Magnetospheric Currents during Substorms

Abstract

One of the most important aspects of the magnetospheric substorm is that during it there occurs a large-scale change of the distribution of electric currents in the magnetosphere and the ionosphere. In Sections 5.5 and 6.5, it was suggested that the main cause of this change is the disruption of the cross-tail current in a limited region in the magnetotail and its diversion to the polar ionosphere. The diverted current should flow into the poleward half of the auroral oval in the morning and forenoon sectors, and out from the oval in the afternoon and evening sectors; see Figure 7.1. In this chapter, this current system is referred to as the substorm current system. It should be noted that the quiet time current system (S q p ) has a similar distribution (Sections 1.3.2, 1.3.6 and 1.3.7) and thus the substorm current system may appear as an intensification of the S q p current system. In Section 7.2 of this chapter, we examine carefully whether the observed magnetic field disturbances Δ B (X, Y, Z) at various points in the magnetosphere during substorms are consistent with those which we expected from the diverted cross-tail current.