bluuebunny/crossref_metadata_2025 huggingface dataset:
Ocean tidal loading models assessment using 28 months of gravimetric tidal records in Dublin, Ireland
Authors: Dykowski Przemysław , Karkowska Kamila , Sękowski Marcin , Kane Paul
Published: March 2021

In June of 2018 a project for the establishment of a modern permanent Absolute Gravity Network  on the island of Ireland was initiated by the National Mapping Agency of Ireland, Ordnance Survey Ireland (OSi) with the cooperation of  Institute of Geodesy and Cartography (IGiK), and Land and Property Services (LPS) in Northern Ireland. The project assumes conducting absolute gravity surveys of the network using  the A10 absolute gravimeter on approximately 60 stations homogenously distributed on the island of Ireland.

Data processing includes time variable corrections for body tides, barometric pressure, polar motion as well as ocean tidal loading. For Ireland the ocean tidal loading effect can reach peaks of between 400 nm/s2 on the west coast and 200 nm/s2 on the east coast. This effect is significant and up to now the authors are unaware of previous historical data or  tidal gravity records being performed in Ireland. Hence it was considered as a valid component of the overall Absolute Gravity Project to evaluate the current situation with ocean tidal loading effect in Ireland using gravimetric tidal records in order to validate available ocean tidal loading models.

In order to assure the most optimal use of ocean tidal model as well as minimize the errors of including ocean tidal correction in absolute gravity processing the LaCoste&Romberg model G spring gravimeter was installed at OSi headquarters in Phoenix Park, Dublin, Ireland. Over a continuous period of 28 months gravity record with more than 99% data completeness at near 2Hz sampling rate was conducted.

The project data was acquired through using a self-programmed Raspberry Pi computer allowing for automatic download and remote access to the data.

A set of CSR, DTU, EOT, FES, GOT, TPXO (ocean tide loading provider – Chalmers, http://holt.oso.chalmers.se/loading/) ocean tidal loading models were used in a joint analysis with the collected tidal record. Analysis included performing tidal adjustment of the gravity data in the ETERNA 3.40 (ET34-X-V73) as well as comparison of IAG (International Association of Geodesy) recommended model combinations with the collected data.

Recommendations by the project team as to which of the ocean tidal models is most suitable to be used in Ireland for the purpose of absolute gravity measurements were made.
A numerical method for simulations of cohesive, porous sediments
Authors: Metelkin Alexander , Vowinckel Bernhard
Published: March 2021

The dynamics of cohesive sediments under various flow conditions are of special interest in the framework of aquatic ecosystems. Being one of the main sources of transport for minerals and organic matter, the constituents of cohesive sediments are the source of food for many aquatic organisms. Due to the additional complexity of physical mechanisms, there are only a few simulation techniques for cohesive sediments, which do not cover all spatial scales. The primary cohesive clay particles are platelets smaller than 2 μm, which is small enough to experience Brownian motion. Composed together under the influence of van der Waals forces, they shape rounded aggregates also known as microflocs that are rather stable. These microflocs can form fragile, larger macroflocs with complex shapes exceeding 100 μm in size. Owing to the huge difference in the spatial scales, it is almost impossible to simulate macroflocs as the assembly of primary clay particles in the context of cohesive sediment transport modeling. In contrast to separate sediment grains, microflocs represent porous aggregates. To perform direct numerical simulations of microflocs transported in a viscous fluid flow, we are developing a computational model for immersed porous particles. The model resolves the flow outside and inside porous aggregates and accurately computes the hydrodynamic forces on the microflocs. The simulation of macroflocs is also attainable by employing cohesive forces between microflocs, which assembles them into bigger aggregates with the propensity of breaking up under high shear rates. Our computational model solves the system of Navier - Stokes equations directly with an additional Darcy term inside the porous aggregate. Using this approach, it becomes feasible to consider the influence of the flow inside porous media, so that we can study its impact on the mean flow characteristics depending on the properties of the porous flocs. The hydrodynamic forces are calculated implicitly based on the pressure and shear stress distribution. By comparison with methods that use Stokes-based drag coefficients, our approach allows estimating the influence of local flow conditions and the presence of neighboring aggregates on the resulting fluid force.

 
Prominence Formation by Levitation-Condensation at Extreme Resolutions
Authors: Jenkins Jack , Keppens Rony
Published: March 2021

We revisit the so-called levitation-condensation mechanism for the ab-inito formation of solar prominences: cool and dense clouds in the million-degree solar atmosphere. Levitation-condensation occurs following the formation of a flux rope in response to the deformation of a force-free coronal arcade by controlled magnetic footpoint motions and subsequent reconnection. Existing coronal plasma gets lifted within the forming rope, therein isolating a collection of matter now more dense than its immediate surroundings. This denser region ultimately suffers a thermal instability driven by radiative losses, and a prominence forms. We improve on various aspects that were left unanswered in the early work, by revisiting this model with our modern open-source grid- adaptive simulation code [amrvac.org]. Most notably, this tool enables a resolution of 5.6 km within a 24 Mm x 25 Mm domain size; the full global flux rope dynamics and local plasma dynamics are captured in unprecedented detail. Our 2.5D simulation (where the flux rope has realistic helical magnetic field lines) demonstrates that the thermal runaway condensation can happen at any location, not solely in the bottom part of the flux rope where the majority of prominence material is assumed to reside. Intricate thermodynamic evolution and shearing flows develop spontaneously, themselves inducing further fine-scale (magneto)hydrodynamic instabilities. Our analysis touches base with advanced linear magnetohydrodynamic stability theory, e.g. with the Convective Continuum Instability or CCI process as well as with in-situ thermal instability studies. We find that condensing prominence plasma evolves according to the internal pressure and density gradients as found previously for coronal rain condensations, but also misalignments therein suggesting the relevance of the Rayleigh-Taylor instability or RTI process in 3D. We also find evidence for resistively-driven dynamics in the prominence body, in close analogy with analytical predictions. These findings are relevant for modern studies of full 3D prominence formation and structuring. Most notably, we anticipate obtaining similar resolutions within a fully 3D setup. Such an achievement will afford us the exciting opportunity to offer crucial explanations as to the persistent discrepancy in prominence appearance when projected off- or on-disk.
Emulation techniques for rapid flow-like geohazards: a case study-based performance analysis
Authors: Yildiz Anil , Baselt Ivo , Edrich Ann-Kathrin , Fischer Jan-Thomas , Mergili Martin , Zhao Hu , Kowalski Julia
Published: March 2021

Several powerful physics-based computational landslide run-out models have been developed and validated throughout the last years. The geohazards community applies these forward models in simulation tools to predict potential landslide run-out outcomes including their uncertainties, and uses inverse approaches to conduct reanalyses and to infer on model parameters for calibration purposes. Yet it remains challenging to turn these computational frameworks into robust, transparent and transferrable simulation-based decision support tools for geohazard mitigation. In particular, the landscape of uncertainties – such as those resulting from the idealised model description itself, input data (e.g., material parameters or topographic data), and numerical scheme related hyperparameters – is still not systematically managed when conducting landslide simulations. Probabilistic hazard maps that take these uncertainties into account imply a large number of model evaluations, which constitutes a computational bottle neck. This issue can be overcome by using High Performance Computing (HPC) resources along with the existing software and resources. Alternatively, physics-informed machine learning strategies use simulation results of the original process model, i.e., the simulator, to train a statistically valid representation, the so-called emulator. Once being trained, the emulator significantly reduces computational costs, while at the same time it grants access to an estimation of the introduced error. A software framework has recently been set up to integrate Gaussian process emulation and the landslide run-out model r.avaflow, an open-source mass flow simulation tool. Emulation-based sensitivity analysis was of comparable quality to conventional studies, and the computational costs were cut significantly. The emulator allowed for the first time to conduct a global sensitivity analyses at every location simultaneously for a complete landslide impact area. A joint effort across different institutes in Europe has been made in this contribution to test the potential and limitation of the emulation techniques by revisiting a number of published case studies. Selection of test cases has been made according to data availability, failure type and computational demand. Preliminary findings suggest that the emulator is capable of reducing the computational effort of modelling various flow-like landslides substantially. Future work will focus on curating a well-defined database of test scenarios across multiple institutes with cases ranging from small to medium-sized debris flows to large rock avalanches.
The impact of modelling decisions in hydrological modelling
Authors: Remmers Janneke , Teuling Ryan , Melsen Lieke
Published: March 2021

Scientific hydrological modellers make multiple decisions during the modelling process, e.g. related to the calibration period and performance metrics. These decisions affect the model results differently. Modelling decisions can refer to several steps in the modelling process. In this project, modelling decisions refer to the decisions made during the whole modelling process, not just the definition of the model structure. Each model output is a hypothesis of the reality; it is an interpretation of the real system underpinned by scientific reasoning and/or expert knowledge. Currently, there is a lack of knowledge and understanding about which modelling decisions are taken and why they are taken. Consequently, the influence of modelling decisions is unknown. Quantifying this influence, which is done in this study, can raise awareness among scientists. This study is based on analysis of interviews with scientific hydrological modellers, thus taking actual practices into account. Different modelling decisions were identified from the interviews, which are subsequently implemented and evaluated in a controlled modelling environment, in our case the modular modelling framework Raven. The variation in the results is analysed to determine which decisions affect the results and how they affect the results. This study pinpoints what aspects are important to consider in studying modelling decisions, and can be an incentive to clarify and improve modelling procedures.
Workflow and tools to analyse the PMIP4-CMIP6 ensemble
Authors: Zhao Anni , Brierley Chris
Published: March 2021

Experiment outputs are now available from the Coupled Model Intercomparison Project’s 6th phase (CMIP6) and the past climate experiments defined in the Model Intercomparison Project’s 4th phase (PMIP4). All of this output is freely available from the Earth System Grid Federation (ESGF). Yet there are overheads in analysing this resource that may prove complicated or prohibitive. Here we document the steps taken by ourselves to produce ensemble analyses covering past and future simulations. We outline the strategy used to curate, adjust the monthly calendar aggregation and process the information downloaded from the ESGF. The results of these steps were used to perform analysis for several of the initial publications arising from PMIP4. We provide post-processed fields for each simulation, such as climatologies and common measures of variability. Example scripts used to visualise and analyse these fields is provided for several important case studies.
Evaluating atmospheric rivers and their influence on precipitation in the Arctic - comparing observational with reanalysis data
Authors: Lauer Melanie , Rinke Annette , Gorodetskaya Irina , Crewell Susanne
Published: March 2021

The Arctic as a whole has been experiencing significant warming and moistening with several potential factors at play. In general, the warming amplifies the Arctic hydrological cycle. There are two processes which could affect the water vapour content in the Arctic. These are the enhanced local evaporation due to reduced sea-ice concentration and extent and the modified poleward moisture transport from lower latitudes due to changing circulation patterns. An important contribution to the total poleward moisture transport comes from Atmospheric rivers (ARs). ARs have rare occurrence but are associated with anomalously high moisture transport compared to tropical cyclones. ARs are typically associated with not only moisture but also with significant heat advection. They can bring precipitation as rain and/or snow. Moreover, additional feedbacks can occur: the warming effect of the ARs on the surface, coupled with rain lowering surface albedo, can cause thinning and melting of Arctic sea ice and snow. This, in turn, could increase the relative role of the local evaporation compared to the moisture transported from lower latitudes.

In this study, we investigate the relationship between the poleward moisture transport by ARs and the precipitation in the Arctic. The focus is on AR events during the ACLOUD (May/June 2017) and AFLUX (March/April 2018) campaign within the Collaborative Research Center “Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC)3”. For these campaigns, existing AR catalogues with the input of ERA5 reanalyses are used to detect AR events. Six ARs are detected: two coming from Siberia and four from the Atlantic.

These AR events are analysed in terms of the macro- and microphysical precipitation properties, including frequency, intensity, and type of precipitation (rain or snow).  For this purpose, we use ERA5 reanalyses data for the water vapour transport, precipitation amount and type, rain and snow profiles (convective, large-scale, total), as well as vertical profile of hydrometeors. Reanalysis products are evaluated using a set of observational data (satellite data and ground-based remote sensing measurements). This new multi-parameter, multi-dataset set will allow to investigate the occurrence of ARs and its influence on precipitation in the Arctic for the last decades.

 

“We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) –Projektnummer 268020496 –TRR 172, within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3.“
Early-Warning Signals For Cenozoic Climate Transitions
Authors: Klinghammer Georg , Böttner Christopher
Published: March 2021

Paleoclimatic records document large-scale shifts in the Earth’s climate history. Among other possibilities, these transitions might have been caused by bifurcations in the leading dynamical modes. Such bifurcation-induced critical transitions are typically preceded by characteristic early-warning signals (EWS), for example in terms of rising standard deviation and lag-one autocorrelation. These EWS are caused by the phenomenon of critical slowing down (CSD) in response to a widening of the underlying basin of attraction as the bifurcation is approached. The presence of EWS prior to an observed transition therefore provides evidence that the transition is caused by a bifurcation. We reveal significant EWS prior to several critical transitions within a paleoclimate record spanning the Cenozoic Era, i.e., the last 67M years. We employed the CENOzoic Global Reference benthic foraminifer carbon and oxygen Isotope Dataset (CENOGRID), comprising two time series of isotope variations of δ18O and δ13C. The standard deviation and lag-one autocorrelation are estimated in sliding windows for both records, to reveal whether CSD occurs ahead of the major abrupt transitions in these records. Specifically, we detect significant EWS for five out of nine previously identified transitions in at least one of the two available records. EWS are recognized for significant increases in both CSD indicators prior to the transition. Our results hence suggest that at least five major climate transitions of the last 67 Ma were triggered by bifurcations in leading modes of variability, indicating bifurcations have likely played a key role in the deep-time evolution of the Earth's climate system.
Automation of (meta-)data workflows from field to data repository
Authors: Baldewein Linda , Kleeberg Ulrike , Möller Lars
Published: March 2021

In Earth and environmental sciences data analyzed from field samples are a significant portion of all research data, oftentimes collected under significant costs and non-reproducibly. If important metadata is not immediately secured and stored in the field, the quality and re-usability of the resulting data will be diminished.  

At the Helmholtz Coastal Data Center (HCDC) a metadata and data workflow for biogeochemical data has been developed over the last couple of years to ensure the quality and richness of metadata and enable that the final data product will be FAIR. It automates and standardizes the data transfer from the campaign planning stage, through sample collection in the field, analysis and quality control to the storage into databases and the publication in repositories.

Prior to any sampling campaign, the scientists are equipped with a customized app on a tablet that enables them to record relevant metadata information, such as the date and time of sampling, the involved scientists and the type of sample collected. Each sample and station already receives a unique identifier at this stage. The location is directly retrieved from a high-accuracy GNSS receiver connected to the tablet. This metadata is transmitted via mobile data transfer to the institution’s cloud storage.

After the campaign, the metadata is quality checked by the field scientists and the data curator and stored in a relational database. Once the samples are analyzed in the lab, the data is imported into the database and connected to the corresponding metadata using a template. Data DOIs are registered for finalized datasets in close collaboration with the World Data Center PANGAEA. The data sets are discoverable through their DOIs as well as through the HCDC data portal and the API of the metadata catalogue service.

This workflow is well established within the institute, but is still in the process of being refined and becoming more sophisticated and FAIRer. For example, an automated assignment of International Geo Sample Numbers (IGSN) for all samples is currently being planned.
Leaky salt: pipe trails record the history of cross-evaporite fluid escape in the northern Levant Basin, Eastern Mediterranean
Authors: Oppo Davide , Evans Sian , Jackson Christopher A-L , Iacopini David , Kabir SM Mainul , Maselli Vittorio
Published: March 2021

Hydrocarbon escape systems can be regionally active on multi-million-year timescales. However, reconstructing the timing and evolution of repeated escape events can be challenging because their expression may overlap in time and space. In the northern Levant Basin, eastern Mediterranean, distinct fluid escape episodes from common leakage points formed discrete, cross-evaporite fluid escape pipes, which are preserved in the stratigraphic record due to the coeval Messinian salt tectonics.

The pipes consistently originate at the crest of prominent sub-salt anticlines, where thinning and hydrofracturing of overlying salt permitted focused fluid flow. Sequential pipes are arranged in several kilometers-long trails that were progressively deformed due to basinward gravity-gliding of salt and its overburden. The correlation of the oldest pipes within 12 trails suggests that margin-wide fluid escape started in the Late Pliocene/Early Pleistocene, coincident with a major phase of uplift of the Levant margin. We interpret that the consequent transfer of overpressure from the deeper basin areas triggered seal failure and cross-evaporite fluid flow. We infer that other triggers, mainly associated with the Messinian Salinity Crisis and compressive tectonics, played a secondary role in the northern Levant Basin. Further phases of fluid escape are unique to each anticline and, despite a common initial cause, long-term fluid escape proceeded independently according to structure-specific characteristics, such as the local dynamics of fluid migration and anticline geometry.

Whereas cross-evaporite fluid escape in the southern Levant Basin is mainly attributed to the Messinian Salinity Crisis and compaction disequilibrium, we argue that these mechanisms do not apply to the northern Levant Basin; here, fluid escape was mainly driven by the tectonic evolution of the margin. Within this context, our study shows that the causes of cross-evaporite fluid escape can vary over time, act in synergy, and have different impacts in different areas of large salt basins.
Systematic Investigation of Dynamic Earthquake Triggering in Japan
Authors: Enescu Bogdan , Takeda Yuki
Published: March 2021

Introduction. Previous studies (e.g., Harrington and Brodsky, 2006) documented a relative scarcity of remote triggering in Japan, compared to other seismic regions. For example, in California, dynamic triggering is reported to occur at levels of stress as small as 0.1 kPa, while in Japan it was reported that levels of 30 kPa or more are required to trigger detectable events (van der Elst and Brodsky, 2010). However, the threshold dynamic triggering level following the 2016 M7.3 Kumamoto earthquake was of just a few kPa (Enescu et al., 2016). Enescu et al. (2016) proposed that one of the possibilities to explain this observation is a change of stress triggering threshold that may have taken place after the 2011 M9.0 Tohoku-Oki earthquake.

Motivation. Given the above observations, this study investigates 1) the occurrence of dynamically triggered earthquakes in Japan after some large earthquakes from 2004, and 2) whether the threshold of dynamic triggering may have changed due to the 2011 Tohoku-Oki earthquake and why this threshold might have changed.

Analysis and Results. First, we investigated dynamic triggering throughout Japan, following some large earthquakes occurred after 2004. As a result, the  threshold appears to decrease following the 2011 Tohoku-Oki earthquake, however the number of earthquakes we have investigated was relatively small, so we could not draw statistically significant conclusions. In the second part of the study, we have focused on a few specific areas within Japan to systematically investigate dynamic triggering, which reduced significantly the computational costs. Thus, we focused on some areas in Tohoku and Hida, where swarm earthquakes occurred after the 2011 Tohoku-Oki earthquake. As a result, the change of the triggering level in an area close to the Yamagata-Fukushima border is considered to be statically significant at a 5% significance level. In other regions, the significance at a 5% level could not be established, however a decrease of this threshold is apparent, except for one region. We speculate that changes in the stress triggering threshold levels might be related to pore pressure changes in the crust following the 2011 Tohoku-Oki earthquake.
Analysis of the isopycnal advection in the Lofoten basin (the Norwegian sea)
Authors: Novoselova Elena V. , Belonenko Tatyana V. , Fedorov Aleksandr M.
Published: March 2021

The Lofoten Basin in the Norwegian Sea is a real reservoir of the Atlantic Waters. The shape of the Basin in the form of a bowl and a great depth with its monotonous increase to the centre results in the Atlantic Water gradually deepen and fill the Basin. The deepening of the Atlantic Waters in the Lofoten Basin determines not only the structure of its waters but also the features of the ocean-atmosphere interaction. Flowing through the transit regions, the Atlantic Waters lose heat to the atmosphere, mix with the surrounding water masses and undergo a transformation, which causes the formation of deep ocean waters. At the same time, the heat input with the Atlantic waters significantly exceeds its loss to the atmosphere in the Lofoten Basin.

We study isopycnal advection and diapycnal mixing in the Lofoten Basin. We use the GLORYS12V1 oceanic reanalysis data and analyze four isosteric δ-surfaces. We also calculate the depth of their location. We establish that δ-surfaces have the slope eastward with maximal deepening where the quasi-permanent Lofoten Vortex is located. We analyze the temperature distribution on the isosteric δ-surfaces as well as the interannual and seasonal variability of their location depth.

The maximal depth on the isosteric surfaces is observed in 2010, which is known as the year of the largest mixed layer depths in the Lofoten Basin according to the ARGO buoys. We demonstrate the same correspondence to in 2000, 2010, 2013.

The maximal depth on the isosteric surfaces is observed is reached in summer. The maximal areas with the greatest depths also are observed in summer in contrast to a minimum in winter. This means certain inertia of changes in the thermohaline characteristics of Atlantic Waters as well as a shift of 1-2 seasons of the influence of deep convection on isosteric surfaces.

It is shown that isopycnal advection in the Lofoten Basin makes a significant contribution to its importance as the main thermal reservoir of the Nordic Seas.
New machine learning approaches for tropospheric profiling based on COSMIC-2 data over Taiwan
Authors: Lasota Elżbieta
Published: March 2021

Precise and reliable information on the tropospheric temperature and water vapour profiles plays a key role in weather and climate studies. Among the sensors supporting the atmosphere's observation, one can distinguish the Global Navigation Satellite System Radio Occultation (RO) technique, which provides accurate and high-quality meteorological profiles of temperature, pressure and water vapour. However, external knowledge about temperature is essential to estimate other physical atmospheric parameters. Hence, to overcome the constraint of the need of a priori temperature profile for each RO event, I trained and evaluated 4 different machine learning models comprising Artificial Neural Network (ANN) and Random Forest regression algorithms, where no auxiliary meteorological data is needed. To develop the models, I employed almost 7000 RO profiles between October 2019 and June 2020 over the part of the western North Pacific in Taiwan's vicinity (110-130° E; 10-30° N). Input vectors consisted of bending angle or refractivity profiles from the Formosa Satellite‐7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 mission together with the month, hour, and latitude of the RO event. Whilst temperature, pressure and water vapour profiles derived from the modern ERA5 reanalysis and interpolated to the RO location served as the models' targets. Evaluation on the testing data set revealed a good agreement between all model outputs and ERA5 targets. Slightly better statistics were noted for ANN and refractivity inputs, however, these differences can be considered as negligible. Root mean square error (RMSE) did not exceed 2 K for the temperature, 1.5 hPa for pressure, and reached slightly more than 2.5 hPa for water vapour below 2 km altitude. Additional validation with 56 colocated radiosonde observations and operational one-dimensional variational product confirms these findings with vertically averaged RMSE of around 1.3 K, 1.0 hPa and 0.5 hPa for the temperature, pressure and water vapour, respectively.
Forecast skill of autumn snow for European winter climate during the 20th century: A multi member seasonal prediction experiment
Authors: Wegmann Martin , Orsolini Yvan , Weisheimer Antje , van den Hurk Bart , Lohmann Gerrit
Published: March 2021

As the leading climate mode to explain wintertime climate variability over Europe, the North Atlantic Oscillation (NAO) has been extensively studied over the last decades. Recently, studies highlighted the state of the Northern Hemispheric cryosphere as possible predictor for the wintertime NAO (Cohen et al. 2014). Although several studies could find seasonal prediction skill in reanalysis data (Orsolini et al. 2016, Duville et al. 2017,Han & Sun 2018), experiments with ocean-atmosphere general circulation models (AOGCMs) still show conflicting results (Furtado et al. 2015, Handorf et al. 2015, Francis 2017, Gastineau et al. 2017). 

Here we use two kinds ECMWF seasonal prediction ensembles starting with November initial conditions taken from the long-term reanalysis ERA-20C and forecasting the following three winter months. Besides the 110-year ensemble of 50 members representing internal variability of the atmosphere, we investigate a second ensemble of 20 members where initial conditions are split between low and high snow cover years for the Northern Hemisphere. We compare two recently used Eurasian snow cover indices for their skill in predicting winter climate for the European continent. Analyzing the two forecast experiments, we found that prediction runs starting with high snow index values in November result in significantly more negative NAO states in the following winter (DJF), which in turn modulates near surface temperatures. We track the atmospheric anomalies triggered by the high snow index through the tropo- and stratosphere as well as for the individual winter months to provide a physical explanation for the formation of this particular climate state.

 
On the best locations for ground-based PSC observations
Authors: Tesche Matthias , Achtert Peggy , Pitts Michael
Published: March 2021

Spaceborne observations of Polar Stratospheric Clouds (PSCs) with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite provide a comprehensive picture of the occurrence of Arctic and Antarctic PSCs as well as their microphysical properties. However, advances in understanding PSC microphysics also require measurements with ground-based instruments, which are often superior to CALIOP in terms of, e.g. time resolution, measured parameters, and signal-to-noise ratio. This advantage is balanced by the location of ground-based PSC observations and their dependence on tropospheric cloudiness. CALIPSO observations during the boreal winters from December 2006 to February 2018 and the austral winters 2012 and 2015 are used to assess the effect of tropospheric cloudiness and other measurement-inhibiting factors on the representativeness of ground-based PSC observations with lidar in the Arctic and Antarctic, respectively. Information on tropospheric and stratospheric clouds from the CALIPSO Cloud Profile product (05kmCPro version 4.10) and the PSC mask version 2, respectively, is combined on a profile-by-profile basis to identify conditions under which a ground-based lidar is likely to perform useful measurements for the analysis of PSC occurrence. It is found that the location of a ground-based measurement together with the related tropospheric cloudiness can have a profound impact on the derived PSC statistics and that these findings are rarely in agreement with polar-wide results from CALIOP observations. Considering the current polar research infrastructure, it is concluded that the most suitable sites for the expansion of capabilities for ground-based lidar observations of PSCs are Summit and Villum in the Arctic and Mawson, Troll, and Vostok in the Antarctic.
Hurricane dynamics and rapid intensification via dynamical systems indicators
Authors: Faranda Davide , Messori Gabriele , Yiou Pascal , Thao Soulivanh , Pons Flavio , Dubrulle Berengere
Published: March 2021

Although the lifecycle of hurricanes is well understood, it is a struggle to represent their dynamics in numerical models, under both present and future climates. We consider the atmospheric circulation as a chaotic dynamical system, and show that the formation of a hurricane corresponds to a reduction of the phase space of the atmospheric dynamics to a low-dimensional state. This behavior is typical of Bose-Einstein condensates. These are states of the matter where all particles have the same dynamical properties. For hurricanes, this corresponds to a "rotational mode" around the eye of the cyclone, with all air parcels effectively behaving as spins oriented in a single direction. This finding paves the way for new parametrisations when simulating hurricanes in numerical climate models.
Future changes in heatwaves over Africa at the convection-permitting scale
Authors: Birch Cathryn , Jackson Lawrence , Finney Declan , Marsham John , Stratton Rachel , Tucker Simon , Senior Cath , Keane Richard
Published: March 2021

Mean temperatures and their extremes have increased over Africa since the latter half of the 20th century and this trend is projected to continue, with very frequent, intense and often deadly heatwaves likely to occur very regularly over much of Africa by 2100. It is crucial that we understand the scale of the future increases in extremes and the driving mechanisms. We diagnose daily maximum wet bulb temperature heatwaves, which allows for both the impact of temperature and humidity, both critical for human health and survivability. During wet bulb heatwaves, humidity and cloud cover increase, which limits the surface shortwave radiation flux but increases longwave warming. It is found from observations and ERA5 reanalysis that approximately 30% of wet bulb heatwaves over Africa are associated with daily rainfall accumulations of more than 1 mm/day on the first day of the heatwave. The first ever pan-African convection-permitting climate model simulations of present-day and RCP8.5 future climate are utilised to illustrate the projected future change in heatwaves, their drivers and their sensitivity to the representation of convection. Compared to ERA5, the convection-permitting model better represents the frequency and magnitude of present-day wet bulb heatwaves than a version of the model with more traditional parameterised convection. The future change in heatwave frequency, duration and magnitude is also larger in the convective-scale simulation, suggesting CMIP-style models may underestimate the future change in wet bulb heat extremes over Africa. The main reason for the larger future change appears to be the ability of the model to produce larger anomalies relative to its climatology in precipitation, cloud and the surface energy balance.
3D modelling of a hydrological structure combining spatial data science and geophysics: Application to a coastal aquifer system in the island of Crete, Greece
Authors: Varouchakis Emmanouil , Azevedo Leonardo , Pereira João L. , Trichakis Ioannis , Karatzas George P. , Jomaa Seifeddine , Soupios Pantelis
Published: March 2021

Groundwater resources in Mediterranean coastal aquifers are under threat due to overexploitation and climate change impacts, resulting in saltwater intrusion. This situation is deteriorated by the absence of sustainable groundwater resources management plans. Efficient management and monitoring of groundwater systems requires interpreting all sources of available data. This work aims at the development of a set of plausible 3D geological models combining 2D geophysical profiles, spatial data analytics and geostatistical simulation techniques. The resulting set of models represents possible scenarios of the structure of the coastal aquifer system under investigation. Inverted resistivity profiles, along with borehole data, are explored using spatial data science techniques to identify regions associated with higher uncertainty. Relevant parts of the profiles will be used to generate 3D models after detailed Anisotropy and variogram analysis. Multidimensional statistical techniques are then used to select representative models of the true subsurface while exploring the uncertainty space. The resulting models will help to identify primary gaps in existing knowledge about the groundwater system and to optimize the groundwater monitoring network. A comparison with a numerical groundwater flow model will identify similarities and differences and it will be used to develop a typical hydrogeological model, which will aid the management and monitoring of the area's groundwater resources. This work will help the development of a reliable groundwater flow model to investigate future groundwater level fluctuations at the study area under climate change scenarios.

 

This work was developed under the scope of the InTheMED project. InTheMED is part of the PRIMA programme supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 1923.
MAX-DOAS measurements of NO2 and HCHO in the city of Kinshasa from 2019-2020
Authors: Yombo Rodriguez , Merlaud Alexis , Pinardi Gaia , Mahieu Emmanuel , Friedrich Martina , Hendrick François , Fayt Caroline , Van Roozendael Michel , Bopili Mbotia Lepiba Richard , Buenimio  Lomami Djibi , Mbungu Tsumbu Jean-Pierre
Published: March 2021

Recent studies in Kinshasa show how much air pollution is present in this large megalopolis of 13 million inhabitants, with levels even exceeding the recommended values (WHO, 2018).

From May 2017 to November 2019, the University of Kinshasa (UniKin: -4.42°S, 15.31°E) has equipped itself with a low-cost instrument operating in single-axis mode. Studies based on measurements made with this instrument have demonstrated the presence of NO2 with highest vertical column densities (VCDs) in June, July and August (R. Yombo, 2020). With this low-cost instrument, information such as aerosol and NO2 profile, which have major impacts on the determination of VCDs could not be obtained, leading to considerable uncertainties in the results obtained.

This work therefore supports the first one as described above, by presenting first results of a new MAX-DOAS (multi-axis differential optical absorption spectroscopy) system built at the IASB, in Belgium, and installed in Kinshsasa at the same location in November 2019. We first present the new MAX-DOAS, which is based on compact Avantes spectrometer (280-550 nm, 0.7 nm FWHM), a small computer, and a scanner.  We describe the analyses for aerosol extinction, HCHO and NO2 using FRM4-DOAS. For these two molecules, we compare with model simulations (GEOS-Chem) and satellite observations (OMI, TROPOMI).
Decadal changes in south west Antarctic Peninsula Ice Shelves
Authors: Holt Tom , Glasser Neil
Published: March 2021

Over the latter half of the 20th Century and beginning of the 21st Century, ice shelves around the Antarctic Peninsula have been losing mass at an accelerating rate, attributable to changes in atmospheric and oceanic conditions. Ice shelves have declined in extent and thickness, and some show signs of structural weakening. Here we investigate the glaciological changes to Bach, Stange and George VI ice shelves that fringe the Southwest Antarctic Peninsula. We used satellite imagery from 2009/10 to 2019/20 (Landsat, Sentinel and ASTER) to measure areal changes, calculate flow speeds, and quantify structural changes, focusing on open fracture width and length. We reveal a total net loss of 797.5 km2 from all three ice shelves since 2009/10, though spatial and temporal patterns of ice loss vary at individual ice fronts. Flow speeds have remained largely stable, but notable acceleration was calculated for Bach Ice Shelf, and at the northern and southern extents of George VI Ice Shelf. Open fractures have widened and lengthened over the observation periods. We conclude that Stange Ice Shelf is stable, and not under any immediate threat of enhanced recession. Continued ice-mass loss and consequential speed up of George VI South may cause further fracturing and destabilisation in the coming decades. Of more immediate concern are the glaciological changes noted for Bach Ice Shelf and George VI North; significant areas of passive ice have already, or will be soon removed, that could result in enhanced recession within the next decade.
The driving processes of concurrent hot and dry extreme events in China
Authors: Tian Fangxing , Klingaman Nicholas , Dong Buwen
Published: March 2021

Sub-seasonal heatwave-driven concurrent hot and dry extreme events (HDEs) can cause substantial damage to crops, and hence to lives and livelihoods. However, the physical processes that lead to these devastating events are not well-understood.

Based on observations and reanalysis data for 1979-2016 over China, we show that HDEs occur preferentially over central and eastern China (CEC) and southern China (SC), with a maximum of 3 events year-1 along the Yangtze Valley. The probability of longer-lived and potentially more damaging HDEs is larger in SC than in CEC. Over SC the key factors of HDEs—positive anomalies of surface air temperature and evapotranspiration, and negative anomalies of soil moisture—begin two pentads before maximising at the peak of the HDEs. These anomalies occur south of a positive height anomaly at 200 hPa, associated with a large-scale subsidence anomaly. The processes over CEC are similar to SC, but the anomalies begin one pentad before the peak. HDE frequency is strongly related to the Silk Road Pattern and the Boreal Summer Intraseasonal Oscillation. Positive phases of the Silk Road Pattern and suppressed phases of the Boreal Summer Intraseasonal Oscillation are associated with positive height anomalies over CEC and SC, increasing HDE frequency by about 35-54% relative to the climatological mean.  Understanding the effects of sub-seasonal and seasonal atmospheric circulation variability, such as the Silk Road Pattern and Boreal Summer Intraseasonal Oscillation, on HDEs is important to improve HDE predictions over China.
Insights into lava dome and spine extrusion using analogue sandbox experiments
Authors: Zorn Edgar , Walter Thomas , Heap Michael , Kueppers Ulrich
Published: March 2021

Lava dome formation is a common process at stratovolcanoes involving the shallow intrusion or extrusion of viscous lava and may lead to the rise of spines. Spines are protrusions observed to extrude episodically during lava dome growth, yet the structural and mechanical factors controlling their formation are only partially understood. Here, we provide new, detailed insight into lava dome growth and the production of spines using a novel set of analogue experiments extruding sand-plaster mixtures from a fixed-diameter conduit under isothermal conditions. We trace displacement and strain with photogrammetric methods for precise and detailed monitoring of the extrusion process. Results show initial dome growth forming a steep-sided and flat-topped shape through extrusion of new material, leading to slumping of oversteepening slopes, forming a talus. Spines are found to protrude at a later stage through the dome surface along discrete circular faults that originate from the conduit walls, starting a cycle of spine growth and collapse. As our spines only appear after prolonged extrusion, we relate their appearance to the compaction and strengthening of material within the conduit. We find that spine diameter, height and volume are positively correlated with increasing cohesion and therefore material strength. The spine diameter was also observed to be smaller or equal to the diameter of the underlying conduit, as shear extrusion occurs along vertical to outward-dipping fault planes. For natural domes, our findings imply that spine growth may be the consequence of compaction and densification via porosity loss, shearing and/or outgassing of conduit magma during ascent. More efficient compaction will yield wider and taller spines as a result of increasing rock strength. Our study further highlights the relevance of analogue experiments in the study of lava domes and spines, which remain one of the most hazardous and unpredictable features at dome-forming volcanoes worldwide.
Carbon isotopes of vegetation as proxy of natural or anthropogenic gas seeps
Authors: Kloppmann Wolfram , Gal Frédérick , Blessing Michaela , Fléhoc Christine
Published: March 2021

There is evidence that the emission of 14C –free CO2 during volcanic emissions creates a bias for radiocarbon dating of volcanic events (Holdaway et al., 2018), showing that integration of “dead” carbon by vegetation can serve as indicator of geogenic gas emissions. We tested 14C activities and stable carbon isotope ratios of tree rings and herbal vegetation in the proximity of a natural gas seep in the French Subalpine chains where both methane (<90% in the main vent) and CO2 (<11%) are present (Gal et al., 2018). Wood samples were taken from two alder trees, at different distances and directions from the main gas vent. Grass leaves and roots (Carex sp.) were analysed for two spots with contrasting soil methane concentrations and fluxes within the zone of diffuse gas emanation around the main vent (Gal et al., 2019). Grass and wood samples show contrasting isotope compositions depending on their species, age, and position with respect to the gas seep, some with 14C activities significantly lower than present day values. This offers perspectives of using vegetation carbon isotopes as proxies for present and past gas emanations, including man-induced gas leaks, e.g. from gas storage or natural gas exploitation facilities.

This research was co-funded by the EU H2020 Programme (grant 764531 – SECURe “Subsurface Evaluation of Carbon Capture and Storage and Unconventional Risk”)

Gal F., Kloppmann W., Proust E., Humez P. (2018) Gas concentration and flow rate measurements as part of methane baseline assessment: Case of the Fontaine Ardente gas seep, Isère, France. Applied Geochemistry, 95, 158-171.

Gal F., Proust E., Kloppmann W. (2019) Towards a Better Knowledge of Natural Methane Releases in the French Alps: A Field Approach. Geofluids, 2019, 1-16.

Holdaway R. N., Duffy B., Kennedy B. (2018) Evidence for magmatic carbon bias in 14C dating of the Taupo and other major eruptions. Nature Communications, 9, 4110.