A METHOD FOR THE ANALYSIS OF GEOMAGNETIC VARIATION FIELD AND ITS APPLICATION TO THE YAER-TO-YAER CHANGE OF Sq ACTIVITY

Abstract

A method to determine the main terms of spherical harmonic coefficients of the geomagnetic variation field is studied with reasonable approximations, under the condition of 'rotation-free'. The method is applied to the investigation of the year-to-year change of Sq activity in a period of the descendent stage of solar activity. The result shows that g2^1, the coefficient of cosine-term, decreases with the declining of sunspot activity, meanwhile h2^1, the coefficient of sine-term, has no significant correlation.