Decay instability of a linearly mode converted plasma wave in the ionosphere

Thide et al (1982) have reported that a high power radio wave, on reflection from the ionosphere, contains a considerably wide spectrum. It seems that the incident radio wave, near the critical layer, linearly mode converts into a plasma wave which is susceptible to paramteric decay into a Langmuir wave and an ion-acoustic wave (IAW). The IAW is a weakly damped mode because Te/Ti>1 due to the ohmic heating of the electrons by the incident radio wave. The decay Langmuir wave, moving backward, mode converts to an eletromagnetic wave, to be observed on the ground. The threshhold power for the parametric instability determined by the convection losses due to finite length of the interaction region, is exceeded in the experiment of Thide et al (1982). (author). 6 refs