Atomic oxygen ion retrieval from 630.0 nm airglow during geomagnetically quiet periods: a mid-latitude case study near Irkutsk

This study develops and validates three photochemical inversion models to retrieve atomic oxygen ion density ([O ⁺ ]) profiles from 630.0 nm airglow emissions in the mid-latitude ionosphere during geomagnetically quiet period. Using passive ground-based instruments and empirical models, the models were tested and compared against electron density data from FORMOSAT-3/COSMIC (F3/C) and DPS-4 digisonde at Irkutsk. Among the models, Inversion Model 3 showed the strongest agreement with observations, particularly in capturing seasonal variations such as the June–July peak and a secondary March–April peak, which were absent in IRI-2012 predictions. These results highlight the potential of Inversion Model 3 for accurate [O ⁺ ] retrieval, offering a novel approach for monitoring ionospheric variability using passive photometric observations.