Influence of IMF-sector polarity on the North-South asymmetry of geomagnetic activity and its relationship with solar wind parameters

North-south asymmetry in response of geomagnetic activity to different solar events

“…Two points are worthy of note: (i) there exists an average asymmetry of about 15% for all categories which is independent of the choice of key days. This is a little higher than the figures of 10% given by Mayaud (1970) (and that shown by Yoshizawa 1984). On the other hand it is well below the asymmetry of about 60% in June solstice and about -5% in December solstice leading to an average above 30% shown by Shah et al (1984).…”

“…For categories (i) and (v) we find that the percentage sharply drops by about 15% before rising up again in the post-passage period. Yoshizawa (1984) found that the asymmetry appears only when IMF is directed southward and is augmented by the solar wind velocity. Here we find that when high speed solar wind sweeps past the earth the asymmetry shows a significant reduction.…”

“…Response of geomagnetic activity to passage of IMF sector boundary has been shown to be more enhanced when the boundaries are associated with solar protons with energies in the range of few MeV (Wilcox 1979) and with high speed solar wind streams (Rangarajan 1983). Yoshizawa (1984) recently demonstrated that (i) the effect of sector polarity of IMF on the N/S asymmetry is due to the By and not the Bx component and (ii) the asymmetry appears only when IMF is directed southward, increasing with enhanced magnitude of the southward component.…”