Abstract
Energy spectra and pitch angle distributions of auroral electrons were obtained by means of two sounding rockets launched respectively into stable auroral arcs in geomagnetically quiet condition, and into active auroral arcs during the expansion phase of a substorm. These rockets were launched from Syowa Station, Antarctica in the austral winter in 1985.
It was found that the observed energy spectra of downward electrons show a plateau extending from about 1keV to several keV in the center of an auroral arc, while they have a mono-energetic peak at the edge, or just outside an auroral arc. This feature suggests that strong wave-particle interaction processes are occurring on auroral field lines.
The pitch angle distribution of auroral electrons at the mono-energetic peak was isotropic in the range from 0° to 90° (0° is upward along the magnetic field line), and was almost isotropic in the energy below the peak. The former feature suggests acceleration of auroral electrons at high altitude, and the latter feature is attributable to secondary electrons produced by auroral electrons.
Just outside an auroral arc, the peak energy decreased with the distance from the arc. This feature can be considered to be an inverted-V structure of precipitating electrons observed at the rocket altitude.
