Solar flare effects on the geomagnetic elements during normal and counter electrojet periods

Abstract

The paper describes the study of solar flare effects (sfe) on horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field at the Indo-USSR chain of magnetic observatories extending from the magnetic latitudes 0° to 45°N, a network not available any where else in the world. Events are selected when strong, normal and reversed (counter) equatorial electrojet are in existence as well as when only a partial counter electrojet is present. During a strong and normal electrojet event time, sfe consists of a positive impulse in H at all stations, the amplitude of H following the latitudinal variation similar to that of the quiet day monthly mean, Sq (H). The sfe in Y is negative at all the stations. Sfe in Z shows positive impulse at the four-electrojet stations and negative at other stations. During a counter electrojet period the effect of solar flare on H field is negative impulse at electrojet stations, positive at low latitude and again negative at stations north of Sq focus. Sfe in Y is small at all the equatorial nd negative at higher latitude stations. However, sfe (Z) is negative at the equatorial latitudes. During a partial counter electrojet period the observed effect is the combination of an increase of the planetary current component and the decrease of the electrojet component, giving rise to a negative impulse in H at equatorial stations and apositive impulse in H, increasing with increasing distance from the equator. These results are presented and discussed.