SPECTRAL WIDTH OF TYPE-2 COHERENT ECHOES AT LARGE MAGNETIC ASPECT ANGLES

The spectral characteristics of smoothly varying type 2 signals were s tudied using two 50-MHz CW radio links. The echoes observed came from two closely located scattering volumes where the geometrical aspect an gles of observations were about 10 degrees for both links but the azim uthal angles differed by 88 degrees. The events reported here were sel ected when the spectra on both links were wide, with a comparable spec tral width, but the mean Doppler shift was almost zero on one Link and very high, sometimes in excess of the ion-acoustic velocity, on the o ther link. Highly shifted Doppler spectra were observed to be more ske wed than the spectra with low shifts. The skewness was negative for ne gative Doppler shifts and positive for positive Doppler shifts in acco rdance with previous radar observations at large magnetic aspect angle s. The variation of spectral width with the radial velocity or with th e magnetic disturbance level exhibited two regions of linear dependenc e, with a larger slope at small values and a much smaller slope at hig her ones. These different slopes likely reflect the change in the rate of the irregularity amplitude increase with the electric field.