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Activité d'éclairs et paramètres physiques issus de l'observation radar dans les orages : application au projet HyMeX

Abstract : Regularly in autumn, high precipitating events occur in southeastern France, leading sometimes to floods or flash-floods having a high societal impact. One of the research topics of the Hydrological cycle in the Mediterranean Experiment (HyMeX) project is the improvement of the understanding and of the forecast of these events. The particularity of thunderclouds is the production of lightning flashes, preceded by the electrification of the cloud. Past studies have shown that the simultaneous presence of graupels, ice crystals and supercooled water in the convective areas was necessary to the establishment of the electrification. So a link exists between these parameters and the occurrence of lightning flashes. The goal of this thesis is to identify and quantify the relationships between cloud-to-ground flashes and thunderclouds parameters for storms in France, and especially in the southeast. In this aim, a multi-parameter analysis is performed based on several data sets: cloud-to-ground lightning impacts (from Météorage), 3D radar reflectivity and wind fields deduced from the multiple-Doppler analysis of operational ARAMIS Doppler data (Météo-France) and microphysics information inferred from observations of the dual polarization radars (Météo-France). The study is lead on two regions: Paris region and the southeast of France. Results show a quantifiable linear relationship between volume of radar reflectivity higher than 40 dBZ and cloud-to-ground flash rates, as well as between precipitating ice mass (mainly composed by graupel) and cloud-to-ground flash rates. An application of the "ice fluxes hypothesis", based on the non-inductive mechanism of electrification of the storm, is also tested. It shows encouraging results between the flash rate and the product of precipitating and non-precipitating ice mass fluxes. The comparison of regional results shows a behavior that seems to be more easily generalized for the relationships between high radar reflectivity and the cloud-to-ground flash rate. On the contrary, the relationships based on the ice masses seem to exhibit a regional behavior. The study of the first event considered as representative of the HyMeX campaign allowed to compare the restitution of ice masses based on data sets from two radars of the operational network of Météo-France: one is a C-band radar and the other an S-band radar. This study shows that the precipitating ice mass seems sensitive to the instrument selected to restitute it while the non-precipitating ice mass (ice crystals and dry snow) does not seem so.
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Magalie Buguet. Activité d'éclairs et paramètres physiques issus de l'observation radar dans les orages : application au projet HyMeX. Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2012. Français. ⟨tel-00761486⟩

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