10 - Driving the plasma sheet

Abstract

The transport of the plasma sheet plasma affects the spatial structure of the whole magnetotail. This structure, its variation in location and time, ultimately depends on changes in the solar wind. Field-aligned currents, the auroral currents, couple the magnetosphere with the ionosphere, which in turn affects plasma transport there. It is now possible to predict the structure of the transport and energization of solar wind plasma under different interplanetary magnetic field conditions. The magnetosphere is constantly being stirred by momentum and energy transfer from the solar wind through the low-latitude boundary layer (LLBL). The primary process behind this inflow has some immediate effect on the aurora via initiation of flow and pressure buildup. The generation of two-cell (or sometimes four-cell) convection patterns is the result. The essential element is the formation of elongated narrow auroral arcs during the growth phase of substorms. The aurora is due to energetic particle impact on the upper atmosphere, but the reasons for the precipitation can differ. All auroras are not of the same kind. One may distinguish major classes: quiescent and dynamic convection-related aurora, growth-phase aurora, diffuse aurora, and very active forms of several kinds such as the westward traveling surge, omega bands, and pulsating aurora. The major entry site for solar wind plasma into the plasma sheet is the LLBL. Because of its electric dipole nature, the electric field is transferred from the magnetosheath into the plasma sheet by the LLBL. The LLBL also supplies the plasma through the polarization drift required to maintain the electric field for tailward flow.