bluuebunny/crossref_metadata_2025 huggingface dataset:
Compaction front controls soil liquefaction dynamics of drained saturated grain layers, as evident by theory, numerical simulations and lab experiments
Authors: Ben-Zeev Shahar , Aharonov Einat , Goren Liran , Toussaint Renaud , Parez Stanislav
Published: March 2020

Soil liquefaction is one of the most impactful secondary hazards of earthquakes. For example, it played a crucial role in driving the devastating landslides following the 2018 Palu earthquake, Indonesia. While traditionally, the initiation of liquefaction is treated as an undrained phenomenon, evidence shows that a well-drained end-member exists.

We develop a theory for the coupled grains - pore fluid system, and conduct numerical discrete element – fluid dynamics simulations and lab experiments under well-drained conditions. Here, a well-drained layer means that the interstitial fluid can flow out of the layer faster than a single earthquake shaking period. Theory, simulations, and experiments, all suggest that a saturated granular layer, although well-drained, can liquefy when subjected to horizontal cyclic shear. The liquefaction event, evident by high pore pressure, loss of shear strength, and dissipation of shear waves is spatially and temporally controlled by a compaction front that swipes upward through the layer. The compaction front separates the grain-fluid system into two sub-layers: The bottom sub-layer, below the front, is fully-compacted, and the pore pressure gradient across it is hydrostatic. The top sub-layer, above the front, is actively subsiding, and its pore pressure gradient reaches the total solid stress gradient. I.e., the fluid fully supports the granular skeleton. The velocity of the compaction front depends on the permeability of the soil layer and the viscosity of the interstitial fluid. Analytic considerations of the propagation rate of the compaction front allows us to evaluate the duration of a liquefaction event, the magnitude of soil subsidence, and the timing of water seepage at the surface level, which are all independent of the time scales related to the earthquake shaking. Our approach, when combined with field stratigraphy and groundwater level data, could explain and predict the occurrence and duration of soil liquefaction when the soil layer is effectively drained.
Current sheets and waves inside magnetosheath jets
Authors: Kajdic Primoz , Blanco-Cano Xochitl , Karlsson Tomas , Raptis Savvas
Published: March 2020

Magnetosheath jets were first discovered by Nemeček et al., 1998 and were defined as events in the magnetosheath that exhibit ion fluxes at least 50 % higher than those in the surrounding plasma. Later authors used different physical quantities in order to study these phenomena, such as velocity, density and dynamic pressure. Magnetosheath jets are usually found in the parts of the magnetosheath that are magnetically connected to the quasi-parallel sections of the Earth's bow-shock, although jets in the so called quasi-perpendicular magnetosheath have also been observed. There are several proposed mechanisms for their formation, the most accepted ones being the formation due to the rippled surface of quasi-parallel shocks, and the transmission of upstream large-amplitude magnetic structures (SLAMS) across the bow-shock. Here we make use of the Magnetospheric Multiscale Mission burst mode data in order to present observations of waves and current sheets inside magnetosheath jets. We show that these phenomena occur commonly and provide additional mechanisms that dissipate the solar wind kinetic energy downstream of the bow-shock.
Analysis of Experimentally Zoned Crystals to Investigate The Thermo-Chemical Evolution of Magma Reservoirs
Authors: Musu Alessandro , Caricchi Luca , Perugini Diego , Corsaro Rosa Anna , Vetere Francesco , Petrelli Maurizio
Published: March 2020

Magma reservoirs are characterized by thermal and chemical gradients producing large variations of the spatial distribution of the physical properties of the magma they contain. Understanding the pre-eruptive thermal, chemical and physical evolution of magma represents an important step to correctly interpret the signs of an impending eruption. In this framework, the chemical zoning of minerals, which provide us a record of these thermal and chemical perturbations, represents an important tool to reconstruct reservoir dynamics. We study the effect of the competition between changing intensive parameters, element diffusion and mineral growth on the chemical zoning of minerals. We grow chemical zoned minerals at the Petro-Volcanology Research Group of the University of Perugia, using tephra from 2002-03 Mt. Etna eruption as starting material. The zonation in minerals is been forced inside a high-temperature furnace by oscillating the temperature under three different conditions: static conditions, using a controlled deformation gradient (concentric cylinder apparatus) and using a chaotic mixing regime (Chaotic Magma Mixing Device – CMMD). We collect major and trace elements distribution maps on a large number of crystals using Electron Probe Micro Analyzer (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), respectively. The data will be analysed using a series of custom built machine learning algorithms to disentangle zoning related to variations of the thermodynamic conditions of crystal growth from the effects of the competition between diffusion and growth. Our data will help deciphering the zoning patterns observed in natural crystals, improve our understanding of magma reservoir dynamics and help the interpretation of monitoring signals in the period preceding a volcanic eruption.
A Study on modification of Aircraft Platform for Air Quality Measurement in Korea
Authors: Seo Beom-Keun , Kim Jongho , Park Soo bog , Yu Jeonghun , Lee Misun
Published: March 2020

The aircraft measurement for air quality is able to fly in three dimensions within the planetary boundary layer of inland and sea. In this study, the Beechcraft B1900D was modified to build a unique aircraft measurement platform for the measurement of particulate matter and gas. This aircraft has a maximum takeoff weight of 7,765kg and this aircraft is loaded with various air quality measurement equipment. The contents of aircraft modification are as follows. The installed contents for air quality measurement are aircraft aerosol inlets, trace gas inlets, discharge tubes, AIMMS-30, and pylon adapter. The power supply of the measurement equipment replaced the generating capacity of starter generators from 300A to 400A (at DC 28V). In addition, this aircraft was installed on the time synchronization and network system of measurement equipment (HR-ToF-AMS, PTR-ToF-MS, CIMS, etc). Currently, the air quality scientists in Korea have been investigating on long-range transport or local large point sources.
Trends and variations in heat uptake of the Arctic climate system
Authors: Mayer Michael , Haimberger Leopold , Mayer Johannes , Tsubouchi Takamasa , Tietsche Steffen , Zuo Hao
Published: March 2020

A recent assessment of the coupled atmosphere-ocean-sea-ice energy budget of the Arctic using largely independent observational data sources demonstrated a high level of consistency of yearly means and annual cycles of lateral and vertical energy fluxes and storage terms. Moreover, contemporary Arctic regional energy imbalance has been found to be of similar magnitude (~1Wm-2) as Earth’s global energy imbalance. This suggests that Arctic amplification is predominantly a surface phenomenon and its imprint on the vertically integrated energy budget is small. Nevertheless, the annual cycle of the observed Arctic energy budget has amplified over the past two decades, with marked changes in seasonal patterns of energy fluxes and storage. This contribution draws on satellite observations, mooring-derived oceanic fluxes, data from the fifth European Re-Analysis (ERA5), and state-of-the-art ocean reanalyses to examine recent changes in Arctic heat accumulation as well as trends and variability in seasonal energy budgets. Implications for seasonal energy transports from mid-latitudes towards the Arctic will be discussed as well.
Drought-induced rapid subsidence in the Central Valley and its impact on the California Aqueduct
Authors: Miller Megan , Jones Cathleen
Published: March 2020

California’s Central Valley is the site of a complex heterogeneous aquifer system composed of alternating layers of coarse sediments and fine-grained confining material. Confined and semi-confined aquifer systems experience groundwater fluctuations coupled with elastic and inelastic land surface deformation. Data from the UAVSAR L-band synthetic aperture radar acquired between May 29, 2013 and November 27, 2018 were used to generate a high resolution deformation time series, and identify and track the development of a small subsidence feature that developed immediately adjacent to the California Aqueduct. By the end of the time series, the feature surface area that subsided 10 cm or more was 4452 hectares. The California Aqueduct supports Central Valley agriculture and large urban populations in Southern California, and a 10.5+ km segment of the aqueduct subsided 10 cm or more due to this one subsidence feature.  The Central Valley experienced a persistent drought starting in 2012, followed abruptly by a wet period from December 2016 to February 2018. The data were analyzed for the drought period in conjunction with hydraulic head level data from nearby wells to solve for aquifer storage parameters and volume storage loss.  We found the inelastic volume storage loss was 7.1x106 m3, or an average rate of 7x103 m3/day.

Compared to satellite SARs, UAVSAR has a higher spatial resolution (<2 m ground resolution) and signal-to-noise ratio. Because of these factors along with spatial averaging to reduce phase noise, accuracy is increased and temporal decorrelation is reduced, so a greater proportion of the scene produces useful measurements while maintaining a spatial resolution of 7mx7m. The resolution achieved with UAVSAR time series processing allows for modeling and monitoring localized subsidence features affecting the aqueduct that were not previously observed by satellite. The data, analysis, model, and results are described in this presentation.  It is notable that UAVSAR is a prototype for the L-band SAR to be launched on the NASA-ISRO SAR Mission (NISAR) in 2022.  In that context, we also discuss and compare the expected performance of the two instruments and highlight how these technologies can be used to study aquifer properties in areas where water level data are sparse in both space and time.
Dynamics of solute transport in capillary tubes delineated by dual energy imaging
Authors: Shokri Nima , Shokri-Kuehni Salomé M.S. , Shojaei Mohammad Javad
Published: March 2020

Saline water evaporation from a single meniscus plays an important role in determining the general dynamics of evaporation from porous media filled with saline water, which is relevant to several processes such as soil salinization, land-atmosphere interaction and soil moisture-precipitation interactions. Fundamental understanding of the mechanisms controlling solute transport and deposition in single capillary tubes is a necessary step to describe saline water evaporation and solute precipitation in complex porous media (Norouzi Rad et al., 2013; Shokri-Kuehni et al., 2017a; Shokri-Kuehni et al., 2017b). Within this context, we utilized dual energy imaging using synchrotron X-ray micro-tomography (Shokri-Kuehni et al., 2018) to investigate solute transport and deposition during evaporation from single capillary tubes of square and circular cross sections with lateral dimension of 1 mm and 3 mm (two sizes per cross section which resulted in four capillary tubes in total). The capillary tubes were filled with CaI2 solution of 5% concentration (by weight) and were placed under similar evaporative conditions. All boundaries were closed except top which was exposed to air for evaporation. The drying capillary tubes were scanned approximately once every hour for nearly 20 hrs. The recorded images enabled us to quantify solute concentration with a high spatial and temporal resolution throughout the capillary tubes with different sizes and cross sections and delineate the key transport mechanisms controlling solute transport and preferential deposition during evaporation. Our findings clearly show the contribution and impact of corner flow observed in square capillary tubes on the spatio-temporal distribution of solute, the evaporative mass losses and the velocity of the receding meniscus. The obtained results extend the fundamental understanding required for describing the transport mechanisms controlling saline water evaporation from porous media.

References

Norouzi Rad, M., N. Shokri, M. Sahimi (2013), Phys. Rev. E, 88, 032404.

Shokri-Kuehni, S.M.S., T. Vetter, C. Webb, N. Shokri (2017a), Geophys. Res. Lett., 44, 5504–5510.

Shokri-Kuehni, S.M.S., M. Norouzirad, C. Webb, N. Shokri (2017b), Adv. Water Resour., 105, 154-161.

Shokri-Kuehni, S.M.S., M. Bergstad, M. Sahimi, C. Webb, N. Shokri (2018b), Sci. Rep., 10, 10731, London: Nature Publishing Group.
Data assimilation framework around the LPJ-GUESS model for the optimised simulation of CH4 emission from Northern wetlands
Authors: Theanutti Kallingal Jalisha , Scholze Marko , Rinne Janne , Lindstrom Johan
Published: March 2020

Wetlands in the boreal zone are a significant source of atmospheric methane, and hence they have been intensively studied with mechanistic models for the assessment of methane dynamics. The arctic-enabled dynamic global vegetation model LPJ-GUESS is one of the models that allow quantification and understanding of the natural methane fluxes at various scales ranging from local to regional and global, but with several uncertainties. Complexity in the underlying environmental processes, warming driven alternative paths of meteorological phenomena and changes in hydrological and vegetation conditions are exigent for a calibrated and optimised LPJ-GUESS. In this study, we used the Markov chain Monte Carlo (using Metropolis-Hastings formula) algorithm to quantify the uncertainties of LPJ-GUESS. Application of this method allows greater search of the posterior distribution, leading to a more complete characterisation of the posterior distribution with reduced risk of sample impoverishment. We will present first results from an assimilation experiment optimising LPJ-GUESS model process parameters using the flux measurement data from 2005 to 2015 from the Siikaneva wetlands in southern Finland. We  analyse the parameter efficiency of LPJ-GUESS by looking into the posterior parameter distributions, parameter correlations, and the interconnections of the processes they control. As a part of this work, knowledge about how the methane data can constrain the parameters and processes is derived.
Statistical Behaviour of Time Occurrences and Magnitude of Aftershock Sequences
Authors: Daminelli Rosastella , Marcellini Alberto
Published: March 2020

The negative exponential distribution of the magnitude (that is the well-known Gutenberg-Richter relation) and the negative exponential distribution of interarrival times constitute the backbone of the seismic hazard analysis.

Our goal is to check if these two distributions could be considered an acceptable model also for aftershock sequences.

We analysed several aftershock sequences, with mainshocks ranging from M=5.45  to M=7.3; six sequences of Californian earthquakes selected from the SCEC database and an Italian sequence, selected from INGV-CNT Catalog.

The results show that the G-R relation fits remarkably the data, with a β value ranging from -1.8  to -2.4. The temporal behaviour shows an acceptable fit to the negative exponential distribution:  all the sequences exhibit a good fit for Δt>2.5 hours, on the contrary for Δt<2.5 hours Weibull distribution is more suitable.
#SciComm via the European Geoscience Union Divisions’ blogs: experiences from the editorial teams.
Authors: Cigala Valeria , Burgard Clara , van Rijsingen Elenora , van Zelst Iris , Trani Olivia , Alberti Tommaso , Sprenger Matthias , Jurikova Hana , Barnard Luke , Amato Gabriele , Roder Giulia , Rizzi Jonathan , Lombardo Luigi , Fernández-Blanco David , Gürer Derya , Papeschi Samuele , Davies Hannah Sophia , Franzke Christian , Faranda Davide , von der Heydt Anna , Vannitsem Stéphane , Dal Zilio Luca , Glerum Anne , Gülcher Anna , Lourenço Diogo , Meier Tobias , Rozel Antoine , Shephard Grace , Coulon Violaine , Berger Sophie , Cavitte Marie
Published: March 2020

In an era where communicating your science goes hand in hand with doing your science, many scientists devote time to develop tools and learn new skills and strategies for Science Communication. The European Geosciences Union (EGU) has put in place one of those tools: the Divisions’ Blog. Most of the current EGU Divisions has an active blog run mainly by one or more volunteer early-career scientists. 
Regularly, both editors, and regular and guest authors write about research in their field, talk about relevant topics discussed within the scientific community, and highlight interesting facts for scientists and the general public. The goal is to provide a platform for enhancing communication among geoscientists in ways that go beyond the means of peer-reviewed publication or scientific conferences. At the same time, we aim at engaging with the general public, by writing in a technically sound, but more accessible form. Each Division’s blog has its character, like the teams behind it, making the blogs a diversified and exciting digital environment.

Here we show the main numbers, statistics, and feedback from each Division Blog, thus providing a measure of the efforts put in and the impact made so far by the broad Geoscience community. We discuss best practices, blog styles and topics which do work well or not, based on readership statistics. We also show the channels chosen for advertising the blogs, such as social media, and the impact of the choices made. Finally, we show that even though EGU has its base in Europe, we reach an audience beyond Europe thanks to active members based outside Europe and to topics addressing particular geographical areas.

We conclude that, within the increasingly essential role played by Science Communication in every research field, the EGU Divisions’ Blogs are successful at sharing research related to their fields with the broad geoscientific and non-scientific community. This success mainly relies on the time, effort, motivation, and creativity of editors and guest authors.
Seasonality of surface stirring by geostrophic flows in the Bay of Bengal
Authors: Paul Nihar , Sukhatme Jai
Published: March 2020

Stirring of passive tracers in the Bay of Bengal driven by altimetry derived daily geostrophic surface currents, is studied on subseasonal timescales. To begin with, Hovmöller plots, wavenumber-frequency diagrams and power spectra confirm the multiscale nature of the flow. Advection of latitudinal and longitudinal bands highlights the chaotic nature of stirring in the Bay via repeated straining and filamentation of the tracer field. An immediate finding is that stirring is local, i.e. of the scale of the eddies, and does not span the entire basin. Further, stirring rates are enhanced along the coast of the Bay and are relatively higher in the pre- and post-monsoonal seasons. Indeed, Finite Time Lyapunov Exponent (FTLE) and Finite Size Lyapunov Exponent (FSLE) maps in all the seasons are patchy with minima scattered through the interior of the Bay. Further, these maps bring out a seasonal cycle wherein rapid stirring progressively moves from the northern to southern Bay during pre- and post-monsoonal periods, respectively. The non-uniform stirring of the Bay is reflected in long tailed probability density functions of FTLEs, that become more stretched for longer time intervals. Quantitatively, advection for a week shows the mean FTLE lies between 0.13±0.07 day-1, while extremes reach almost 0.6 day-1 . Averaged over the Bay, Relative dispersion initially grows exponentially, followed by a power-law at scales between approximately 100 and 250 km, which finally transitions to an eddy-diffusive regime. Quantitatively, below 250 km, a scale dependent diffusion coefficient is extracted that behaves as a power-law with cluster size, while above 250 km, eddy-diffusivities range from 6 × 103 - 1.6 × 104   m2s-1 in different regions of the Bay. These estimates provide a useful guide for resolution dependent diffusivities in numerical models that hope to properly represent surface stirring in the Bay.
Can non-Methane hydrocarbons inform oil and gas emissions studies?
Authors: Herndon Scott , Daube Conner , Krechmer Jordan , Majluf Francesca , Fortner Edward , Dyroff Christoph , Yacovitch Tara
Published: March 2020

Recently, the Aerodyne Mobile Laboratory quantified emissions of methane from oil and gas production sites in two very different oil and gas “plays”. The emission profile of non-methane hydrocarbons shows differences that are associated with the geologic source itself. Further analysis reveals that variations in the non-methane hydrocarbon profile can be exploited to pinpoint the specific piece of equipment that is emitting methane.  The mobile lab was outfitted with tunable infrared laser direct absorption spectrometers and a high resolution Vocus proton transfer reaction mass spectrometer.    This presentation will illustrate the key points with empirical examples and examine methods to attribute observed methane emission sources.      
Critical fluid volumes and the start of 'self-sustaining' fracture ascent
Authors: Davis Timothy
Published: March 2020

In theory, pockets of fluid in brittle media can be transported large distances, provided that both the fluid volume is large enough, such that fluid pressures can fracture the rock, and that stress gradients exist causing asymmetric growth of the fracture's front. Currently, industrial injections are deemed safe based on empirical observations of volumes, rates and pressures from closed-access industrial data. Existing theoretical models are difficult to use a priori to predict the critical volume of fluid that will cause unhindered fracture ascent, as they are expressed in terms of the fracture’s length, which is hard to predict a priori and difficult to measure. Here we constrain scale-independent critical volumes as a function of only rock and fluid properties by supplementing simple analytical models with numerical simulations in three dimensions. We apply our model to laboratory and natural settings, showing that the volumes we estimate match well with laboratory data and can be used as a conservative estimate in geological applications.
Scattering of Interstellar Neutral Atoms in the Outer Heliosheath
Authors: Swaczyna Pawel , McComas David J. , Zirnstein Eric J. , Heerikhuisen Jacob
Published: March 2020

Interstellar neutral (ISN) atoms from the very local interstellar medium (VLISM) penetrate the heliosphere and are observed by detectors located near 1 au, e.g., on the Interstellar Boundary Explorer (IBEX), and in the future on the Interstellar Mapping and Acceleration Probe (IMAP). Interpretation of these observations provides insight into the physical conditions in the VLISM but requires modeling of the processes that change distributions of ISN atoms inside the heliosphere and beyond. Here, we focus on the consequences of collisional scattering in the outer heliosheath (OHS), beyond the heliopause. Charge exchange collisions create secondary atoms from the OHS ions, which have a different flow speed and temperature than pristine ISN atoms, especially close to the heliopause. It is widely assumed that these collisions do not change directions of interacting particle velocities. We show that this assumption is not justified for the typical collisions speed in the OHS, and therefore the distribution functions of secondary atoms are different than those calculated without this momentum exchange.  This angular scattering in charge exchange collisions results in secondary atom production terms that show elongated distributions aligned with the relative bulk speed of the parent populations, as well as higher temperatures (up to ~3000 K) and shifted bulk speeds (up to ~2 km s-1). Distributions of ISN atoms are also affected by elastic collisions that similarly show significant scattering for collision energies typical in the OHS. Eventually, these scattering processes modify distributions of ISN atom observed in the heliosphere directly and as pickup ions. These effects may help explain systematical discrepancies between the IBEX data and current models.
Temporal variations in ITRF station displacements analyzed with vector spherical harmonics
Authors: Soja Benedikt , Abbondanza Claudio , Chin T. Mike , Gross Richard , Heflin Michael , Parker Jay , Wu Xiaoping
Published: March 2020

The ITRF2014 candidate solutions DTRF2014 and JTRF2014 provide time-dependent station coordinates accounting for irregular station motions. DTRF2014 by DGFI-TUM expands the secular coordinate model via non-tidal loading corrections caused by changes in the atmosphere and continental water storage. JTRF2014 by JPL follows a time series approach to TRF determination based on Kalman filtering, providing weekly updates to station coordinates. The process noise model of the Kalman filter is derived from non-tidal loading deformations.

Global features in station displacements have been studied in the past by determining coefficients of spherical harmonics. So far, studies have mostly focused on individual coordinate components at a time. Typically, the vertical coordinate component is of most interest, since it most often contains the largest signals.

In this work, we apply the concept of vector spherical harmonics (VSH) to study temporal variations in station displacements of DTRF2014 and JTRF2014. The advantage of VSH compared to scalar spherical harmonics is that all three coordinate components can be considered at the same time. We estimate VSH coefficients up to degree-2, which includes dipole and quadrupole deformations. Degree-1 deformations represent translations and rotations of the frame, while degree-2 terms contain, inter alia, information on the oblateness of the Earth. We use VSH to analyze station displacements of DTRF2014 and JTRF2014 individually and to conduct comparisons between the two frames. Furthermore, since the temporal variations in both DTRF2014 and JTRF2014 are linked to non-tidal loading deformations, our analysis of temporal variations in VSH coefficients allows for geophysical interpretation.

 
Crustal Thickness and Composition of the São Paulo Plateau and Florianópolis Ridge, SE Brazilian Margin
Authors: Graça Michelle , Cowie Leanne , Kusznir Nick , Stanton Natasha
Published: March 2020

The São Paulo Plateau (SPP) and the Florianópolis Ridge (FR), located on the Santos segment of the SE Brazilian margin in the South Atlantic, are large positive bathymetric features with a combined lateral dimension of approximately 500 km. An important question is whether they are underlain by thinned continental crust or by anomalously thick magmatic crust. Each hypothesis has implications for the breakup of the South Atlantic and the evolution of the overlying saline Santos basin.

Integrated quantitative analysis consisting of gravity inversion, RDA (residual depth anomaly) analysis and flexural subsidence analysis has been applied to a deep long-offset seismic reflection line running NW-SE across the SPP and FR. Gravity inversion predicts crustal basement thicknesses in the range of 12 to 15 km for the SPP and FR, deceasing to 7-8 km thickness at the extreme SE end of the profile. The SPP and FR are separated by a region of thinner crust approximately 80 km wide. Thinning factors from subsidence analysis for SPP and FR are typically between 0.6 and 0.7.

RDA values close to zero and a thinning factor of 1 were obtained for the region with 7-8 km thick crust at the SE end of the profile which are all consistent with normal oceanic crust rather than previously interpreted exhumed mantle. This oceanic crust is highly tectonised and corresponds to the location of the Florianópolis Fracture Zone.

Flexural backstripping and reverse thermal subsidence modelling were performed to calculate palaeo-bathymetry at breakup and give 2.5 km below sea level at the SE end of the profile consistent with this region being oceanic crust. Flexural subsidence analysis applied to base salt shows that the observed base salt subsidence requires a component of syn-tectonic subsidence as well as post-rift thermal subsidence, and that the salt was deposited while the crust was still thinning.

Joint inversion of time seismic reflection and gravity data to determine the lateral variation in basement density by comparing seismic and gravity Moho in the time domain gives a basement density under the SPP and FR of between 2600 and 2700 kg/m3. The same method gives a basement density of 900kg/m3 for the oceanic crust at the SE end of the profile. The FR basement in the NW shows a basement density similar to that of the SPP while in its SE the basement density is much higher approaching 2950 kg/m3.  We interpret the relatively low basement densities of the SPP with respect to that of oceanic crust as indicating a continental rather than magmatic composition. A similar analysis to determine basement density applied to the Evain et al. (2015) seismic refraction profile in the same location also gives a SPP basement density that supports a continental composition.
Sensitivity of the Atlantic meridional overturning circulation (AMOC) to the tropical Indian Ocean warming.
Authors: Ferster Brady , Fedorov Alexey , Mignot Juliette , Guilyardi Eric
Published: March 2020

The Arctic and North Atlantic Ocean play a fundamental role in Earth’s water cycle, distribution of energy (i.e. heat), and the formation of cold, dense waters. Through the Atlantic meridional overturning circulation (AMOC), heat is transported to the high-latitudes. Classically, the climate impact of AMOC variations has been investigated through hosing experiments, where anomalous freshwater is artificially added or removed from the North Atlantic to modulate deep water formation. However, such a protocol introduces artificial changes in the subpolar area, possibly masking the effect of the AMOC modulation. Here, we develope a protocol where AMOC intensity is modulated remotely through the teleconnection of the tropical Indian Ocean (TIO), so as to investigate more robustly the impact of the AMOC on climate. Warming in the TIO has recently been shown to strengthen the Walker circulation in the Atlantic through the propagation of Kelvin and Rossby waves, increasing and stabilizing the AMOC on longer timescales. Using the latest coupled-model from Insitut Pierre Simon Laplace (IPSL-CM6), we have designed a three-member ensemble experiment nudging the surface temperatures of the TIO by -2°C, +1°C, and +2°C for 100 years. The objectives are to better quantify the timescales of AMOC variability outside the use of hosing experiments and the TIO-AMOC relationship.  In each ensemble member, there are two distinct features compared to the control run. The initial changes in AMOC (≤20 years) are largely atmospherically driven, while on longer timescales is largely driven by the TIO teleconnection to the tropical Atlantic. In the northern North Atlantic, changes in sensible heat fluxes range from 15 to 20 W m-2 in all three members compared to the control run, larger than the natural variability. On the longer timescales, AMOC variability is strongly influenced from anomalies in the tropical Atlantic Ocean. The TIO teleconnection supports decreased precipitation in the tropical Atlantic Ocean during warming (opposite during TIO cooling) events, as well as positive salinity anomalies and negative temperature anomalies. Using lagged correlations, there are the strongest correlations on scales within one year and a delayed response of 30 years (in the -2°C ensembles). In comparing the last 20 years, nudging the TIO induces a 3.3 Sv response per 1°C change. In summary, we have designed an experiment to investigate the AMOC variability without directly changing the North Atlantic through hosing, making way for a more unbiased approach to analysing the AMOC variability in climate models.
Explanation of global plasmapause characteristics in the frame of interchange instability mechanism
Authors: Verbanac Giuli , Bandic Mario , Pierrard Viviane
Published: March 2020

Recent statistical studies based on CLUSTER, CRRES, and THEMIS satellite data have provided insight into global plasmapause characteristics: start of erosion between 21-07 MLT and eastward azimuthal propagation. The observed plasmapause behavior is found to agree with the theory of the interchange instability mechanism. We present the results of the plasmapause characteristics obtained with simulations based on this mechanism.

Here we aim to obtain the same plasmapause characteristics that we previously obtained with simulations using real values of geomagnetic Kp index (which are the proxies for the convection electric field), but using synthetic Kp changes. We show that for that, completely unexpected, instead of many combinations of Kp changes occurring at different UT times (generated for instance with Monte Carlo methods), only 3 Kp jumps occurring at one UT time, leads to the same plasmapause characteristics obtained with simulations using the real Kp values. Therefore, two plasmapause datasets are constructed by setting the following input in the simulations: (a) real values of the geomagnetic Kp index, (b) certain types of time-dependent changes in the Kp (Kp jumps). The Kp jumps include sharp Kp increase, sharp Kp decrease, short time burst enhancement (increase-decrease within 3 hours) in Kp and their combinations in order to obtain plumes, shoulders, and notches, the structures most often observed in nature. The modeled plasmapause is cross-correlated with the Kp index at different 1-hour MLT bins.

We have shown that the cross-correlation curves provide deep insight into the physical processes related to the plasmapause dynamic and evolution. In single events, plasmapause may undergo complex and different dynamics. Here, we show that global plasmapause motions and deformation in time may be simply explained, at least in the statistical sense. Accordingly, we will demonstrate and discuss that three plasmapause structures and their combinations statistically leave the same imprint in the passage through a specific MLT sector as a combination of the plasmapauses created with a large number of the real Kp changes.  
Hisparc cosmic ray detector’s response to heavy rain
Authors: van Deursen Alexander P. J. , Fokkema David , van Dam Kasper , van Eijk Bob
Published: March 2020

Cosmic ray particles have extreme energies, 1016 eV/nucleon and up. Upon arrival at the higher atmosphere and collisions with the gas molecules there, the cosmic ray particles convert into an cascade of different secondary particles that finally arrive at soil level in the form of an extensive air shower (EAS): high-energy gamma’s, electrons and muons. In the HIgh School Project on Astrophysics Research with Cosmics (Hisparc, www.hisparc.nl) about 100 EAS detector stations are distributed over the Netherlands and several neighboring countries. These stations are mostly placed on the roof of secondary schools, where they have been built by pupils to attract them towards STEM studies.

Each station consists of two or four detectors with 0.5 m2 plastic scintillator plates to record the passage of the EAS. At coincidence, the scintillator signals are individually recorded, accurately timed with GPS. All data are sent to and collected at the NIKHEF institute (www.nikhef.nl) and made available (open-access) for further analysis by pupils and scientists.

The sensitivity of the detectors is commonly adjusted such that each detector records a few hundred hits per second. The number of coincidences within 1.5 μs is then about 1 in 3 seconds, in part due to an actual EAS, in part due to random local radioactive processes.

During intense rainfall of a particular summer storm several two-detector systems recorded an increase in the coincidence frequency of up to a factor of 7. When comparing different stations we could follow the associated storm front moving northwards over NL. Within the coincidence interval of 1.5 μs the increased individual signals of both detectors were evenly distributed. Actual EAS signals tend to be synchronous to within 100 ns. We therefor attribute the increase to random signals. As possible source we suggest gamma radiation due to radon daughters in the atmosphere that are washed out by the rain and accumulate on the roof close to the detectors. The delay between rain and signal increase is noted and in accordance with the washing process time.
Gender equality in science can be achieved, but it requires ambitious effort from society, institutions and individual leaders.
Authors: Sojtaric Maja , Andreassen Karin
Published: March 2020

Gender equality is rare in science, technology, engineering and mathematics (STEM) fields, with men dominating the scientific positions. However, for CAGE Centre for Arctic Gas Hydrate Environment and Climate at UiT The Arctic University of Norway achieving gender equality has never been a problem. The Norwegian centre of excellence has had gender equality in all positions from its start in 2013. During this time, CAGE scientists have produced over 300 scientific papers and welcomed 18 CAGE-babies to the world. The leadership group consists of 75 percent women, while the Steering Board of CAGE is an even split between genders. How is it possible for a centre that has geosciences as primary fields of research, to achieve gender equality? CAGE is an excellent case study on how larger societal and structural incentives, as well as leadership ambitions, can make gender equality in STEM more than a pipe dream. There are several aspects that have helped us reach and maintain gender equality: good parental leave and heavily regulated working conditions in Norway that make work/life balance achievable, which in turn makes us attractive to qualified young female scientists; institutional incentives help us find good female candidates and nurture them to more prominent positions, and CAGE center structure allows us to maintain a good progression in our projects, even when the project managers are away on parental leave.
Spatiotemporal modelling of induced seismicity with a stress-based statistical approach applied to different production sites
Authors: Richter Gudrun , Hainzl Sebastian , Niemz Peter , Silverii Francesca , Dahm Torsten , Zöller Gert , Zang Arno , Maccaferri Francesco
Published: March 2020

In the framework of the Geo:N project SECURE (Sustainable dEployment and Conservation of Underground Reservoirs and Environment) we developed a Python software toolbox to model the rate and distribution of seismicity induced by anthropogenic stress changes at various production sites (gas production, hydrofracturing, gas storage). This toolbox tests different frictional behavior of the underground (linear or rate-and-state stressing rate dependent, critically or subcritically prestressed faults) and takes into account the uncertainties of the production site parameters. The knowledge on the location and orientation of pre-existing faults can be considered as well. Model parameters are estimated by fitting the model to recorded historical seismicity using a maximum likelihood approach. We discuss applications at conventional gas fields, hydraulic fracturing experiments and an aquifer gas storage site, covering a wide range of spatial and temporal scales of induced seismicity in different settings and for different production schemes. This enables to investigate the underlying physical processes by the comparison of the different models. Additionally, the model parameters are linked to frictional material properties and the best performing model can be used to forecast the seismicity rates in space and time with their uncertainties according to the production plans.

Induced seismicity at gas fields in the Northern Netherlands and in Germany have similar tectonic settings but very different extents, depths and production histories. The data set of two sites are compared which both show a large delay of the first recorded seismicity after the start of production. Using our model we can reproduce the long delay for both sites. Thanks to the long and detailed data set we successfully reproduce the spatiotemporal pattern of the seismicity of one site, whereas the limited number of seismic events result in large uncertainties for the other site. In the comparative testing of the models the critically prestressed rate-and-state model performs best. This means that the complete stressing history influences the resulting seismicity. We also applied the model to a hydraulic fracturing experiment in granite comparing data sets for different fracturing methods and different phases of a stimulation experiment. Hundreds of microearthquakes are localized in a volume of roughly 15x15m with increasing number of events for later refraction stages indicating the growth of rock fracturing. A third application is run for a gas storage in an aquifer layer, which is loaded by injection and production operations. Here the proportion of the tectonic versus the anthropogenic induced seismicity is investigated analyzing the varying number of small local earthquakes in the region.
Improving solar wind forecasts using data assimilation
Authors: Lang Matthew , Owens Mathew , Lawless Amos
Published: March 2020

Data assimilation has been used in Numerical Weather Prediction models with great success, and it can be seen that the improvement of data assimilation methods has gone hand-in-hand with improvements in weather forecasting skill. The implementation of data assimilation for solar wind forecasting is still in its infancy and is still underused in the field. Hence, it is important to investigate the optimal implementation of these methods to improve our understanding of the solar wind.

To do this, we have generated a variational data assimilation scheme for use with a steady-state solar wind speed model based upon the Burger equation. This relatively simple scheme has the advantage of updating the inner-boundary conditions of the solar wind model allowing the updates to persist and improve the solar wind estimates throughout the whole domain.

To this effect, we present numerical experiments using our data assimilation scheme with STEREO and ACE data to improve estimates and forecasts of the solar wind in near-Earth space. Particular focus will be applied to assimilating data when the satellites are 60 degrees apart, such that they simulate Earth-L5 forecasting scenarios.
Revised sediment transport model for estimation of suspended sediment flux and chemical composition of the Irrawaddy and Salween rivers
Authors: Baronas J. Jotautas , Tipper Edward T. , Bickle Michael J. , Hilton Robert G. , Stevenson Emily I. , Hackney Christopher , Parsons Daniel , Darby Stephen , Larkin Christina S. , Khaing Aung Myo
Published: March 2020

A large portion of freshwater and sediment is exported to the ocean by just several of the world's major rivers. Many of these mega-rivers are under significant anthropogenic pressures, such as damming and sand mining, which are having a significant impact on water and sediment delivery to deltaic ecosystems. However, accurately measuring the total sediment flux and its mean physicochemical composition is difficult in large rivers due to hydrodynamic sorting of sediments. To account for this, we developed an updated semi-empirical Rouse modeling framework, which synoptically predicts sediment concentration, grain size distribution, and mean chemical composition (organic carbon wt%, Al/Si ratio) with depth and across the river channel.

We applied this model to derive new sediment flux estimates for the Irrawaddy and the Salween, the last two free-flowing mega-rivers in Southeast Asia, using a newly collected set of suspended sediment depth samples, coupled to ADCP-measured flow velocity data. Constructing sediment-discharge rating curves, we calculated an annual sediment flux of 326 (68% confidence interval of 256-417) Mt/yr for the Irrawaddy and 159 (109-237) Mt/yr for the Salween, together accounting for 2-3% of total global riverine sediment discharge. The mean flux-weighted sediment exported by the Irrawaddy is significantly coarser (D84 = 193 ± 13 µm) and OC-poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 µm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of 1.9 (1.0-3.3) Mt C/yr, contributing ~1% of the total riverine POC export to the ocean. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment fluxes, given the increasing anthropogenic pressures on these river basins.
Multi-source quantification of precipitation in the global water cycle
Authors: Vargas Godoy Mijael Rodrigo , Pradhan Rajani Kumar , Pratap Shailendra , Rahim Akif , Markonis Yannis
Published: March 2020

The knowledge of global precipitation is of crucial importance to the study of climate dynamics and the global water cycle in general. Although global precipitation climatologies have existed for some time, and their understanding has improved dramatically due to the vast amount of different data sources, their information has not been comprehensive enough due to precipitation spatial-temporal variability. Thus, ground station reports are, in some cases, not representative of the surrounding areas. Remote sensing data and model simulations complemented the traditional surface measurements and offered unprecedented coverage on a global scale. It is important to note that satellite data records are now of sufficient time frame lengths and with methods “mature” enough to develop meaningful precipitation climatologies that are able to provide information on precipitation patterns and intensities on a global scale. While data (and in some cases exploration/visualization tools as well) are widely available, each dataset comes with different spatial resolution, temporal resolution, and biases.

Consequently, this unique opportunity to obtain a robust quantification of global precipitation has been hindered by the uncertainty, already revealed in the first attempts of the unification of different data products. Herein, we present a multi-source quantification of global precipitation, focusing on the description of the underlying uncertainties. Our approach combines station (CRU, GHCN-M, PRECL, UDEL, and CPC Global), remote sensing (PERSIANN, PERSIANN-CCS, PERSIANN-CDR, GPCP, GPCP_PEN_v2.2, CMAP, and CPC-Global) and reanalysis (NCEP1, NCEP2, and 20CRv2) data products, providing an updated overview of the role of precipitation in global water cycle.