Excitation of Langmuir and Ion–Acoustic Turbulence in the High-Latitude Ionosphere by a High-Power HF Radio Wave Simultaneously Below and Above the F 2 -Layer Maximum

We present the results of experimental studies of the generation peculiarities and features of the Langmuir and ion–acoustic turbulence in the F region of the high-latitude ionosphere excited by high-power HF O-mode radio waves emitted by the EISCAT/Heating facility (Tromso, Norway) in the direction of the Earth’s magnetic field. The experiment was carried out at frequencies fH close to the fourth gyroharmonic, fH < 4fce, and the cutoff frequency of the F2 layer, foF2 , fH < foF2 < fH+fce/2, where fce is the electron gyrofrequency. By using the EISCAT incoherent scatter radar (930 MHz), a joint analysis of the plasma and ion line spectra simultaneously below and above the F2-layer maximum was performed. The excitation of the HF-induced plasma lines outshifted by 0.35–0.45 MHz from the pump-wave frequency and HF-enhanced ion lines simultaneously below and above the F2-layer maximum was found for the first time. The mechanisms of the pump-wave propagation to altitudes above the F2-layer maximum and a plausible mechanism for the excitation of the instability responsible for the generation of HF-enhanced ion lines and HF-induced plasma lines above the F2-layer maximum are discussed.