Pulsating auroras: Evidence for noncollisional thermalization of precipitating electrons

Observations with a stereo television system show that many pulsating auroras have vertical extents of less than 2 km. This is significantly less than has been calculated based on collisions between precipitating electrons and the atmosphere. Assuming that the pulsating auroras are caused by precipitating electrons, the data suggest that noncollisional interactions, localized in the lower E region (90–107 km), where most of the pulsations are observed, may play a dominant role in thermalizing the particles. Proximate pulsating forms may be at different altitudes, but invariably, the pulsating auroras appear at lower altitudes than interspersed nonpulsating forms. The altitude is essentially constant during an individual pulsation as well as between succeeding similar pulses in a series, but the average altitude of all pulsations appears to increase toward dawn.