Rayleigh lidar observations of gravity wave characteristics in the middle atmosphere at Gadanki (13.5°N, 79.2°E)

Rayleigh lidar observations of temperature in the stratosphere and mesosphere are carried out at Gadanki (13.5degreesN, 79.2degreesE) from February 29 to March 31, 2000, which provided a powerful means of studying the gravity wave characteristics over the tropical atmosphere during winter. The potential energy per unit mass associated with the gravity wave activity in the upper stratosphere and mesosphere is found to undergo periodic fluctuations, which are closely correlated with the zonal wind fluctuations in the stratosphere produced by the equatorial waves. This provides the first observational evidence for the modulation of the gravity wave activity by the long period equatorial waves over the tropical middle atmosphere. The vertical wave number spectra of gravity waves shows that power spectral density (PSD) decreases with increase in wave number with a slope less than that expected for the saturated gravity wave spectrum in the stratosphere and mesosphere. PSD decreases for vertical wavelengths smaller than about 10 kin in the stratosphere while the decreases is observed for the complete range of observed gravity wave spectrum in the mesosphere. A monochromatic upward propagating gravity wave with periodicity of 6 hour, amplitude of about I K to 3 K and vertical wavelength of 11 km was observed on 22 March, 2000.