Satellite data like those of the Cluster-Mission are important for the study of physical processes caused by the interaction between the interplanetary magnetic field (IMF) and the solar wind with the magnetosphere of the Earth.
One of these processes is the so-called reconnection of magnetic field lines of the IMF and the terrestrial magnetic field at the Earth magnetopause. The theoretical description of magnetic field line reconnection starts with antiparallel field lines separated by a tangential discontinuity. In a very small region, the so-called "diffusion region" (DR), where the local conductivity reaches a finite value, terrestrial field lines are opened and "reconnected" with field lines of the IMF. Regardless of the precise mechanism, the DR acts as a source of MHD waves, which propagate into the surrounding medium. Under special circumstances these waves steepen and maybe considered as large-amplitude discontinuities. In this structure, incoming plasma from the magnetosheath is accelerated through a conversion of magnetic energy to kinetic energy along the magnetopause and is transported to the night side. In the case of time dependent reconnection a so-called reconnection pulse travels along the Magnetopause and can be identified in observations as so-called flux transfer events (FTE).