Gravity waves in the tropical middle atmosphere: Characteristics and wave-mean flow interaction

High-resolution Rayleigh lidar observations of temperature in the altitude region of 27–60 km over Gadanki (13.5°N, 79.2°E) during the period of January 18 to March 5 1999 and February 29 to March 31 2000 were used to study the gravity wave characteristics in the tropical middle atmosphere. The vertical wavenumber spectra of gravity waves and the altitude variation of the potential energy per unit mass (Ep) associated with gravity wave activity are found to be similar during both these years. Altitude profile of Ep indicates that significant wave damping occurs in the stratosphere while nearly non-dissipating gravity wave growth is observed in the lower mesosphere. The slope of the vertical wave number spectra is observed to be about −2.1, which is less than that expected for saturated spectra (−3). The gravity wave activity in the stratosphere and lower mesosphere is found to undergo temporal variations, which are correlated with the temperature fluctuations in the middle atmosphere. A longer period wave with a mean vertical wavelength of about 12.8 km and wave period of about 8–14 hours is also observed on several nights.