AURORAL ELECTROJET ACTIVITY DURING ISOLATED SUBSTORMS AT DIFFERENT LOCAL-TIMES - A STATISTICAL STUDY

Magnetic variations processed from the AE observatories and IMP-8 meas urements of the solar wind and interplanetary magnetic field (IMF) are used to study the response of the auroral electrojets at different lo cal times to solar wind and IMF parameters. On the basis of an interpo lation technique, magnetic variations at four different local times (0 000, 0600, 1200, and 1800 MLT) are estimated, which constitutes our da ta base for this statistical study. Forty two events in 1979 met our ' 'isolated substorm'' criteria. It is found that electrojet variations at different local times are significantly different. The substorm exp ansion current system at midnight appears to be initiated when IMF bec omes less southward, and the current systems at dawn and dusk are alre ady active when the substorm expansion current begins and remain activ e even after the midnight substorm current recovers to its pre-substor m level. During the initial stage of the recovery phase (in terms of t he midnight current), the westward electrojet at 0600 MLT continues to intensify while the 1800 MLT eastward electrojet slowly decays.