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AbstractAbstract
[en] Magnetic clouds (MCs), described as large-scale structures with a magnetic flux-rope topology, interact with the surrounding interplanetary medium during their propagation. McComas et al. (1988), and later Dasso et al. (2006), were the first to propose that magnetic reconnection might peel off the outer magnetic structure of ICMEs. This erosion process is the core subject of this thesis. First, we confirm the occurrence of MC erosion, thanks to a multi-spacecraft study combining a set of key signatures expected from this process. Based on careful determination of the MC main axis, we estimate the amount of magnetic flux eroded by analyzing the azimuthal flux imbalance during the spacecraft sampling of the flux rope. Consistent with this process, we also find clear magnetic reconnection signatures at the MC front boundary. Finally, we investigate the characteristics of suprathermal electrons in the back region of the MC. Those electrons are shown to signal large-scale topological changes also expected from the erosion process. In a second part, a statistical analysis of all MCs of solar cycle 23 is performed in order to quantify this process. We show that the process is very frequent. It often occurs in large amounts, and at both the front and back boundaries of MCs. The statistics of reconnection jets at these boundaries confirms the significance and high recurrence of the process even up to 1 AU. In a last part, since the erosion mechanism can lead to the removal of part of the southward oriented magnetic field at the front or the rear of MCs, we study the potential impact of this mechanism on their geo-effectiveness by using a standard MC model and an empirical model of the ring current strength. We also estimate the radial evolution of this process based on simple models. We conclude that most of the erosion is expected to occur within Mercury's orbit. (author)
[fr]
Les nuages magnetiques ('Magnetic Clouds', MCs) sont assimiles a des structures helicoidales a grande echelle interagissant avec le milieu interplanetaire au cours de leur propagation. McComas et al. (1988), suivi par Dasso et al. (2006), ont envisage la reconnexion magnetique comme processus pouvant graduellement eroder la structure externe des ejections de masse coronale interplanetaires. Ce processus d'erosion est le sujet central de cette these. Tout d'abord, nous confirmons l'existence de l'erosion d'un nuage magnetique grace a une etude multi-satellites combinant un ensemble de signatures cles. Apres avoir determine l'orientation des axes du MC par differentes methodes, nous estimons le taux de flux magnetique erode en analysant les variations du flux magnetique azimutal du MC. Nous demontrons aussi la presence de signatures de reconnexion magnetique a la frontiere avant du MC, tel qu'attendue. Finalement, nous etudions les caracteristiques de la distribution en angle d'attaque des electrons suprathermiques dans la region arriere du MC. Ces electrons indiquent des modifications topologiques a grande echelle, attendues du processus d'erosion. Dans une seconde partie, une analyse statistique de tous les nuages magnetiques observes au cours de la periode 1995-2008, est realisee dans le but de quantifier ce processus. Nous montrons que ce processus est recurrent: l'erosion est relevee a l'avant et a l'arriere dans les memes proportions. Cela est confirme par l'etude statistique des jets de plasma aux frontieres, qui demontre independamment la frequence elevee du processus d'erosion. Dans une derniere partie, parce que le mecanisme d'erosion est susceptible de supprimer une partie de flux magnetique oriente vers le Sud d'un MC, a l'avant ou a l'arriere, nous etudions l'impact potentiel de l'erosion sur la geo-efficacite resultante, en utilisant un modele de MC combine a un modele empirique de l'intensite du courant annulaire terrestre. Nous modelisons aussi l'evolution radiale de ce processus. Nous concluons que la majeure partie de l'erosion se produit a l'interieur de l'orbite de Mercure. (auteur)Original Title
Observation et modelisation de l'erosion des nuages magnetiques solaires par reconnexion magnetique
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29 Nov 2013; 187 p; 174 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; These de Doctorat de l'Universite de Toulouse, specialite: Astrophysique, Sciences de l'Espace, Planetologie
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