Radiosonde Observations of Turbulence in the Troposphere and Lower Stratosphere over Indian Monsoon Region
Tuesday, 16 December 2014
Altitude structure of turbulence in the troposphere and lower stratosphere at Trivandrum (8.5°N, 76.9°E) and Gadanki (13.5°N, 79.2°E) are studied using GPS-radiosonde observations (~1000 profiles) during the period December 2010 to March 2014 as part of the Tropical Tropopause Dynamics (TTD) Experiment under CAWSES-India program. In the this study, the turbulence in the troposphere and stratosphere were delineated by applying the raw data of temperature, pressure and humidity obtained from radiosondes to Thorpe analysis by taking into account the effect of saturation in the temperature profiles and also the instrument noise. The study shows that turbulence strength decreases with altitude in the troposphere and is found to be high during the Indian summer monsoon season in the altitude region 2 to 10 km. Thin layers of turbulence are persistently observed within the Tropical Tropopause layer (TTL). This study also showed that, the occurrence of turbulence is relatively large in the altitude region 10-15 km than in altitude region of 3 to 8 km. In the TTL region, occurrence of turbulence is very small and least in the stratosphere. The gross structure of turbulence in the troposphere and stratosphere at the two stations are similar. The mean structure of occurrence of the turbulence are closely associated with altitude structure of stability parameters. This study indicates that, the mechanisms responsible for the generation of turbulence in the troposphere at the two stations are the same. While the turbulence in the 10-15 km region is mainly governed by the convective instabilities, the turbulence in the TTL region is caused by both dynamic and convective instabilities. The generation of turbulence in the lower stratosphere could be due to strong wind shear. These features of turbulence will have different implications in determining the distribution of minor constituents and alter the composition and microphysics in that region.