Comparison and validation of photochemical models for atomic oxygen ion retrieval from ground-based observations of 630.0 nm airglow near Irkutsk

This study presents three photochemical inversion models derived to retrieve the atomic oxygen ion density ([O+]) profile from the first excited state of oxygen (O(1D)) 630.0 nm intensity. It is known that atomic oxygen ion (O+) is the dominant chemical constituent of the ionospheric F-region, playing a crucial role in the longer lifetime of ionospheric plasma in this region. The models are intended to be used in conjunction with the ground-based photometer and spectrometer observations, to provide an additional option for ionospheric F-region observations using passive instrumentation. The performance of the photochemical inversion models was evaluated with a series of observing system simulation experiments and validations by using Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) results, with the derived [O+] showing a high correlation for each with the TIE-GCM model truth. Furthermore, the uncertainty testing results reveal the significant influence of the charge exchange of O^{+} + O_2→O_2^{+} + O in this photochemical process, while the transitions of the atomic nitrogen (N) excited states were considered in the processes responsible for the production of O(1D) as well (Bates, 1982) to establish a result closer to the real-world condition than the ones derived from general formulas by Link et al. (1981) and Sobral et al. (1993). Consequently, the photochemical inversion model derived from the unbalanced equation by Khomich et al. (2008) was modified according to the photochemical theory for the first time in this study. The results indicate that the modified model is capable of revealing an estimation of the retrieved [O+] similar to both FORMOSAT-3/COSMIC and the digisonde DPS-4 observations at Irkutsk station IR352 by using empirical models and 630.0 nm visible airglow observations from Irkutsk, Russia, manifesting promise for further usage to monitor mid-latitude ionospheric F region variability using passive photometric observations.