Post midnight spread - F occurrence over Waltair ( 17 . 7 ◦ N , 83 . 3 ◦ E ) during low and ascending phases of solar activity

A study carried out on the occurrence of post midnight spread-F events at a low-latitude station, Waltair (17.7 N, 83.3 E), India revealed that its occurrence is maximum in the summer solstice months of the low solar activity period and decreases with an increase in the sunspot activity. The F-region virtual height variations show that 80% of these spread-F cases are associated with an increase in the Fregion altitude. It is suggested with the support of the night airglow 6300 A zenith intensity data obtained with co-located ground-based night airglow photometer and electron temperature data from the Indian SROSS C2 satellite that the seasonal variation of the occurrence and probable onset times of the post midnight spread-F depend on the characteristics of the highly variable semipermanent equatorial Midnight Temperature Maximum (MTM).