Imager observation of concentric mesospheric gravity waves over Srinagar, Jammu and Kashmir, India

Abstract

Using the NARL airglow imager in the Indian subtropical station of Srinagar, Kashmir, India, we report the characteristics of the concentric deformed circular pattern of gravity waves detected at ∼85 km height. OH molecular emission intensities from the height of ∼85 km as observed by the imager in the wide band optical filter of centre wavelength of 840 nm show concentric deformed circular gravity waves drifting northwestward. Using Atmospheric Infrared Sounder (AIRS) image at the centre wavelength of 8.1 µm, deep convective activity around the imager site in the lower atmosphere is recognized as the source mechanism of the observed concentric gravity waves in the mesosphere. The determined phase speed, direction and period of these concentric gravity waves (CGWs) is ∼47 m/s, 150° north of east and ∼10 min (intrinsic period ∼8 min) respectively. At heights of ∼97 km [OI (1S)] and ∼250 km [OI (1D)], these concentric gravity waves are sporadically visible depending on the possible vertical movement of airglow layer height. The dissipated portions of these concentric gravity waves get converted into turbulence at these heights. Using anelastic gravity wave dispersion relation, decreasing horizontal wavelength from the centre of concentric gravity waves is explained. This result is novel in the sense that it disagrees with most of the earlier interpretations of such observations.