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A -190-nT negative bay in\ud the geomagnetic X component measured at Macquarie Island ( -65° L)\ud showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27\ud February 2000. Signatures of an auroral westward flow channel (AWFC) were\ud observed nearly simultaneously in the backscatter power, LOS Doppler velocity,\ud and Doppler spectral width measured using the Tasman International Geospace\ud Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of\ud the characteristics of the AWFC were similar to those occurring during a\ud polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that\ud it may have been a pre-cursor to a fully developed, intense westward flow\ud channel satisfying all of the criteria defining a PJ/SAID. A beam-swinging\ud analysis showed that the westward drifts (poleward electric field) associated\ud with the flow channel were very structured in time and space, but the smoothed\ud velocities grew to ~ 800 ms-1 (47 mVm-1) during the\ud 22-min substorm onset interval 09:56 to 10:18 UT. Maximum west-ward drifts of\ud >1.3 km s-1 (>77 mVm-1) occurred during a ~ 5-min\ud velocity spike, peaking at 10:40 UT during the expansion phase. The drifts\ud decayed rapidly to ~ 300 ms-1 (18 mVm-1) during the 6-min\ud recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of\ud 74 min, and was located near -65° L in the evening\ud sector west of the Harang discontinuity. The large westward drifts were\ud confined to a geographic zonal channel of longitudinal ex-tent >20°\ud (>1.3 h magnetic local time), and latitudinal width ~2° L.\ud Using a half-width of ~ 100 km in latitude, the peak electric potential was\ud >7.7 kV. However, a transient velocity of >3.1 km s-1 with\ud potential >18.4 kV was observed further poleward at the end of the recovery\ud phase. Auroral oval boundaries determined using DMSP measurements suggest the\ud main flow channel overlapped the equatorward boundary of the diffuse auroral\ud oval. During the ~ 2-h interval following the flow channel, an ~ 3° L\ud wide band of scatter was observed drifting slowly toward the west, with speeds\ud gradually decaying to ~ 50 ms-1 (3 mVm -1). The scatter\ud was observed extending past the Harang discontinuity, and had Doppler\ud signatures characteristic of the main ionospheric trough, implicating the flow\ud channel in the further depletion of F-region plasma. The character of this\ud scatter was in contrast with the character of the scatter drifting toward the\ud east at higher latitude. Key words. Ionosphere (auroral\ud ionosphere; electric fields and currents; ionosphere-magnetospehere\ud interactions) Magnetospheric physics (storms and substorms

On the lifetime and extent of an auroral westward flow channel (AWFC) observed during a magnetospheric substorm