Solar flare effects in geomagnetic field at Indian stations—Part II : Annamalainagar, near the edge of electrojet

Abstract

The solar flare effects (SFEs) in horizontal (<i>H</i>),<i> </i>eastward (<i>Y</i>) and vertical (<i>Z</i>) components of the geomagnetic field at Annamalainagar have been described .The SFE in <i>H </i>is maximum at 0930 hrs LT, which is significantly earlier than noon. The SFE in <i>Y </i>showed a broad minimum around midday. The SFE in Z or Δ<i>Z</i>/Δ<i>H </i>did not show any diurnal variation. The Δ<i>Y </i>was negative during normal electrojet period and positive during counter electrojet period. The Δ<i>Z</i> value was negative during counter electrojet, but during normal electrojet period Δ<i>Z</i> had equal possibility of being positive or negative. The Δ<i>Z</i> value was found to be negative for flares with slow growth and positive for flares with fast growth. It is suggested that during fast solar flare the abnormal electromagnetic induction is much enhanced extending positive Δ<i>Z</i> effects to larger distances from the Palk Strait. The observed SFE in <i>Z</i> at Annamalainagar is due to combined effects of the normal ionospheric current and due to the electromagnetic induced current in Palk Strait, the intensity of which is related to the rise time of the solar flare.