In recent years “Tropical Tropopause” has been receiving immense scientific interest because of its sensitivity to anthropogenic activities leading to climate change. The focus is mainly on chemistry, dynamics, radiation as well as transport within the Tropical Tropopause region/layer. There is an immediate need to link the TTL processes to climate, which requires the inclusion of radiation and chemistry in the conceptual framework. Convection in the tropics plays a key role in redistributing trace gases and aerosols in the upper Troposphere–lower stratosphere (UTLS) region, and the interaction between cloud dynamics, radiation and microphysics is of fundamental importance in these processes. Among these the convective detrainment and the effect of overshooting convection on the heat balance of the TTL remain elusive. With a view to address this important and complex interplay, particularly over Indian region, a focused field experiment “Tropical Tropopause Dynamics (TTD)” has been formulated under the CAWSES-India Phase-I program of ISRO since 2004.
In Phase II of this program (under Theme-III) coordinated experiment campaigns are being carried out at Trivandrum [8.5°N, 77°E] and Gadanki [13.5°N, 79.2°E] since December 2010. This involves intense observations on three consecutive days in each month using lidars at Trivandrum and Gadanki (mostly night) along with continuous measurements of vertical wind using the MST radar at Gadanki, in addition to insitu measurements of atmospheric temperature, humidity and winds using balloon borne GPS-sondes (Radiosondes and Ozonesondes) at these stations at a regular interval of 3 hrs. Satellite (KALPANA / CALIPSO) data on these days obtained from the respective data archives are also used to study the regional distribution of cirrus clouds.
The main objective is to understand (a) the association between semi-transparent cirrus (STC) and the tropospheric convection (b) the temporal evolution of Tropical Tropopause Layer (TTL) on shorter time scales and its association with the tropospheric convection (c ) what is the characteristics difference between TTL and non-TLL cirrus (d) the association of Cirrus with tropopause characteristics (e) influence of cirrus on thermal structure of tropopause region (f) turbulence structure within the TTL region and (g) the role of atmospheric waves in manifestation of cirrus as well as modulating the thermal structure. As part of the TTD experiment, Twenty Eight campaigns were conducted successfully during the period December 2010 to April 2013.