Solar Wind-Magnetosphere-Ionosphere Coupling

Abstract

The flowing solar wind imparts mass, momentum, and energy to the magnetosphere. It does so in the outer region of the magnetosphere, the boundary layer, both by direct entry of solar wind plasma into closed flux tubes of the boundary layer and by connection of interplanetary magnetic field (IMF) lines to the Earth’s magnetic field. The latter mechanism seems to be dominant when the IMF has an appreciable southward component and several observations demonstrating its importance are discussed. The former may be responsible for the enduring presence of the magnetotail during even prolonged intervals of northward IMF. By either mechanism of interaction the basic process, transfer of momentum, is accompanied by electric polarization of the interaction region. The polarization charge leaks away as a depolarizing current that flows along magnetic field lines to the ionosphere where it imparts momentum to the ionospheric plasma. At the same time the momentum exchange in the interaction region stretches the field lines there downstream to form the magnetotail — a reservoir of stored magnetic energy that frequently releases stored energy to the nightside of the Earth — creating substorms. Recent evidence suggests that the field aligned currents from the interaction region create field aligned electric fields at altitudes of 1 to 2 RE and that these are responsible for the acceleration of the particles that produce auroral arcs.