Modeling and causative mechanism of OI 630.0 nm nightglow emission over Cachoeira Paulista (22.7oS, 45oW) – Brazil: Seasonal and temporal variability

The seasonal and temporal variability of the OI 630.0 nm nightglow emissions were observed over Cachoeira Paulista (22.7oS, 45oW; dip latitude −35°) in Brazil by multichannel photometer during 2014 and 2015. The temporal variation of the OI 630.0 nm nightglow intensity shows a peak during post-midnight hours (∼25 h00 LT) during the summer. During autumn, this peak is shifted towards pre-midnight at ∼ 22 h00 LT. It is noticed that this peak again shifted towards post-midnight at 26 h30 LT and 25 h30 LT during winter and spring, respectively. The intensity increases by a factor of 2–4 in the summer than that observed in other three seasons. The modelling of the nightglow measurements in 2015 is carried out by calculating the excitation rate, emission rate and intensity of OI 630.0 nm nightglow emission in the upper atmosphere at low latitudes. Our calculation suggests that the dissociative recombination of O2+ with electrons is the main source for the OI 630.0 nm nightglow emission. We report that the model intensities are in good agreement with the measurements at Cachoeira Paulista for all four seasons and the model reproduces all features of peak intensities very well.