Magnetosphere-Ionosphere Coupling Theory for Substorm Generation

W. Lyatsky¹

Physics Department, University of New Brunswick, Fredericton, N.B., Canada

¹Also: Polar Geophysical Institute, Apatity, Russia

ABSTRACT

Substorm generation can be described as a strong explosion-like increase in the magnitude of upward field-aligned currents in the nightside auroral zone, which are responsible for strong acceleration of precipitating particles that is the most evident feature of substorms from ground-based observations. Since field-aligned currents close ionospheric currents, their magnitude is controlled by ionospheric conductivity. Before substorm onset, the nightside ionospheric conductivity is small, and field-aligned currents are weak. Increasing the polar cap electric field leads to an increase in field-aligned currents. When the magnitude of these currents becomes sufficiently large for the acceleration of precipitating electrons, a feedback mechanism becomes possible. Precipitating electrons, associated with upward field-aligned currents, increase the ionospheric conductivity, which in turn leads to a further increase in field-aligned currents. This stimulates an explosion-like increase in field-aligned currents. This instability may be related to substorm generation.