Relative importance of solar radiation and gravitational tide in causing geomagnetic variations

Abstract

For an assumed model of the ionosphere, partial coherence functions have been computed to investigate the contribution of solar radiation and of gravitational tide in causing geomagnetic variations (and hence the tides in the ionosphere). It is found that (1) at the diurnal frequency solar radiation contributes about 99% to geomagnetic variation, the gravitational contribution being negligible, and (2) at the semidiurnal frequency solar radiation and gravitational tide contribute nearly 90% and 10%, respectively, to geomagnetic variations.