Substorm dynamics revealed by ground observations of two-dimensional auroral structures on 9 October 2000

Multi-instrument observations of a small substorm event on 9 October 2000 provide, with high time resolution, two-dimensional information about substorm dynamics. A sequence of three optical intensifications, each associated with a Pi2 burst, were found, in which the third auroral intensification marked the onset of a small substorm. All three intensifications originated close to midnight, but evolved progressively eastward. Within each of the three optical intensifications, a few azimuthally-spaced patches appeared, the first one near midnight and the subsequent patches successively eastward in the postmidnight sector, providing evidence for drift wave activity in the near-geosynchronous-orbit plasma sheet (NGOPS). The SuperDARN measurements reveal the development of eastward electric fields at NGOPS latitude within each Pi2 burst interval. These observations can be interpreted as supporting the drift-Alfven-ballooning (DAB) mode instability and its role in substorm expansion at NGOPS.