Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771

The storm-substorm relationship is one of the central issues in magnetospheric physics. Whether there is a unique relationship between substorms and storms is still being debated. During geomagnetic storm periods, magnetic disturbances take place globally, and auroras become very active over the entire oval. These often make identification of a substorm, which has smaller magnetic and optical effects, difficult, if not impossible. This study is based on 23 storm events that occurred from May 1996 to October 1998 with simultaneous global ultraviolet auroral observations from NASA's Polar mission. It is found that the auroral breakups occurred more frequently in the main phase than in the recovery phase within the storms; ~ 45% of the studied events occurring within 10 hours before the end (start) of the storm main (recovery) phase; the storm intensity (Dst) does not affect the occurrence of auroral breakup; and Dst changes (∆ Dst) have no effect on the occurrence frequency of auroral breakup.

submitted, JASTP, 2002