Geomagnetic storms and electric fields in the equatorial ionosphere

Abstract

Large variations of the geomagnetic field observed at ground level during a geomagnetic storm are generally attributed to various magnetospheric changes following the arrival of the solar plasma ejected during the solar flare. Using the direct measurements of equatorial electric field during a geomagnetic storm, it is shown here that the large decrease in the field observed near the dip equator is due to the reversal of the equatorial electrojet current. This event is caused by the imposition of an additional westward electric field on the equatorial ionosphere which was originated by the interaction of solar wind with the interplanetary magnetic field.