The interpretation of surface equatorial magnetic daily variations on disturbed days

Abstract

Reference is made to the results of an analysis of magnetic data from the lowlatitude station M'Bour—published in the Annls Géophys., 1970 No. 4—from which it is apparent that the contribution of non-ionospheric currents to surface magnetic daily variations is considerable on all days other than magnetically Q days. It is shown that correction for the symmetric ring current using Sugiura's D st values does not completely account for the difference between Q and D days and it is suggested that the discrepancy arises from the asymmetric part of the ring current. On disturbed days at equatorial stations, it is found, from examination of South American IGY data, that in addition to the contributions of the symmetric and asymmetric ring currents, there are superimposed fluctuations in the H component of duration 1–2 hr. These are enhanced around local noon and at the dip equator. In the Z component, there are corresponding fluctuations which appear to be enhanced near the edges of the electrojet region. Possible sources of these fluctuations are suggested.