Effects of ionospheric, magnetospheric and induced current on equatorial electrojet over India

Abstract

The paper describes the diurnal and latitudinal variations of the horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field at Central African, East Brazilian and Indian sectors based on the chain of magnetic observatories operated in these areas. The observations in Brazil and African sectors conform fairly well with the expectations of Chapman's theory of equatorial electrojet. In Indian longitudes the latitudinal variation of ΔZ shows a large maximum simultaneously with the peak of ΔH over the dip equator. The daily variation of ΔZ shows a peak around 0900 hrs LT when the rate of increase of ΔH with time is largest. The peak of ΔZ is largest at Kanyakumari and decreases with increasing latitude of the station. The phenomenon is suggested due to sub-surface induction in southern Indian region and not confined to Palk Street. Solar flares cause a temporary increase of the ionospheric current along the pre-flare direction. Faster flares indicate induction effects at each of the equatorial stations. The storm time variation of Z also shows the sub-surface induction effects at electrojet stations in India. Storm time variations in H are shown to be enhanced over the stations close to the dip equator during the local mid-day hours. The equatorial electrojet is shown to be closely affected by ionospheric as well as magnetospheric currents and by the currents induced by these in sub-surface conducting regions.