Characteristics of atmospheric waves in the upper troposphere observed with the Gadanki MST Radar—RASS

Indian MST Radar at Gadanki (13.46ºN, 79.17ºE) working at 53 MHz was operated continuously in Radio Acoustic Sounding System (RASS) mode with six distributed acoustic exciters during 22–25 August 2007 for about 69 h in RASS and turbulence echo modes alternately, with one cycle spanning about 20 min. Temperature and wind velocity were observed in the altitude range 3.6–12 km most of the time and 3.6–20 km, respectively, with a range resolution of 150 m. Presence of an inertia–gravity wave in the lower stratosphere was identified. Perturbations in the wind and temperature fields in the troposphere, however, indicated a mixture of waves with a wide frequency range, within which a dominant periodicity of ∼8 h with a vertical wavelength of ∼4 km was revealed by two-dimensional spectral analysis. Further, signatures of diurnal tide were also observed and the temperature phase profile was found to exhibit a close match with the Global Scale Wave Model (GSWM02). From the RASS virtual temperature profiles, time–height section of Brunt-Väisälä frequency squared was computed to deduce the background atmospheric stability, which showed stable layered structures with slow downward phase progression. Outgoing Longwave Radiation (OLR) over Gadanki and TRMM precipitation data over peninsular India was used as an indicator of convective activity. During the beginning of the observation period, even though lower OLR was seen, corresponding convective activity or precipitation was not seen in the TRMM data. On 24 August, enhanced temperature perturbations could be related to widespread precipitation shown by TRMM.