High frequency induced enhancements of the incoherent scatter spectrum at Arecibo. II

When the ionospheric F region is illuminated with a strong O mode HF radio wave, excitations of longitudinal plasma and acoustic waves are observed by 430-MHz radar scattering. The frequency structure of the excited waves and their variability with local parameters, time, and space are described. The observations are interpreted in terms of parametric instability theory. The spectra of the observed features and the correlation of their amplitudes are shown. The upshifted and downshifted plasma lines exhibit some marked asymmetries. Absolute as well as relative amplitudes of the enhancement are presented.