Equatorial and mid-latitude ionospheric currents over the Indian region based on 40 years of data at Trivandrum and Alibag

Abstract

Forty years of geomagnetic data obtained from two Indian stations, Trivandrum (TRD) located near the magnetic equator; and Alibag (ABG) located away from the magnetic equator, for the period 1958-1998 are examined to study the daily ranges in H and in the strength of the equatorial electrojet (EEJ) obtained from the differences in the ranges at the two stations. Mean diurnal and seasonal variations in H, averaged over the 40 years are described for the two stations and for EEJ. The annual mean ranges in H show linear increases with sunspot number (Rz) and vary from 65 to 140 nT at TRD, 30 to 70 nT at ABG and from 40 to 72 nT for the EEJ. The rate of increase in H is faster at TRD than at ABG. Seasonal variations show equinoctial maxima for TRD and EEJ during the months of April and October. The range of H at ABG shows a weak secondary maximum during June-July, in addition to maxima during April and October. During the months of June-July, the range of H at ABG is stronger than that of EEJ. The occurrence of the afternoon counter electrojet is highest during low sunspot years and seasonally, during the June solstices.