Observations of deep convective updrafts in tropical convection and their role in the generation of gravity waves

A few sequential strong updrafts of magnitude about 8-10 m/s in the upper troposphere were observed by the MST radar at Gadanki (13.5degreesN, 79.2degreesE), India on 21-22 and 22-23 June 2000. On both days, convective storms with rainfall appeared over the radar site. The updrafts region shifted upward by a distance of about 3-4 km within a time-range of 8-10 minutes, and terminated around 15-16 km (the level of neutral buoyancy). The signature of the gravity wave was seen in both the upper troposphere and lower stratosphere. The main mechanism involved in the generation of the gravity waves most likely came from a vertically oriented oscillator, which triggered by convective updrafts near the neutral buoyancy level analogous to the mechanical oscillator. The resultant gravity waves had a vertical wavelength of about 2-5 km, and dominant wave periods of 10-20 minutes (above tropopause) and similar to10 minute (below tropopause). However, variations whose period is below 10 minutes in the troposphere are thought to be not due to the gravity waves, but due to oscillatory behavior of the updrafts. The horizontal wavelengths, and intrinsic group velocity corresponding to these gravity waves, in the lower stratosphere, are estimated in the range of 10 to 20 km, and 10-12 m/s, respectively. The direction of average group velocity is estimated at about 15-20 degrees from the horizontal.