On parametric instabilities in HF heating of the ionosphere

The initial processes excited directly by high-frequency (HF) heating waves include parametric decay instabilities, which decay the HF heating wave to a frequency-downshifted Langmuir/upper hybrid sideband together with an ion acoustic/lower hybrid wave as the decay mode, and oscillating two stream instabilities, which decay the HF heating wave to two oppositely propagating Langmuir/upper hybrid sidebands and purely growing mode/field-aligned density irregularities. These instabilities provide effective channels to convert heating waves to electrostatic plasma waves in the F region of the ionosphere. The following-up parametric instabilities include the cascades of Langmuir pump waves into Langmuir sidebands and ion acoustic waves/lower hybrid waves, and the decay of upper hybrid waves to Langmuir sidebands and ion decay modes, as well as the filamentation of those HF electrostatic waves to generate field-aligned density irregularities. The instability thresholds, growth rates, angular distribution and regions of excitation are determined.