Short-period geomagnetic variations at two stations in Sri Lanka and their relation to channelling of induced currents through a conducting region beneath the Palk Strait

Abstract

Electric currents induced in the deep ocean and channelled through a conducting region beneath the Palk Strait have been invoked by earlier workers to explain anomalies in transient geomagnetic variations such as bays, SSCs and substorms observed at some South Indian coastal stations. The need for confirmation of this idea by measurement on the Sri Lankan side across the Palk Strait has been emphasised by these workers. In the present study, rates of change in the geomagnetic field components in the period range 20–600 s recorded at Kondavil and Hikkaduwa, two stations in the equatorial electrojet belt near the northern and southwestern coasts, respectively, of Sri Lanka, have been analysed and discussed. The results are presented in the form of variation with period of ΔZ/ ΔH and ΔD/ ΔH at Kondavil, ΔZ/ ΔH at Hikkaduwa and of ΔH C/ ΔH H, the ratio of H components at Colombo and Hikkaduwa. They provide strong confirmatory evidence for channelling of induced currents through a conducting region beneath the Palk Strait and could serve as valuable control data in any detailed modelling of the conductivity structure beneath the Palk Strait. A day-time enhancement of ΔZ/ ΔH at Hikkaduwa at all periods in the observed range and a similar enhancement of ΔH C/ ΔH H were observed. These enhancements are possibly due to the effect of the equatorial electrojet on the short-period variations.