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Détermination des distributions d’ondes de type choeur dans la magnétosphère interne de la Terre et leurs conséquences sur la dynamique de la ceinture de radiation externe

Abstract : Chorus type whistler waves are one of the most intense electromagnetic waves observed in the Earth’s inner magnetosphere, and play a crucial role in the dynamics of radiation belts which is a critical issue in space weather. They are indeed responsible for acceleration and loss of the energetic electron population that shape the outer belt. As spacecraft trajectories cannot entirely cover the inner magnetosphere, satellite measurements are poor in some regions. The aim of this thesis is thus to be able to complete observational data making use of numerical simulations, by determining the statistical distributions of chorus waves in the inner magnetosphere. In order to achieve this aim, a ray tracing code has been developed, including a realistic model of the inner magnetosphere. First, wave propagation by means of this program is described in this work, emphasizing notably the significance of wave azimuthal angle. Then, making use of the trajectory database computed for typical source chorus parameters, the reconstruction of statistical distributions recorded on Cluster spacecraft is presented. It is thereby demonstrated that quasi-longitudinal approximation, used in numerous simulations of radiation belts dynamics, is no longer valid at medium and high latitudes. Taking these realistic distributions as a basis, it is then demonstrated the major discrepancy obtained for energetic electrons losses. Subsequently, the accuracy of our numerical simulations for the study of magnetospherically reflected chorus waves is highlighted, as well as their importance due to the lack of observational data. Our simulations notably indicate that falling tone chorus emissions can originate from the magnetospheric reflection of rising tone elements.
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Hugo Breuillard. Détermination des distributions d’ondes de type choeur dans la magnétosphère interne de la Terre et leurs conséquences sur la dynamique de la ceinture de radiation externe. Autre. Université d'Orléans, 2012. Français. ⟨NNT : 2012ORLE2081⟩. ⟨tel-00843653⟩

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