Geomagnetic storm effects on zonal and meridional equatorial electrojet currents

Abstract

The sudden commencements of geomagnetic storms at the equatorial electrojet station Kondaikanal are characterized by simultaneous increases of both the horizontal field H and the westerly declination D(W) or the decrease of eastward field, Y. The amplitudes of the SSC in H or Y fields (ΔH and ΔY) show a maximum deviation around midday hours. The ratio of ΔY to ΔH is about 0.23 for any hour of the day or night. During the main phase of the storm, the fluctuations in the H and Y components at Kodaikanal vary in unison with each other. Occasional large decreases of the H field at Kodaikanal at daytime hours during the main phase of the storm do not have corresponding decrease of H at Alibag or in the equatorial Dst index. These events are shown to be associated with the sudden disappearance of the equatorial type of sporadic E(Esq) at Kodaikanal indicating a temporary reversal of the ionospheric electric field over the magnetic equator to westward direction. The observed storm time variations of the magnetic fields at an equatorial electrojet station are suggested to be due to the combined effects of the equatorial ring current and of the electric field changes at the ionospheric region transmitted from high latitudes.