Seasonal Transition Study of Thermospheric Atmospheric Composition Ratios at Twilight Based on Fengyun-3E Satellite Detection

Two Fengyun-3 satellites are equipped with Ionospheric Photometers capable of detecting the integrated radiant flux of the OI 135.6 nm and N₂ LBH band airglow emissions, from which the ratio (referred to as the 135.6/LBH ratio) is derived. Among them, the Fengyun-3E satellite, the second generation of near-polar sun-synchronous orbit satellites, provides airglow observations during dawn-dusk orbits. The 135.6/LBH ratio is typically proportional to the thermospheric atmospheric composition ratio of [O]/[N₂], reflecting variations in this ratio, which is a significant parameter influencing changes in ionospheric electron density. This paper collects data from Fengyun-3E satellite in the past two years to analyze the seasonal conversion patterns of 135.6/LBH ratio and corresponding parameters in mid to low latitudes. The results showed that the seasonal variation of OI 135.6 nm and N₂ LBH band radiation intensity was mainly in winter and summer, with rapid changes in spring and autumn, and this change varies with latitude. The 135.6/LBH ratio also shows a rapid transition in spring and autumn, but its peak and valley periods are different from the aforementioned two radiation intensities. The mid latitude region shows a seasonal characteristic of high in winter and low in summer, while the opposite is true near the equator, showing a semiannual variation cycle. The study also found that there is asymmetry in the seasonal transition of the 135.6/LBH ratio, which is significantly influenced by latitude and hemisphere. These results demonstrate that the Fengyun satellite ionospheric photometer has good performance in detecting seasonal, latitudinal, and hemispheric variations in the composition ratio of the thermosphere atmosphere, providing important basis for research, modeling, and space weather forecasting of the ionospheric thermosphere.