Analysis of auroral arc dynamics based on a model of magnetic reconnection in the magnetotail

Abstract

We present results of an analysis using a model recently proposed to predict the motion of nightside auroral arcs during the expansion phase of a magnetospheric substorm. This model is based on the hypothesis that reconnection in the magnetotail plays a central role in substorm development. Auroral arcs are interpreted as the ionospheric manifestation of upward field-aligned currents, induced by shock waves generated during one or more reconnection pulses in the vicinity of an X-line in the magnetotail current sheet. The non-uniform plasma medium in the magnetotail leads to dispersion of the shock waves, resulting in poleward and/or equatorward moving auroral arcs. Furthermore, we show that the morphology and location of the arcs depend on the reconnection electric field in the diffusion region, the plasma density distribution in the magnetotail, and the location of the magnetotail X-line. Comparison of the results obtained from simple numerical simulations of auroral dynamics presented here with actual observations shows that the proposed model could explain the small-scale structure and several other features associated with observed auroral intensifications.