDS recommendations to mitigate the non-conservative force model error on satellites, to mitigate the effect of the South Atlantic Anomaly on the DORIS receivers and to improve the stability of the DORIS scale.

A Precise Orbit Determination (POD) status for DORIS satellites by taking into account all these improvements will be presented for the processed time span. We will give statistical results such as one per revolution empirical acceleration amplitudes and orbit residuals. We will also give some comparisons to some external precise orbits used for altimetry. Some external validations of our orbits will be done, such as with independent SLR measurements processing as well as through the use of altimeter crossovers when available. We will also look at the impact of our new ITRF2020 configuration on the DORIS geocenter and scale.
Occurrence of Polar Stratospheric Clouds using ground-based DOAS observations
Authors: Lauster Bianca , Dörner Steffen , Frieß Udo , Gu Myojeong , Pukite Janis , Wagner Thomas
Published: March 2021

Polar Stratospheric Clouds (PSCs) favour heterogeneous reactions and thus are an important component of ozone depletion processes in polar regions. Although satellite observations already yield high spatial coverage, the sampling frequency of a specific air volume depends on the measurement method. Here, continuous ground-based measurements with high temporal resolution can be a valuable complement.

Since 1999, a MAX-DOAS (Multi AXis-Differential Optical Absorption Spectroscopy) instrument has been operating at the German research station Neumayer (70° S, 8° W), Antarctica. Primarily, slant column densities of trace gases such as NO2, BrO and OClO are retrieved. However, in this study the so-called colour index (CI), i.e. the colour of the zenith sky, is investigated. Defined as the ratio between the observed intensities of scattered sun light at two wavelengths, it enables to monitor the occurrence of polar stratospheric clouds during twilight even in the presence of tropospheric clouds.

Using the radiative transfer model McArtim, the CI changes in the presence of polar stratospheric clouds can be analysed. Especially the height of the PSC layer affects the retrieved signal, but also the choice of the wavelengths has a strong impact. Here, it is advantageous that measurements are available in the UV and visible spectral range which allows a more extensive comparison of different CI choices. In order to assess the application of the colour index method, meteorological data are used to identify PSC cases in the data set.

The aim is to improve and evaluate the potential of this method. It is then used to infer the occurrence of PSCs throughout the measurement time series of more than 20 years.
The 2011-2020 long-term sustained inflation at Long Valley Caldera:  investigation of the interaction of magmatic and tectonic processes
Authors: De Paolo Erica , Trasatti Elisa , Tolomei Cristiano , Montgomery-Brown Emily K.
Published: March 2021

The Long Valley Caldera, California (USA), has been restless over the past few decades, experiencing seismic swarms and ground deformation episodes. The last inflation began in late 2011, when a radially symmetric tumescence was detected coinciding with a large resurgent dome within the caldera. Since then, a continuous inflation with quasi-steady rate of ~1.5 cm/yr has been observed.  Earthquakes mostly occur within the caldera along the South Moat Seismic Zone, to the south of the maximum deformation area. Although the area is tectonically active, increased seismic activity has been documented during periods of renewed inflation since the onset of this tumescence in 1978. In this study, we aim to investigate the nature and dynamics of the long-term unrest at Long Valley Caldera, as well as to provide new insights into the interaction between magmatic and tectonic processes. For this purpose, we consider a variety of datasets including geodetic and seismic records over the period spanning from late 2011 to the end of 2020. A complete seismic catalog supports our study, with more than 200 M2.5-4.5 earthquakes recorded since 2011, most with epicenters located within the caldera. Measurements from a dense network of continuous GPS stations collected in the last 10 years are analyzed in combination with high resolution Interferometric Synthetic Aperture Radar (InSAR) data. For full temporal coverage, we integrate InSAR velocities obtained from the acquisition of different satellite missions. We use, in particular, data from SAR systems operating with X and C-bands such as TerraSAR-X, COSMO-SkyMed and Sentinel-1. The multi-sensor dataset (i.e., GPS and multi-mission InSAR data) compensate the limitations of each technique, with reliable mapping of the deformation pattern evolving over several years. Data analysis highlights uplift velocities with peaks of ~2 cm/yr within the caldera and beyond its southern rim. Moreover, compared to the first half of the period of analysis (2011-2014), the area affected by high deformation rates is broader in the last several years (2017-2020). Models based on the geodetic data are developed to constrain the deformation source and to better interpret the observed signals. This study is motivated as a contribution to the understanding of this long-lived caldera unrest, for a more reliable hazard assessment.
Modeling snow isothermal metamorphism at the pore scale with the phase-field model Snow3D
Authors: Bouvet Lisa , Calonne Neige , Flin Frédéric , Geindreau Christian
Published: March 2021

Representing snow isothermal metamorphism is key to model the evolution and properties of the snow cover. Recently, a new phase-field model allowing to describe 3D microstructure induced by curvature effects has been proposed (Bretin et al, Esiam: M2an, 2019). In the present work, this model is used to simulate isothermal metamorphism of snow at the pore scale, considering the only process of moving interfaces by sublimation-deposition driven by curvatures. This model runs on real 3D microtomographic images and gives a temporal series of 3D images simulating isothermal metamorphism. To determine the condensation coefficient to use in the model, which shows complex dependencies and is still poorly known, we calibrated it by reproducing the time evolution of the specific surface area (SSA) measured during an isothermal experimental time-series at -2°C (Flin et al., Ann. Glaciol., 2004). This calibration has led to a value of the condensation coefficient of 9.9 ± 0.6 10−4. Using this calibration, we obtained a good agreement between simulations and an independent series of isothermal metamorphism at -2°C (Hagenmuller et al., The Cryosphere, 2019). Finally, 4 images representing different types of snow microstructure have been chosen as input to simulate isothermal metamorphism at -2°C during 75 days. The obtained temporal series of 3D images were then used to calculate microstructural (porosity, SSA, covariance lengths) and physical transport properties (thermal conductivity, effective diffusion, permeability) evolution. Comparing our numerical estimations of physical properties to current parameterizations gives overall good agreement. An interesting new result arising from the simulations is the conservation or enhancement of the structural anisotropy under isothermal conditions for the samples that were initially strongly anisotropic.

 