Geomagnetic field variations at the equatorial electrojet observatory, Etaiyapuram

Abstract

<span style="mso-bidi-language:HI">The extent of the effect of electromagnetic induction in sub-surface has been investigated using geomagnetic data for the period 1980-1986 from a station Etaiyapuram situated between Trivandrum and Kodaikanal and away from the seacoast, but close to the magnetic equator. The station Etaiyapuram exhibits forenoon maximum and afternoon minimum in Z component for all seasons, similar to that for Trivandrum, contrary to the expectations from Chapman's theory of equatorial electrojet. Daily variation of Z shows characteristic features for Trivandrum during the years when sun is active, but characteristic features for Kodaikanal when sun is calm suggesting that the latitudinal extent of anomalous induction in Palk Strait decrease with decreasing solar activity. This abnormal induction effect at Etaiyapuram is found to be enhanced during periods of strong electrojet current. The daily variation of disturbance in geomagnetic Z field does not indicate any abnormal effect due to induction, but storm time <i>D</i>_st(Z) variation shows clearly the induction effects. Similarly, the amplitude of storm sudden commencement (SSC) in <span style="mso-bidi-font-family: Arial;mso-bidi-language:HI">ΔZ<i> </i><span style="mso-bidi-language: HI">at Etaiyapuram is found to be affected by electrojet as well as by the sub-surface currents.

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