Role of deep convection on the tropical tropopause characteristics at sub-daily scales over the South India monsoon region

• Role of deep convection on the tropical tropopause parameters is investigated.
• Convection is classified into six categories based on its life cycle.
• Decrease in TTL thickness is observed not only because of pushing up the COH but also due to decrease of CPH.
• Both diabatic and adiabatic processes are dominant during active convection.

The role of deep convection on the tropical tropopause parameters at sub-daily scales using radiosonde observations at two locations in South-India affected by monsoon has been investigated. Special experiments were conducted under the Tropical Tropopause Dynamics (TTD) campaigns from two stations, (Gadanki (13.5°N, 79.2°E) and Trivandrum (8.5°N, 76.9°E) as a part of CAWSES India Phase-II programme during December 2010 to September 2013. In addition, data from regular radiosonde launches available from April 2006 to September 2013 are also utilized in the present study. Using satellite based infrared brightness temperature data, convection is classified into six categories based on the life cycle of the convection prevailing 3 h before and after the balloon reaching the tropical tropopause. Cold-point and lapse rate tropopause altitudes (CPH, LRH) and temperatures (CPT, LRT), convective outflow level (COH) and tropical tropopause layer (TTL) thickness extracted from individual soundings are grouped into six convection categories. Large amount of water vapour with diabatic cooling prevailed near the CPH during active convection leading to STE processes. At the same time, decrease in TTL thickness is observed not only because of pushing up of the COH but also due to decrease of CPH. On an annual basis a decrease (increase) in CPH and LRH (CPT and LRT) is noticed during active convection. This feature is more significant at Gadanki compared to Trivandrum. During the monsoon and pre-monsoon periods when the convection is rather widespread, CPH (CPT) shows a decrease (increase) at Gadanki while it increases (decreases) over Trivandrum. Large seasonal variation is noticed in the tropopause parameters even when they are segregated into different convective categories mainly due to intensity of the convection being different. During active convection, diabatic and adiabatic processes seem to be dominant at Gadanki and Trivandrum, respectively.