The interaction of CMEs and associated shocks with the Earth's bow shock, magnetosheath, and magnetopause will be studied. CMEs and associated shocks arrive at the Earth as magnetic clouds . It is important to study how the geo-effective properties of magnetic clouds depend on the properties of initial coronal structures and how they are changed during propagation towards the Earth (see above). The interaction of arriving magnetic clouds with the Earth's bow shock will be studied. The interaction with the magnetopause and the connection with the ionosphere will be included in a second phase, while in a first phase the attention will be focused on changes in the bow shock location and in the magnetosheath flow. Special attention will be given to the possible formation of secondary slow shock structures behind the bow shock and the corresponding change of the magnetic topology in the magnetosheath will be studied .
Although it is known that the MHD approximation is not fully justified in large parts of the magnetosphere , we intend to use it as a first approximation, and to explore its limitations. In this respect, we intend to develop the boundary conditions describing the coupling to the ionosphere, which are crucial for realistic simulations. A second topic would be the extension of the MHD code to include the Hall-MHD terms (reflecting some aspects of plasma kinetic theory). Low-resolution simulations of the overall magnetosphere will be conducted under prescribed solar wind conditions, including the effect of sector boundaries and an impacting CME, in order to investigate the response of the bow shock and the magnetopause (which are believed to be reasonably well modeled in the MHD approach). Also, high-resolution 3D simulations are planned of the impulsive penetration for typical conditions, both in the MHD and Hall-MHD approaches. Finally, the predictions of coupled solar wind-magnetosphere simulations will be compared with Cluster II observations.