Spectral features of ionospheric plasma waves excited by powerful HF radio waves radiated at frequencies near electron gyroharmonics and F2-layer critical frequency

We present the result of studies into characteristics high-latitude ionospheric F-region longitudinal plasma waves (Langmuir and ion-acoustic), caused by impact powerful HF radio ordinary (O-mode) or extraordinary (X-mode) polarization EISCAT/Heating facility, Tromsø, Norway. The on October 20, 2012 February 26, 2013 were emitted in direction magnetic zenith with a step change effective radiation power (ERP). frequency fH facility was close to F2-layer critical foF2 (fH/foF2~1) exceeded electron gyroresonance fH>5fce. On 2012, conditions fH/foF2~0.85–0.95 fH<6fce fulfilled. Analysis EISCAT measurements an incoherent scatter radar (ISR) at 930 MHz, spatially aligned heating for ERP<200 MW, has shown that parametric decay instabilities are excited heights where pump is Langmuir frequency, fH≈fPL. have studied peculiarities excitation as function height ionosphere wave polarization, ratios between foF2, also nfce.