bluuebunny/crossref_metadata_2025 huggingface dataset:
Application-Oriented Methods for Obtaining Geometrically Robust Digital Surface Models for Flood Hazard Assessment
Authors: Bodoque del Pozo Jose Maria , Aroca Jiménez Estefanía , Eguibar Galán Miguel Ángel , García Martín Juan Antonio
Published: March 2022

Digital surface models (DSMs) play a critical role in obtaining reliable flood hazard maps for urban areas. Widespread availability of LiDAR data (where available) greatly facilitates obtaining geometrically sound DSMs. However, to date, insufficient attention has been paid to generating methodological approaches to obtain geometrically consistent DSMs. Here, we propose an application-oriented protocol to obtain a geometrically robust DSM (DSM1 hereafter). Additionally, two further DSMs were produced considering, firstly, depiction of streets using breaklines as ancillary information (DSM2) and, secondly, direct interpolation of LiDAR data (DSM3). Geometric robustness of these DSMs was evaluated qualitatively, by plotting longitudinal profiles and cross sections to dominant runoff pathways, as well as quantitatively, through assessing DSMs vertical accuracy. We also assessed impact on hazard maps depending on geometric consistency of DSMs employed. To do so, hydraulic outputs resulting from DSM1 were used as a benchmark to compare hydraulic outputs obtained from DSM2 and DSM3. This comparison was made at two spatial resolution levels: i) considering total area flooded in each case through determining the F statistic; and ii) at the level of each pixel by calculating the kappa statistic from a confusion matrix. Our results revealed that: 1) DSM1 defined geometrically consistent configurations for main runoff pathways; 2) in urban areas with higher street and building density DSM1 provided better vertical accuracies than DSM2 and DSM3; and 3) reliability of flood hazard maps strongly depend on geometric quality of the DSMs produced. Findings deployed here, might be very valuable in achieving further reduction and better flood risk management.
CO2 ecosystem-atmosphere exchange in Krakow, Poland – preliminary results from a new European Fluxes Database Cluster EC urban station
Authors: Jasek-Kaminska Alina , Zimnoch Miroslaw , Chmura Lukasz , Bartyzel Jakub
Published: March 2022

Urban areas, being a considerate source of CO2, at the same time are one of the most complicated ecosystems, with some uncertain components still present in the local carbon cycle. Complications with CO2 dynamics monitoring arise from high heterogeneity of the area and the presence of various sources, but also from a not entirely explored impact of urbanization on the local biosphere. There is a growing need for experimental data to verify existing CO2 emission inventories and to serve as a reliable input to climate models.

In February 2021, an eddy covariance site was established in Krakow, southern Poland, to investigate CO2 exchange in its urban ecosystem. The neighborhood of the site is highly heterogeneous, including various anthropogenic sources such as traffic, household heating, and humans themselves; however, a considerable part of the source area is covered with green, including home gardens, a soccer stadium, and a municipal park.

We present a first sight of the CO2 eddy covariance flux results that were obtained since the site was established. The city is undoubtedly a net CO2 source. A significant diurnal variation in the CO2 flux amplitude was observed in the warm season as compared to winter, with the highest positive values during the night and negative values during the day, indicating effective CO2 photosynthetic uptake. Morning and afternoon traffic peaks were not clearly pronounced: the area is highly heterogeneous and includes other sources as well that may have their own diurnal variability overlapping the traffic signal.

This project has been partially supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 958927, and the subsidy of the Ministry of Education and Science.
Idealized high resolution modelling of plume dynamics and basal melting at Ryder Glacier
Authors: Wiskandt Jonathan , Koszalka Inga , Nilsson Johan
Published: March 2022

Using a two dimensional, high resolution, non-hydrostatic regional model, this study explores the melt induced circulation under the floating ice tongue of Ryder Glacier (RG) and the influence of different aspects of the simulation, like ambient water temperature and ice base geometry, on the circulation.

RG is located at the southern tip of Sherard Osborn Fjord (SOF) in the north of Greenland, which was for the first time surveyed oceanographically in 2019. Low grounding-line water temperatures, complex ice-tongue and sill geometries, and permanent sea-ice cover outside the fjord, potentially make the ice-ocean interactions in SOF rather different from those in the more well-studied nearby Petermann Fjord. 

The control simulation uses 2019 hydrographic observations as initial conditions. A set of model experiments is conducted to analyze the dependency of the plume behavior on the slope of the ice base and the temperature forcing from the in-flowing Atlantic water. 

 The simulated circulation and melt rates are qualitatively similar to previous modelling studies of North Greenlandic fjords. Based on observed ice-thickness transects along RG, two idealized ice tongue profiles are examined: one steeper and one shallower. The simulations with shallower slopes have a greater net basal melt and a stronger overturning fjord circulation, even though the melt plume initially is faster on the steeper slope. The results further suggest a direct relationship between the thermal forcing and the melt rate and resulting overturning time scale.

Additionally we discuss the possible numerical and physical implications of these results for future model experiments targeting the influence of basal melt on fjord circulations.
Multivariate Analysis and Assessment of Regional Drought Risks under Climate Change using Copulas
Authors: Datta Rajarshi , Reddy Manne Janga
Published: March 2022

This study intended to understand the effect of climate change on spatiotemporal characteristics of multivariate drought risk over the Vidarbha region of India. The Standardized Precipitation Evapotranspiration Index (SPEI) is employed to characterize droughts in the region. Gridded daily precipitation and temperature data produced by the Indian Meteorological Department (IMD) and Coupled Model Inter-comparison Project Phase 6 (CMIP6) were utilized for estimating the SPEI. The drought events were identified and subsequently characterized by duration, severity, and peak. Different goodness of fit tests was applied to select the best fitting marginal distributions of the individual drought characteristics. Several symmetric and asymmetric Archimedean trivariate copulas and seven bivariate copula families were evaluated for joint distribution modeling. Maximum pseudo-likelihood and genetic algorithms have been applied to estimate the copula parameters accurately. The asymmetric Frank copula was selected to construct the trivariate distribution of the drought characteristics. Frank, Student’s t and Clayton copulas were chosen to build the bivariate distribution of duration-severity, duration-peak, and severity-peak, respectively. The joint distributions were applied for computing the joint return periods of drought events. The drought risk over the region was illustrated using zoning maps for historical along with near and far future periods. The inferences derived from the study will help policymakers to prepare better mitigation strategies under the changing environment.
Agyrotropy patterns in 3D small-scall turbulent reconnection
Authors: Agudelo Rueda Jeffersson Andres , Verscharen Daniel , Wicks Robert T. , Owen Christopher J. , Walsh Andrew P. , Germaschewski Kai
Published: March 2022

Turbulence and magnetic reconnection are at the core of the long-standing problem of energy dissipation in collisionless plasmas. More than two decades of research on magnetic reconnection have led us to understand the characteristic plasma flows and particle agyrotropy patterns present in collisionless reconnection events. However, it is still not clear what the agyrotropy patterns associated with reconnection events are that form in a turbulent cascade. In this work, we use an explicit fully kinetic particle-in-cell code to study the plasma particles’ agyrotropy associated with three-dimensional small-scale magnetic reconnection events generated by anisotropic and Alfvénic decaying turbulence. We select one reconnection event involving two reconnecting flux ropes. Although we observe similarities with agyrotropy patterns known from two-dimensional steady-state reconnection events, the agyrotropy patterns in our event are more complex. This has further implications for the energy transfer channels available in three-dimensional turbulent reconnection.

 
Analysing the impact of calibrating a low-cost soil moisture sensor on FAO Aquacrop model performance.
Authors: Adla Soham , Bruckmaier Felix , Arias Rodriguez Leonardo Francisco , Tripathi Shivam , Disse Markus , Pande Saket
Published: March 2022

Poverty reduction programs across the world have invested in the agriculture sector, specifically in agricultural technology. Irrigation remains a crucial input to agriculture, and the lack of access to supplemental irrigation aggravates the distress of farmers, particularly, smallholders. Crop simulation models use parameters like crop characteristics, environmental conditions and management practices in combination with the local input data, to compute the 'yield response of crops to water', to better inform irrigation decision-making, for saving resources and/or increasing yield. Soil moisture data can be critical to develop more representative crop models by influencing soil hydraulic parameter estimation, and consequently improving the simulation of soil water movement. The dearth of cost-effective soil moisture sensors is a limitation to their effective incorporation in crop modelling, but calibrating them against primary or secondary standards can expand their scope of application. This study applies different calibration techniques on the low-cost capacitance based soil moisture sensor, Spectrum SM100. Calibration techniques include segmented linear regression, polynomial regression, spline regression, and machine learning algorithms such as support vector regression, random forest regression, multi-layer perceptron, extreme learning machine and support vector categorization. Independent soil moisture data are taken as both continuous and categorical variables, are calibrated both in the laboratory and field, and validated using field data. Field data is obtained from an experimental field in Kanpur (India) during a wheat cropping season in 2018. The experimental site is representative of an intensively managed rural landscape in the Ganga river basin, India. The calibrated soil moisture data are subsequently used in the  crop-water productivity model FAO Aquacrop to tune its soil hydraulic properties. Various models are developed with soil hydraulic parameter sets estimated using the calibrated soil moisture data. The respective performances of these models are compared with the default model performance (with parameters derived from the literature), based on outputs of interest such as above ground biomass, crop yield and water use efficiency. A representative crop model is then used to develop scenarios of irrigation scheduling, with varying degrees of water stress. Results indicate that calibrating the soil moisture sensors in laboratory conditions alone is not sufficient to parameterize soil hydraulic properties, and adequate parameterization requires sensor calibration in field conditions. Further, a cost-benefit analysis is conducted to assess and critically discuss the tradeoffs between the cost of soil moisture monitoring and the obtained crop yield.
Current sheets in front of geoeffective streams and flows as precursors of geomagnetic storms
Authors: Fridman Mikhail , Khabarova Olga , Sagitov Timofey , Kislov Roman
Published: March 2022

The number of current sheets observed at 1 AU depends on the corresponding type of the solar wind plasma flow or stream in which current sheets occur. Prior studies have shown that the maximum of the current sheet rate is detected in turbulent and hot flows and streams such as corotating/stream interaction regions (CIRs/SIRs) and the coronal mass ejection (ICME) sheath (Khabarova et al. JGR, 2021,  https://doi.org/10.1029/2020JA029099).  It is also known that the number of current sheets per hour begins to rise several hours before the arrival of potentially geoeffective CIRs/SIRs and ICMEs. This effect has been interpreted in literature as a crossing of so-called magnetic cavities filled with coherent structures (Khabarova et al. Sp Sci Rev. 2021, https://doi.org/10.1007/s11214-021-00814-x).

On the other hand, it is known that geomagnetic storms are preceded by ULF variations in the interplanetary magnetic field and solar wind density. We show that such ULF variations are associated with crossings of magnetic islands and current sheets inside magnetic cavities formed in front of geoeffective high-speed streams and flows.
A statistical analysis of the occurrence of current sheets prior to geomagnetic storms has been carried out employing the multi-year database of current sheets at 1 AU for 2011-2013 (see https://csdb.izmiran.ru) . 43 geomagnetic storms with Dst index lower than  -50nT were detected during that period . The results show that there is an 80% increase in the number of current sheets before a geomagnetic storm commencement with a 10-hour advance time, on average. Therefore, current sheets can potentially be used as geomagnetic storm precursors.

A mid-term geomagnetic storm forecast technique using a Recurrent Neural Network for an automatic pattern search is proposed, based on this phenomenon. The minute data of the solar wind density, the number of current sheets, and the window Fourier transform results are taken as input data. Examples of the mid-term prognosis of geomagnetic storms are presented.
The role of stream heterogeneity in gas emissions from headwater streams.
Authors: Botter Gianluca , Carozzani Anna , Peruzzo Paolo , Durighetto Nicola
Published: March 2022

Headwater streams represent a key component of the global carbon cycle, as they are hotspots for the evasion of carbon dioxide from surface waters. Gas emissions from rivers and streams are modulated by the gas transfer velocity at the water-air interface, k, which is physically related to the energy dissipated by the flow field, ε. Here we study how local relations between gas transfer rate and energy dissipation can be spatially averaged in presence of heterogeneous flow fields, e.g. as induced by changes in the local slope. Furthermore, we develop mathematical tools for the quantification of the fraction of gas emission that is related to localized energy losses (e.g. sudden drops and step-pool formations). The study complements numerical simulations and direct measures of stream CO2 outgassing in an Italian headwater catchment. Our theoretical results indicate that reach-scale relations between k and ε in general differ from the corresponding local scaling laws. In particular, we show that high energy heterogeneous streams are characterized by a gas transfer velocity significantly higher than that of an equivalent homogeneous stream. The empirical data suggest that the outgassing is highly heterogeneous along a river network, with the outgassing generated by localized gas emissions in correspondence of hydraulic discontinuities that might be a dominant contribution to the total gas evasion in many settings. These results offer a clue for the interpretation of empirical data about stream outgassing in heterogeneous reaches and complex river networks.
Sensitivity analysis of a forward stratigraphic model to study carbonate production in the Oligo-Miocene Maldives carbonate platform
Authors: Van der Looven Thomas , Winterleitner Gerd , Mutti Maria
Published: March 2022

Forward stratigraphic models quantify geological processes over time to reproduce the stratigraphic architecture of a sedimentary body. Due to the great number of interacting input parameters and their uncertainties, their individual impact on the stratigraphy can be obscured. A sensitivity analysis of such models can identify key factors in the stratigraphic evolution of real-world examples.

The isolated Maldives carbonate platform offers an ideal case study to disentangle the complex web of stratigraphic controls. The stratigraphic architecture of the western margin is well-documented by seismic and well data, providing a robust framework for model calibration. The platform evolution from the latest Oligocene to the Middle Miocene correlates remarkably well with eustatic sea-level changes, suggesting eustasy as the primary control. Nevertheless, the studied time interval is also notorious for climatic changes affecting carbonate production, and the development of drowning sequences around the globe. Previous modelling efforts have illustrated the great uncertainty of carbonate production rates and its significant impact on stratigraphic architecture. In case of the Maldives carbonate platform, we investigate this uncertainty through automated multi-realizations of a forward stratigraphic model combined with a sensitivity analysis.

Firstly, a reference model was designed with a selection of input parameters that reflect the most relevant geological processes to the studied section. This includes the evolving basin conditions (such as eustasy, subsidence and hydrodynamics), and the production and transport of carbonate sediments. For our model purpose, we subdivided the tropical carbonate factory into smaller-scale sediment classes with distinct biological, ecological and physical properties. Each class is characterized by spatial production constraints that interact with the simulated basin conditions over time. The maximum production potentials of the sediment classes remain poorly constrained and are therefore used as calibration variables. Calibration of the reference model exposed the uncertainty and significant impact of these parameters on the platform stratigraphy.

Subsequently, we conducted a sensitivity analysis on the carbonate production rates to quantitatively assess their individual and combined effect. Due to the different biotic nature of the sediment classes, the carbonate production rates can be assumed to fluctuate independent, parallel or inversely, depending on the root cause of the change. We investigated this further by generating multiple automated realizations for all scenarios. The results enable us to speculate on the cause of the carbonate sediment fluctuations and the nature of associated environmental changes across the studied time interval.
The Impact of Solar and Magnetospheric Conditions on High-Latitude Irregularity Spatial-Scales as Observed Using Advanced Radar Techniques
Authors: Goodwin Lindsay , Perry Gareth
Published: March 2022

To provide new insights into the relationship between geomagnetic conditions and plasma irregularity scale-sizes, high-latitude irregularity spectra are developed using a novel Incoherent Scatter Radar (ISR) technique. This new technique leverages: 1) the ability of phased array Advanced Modular ISR (AMISR) technology to collect volumetric measurements of plasma density, 2) the slow F-region cross-field plasma diffusion at scales greater than 10 km, and 3) that high-latitude geomagnetic field lines are nearly vertical. The resulting irregularity spectra are of a higher spatial-temporal resolution than has been previously possible with ISRs, capable of resolving approximately 20 km structures in less than two minutes (depending on the radar mode). By comparing irregularity spectra from high-latitude Resolute Bay ISR data to solar and magnetospheric conditions, we have found that although structures 100s of km wide can be prevalent for a variety of geomagnetic conditions, polar cap structures 10s of km will become more prevalent during quiet geomagnetic conditions. Furthermore, structures that are 10s of km wide will also become more dominant near midnight, reflecting the role of polar cap convection in breaking down structures as they travel from the dayside ionosphere to the nightside. This presentation will expand on these and other findings, as well as discuss the future goals of this work.
An intrusive complex imaged within the roots of an oceanic core complex using 3D full-waveform inversion 
Authors: Paulatto Michele , Oxford Toby , Bardner Rory
Published: March 2022

3D full waveform inversion (FWI) has been applied to the seismic refraction data of the MARINER (Mid-Atlantic Ridge INtegrated Experiment at Rainbow) experiment to create a robust high-resolution model of the seismic velocity structure of the Rainbow massif. The Rainbow massif is an oceanic core complex located on a non-transform discontinuity (NTD) in a magma-starved region of the mid-Atlantic Ridge. Despite the low magmatic input, the core complex hosts a high-temperature hydrothermal vent field  (>340°C) that requires a long-lived magmatic heat source. The FWI results show that deep within the massif, ∼3-8 km below the seafloor, is a low-velocity body that represents a partially molten sill complex with >20% gabbro intrusions. The complex extends out north to the AMAR Minor N segment suggesting an increased magmatic input into this segment, forcing the NTD to migrate southwards. Extensive magmatic intrusion into the core complex was likely responsible for the termination of slip on the detachment fault. Above the sill complex, we image a channel of lower velocity material that cuts through the main hydration front to the deep sill region. Velocity values and micro-seismicity correlation suggests that this channel consists of 10-30% serpentinized peridotite and fracturing from serpentinization reactions create fluid pathways for fluids to exchange between the deeper partially molten heat source and the fluid network of the hydrothermal vents. A high-velocity chimney below the extinct vent sites of the massif may represent the abandoned stockwork of these extinct hydrothermal systems.
Monitoring and integrating the expansion of vegetated areas with the rate of groundwater use in arid regions
Authors: Morsy Mona , Michaelides Silas , Scholten Thomas , Dietrich Peter
Published: March 2022

Frequent water table measurements are crucial for sustainable groundwater management in arid regions. These locations have developed a problem with excessive withdrawal throughout time. However, continuous readings are not available for the majority of these locations. Therefore, an approximate estimate of the rate of increase/decrease in water consumption over time may serve as a temporary substitute for the missing database. The goal is achieved by tracking the increase/decrease in vegetated areas that will generally correlate with changes in the rate of water use. The technique is based on two remote sensing data sets: Landsat7&8 from 2001 to 2021 and Sentinel2A from 2015 to 2021, as well as five vegetation indices: Normalized Difference Vegetation Index (NDVI), Renormalized Difference Vegetation Index (RDVI), Soil Adjusted Vegetation Index (SAVI), Enhanced Vegetation Index (EVI), and Transformed Vegetation Index (TVI). The datasets chosen provided the best performance for small-scale land farms at the research location. (Landsat7) data with a resolution of 30m revealed a substantial increase in land farms from 2.9km2 in 2001 to 23.3km2 in 2021. The use of the five indices with (Sentinel2A) allowed the classification of vegetated regions as heavy, moderate, or light, as well as the tracking of each class's increase from 2015 through 2021. Additionally, preliminary scenarios were built to measure the pace of growth in water use at the research site by evaluating the rise in vegetated areas and obtaining general information about crop types from farmers. Finally, the NDVI index was modified to better suit the arid areas. The new index is named Arid Vegetation Index or (AVI).
DCG-MIP: The Debris-Covered Glacier melt Model Intercomparison exPeriment 
Authors: Pellicciotti Francesca , Fontrodona-Bach Adria , Rounce David R , Fyffe Catriona L. , McCarthy Mike , Miles Evan , Shaw Thomas E.
Published: March 2022

As glaciers respond to climate change, the scientific community has dedicated increasing attention to the development of melt models for debris-covered glaciers. Here, we present an intercomparison aimed at advancing our understanding of the skills of models of different complexity to simulate ice melt under a debris layer. We compare 14 models with different degrees of complexity at nine sites in the European Alps, Caucasus, Chilean Andes, Nepalese Himalaya and the Southern Alps of New Zealand, over one melt season. We run the models with meteorological data from automatic weather stations and estimated or measured debris properties. Model performance is evaluated using on-site measurements of sub-debris melt (for all models) and surface temperature (for models based on the surface energy balance) at each site. We find that the two main categories of models considered, physically-based energy balance (EB) models and empirical temperature index (TI) models perform in a distinct manner. Temperature index models are reliably accurate when they are recalibrated, and show a range of results when parameters are uncalibrated. The most accurate energy balance models are those with the highest degree of complexity at the atmosphere-debris interface. However, we also find that additional complexity within the debris and at the debris-ice interface does not improve performance, which results from a lack of data to accurately force the models to represent these processes. The difficulty to properly estimate the physical properties of debris layers and within-the-debris processes are a likely cause. One of our main conclusions is thus that sophisticated models need high quality input data. An important data gap emerged from our experiment: the poor performance of all models at three sites was related to poor knowledge of debris properties; specifically, of thermal conductivity. Since debris properties are a major control on melt model simulations, we demonstrate that consistent data acquisition efforts are required to more rigorously evaluate existing models and support new model developments. Future work should seek to advance models by improving how they account for processes such as debris-snow interactions, moisture in the debris and refreezing. We suggest that a systematic effort of model development using a single model framework could be carried out in phase II of the Working Group.
LanderPick, a Remote Operated Trawled Vehicle to cost-effectively deploy and recover lightweight oceanographic landers
Authors: Gonzalez-Pola Cesar , Sánchez Francisco , Rodriguez Cobo Luis , Graña Rocío , Rodriguez Juan Manuel , Valdiande-Gutierrez Jose , Hernandez-Urbieta Daniel , Aierbe Eneko
Published: March 2022

Landers are modular structures equipped with miscellaneous sensors and monitoring equipment which are positioned directly on the seabed to operate autonomously for a defined timeframe. A drawback of landers intended to operate for prolonged periods in the deep ocean is the high cost of recovery systems, typically depending on buoyancy modules plus expendable ballast, or requiring ROVs assistance. LanderPick concept consists of the design of a specific trawled vehicle to deploy and recover lightweight oceanographic landers not provided with recovery elements, but having a capture mesh that facilitates their hitching. The LanderPick vehicle is technically a ROTV (Remote Operated Trawled Vehicle) controlled through a standard coaxial electromechanical cable that allows real-time control from the vessel. Navigation is enabled by a low-light high-definition camera, aided by spotlights and laser pointers. Small propellers aid in the final precision approach maneuvers. A mechanical release allows the precise placement at the sea bottom of landers carried as a payload, as well as their recovery by means of a triple hook. First sea missions of the system were carried out successfully in 2021 in southern Biscay. A 4-month deployment of a lander array equipped with current-meters along an energetic canyon axis provided unprecedented detail in the progression of the internal tidal bore. Short (48-hours) deployments of a fully-instrumented lander, including lapse-time image and baits in a deep seamount summit within a marine protected area, provided insights on the biodiversity of a unique ecosystem. The LanderPick novel approach to cost-effectively and precisely deploy and recover lightweight oceanographic landers allows to conceive (i) monitoring systems based on the deployment of arrays or fleets of low-cost landers and (ii) experiments associated with deep habitats such as coral reefs in which it is necessary to locate landers with great precision.
Stratospheric composition feedbacks in a changing climate: a review
Authors: Chiodo Gabriel , Friedel Marina
Published: March 2022

The important role of stratospheric feedbacks for the climate system – most notably how the ozone layer responds to anthropogenic forcings, and how that response then feeds back on the climate itself – remains largely unexplored, apart from the effects associated with gases regulated by the Montreal Protocol. This is because, to date, most models participating to CMIP inter-comparisons do not account for the complex interplay between stratospheric composition, dynamics and radiation. Here, we are providing a review of recent work highlighting the importance of such interplay on a broad range of time-scales, encompassing short-term variability to long-term climate change. First, we will show that increasing carbon dioxide levels lead to substantial changes in the ozone layer, and that these changes have a substantial effect on the circulation response to that forcing in both hemispheres (Chiodo & Polvani 2017; 2019). Then, we will review recent work on stratospheric water vapor (SWV) feedbacks under global warming, showing contrasting results concerning the effects on surface climate. Lastly, we will explore the connection between Arctic ozone and surface climate, highlighting the impacts of springtime ozone depletion on surface climate, and the sizable contribution of ozone feedbacks. Such findings demonstrate that stratospheric composition feedbacks play a key role in shaping climate response to anthropogenic forcings and stratosphere-troposphere coupling, both via radiative and dynamical processes. However, the coupling between ozone, SWV and climate is still subject to large uncertainties. We will discuss sources of uncertainty and model limitations, and implications for CMIP6.
New insights on the practical significance of numerical methods for surface water pollution source identification
Authors: Yang Ruiyi , Jiang Jiping , Pang Tianrui , Men Yunlei , Zheng Yi
Published: March 2022

The source identification of surface water pollution is the key issue in environmental management and has important practical needs. Model-based numerical inversion methods have received widespread attention that there are many research reports. However, most of the existing research on the pollution source identification (PSI) problem focuses on the combination innovation and theoretical analysis of the inversion algorithm, and does not consider the urgent time constraints of the emergency response process, which has become an important technical bottleneck. To this end, this study focuses on the timeliness and operability of numerical inversion methods in the emergency response process, and makes full use of multi-source information of pollutants to explore robust and fast sampling and numerical inversion methods in practical operations. The study adopts the Adative Metroplis Monte Carlo (AM-MCMC) Bayesian method as the basic source identification inversion framework, and takes the USGS tracer test in Truckee River from 2006 to 2007 as the basic scenario to carry out numerical experiments. Through the data assimilation method, the pollution source information is dynamically updated. With the input of new monitoring data, the accuracy of the inversion results is gradually improved; By integrating multiple pollutants information, greatly improves the robustness and practical ability of the numerical source identification technology. The study establishes the best practice method of parallel sampling, which can achieve reliable numerical inversion accuracy in the early stage of sampling. The quantitative design criteria of the minimum sampling cost required for inversion to meet a certain error limit under different river hydrological conditions are discussed, and the relative critical time Λ of sampling and Peclet number (Pe) that characterizes river hydrodynamics are found as follow relation: Λ=-0.816×Pe-1/2-0.978×Pe-1/2lnPe-1/2+0.554, R2=0.938, and has been proved by information entropy theory. The precise design process of the emergency PSI monitoring scheme with the timeliness as the optimization goal is further proposed. This study provides important theoretical guidance for the innovative application of new monitoring methods in scenarios such as leakage detection and emergency monitoring under the background of environmental Internet of Things.
Accounting for long-term climatic trends in Probable Maximum Precipitation estimation
Authors: Bhatt Jaya , Srinivas Venkata Vemavarapu
Published: March 2022

The compounding evidence on the aberrant behavior of extreme precipitation has drawn attention of hydrometeorologists towards re-evaluating the existing hydraulic design criteria for protection of large structures (e.g., spillways of dams, nuclear power plants) in changing climate. Traditionally, design flood estimates for those structures were based on Probable Maximum Precipitation (PMP) to minimize or avert the risk of failure and consequent catastrophic damage to mankind and the environment. PMP, as defined by the World Meteorological Organization (WMO), does not account for long-term climatic trends. However, in recent decades, there has been an increase in frequency and magnitude of extreme precipitation events in different parts of the globe. This necessitates devising potential strategies to arrive at effective PMP estimates to re-assess the existing design criteria.  Against this backdrop, researchers have been actively developing new methods or modifying the existing ones to adapt to changing climate. The majority of these methods are physics-based whose application demands voluminous data on various hydrometeorological variables and computationally intensive systems to run simulations on weather models. In comparison, statistical approaches are simple and not data intensive. Among available statistical approaches, Hershfield method is widely used due to its ease of application. There is a dearth of attempts to extend it for use in climate change scenarios.

In the present study, a new variant of Hershfield method is proposed which yields reliable PMP estimates by accounting for long-term trends in precipitation data for better estimation of at-site frequency factor in the climate change scenario. The applicability of the proposed method is illustrated over India considering 119 years (1901-2019) long 0.25-degree gridded precipitation records from IMD (India Meteorological Department). The country has more than 5000 dams, and currently PMP estimates are being considered for risk analyses of several ageing dams through the aid of the World Bank, under DRIP (Dam Rehabilitation and Improvement Project). The proposed methodology is applied to arrive at PMP estimates for sites/grids in homogeneous precipitation regions delineated in the country using cluster analysis. The overall impact of increasing/decreasing trend of precipitation on the regional estimate of frequency factor and one-day PMP estimates is clearly demonstrated using the proposed and conventional Hershfield methods.
Magnetosheath jets during an CME passage: A case study
Authors: Preisser Luis , Plaschke Ferdinand , Koller Florian , Temmer Manuela , Roberts Owen
Published: March 2022

Localized enhancements in dynamic pressure observed in the Earth’s magnetosheath (EMS) have been studied since 20 years ago. These structures known as jets can propagate through the EMS transporting mass, momentum and energy being able to reach and perturb the Earth’s magnetopause.
Large scale solar wind (SW) structures called Coronal Mass Ejections (CMEs) travel through the interplanetary medium and depending on their direction they may impact the Earth. How the different SW conditions triggered by the CMEs (upstream side – shock/sheath – magnetic ejecta) change the production of jets in the EMS is a topic that is just beginning to be explored.
In this case study we characterize jets observed by THEMIS A, E and D during a CME passage. We find clear differences in number and size between the jets associated with the different CME regions arriving at the EMS. Comparing WIND and THEMIS data we discuss how these differences are associated with the SW conditions and with different jet generation mechanisms.
Trends in suspended sediment fluxes and sediment budgets across the river Rhine basin (1990-present)
Authors: Edler Tatjana , Van der Perk Marcel , Middelkoop Hans
Published: March 2022

Suspended sediment transport is a vital process in healthy river systems as it provides a source of nutrients in the soils of riverbanks and floodplains that eventually forms the principal building material of downstream river deltas. Deltas require sufficient sediment supply from the upstream river basin to sustain area and elevation on the long-term. Recent decades, the delivery of suspended sediment to many deltas in the world has decreased, which, together with sediment extraction through dredging, resulted in negative sediment budgets of these deltas. To design strategies to attenuate or reverse the decreased sediment delivery, a quantitative understanding of the sources, fluxes, and budget of suspended sediment in river basins is essesntial.

The aim of this study is to quantify the contribution of different tributaries to the suspended sediment budget in the Rhine river basin between 1995 and 2015. For this, we used fortnightly to monthly measurements of suspended sediment concentrations and daily discharge measurements at 34 stations along the main branch of the Rhine river and its four major tributaries Aare, Neckar, Main, Mosel. Annual suspended sediment loads were estimated by means of the sediment rating curve method, which allowed establishing the annual sediment budgets for 28 river sections.

For the first time we were able to show the relative contribution of different tributaries to the overall decreasing suspended sediment load of the upper Rhine river (between 1995 and 2015). A decline of 70% percent in suspended sediment at Lobith between 1950 and 2016 and an observed consistent decline further upstream suggests an overall decline of sediment delivered to the lower lying delta. The causes must be sought in basin wide changes such as land-use, land management, hydrology, or climate. This is a trend that is observed in many river basins in recent decades.

 

 
A methodological framework  for mapping frost occurrence utilizing a cloud-based platform & geospatial data
Authors: Petropoulos George P. , Detsikas Spyridon E. , Sandric Ionut
Published: March 2022

Frost is one of the most damaging hazards in agriculture as its impacts negatively cropland yield and agro-ecosystems, affecting price commodities of agricultural products. Locating the spatiotemporal patterns of frost events can be a challenging and costly task since a dense network of weather stations is required to accurately characterize frost distribution. The recent advancements in geoinformation technology have enhanced our ability to retrieve parameters that are critical to the development of frost conditions such as land surface temperature (LST). In addition, the availability of cloud-based imagery processing platforms allows to easily acquire and process LST data over large scales setting the EO field as the optimal mean for frost risk mapping. The present study imprints the frost’s spatial patterns analyzing geospatially referenced frost incident field-based data conducted by the Greek National of Agricultural Payments Agency (ELGA) during the period 2015-2020. In addition, a cloud-based methodological framework is introduced herein based on a time series analysis with LST data from ESA's Sentinel-3 LST operational product to map frost occurrence. The proposed approach was implemented for the same time period as that of the ELGA data. The frost frequency maps developed by the two approaches were  compared using appropriate geospatial data analysis methods in order to determine their correspondence. Results generally demonstrated the added value of EO data in identifying the frost risk degree and geographical extent for all the years analysed. Our proposed methodology has a promising potential to be used at operational scale to map frost risk conditions and to also support decision making in frost hazard mitigation.

KEYWORDS:  cloud-based platform, LST,  Sentinel 3, frost risk, geospatial analysis
Data-driven gap filling and spatio-temporal filtering of the GRACE-GRACE-FO records
Authors: Gauer Louis-Marie , Chanard Kristel , Fleitout Luce
Published: March 2022

The Gravity Recovery And Climate Experiment (GRACE; April-2002-June 2017) and current GRACE-Follow On (GRACE-FO; June 2018-present) missions have provided monthly global measurements of the space and time varying Earth’s gravity field, monitoring changes in the ice-sheets and glaciers, hydrological water storage, sea level and within solid Earth. Yet, temporal gaps, including the long 11 months gap between missions, prevent the interpretation of long-term mass variations. Moreover, despite the data processing strategy adopted, GRACE and GRACE-FO solutions show high level of distinctive unphysical noise.  
Consequently, we use the Multi-Channel Singular Spectrum Analysis (MSSA) and exploit both spatial and temporal information contained in multiple solutions of GRACE and GRACE-FO to fill the observational gaps and develop a data-driven spatio-temporal filter to enhance the data signal-to-noise ratio. 
First, we use the well-established decorrelation DDK7 filter to remove a large part of the distinctive noise in a North-South striping patterns. Because we detect persisting noise at high orders, we develop a complementary filter based on the residual noise between fully-processed data and parametric fit to the observations. We then fill observational gaps using an iterative M-SSA approach and series of equivalent water height from four Level-2 solutions (CSR, GFZ, JPL, TU-GRAZ). The method is validated on a synthetic test, where we remove and reconstruct one year of the time series. By using multiple solutions in the process, we form a combined solution based on their common modes of variability. Finally, we take full advantage of the M-SSA to reduce residual spatially uncorrelated noise, namely stripes, by conserving common signals between times series of each point on the globe and its neighbors.  
Comparison of the GRACE-GRACE-FO M-SSA solution with independent observations of the low-degree Earth’s gravity field via Satellite Laser Ranging validates the method’s potential to recover missing observations. Furthermore, comparisons with other solutions show a significant noise reduction compared to spherical harmonic solutions, and the ability to retrieve short-wavelengths geophysical signals masked by Mascons-type processing strategy.
The effect of natural surfactants on air-water momentum exchange under light wind conditions in Lake Geneva
Authors: Foroughan Mehrshad , Lemmin Ulrich , Barry David Andrew
Published: March 2022

Randomly distributed patches of smooth or rough/rippled surfaces are readily observed on most water bodies. Smooth surface patches are called natural slicks and typically form under low wind conditions (< 6 m s-1) when biogenic surfactants in the surface microlayer accumulate above a certain threshold. They may have spatial scales from tens of meters to kilometers. Slicks suppress the formation of wind-induced Gravity-Capillary Waves (GCW), leading to altered surface reflectance of light and microwaves and can also affect near-surface turbulent motions. Therefore, it is of interest to determine the effect slicks can have on the air-water exchange of momentum, heat, and gas, which can influence the biogeochemical dynamics in the near-surface layer of lakes and oceans.

We investigated the spatiotemporal variability in momentum flux caused by slicks in Lake Geneva during several field campaigns using eddy covariance instrument setups mounted on an autonomous catamaran. The measurements were combined with aerial and shore-based imagery (both RGB and thermal). In addition, surface microlayer sampling was conducted from an accompanying boat to determine whether visually-identified smooth patches were associated with higher enrichments of fluorescent dissolved organic matter, a proxy for natural surfactants. Wavelet analysis was used to explore short-time (~1 min) averaged air-water exchange variations related to the transition from smooth slicks to rough surface areas that cannot be captured by the conventional eddy covariance analysis method.

Our results suggest that under light wind conditions and in the absence of short GCW on the surface of slicks, wind stress cannot be effectively transferred to the water, leading to reduced momentum exchange inside slicks compared to the surrounding non-slick areas. This results in lateral gradients in vertical mixing that can affect air-water exchange processes and contribute to spatial variability in surface temperature and near-surface heat content.

 
Impact of sub-seasonal atmosphere-ocean interactions in a large ensemble
Authors: Aengenheyster Matthias , Sparrow Sarah , Watson Peter , Wallom David , Zanna Laure , Allen Myles
Published: March 2022

Air-sea coupling is critical in influencing atmospheric temperature and precipitation. The effect of greenhouse gases has influenced atmospheric variability and extreme events. Understanding and quantifying the effect of air-sea feedback on atmospheric variability and extremes remains unknown.

In this work we show results obtained from two numerical experiments. We use the HadSM4 configuration that couples the HadAM4 model at N144 resolution with a Slab Ocean to generate a large ensemble (~1000 members) of realizations of the 2013-14 October-March winter season, forced with a calibrated ocean heat convergence flux.

A twin experiment is performed by forcing HadAM4 with the diagnosed SST and sea ice from the ensemble, yielding a new ensemble with identical realizations of SST and sea ice. The only difference between the two ensembles is the enabling or disabling of the feedback of air-sea heat fluxes on SST.

While the impact of the feedback on the mean climate is relatively small, we show that its influence has important consequences for the variability of many important quantities, including air-sea fluxes and return periods of extreme events.