Gravity waves are well known to deform the bottomside plasma of the F-region into the wavelike ionization structures which then act as a seed to Rayleigh-Taylor instability, which, in turn, generates irregularities. Present study features midnight fossil airglow depletions that revived due to undergoing GW activity and turned into an active depletion.

Using an empirical approach put forward by Makela et al. (2001), firstly, we propose a novel technique to calibrate OI 777.4 and 630.0 nm emission intensities using COSMIC/FORMOSAT-3 electron density profiles. Next, electron density maximum (Nm) and its height (hmF2) of the F layer are derived from the information of two calibrated intensities. Sample Nm and hmF2 maps are also generated to show the usefulness of this technique in studying ionospheric processes.

This study investigates the long-distance propagation (~ 1200–2000km) of gravity waves in the Indian subcontinent using coordinated nightglow measurements at Allahabad and Gadanki (separated by ~ 12º latitude). On few occasions, an identical wave (period in range ~ 2.2–4.5h) was seen at both sites that shared a common source. Waves had large horizontal wavelength (~ 1194–2746km) and phase speed (77–331m/s). The m2 profile analysis suggests the ducted propagation of the common waves.