Field-aligned auroral electron fluxes

Abstract

Out of a series of five auroral sounding rocket flights, electron fluxes in three of the flights were observed to be sharply field-aligned. The electrons were detected with an array of electrostatic analyzers making 50-point spectral samples from 0 to 15 keV. The field-aligned fluxes resulted in a peak in the spectrum at a lower energy than that of another monoenergetic peak in the spectrum seen consistently when it was conjugate to bright auroral forms giving multiply peaked spectra. The field-aligned peak in the spectrum is apparently a phenomenon distinct from the isotropic peak and was observed to occur at various times in the energy range from a few hundred electron volts to 5 keV. The field-aligned electrons were highly collimated, having pitch angles less than 20 deg and at times less than 10 deg. The high degree of field alignment and the monoenergetic character support the model that these events can be attributed to relatively cool plasma falling through an electric potential at altitudes not too far removed from the rocket.