EVOLUTION OF THE GLOBAL AURORA DURING POSITIVE IMF B-Z AND VARYING IMF B-Y CONDITIONS

The DE 1 imaging instrumentation provides a full view of the entire am oral oval every 12 min for several hours during each orbit. We examine d five examples of global evolution of the aurora that occurred during the northern hemisphere winter of 1981-1982 when the a component of t he interplanetary magnetic field was positive and the y component was changing sign. Evolution of an expanded amoral emission region into a theta aurora appears to require a change in the sign of B-y during nor thward interplanetary magnetic field (IMF). Theta aurora are formed bo th from expanded duskside emission regions (B-y changes from positive to negative) and dawnside emission regions (B-y changes from negative to positive), however the dawnside-originating and duskside-originatin g evolutions are not mirror images. The persistence of a theta aurora after its formation suggests that there may be no clear relationship b etween the theta aurora pattern and the instantaneous configuration of the IMF.