CASCADING OF THE UPPER HYBRID ELECTRON BERNSTEIN WAVE IN IONOSPHERIC HEATING EXPERIMENTS

Parametric decay of an upper hybrid/electron Bernstein pump wave into an upper hybrid/electron Bernstein sideband wave and a lower hybrid decay wave in the long-wavelength regime is studied. It is found that the process associated with the electron Bernstein pump wave has a lower threshold field than that of a similar decay process of the upper hybrid pump wave when the instability is excited in the region away from the double resonance layer. Near the double resonance layer, where the upper hybrid resonance frequency equals a harmonic of the electron cyclotron frequency, the upper hybrid wave and the electron Bernstein wave become linearly coupled, and the threshold field of the parametric decay process changes back to a similar functional dependence as that of the upper hybrid decay process. Thus, their threshold fields approach each other. When incorporated with appropriate nonlinear scattering processes, this instability process along with its cascading is proposed to be the generation mechanism for the downshifted maximum (DM), 2DM, 3DM, ... etc. features as well as the upshifted maximum (UM) feature in the stimulated electromagnetic emission spectrum observed in ionospheric heating experiments.