bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of river weirs on bedload dynamics in low to medium energy rivers
Authors: Tamisier Vincent , Gob Frédéric , Gautier Emmanuèle , Houbrechts Geoffrey , Dépret Thomas
Published: March 2021

Assessing the impact of weirs in low- to medium-energy rivers, especially their influence on the bedload continuity, is an important issue for the understanding and management of river hydrosystems. The implementation of European regulations has for example led to an increasing number of restoration projects involving the total or partial dismantling of weirs. The effect of weirs on sedimentary continuity is beginning to be studied but remains poorly understood. In this study we present the results of monitoring over three hydrological seasons of 900 particles equipped with PIT tags set up around two weirs on the Rognon river (France) and the Amblève river (Belgium). For the two sites studied, and while floods were relatively frequent (max 5 return-interval years for the Rognon River and 2 return-interval years for the Amblève River), nearly 80% of the tagged particles positioned just upstream of the weirs were exported downstream of them during the study period. However, the tagged particles in the control reaches, non-influenced by weirs, travelled distances 2 to 2.5 times greater than the particles injected in the impoundment. Mobilisation rates are also significantly higher in the control reaches. Whereas the size of the mobilised particles (D50, D90) is similar between the impoundment and the control reaches in the Amblève river, mobilised particles are significantly smaller in the impoundment reach in the Rognon river. This data indicates that these weirs can have a significant effect by slowing down the bed load velocity, especially its coarsest part. Nevertheless, in the current weir operating, weirs do not interrupt the bedload continuity. This type of structure does not seem to constitute a real obstacle to sedimentary continuity and the question of their dismantling may be raised in view of the potential impacts they could have on the other components of ecological continuity.
Comparing large eddy simulations with sonic anemometer and LIDAR measurement data during Foehn events in complex terrain
Authors: Spirig Curdin T. , Fluck Stefan , Vogt Kenneth , Anet Julien G.
Published: March 2021

Simulations of turbulent wind flows in complex, mountainous terrain prove to be challenging tasks for today’s numerical simulation models. However, knowing about these wind flow patterns and speeds would be beneficial to assess potential environmental risks for various stakeholders – aviation, wind farms, ski resorts, cable cars or others. With the PALM model system, a state-of-the-art turbulence resolving meteorological model for atmospheric boundary layer flows is available, that can be used to assess these types of questions. By treating topography on a cartesian grid, complex terrain can be accurately represented in simulations.

In this study, the complex local flow patterns in mountainous terrain were analyzed by means of high-resolution large eddy simulations with the PALM model system. This was conducted for the Rhine valley region focusing on a small peculiar topographic feature upstream of Balzers in the area of the border between the Principality of Liechtenstein and Switzerland, were flow splitting is known to occur. There, Foehn events lead to pronounced local wind maxima and pose a damaging risk to the upwind part of the village. The model results were compared with data from measurement masts equipped with sonic and cup-anemometers at the position of assumed wind speed maxima. As well, measurements of a continuous-wave LIDAR system located at the outflow of the side valley were integrated in our study. The validation measurements for the Foehn events in Balzers were taken in December 2020, during which two pronounced Foehn events took place.

In PALM, a nested simulation approach was chosen, with the smallest domain having a resolution of only a few meters. The simulation was forced by COSMO-1 model results in order to factor in the synoptic weather conditions of the respective days. We show model results of the flow patterns that occur in this complex topography, analyze the wind maxima present in the valley and compare the results with local measurement data. This study demonstrates how large eddy simulation tools like PALM can produce insights into complex flow structures in mountainous terrain, and how these insights can be used to make more informed decisions to protect residents from damaging outcomes of environmental risks.
Using Sentinel-5P time-series products for Nitrogen Dioxide (NO2) Spatio-Temporal Analysis over Europe During the Coronavirus Pandemic Lockdown
Authors: Vîrghileanu Marina , Săvulescu Ionuț , Mihai Bogdan-Andrei , Nistor Constantin , Dobre Robert
Published: March 2021

Nitrogen dioxide (NO2) is one of the main air quality pollutants of concern in many urban and industrial areas worldwide. Being emitted by fossil fuel burning activities including mainly road traffic, the NO2 pollution is responsible for population health degradation and secondary pollutants formation as nitric acid and ozone. In the European region, almost 20 countries exceeded in 2017 the NO2 annual limit values imposed by European Commission Directive 2008/50/EC (EEA, 2019). Therefore, NO2 pollution monitoring and regulation is a necessary task to help decision makers to search for a sustainable solution for environmental quality and population health status improvement. In this study, we propose a comparative analysis of the tropospheric NO2 column density spatial configuration over Europe between similar periods from 2019 and 2020, based on ESA Copernicus Sentinel-5P products. Our results highlight the NO2 pollution dynamics over the abrupt transition from a normal condition situation to the COVID-19 outbreak context, characterized by short-time decrease of traffic intensities and industrial activities, this situation being also reflected by the national level statistics referring to COVID-19 cases and economic indicatiors. The validation approach provides high correlation between TROPOMI derived data and independent data from ground-based observations with encouraging values of the R2 ranging between 0.5 and 0.75 in different locations.  
Can laboratory experiments reach regimes relevant for the oceanic dynamics?
Authors: Rodda Costanza , Savaro Clement , Campagne Antoine , Calpe Linares Miguel , Augier Pierre , Sommeria Joël , Valran Thomas , Viboud Samuel , Mordant Nicolas
Published: March 2021

Atmospheric and oceanic energy spectra are characterized by global scaling laws, suggesting a common mechanism driving the energy route to dissipation. Although several possible theories have been proposed, it is not clear yet what the phenomena contributing the most to the energy at the different spatial scales are. One possible scenario is that internal gravity waves, which can be ubiquitously found in the atmosphere and the ocean and play a fundamental role in the energy transfer, cause the observed spectral slopes at the mesoscales in the atmosphere and submesoscales in the oceans. In the context of this open field of investigation, we present an experimental study where internal gravity waves are forced at a given frequency by the oscillating walls of a large pentagonal-shaped domain filled with a stably stratified fluid. The setup is built inside the 13-meters-diameter tank at the Coriolis facility in Grenoble, where geophysical regimes (with high Reynolds number and low Froude) can be achieved and rotation can also be added. The purpose of our investigation is to determine whether it is possible to induce a wave turbulence cascade by forcing internal waves at the large scales. Following a previous study1, where instead of the pentagonal a square domain was utilized, we obtained the velocity field employing time-resolved particle image velocimetry and then calculated the energy spectra. The previous study inside a square domain showed some evidence of a cascade, but it was strongly affected by 2D modes that sharpened the spectrum. Therefore, we changed the domain shape to a pentagon to reduce this finite-size effect. When the waves are forced at frequency ωF=0.4 N, our data shows that the spectra follow the scaling law ω-2 at frequencies larger than the forcing frequency and extending beyond N. The experimental spectra strikingly resemble the characteristic Garret-Munk spectrum measured in the ocean. As the interaction of weakly non-linear waves dominates the dynamics at frequencies smaller than the buoyancy frequency N, we can conclude that the experimental spectra are generated by weak internal wave turbulence driving the turbulent cascade at the high-frequency end of the spectrum. 

 

1 "Generation of weakly nonlinear turbulence of internal gravity waves in the Coriolis facility", C. Savaro, A. Campagne, M. Calpe Linares, P. Augier, J. Sommeria, T. Valran, S. Viboud, and N. Mordant, PRF 2020
Bathymetry and uplift rate of the Gulf of Aqaba, Dead Sea Fault.
Authors: Ribot Matthieu , Klinger Yann , Pons-Branchu Edwige , Lefevre Marthe , Jónsson Sigurjón
Published: March 2021

Initially described in the late 50’s, the Dead Sea Fault system connects at its southern end to the Red Sea extensive system, through a succession of left-stepping faults. In this region, the left-lateral differential displacement of the Arabian plate with respect to the Sinai micro-plate along the Dead Sea fault results in the formation of a depression corresponding to the Gulf Aqaba. We acquired new bathymetric data in the areas of the Gulf of Aqaba and Strait of Tiran during two marine campaigns (June 2018, September 2019) in order to investigate the location of the active faults, which structure and control the morphology of the area. The high-resolution datasets (10-m posting) allow us to present a new fault map of the gulf and to discuss the seismic potential of the main active faults.

We also investigated the eastern margin of the Gulf of Aqaba and Tiran island to assess the vertical uplift rate. To do so, we computed high-resolution topographic data and we processed new series of U-Th analyses on corals from the uplifted marine terraces.

Combining our results with previous studies, we determined the local and the regional uplift in the area of the Gulf of Aqaba and Strait of Tiran.

Eventually, we discussed the tectonic evolution of the gulf since the last major change of the tectonic regime and we propose a revised tectonic evolution model of the area.

 
Hf isotopic constraints for Austroalpine basement evolution of Eastern Alps: review and new data
Authors: Chang Ruihong , Neubauer Franz , Genser Johann , Liu Yongjiang , Yuan Sihua , Huang Qianwen , Guan Qingbin , Yu Shengyao
Published: March 2021

The Alps as part of the Alpine mountain belts are one of the classical examples of orogenesis where the Mesozoic-Cenozoic tectonic evolution is well known, but not of the basement because poor age data. New data from the  pre–Alpine basement of the Austroalpine megaunit indicate that this basement is composed of a series of continental rocks, island arcs, ophiolites and subduction mélanges，accretionary wedges, and seamounts with different metamorphic, but often amphibolite facies grade. This study presents new results of LA–ICP–MS U–Pb and MC–ICP–MS Lu–Hf dating of zircons from three key areas of Austroalpine basement units: i) the Wechsel–Waldbach–Sieggraben, (ii) the Saualpe–Koralpe –Pohorje, and (iii) the Schladming Mts. areas. As a result, the Wechsel unit is a continental magmatic arc during 500-560 Ma, and 2.1 to 2.2 Ga-and 2.5 to 2.8 Ga age show the close relationship to northern Gondwana, with depleted mantle model ages as old as 3.5 Ga. Even the Wechsel Phyllite Unit overlying the Wechselgneiss, but they have partly different sources, include juvenile crust formed at ca. 530 Ma. The Waldbach Complex is constantly added new crustal material during 490-470Ma, and considerably more positive εHf(t) values from 700 to 500 Ma interpreted being part of a magmatic arc during closure of the Prototethys and got metamorphosed during Variscan orogenic events. We consider that Schladming to Wechsel Complexes represent a Cambrian-Ordovician volcanic-magmatic arc system followed proto-Tethys subduction, and the ophiolitic Speik complex represent a back-arc basin. Many granites were formed during Permian (Grobgneiss and various granites in Pohorje Mts.) likely in an extensional environment, remelting a crust with mainly Middle Proterozoic model Hf isotopic model ages. The Plankogel Complex represents accreted oceanic, ocean island and continental-derived materials, it should belong to the accretion complex formed during Permotriassic closure of Paleotethys. We argue that the various basement complexes of the Austroalpine are different sources of ages of different tectonic evolutionary histories and likely represent, different locations before drifting. Consequently, the Austroalpine meagunit represents a composite pre-Alpine mega-unit likely assembled not earlier as Permian or Triassic times.
Mobile Optical Remote Sensing for quantification of Ammonia and Methane emissions from Dairy Farms in California.
Authors: Vechi Nathalia Thygesen , Mellqvist Johan , Offerle Brian , Samuelsson Jerker , Scheutz Charlotte
Published: March 2021

Solar occultation flux (SOF) and Mobile extractive FTIR (MeFTIR) are techniques used for over 20 years to quantify industrial emissions of VOCs, CH4, and others, from refineries in the USA, Europe, and Asia. Here, they were combined to assess methane (CH4) and ammonia (NH3) from concentrated animal feeding operations (CAFOs) in the San Joaquin Valley (SJV), California. SOF and MeFTIR were used to measure NH3 column, and ground concentrations of NH3 and CH4, respectively. SOF retrieves the gas column concentration from the solar spectra using a solar track, directing the light to a FTIR spectrometer, while crossing the gas plume. Subsequently, a direct flux approach combines the retrieved columns with wind information to obtain the mass fluxes of ammonia. In this survey, the wind information was acquired by a wind LIDAR, which measures wind speed and direction in the interval of 10 – 300 m. On the other hand, Methane emissions were quantified using a unique indirect flux approach by combining the estimated ammonia fluxes and the NH3:CH4 ratios measured from the ground concentration using MeFTIR.

Two field campaigns performed in spring and autumn studied emissions from 14 single dairy CAFOs. The daily emissions from the single farms averaged 96.4 ± 38.4 kgNH3 h-1and 411 ± 185.4 kgCH4h-1, respectively, for NH3 and CH4 with the corresponding emission factors (EF) per animal unit of 11.3 ± 3.8 gNH3h-1AU-1and 50.3 ± 24.1 gCH4h-1AU-1. The uncertainty of ammonia measurements was 17 % in a standard confidence interval (CI) and 37 % in a 95 % CI, with the largest uncertainty associated with the wind measurements. Furthermore, the methane uncertainty estimations averaged 27 % in a standard CI, and 52 % in a 95 % CI, dominated by the ammonia fluxes uncertainty. Comparison between Annual or daily EFs obtained by SOF to other quantification approaches, have to take into consideration the SOF measurement conditions, day-time and sunny weather, due to their effects on the NH3 emissions. The study contributed to develop the knowledge of dairy CAFOs emission, and to strengthen the role of optical remote sensing techniques, bridging the gap between satellites and stationary measurement approaches.
Potential and scientific requirements of optical clock networks for validating satellite gravity missions
Authors: Schröder Stefan , Stellmer Simon , Kusche Jürgen
Published: March 2021

The GRACE mission, now continued as the GRACE-FO mission, has provided an unprecedented quantification of large-scale changes in the water cycle.
Meanwhile, stationary optical clocks show fractional instabilities below 10-18 when averaged over an hour, and continue to be improved in terms of precision and accuracy, uptime, and transportability. The frequency of a clock is affected by the gravitational redshift, and thus depends on the local geopotential; a relative frequency change of 10-18 corresponds to a geoid height change of about 1 cm. This effect could be exploited for sensing temporal geopotential changes via a network of clocks distributed at the Earth's surface. 
Here, we concentrate on how the measurements of an ensemble of optical clocks connected accross Europe via optical fibre links could be used to validate and complement gravity field solutions from GRACE-FO and potential future gravity missions.
Through simulations it is shown how hydrology (water storage) and atmosphere (dry and wet air mass) variations over Europe could be observed with clock comparisons in a future network. We assume different scenarios for clock and GNSS uncertainties, where we deem the latter to be nessecary to separate local height changes from the mass redistribution signals. Our findings suggest that even under conservative assumptions -- a clock error of 10-18 and vertical height control error of 1.4 mm for daily measurements -- hydrological signals at the annual time scale and atmospheric signals down to the weekly time scale could be observed.
However, the requirements to an optical clock network used for validation of GRACE-FO and future gravity missions are higher than that, which is demonstrated along with the according spatial resolutions.
Reconsidering the paleoclimate implications of magnetic susceptibility records of Holocene loessic soils
Authors: Jordanova Diana , Jordanova Neli
Published: March 2021

Mass specific magnetic susceptibility variations with depth along soil profiles developed on loess parent material is one of the most frequently used physical parameters in local, regional and global correlations of loess deposits. It is also utilized as a paleo-precipitation proxy, defined either as absolute difference between susceptibilities of the enhanced B-horizon and parent loess, or as relative enhancement using ratios of magnetic parameters. These different approaches in the application of magnetic susceptibility as paleoclimate proxy lead us to perform a comparative study on a number of Holocene soil profiles developed on loess from European loess area and the Chinese Loess Plateau (CLP). We made a compilation of data including 20 profiles from North Bulgaria, 28 profiles from Eastern and Central Europe; and 26 profiles from the CLP. Minimum magnetic susceptibilities of the last glacial loess (Xmin) from the compiled data base for European and Chinese profiles show climate related variability, revealing multi linear relationship with both present day MAP and MAT values for the corresponding locations. Strong deviations of Xmin from this dependence display sites located at low elevation river terraces, Black sea coast and possessing large content of coarse silt and sand fractions. Pedogenic magnetic susceptibility (Xpedo) defined as (Xmax - Xmin) with  Xmax determined from the youngest part (last 1500 – 2000 years B.P.) of the Holocene magnetic susceptibility records of Chinese sections and absolute Xmax of the European sites show systematic dependence on modern MAP and MAT values. This dependence is uniform for all sites with steppe vegetation, while higher scatter and steeper regression trends are observed for sites under mixed (steppe – forest) and forest vegetation. The study is financially supported by project No KP-06-N34/2 funded by the Bulgarian National Science Fund.
Probing the damage zone on the San Andreas Fault at Parkfield
Authors: Delorey Andrew , Johnson Paul
Published: March 2021

Rocks are heterogeneous materials that exhibit nonlinear elastic (anelastic) behavior in both the laboratory and Earth. In the laboratory, investigators have observed complex relationships between stress and strain that include hysteresis, finite relaxation times, and rate and stress path dependence.  These behaviors are linked to stress, porosity, permeability, material integrity and material failure, many of the characteristics we care about in the upper crust.  A limited number of studies in the Earth have confirmed that nonlinear elasticity can be measured in situ, but due to logistical challenges these investigations have not achieved the full potential of what can ultimately be learned from this type of investigation.  We adapted a ‘pump-probe’ type experiment common in laboratory studies, using solid earth tides as the low frequency pump and empirical Green’s function as the high frequency probe.  By probing the velocity at different points in the pump cycle, we constrain some important information about the stress-strain relationship.  Near the San Andreas Fault, we observe strongly nonlinear elastic behavior that increases with decreasing distance to the fault that characterizes the damage zone.  We also constrain important aspects of hysteretic behavior that are related to damage properties and possibly pore pressure.
Sensitivity enhancement of the ambient noise tomography and analysis of seasonal variations of noise sources to refine velocities in the lower crust in central Europe
Authors: Kvapil Jiri , Plomerova Jaroslava , Working Group AlpArray
Published: March 2021

The capability of the ambient noise tomography (ANT) to image subtle regional-scale velocity variations in the lower crust is limited by strong directionality of ambient noise sources in central Europe, which affects the quality of dispersion curves. Significant decrease of sensitivity kernels and sparse coverage of long interstation ray-pathes result in lower resolution at longer periods and thus increase uncertainty of the inversion solution in depth. If these well-known ANT limitations are properly addressed, the ANT is able to retrieve reliable high-resolution 3‑D shear velocities of the lower crust.

In this study we focus on seasonal variations of ambient noise sources in selected sites in different tectonic settings. We analyse ambient noise sources on continusly recorded wavefields from permanent observatories and temporary stations of AlpArray passive experiment with its complementary experiment and PACASE. These seismic networks with densely-spaced stations are well-suited for detailed analysis of period-dependent directionality of ambient noise sources and their effects on FTAN appearance and consequently on the quality of dispersion curves. In the second part of this study, we advocate a concept of layer-stripping during the stochastic inversion (enhanced ANT). It proved to be an efficient technique to explore the model space, particularly in the lower part of the crust. We discuss the sensitivity of the enhanced ANT to the imaged small-scale velocity features in the lower part of the crust, as well as the sensitivity to the sharp or gradational Moho in the models.
High-resolution regional projections of sea level changes along Western European coasts during the 21st century
Authors: Chaigneau Alisée , Reffray Guillaume , Voldoire Aurore , Melet Angélique
Published: March 2021

Coastal regions are subject to an increasing anthropogenic pressure. Projections of coastal sea level changes are of great interest for coastal risk assessment and decision-making processes. Sea level projections are typically produced using global climate models. However, their coarse resolution limits the realism of the representation of coastal dynamical processes influencing sea level changes at the coast, potentially leading to substantial biases. Dynamical downscaling methods can be used to refine projections at regional scales by increasing the model spatial resolution and by explicitly including more processes. Such methods rely on the implementation of a high-resolution regional climate model (RCM). 

In this work, we developed the IBI-CCS regional ocean model based on a 1/12° North Eastern Atlantic NEMO ocean model configuration. IBI-CCS includes coastal processes such as tides and atmospheric pressure forcing in addition to the ocean general circulation (dynamic sea level). This RCM is used to perform a dynamical downscaling of CNRM-CM6-1-HR, a global climate model (GCM) developed by the Centre National de Recherches Météorologiques (CNRM) with a 1/4° resolution over the ocean. CNRM-CM6-1-HR contributes to the Coupled Model Intercomparison Project 6th Phase (CMIP6). IBI-CCS is thus forced by the GCM ocean and atmospheric outputs at the lateral and air-sea boundaries. Several corrections were applied to the GCM forcings to avoid the propagation of climate drifts and biases into the regional simulations. The computations are performed over the 1950 to 2100 period for several CMIP6 climate change scenarios.

In order to validate the dynamical downscaling method, the regionally downscaled (IBI-CCS) and GCM (CNRM-CM6-1-HR) simulations are compared to reanalyses and observational datasets over the 1993-2014 period. These comparisons are performed at different time scales for a selection of ocean variables including sea level. The results show that large scale performances of IBI-CCS are better than those of the GCM thanks to the corrections applied. In addition, high frequency diagnostics are carried out and highlight for example that IBI-CCS sea level extreme events are similar to those of a reference regional ocean reanalysis. In a second phase, the RCM and GCM sea level rise projections are compared over the 21st century. These comparisons allow to investigate the impact of the model resolution and of a more complete representation of coastal processes for the simulation of projected sea level changes. 
A Bayesian framework for simultaneous determination of susceptibility and magnetic thickness from magnetic data
Authors: Ebbing Jörg , Szwillus Wolfgang , Dilixiati Yixiati
Published: March 2021

The thickness of the magnetized layer in the crust (or lithosphere) holds valuable information about the thermal state and composition of the lithosphere. Commonly, maps of magnetic thickness are estimated by spectral methods that are applied to individual data windows of the measured magnetic field strength. In each window, the measured power spectrum is fit by a theoretical function which depends on the average magnetic thickness in the window and a ‘fractal’ parameter describing the spatial roughness of the magnetic sources. The limitations of the spectral approach have long been recognized and magnetic thickness inversions are routinely calibrated using heat flow measurements, based on the assumption that magnetic thickness corresponds to Curie depth. However, magnetic spectral thickness determinations remain highly uncertain, underestimate uncertainties, do not properly integrate heat flow measurements into the inversion and fail to address the inherent trade-off between lateral thickness and susceptibility variations.

We present a linearized Bayesian inversion that works in space domain and addresses many issues of previous depth determination approaches. The ‘fractal’ description used in the spectral approaches translates into a Matérn covariance function in space domain. We use a Matérn covariance function to describe both the spatial behaviour of susceptibility and magnetic thickness. In a first step, the parameters governing the spatial behaviour are estimated from magnetic data and heat flow data using a Bayesian formulation and the Monte-Carlo-Markov-Chain (MCMC) technique. The second step uses the ensemble of parameter solution from MCMC to generate an ensemble of susceptibility and thickness distributions, which are the main output of our approach.

The newly developed framework is applied to synthetic data at satellite height (300 km) covering an area of 6000 x 6000 km. These tests provide insight into the sensitivity of satellite magnetic data to susceptibility and thickness. Furthermore, they highlight that magnetic inversion benefits greatly from a tight integration of heat flow measurements into the inversion process.
Sea level fingerprints due to ongoing land ice melt in altimetry data
Authors: Moreira Lorena , Cazenave Anny
Published: March 2021

The Global Mean Sea Level (GMSL) is rising at a rate of 3.3 mm/year over the altimetry era but at regional scale the behaviour is quite different. In some regions, the sea level rates are up to 2-3 times the global mean rate. The mechanisms behind these discrepancies are explained through the differences in the processes that affect the sea level at different scales. The concept of budget is used to express the superposition of signals that contribute to the change in sea level. At regional scale, apart from the contributions from steric and ocean mass components which are also present in the GMSL budget, the budget is also affected by atmospheric loading component and the static factors component. The static terms (also called fingerprints) include solid Earth’s deformations and gravitational changes in response to mass redistributions caused by land ice melt and land water storage changes. The goal of this study is to detect the fingerprints of the static factors using satellite altimetry-based sea level grids corrected for steric and ocean mass effects. Our preliminary results show a statistically significant correlation between observed and modelled fingerprints in some regions of the oceanic basins.
Ambient noise tomography of Gran Canaria island (Canary Islands)
Authors: Cabrera Pérez Iván , Soubestre Jean , D'Auria Luca , Cervigón-Tomico Germán , Martínez van Dorth David , Barrancos José , Padilla Germán D. , Pérez Nemesio M.
Published: March 2021

The island of Gran Canaria is located in the Canarian Archipelago, with an area of 1560 km2 and a maximum altitude of 1956 m.a.s.l., being the third island of the archipelago in terms of extension and altitude. The island has two very well differentiated geological domains: the southwest domain or Paleo-Canarias, which is the geologically oldest part, and the northeast domain or Neo-Canarias, where are located the vents of the most recent Holocene eruptions. This volcanic island hosted Holocene eruptions. Therefore, apart from being affected by volcanic risk, it potentially hosts geothermal resources that could be exploited to increase the percentage of renewable energy in the Canary Islands.

The main objective of this work is to use Ambient Noise Tomography (ANT) for retrieving a high-resolution seismic velocity model of the first few kilometres of the crust, to improve local earthquake location and detect anomalies potentially related to active geothermal reservoirs. Currently, the 1-D velocity model of the island does not allow a correct determination of the hypocenters, being unable to take into account the substantial horizontal velocity contrasts correctly.

To realize the ANT, we deployed 28 temporary broadband seismic stations in two phases. Each campaign lasted at least one month. We also exploited data recorded by the permanent seismic network Red Sísmica Canaria (C7) operated by INVOLCAN. After applying standard data processing to retrieve Green’s functions from ambient noise cross-correlations, we retrieved the dispersion curves using the FTAN (Frequency Time ANalysis) technique. The inversion of dispersion curves to obtain group velocity maps was realized using a novel non-linear multiscale tomographic approach (MAnGOSTA, Multiscale Ambient NOiSe TomogrAphy). The forward modelling of surface waves traveltimes was implemented using a shortest-path algorithm that allows the topography to be taken into account. The MANgOSTA method consists of successive non-linear inversion steps on progressively finer grids. This technique allows retrieving 2-D group velocity models in the presence of substantial velocity contrasts with up to 100% of the relative variation. Then, we performed a depth inversion of the Rayleigh wave dispersion curves using a transdimensional Bayesian formulation. The final result is a 3-D model of P- and S-wave velocities of the island. The preliminary results show the presence of a low-velocity zone in the eastern part of the island that coincides spatially with anomalies observed in previous geophysical and geochemical studies and which could be related to actual or fossil geothermal reservoirs. Furthermore, the model shows the presence of high-velocity anomalies that are associated with the mafic core of the island.
Observed exacerbation of the European water-budget deficit during multi-year droughts 
Authors: Massari Christian , Avanzi Francesco , Bruno Giulia , Gabellani Simone , Camici Stefania
Published: March 2021

In Mediterranean climates, prolonged droughts lead to a significant shift in the precipitation -runoff relationship, usually in the direction of proportionally less precipitation allocated to runoff compared to wet periods. This shift may impact discharge predictions, as many hydrological and land surface models assume that hydrological processes are stationary even under a significant change of the climate (i.e., multi-year droughts) and are generally calibrated with more weight on discharge peaks than low flows. 

Here, we investigate whether multi-year droughts result in a change in the precipitation-runoff relationship over continental European climates (which has never been fully explored before). 30-year records of annual rainfall and runoff from a dataset (>200) of small- and medium-scale (150 to 10000 km2) European catchments were used to test the existence of statistical shifts in the precipitation–runoff relationship. This was achieved by fitting a multivariate regression across annual cumulative full-natural flow, basin-wide annual precipitation, and a categorical variable denoting multi-year drought and non-drought years.

Results demonstrate that multi-year droughts cause a shift in the precipitation–runoff relationship regardless of predominant climate , with the magnitude of this shift ranging between 20 and 80%. We explore mechanisms of these shifts and potential explanatory factors, including catchment properties and characteristics.

Understanding changes in the precipitation-runoff relationship is paramount to make models and water resource management more robust to droughts, especially in a warming and more variable climate.
Coastal sea level change from Sentinel-3A SRAL over the U.S. Eastern seaboard
Authors: Abele Anrijs , Royston Sam , Bamber Jonathan
Published: March 2021

Several satellite missions are planned or have been launched to contribute to our understanding of coastal oceanography and to observe sea level, a variable of high societal importance. One of those satellites is Sentinel-3A, which was launched in February 2016, giving near-global coverage at 27-day repeat cycle and carrying Ku- and C-band synthetic aperture radar altimeter (SRAL). SRAL has enabled more reliable remote sensing of coastal ocean sea level with a higher resolution than conventional altimetry. Here, the ability to robustly discern coherent sea level changes with Sentinel-3A SRAL products is evaluated at the oceanographically complex coastal regions of the Atlantic coast of North America.

We used RADS (Radar Altimeter Database System) L2 product to calculate sea surface height anomaly (SSHA) at a set of comparison points (CP)—interpolating the measurements onto nominal ground tracks—within 250 km around selected tide gauges (TG). We compared these CP with TG measurements and ECCO2 Cube92 model output to determine the correlations and obtain spatial scales and patterns of decorrelation between the SRAL observations and the other source of data (in situ and the model).
Sediment-laden meltwater plume variability in Kongsfjorden, Svalbard
Authors: Tallentire Guy D. , Evans Jeff , Hodgkins Richard
Published: March 2021

The Arctic is warming at a rate of at least twice the global average. This is directly impacting upon the hydrological cycle; changing the balance of rain and snowfall, increasing losses of snow and glacier cover, and subsequently shifting the volumes and timing of meltwater runoff to nearby fjords and oceans. Sediment-laden meltwater plumes which are easily observable using satellite remote sensing, are good proxies for glacier runoff, both from subaerial rivers draining land-terminating glaciers, and subglacial discharge at tidewater glacier systems; they to bridge the gap between infrequent field observations and regular satellite data acquisitions. In-situ surface reflectance and surface water measurements were collected in July 2019, at the terrestrial glacier-fed Bayelva river plume, and the Blomstrandbreen subglacial discharge plume. These in-situ measurements, combined with Moderate Imaging Spectroadiometer (MODIS) satellite data were used to calibrate a relationship between surface reflectance and suspended sediment concentration at the two sediment-laden meltwater plumes. Using these empirical relationships, we determined seasonal sediment flux by establishing the thickness of the plume layer through conductivity, temperature and depth (CTD) profiles. Additionally, we determined plume metrics (area, extent or planform morphology and distribution), by integrating CTD profiles and measurements of meltwater runoff and sediment collected at the Bayelva hydrometric gauge, along with modelled datasets. We find that the sediment-laden meltwater plumes are extremely sensitive to variable inputs of meltwater runoff, with distinct changes in plume morphometry and sediment concentrations occurring at various points throughout the melt season, evidenced clearly during the transition from snow to firn and glacier ice melt, and after episodic rainfall events. Future work will apply these empirical relationships to other satellite datasets (including Planet, Sentinel and Landsat) from the last 20 years to determine long-term changes in the  sediment-laden meltwater plume systems, including their wider effects on fjord hydrography, and glaciomarine sedimentary processes in response to climatically-induced changes in the hydrology of the glacier systems.
Continuous CH4 and  d13CH4 measurements in London demonstrate under-reported natural gas leakage
Authors: Saboya Eric , Zazzeri Giulia , Graven Heather , Manning Alistair J. , Michel Sylvia Englund
Published: March 2021

Assessment of bottom-up greenhouse gas emissions estimates through independent methods is needed to demonstrate whether reported values are accurate or if bottom-up methodologies need to be refined. Previous studies of measurements of atmospheric methane (CH4) in London revealed that inventories substantially underestimated the amount of natural gas CH4 1,2. We report atmospheric CH4 concentrations and δ13CH4 measurements from Imperial College London since early 2018 using a Picarro G2201-i analyser. Measurements from Sept. 2019-Oct. 2020 were compared to the values simulated using the dispersion model NAME coupled with the UK national atmospheric emissions inventory, NAEI, and the global inventory, EDGAR, for emissions outside the UK. Simulations of CH4 concentration and δ13CH4 values were generated using nested NAME back-trajectories with horizontal spatial resolutions of 2 km, 10 km and 30 km. Observed concentrations were underestimated in the simulations by 22 % for all data, and by 16 % when using only 13:00-17:00 data. There was no correlation between the measured and simulated δ13CH4 values. On average, simulated natural gas mole fractions accounted for 28 % of the CH4 added by regional emissions, and simulated water sector mole fractions accounted for 32 % of the CH4added by regional emissions. To estimate the isotopic source signatures for individual pollution events, an algorithm was created for automatically analysing measurement data by using the Keeling plot approach. Nearly 70 % of isotopic source values were higher than -50 ‰, suggesting the primary CH4 sources in London are natural gas leaks. The model-data comparison of δ13CH4 and Keeling plot results both indicate that emissions due to natural gas leaks in London are being underestimated in the UK NAEI and EDGAR.

 

1 Helfter, C. et al. (2016), Atmospheric Chemistry and Physics, 16(16), pp. 10543-10557

2 Zazzeri, G. et al. (2017), Scientific Reports, 7(1), pp. 1-13
State-dependency of temperature variability in transient simulations of the last Deglaciation from models of varying complexity
Authors: Ziegler Elisa , Andres Heather , Ellerhoff Beatrice , Kapsch Marie-Luise , Kutterolf Steffen , Mikolajewicz Uwe , Schindlbeck-Belo Julie Christin , Toohey Matthew , Wirths Christian , Weitzel Nils , Rehfeld Kira
Published: March 2021

Much about the response of temperature variability to a change in the climate's mean state, as the one projected for the current century, remains uncertain. These uncertainties include spatiotemporal patterns, the magnitude, and, in some cases, even the sign. For the last Deglaciation, - the last change in global mean temperature of a similar degree to that expected in projections - variability analyses of climate model simulations and temperature proxies produce conflicting results. 

Here, we build a hierarchy of transient simulations covering the period since the Last Glacial Maximum about 26k years ago. We include a range of climate models, from conceptual to complex Earth System Models. The simulations cover a variety of temporal and spatial resolutions, parameterizations, and modeled processes. For annual to multi-millennial temporal as well as regional to global spatial scales, we compare variability patterns and power spectra and analyze how they relate to model properties and the background state of Earth's climate. This allows for the examination of regional temperature differences between low, middle, and high latitudes and at locations of available paleoclimate proxy records. For sets of sensitivity experiments, we investigate effects of changes to ice sheets, sea ice, and in volcanic, solar, greenhouse, and orbital forcing on modeled climate variability.  

Thus, our analysis provides insights into when and how models disagree with each other and with proxies, and what differences arise due to specific models, simulation setups, and boundary conditions. Based on these results, we can then gauge the degree of complexity which is required to reproduce past temperature variability and predict its changes in the future. 
A modeler's guide to studying the resilience of social-technical-environmental systems
Authors: Tamberg Lea , Heitzig Jobst , Donges Jonathan
Published: March 2021

The concept of `resilience' is increasingly being applied in the study of social-technical-environmental systems in Earth system and sustainability science. However, the diversity of resilience concepts and a certain (sometimes intended) openness of proposed definitions can lead to misunderstandings and impede their application to systems modelling. We propose an approach that aims to ease communication as well as to support systematic development of research questions and models in the context of resilience. It can be applied independently of the modelling framework or underlying theory of choice. At the heart of this guideline is a checklist consisting of four questions to be answered: (i) Resilience of what? (ii) Resilience regarding what? (iii) Resilience against what? (iv) Resilience how? We refer to the answers to these resilience questions as the "system", the "sustainant", the "adverse influence", and the "response options". The term `sustainant' is a neologism describing the feature of the system (state, structure, function, pathway etc.) that should be maintained (or restored quickly enough) in order to call the system resilient.
The use of this proposed guideline is demonstrated for two application examples: fisheries, and the Amazon rainforest. The examples illustrate the diversity of possible answers to the checklist's questions as well as their benefits in structuring the modelling process. The guideline supports the modeller in communicating precisely what is actually meant by `resilience' in a specific context. This combination of freedom and precision could help to advance the resilience discourse by building a bridge between those demanding unambiguous definitions and those stressing the benefits of generality and flexibility of the resilience concept. 
Analysis of correlation between structural response and ground motion intensity measures.
Authors: Aquib Tariq Anwar , Sivasubramonian Jayalakshmi , Mai Paul Martin
Published: March 2021

Loss estimation for buildings that experienced earthquake shaking is an important step in Performance Based Earthquake Engineering (PBEE), comprising four major components – seismic hazard, building response, probability of damage, and the costs incurred in losses and repair works. The implementation of PBEE strongly depends on the ability to predict Engineering Demand Parameters (EDPs) that are usually defined in terms of maximum story drifts, plastic hinge rotations, and floor accelerations.

In this study, we compute building responses for large sets of recorded ground motions considering frames with different natural periods (0.1-1.5s). The ground motion data used in our analysis comprise near field records from moderate-to-large earthquakes; these may generate shaking levels high enough to be of concern for the design and safety of buildings. We select the frames by varying the number of storys and bays to obtain a wide range of natural building periods. We compute ground motion intensity measures (IM) from the recorded dataset and extract engineering demand parameters (EDP) from building response analyses. Our results indicate that the inter-story drift correlates strongly with spectral measures of ground motion intensity (correlation coefficient above 0.85). We also investigate the effect of natural period on the estimated correlations. We find that the correlations with spectral intensity measures do not strongly depend on Vs30 and epicentral distance. Our results are useful in the context of applied performance-based design of structures, especially if uncertainties in seismological parameters due to limited knowledge of source, site or path effects play an important role in earthquake ground motions.
Implications of current net zero targets for long-term emissions pathways and warming levels
Authors: Geiges Andreas , Fyson Claire , Hans Frederic , Jeffery Louise , Mooldijk Silke , Gidden Matthew , Ramapope Deborah , Hare Bill , Stockwell Claire , Gonzales Sofia , Nascimento Leonardo
Published: March 2021

In 2020, climate target announcements were dominated by net-zero commitments, including by a number of major emitters. Despite the urgency of more ambitious NDCs in the short term, long-term net-zero targets are important for the transition to global zero emissions. Tracking progress towards and assessing the adequacy of these targets requires an assessment of what they mean for transition pathways and associated emissions trajectories at both national and global levels. 

We present an assessment of net-zero targets of the major emitting countries and their implications for long-term emissions trajectories and warming levels. Based on the work of the Climate Action Tracker, country-specific analyses are aggregated to a global emissions pathway to derive a best estimate for a resulting global warming in 2100. Undertaking this analysis requires assumptions to be made regarding projected emissions and removals from the land-use sector, non-CO2 emissions, and the trajectory of total net emissions after net-zero, which we explain and explore. For example, by computing the cumulative emissions of our aggregated net-zero target emissions pathway, we can compare this pathway with modelled global emissions pathways from the IPCC's SR1.5 Special Report, to draw broad conclusions over what current net-zero commitments might mean for carbon dioxide removal and non-CO2 emissions, and the uncertainties therein.