Seasonal variations of tropical F-region nightglow emissions and correlative ionospheric studies

Abstract

Simultaneous zenith measurements of the forbidden OI 630 nm and permitted 777.4 nm nightglow emissions have been carried out at Cachoeira Paulista (22.7°S, 45.0°W; geomag. 11.9° S), Brazil, during the period February 1983-May 1984, a period of medium solar activity. This first long series of simultaneous observations has been analysed to study the mean seasonal-nocturnal variations of these emissions in conjunction with simultaneous ionospheric data, obtained at the same location. Salient features of these observations are presented and discussed. The OI 630 nm emission mean seasonalnocturnal variations show the presence of pre- and post-midnight enhancements, with intensity levels slightly lower in the winter season. The OI 777.4 nm emission mean seasonal-nocturnal variations show a monotonie intensity decrease in time, with very low intensity levels during the winter season. A comparison has been made between the F-region peak electron densities, and heights determined from the optical and ionosonde remote sensing methods. In general, a good correlation is found between the measured and the nightglow inferred ionospheric parameters. The observed airglow intensity variations are also compared with those predicted by a semi-empirical low latitude ionospheric model.