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Spatial and temporal analysis of the sand dynamics in alpine rivers for 3D numerical modelling
No full textInternational audienceHydraulic structures can impact the sediment continuity of the river and can create a sediment imbalance downstream of dams according to the different sediment classes (silt, sand, gravel). For operators, one important issue is the presence of sand (d>63 μm), which can lead to exploitation difficulties, issues for flushing or emptying operations as well as to ecological, in-dustrial or safety issues. It was recognized that the percentage of sand particles that is transported by suspension compared to bedload transport can often prevail. However, today it is still a real challenge to evaluate the spatial and temporal variability of these sand concentrations in gravel-bed rivers since sand dynamics are generally supply limited. Using 3D hydro-sedimentary modelling could help to better understand processes of sand transport in rivers. In this article, we will present results from experimental monitoring that will then be used for 3D numerical modelling (TELEMAC 3D + Gaia) on engineered rivers in the Northern French Alps
Quantification Approaches in Non-Target LC/ESI/HRMS Analysis: An Interlaboratory Comparison
No full textInternational audienceNontargeted screening (NTS) utilizing liquid chromatography electrospray ionization high-resolution mass spectrometry (LC/ ESI/HRMS) is increasingly used to identify environmental contaminants. Major differences in the ionization efficiency of compounds in ESI/ HRMS result in widely varying responses and complicate quantitative analysis. Despite an increasing number of methods for quantification without authentic standards in NTS, the approaches are evaluated on limited and diverse data sets with varying chemical coverage collected on different instruments, complicating an unbiased comparison. In this interlaboratory comparison, organized by the NORMAN Network, we evaluated the accuracy and performance variability of five quantification approaches across 41 NTS methods from 37 laboratories. Three approaches are based on surrogate standard quantification (parent-transformation product, structurally similar or close eluting) and two on predicted ionization efficiencies (RandFor-IE and MLR-IE). Shortly, HPLC grade water, tap water, and surface water spiked with 45 compounds at 2 concentration levels were analyzed together with 41 calibrants at 6 known concentrations by the laboratories using in-house NTS workflows. The accuracy of the approaches was evaluated by comparing the estimated and spiked concentrations across quantification approaches, instrumentation, and laboratories. The RandFor-IE approach performed best with a reported mean prediction error of 15× and over 83% of compounds quantified within 10× error. Despite different instrumentation and workflows, the performance was stable across laboratories and did not depend on the complexity of water matrices
Estações multimodais: Uma Estratégia de Planejamento Urbano para Promover a Intermodalidade em Territórios de Baixa Densidade?
No full textInternational audienceThe development of "mobility stations" appears as one of the options in the "catalogue of available solutions" for mobility actors in low-density spaces (Zittoun, 2013). Sometimes existing under different terms, these multimodal arrangements are defined by Cerema as "the convergence of shared and active mobility services (such as carpooling, car-sharing, or bike-sharing) in a single accessible location to enhance alternatives to solo driving" (Cerema, 2022). While these arrangements are only relevant when considered in a "networked" approach (Hached et al., 2023), what about reflections on the intermodality of low-density territories when it comes to their design? Are these arrangements intended to promote intermodality across the entire territory? In other words, to what extent do mobility actors organize themselves in the creation of mobility areas to ensure intermodality in low-density spaces? This research focuses on the Vallée de l'Hérault and the Pays de Lumbres to attempt to answer this question through documentary study and semi-structured interviews. First, we provide an overview of the mobility areas in these territories. Next, we discuss the actors and tools that facilitated their development. Finally, we identify key elements in the creation of these arrangements that interfere with the development of intermodality in the studied territories.L'aménagement d' « aires de mobilités » apparaît comme l'une des options du « répertoire de solutions disponibles » pour les acteurs des mobilités dans les espaces peu denses (Zittoun, 2013). Parfois existantes sous d'autres termes, ces aménagements multimodaux sont définis par le Cerema comme étant « la convergence de services de mobilité partagée et active (comme le covoiturage, l'autopartage ou les vélos en libre-service) en un même lieu accessible afin de valoriser les offres alternatives à l'autosolisme » (Cerema, 2022). Si ces aménagements ne sont pertinents que lorsqu'ils sont réfléchis « en maillage » (Hached et al, 2023), qu'en est-il des réflexions sur l'intermodalité des territoires peu denses lorsqu'il s'agit de les concevoir ? Ces aménagements sont-ils pensés pour favoriser l'intermodalité sur l'ensemble du territoire ? En d'autres termes, dans quelles mesures les acteurs de la mobilité s'organisent dans la fabrique des aires de mobilité pour assurer l'intermodalité dans les espaces peu denses ? Cette recherche s'intéresse à la Vallée de l'Hérault ainsi qu'au Pays de Lumbres pour tenter de répondre à cette question en s'appuyant sur de l'étude documentaire et d'entretiens semi-directifs. Nous dressons dans un premier temps un état des lieux des aires de mobilité de ces territoires. Dans un second, nous revenons sur les acteurs et les outils qui ont permis leur développement. Enfin, nous constatons les éléments clefs dans la fabrique de ces aménagements qui interférent dans le développement de l'intermodalité dans les territoires étudiés
Designing a Fully-Tunable and Versatile TKE-l Turbulence Parameterization for the Simulation of Stable Boundary Layers
No full textInternational audienceThis study presents the development of a so-called Turbulent Kinetic Energy (TKE)-l, or TKE-l, parameterization of the diffusion coefficients for the representation of turbulent diffusion in neutral and stable conditions in large-scale atmospheric models. The parameterization has been carefully designed to be completely tunable in the sense that all adjustable parameters have been clearly identified and the number of parameters has been minimized as much as possible to help the calibration and to thoroughly assess the parametric sensitivity. We choose a mixing length formulation that depends on both static stability and wind shear to cover the different regimes of stable boundary layers. We follow a heuristic approach for expressing the stability functions and turbulent Prandlt number in order to guarantee the versatility of the scheme and its applicability for planetary atmospheres composed of an ideal and perfect gas such as that of Earth and Mars. Particular attention has been paid to the numerical stability and convergence of the TKE equation at large time steps, an essential prerequisite for capturing stable boundary layers in General Circulation Models (GCMs). Tests, parametric sensitivity assessments and preliminary tuning are performed on single-column idealized simulations of the weakly stable boundary layer. The robustness and versatility of the scheme are assessed through its implementation in the Laboratoire de Météorologie Dynamique Zoom GCM and the Mars Planetary Climate Model and by running simulations of the Antarctic and Martian nocturnal boundary layers. Plain Language SummaryIn planetary atmospheres, turbulent motions actively contribute to the mixing of quantities such as heat, momentum, and chemical species. Such motions are not resolved in coarsegrid atmospheric models and have to be parameterized. The parameterization of turbulent mixing should ideally be based on physical laws and sufficiently sophisticated to realistically represent the full spectrum of motions over the full range of stability encountered in the atmospheres. However, it also necessarily contains a number of closure parameters not always well identified and whose values are determined empirically-thereby questioning the universality of the parameterization and its potential application over the full globe or even to other planets-or adjusted to guarantee the numerical stability of the model. This study presents the design of a turbulent mixing parameterization that can be fully calibrated and applied in planetary atmospheres such as that of Mars. We then calibrate the parameterization on an idealized simulation set-up and test its robustness and performance by running simulations of the Antarctic and Martian atmospheres
Impact of air quality model settings for the evaluation of emission reduction strategies to curb air pollution
No full textInternational audienceFor air quality management, while numerical tools are mainly evaluated to assess their performances on absolute concentrations, this study assesses the impact of their settings on the robustness of model responses to emission reduction strategies for the main criteria pollutants. The effect of the spatial resolution and chemistry schemes is investigated. We show that whereas the spatial resolution is not a crucial setting (except for NO), the chemistry scheme has more impact, particularly when assessing hourly values of the absolute potential of concentrations. The analysis of model responses under the various configurations triggered an analysis of the impact of using online models, like WRF-chem or WRF-CHIMERE, which accounts for the impact of aerosol concentrations on meteorology. This study informs the air quality modeling community on what extent some model settings can affect the expected model responses to emission changes. We suggest to not activate online effects when analyzing the effect of an emission reduction strategy to avoid any confusion in the interpretation of results even if an online simulation should represent better the reality
Exploring The Potential Of History Matching For Land Surface Model Calibration
No full textInternational audienceWith the growing complexity of land surface models used to represent the terrestrial part of wider Earth system models, the need for sophisticated and robust parameter optimisation techniques is paramount. Quantifying parameter uncertainty is essential for both model development and more accurate projections. In this study, we assess the power of history matching by comparing results to the variational data assimilation approach commonly used in land surface models for parameter estimation. Although both approaches have different setups and goals, we can extract posterior parameter distributions from both methods and test the model-data fit of ensembles sampled from these distributions. Using a twin experiment, we test whether we can recover known parameter values. Through variational data assimilation, we closely match the observations. However, the known parameter values are not always contained in the posterior parameter distribution, highlighting the equifinality of the parameter space. In contrast, while more conservative, history matching still gives a reasonably good fit and provides more information about the model structure by allowing for non-Gaussian parameter distributions. Furthermore, the true parameters are contained in the posterior distributions. We then consider history matching's ability to ingest different metrics targeting different physical parts of the model, thus helping to reduce the parameter space further and improve the model-data fit. We find the best results when history matching is used with multiple metrics; not only is the model-data fit improved, but we also gain a deeper understanding of the model and how the different parameters constrain different parts of the seasonal cycle. We conclude by discussing the potential of history matching in future studies
Dynamical Phenomena in the Martian Atmosphere Through Mars Express Imaging
No full textInternational audienceThis review describes the dynamic phenomena in the atmosphere of Mars that are visible in images taken in the visual range through cloud formation and dust lifting. We describe the properties of atmospheric features traced by aerosols covering a large range of spatial and temporal scales, including dynamical interpretations and modelling when available. We present the areographic distribution and the daily and seasonal cycles of those atmospheric phenomena. We rely primarily on images taken by cameras on Mars Express
Implementing and simulating the water isotopes (δ18O and δD) distribution in the Mediterranean Sea using a high-resolution oceanic model
No full textInternational audienceWater isotopes are one of the most widely used proxies in ocean climate research. However, there are still gaps in our understanding of the processes that control their composition. Compared to other large ocean basins, the Mediterranean is ideally suited to improve our understanding of the processes influencing and driving oxygen isotopic variability, and to refine the current modelling approach. For the first time in a high-resolution Mediterranean dynamical model (NEMO-MED12), stable water isotopes (δ18O and δD) were successfully implemented and simulated in the whole basin. The well-known east-west gradient of δ18O in Mediterranean water masses is successfully simulated by the model. Results also show good agreement between simulated and observed δD. δD shows a strong linear relationship with δ18O (r2 = 0.98) and salinity (r2 = 0.94) for the entire Mediterranean basin. Furthermore, the modelled δ18O/salinity relationships are in good agreement with observations, with a weaker gradient simulated in the eastern basins than in the western basins. We investigate the relationship of the isotopic signature of the CaCO3 shell (δ18Oc) with temperature and the influence of seasonality. Our results suggest a more quantitative use of δ18O records, combining reconstruction with modelling approaches. This opens up broad perspectives for paleoclimate-related applications
The effect of stress barriers on unconventional-singularity-driven frictional rupture
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Degree centrality, von Neumann-Morgenstern expected utility and externalities in networks
No full textDocuments de travail du Centre d'Economie de la Sorbonne 2023.12R (Version révisée) - ISSN : 1955-611XVersion originale Août 2023, révisée en Juin 2024.Voir aussi l'article basé sur ce document de travail paru dans European Journal of Operational Research, 2024, 319, 2, 669-677International audienceThis paper aims to connect the social network literature on centrality measures with the economic literature on von Neumann-Morgenstern expected utility functions using cooperative game theory. The social network literature studies various concepts of network centrality, such as degree, betweenness, connectedness, and so on. This resulted in a great number of network centrality measures, each measuring centrality in a different way. In this paper, we aim to explore which centrality measures can be supported as von Neumann-Morgenstern expected utility functions, reflecting preferences over different network positions in different networks. Besides standard axioms on lotteries and preference relations, we consider neutrality to ordinary risk. We show that this leads to a class of centrality measures that is fully determined by the degrees (i.e. the numbers of neighbours) of the positions in a network. Although this allows for externalities, in the sense that the preferences of a position might depend on the way how other positions are connected, these externalities can be taken into account only by considering the degrees of the network positions. Besides bilateral networks, we extend our result to general cooperative TU-games to give a utility foundation of a class of TU-game solutions containing the Shapley value