OCCURRENCE OF TYPE-I PLASMA-WAVES IN THE EQUATORIAL ELECTROJET DURINGMORNING AND EVENING HOURS

Type I waves are generally observed under strong electrojet (EEJ) cond itions because of the threshold condition on the electron drift veloci ty (with respect to ions) for their generation. In this paper we prese nt observation of type I waves during morning and evening hours under weak (as revealed from the low values of mean drift velocity of type I I waves and also from low ground magnetic field values) EEJ conditions . In these conditions, type I waves are observed when the plasma turbu lence in the EEJ as revealed by the width of the Doppler spectra is hi gh even though the electron drift velocity as given by the mean Dopple r frequency is much smaller than the ion acoustic velocity. This sugge sts that there are regions within the volume probed by the radar where in the electron drift velocity exceeds the ion acoustic velocity C-s ( even though the mean electron drift velocity is very much less than C- s) due to the irregular electric fields of the primary irregularities.