Accueil Imprimer Annuaire Plan du site Crédits Fil RSS du site Twitter Plans d'accès Contacts Annuaire Webmail Intranet Logo

Accueil > Séminaires et conférences > Séminaires, soutenances de thèses et HDR précédents > 2015 > Séminaires 2015 > Le jeudi 1er octobre à 11h

Le jeudi 1er octobre à 11h

Claudia Rossi (Pise)- Kelvin-Helmholtz instability at the magnetopause : theory and observations

Lieu : Jussieu avec visioconférence à Palaiseau

Résumé : The interaction between the solar wind and the Earth’s magnetosphere is mediated by the magnetopause. The dynamics occurring at this boundary depends on various aspects as, e.g., the solar wind dynamic pressure or the direction of the Interplanetary Magnetic Field. During northwards conditions one observe the formation of a wide boundary layer at the low latitude. This boundary layer is thought to be the result of the observed plasma transfer driven by the development of the Kelvin-Helmholtz (K-H) instability. This instability, originating from the velocity shear between the solar wind and the almost static near-Earth plasma, develops along the flanks of the magnetopause giving rise to vortex like structures that in turn create the favorable conditions for solar wind plasma transfer. Last ten years of simulations have shown that the competition between the vortex - merging mechanism and the development of secondary instabilities depends strongly on the large scale field profiles used as initial conditions in the simulations. Therefore it is imperative to combine satellite data and numerical simulations. The idea here is to initialize numerical simulations by using direct in-situ observations.

In particular we study the non-linear K-H dynamics eventually leading to turbulence and we look for observational events when satellites cross the magnetopause under K-H condition but before the instability develops and to recover the profiles of the principal physical quantities and to use them to initialize our numerical simulations. In this study a “two-fluid” plasma model is adopted using 2D simulations while from the experimental point of view, we use data from the ACE satellite orbiting in the solar wind to monitor the IMF conditions and the measurement from Cluster and Geotail satellites to study the magnetopause. By combining these two aspects we characterize the turbulence and the small scale magnetic reconnection events responsible for the observed intermittency ; select one event in particular where we have the combination of a satellite measurement before and after K-H develops and find that the density and velocity profile centers are shifted by a distance comparable to their shear lengths and that this initial shift cause a different evolution of the K-H instability leading to a final state in agreement with satellites observations. The combination of spacecraft data and numerical simulations is the most effective way to study complex phenomena of plasma transport across frontiers, such as Kelvin-Helmholtz instability at the magnetopause.

Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
©2009-2019 Laboratoire de Physique des Plasmas (LPP)

Mentions légales
Exploitant du site : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Pascal Chabert (Directeur)