bluuebunny/crossref_metadata_2025 huggingface dataset:
A new SIF (solar‐induced chlorophyll fluorescence) product derived from TROPOMI onboard Sentinel-5 Precursor
Authors: Bacour Cédric , Guanter Luis , Schneider Andreas , Aben Ilse , Maignan Fabienne , Grignon Leo , El Hajj Mahmoud , Retscher Christian
Published: March 2021

The total amount of CO2 absorbed and turned into organic matter through photosynthesis can be quantified as Gross Primary Productivity (GPP). Terrestrial vegetation GPP is responsible for offsetting about 30% of carbon dioxide emissions released by anthropogenic activities into the atmosphere. This corresponds to approximately 120 to 170 PgC/year, making terrestrial vegetation both the largest and most uncertain component of the global carbon cycle. Over the last few years, solar- induced chlorophyll fluorescence (SIF) observations from space have emerged as a promising resource for evaluating the spatio-temporal distribution of GPP by terrestrial ecosystems. SIF is an electromagnetic signal emitted by the chlorophyll a of green plants: part of the absorbed energy not used for photosynthesis is emitted at longer wavelengths as a two-peak spectrum roughly covering the 650–850 nm spectral range. The SIF signal responds instantaneously to perturbations in  environmental conditions such as light and water stress, which makes it a direct proxy for photosynthetic activity.

SIF has been estimated at the global scale from several space-borne spectrometers originally intended for atmospheric research because they provide the necessary spectral  resolution and radiometric sensitivity. However, the exploitation of SIF estimates has remained limited by their coarse spatial resolution (GOSAT, GOME-2) or low number of observations (OCO-2). This has been strongly alleviated by the advent of the TROPOspheric Monitoring Instrument (TROPOMI) onboard Sentinel-5 Precursor which combines a global continuous spatial sampling with a 5.5 km x 3.5 km pixel size at nadir, a daily  revisit time, a wide spectral coverage and an enormous increase in the number of clear-sky measurements per day in comparison to previous missions, as demonstrated by the first SIF retrievals from TROPOMI derived by Caltech (Köhler et al. 2018).

In this study, we present a new independent SIF product derived from TROPOMI observations using two fitting windows at 743-758 nm (all sky SIF) and 735-758 nm (clear sky SIF). The first one is very robust against atmospheric effects (especially cloud contamination) whereas the second one is less sensitive to estimation errors (due to the greater number of spectral points in the fitting window). The retrieval scheme is not much different from the one from Caltech (in 743-758 nm) but relies on different cloud fraction inputs. We will present the principles of the retrieval scheme, the format of the output TROPOSIF product, and the results of the comparison of our SIF estimates against the Caltech ones as well as SIF data derived from OCO-2 which show a very good consistency between all SIF products.
Labrador Slope Water Connects the Subarctic with the Gulf Stream
Authors: New Adrian , Smeed David , Czaja Arnaud , Blaker Adam , Mecking Jenny , Mathews Jamie , Sanchez-Franks Alejandra
Published: March 2021

Labrador Slope Water (LSLW) is found in the Slope Sea on the US-Canadian eastern shelf-slope as a relatively fresh and cool water mass, lying between the upper layer water masses and those carried by the Deep Western Boundary Current. It originates from the Labrador Current and has previously only been reported in the Eastern Slope Sea (east of 66°W). We here use the EN4 gridded database and the Line W hydrographic observations to show for the first time that the LSLW also penetrates into the Western Slope Sea, bringing it into close contact with the Gulf Stream. We also show that the LSLW spreads across the entire Slope Sea north of the Gulf Stream, and is both fresher and thicker when the Atlantic Meridional Overturning Circulation (AMOC) is high at the RAPID array at 26°N. The fresher, thicker LSLW is likely to contribute an additional 1.5 Sv of Gulf Stream transport. The spreading of the LSLW is also investigated in a high-resolution ocean general circulation model (NEMO), and is found to occur both as a western boundary current and through the extrusion of filaments following interaction with Gulf Stream meanders and eddies. The mechanism results in downward vertical motion as the filaments are entrained into the Gulf Stream. We conclude that the LSLW (rather than the deeper Labrador Sea Water) provides the intermediate depth water masses which maintain the density contrast here which partly drives the Gulf Stream, and that the transport of the LSLW from the Labrador shelf-slope offers a potential new mechanism for decadal variability in the Atlantic climate system, through connecting high latitude changes in the Subarctic with subsequent variability in the Gulf Stream and AMOC.
The post-Messinian translation of the Southern Apennines-Calabrian Arc in the Bradano basin (Northern Ionian Sea)
Authors: Artoni Andrea , Basso Jessica , Torelli Luigi , Polonia Alina , Chizzini Nicolò , Gasperini Luca , Carlini Mirko
Published: March 2021

In Northern Calabria, the Southern Apennines orogenic wedge bends and passes to the Calabrian Arc while they are both colliding with the subducting Apulia plate. The boundary between Southern Apennines and Calabrian Arc is commonly placed along the NW-SE trending Sangineto Lineament whose offshore prolongation is not clearly defined. A multi-scale seismic reflection dataset combined with exploration wells and seafloor bathymetry allowed us to define the post-Messinian tectono-sedimentary evolution of the Bradano Basin adjacent to the orogenic belt.  

After Messinian times, two main tectono-sedimentary events deeply modified the Bradano Basin. During the first event (early Pliocene-early Pleistocene), a left-lateral transpressive system, about 20-30 km wide, was part of an oblique convergent margin along which the Southern Apennines and the Calabrian Arc collided; remnants of this transpressive system are now buried under the western portion of the Bradano Basin near the Calabrian margin. Shelf to deep marine turbiditic deposits were prevailing during this first event. Around the Pliocene-Pleistocene boundary (2.58 Ma), a sudden and widespread basin rearrangement occurred. During the second event (early Pleistocene-Present) the orogenic front of the Southern Apennines and the earlier transcurrent systems were suddenly translated to the NE of about 50 km and the left-lateral transpressive boundary between the Southern Apennines and Calabrian Arc became part of the orogenic wedge. During this second event, both upper and lower converging plates were shortened together along multiple detachments levels and out-of-sequence thrusts. The second tectono-sedimentary event is characterized by prograding deltaic and shelfal deposits that seal the earlier transpressive system and pass to deep marine deposits in the central part of the Bradano basin.

The study reveals that the eastern boundary between Southern Apennine and Calabrian Arc is a wide deformation belt including the Sangineto Lineament while the Messinian-Pliocene orogenic transpressive system is buried and translating toward the NE since Early Pleistocene.
Development of a small unmanned aircraft system to derive CO2 emissions of anthropogenic point sources
Authors: Reuter Maximilian , Bovensmann Heinrich , Buchwitz Michael , Borchard Jakob , Krautwurst Sven , Gerilowski Konstantin , Burrows John P.
Published: March 2021

A reduction of the anthropogenic emissions of CO2 (carbon dioxide) is necessary to stop or slow down man-made climate change. To verify mitigation strategies, a global monitoring system such as the envisaged European Copernicus anthropogenic CO2 monitoring mission (CO2M) is required. Those satellite data are going to be complemented and validated with airborne measurements. UAV (unmanned aerial vehicle) based measurements can provide a cost-effective way to contribute to these activities. Here we present the development of a sUAS (small unmanned aircraft system) to quantify the CO2 emissions of a nearby point source from its downwind mass flux without the need for any ancillary data. Specifically, CO2 is measured by an in situ NDIR (non-dispersive infrared) detector and the wind speed and direction is measured with a 2D ultrasonic acoustic resonance anemometer. In order to minimize the effect of rotor downwash, we calibrate the anemometer by analyzing wind measurements taken while following a suitable flight pattern and assuming stationary wind conditions. We quantify the quality of the CO2 and wind measurements with an in-flight validation at the ICOS (Integrated Carbon Observation System) atmospheric station Steinkimmen (STE) near Bremen, Germany. By means of two flights downwind of the ExxonMobil natural gas processing facility in Großenkneten about 40km east of Bremen, Germany, we demonstrate how the measurements of elevated CO2 concentrations can be used to infer mass fluxes of atmospheric CO2 related to the emissions of the facility.
Night-time chemistry of biomass burning plumes in urban areas: A dual mobile chamber study
Authors: Jorga Spiro , Florou Kalliopi , Kaltsonoudis Christos , Kodros John , Vasilakopoulou Christina , Nenes Athanasios , Pandis Spyros
Published: March 2021

Biomass burning including residential heating, agricultural fires, prescribed burning, and wildfires is a major source of gaseous and particulate pollutants in the atmosphere. Although, important changes in the size distributions and the chemical composition of the biomass burning aerosol during daytime chemistry have been observed, the corresponding changes at nighttime or in winter where photochemistry is slow, have received relatively little attention. In this study, we tested the hypothesis that nightime chemistry in biomass burning plumes can be rapid in urban areas using a dual smog chamber system.

 

Ambient urban air during winter nighttime periods with high concentrations of ambient biomass burning organic aerosol is used as the starting point. Ozone was added in the perturbed chamber to simulate mixing with background air (and subsequent NO3 production and aging) while the second chamber was used as a reference. Following the injection of ozone rapid organic aerosol (OA) formation was observed in all experiments leading to increases of the OA concentration by 20-70%. The oxygen to carbon ratio of the OA increased by 50% on average and the mass spectra of the produced OA was quite similar to that of the oxidized OA mass spectra reported during winter in urban areas. Good correlation was also observed with the produced mass spectra from nocturnal aging of laboratory biomass burning emissions showing the strong contribution of biomass burning emissions in the SOA formation during cold nights with high biomass burning activities. Concentrations of NO3 radicals as high as 25 ppt were measured in the perturbed chamber with an accompanying production of 0.2-1.2 μg m-3 of organic nitrate. These results strongly indicate that the OA in biomass burning plumes can evolve rapidly even during wintertime periods with low photochemical activity.
Greenhouse gas exchange of young rewetted swamp in northern Netherlands
Authors: Kruijt Bart , Berghuis Hanne , Biermann Jan , Jans Wilma , Franssen Wietse , Nijhof Ed , Peltenburg Ad , Lettink Rien , Jacobs Cor , Hutjes Ronald , Veraart Jeroen
Published: March 2021

There are many initiatives to re-wet drained nature or former agricultural land. These young wetlands provide a natural habitat for a range of endangered species, while serving as a natural climate buffer by retaining water, regulating air temperature, and sequestering CO2 from the atmosphere. However, wetlands may also emit CH4, which has a global warming potential (GWP) of about 30. Thus, all carbon fluxes need to be quantified in order to assess if, from a climate perspective, CO2 uptake outweighs CH4 emission.

To assess the net effect of young wetlands on Greenhouse Gas exchange, we study the CO2 and CH4 fluxes of two recently rewetted areas near Groningen, the Netherlands. The fluxes are measured directly using the Eddy Covariance (EC) technique on a moveable station, alternating between the two sites. Meteorological observations are performed at these stations as well, along with other supportive measurements such as soil/water temperature. The alternating time gaps are filled by interpolation based on observed ecosystem responses. Footprint analysis provides insight into the role of various vegetation types inside these swamps. The resulting carbon budgets provide insight into GHG exchange over typically small temporal and spatial scales.

The study also examines the feasibility of these moveable stations, as they may reduce the relatively high research costs of EC measurements. The data from moveable stations is reliable if the data is regular, as the time gaps are filled by interpolation. At this stage, the timeseries is too short to draw any conclusions upon the reliability of the data. However, the moveable stations appear to be feasible from a practical point of view, as the station can be relocated relatively easy within the time span of a day.

The first results suggest both substantial CO2 uptake and CH4 emissions but a full year of data was not collected yet. Observed exchange compares well to similar studies previously performed.  

Ultimately, annual budgets of the carbon exchange response will be correlated to weather conditions but also to hydrological measures such as water levels. This should allow extrapolation of the data, which may serve as a basis for policy makers to manage the carbon balance when re-wetting nature to achieve net mitigation of greenhouse warming potential.
Slow deformation event between large intraslab earthquakes at the Tonga Trench inferred from geodetic and seismological data
Authors: Mitsui Yuta , Muramatsu Hinako , Tanaka Yusaku
Published: March 2021

Slow deformations associated with a subducting slab can affect quasi-static displacements and seismicity over a wide range of depths. Here, we analyse the seismotectonic activities at the Tonga-Trench subduction zone, which is the world’s most active area with regard to deep earthquakes, using data from GNSS and an earthquake catalogue. We find that trenchward transient displacements and quiescence of deep earthquakes, in terms of background seismicity, were bounded in time by large intraslab earthquakes in 2009 and 2013. We call this event as "slow deformation event”. It may have been triggered by a distant and shallow M8.1 earthquake, which implies a slow slip event at the plate interface or a temporal acceleration of the subduction of the Pacific Plate.
Black carbon concentration in the central Himalayas: impact on glacier melt and potential source contribution
Authors: Gul Chaman , Sarathi Mahapatra Parth , Kang Shichang , Kumar Singh Praveen , Wu Xiaokang , He Cenlin , Kumar Rajesh , Rai Mukesh , Xu Yangyang , Puppala Siva Praveen
Published: March 2021

This study discusses year-long (October 2016–September 2017) observations of atmospheric black carbon (BC) mass concentration, its source and sector contributions using a chemical transport model at a high-altitude (28°12'49.21"N, 85°36'33.77"E, 4900 masl) site located near the Yala Glacier in the central Himalayas, Nepal. During a field campaign, fresh snow samples were collected from the surface of the Yala Glacier in May 2017, which were analysed for BC and water-insoluble organic carbon mass concentration in order to estimate the scavenging ratio and surface albedo reduction. The maximum BC mass concentration in the ambient atmosphere (0.73 μg m-3) was recorded in the pre-monsoon season. The BC and water-insoluble organic carbon analysed from the snow samples were in the range of 96–542 ng g-1 and 152–827 ng g-1, respectively. The source apportionment study using the absorption Ångström exponent from in situ observations indicated approximately 44% contribution of BC from biomass-burning sources and the remainder from fossil-fuel sources during the entire study period. The source contribution study, using model data sets, indicated ~14% contribution of BC from open-burning and ~77% from anthropogenic sources during the study period. Our analysis of regional contributions of BC indicated that the highest contribution was from both Nepal and India combined, followed by China, while the rest was distributed among the nearby countries. The surface snow albedo reduction, estimated by an online model – Snow, Ice, and Aerosol Radiation – was in the range of 0.8–3.8% during the pre-monsoon season. The glacier melt analysis suggested that BC contributed to approximately 28% of the total melting in the pre-monsoon season. 
Detection of geomagnetic disturbances with ionospheric calibration solutions of LOFAR astronomical observations
Authors: Budzińska Katarzyna , Mevius Maaijke , Grzesiak Marcin , Pożoga Mariusz , Matyjasiak Barbara , Rothkaehl Hanna
Published: March 2021

Perturbation of an electromagnetic signal due to its passing through the Earth’s ionosphere is one of the limiting factors in obtaining high quality astronomical observations at low frequencies. Since the establishment of the Low Frequency Array (LOFAR) radio interferometer, which is operating  in the frequency range between 10  and 240 MHz, effort has been made in order to properly remove this effect during the calibration routine.

In this study we use differential TEC solutions obtained from calibration of Epoch of Reionization project’s observations and investigate their sensitivity to weak geomagnetic disturbances with wavelet transform analysis. Comparison to the different geomagnetic indices allows us to study the possible origin of medium scale ionospheric structures that have been detected.
Shear instability of wind drift as the initiation mechanism for the bag-breakup fragmentation of the air-water interface at high winds.
Authors: Troitskaya Yuliya
Published: March 2021

The "bag breakup" fragmentation is the dominant mechanism for generating spray in hurricane winds, which parameters substantially affect the exchange processes between the ocean and the atmosphere and, thereby, the dynamics of the development of sea storms. This fast process can only be studied in lab using sophisticated experimental techniques based on high-speed video filming. In such circumstances, the transfer of laboratory data to field conditions requires a kind of theoretical model that describes how the initiation of disturbances occurs, which then lead to fragmentation events, what is the threshold for fragmentation, what is the volume of liquid, which determines the size of spray droplets, that undergoes fragmentation, and how it depends on wind parameters, etc. The conclusions of the model can be first verified in the laboratory experiment and then applied to field conditions.

In the present work, such a model is proposed. First of all, a linear theory of small-scale disturbances on the water surface under the action of a strong wind has been built, which makes it possible to describe their structure, dispersion properties and determine the threshold value of the dynamic air flow velocity at which such disturbances become growing. These disturbances comprise small-scale ripples concentrated within the thin surface layer and growing fast due to shear instability of the wind drift flow in the water. The peculiarity of the structure of these disturbances enables one to consider the nonlinear stage of their evolution within the Riemann simple wave equation modified to describe the increasing disturbances. The analytical solution of the obtained equation suggests the scaling of the volume of liquid undergoing the "bag-breakup" fragmentation, to estimate the scale of the formed droplets and the speed of their injection into the atmosphere. The scaling correctly describes the dependencies of these quantities on the wind friction velocity obtained in laboratory experiments.

The obtained results are applied for the construction of the fetch-dependent spray generation function, which is applicable in the field. Within the Lagrangian stochastic model for the inertial droplets in the marine boundary layer, the momentum, heat, moisture and enthalpy exchange coefficients are calculated. One should notice substantial  feedback effect on the atmosphere caused by the presence of spray in hurricane conditions.

This work was supported by RFBR grant 19-05-00249 and RSF grant 19-17-00209.

 
PreMevE: A Machine-Learning Based Predictive Model for MeV Electrons inside Earth’s Outer Radiation Belt
Authors: Chen Yue , Pires de Lima Rafael , Sinha Saurabh , Lin Youzuo
Published: March 2021

The presence of megaelectron-volt (MeV) electrons in the Earth’s outer radiation belt poses a hazardous radiation environment for spaceborne electronics through the total ionization dose effect and deep dielectric charge/discharge phenomenon. Thus, developing a reliable forecasting model for MeV electron events has long been a critical but challenging task for space community. Here we update our recent progresses on the PREdictive model for MEV Electrons (PreMevE). This model exploits the power of machine learning algorithms, takes advantage of the coherence caused by local wave‐electron resonance, and uses electron observations from NOAA POES satellites in low‐Earth orbits as inputs—along with the upstream solar wind speeds and densities and GEO measurements—to provide high‐fidelity 1- and 2-day predictions of 1 MeV, 2 MeV and > 2 MeV electron flux distributions across the whole outer radiation belt. Using near-equatorial long-term electron data from the NASA Van Allen Probes mission, we trained, validated and demonstrated that the PreMevE model has L-shell averaged performance efficiencies of ~0.6 for out-of-sample 1-day forecasts and ~0.5 for 2-day forecasts. This study adds new science significance to an existing LEO and GEO space infrastructure, provides reliable and powerful tools to the whole space community, and also suggests for the development of more future tailored space weather models driven by similar methodologies.
pyBL: An open source Python package for stochastic high-resolution rainfall modelling based upon a Bartlett Lewis Rectangular Pulse model
Authors: Wang Li-Pen , Dai Ting-Yu , He Yun-Ting , Chou Ching-Chun , Onof Christian
Published: March 2021

Stochastic rainfall modelling is an increasingly popular technique used by the water and weather risk industries. It can be used to synthesise sufficiently long rainfall time series to support hydrological applications (such as sewer system design) or weather-related risk analysis (such as excess rainfall insurance product design). The Bartlett-Lewis (BL) rectangular pulse model is a type of stochastic model that represents rainfall using a Poisson cluster point process. It is calibrated with standard statistical properties of rainfall data (e.g. mean, coefficient of variation, skewness and auto-correlation and so on), but it can well preserve extreme statistics of rainfall at multiple timescales simultaneously. In addition, it is found to be less sensitive to observational data length than the existing rainfall frequency analysis methods based upon, for example, annual maxima time series, so it provides an alternative to rainfall extremes analysis when long rainfall datasets are not available. 

In this work, we would like to introduce an open source Python package for a BL model: pyBL, implemented based upon the state-of-the-art BL model developed in Onof and Wang (2020). In the pyBL package, the BL model is separated into three main modules. These are statistical properties calculation, BL model calibration and model sampling (i.e. simulation) modules. The statistical properties calculation module processes the input rainfall data and calculates its standard statistical properties at given timescales. The BL model calibration module conducts the model fitting based upon the re-derived BL equations given in Onof and Wang (2020). A numerical solver, based upon Dual Annealing optimization and Nelder-Mead local minimization techniques, is implemented to ensure the efficiency as well as to prevent from being drawn to local optima during the solving process. Finally, one can use the sampling module to generate stochastically rainfall time series at a given timescale and for any required data length, based upon a calibrated BL model.

The design of the pyBL is highly modularized, and the standard CSV data format is used for file exchange between modules. Users could easily incorporate given modules into their existing applications. In addition, a team, consisting of researchers from National Taiwan University and Imperial College London, will consistently implement the new breakthroughs in BL model to the package, so users will have access to the latest developments. The package is now undergoing the final quality check and will be available on Github (https://github.com/NTU-CompHydroMet-Lab/pyBL) in due course. 
HighResMIP climate simulations with NICAM and beyond on supercomputer Fugaku
Authors: Kodama Chihiro , Yamada Yohei , Ohno Tomoki , Seiki Tatsuya , Yashiro Hisashi , Noda Akira T. , Nakano Masuo , Roh Woosub , Satoh Masaki , Nitta Tomoko , Goto Daisuke , Miura Hiroaki , Nasuno Tomoe , Miyakawa Tomoki , Chen Ying-Wen , Sugi Masato
Published: March 2021

The Non-hydrostatic ICosahedral Atmospheric Model (NICAM), a global model with an icosahedral grid system, has been under development for nearly two decades. Here, we present its recent updates for the Coupled Model Intercomparison Project Phase 6, High Resolution Model Intercomparison Project (HighResMIP) and their impact on the simulated mean states using 56-14km mesh model. Major updates include updates of the cloud microphysics scheme and land surface model, introduction of natural and anthropogenic aerosols and a subgrid-scale orographic gravity wave drag scheme, and improvement of the coupling between the cloud microphysics and the radiation schemes. A short-term sensitivity experiments demonstrate improvements in the ice water content, high cloud amount, surface air temperature over the Arctic region, location and strength of zonal mean subtropical jet, and shortwave radiation over Africa and South Asia. The decadal climate simulations further reveal an improvement in the genesis and structure of the tropical cyclones compared with those with the previous model. Finally, we will address outlook toward the cloud-resolving climate simulation based on a fresh benchmark result on supercomputer Fugaku, a flagship supercomputer in Japan.
Autogenic progradation of Bayhead deltas during sea-level rise wIthin incised valleys : theory, experiment and field examples    
Authors: Guerit Laure , Foreman Brady , Chen Chen , Paola Chris , Castelltort Sébastien
Published: March 2021

The evolution of sedimentary landscapes is primary driven by the interplay between the rate of accommodation creation A, controlled by sea-level and subsidence, and the rate of sediment supply S, controlled by erosion and sediment transport. In simple terms, the balance between A and S can be used to predict periods of progradation (when sediment supply exceeds accommodation) and periods of retrogradation (when accommodation exceeds sediment supply). However, a growing list of observations show that internal feedbacks within the sediment transport system can generate large-scale, autogenic stratigraphic patterns that are not anticipated by the A/S theory. These observations call for a reanalysis of several sequence stratigraphic precepts that assume a deterministic relationship between external forcings and stratigraphic products. Here, we focus on the filling of incised valleys during constant sea-level rise, and by a constant sediment flux. We develop a simple conceptual model of valley filling and we show that the classic sequence stratigraphic phenomenon of bayhead deltaic systems can be generated by purely autogenic progradation during the late stage of valley flooding. This transient “auto-advance” event results from a strong decrease of in-valley accommodation as base-level rises towards the valley apex. To test this model, we build a laboratory experiment that successfully reproduces the dynamics predicted by the model. Finally, we apply our model to two similar field examples, the Trinity and Brazos rivers incised valleys (Texas, USA). There systems are broadly similar in dimension and sea-level history but were filled at different sediment rates. We propose that this led to auto-advance event in the Trinity River valley while no advance is observed in the Brazos system. We thus show by conceptual, experimental and natural examples that auto-advance can produce out-of-sequence regressive bayhead diastems during highstands similar to a transient change in allogenic forcing. Combined with other recent studies, our findings support the idea that meso-scale autogenic patterns are ubiquitous in the fluvio-deltaic record, and need to be more extensively incorporated into reconstructions of Earth surface evolution and reservoir models.
Using space observations to monitor reservoir operations in the Lancang River
Authors: Trung Vu Dung , Duc Dang Thanh , Galelli Stefano
Published: March 2021

Being a part of the Water Tower of Asia, the Mekong River originates from the Tibetan Plateau and flows through China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. Its upper portion, also called the Lancang River, has abundant hydropower potential, which has been largely exploited during the three recent decades. To date, there are 11 operational dams (10 of them have a volume larger than 100 MCM) on the mainstream of the Lancang, controlling about 40% of the annual flow at Chiang Saen (the most upstream station of the Lower Mekong). The amount of water withheld in these dams is a potential source of controversy between China and downstream countries because it affects both the timing and volume of available water. Assessing the real impacts of these dams is a challenging task owing to the chronic lack of data on reservoirs' storage and operating patterns. To overcome this challenge, we exploit satellite images and altimetry data. The analysis focuses on 10 reservoirs and is conducted in three steps. First, we estimate the relationship between water elevation and surface area (E-A curve) for each reservoir. For this purpose, we either use DEM data or water surface area data (derived from satellite images) paired with altimetry-derived water levels. Second, with the Elevation-Area-Storage curve converted from each E-A curve, we calculate storage variability over time by using satellite image-derived reservoir water surface area. The result is collated with storage variability derived from altimetry data. In the last part of our analysis, focusing on the period 2008-2020, we show how the total withheld storage changed over time, we determine the rule curve of each reservoir and elucidate the role of reservoir filling strategies.
Role of Regional Ocean Dynamics in Dynamic Sea Level Projections by the end of the 21st Century over Southeast Asia
Authors: Samanta Dhrubajyoti , Jevrejeva Svetlana , Palanisamy Hindumathi K. , Karnauskas Kristopher B. , Goodkin Nathalie F. , Horton Benjamin P.
Published: March 2021

Southeast Asia is especially vulnerable to the impacts of sea-level rise due to the presence of many low-lying small islands and highly populated coastal cities. However, our current understanding of sea-level projections and changes in upper-ocean dynamics over this region currently rely on relatively coarse resolution (~100 km) global climate model (GCM) simulations and is therefore limited over the coastal regions. Here using GCM simulations from the High-Resolution Model Intercomparison Project (HighResMIP) of the Coupled Model Intercomparison Project Phase 6 (CMIP6) to (1) examine the improvement of mean-state biases in the tropical Pacific and dynamic sea-level (DSL) over Southeast Asia; (2) generate projection on DSL over Southeast Asia under shared socioeconomic pathways phase-5 (SSP5-585); and (3) diagnose the role of changes in regional ocean dynamics under SSP5-585. We select HighResMIP models that included a historical period and shared socioeconomic pathways (SSP) 5-8.5 future scenario for the same ensemble and estimate the projected changes relative to the 1993-2014 period. Drift corrected DSL time series is estimated before examining the projected changes. Due to improved simulation of heat, salt, and mass distribution in the ocean, HighResMIP models not only reduce mean state biases in the tropical Pacific (such as cold-tongue sea surface temperature bias), but also near Southeast Asia including DSL. Despite intermodel diversity, there is an overall agreement of increasing sea-level over Southeast Asia. The multimodel ensemble of HighResMIP models suggests a rise of 0.2 m sea level in dynamic sea level (combined with thermosteric component) over Southeast Asia by 2070. Sea-level rises further up to 0.5 m by the end of the 21st century. Further, we found regional heat and mass transport changes have a major role in the projected sea-level pattern over Southeast Asia. For example, heat convergence to the east of Vietnam can account for most of the sea-level rise in the region. Our study can provide better insight into the contribution of regional ocean dynamics to DSL projections and useful to suggest for further ocean modelling studies.
Communicating ACTRIS science in times of COVID-19
Authors: Saponaro Giulia , Dubost Ariane , Juurola Eija , Laj Paolo
Published: March 2021

The identification of the severe COVID-19 virus in December 2019 led the World Health Organization to declare a global pandemic by March 2020. Up till recently with the first available vaccines, the only prevention measures include strict social, travel, and working restrictions in a so-called lockdown period that lasted for several weeks (mid-March to the end of April 2020 for most of Europe). This abrupt change in social behavior is expected to impact local but also regional atmospheric composition, and the environmental impact is potentially of high interest to policy and decision-makers.

The Aerosol, Clouds, and Trace Gases Research Infrastructure (ACTRIS) is a pan-European research infrastructure producing high-quality data and information on short-lived atmospheric constituents and on the processes leading to the variability of these constituents in natural and controlled atmospheres. Realizing the crucial scientific value of ACTRIS observations of atmospheric composition changes across Europe, the ACTRIS community promptly actioned internal communication [AD1] thread to organize and set-up COVID-19 related activities.  Such reactive internal involvement of ACTRIS partners generated timely outcomes. In fact, during the lockdown period in spring 2020, most of the ACTRIS observational and exploratory platforms were operational providing continuous access to data on air quality and atmospheric composition and, as a tailored service arrangement, to reinvent ACTRIS simulation chambers for testing mask filtering efficiencies. [AD2] 

ACTRIS response to the COVID-19 pandemic showcases multiple benefits to policy- and decision-makers focused on environmental and societal impacts of COVID-19 and the closing down of several sectors of society (e.g. transport, industry, services). To boost the visibility of ACTRIS COVID-19 response at the European level, ACTRIS actively engaged and collaborated with the wider community of Research Infrastructures (ESFRI, ENVRI, and ERF-AISBL) in Europe to support joint activities for SARS-CoV-2.  The Open Science Session on COVID-19 during the ACTRIS week event brought together a broad audience and key-note speaker from major European agencies and organizations (ESA, ECMWF, FMI, ICOS). The online format of the event created the opportunity to open ACTRIS science to a broader public. At the national level, atmospheric scientists were interviewed on COVID impacts raising awareness on the work undertaken in the research infrastructure to the general public.

ACTRIS aims at establishing further engagement and direct communication with decision and policy-makers and, for that, envisage the implementation of ad-hoc efforts. This presentation will showcase the various efforts and success stories to capture society as well as policy- and decision-makers.
Flow dependence of wintertime subseasonal prediction skill over Europe
Authors: Ardilouze Constantin , Specq Damien , Batté Lauriane , Cassou Christophe
Published: March 2021

Issuing skillful forecasts beyond the typical horizon of weather predictability remains a challenge actively addressed by the scientific community. This study evaluates winter subseasonal reforecasts delivered by the CNRM and ECMWF dynamical systems and identifies that the level of skill for predicting temperature in Europe varies fairly consistently in both systems. In particular, forecasts initialized during positive NAO phases tend to be more skillful over Europe at week three in both systems. Composite analyses performed in an atmospheric reanalysis, a long-term climate simulation and both forecast systems unveil very similar temperature and sea-level pressure patterns 3 weeks after NAO+ conditions. Furthermore, regressing these fields onto the 3-week previous NAO index in a reanalysis shows consistent patterns over Europe but also eastern North America, thereby revealing a lagged teleconnection, either related to the persistence or recurrence of the NAO+ weather regime. Since this feature is well captured by forecast systems, this is a key mechanism for determining a priori confidence in the skill of wintertime subseasonal forecasts over Europe and North America.
Water Accounting Plus (WA+) through Remote Sensing in the Yarmouk Tributary Basin
Authors: Abdallah Chadi , Tarhini Gina , Daher Mariam , Khatib Hussein , Zeitoun Mark
Published: March 2021

Coping with the issue of water scarcity and growing competition for water among different sectors requires effective water management strategies and decision processes. ‘Getting it right’ becomes doubly important when dealing with intenational transboundary rivers. The Yarmouk tributary to the Jordan River is one highly exploited in the Middle East, and is enveloped by ambiguous treaties and decades of violent and non-violent conflict. Seeking to chart a more sustainable and equitable future, this work performs a 'water accounting plus' methodology employing readily available remotely sensed satellite-based data coupled with available measurements.  A variety of methods described herein were used to detect irrigated crops and produce maps showing the distribution throughout the basin. The framework also focuses on the classification of land use categories and the processes by which water is depleted over all land use classes that contributes to separate the beneficial from non-beneficial usage of water. The analysis was started prior to the 2011 start of the Syrian war in order to study the initial distribution of land use classes as well as the water depletion processes before any change in the basin. It shows that more than half of the exploitable water is not consumed within the basin and depleted outside. In contrast, most of the water consumed within the basin is wasted and depleted in a non-beneficial way. Roughly 35% of the cultivated area shown to be irrigated through withdrawals which exceed the capacity of the source. This result reflects the high abstraction rates from groundwater via a large number of unlicensed wells mostly located at the Syrian side. This study also detect a deficiency in the water balance of the Yarmouk River. The findings are relevant to sustainable management not only for water-dependent sectors but also for geopolitical stability among the riparian countries. In this way, open- access remote sensing derived data can provide useful information about the status of water resources especially when ground measurements are poor or absent.

 

Keywords: Yarmouk, Water Accounting Plus, IWM, Irrigated crops, WAPOR.
The prognostic value of foreshocks - a statistical reevaluation
Authors: Manganiello Ester , Herrmann Marcus , Marzocchi Warner
Published: March 2021

The ability to forecast large earthquakes on short time scales is strongly limited by our understanding of the earthquake nucleation process. Foreshocks represent promising seismic signals that may improve earthquake forecasting as they precede many large earthquakes. However, foreshocks can currently only be identified as such after a large earthquake occurred. This inability is because it remains unclear whether foreshocks represent a different physical process than general seismicity (i.e., mainshocks and aftershocks). Several studies compared foreshock occurrence in real and synthetic catalogs, as simulated with a well-established earthquake triggering/forecasting model called Epidemic-Type Aftershock Sequence (ETAS) that does not discriminate between foreshocks, mainshocks, and aftershocks. Some of these studies show that the spatial distribution of foreshocks encodes information about the subsequent mainshock magnitude and that foreshock activity is significantly higher than predicted by the ETAS model. These findings attribute a unique underlying physical process to foreshocks, making them potentially useful for forecasting large earthquakes. We reinvestigate these scientific questions using high-quality earthquake catalogs and study carefully the influence of subjective parameter choices and catalog artifacts on the results. For instance, we use data from different regions, account for the short-term catalog incompleteness and its spatial variability, and explore different criteria for sequence selection and foreshock definition.
Wind speed variability over the South Shetland Islands, 1988-2019: the relationship between easterlies winds and SAM
Authors: Andres Martin Miguel , Azorin Molina Cesar , Utrabo Carazo Eduardo , Bedoya Valestt Shalenys , Guijarro Jose Antonio
Published: March 2021

The Antarctic Peninsula is one of the most affected regions in a warming climate. Climate change not only involves rising air temperatures or changing precipitation patterns, but also wind. Over the past few decades, one of the most prominent changes in the near-Antarctic climate has been the southward shift of the westerly winds, associated with a positive trend in the Southern Annular Mode index (SAM). Some studies revealed that the poleward shift of the westerlies results in an increased in the seasonality of the coastal easterlies, concretely an increase in the difference between weak easterly winds in summer and strong easterlies in winter. The assessment and attribution of the variability of the easterly winds that encircle the coastline is crucial due to its influence e.g. (i) in the sea ice formation and export, (ii) a variation in the easterly winds can modify the Antarctic Bottom Water formation and properties, (iii) the heat transport trough the continent. Due to operational challenges of measuring weather data in the Antarctic region, there are few long-terms time series and studies dealing with wind trends and variability. In this work, wind series from 1988 to 2019 from the Spanish Juan Carlos I Base, located in the South Shetland Islands, specifically in Livingston Island , have been used for the first time to fill this research niche. Speed series have been subjected to a robust quality control and homogenization protocol in Climatol. The results of the magnitude, sign and decadal variability of this series have been compared with the same results for the same time period for the data of ERA5 reanalysis, all of them at three time scales: annual, seasonal and monthly. For both observations and ERA5 we investigate the relationship between speed series and SAM.
Control of chemically-driven convective dissolution by differential diffusion effects
Authors: Jotkar Mamta , Rongy Laurence , De Wit Anne
Published: March 2021

We numerically study the effect of differential diffusion in chemically-driven convective dissolution that can occur upon the reaction of a dissolving species A in a host phase when the chemical reaction destabilizes an otherwise stable density stratification. For example, an A+B→C reaction is known to trigger such convection when, upon dissolution into the host solution, A reacts with B present in the solution to produce C if the difference between C and B in the contribution to the solution density is above a critical threshold. We show that differential diffusivities impact the convective dynamics substantially giving rise to additional convective effects below the reaction front, where C is generated. More specifically, we show that below the reaction front either double-diffusive or diffusive-layer convection can arise, modifying the local Rayleigh-Taylor instability. When B diffuses faster than C, a double-diffusive instability can develop below the reaction front, accelerating the convective dynamics and conversely, when B diffuses slower than C, diffusive-layer convection modes stabilize the dynamics compared to the equal diffusivity case. Our results are relevant for various geological applications or engineering set-ups that involve non-reactive stable density stratifications where transport can be enhanced by reaction-induced convection.
Optimal monitoring of the ocean surface by observing the transport crossroads
Authors: Hernández-García Emilio , Baudena Alberto , Ser-Giacomi Enrico , Lopez Cristobal , d'Ovidio Francesco
Published: March 2021

In the context of tracer transport in the ocean, we introduce a quantity, the crossroadness [1], which allows identifying the optimal disposition of a set of locations in order to monitor a given ocean surface region. The optimization is performed so that these sites observe the largest amount of water coming from the region and, at the same time, monitor waters coming from separate parts of the ocean. These are key criteria when deploying a marine observing network. Considering surface circulation, crossroadness measures at any location the extent of the ocean surface which transits in its neighborhood in a given time window. When the analysis is performed backward in time, this method allows us to identify the major sources which feed a target region. The method is first applied to a minimalistic model of a mesoscale eddy field, and then to realistic satellite-derived ocean currents in the Kerguelen area. In this region, we identify the optimal location of fixed stations capable of intercepting the trajectories of 43 surface drifters. We then illustrate the temporal persistence of the stations determined in this way. Finally, we identify possible hotspots of micro-nutrient enrichment for the recurrent spring phytoplanktonic bloom occurring there. Promising applications to other fields, such as larval connectivity or contaminant detection are discussed.

[1] A. Baudena, E. Ser-Giacomi, C. López, E. Hernández-García, F. d’Ovidio, Crossroads of the mesoscale circulation, Journal of Marine Systems 192, 1-14 (2019).
Time-dependent soft-bedded sliding laws
Authors: Warburton Katarzyna , Hewitt Duncan , Neufeld Jerome
Published: March 2021

The dynamics of soft-bedded glacial sliding over saturated till are poorly constrained and difficult to realistically capture in large scale models. While experiments characterise till as a plastic material with a pressure dependent yield stress, large scale models rely on a viscous or power-law description of the subglacial environment to efficiently constrain the basal sliding rate of the ice. Further, the subglacial water pressure may fluctuate on timescales from annual to daily, leading to transient adjustment of the till.

We construct a continuum two-phase model of coupled fluid and solid flows, using Darcy flow for the fluid phase and a recently described saturated granular model for the solid. After verifying our model against the steady-state experiments, we force the model with a fluctuating effective pressure at the ice-till interface and infer the resulting relationships between basal traction, porosity, rate of deformation, and till flux. Shear dilation introduces internal pressure variations, leading to hysteretic behaviour in low-permeability materials, resulting in a time-dependent effective sliding law.