bluuebunny/crossref_metadata_2025 huggingface dataset:
Possible Explanation for Interannual Variations in Trans-Pacific Transport of East Asian Dust
Authors: Wang Mingxing , Peng Yiran , Zhao Tianliang
Published: March 2021

East Asian dust aerosols prevail during spring season and transport cross Pacific Ocean. Satellite retrieval data show that dust AOD in downwind plume region over Pacific is significantly high and extends northward and eastward in 2003 comparing to 2002. In this study, we investigate the possible mechanism behind the differences in dust plume over Pacific by analyzing aerosol observations from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) and MISR (Multi-angle Imaging SpectroRadiometer) satellite platforms and ERA-Interim reanalysis data of meteorological fields. Firstly, we derive dust aerosol optical depth (AOD) in spring of 2002 and 2003 from MISR data by referring to the climatological mass ratio of dust to total aerosol from CALIPSO aerosol retrievals during 2007-2016. Second, we illustrate the axis of dust plume over Pacific by mimicking the center-of-gravity method for dust distribution, which clearly demonstrates that the axis shifts more northward and eastward and dust AOD is noticeably higher in April to May of 2003 than 2002. Thirdly, we look into the relationships between dust AOD and meteorological fields. Our results show that stronger surface wind speed in Northwest China (the source regions of East Asian dust) leads to higher dust emission in spring of 2003 than 2002. The updraft velocity in dust source regions is also stronger in 2003, which favors the uplifting of emitted dust. The precipitation over Pacific shows similar pattern between 2002 and 2003, indicating that wet deposition of dust has similar impacts on the dust aerosol transported cross Pacific Ocean. Lastly, we found that stronger southerly wind prevails over western North Pacific in May of 2003 than 2002, where negative vorticity is observed and might be related to certain features of Rossby wave. It is likely responsible for the northward axis of dust plume over Pacific. Therefore we conclude that the stronger and more easterly extended dust plume over Pacific Ocean in 2003 is resulted from excessive dust emission and stronger uplift in dust source regions of East Asia. The stronger southerly winds cause to the further northward axis of dust plume over western North Pacific. In the current stage, we extend the above investigation for the past two decades, to explain the interannual variations of East Asian dust related to emission in source regions, Trans-Pacific transport, meteorological fields and climatic indices.
The mitigation effect of urban green infrastructure (UGI) on urban waterlogging
Authors: Zhang Qifei , Wu Zhifeng , Tarolli Paolo
Published: March 2021

With the acceleration of urbanization, the impervious surfaces of urban areas have increased dramatically, changing the natural water cycle of the city. It is of great significance for the improvement of urban living environment and the risk management of urban waterlogging to fully understand and play the positive role of UGI in alleviating urban waterlogging. This study attempts to identify the critical factors that alleviate urban waterlogging and examine the effectiveness and stability of UGI in mitigating urban waterlogging in multiple locations. We looked at two highly-urbanized Chinese cities (Guangzhou and Shenzhen) in a comparative study. The waterlogging records from 2009 to 2015 were obtained from the local water authority and the UGI was extracted from the 0.5-m resolution remote sensing images. The complex relationship between urban waterlogging and green infrastructure was quantified and compared through partial redundancy analysis and piecewise linear regression after controlling the conditions of topography, precipitation, and drainage network. The results indicated that the spatial distribution of urban waterlogging events presents a strong agglomeration effect, while the clustering pattern varies in different cities. Furthermore, after controlling the impact of elevation, rainfall, and drainage network, the area percentage and biophysical parameters of green infrastructure are the two most important factors to alleviate urban waterlogging. The influence of these two factors on urban waterlogging is consistent in different cities. This result indicates that more attention should be paid to the area size of green infrastructure and its vegetation biophysical parameters to mitigate urban waterlogging magnitude to the greatest extent. However, the area of green infrastructure must be controlled within a certain range in order to play a corresponding role in alleviating urban waterlogging. We also found that the spatial configuration of UGI also matters. Holding UGI’s composition constant, the degree of urban waterlogging can be reduced by optimizing the spatial configuration of UGI. This finding provides additional insights that the urban waterlogging can be alleviated by balancing the relative composition of UGI as well as by optimizing their spatial configuration, which is particularly important for a highly urbanized area where land resources for UGI are scarce. This study expands our understanding of the complex mechanism of UGI on urban waterlogging mitigation and provides beneficial enlightenment for the design of UGI.
Regional patterns of ocean mass sea-level change over the satellite altimetry era (1993-2017)
Authors: Camargo Carolina M. L. , Riva Riccardo E. M. , Slangen Aimée B. A.
Published: March 2021

Ocean mass variation is one of the main drivers of present-day sea-level change (SLC). Also known as barystatic SLC, those fluctuations are due to the melting of continental ice from glaciers and ice sheets, and variations in landwater storage. While a large number of studies have quantified the contribution of barystatic SLC to global mean SLC, fewer works have looked into how much ocean mass has contributed to regional SLC. Besides, most of the regional studies have focused only on the effect of one of the components (e.g., melt from Antarctica), or on the period and results of the GRACE satellite mission (since 2002). This work aims at providing a comprehensive analysis of global and regional barystatic SLC since 1993. For that, we collect a suite of estimates of the individual freshwater sources, namely the Antarctic and Greenland ice sheets, glaciers and terrestrial water storage. We then use them as input on the sea-level equation to obtain regional patters (fingerprints) of barystatic SLC, and validate our results by comparing the individual estimates with the values obtained from GRACE products. We finalize our analysis by looking into trend uncertainty patterns related to each contribution.
Retrieving cloud condensation nuclei concentrations from spaceborne lidar measurements
Authors: Choudhury Goutam , Tesche Matthias
Published: March 2021

Aerosols interact with atmospheric radiation either directly through scattering and absorption or indirectly by acting as cloud condensation nuclei (CCN) and ice nucleating particles (INP), thereby altering cloud properties. The latter aerosol-cloud interaction (ACI) effects are still poorly understood and believed to be one of the key uncertainties in climate models. In the present scenario, the observations of CCN are still sparse as in-situ measurements are expensive and often restricted to specific locations and limited time periods. An alternative is to turn to satellite observations for ACI studies. The Cloud Aerosol Lidar with Orthogonal Polarisation (CALIOP) is a spaceborne lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. It provides high-resolution vertical profiles of aerosol related parameters such as the aerosol extinction coefficient, backscatter coefficient, aerosol subtypes, and depolarization ratio. In order to estimate the CCN concentrations, we use these parameters along with the normalised lognormal bimodal volume size distributions and complex refractive indices of different aerosol subtypes given in the CALISPO aerosol model.

                The normalised size distribution, the refractive index and the relative humidity are first used to compute the extinction coefficient using the MOPSMAP package. For this, all the aerosol types are treated as spherical particles except the dust which is treated as spheroid. The size distribution is then modified until the estimated extinction agrees with that measured by the CALIPSO. The modified size distribution is integrated to compute the number concentration of aerosols that form the favourable CCN reservoir. To estimate the uncertainty in the retrieval algorithm, we performed the sensitivity analysis by varying the initial normalised volume size distribution by up to +/- 50 % for each mode (fine and coarse). The results are presented as case studies with some preliminary validation against in-situ measurements. The purpose of this work is to obtain a global 3D CCN climatology for use in ACI studies and improving the performance of the global climate models.
Estimating variations in Earth rotation using GPS, GLONASS, and Galileo
Authors: Zajdel Radosław , Sośnica Krzysztof , Bury Grzegorz , Kazmierski Kamil
Published: March 2021

Variations in the Earth's rotation can be examined in the low-frequency and high-frequency temporal scales. The low-frequency variations are dominated by the annual and Chandler wobbles, while the high-frequency variations are primarily caused by tidal effects and mass redistributions within the system Earth. Depending on the purpose, the Earth Rotation Parameters (ERPs) can be estimated in different time resolutions using space-geodetic techniques, especially using GNSS. However, the residual signals between different space geodetic techniques or satellite constellations indicate system-specific differences, which have to be correctly identified.

This research provides the daily, and sub-daily series of Earth Rotation Parameters (ERPs) estimated using GPS, GLONASS, and Galileo observations. We test different sampling intervals of estimated ERPs from 1h to 24h. The GNSS-based sub-daily estimates have been compared with the external models of variations in ERPs induced by the ocean tides from the IERS 2010 Conventions, a new model by Desai-Sibois, and the VLBI-based model by Gipson.

Any system-specific ERPs are affected by the orbital and draconitic signals. The orbital signals are visible in all system-specific ERPs at the periods that arise from the resonance between the Earth's rotation and the satellite revolution period, e.g., 8.87h, 34.22h, 3.4 days, 10 days for Galileo; 7.66h, 21.29h, 3.9 days, 7.9 days for GLONASS; 7.98h (S3 tidal term), 11.97h (S2 tidal term), 23.93h (S1 tidal term) for GPS. In the Galileo and GLONASS solutions, the artificial non-tidal signals' amplitudes can reach up to 30 µas. The GPS-derived sub-daily ERPs suffer from the overlapping periods of the diurnal and semidiurnal tidal terms and the harmonics of the GPS revolution period. After recovery of 38 sub-daily tidal terms, the Galileo-based model is more consistent with the external models than the GPS-based model, especially in the prograde diurnal band. The results confirmed that the Desai–Sibois model is more consistent with GNSS observations than the currently recommended model by the IERS 2010 Conventions. Moreover, GPS-based length-of-day (LoD) is systematically biased with respect to the IERS-C04-14 values with a mean offset of −22.4 µs/day, because of the deep resonance 2:1 between the satellite revolution period and the Earth rotation. The Galileo-based and GLONASS-based solutions are almost entirely free of this issue. Against the individual system-specific solutions, the multi-GNSS solution is not affected by most of the system-specific artifacts. Thus, multi-GNSS solutions are clearly beneficial for the estimation of both daily and sub-daily ERPs.
IPSCAT: A Catalogue of Solar Transients Identified through Interplanetary Scintillation Analysis
Authors: Barnes David , Bisi Mario , Davies Jackie , Harrison Richard
Published: March 2021

We present a catalogue, IPSCAT, of the results of Interplanetary Scintillation (IPS) analysis applied to observations that are compiled using data from three European radio networks, EISCAT, MERLIN and LOFAR, during the early science phase of the STEREO mission, from 2007 to 2012. These analyses provide a means to study the solar wind and interplanetary transients, which we complement with observations from the Heliospheric Imagers on-board STEREO. Within the IPS data set we identify transient phenomena, specifically Coronal Mass Ejections (CMEs) and Stream Interaction Regions (SIRs), via both visual inspection and an automatic feature-finding algorithm. We study the effectiveness of the automated detection algorithm and find it to be successful at classifying CMEs, whilst the identification of SIRs is less easily established. A discussion of the statistical properties of IPSCAT is presented, together with a comparison between the IPS and HI results. Finally, we present a case study of successive CMEs within the IPSCAT data set, which were also observed by the HIs on both STEREO spacecraft and analysed using the Stereoscopic Self-Similar Expansion (SSSE) method. This work was carried out as part of the EU FP7 HELCATS (Heliospheric Cataloguing, Analysis and Techniques Service) project (http://www.helcats-fp7.eu/).
Microplastic in fluvial environments - an example of the Elbe river near Dessau-Roßlau, Germany
Authors: Kruse Jonas , Laermanns Hannes , Stock Friederike , Foeldi Corinna , Schaefer Dirk , Scherer Christian , Bogner Christina
Published: March 2021

Accumulation of microplastics (MPs) in aquatic environments is an issue of emerging concern. After research initially focused on marine systems, more and more studies have been published investigating the abundance of MPs in freshwater environments in recent years.

The objective of our research is to examine, whether the Mulde river represents an input pathway for MP particles to the Elbe discharge system. Our hypothesis is that the chemical industries located in the catchment area of the Mulde act as a discharge source of primary MPs which are subsequently transported downstream towards the Elbe. Accordingly, there should be more (primary) MPs just downstream of the river mouth, compared to upstream. Therefore, 2 sediment samples and 18 water samples from the Elbe river upstream and downstream the Mulde confluence were taken and analysed on their MP contents.

To extract MPs, sample preparation requires various steps including drying, size-fractionation, reduction of organic matter and density separation. The gained fractions are then filtered through glass microfibres paper using a vacuum pump. The dried filters are photographed and examined for MPs under a digital microscope. Representative particles are picked and measured. Finally, we determine their polymer type by pyrolysis or µFTIR.

A key result is that both, sediment and water samples, show a substantial increase in primary MPs (especially spheres) just downstream the mouth of the Mulde. Regarding the sampling technique of water samples, we observe differences in the amount and shape of MP particles between filter cascades and filter nets.
Calculating and communicating ensemble-based volcanic ash concentration risk for aviation
Authors: Harvey Natalie , Dacre Helen , Capponi Antonio
Published: March 2021

During volcanic eruptions Volcanic Ash Advisory Centers (VAAC) produce forecasts of ash location and concentration. However, these forecasts are deterministic and do not take into account the inherent uncertainty in the forecasts due to incomplete knowledge of the volcano’s eruption characteristics and imperfect representation of atmospheric processes in numerical models. This means flight operators have incomplete information regarding the risk of flying following an eruption, which could result in overly conservative decisions being made. There is a need for a new generation of volcanic ash hazard charts allowing end users to make fast and robust decisions using risk estimates based on  state-of-the-art probabilistic forecast methods .

 

In this presentation, a method for visualizing ash concentration matrix using a risk-matrix approach will be applied to two volcanic eruptions, Grimsvotn (2011) and Raikoke (2019). These risk-matrix graphics reduce the ensemble information into an easy-to-use decision-making tool. In this work the risk level is determined by combining the concentration of volcanic ash and the likelihood of that concentration occurring.

 

When applying this technique to the Grimsvotn eruption, the airspace containing volcanic ash concentrations deemed to be associated with the highest risk (high likelihood of exceeding a high concentration threshold) to aviation are reduced by over 85% compared to using an ensemble that gives an ash distribution similar to the VAAC issued deterministic forecast. The reduction during the Raikoke eruption can be as much as 40% at a forecast lead time of 48 hours. This has the potential to reduce the disruption to airline operations.  This tool could be extended to include other aviation hazards, such as desert dust, aircraft icing and clear air turbulence.

 
Skilful predictions of multi-year US hurricane insured losses by decadal prediction systems
Authors: Lockwood Julia , Dunstone Nick , Hermanson Leon , Scaife Adam , Smith Doug , Thornton Hazel
Published: March 2021

North Atlantic tropical cyclones are the costliest natural hazard affecting the US, and are capable of causing hundreds of billions of dollars of insured losses in a single season.  Tropical cyclone activity has been observed to show considerable decadal variability, linked with variations in sea surface temperatures in regions of the North Atlantic such as the main hurricane development region (MDR) and sub-polar gyre (SPG).

In this presentation we show that a multi-model ensemble of decadal prediction systems can skilfully predict north Atlantic hurricane activity and consequent US insured losses on multi-annual timescales, with a correlation coefficient of greater than 0.7 for 5 year mean hurricane activity.  Rather than tracking tropical cyclones directly in the dynamical models, we make predictions using an index based on predicted temperatures over the north Atlantic.  The skill of the dynamical models outperforms persistence, and could aid decision making for the (re)insurance industry over the US.  As part of the Copernicus Climate Change Service, a publicly available probabilistic forecast of 5 year mean north Atlantic hurricane activity and US insured losses has been produced and will be presented here.
Micro-bathymetric mapping of the North Alfeo strike-slip fault (offshore Catania Sicily): preliminary results from the FocusX1 expedition
Authors: Gaillot Arnaud , Gutscher Marc-André , Murphy Shane , Klingelhoefer Frauke
Published: March 2021

In October 2020, during the marine expedition FocusX1 onboard the research vessel PourquoiPas? microbathymetric mapping was performed using the ROV Victor6000. The main goal was to map the seafloor expression of the North Alfeo fault and select the best path for deployment of a 6-km long fiber optic strain cable designed to monitor movement along the fault and the deployment sites for 8 geodetic stations.

Bathymetric data were collected through a Reson Seabat 7125 multibeam echosounder (400 kHz). ROV navigation data were processed using DelphINS, resulting in an optimal merging of navigation sensors (GPS, USBL, DVL, pressure). The MBES data processing (GLOBE software) mainly consisted in estimating and correcting static angular offsets, applying actual in-situ sound speed profile, and finally performing an automatical and manual soundings filtering.

The resulting bathymetric grid spans a region of roughly 3 km x 1.5 km, with a 1m cell size, and allows  us to identify a variety of morphological features:

1 - a set of narrow, linear, E-W oriented gulleys, all parallel (not merging/branching) on a regional E dipping 5-15° slope

2 - a striking, continuous curvi-linear feature, which is interpreted as the primary surface expression of the fault.The fault morphology changes from a smooth less than 10 m depression in the NW to a up to 10-20m high scarp with slopes of 20-30°, and locally sub-vertical cliff faces.

3 - a local bathymetric plateau (mesa like feature) with a gently E-dipping summit region, showing signs of eastward sliding / rafting tectonics, indicated by N-S oriented gashes/depressions.

The 3-km long segment of the fault covered by our survey includes the mesa-like bathymetric high (at the NW extremity) interpreted as a transpressional pop-up feature and an elongated, fault bounded trough (at the SE extremity) interpreted as a transtensional pull-apart basin. Video-camera images recorded by ROV Victor6000 from the seafloor provide visual documentation of the fault scarp and seafloor morphology. Future surveys with a sub-bottom profiler and/or HR- seismics can help confirm these interpretations. The ongoing monitoring with the fiber-optic strain cable is being calibrated by a 3-4 year deployment of seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) which started in Oct. 2020, and will allow us to quantify relative displacement across the fault.
Melt migration by reactive porosity waves
Authors: Bessat Annelore , Pilet Sébastien , Schmalholz Stefan M. , Podladchikov Yuri
Published: March 2021

The formation of alkaline magmas observed worldwide requires that low degree-melts, potentially formed in the asthenosphere, were able to cross the overlying lithosphere. Fracturing in the upper, brittle part of the lithosphere may help to extract this melt to the surface. However, the mechanism of extraction in the lower, ductile part of the lithosphere is still contentious. Metasomatic enrichment of the lithospheric mantle demonstrates that such low-degree melts interact with the lithosphere, but the physical aspect of this process remains unclear.

Here, we aim to better understand, first, the percolation of magma in a porous viscous medium at pressure (P) and temperature (T) conditions relevant for the base of the lithosphere, and second, the impact of chemical differentiation on melt migration. We investigate theoretically the process of melt migration employing the fundamental laws of physics and thermodynamics. We simulate melt percolation numerically with a one-dimensional (1-D) Thermo-Hydro-Mechanical-Chemical (THMC) model of porosity waves coupled with thermodynamic results obtained from numerical Gibbs energy minimisation calculations. We perform THMC modelling and Gibbs energy minimisations with self-developed numerical algorithms using MATLAB and linear programming routines. We employ a simple ternary system of Forsterite/Fayalite/Enstatite for the solid and melt. Model variables, such as solid and melt densities or mass concentrations of MgO and SiO in solid and melt, are a function of pressure (P), temperature (T) and total silica concentration of the system (X). These variables are pre-computed with Gibbs energy minimisation and implemented in the THMC porosity wave transport code via parameterized equations, determining the T-P-X dependence of the model variables.

First results show that the total silica concentration and the temperature gradient are important parameters to consider in melt migration by reactive porosity waves. We discuss results of a systematic series of 1-D simulations and we present preliminary results form a 2-D reactive porosity wave model.
Magnetic Reconnection in the Corona as a Source of Switchbacks in the Solar Wind
Authors: Drake James , Agapitov Oleksiy , Swisdak Marc , Badman Sam , Bale Stuart , Horbury Timothy , Kasper Justin , MacDowal Robert , Mozer Forrest , Phan Tai , Pulupa Marc , Szabo Adam , Velli Marco
Published: March 2021

The observations from the Parker Solar Probe during the first
perihelion revealed large numbers of local reversals in the radial
component of the magnetic field with associated velocity spikes. Since
the spacecraft was magnetically connected to a coronal hole during the
closest approach to the sun, one possible source of these spikes is
magnetic reconnection between the open field lines in the coronal hole
and an adjacent region of closed flux. Reconnection in a low beta
environment characteristic of the corona is expected to be bursty
rather than steady and is therefore capable of producing large numbers
of magnetic flux ropes with local reversals of the radial magnetic
field that can propagate outward large radial distances from the
sun. Flux ropes with a strong guide field produce signatures
consistent with the PSP observations. We have carried out simulations
of "interchange" reconnection in the corona and have explored the
local structure of flux ropes embedded within the expanding solar
wind. We have first established that traditional interchange
reconnection cannot produce the switchbacks since bent field lines
generated in the corona quickly straighten. The simulations have been
extended to the regime dominated by the production of multiple flux
ropes and we have established that flux ropes are injected into the
local solar wind. Local simulations of reconnection are also being
carried out to explore the structure of flux ropes embedded in the
solar wind for comparison with observations. Evidence is presented
that flux rope merging may be ongoing and might lead to the high
aspect ratio of the switchback structures measured in the solar wind.
How can computer models help us understand mineral forming processes?
Authors: Valentini Luca
Published: March 2021

The birth (and death) of minerals is controlled by a series of basic physical and chemical processes such as nucleation, growth, dissolution, diffusion and adsorption, which normally occur over time and length scales that are not easily accessible to common experimental investigation methods. However, reconciling these microscopic processes with macroscopic observations may represent a key to the interpretation of the geological archive as well as to optimizing the engineering of geomaterials based on the exploitation of mineral resources.
Motivated by this need, an overview of commonly used numerical techniques for the simulation of mineral forming processes, and their relevant input parameter, is provided, with the aim of assessing the potential and limitations of specific computational tools in different scenarios.
The scope and suitability of methods such as Molecular Dynamics, Kinetic Modelling, Cellular Automata, Monte Carlo and Population Balance are illustrated, with a brief introduction of the theoretical principles, followed by examples of applications to specific case studies.  
Challenges and future perspective, with emphasis on multiscale modelling, are discussed.
Repeating earthquakes follow afterslip gradient in the aftermath of the 16th April 2016 M7.8 Pedernales earthquake in Ecuador
Authors: Chalumeau Caroline ,   Pedernales research team
Published: March 2021

Repeating earthquakes are earthquakes that repeatedly break a single, time-invariant fault patch. They are generally associated with aseismic slip, which is thought to load asperities, leading to repeated rupture. Repeating earthquakes are therefore useful tools to study aseismic slip and fault mechanics, with possible applications to earthquake triggering, loading rates and earthquake forecasting.

In this study, we analyze one year of aftershocks following the 16th April 2016 Mw 7.8 Pedernales earthquake in Ecuador to find repeating families, using data recorded by permanent and temporary seismological stations. In our area, seismicity during both the inter-seismic and post-seismic periods has been previously linked to aseismic slip. We calculate waveform cross-correlation coefficients (CC) on all available catalogue events, which we use to sort events into preliminary families, using a minimum CC of 0.95. These events were then stacked and used to perform template-matching on the continuous data. In total, 376 earthquakes were classified into 62 families of 4 to 15 earthquakes, including 8 from the one-year period before the mainshock. We later relocated these earthquakes using a double-difference method, which confirmed that most of them did have overlapping sources.

Repeating earthquakes seem to concentrate largely around the areas of largest afterslip release, where afterslip gradient is the highest. We also find an increase in the recurrence time of repeating events with time after the mainshock, over the first year of the postseismic period, which highlights a possible timeframe for the afterslip’s deceleration. Our results suggest that while most repeating aftershocks are linked to afterslip release, the afterslip gradient may play a bigger role in determining their location than previously thought.
Sentinel-1 InSAR data by LiCSAR system
Authors: Lazecky Milan , Maghsoudi Mehrani Yasser , Watson Scott , Morishita Yu , Elliott John , Hooper Andrew , Wright Tim
Published: March 2021

Looking Into the Continents from Space with Synthetic Aperture Radar (LiCSAR) is a system built for large-scale interferometric processing of Sentinel-1 data. LiCSAR automatically produces geocoded wrapped and unwrapped interferograms combining every acquisition epoch with four preceding epochs, and complementary data (coherence, amplitude, line-of-sight unit vectors, digital elevation model, metadata, and atmospheric phase screen estimates by the Generic Atmospheric Correction Online Service, GACOS).

The LiCSAR products are generated in frame units where a standard frame covers ~220x250 km, at 0.001° resolution (WGS-84 coordinate system). Frames are continuously updated for tectonic and volcanic priority areas. In 2020, the LiCSAR system covered about 1,500 global frames in which we have processed over 89,000 Sentinel-1 acquisitions and generated over 300,000 interferograms. Among these, 470 frames cover 1,024 global volcanoes. We aim to cover the global seismic mask defined by the Committee on Earth Observation Satellites (CEOS), but focus initially on the Alpine-Himalayan belt and East African Rift.

We serve the products as open and freely accessible through our web portal: https://comet.nerc.ac.uk/comet-lics-portal and aim to provide them to shared infrastructures as the European Plate Observing System (EPOS). We also generate rapid response coseismic interferograms for earthquakes with moment magnitude (Mw)> 5.5  a few hours after the postseismic data become available, and we update frames covering active volcanoes twice per day.

Our products can be directly converted to displacement time series and velocities using  the LiCSBAS time series analysis software. We present solutions implemented in LiCSAR, and show several case studies that use LiCSAR and LiCSBAS products to measure tectonic and volcanic deformation.
Global to local impacts on atmospheric CO2 caused by COVID-19 lockdown
Authors: Zeng Ning
Published: March 2021

The world-wide lockdown in response to the COVID-19 pandemic in year 2020 led to economic slowdown and large reduction of fossil fuel CO2 emissions 1,2, but it is unclear how much it would reduce atmospheric CO2 concentration, the main driver of climate change, and whether it can be observed. We estimated that a 7.9% reduction in emissions for 4 months would result in a 0.25 ppm decrease in the Northern Hemisphere CO2, an increment that is within the capability of current CO2 analyzers, but is a few times smaller than natural CO2 variabilities caused by weather and the biosphere such as El Nino. We used a state-of-the-art atmospheric transport model to simulate CO2, driven by a new daily fossil fuel emissions dataset and hourly biospheric fluxes from a carbon cycle model forced with observed climate variability. Our results show a 0.13 ppm decrease in atmospheric column CO2 anomaly averaged over 50S-50N for the period February-April 2020 relative to a 10-year climatology. A similar decrease was observed by the carbon satellite GOSAT3. Using model sensitivity experiments, we further found that COVID, the biosphere and weather contributed 54%, 23%, and 23% respectively. In May 2020, the CO2 anomaly continued to decrease and was 0.36 ppm below climatology, mostly due to the COVID reduction and a biosphere that turned from a relative carbon source to carbon sink, while weather impact fluctuated. This seemingly small change stands out as the largest sub-annual anomaly in the last 10 years. Measurements from global ground stations were analyzed. At city scale, on-road CO2 enhancement measured in Beijing shows reduction of 20-30 ppm, consistent with drastically reduced traffic during the lockdown, while station data suggest that the expected COVID signal of 5-10 ppm was swamped by weather-driven variability on multi-day time scales. The ability of our current carbon monitoring systems in detecting the small and short-lasting COVID signal on the background of fossil fuel CO2 accumulated over the last two centuries is encouraging. The COVID-19 pandemic is an unintended experiment whose impact suggests that to keep atmospheric CO2 at a climate-safe level will require sustained effort of similar magnitude and improved accuracy and expanded spatiotemporal coverage of our monitoring systems.
Monitoring data analysis and groundwater flow modelling at a former uranium mine in France
Authors: L'hermite Pierre , Plagnes Valérie , Jost Anne , Reile Benoît , Kern Guillaume , Descostes Michael , Chautard Camille
Published: March 2021

Mining companies are responsible for after-mining and environmental monitoring to ensure that mining waters released in the environment meet environmental quality standards. Water treatment plants can be used to mitigate surface waters when impacts related to past mining activities is evidenced. Indeed, meteoric recharge through waste rocks and tailings stored on sites often creates Acid Mining Drainage (AMD) or metallic signature that can be transferred to rivers through groundwater flow.

We studied a former uranium mine in Bertholène, Aveyron (France), where tailings, covered by waste rock, are stored in a valley behind a waste rock dyke. Mining waters, coming from both tailing drainage and mine facilities (galleries and open pit mine), are collected to a water treatment plant before release in the environment, meeting the environmental standards. Groundwater flow modelling is required to understand and quantify the different sources of AMD and their fate. The objective of this study is to give new insights on flows to guide the potential additional remediation of the site by testing different management solutions. For this purpose, we have developed a 3D hydrogeological model (MODFLOW) for the entire watershed.

This work is divided into two parts. We first analysed all available climatic and hydrogeological data (precipitation, water level, surface water flow, electric conductivity) using auto-correlations, cross-correlations and water balance calculations. These data come from long-term monitoring (14 years) on 13 piezometers and 4 discharge points. Recent two-year daily monitoring of groundwater levels completes the data set and provides a better understanding of the dynamic of the hydrosystem after precipitation. There is a 5 to 10-day time lag between rainfall and increases in water level and flow rate. The analysis also concludes that flows in the tailings occur under unsaturated conditions and that the water level in the gneiss aquifer never reaches the tailings.

Steady-state modelling developed at the watershed scale confirms that water level does not reach the tailings and allows simulating the impact of different management scenarios. Particle tracking has also been used to identify hydrogeological sub-watersheds of interest, such as those of the former open pit mine or the tailings to compute their water balance.
Integrated carbon-nitrogen-phosphorus cycling for sustainable agriculture – a knowledge gap and investigation of the role of phosphatase enzymes
Authors: Janes-Bassett Victoria , Haygarth Phil , Blackwell Martin , Mezeli Malika , Stewart Gavin , Blair Gordon , Davies Jess
Published: March 2021

Phosphorus is closely linked to other nutrient cycles, notably carbon and nitrogen, therefore, to understand potential risks to food production models are required that simulate integrated nutrient cycling over long timescales. The soil-plant system model N14CP meets these requirements and simulates both semi-natural and agricultural environments. N14CP has been validated both spatially and temporally across a range of long-term agricultural experimental sites comparing soil C, N and P, and crop yields, and in most instances performs well. However, under experimental conditions where N is applied in the absence of P, the model indicates exhaustion of P reserves and a decline in yields that is not observed at these sites, highlighting a gap in the model process representation. Potential sources of this ‘missing P’ such as enhanced atmospheric deposition, weathering and flexible plant stoichiometries were explored yet cannot account for this deficit. We hypothesise that access of organic P through other mechanisms not fully represented within the model, such as phosphatase enzymes, could be part of this explanation.

In order to test this, we conducted a meta-analysis of phosphatase enzyme activity in agricultural settings, comparing response to P sufficient and deficient conditions. Results suggest phosphatase enzyme activity is higher in P deficient conditions compared to inorganic P addition, yet lower compared to organic P addition. Meta-regression analysis indicates magnitude of P addition and pH of substrate are significant factors influencing enzyme response. However, due to numerous additional processes and adaption strategies in response to P deficiency and the difficulty isolating the role of phosphatase enzymes it is not possible to determine the degree to which this mechanism alone accounts for the missing P. We discuss the continuing need for additional empirical evidence to understand the cycling of organic P, and the development of models to include these processes to inform sustainable land management and ensure long-term food security.
National-scale assessment of river migration at critical bridge infrastructure in the Philippines using Google Earth Engine
Authors: Boothroyd Richard , Williams Richard , Hoey Trevor , Tolentino Pamela , Yang Xiao
Published: March 2021

River migration represents a geomorphic hazard at sites of critical bridge infrastructure, particularly in rivers where migration rates are high, as in the tropics. In the Philippines, where exposure to flooding and geomorphic risk are considerable, the recent expansion of infrastructural developments warrants quantification of river migration in the vicinity of bridge assets. We analysed publicly available bridge inventory data from the Philippines Department of Public Works and Highways (DPWH) and leveraged freely available satellite imagery in Google Earth Engine (GEE) to assess river migration. Specifically, we extracted active river channel masks of the bankfull extent (including the wetted channel and unvegetated, alluvial deposits) from Landsat products (Landsat 5, 7 and 8) using multi-spectral indices, before identifying river planform adjustments over decadal and engineering (30-year) timescales. For 74 bridges, we calculated similarity coefficients (Jaccard index) to indicate planform (dis)similarity and quantified changes in river channel width using RivWidthCloud.

Monitoring revealed the diversity of river planform adjustment at bridges in the Philippines (including channel migration, contraction, expansion and avulsion). The mean Jaccard index over decadal (0.65) and engineering (0.50) timescales indicated considerable planform adjustment throughout the national-scale inventory. However, planform adjustment and morphological behaviour varied between bridges. Some inventoried bridges were characterised by substantial planform adjustment and river migration, with maximum active channel contraction and expansion over decadal timescales equal to approximately 25% of the active channel width. This represents considerable lateral adjustment and when left unmanaged could pose a substantial geomorphic hazard. However, for other inventoried bridges the planform remained approximately stable and changes in channel width were limited. We suggest that multi-temporal analysis from satellite remote sensing offers a low-cost approach for monitoring the relative risk of river migration at critical bridge infrastructure; the approach can be extended to include other critical infrastructure adjacent to rivers (e.g., road, rail pipelines) and extended elsewhere to other dynamic riverine settings.
Chlorophyll fluorescence-gross primary productivity relationships during the spring awakening of an evergreen needleleaf forest
Authors: Schwarz Michaela , Sakowska Karolina , Ziemblińska Klaudia , Dukat Paulina , Urbaniak Marek , Olejnik Janusz , Hammerle Albin , Wohlfahrt Georg
Published: March 2021

Solar-induced chlorophyll fluorescence (SIF) has been shown as a promising approach for the estimation of gross primary productivity (GPP), but whether SIF is merely a function of canopy structure or also contains precious physiological information, is presently heavily discussed. In this study, the SIF-GPP relationship was quantified at a Pinus sylvestris forest (Mezyk, Poland) during a series of short-term cold spells throughout the spring awakening to investigate the potential of SIF as a proxy for GPP during this period characterized by cold stress. GPP was inferred from the net ecosystem CO2 exchange measured by the eddy covariance technique. Canopy-scale SIF was measured using a high-resolution spectrometer system and retrieved via spectral fitting (SFM) algorithms. Active leaf-scale chlorophyll fluorescence measurements were conducted on seven branches using an automated field-deployable fluorometer system. Our results demonstrate a clear difference in GPP and the utilization of chlorophyll-absorbed energy between cold spell and warm days. At short, sub-daily time scales, the correlation between SIF and GPP was minor, but increased significantly when observed over extended temporal periods, when SIF exhibited a seasonal pattern that was more closely aligned with the GPP. Furthermore, the strong relationship between non-photochemical quenching (NPQ) and the photochemical reflectance index (PRI) shows good potential to better estimate GPP when integrated in the SIF-GPP model, as the integration of PRI overall increased the relation between SIF and GPP.
Noise Correlations of Wavefield Gradients to Improve Sensitivity to (near surface, time-dependent) Structural Heterogeneity
Authors: Celik Betul , Sager Korbinian , Igel Heiner
Published: March 2021

We assess the potential of rotational ground motions to resolve time-dependent near surface structural heterogeneities using noise correlations. Recent studies reveal an increased sensitivity of gradient related observations to near surface structural heterogeneities (e.g., material contrast, cavities) compared to directly measured wavefields (and their time derivatives). The development of new sensing technologies, such as rotational ground motion sensors and distributing acoustic sensing (DAS), enable measurements of strain and rotations and motivate this study. Combining gradient related observations with ambient noise-based monitoring methods has the potential to increase both spatial and temporal resolution. In order to investigate the suggested benefits, we perform a numerical study in 2D, where we simulate seismic noise with random sources at random locations. We apply interferometric principles and calculate cross-correlations of the resulting noise traces recorded at different receiver locations for multiple realizations of the noise field. After analysing the convergence of the correlation functions in terms of simulation length and number of simulations, we compare noise correlations of acceleration and rotation rate for a homogenous reference and a perturbed model. Ultimately, we establish that noise correlations of wavefield gradients are more sensitive than noise correlations of wavefields to small-scale heterogeneity.
Flash droughts in southern South America as captured by ERA5 reanalysis data
Authors: Lovino Miguel A. , Berbery Ernesto H. , Müller Gabriela V. , Pierrestegui M. Josefina
Published: March 2021

This study investigates the frequency of occurrence of two types of flash droughts in southern South America: heatwave flash droughts (HWFD) and precipitation deficit flash droughts (PDFD). To this end, we employ ERA5 products at 0.25° horizontal resolution under the assumption that they add valuable information in regions of scarce observations. The analysis is based on 1979-2019 ERA5 pentad data of precipitation (P), 2-m air mean temperature (T), evapotranspiration (ET), and root-zone soil moisture (SM). HWFD and PDFD exhibit different functional mechanisms related to surface moisture and surface energy fluxes. In HWFD, high T causes ET to increase and lead to decreases of SM. When combined with negative P anomalies before a drought's onset, there is a significant increase in the magnitude of negative SM anomalies. The mechanism of PDFD formation starts with a precipitation deficit prior to the drought onset. The lack of precipitation causes a reduction in SM and ET, which results in increased T (the Bowen ratio and T increase in response to the decreased ET). 

HWFDs at each grid point and each pentad are identified as those that meet the following conditions: (a) T anomalies are larger than one standard deviation (SD) computed from the 1979-2019 period for that pentad, (b) ET anomalies are positive, (c) P anomalies are negative, and (d) the SM is below the 40th percentile. PDFDs are identified when (a) P is below the 40th percentile, (b) SM% < 40, (c) ET anomalies are negative, and (d) T anomalies > 1 SD. The frequency of occurrence (FOC) of HWFD or PDFD is defined as the percentage of pentads exceeding those thresholds. Composites of all variables for pentads under HWFD or PDFD were prepared to determine such droughts' spatial structure.

Our results indicate that cases of HWFD are more common than those of PDFD. HWFDs are more likely to occur over the arid western region and central-eastern Brazil. HWFDs are more common in both areas in spring (SON) and summer (DJF), reaching FOC values of 14-16% over each season. On the other hand, PDFDs can occur almost everywhere but less frequently. The maximum annual FOC for PDFD (4 - 6%) is located towards Brazil's center. Composite maps show that the most frequent HWFDs occur in regions of highest T and ET anomalies, with a SM decrease to the 10-20th percentile range.

In contrast, the most frequent PDFDs do not occur in regions of highest P deficit, i.e., northeastern Argentina and southern Brazil. However, the precipitation deficit towards the center of Brazil, the area with the highest frequency of PDFD, is significant ( -3 mm / day). This P deficit leads to decreased soil moisture to the 20-30th percentile range and mean ET anomalies between -0.2 and -0.5 mm/day.