Equatorial E region electric field changes associated with a geomagnetic storm sudden commencement

Abstract

The sudden commencement of geomagnetic storms occurring during daytime hours is shown to amplify or even to initiate equatorial ionospheric instabilities associated with the q type of sporadic E layer and the scatter propagation of VHF radio waves. The negative impulse of a ssc- + type of event is seen to be reproduced faithfully in the transequatorial VHF radio wave propagation, first as a sudden decrease of the signal strength and then as an increase. It is suggested that the enhancement of the H field over the magnetic equator during ssc events is due to the imposition of an additional electric field over the equatorial region, causing additional ssc-associated electrojet currents.