Field-aligned currents in the magnetosphere

Abstract

Field-aligned currents flow everywhere in the magnetosphere, not only at high latitudes but aiso at middle and low latitudes, but their experimental detection by satellites has been possible only in the region over the auroral zones. The existence of field-aligned currents at middle and low latitudes can be inferred from an analysis of theiground magnetograms, in particular from the seasonal difference in the daily variation of the geomagnetic field. At middle1 latitudes the dominant component of the field-aligned currents is the winter-to-summer transequatorial currents combining the regions f Sq current foci in the northern and southern hemispheres. At low latitudes near the equator, the field-alig~ed current direction is summer-to-winter in the forenoon and winter-to-summer at dusk hours.