Geomagnetic implications of a simple IMF model

The geomagnetic consequences of a tilted current sheet corotating with the sun were evaluated, based on the assumption that the strength of the interaction between the solar wind and the earth's magnetosphere is only determined by the amount of the southward component of the interplanetary magnetic field as observed in a magnetospheric coordinate system (Russel and McPherron, 1973). It is shown that, in addition to the semi-annual variation, the current sheet rotation may lead to the appearance, in the power spectra of the geomagnetic indices, of doublet structures with periods close to the values of the period of the solar rotation as seen from the earth and one-half of this period. These results indicate that the long term evolution of the geomagnetic activity may be related to the long term evolution of the current sheet orientation.