Propagation of Interplanetary Shocks Across the Bow Shock

An important problem of the Space Weather Program is the interaction of interplanetary (IP) shocks with the Earth magnetosphere because their interaction often (but not always) leads to major geomagnetic storms. Since the huge interaction region can be covered by simultaneous spacecraft observations only sporadically, global MHD modeling can help in our understanding of the interaction process. Using one IP shock observed by Geotail, we compare its passage through the magnetosheath with predictions of the global BATS-R-US MHD code. We demonstrate oscillations of the whole system with a period of 10-12 minutes. Moreover, we suggest that the information about the IP shock hitting the subsolar magnetopause reaches the nightside magnetopause earlier than the IP shock can arrive. This information is mediated by fast magnetosonic waves in the inner magnetosphere.