Effects of seasonal changes in the ionospheric conductances on magnetospheric field-aligned currents

Abstract

Through the seasons of the year, the ionospheric potential doesn't change significantly, while the solar driven conductance changes dramatically. This means that the magnetospherically driven field-aligned currents must be significantly reduced in the winter hemisphere and enhanced in the summer hemisphere. It is shown that, if this simplistic view of the conductance is used, the ratio between the maximum winter FAC and maximum summer hemisphere FAC is on the order of a factor of four. FAC data shows that the true factor is closer to two. When a seasonally dependent auroral precipitation is used to increase the auroral conductance in the winter hemisphere, the ratio between the maximum FAC in the summer and winter is reduced to 1.6. It is shown that the measured hemispheric power does indeed show a seasonal difference, with the winter hemisphere receiving more power by approximately 3.8 GW (about 20%). Copyright 2007 by the American Geophysical Union.