Rocket observation of electron fluxes over a pulsating aurora

Abstract

A sounding rocket S-520-12 was launched from Andøya, Norway at 02:06:00 U.T. on 26 February 1990, into pulsating aurora. Electron energy spectra were observed with a quadrispherical electrostatic analyzer (QESA). The rocket flew from one pulsating patch to another, and we observed the spectral variation of precipitating electron flux following this transition. Pulsation of particle flux was observed in the precipitating electrons above 4 keV and the spectrum was fitted with a power-law distribution, although the electrons with energy less than 4 keV did not show significant pulsation. We found that the pulsation periods obtained through Fourier analysis for the auroral emission recorded by ground TV camera and for the in-situ energy flux data of the precipitating electrons agreed well. However, the one-to-one correlation between the electron energy flux and the auroral intensity was relatively poor. We attributed this to the spatial nonuniformity of the boundary region between two pulsating patches, and to the unstable phase relationship between the dominant Fourier components of the auroral emission and the electron energy flux. This might be caused by the propagating and streaming nature of the pulsating aurora during the time of the observation. We also found low-energy electron precipitation at the boundary region between the two pulsating patches, which can be attributed to the acceleration of the electrons at an altitude of several thousand kilometers by upward-propagating kinetic Alfvén waves. That wave might be generated in association with the ionospheric conductivity change caused by the precipitation of the auroral electrons and the resultant enhancement of ionization of the upper atmosphere.