Solar control of the annual variation of the quiet-day horizontal component of geomagnetic force

Abstract

The predominant component of the mean annual variation of Hq for Alibag for the period 1904 to 1958 is the 12 monthly component. For Huancayo, for the period 1923-1946, it is the 6 monthly component which is found to be predominant. This difference is accounted for by considering the annual variation of Hq as a consequence of the superposition of Sq on Hq. Huancayo being much closer to the geomagnetic as well as geographic equators than Alibag, the variation in the feature for Huancayo, while for Alibag this variation will largely be annual feature.

While the amplitudes of the 12 monthly components of individual years show very little correspondence with sunspot numbers, the amplitudes of the 6 monthly components show appreciable corrospondence with sunspot numbers. To explain this feature the variation in the heliographic latitude of the earth, in the course of the year, coupled with emanation of shortwave radiation of high ionization potential from solar active regions, which are known to form two average belts 10-15 deg. N and S of the solar equator, is suggested in the preference to the incidence of disturbance on Hq, since the dates of maxima of the 6 monthly component for years of high sunspot numbers are found to be closer to the equinoxial months.