Waves with harmonic structure below and above the lower hybrid resonance observed on the CENTAUR 35.001 and 35.002 rockets

Abstract

Measurements obtained from the 0- to 10-kHz electric-wave experiment and the 0- to 4.2-kHz electron-density fluctuation experiment on the CENTAUR 35.001 and 35.002 rockets launched in December 1981 are presented. The observations include (i) spectacular narrow-banded signals with harmonic structure related to the proton gyrofrequency. The bands are observed both below and above the lower hybrid frequency, from 2 to 10 kHz, and are modulated in frequency during a rocket spin, typically by 2 kHz. The character of the signals indicate that they are generated by the presence of the payload in the plasma. The source of free energy remains unidentified; we suggest, however, a perpendicular ion beam emitted by or created by the presence of the payload, generating flute-mode ion cyclotron harmonic waves. (ii) Bursts of harmonic waves are received primarily below 2 kHz. The fundamental frequency of these emissions varies over a large range, from 47 to 700 Hz, and is rarely at any of the characteristic frequencies of the plasma. (iii) Waves with a clear lower cutoff at the lower hybrid frequency are also observed. The lower hybrid frequency estimated from magnetic field and density measurements and from the wave measurements agree within 6% (500 Hz).