Role of gravity wavelike seed perturbations on the triggering of ESF – A case study from unique dayglow observations

Abstract

First observational evidence, from the Indian longitudes, for the presence of gravity wavelike perturbations with periods of 20-30 min, acting as probable seeds for Equatorial Spread F (ESF) irregularities is described. The study is based on the daytime optical measurements of the mesopause temperature and the intensity of the thermospheric O(1D) 630.0 nm dayglow emissions using the unique MultiWavelength Dayglow PhotoMeter from Trivandrum (8.5° N; 77° E; dip lat ∼0.5° N), a dip equatorial station. Measurements during the equinoctial months of a solar maximum (2001) and a solar minimum year (2006) have been used in this study. It is shown that under identical background ionospheric conditions within a solar epoch, the power of the gravity waves have a deterministic role in the generation of ESF. The mesopause temperature simultaneously observed, indicate that possible source regions for these perturbations lie in the lower atmosphere.