Ionospheric disturbances induced by substorm associated electric fields in the low-latitude F-region.

Examination of the topside density distribution obtained by the Hinotori-IMP observations of the low-latitude ionosphere during February 1981-June 1982 revealed well-defined signatures associated with substorm activity. The observed events are a nightside enhancement and dayside suppression of the equatorial anomaly during disturbed periods. The results are consistent with the disturbance of the equatorial topside ionosphere as described by Sato (1968), but include several new aspects of the topside signatures of low-latitude ionospheric disturbances, such as the spatial extent of the enhanced area, the local time distribution of the event, and precise time sequence of the evolution with respect to the substorm activities (AE index).