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 ΔZ/ΔH exceeded 1.0 in most of the cases, the mean value being 1.34. During counter electrojet period both ΔH and ΔZ were negative maintaining similar high ΔZ/ΔH values. These abnormal values of ΔZ 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.