The IMF B Y control of the motion pattern and the location of cusp auroral activity has been continuously monitored in a case when the B Y component of the interplanetary magnetic field (IMF) went from −15 nT to +15 nT in the course of 20 minutes. This is the first time a direct observation of an IMF B Y regulated shift in the longitudinal position of the auroral cusp has been documented. The IMF B Y regulation of the cusp is regarded to be a unique signature of magnetopause reconnection. In this particular case the zonal shift of the cusp centre is estimated to be at least 3 hours in magnetic local time. The observations indicate that the cusp reconfigured within a few minutes after the B Y polarity change imposed on the magnetopause.
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Moen et al. (1999) studied this question.