In recent years the debate over the causes of seasonal and diurnal variations in magnetic activity has been revived. Popular explanations rely primarily on the orientation of the terrestrial magnetic dipole relative to heliospheric topology. We investigate the signatures of this geometry in the dynamics of Dst, the ring current index. We show that the Russell-McPherron effect is present; however, enhancements in Dst, as measured by the Dst index, exhibit a seasonal and diurnal pattern that is significantly different from the Russell-McPherron (RM) effect. Specifically, the dynamics of Dst, which accommodate the RM effect, demonstrate seasonal and diurnal variations associated with ψ the magnetic colatitude of the subsolar point. Specifically, it is primarily the diurnal signature that distinguishes between various mechanisms for semiannual variations. We suggest that these variations are most consistent with the hypothesis that ψ modulates the depth of penetration of the magnetosheath field into the magnetopause and thereby the amount of magnetic merging and the strength and orientation of magnetopause currents.