AMPLITUDE-MODULATION OF THE EQUATORIAL ELECTROJET (EEJ) DURING A MAGNETOSPHERIC STORM

An encounter of the Earth with a high velocity solar wind-stream trigg ered the magnetic storm of 29 January 1995. The storm lasted for the f ollowing seven days, keeping the level of the Dst index in the range o f -25-50 nT. At the dip-equator, a regular enhancement of the magnetic H component during daytime, referred to as the Equatorial Electrojet (EEJ), was seen to be suppressed and modified during this storm interv al. We attempted to classify the type of the EEJ modification by analy zing magnetometer data from two stations at the dip-equator but locate d in the opposite hemisphere, and energetic particle data from two geo synchronous satellites located close to the ground magnetometer meridi an. As a result, three different types of modulation of EEJ amplitudes , with time scales of 15 min to 1 day, were found to appear during the periods when the flux level of low energy charged particles (>30 keV) in-the midnight magnetosphere was increased above the quiet level. Th ese modulations were characterized by referring to the nightside parti cle signatures. We argue that, although the EEJ is a local enhancement of the ionospheric currents at the dayside dip-equator, the EEJ is de finitely affected by changes of the magnetosphere, probably in various ways arising from the complexities of the storm effects. (C) 1998 Els evier Science Ltd. All rights reserved.