FIELD-ALIGNED DRIFTS IN SUBAURORAL ION DRIFT EVENTS

Calculations of the response of F region plasma to rapid subauroral io n drifts (SAID) show that the maximum field-aligned drift is a strong function of the time scale over which the SAID is applied. For SAID ve locities of 2 km s-1 the peak field-aligned drifts can vary by almost a factor of 10 for differences in the onset time scale from a few seco nds to a few minutes. Reasonable considerations of the convective conf iguration in a SAID event suggest that acceleration times between 10 a nd 20 min might typically be expected. In such cases, much smaller fie ld-aligned velocities should be observed than would be predicted assum ing an essentially instantaneous turn on of the SAID event.