Variations in the doppler profile of Hα in aurorae

Abstract

Variations in the observed Doppler profile of Hα emitted from high latitude aurorae are reported. On one particular night the half-width of the horizon profile ranged from about 15 to 23 A. The variations are interpreted as changes in the pitch angle and velocity distributions of the incident protons. With an assumed pitch angle distribution of the form cos n θ the index n seems to vary from below 0 to about 6. Theoretical considerations show that this may indicate that the protons are accelerated in the vicinity of the Earth.