The geomagnetic Sqvariation—annual, semi-annual and solar cycle variations and ring current effects

Abstract

The difference between H at two magnetic observatories having the same longitude, but latitudes equatorwards and polewards of the latitude of the S q focus, yields a measure of S q intensity largely free from disturbance. Data from all days may be used, which results in improved time resolution of the variations of S q . As well as an annual variation in S q with a maximum in local summer, there is a substantial semi-annual variation with equinoxial maxima. It is proposed that the annual variation is due mainly to the annual variation in conductivity of the E-region and that the semi-annual variation arises from the semi-annual variation in the thermospheric neutral temperature. The solar cycle variation is also delineated. There is a non- S q annual variation in the midnight values of H that appears to exist also at other hours of the night and probably throughout the 24 h. It is consistent with an annual north-south motion of the ring current. The implication of this for the S q baseline problem is discussed.