Transient events at the magnetopause and bipolar magnetic signatures

Bipolar signatures in the magnetic field component perpendicular to a nominal magnetopause surface accompanied with an increase of the magnetic field strength are regularly attributed to flux transfer events (FTEs) crossing the spacecraft. The detailed analysis of one such event shows that the magnetic signatures are consistent with the FTE but the timing of multipoint observations and the interpretation of changes of plasma parameters in terms of FTEs requires additional assumptions. We argue that although the event exhibits clear FTE signatures, an explanation of the observations as a local magnetopause surface deformation associated with a change of the magnetosheath density better fits to the data. The deformation caused by this density depression at the magnetopause is associated with a rotation of the magnetosheath magnetic field.