First Observations of 140 Mhz Plasma Line Backscatter During Heating Experiments at Tromsoe

摘要

The VHF plasma line backscatter was obtained from the ionosphere illuminated by strong HF radiation from a heating facility. The downshifted plasma line was observed during two periods when the heater operated on a frequency lower than critical. The plasma line was never observed earlier than 5 to 20 sec after heater turn-on and the intensity was very variable in time. Plasma line scattering is thought to be caused by Langmuir waves generated by direct conversion of the heating wave due to interactions with striations built up slowly in the modified ionospheric region. Data indicate a positive correlation between occurrence of plasma line backscatter and increase in intensity of the ionospherically scattered heater wave.