Interaction of magnetic clouds with the Earth's magnetosphere
Résumé
Magnetic clouds (MC) are well-defined solar wind structures, known to trigger intense geomagnetic storms. When studying their impact on the Earth's environment, it is generally assumed that the structures observed in the upstream solar wind are unchanged when they interact with the magnetosphere. However, before encountering the magnetopause, the MCs cross the terrestrial bow shock which alters their structure. Therefore their expected geoeffectivity may be modified by the shock. In this study, we focus on the magnetic structure of MCs. A simple 3D MHD model is used to describe the interaction of a MC with the bow shock and its propagation in the magnetosheath. Several cases are presented, corresponding to different orientations of the MC axis and different impact parameters. The results show that the shock obliquity plays a major role in determining the variation of the magnetic field direction. Asymmetries can be observed inside the magnetosheath. Moreover, the Bz component can even reverse in some parts of the magnetosheath. The outputs of the model are compared to spacecraft observations, and the implications on a MC's geoeffectivity are discussed.