Spike-like change of the vertical E x B drift in the equatorial region during very large geomagnetic storms

Abstract

We investigate the characteristics of the storm-time disturbance electric fields in the equatorial region using the measurements of the vertical ion velocity from the Defense Meteorological Satellite Program F13 and the first Republic of China Satellite during the selected 43 geomagnetic storms of Dst < -100 nT in 2000-2004. The distinguishing feature in both observations is the occurrence of the spike-like vertical E x B drift during the main phase of very large storms (Dst < -150 nT). The spikes occur simultaneously at different local times but the direction of the spikes shows a dependence on the local time. The spikes are upward on the dayside and downward on the nightside. The observed characteristics of the spikes can be explained by the penetration of the dawn-to-dusk polar cap electric field to low latitude.