Energetic particle measurements in a pulsating aurora

Abstract

Electron and proton precipitation at energies greater than 25 kev were measured in an early morning pulsating aurora by rocket-borne particle detectors. Pulsations found in the lower energy (25≤E≤80 kev) electron precipitation were in phase with ground-based photometric observations of the 3914-A emission. In the intervals between the trains of pulsations, (hard) electron and more intense (soft) proton precipitation was reasonably stable. During the pulsations large increases (factors of 4 or 5) in lower energy electron intensities were measured, which resulted in nearly identical electron and proton spectral distributions at the pulsation peak, whereas proton and energetic (E>100 kev) electron precipitation exhibited no detectable variation. Upper limits on intensity fluctuations of protons and energetic electrons were set at 5% and 10%, respectively. Lower energy electrons were found to have anisotropic pitch angle distributions peaked at 90° going isotropic during a pulsation and were responsible for a significant fraction of the 3914-A intensity modulation. Angular distributions of protons and energetic electrons were isotropic for the duration of the flight. These measurements indicate that auroral pulsations result primarily from increases in pitch angle diffusion that cause large electron precipitation enhancements in the energy range 15 to 80 kev. Certain requirements of theoretical pulsation models are discussed.