Coordinated measurements of slot region electron precipitation by plasmaspheric wave bands

Abstract

It has been hypothesized by Lyons et al. that electrons in the slot region are precipitated by cyclotron resonance interactions with the plasmaspheric whistler mode wave bands. The energy spectra and the variations with L shell of the energy bands of the precipitating electrons have been found by Imhof et al. (1974) to be consistent with cyclotron resonance by waves in the few hundred Hz to few kHz range. Now, for the first time, simultaneous measurements have been made of the precipitating electron spectra, the wave frequency distributions, and the plasma density profiles. The electron measurements were performed from the P78‐1 low‐altitude satellite, whereas the wave and plasma density observations were made with the plasma wave experiment on the ISEE 1 spacecraft. Broad bands are often observed in the electron energy spectra with a well‐defined low‐energy cutoff that decreases in energy with increasing L value in a manner consistent with that calculated for first‐order cyclotron resonance with waves at the high‐frequency cutoff of the band. On the basis of the electron spectra from P78‐1 and the plasma densities obtained from the upper hybrid resonance frequencies measured on ISEE 1, the hiss cutoff frequencies are calculated for an assumed first‐order cyclotron resonance interaction and compared with the wave spectral density profiles measured on ISEE. Overall, the plasma wave and the electron measurements are consistent with each other, supporting the earlier hypothesis for the precipitation mechanisms.