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Accueil > Séminaires & Soutenances > Séminaires, soutenances de thèses et HDR précédents > 2019 > Soutenances de thèses et HDR 2019 > Le mardi 17 décembre 2019 à 14h
Le mardi 17 décembre 2019 à 14h
Soutenance de thèse de Roberto Manuzzo
Lieu : salle 509, tour 24/34, LPP, 5ème étage, campus Jussieu, Paris.
Title : Magnetopause study by means of a multi-fluid approach
Abstract :
The Earth’s magnetopause is the boundary between the solar wind plasma and the Earth’s magnetospheric one. Across this current sheet (which is thin in comparison to the magnetosphere), the two plasmas mix in a poorly known way, controlling the exchanges of mass, energy and momentum between the two regions. Beyond the interest in understanding how these processes could impact on our lives (space weather), this system is worth studying in order to understand how two different plasma systems interact without laboratory set-up constraints.
In this thesis, new methods are presented which are able to obtain a "realistic" multi-fluid analysis of the solar wind - magnetosphere interaction. This goal is reached in three main steps : (1) the analysis of spacecraft data acquired across the magnetopause, (2) the set up of an analytical multi-fluid equilibrium model able to predict profiles consistent with observations, (3) the development of a multi-fluid code able to simulate the temporal evolution of the analytical profiles.
The analysis of spacecraft data acquired across the magnetopause is done by means of new techniques which relax most of the hypotheses usually assumed about the observed plasma structures. These techniques help in disentangling the principal causes of misunderstanding in data interpretations by discerning whether the observed variations are due to the magnetopause motion in the spacecraft frame or due to the purely temporal variations of the magnetopause structure. The new methods show consistent results but each of them demands to fix some threshold parameters. These thresholds are determined, in an objective way, by dedicated optimization techniques.
The spatial profiles obtained from the new data analysis techniques feed a new 3fluid analytical model (two ion and one electron populations) able to spatially confine the magnetospheric and magnetosheath plasmas in their own regions and letting them to partially overlap close to the contact boundary (the magnetopause). This model helps also in determining the magnetospheric and magnetosheath contributions to the total ion population where this information is not accessible analysing the distribution functions (\textite.g. in the mixing regions).
The 3fluid equilibrium computed by the analytical model is then perturbed and evolved in time by means of a new 3fluid numerical code, explicitly coded to take the 3fluid model outputs as inputs. The numerical model of the magnetopause develops a magnetic reconnection instability, in agreement to what is observed close to the analysed magnetopause crossing.
The results lead to very preliminary conclusions about the temporal evolution and the spatial distribution of the mixing processes close to the magnetopause.
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