Exploring HF-induced ionospheric turbulence by Doppler sounding and stimulated electromagnetic emissions at the high frequency active auroral research program heating facility

We report on the features of the F region plasma perturbations during HF heating experiments at the High Frequency Active Auroral Research Program facility in March–April 2011 and May–June 2014. The diagnostics included multifrequency Doppler (phase) sounding (MDS) and stimulated electromagnetic emission (SEE). The results concern modification of the electron density profile near the reflection and upper hybrid heights, as well as correlation of the density modification with temporal behavior of narrow continuum, downshifted maximum, and broad continuum SEE spectral features. We reveal also a new SEE spectral feature which appears in the SEE spectra for the pump frequency f0 near the third and fourth electron gyroharmonics. It is located in the SEE spectrum well below the pump wave frequency, f — f0 ∼ –(40–220) kHz, occupies a wide frequency range till 100–150 kHz, and is termed the broad downshifted emission.