Anti-sunward space current below the Magsat level during magnetic storms

A direct application of Ampere's theorem enables us to calculate the total amount of electric current passing through the plane enclosed by the MAGSAT orbit, through the line-integration of the observed magnetic field component tangential to the MAGSAT orbit. After eliminating the spurious effect arising from the earth's rotation under the MAGSAT orbit, it is concluded that the space current of a few million A flows anti-sunward below the MAGSAT level during magnetic storms in good correlation with the AE-index, whereas such a space current is almost absent under quiet conditions. The existence of an anti-sunward space current on disturbed days gives a strong support to the development of a partial ring current in the magnetosphere during magnetic storms.