HF RADAR STUDIES OF 2-STREAM INSTABILITY DURING AN EQUATORIAL COUNTER-ELECTROJET

A very strong daytime counter-electrojet was observed on January 21, 1977, near the magnetic equator in Africa. This phenomenon was investigated for the first time using simultaneous magnetic and radar measurements. As predicted by the linear theory, irregularities associated with the two-stream instability were detected in the absence of the usual turbulence related to the cross-field effect (or type 2 irregularities). In addition, taking advantage of the refraction of the HF radio waves in the E layer, horizontal or quasi-horizontal plasma waves were detected for the first time together with the usual oblique waves. Two kinds of spectra were distinguished from the radar observations. A hypothesis is proposed to explain the observation.