Storm-time electric field distribution in the inner magnetosphere

The distribution of the storm-time electric field in the inner magnetosphere has been investigated by using the Akebono/EFD data within a period from 1989 to 1995. During the main phase of geomagnetic storms, the strong electric field appears between L = 2 and L = 6 in both dawn and dusk sectors with the magnitude from 2 to 4 mV/m, and the maximum value appears at L = 3 in the dusk sector. During the recovery and weakly disturbed period, the region with intense electric field moves outward with decreasing the amplitude. This structure of the localized electric field is quite different from the Volland-Stern electric field model, suggesting the existence of another electric field source other than the large-scale convection electric field. During quiet periods, although the electric field fairly follows the corotation electric field, the distribution at L = 3.5 indicates a small deviation from pure corotation.