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Propagation des ondes MHD dans les couches de courant.
Structure des modes et transferts énergétiques.
Comparaison avec les données CLUSTER.

Abstract : Since the success of the CLUSTER mission the tridimensional structure of the
low frequency perturbations propagating in the key regions of the Earth magnetosphere can be
studied. In order to help the interpretation of these data, this thesis propose a theoretical and
self-consistent model aiming the study of the linear response of an inhomogeneous plasmasheet to an
initial excitation, in the frame of the ideal MHD. Especially the calculus is lead to the final
reconstruction of the spatial-temporal signals with a discussion of the amplitudes and of the
energetic transfers. This last step is essential for a precise comparison with CLUSTER
data.

The study of the eigenmodes of the magnetotail shows the existence of two kind of oscillations:
global modes oscillating at discrete frequencies and confined within the sheet, and continuous
modes linked to the process of resonant absorption and whose amplitude decreases with time. Using
different geometries of initial pulses, we study the coupling between the excitation and the modes.
The coupling is optimal for a pulse whose spatial scale is close to the width of the sheet, but
even in that case the fluctuations remain very modest. On the contrary with the same initial pulse,
the absorption in the continuum is efficient and leads to a non negligible energetic transfer from
the waves to the plasma.

Finally, an example of magnetic oscillations observed by CLUSTER is analysed and compared
to the theoretical model. It is indeed possible using the theoretical results to specify the nature
of the perturbations so as their origin, in the assumption that these fluctuations obey to a MHD
description.
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https://tel.archives-ouvertes.fr/tel-00094680
Contributor : Gabriel Fruit <>
Submitted on : Thursday, September 14, 2006 - 5:40:41 PM
Last modification on : Thursday, October 15, 2020 - 4:07:41 AM
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Gabriel Fruit. Propagation des ondes MHD dans les couches de courant.
Structure des modes et transferts énergétiques.
Comparaison avec les données CLUSTER.. Astrophysique [astro-ph]. Université Paul Sabatier - Toulouse III, 2003. Français. ⟨tel-00094680⟩

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