Solar flare effects in geomagnetic field at Indian stations—Part I : Trivandrum, the centre of equatorial electrojet

Abstract

The paper describes the solar flare effects (SFEs) in horizontal (<i>H</i>),<i> </i>eastward (<i>Y</i>)<i> </i>and vertical (<i>Z</i>) components of the geomagnetic field at Trivandrum for the period 1957-1982. The impulse in <i>H</i> and <i>Z</i> fields shows a maximum at 1030 hrs LT, significantly before noon. The SFE impulse in <i>Y </i>shows a maximum in forenoon and minimum in afternoon hours. The ratio Δ<i>Z</i>/Δ<i>H </i>is abnormally large (≈ 1.2) and is almost constant for any time of the day. The individual values of Δ<i>Z</i>/Δ<i>H </i>are larger for faster growth of the flare. The abnormal SFE (<i>Z</i>) is suggested to be due to the concentration of general induced current over wide latitude zone both sides of the equator through Palk Strait, besides the electromagnetic induction of ionospheric current in the narrow band of conducting graben in Palk Strait between India and Sri Lanka. The induction is shown to be directly proportional to the growth time of the flare impulse in <i>H </i>field.