Electromagnetic induction due to solar flares at equatorial stations

Abstract The solar flare effects (sfe) in the horizontal ( H ), vertical ( Z ) and eastward ( Y ) geomagnetic fields at the equatorial electrojet stations around the world operating during International Geophysical Year and International Geophysical Cooperation Year (IGY–IGC, 1957–59) period have been examined. The amplitude of sfe( H ) at any station was maximum around midday hours. The amplitude of sfe( Z ) showed an abnormally large positive value at Trivandrum in spite of it being only 0.3° south of the magnetic equator. The ratio of Δ Z /Δ H exceeded 1.0 in most of the cases, the mean value being 1.34. During counter electrojet period both Δ H and Δ Z were negative maintaining similar high Δ Z /Δ H values. These abnormal values of Δ Z at Trivandrum are due to induction of electrojet current in the conducting graben in Palk Strait, between India and Sri Lanka. The latitudinal extent of induction effects in sfe( Z ) in India depends on the sharpness of the temporal growth of the flare.