Etude des émissions naturelles dans la plasmasphère, reliées à la gyrofréquence électronique, à l'aide de données de la mission multi satellite CLUSTER

Abstract : This dissertation gathers a series of investigations about natural emissions observed in the external part of the plasmasphere by CLUSTER multi satellite mission and more precisely by WHISPER instrument. Among the observed emissions, we can quote the electrostatic electron cyclotron harmonics, observed between two successive electron gyrofrequency. These waves are usually called (n+½)fce emissions, they are observed in Earth's magnetosphere as well as in the vicinity of other planets. We propose a classification of the natural emissions observed in the plasmasphère, based on spectral characteristics. We focus on three principal types of waves: emissions at n(1.1)fce, at (n+½)fce, and at nfce. The last ones have been highlighted thanks to the good resolution of WHISPER instrument, they had never been observed before. A systematic study over three years of data (from 2002 - 2004) permit the localisation of the different emissions observed in MLT sector, and with magnetic latitude. Using multi satellite event studies and statistical study, we show the importance of the radial distance to the plasmapause on the characteristics features (intensity, number of harmonics) of the emissions at (n+½)fce. To characterize this distance to the plasmapause we define a proxy using the value of the equatorial plasma frequency, fpeq, measured by WHISPER instrument. We also studied the influence of the geomagnetic activity, through the variations of indices AE, Kp and Dst, on the three types of emissions observed. Some signatures on the electron distribution function have been examined. Two distinct forms of this distribution function, related to the intensity of the emissions at (n+½)fce, are observed. Finally, we present preliminary results of numerical simulations using a particle code and we find the eigen modes of the plasma predicted by the linear theory.
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Submitted on : Thursday, November 20, 2008 - 11:34:06 AM
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Farida El-Lemdani Mazouz. Etude des émissions naturelles dans la plasmasphère, reliées à la gyrofréquence électronique, à l'aide de données de la mission multi satellite CLUSTER. Physique [physics]. Université d'Orléans, 2008. Français. ⟨tel-00340250⟩

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