H-Component residual Geomagnetic field variation at low and equatorial stations during the geomagnetic storm of May 29-31, 2003

Abstract

The variation of the H-component residual geomagnetic field during the storm of 29-31 May, 2003 has been studied for features of induced current at low and equatorial stations. Five stations (three from the Indian chain of stations) lying close to the dip equator but within less than 7 hrours apart were used to investigate the nature of the response of the ground stations to possible induced fields other than the usual solar quiet daily variation and the field associated with the ring current which are dominant during geomagnetic storms.  The residual field was obtained by subtracting the Sq field obtained from the five international quietest days and the Dst representing the strength of the equatorial ring current during the period of the storm. It was observed that the northern Hemisphere stations (TIR AGB, PON and AAE) all exhibited strong positive excursions (~50-70nT) of the residual fields during the main phase of the geomagnetic storm. The southern hemisphere station ASC showed a negative excursion which was approximately the same strength as the stations in the Northern hemisphere. The variations in the residual field during the main phase cannot be attributed to the EEJ but to local induced currents associated with the intensification of the geomagnetic storm. An negative excursion was observed during the recovery phase of the geomagnetic storm and it was observed in all the stations in the northern hemisphere stations. It is suggested that such i variation at the dusk/dawn sector has its origin at the aurora but conveyed to the equatorial and low latitudes by field aligned currents.