The transition from the magnetosheath to the magnetosphere

Electron measurements are studied in the transition region where the magnetosheath merges with the magnetosphere. The outer part of the transition is found to be a depletion region, in which a reduction in the electron thermal pressure coincides with compression of the magnetic field. It is suggested that the compression is associated with the draping of the interplanetary field around the inner part of the region, which is a region of closed magnetic field lines. Implications for the topology of boundary layers throughout the magnetosphere are discussed.