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Home > Seminars and Workshops > Past seminars, PhD & HDR defense > 2012 > Séminaires 2012 > Le lundi 22 octobre à 11h

Le lundi 22 octobre à 11h

Hannu Koskinen (Univ. Helsinki & FMI ) - The role of the magnetosheath in the solar wind – magnetosphere coupling

Lieu : Palaiseau, salle de réunion de l’aile 0 (ex-LIX)

Résumé :
The solar wind interacts with the magnetosphere through the magnetosheath located between the bow shock and the magnetopause. While this is a fact that everybody knows, the sheath region often remains ignored in studies of how the solar wind drives the magnetosphere. In numerous statistical analyses correlating solar wind properties with magnetospheric activity indices, linear correlation coefficients of 0.6–0.7 are found, which makes some investigators pleased, some other frustrated. The fairly low correlations may have several reasons. The magnetospheric response is complicated and hard to describe in terms of any single activity index or a combination of them. However, the loss of information embedded in the solar wind already begins in the magnetosheath. The well-developed solar wind turbulence becomes more intermittent in the sheath. The largest-scale patterns no more fit in the dayside sheath region and the system gives rise to new plasma structures. During last several years a number of new phenomena have been observed, in particular, behind the quasi-parallel shock, including Alfvén vortices, small-scale reconnection, and MHD-scale ripples penetrating from the shock deep into the sheath region. The different local properties of quasi-perpendicular and quasi-parallel bow shocks introduce asymmetry to the flow actually impinging the magnetopause. These asymmetries and sheath-specific fluctuations may affect the local rates of reconnection and dynamo processes in the different parts of the magnetopause. The shock is also a current sheet and the closure of this current is an intriguing part of the large-scale problem of the solar wind–driven magnetosphere. For example, the closure of the magnetospheric region 1 current to the bow shock has recently been proposed as an explanation for the saturation of the ionospheric polar cap potential during very strong solar wind driving.

Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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