Solar flare effects in equatorial counter electrojet currents

Abstract

THE solar flare effect on the horizontal component of the geomagnetic field (H) during the period of counter equatorial electrojet current is characterised by a negative crochet (decrease of the H field) at an equatorial electrojet station and a positive crochet (increase of H field) at a low latitude station outside the electrojet belt. During the period of partial counter electrojet, the crochet in H may be positive at all low latitude stations but the amplitude decreases at stations nearer to the equator. We explain this as the combined effect of the solar flare on the normal eastward currents over the Equator associated with Sq current system (around 107–110 km) as well as on the westward counter electrojet current (∼ 100 km) both flowing simultaneously over the low latitude stations, while at stations outside the equatorial region the solar flare effect is due to only the eastward Sq currents. (The Sq currents are currents in the upper atmosphere arising from convective motion through the geomagnetic field1,2.)