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

Le Sud-Est de la France est régulièrement soumis à des épisodes de pluies intenses en automne, entraînant parfois des inondations ayant un fort impact sociétal. L'un des sujets de recherche du projet HyMeX (Hydrological cycle in the Mediterranean Experiment) porte d'ailleurs sur l'amélioration de la compréhension et de la prévision de tels phénomènes. La particularité du nuage orageux est la production d'éclairs, précédée par l'électrisation du nuage. Des études ont montré que la présence simultanée de graupels, de cristaux de glace et d'eau surfondue dans les zones convectives était nécessaire à l'établissement de l'électrisation. Il existe donc un lien entre ces paramètres et l'occurrence d'éclairs. Le but de cette thèse est d'identifier et de quantifier des relations entre éclairs nuage-sol et paramètres nuageux en France métropolitaine et particulièrement dans le Sud-Est. Pour ce faire une analyse multi-variables a été réalisée à partir de plusieurs jeux de données : électrique (observation d'éclairs nuage-sol, Météorage) et radar (Dopplers : restitution des champs 3D de réflectivité et de vent, et polarimétriques : restitution de la microphysique, Météo-France). L'étude a été menée sur deux régions : la région parisienne et la région Sud-Est. Les résultats obtenus permettent notamment d'établir des relations linéaires quantifiables entre volume de réflectivité supérieure à 40 dBZ et taux d'éclair nuage-sol ainsi qu'entre masse de glace précipitante (principalement composée de graupel) et taux d'éclair. Une application de " l'hypothèse des flux de glace " basée sur le mécanisme d'électrisation non-inductif des orages a également été testée et montre des résultats encourageants entre produits des flux de masse de glace précipitante et non précipitante et taux d'éclair. La comparaison des résultats régionaux a montré un caractère plus facilement généralisable de la relation entre forte réflectivité et taux de CG. Au contraire, les relations basées sur les masses de glace semblent plutôt avoir un caractère régional. L'étude du premier cas considéré comme représentatif de la campagne HyMeX a permis la comparaison de la restitution des masses de glace à partir des données provenant de deux radars du réseau opérationnel de Météo-France (l'un en bande C, l'autre en bande S). Cette étude fait apparaître que la masse de glace précipitante semble sensible à l'instrument utilisé pour la restituer contrairement à la glace non précipitante (cristaux de glace et neige sèche).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

Observation of cloud-to-ground lightning channels with high-speed video camera

Between May and October 2013 (period of sustained thunderstorm activity in France), several cloud-to-ground lightning flashes have been observed in Paris area with a high-speed video camera (14000 frames per second). The localization and the polarity of the recorded cloud-to-ground flashes have been obtained from the French lightning detection network M{\'e}t{\'e}orage which is equipped with the same low frequency sensors used by the US NLDN. In this paper we focused on 7 events (3 positive cloud-to-ground lightning flashes and 4 negative cloud-to-ground lightning flashes). The propagation velocity of the leaders and its temporal evolution have been estimated; the evolution of branching of the negative leaders have been observed during the propagation of the channel which get connected to ground and initiate the first return stroke. One aim of this preliminary study is to emphasize the differences between the characteristics of the positive and of the negative leaders

Analyse du champ électrostatique d'un nuage d'orage lors d'un fourdroiement en vol d'un Flacon 20

International audienceSince the 70’s, ONERA has been involved in the understanding and characterization of the physical processes occurring during a lightning strike to the aircraft which has led to the development of on board sensors for atmospheric characterization. In the 80’s, a first electric field mill network had been designed to measure the electrostatic field inside thundercloud. The system was installed on a CONVAIR (CV580) and a TRANSALL (C160). A new version of this electric field mill network, called AMPERA (Atmospheric Measurement of Potential and ElectRic field on Aircraft), has been developed since 2010. From September to October 2018, an in-flight campaign was performed over Corsica (France) in the framework of EXAEDRE (EXploiting new Atmospheric Electricity Data for Research and the Environment) project to investigate the electrical activity in thunderstorm. During this campaign, 8 scientific flights were done with a FALCON 20 (F20) of SAFIRE inside or in the vicinity of thunderstorm. During the flight of the 8 of October 2018, the aircraft was struck by lightning at an altitude of 8500m. The electrostatic field time variations show that a vertical electric polarization of the aircraft occurred just before the lightning strike. The inverse method to compute the components of the atmospheric electric field from the data of the electric field network is presented. The atmospheric electric field time evolution is shown. The value of the atmospheric electric field just before the lightning strike is about 90kV/m. This electric field value has been processed to be compared with the ones measured during TRANSALL campaigns. The altitude effect is taken into account by computing the reduced electric field (Electric field divided by air density). The comparison is presented taking into account the size of the aircraft and the electric field direction. To conclude a discussion is done on the electric field threshold for a lightning strike to aircraft.Dans les années 70, l'ONERA a mené des recherches pour caractériser et comprendre les processus physiques intervenant lors d'un foudroiement en vol d'un avion ce qui a conduit au développement de capteurs pour caractériser l'atmosphère. Dans les années 80, une première version de moulin à champ a été conçue pour mesurer les composantes du champ électrostatique à l'intérieur du nuage depuis un avion. Le système a été installé sur une CONVAIR (CV580) et sur un TRANSALL (C160). Une nouvelle version du système, appelé AMPERA (Atmospheric Measurement of Potential and ElectRic field on Aircraft), a été développée depuis 2010. De septembre à octobre 2018, une campagne en vol a été réalisée en Corse (France) dans le cadre du projet ANR EXAEDRE (EXploiting new Atmospheric Electricity Data for Research and the Environment) pour étudier l'activité électrique des orages.Pendant cette campagne, 8 vols scientifiques ont été réalisés par a FALCON 20 (F20) de SAFIRE à l'intérieur ou à proximité d'un nuage orageux. Pendant le vol du 8 octobre, l'avion a été foudroyé à une altitude de 8500 m. La variation temporelle du champ électrostatique montre que l'avion est polarisé verticalement au moment du foudroiement. La méthode inverse pour calculer les composantes du champ électrostatique est présentée. La valeur du champ atmosphérique au moment du foudroiement est de 90 kV/m. Ce champ électrique a été normalisé pour être comparé aux champs électriques mesurés lors des campagnes TRANSALL. L'effet de l'altitude a été prise en compte en calculant le champ électrique réduit (Champ électrique divisé par la densité de l'air). La taille de l'avion et la direction du champ électrique a été pris en compte pour la comparaison. Pour conclure, une discussion sur le seuil du champ électrique pour déclencher un foudroiement sur un avion

Cerebral and Peripheral Changes Occurring in Nitric Oxide (NO) Synthesis in a Rat Model of Sleeping Sickness: Identification of Brain iNOS Expressing Cells

International audienceBACKGROUND: The implication of nitric oxide (NO) in the development of human African trypanosomiasis (HAT) using an animal model, was examined. The manner by which the trypanocidal activity of NO is impaired in the periphery and in the brain of rats infected with Trypanosoma brucei brucei (T. b. brucei) was analyzed through: (i) the changes occurring in NO concentration in both peripheral (blood) and cerebral compartments; (ii) the activity of nNOS and iNOS enzymes; (iii) identification of the brain cell types in which the NO-pathways are particularly active during the time-course of the infection. METHODOLOGY/PRINCIPAL FINDINGS: NO concentration (direct measures by voltammetry) was determined in central (brain) and peripheral (blood) compartments in healthy and infected animals at various days post-infection: D5, D10, D16 and D22. Opposite changes were observed in the two compartments. NO production increased in the brain (hypothalamus) from D10 (+32%) to D16 (+71%), but decreased in the blood from D10 (-22%) to D16 (-46%) and D22 (-60%). In parallel with NO measures, cerebral iNOS activity increased and peaked significantly at D16 (up to +700%). However, nNOS activity did not vary. Immunohistochemical staining confirmed iNOS activation in several brain regions, particularly in the hypothalamus. In peritoneal macrophages, iNOS activity decreased from D10 (-83%) to D16 (-65%) and D22 (-74%) similarly to circulating NO. CONCLUSION/SIGNIFICANCE: The NO changes observed in our rat model were dependent on iNOS activity in both peripheral and central compartments. In the periphery, the NO production decrease may reflect an arginase-mediated synthesis of polyamines necessary to trypanosome growth. In the brain, the increased NO concentration may result from an enhanced activity of iNOS present in neurons and glial cells. It may be regarded as a marker of deleterious inflammatory reactions

Actes du Congrès Collèges célébrations 92

Également disponible en version papierTitre de l'écran-titre (visionné le 12 août 2009)Notes (part. bibliogr.): p.

Determinants of compliance with malaria chemoprophylaxis among French soldiers during missions in inter-tropical Africa

International audienc

Actigraphy in Human African Trypanosomiasis as a Tool for Objective Clinical Evaluation and Monitoring: A Pilot Study

The clinical picture of the parasitic disease human African trypanosomiasis (HAT, also called sleeping sickness) is dominated by sleep alterations. We here used actigraphy to evaluate patients affected by the Gambiense form of HAT. Actigraphy is based on the use of battery-run, wrist-worn devices similar to watches, widely used in middle-high income countries for ambulatory monitoring of sleep disturbances. This pilot study was motivated by the fact that the use of polysomnography, which is the gold standard technology for the evaluation of sleep disorders and has greatly contributed to the objective identification of signs of disease in HAT, faces tangible challenges in resource-limited countries where the disease is endemic. We here show that actigraphy provides objective data on the severity of sleep-wake disturbances that characterize HAT. This technique, which does not disturb the patient's routine activities and can be applied at home, could therefore represent an interesting, non-invasive tool for objective HAT clinical assessment and long-term monitoring under field conditions. The use of this method could provide an adjunct marker of HAT severity and for treatment follow-up, or be evaluated in combination with other disease biomarkers in body fluids that are currently under investigation in many laboratories