Diurnal variation of atmospheric stability and turbulence during different seasons in the troposphere and lower stratosphere derived from simultaneous radiosonde observations at two tropical stations, in the Indian Peninsula

Diurnal variability of atmospheric stability as well as the occurrence and strength of turbulence in the troposphere and lower stratosphere at two tropical stations, Trivandrum (8.5°N, 76.9°E) and Gadanki (13.5°N, 79.2°E), situated in the Indian Peninsula is studied. For the analysis three years of GPS-radiosonde data, collected as a part of the Tropical Tropopause Dynamics (TTD) Experiment under the CAWSES-India program, has been used. Thorpe method is adopted to estimate the turbulent parameters from radiosonde observations. This study shows that in the atmospheric boundary layer, both stability and turbulence parameters depict a pronounced diurnal variation. Over Trivandrum, the occurrence of turbulence as well as its strength peaks during night and falls off during the day, while at Gadanki it shows an opposite pattern. At both the stations, in the 3-10 km altitude layer, the occurrence and strength of turbulence are relatively high during night compared to day. Although the turbulence strength in the 10-15 km altitude layer is rather weak at both the stations, the occurrence of turbulence shows a clear diurnal pattern (high during the day), especially over Trivandrum. In the 3-15 km altitude layer, while the occurrence of convective instability is fairly the same at both the stations, the wind shear is significantly large at Trivandrum compared to Gadanki, with high values during night compared to the day. This shows that in this altitude region, while convective instability is mainly responsible for the generation of turbulence at Gadanki, wind shear induced dynamic instability is also responsible for the generation of turbulence at Trivandrum especially during night. Above 15 km, where wind shear driven instability leads the convective instability, turbulence at both the stations does not show any significant diurnal variability.