Influence of the polarity of the interplanetary magnetic field on the annual and diurnal variations of the magnetic activity, paper presented at

The annual variation of magnetic activity and its variation with universal time are analyzed separately for days sorted according to the polarity of the interplanetary magnetic field (IMF). A coherent interpretation of the observed effects is obtained (1) by taking into account the variations of the southward component of IMF in GSM (geocentric solar magnetospheric) oordinates, as was suggested by Russell and McPherron (1973) (the effect expected from this mechanism is calculated and compared to the observed ones), and (2) in the case of Am, by taking into account he annual and diurnal variations of the angle between the dipole axis and the earth-sun line. The annual variation of the magnetic activity exhibits two mechanism proposed by Russell and McPherron [1973], and equinoctial maxima which have been shown to exist by several we show that a coherent explanation of the observed effects is different studies based on the analysis of the occurrence of obtained by taking into account both this mechanism and that magnetic storms [Cortie, 1912] or of variations of either the C put forward first by Bartels [1925] and later by Mcintosh and U indices [Chapman and Bartels, 1940] or the K, Ap, or Am indices [Mcintosh, 1959; Mayaud, 1967, 1970, 1974]. The vari-ous explanations that have been proposed so far may be di-vided into 'heliocentric ' theories, which attempt to relate th