Preliminary analysis of geomagnetic day to day variations in the equatorial zone

Under quiet geomagnetic conditions the variations of the three geomagnetic elements H, Z, and D from one day to the next in June, October, and December 1986 at eight Indian observatories from about 0° to 22° dip latitude have been studied. The day to day variability is measured by sequential variability, SV(1). In all the three months, the magnitude of day to day variability in H, Z, and D has a diurnal variation with maximum around local noon and minimum in the night. This is most likely controlled by the diurnal variation of ionospheric conductivity. In the worldwide part of sq (WSq) zone, the SV in H, Z, and D is smaller in October than in June and December 1986, but SV(z) is greater than SV(H) and SV(D) in all the three months. In the equatorial electrojet (EEJ) zone, the SV due to the EEJ alone in H, Z, and D is greater in June than in October and December contrary to the seasonal variation of sq(H) and sq(Z) in the EEJ zone. The SV(D) due to the EEJ alone has a surprisingly large magnitude. There is evidence that the day to day variability of EEJ and the WSq are not in phase and consequently combine somewhat destructively within the EEJ Zone.