Magnetic variations processed from the AE observatories and IMP-8 measurements of the solar wind and interplanetary magnetic field (IMF) are used to study the response of the auroral electrojets at different local times to solar wind and IMF parameters. On the basis of an interpolation technique, magnetic variations at four different local times (0000, 0600, 1200, and 1800 MLT) are estimated, which constitutes our data 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 substrom expansion current system at midnight appears to be initiated when IMF becomes less southward, and the current systems at dawn and dusk are already active when the substorm expansion current begins and remain active even after the midnight substorm current recovers to its pre-substorm level. During the initial stage of the recovery phase (in terms of the midnight current), the westward electrojet at 0600 MLT continues to intensify while the 1800 MLT eastward electrojet slowly decays.