A detailed case study of the excitation of a more than 200 km wide flow channel with ionospheric drift speeds exceeding 2 kms-1 is presented. The flow channel is excited during a slowly northward turning IMF and strong IMF By conditions. A brief southward spike in the IMF moves the flow channel equatorward. Thereafter the enhanced flow decreases, consistent with a decreasing IMF By component. The presence and location of the flow channel appear to be entirely determined by the IMF conditions. The flow channel is distinctly different from the poleward propagating convection disturbances associated with strong IMF By for strongly southward IMF Bz. ¿ 1997 American Geophysical Union