Time variation of instantaneous equivalent Sq current system

Abstract

We have examined the time variation of the instantaneous equivalent S q current system during 1–18 March 1980, by removing the averaged UT variation caused by the difference between geographic and geomagnetic coordinate systems. The additional current system thus obtained shows several typical patterns which explain the variation field. Some of them may be explained by the IMF polarity effect or by the geomagnetic disturbance field of polar origin, but others appear to be caused by the variation of the ionospheric dynamo. The latter lasts for several hours or sometimes for over ten hours and may be explained by the variation of diurnal or semi-diurnal tidal winds.