A simulation study of 630 nm and 557.7 nm airglow variations due to dissociative recombination and thermal electrons by high-power HF heating

One of the important effects of the ionospheric modification by high-power waves is the airglow enhancement. Both the thermal electrons and the dissociation recombination contribute to generate the airglow emissions during HF heating. However, the relative importance of the airglow emission induced by dissociative recombination and thermal electrons has been rarely investigated. In this study, we carry out a simulation study on the airglow produced by high-power HF heating at nighttime associated with dissociative recombination and thermal electrons. SAMI2 (Sami2 is Another Model of the Ionosphere) is employed to simulate the ionospheric variations during the HF heating. The main conclusions from this study are as follows: (1) For the airglow induced by dissociative recombination, both 630.0 nm and 557.7 nm emissions show a decrease at the heating wave reflection height during the heating period, while when the heating is turned off, an increase is shown at lower altitudes. The reduction of airglow during the heating is caused by the rapid increase of electron temperature and the diffusion of plasmas dominates the after-heating airglow enhancement. (2) 630.0 nm emission due to thermal electrons is greatly enhanced at the wave reflection height, indicating that thermal electrons play a major role in exciting 630.0 nm emission. For the 557.7 nm emission, the excitation threshold (4.17 eV) is too high for thermal electrons. (3) The combined effect of dissociative recombination and thermal electrons could be the possible reason for the observed X-mode (extraordinary mode) suppression of 630.0 nm airglow during O-mode (ordinary mode) enhancement.