A Huge Deformation and Motion of Magnetospheric Boundaries

The magnetopause and bow shock motions are generally driven by variations of the solar wind dynamic pressure. On the other hand, a contribution of other parameters like tilt angle and IMF orientation is usually small. However, the spacecraft often found both boundaries several Re away from their nominal locations. A sudden and very strong deformation of the bow shock and magnetopause surface was observed by the Themis and Cluster spacecraft on November 26, 2008. The contribution presents multi-point observations of a large set of the spacecraft located at different places in the solar wind, in the magnetosheath, in the inner magnetosphere, and on the geostationary orbit and tries to find a source of this huge deformation/motion of both boundaries. We compared the observations on both dusk and dawn flanks and found that the cause of boundary deformation is the interaction of the magnetic field discontinuity with the bow shock that creates two HFAs, one in the dawn and the other in the dusk magnetosheath.