Equatorialand mid-latitude ionospheric currents over the Indian region based on 40 yearsof data at Trivandrum and Alibag

Abstract

Forty years of geomagneticdata obtained from two Indian stations, Trivandrum (TRD), located near themagnetic equator and Alibag (ABG), located away from the magnetic equator for theperiod 1958-1998 are examined to study the daily ranges in H and in the strengthof the equatorial electrojet (EEJ). Mean diurnal variations in H, averaged overthe 40 years, show a maximum range in H of 92 nT at midday over Trivandrum and 43 nT (at 1300 h) over Alibag.The corresponding maximum electrojet strength was found to be 51 nT at midday.  The annual mean ranges in H show linearincreases with sunspot number (Rz) and vary from 65 nT to 140 nT at TRD, 30 nTto 70 nT at ABG and from 40 nT to 72 nT for the EEJ. The rate of increase in H isfaster at TRD than at ABG. Seasonal variations show equinoctial maxima for TRDand EEJ during the months of April and October. The range of H at ABG shows, inaddition to maxima during April and October, a weak secondary maximum duringJune-July. During the months of June-July the range of H at ABG is strongerthan that of EEJ. The occurrence of the afternoon counter electrojet is highestduring low sunspot years and if considered seasonally, during the June-solstices.