Analysing Seasonal Variations in the Tropical Tropopause and the Impact of Deep Convection on the Tropopause Structure Over a High-Altitude Station in the Western Ghats

The present work examines the structure and variability of the tropopause over a high-altitude site in the Western Ghats (WG) and attempts to understand the impact of deep convection on the thermal structure of the tropopause. The characteristics of the seasonal variations in the cold-point tropopause (CPT), lapse rate tropopause (LRT), convective tropopause (COT) and tropical tropopause layer (TTL) are studied using highresolution radiosonde observations from 2012 to 2019 over Mahabaleshwar (17.92 degrees N, 73.66 degrees E; 1.38 km amsl) in the WG. On seasonal time scales, the altitude (temperature) of CPT, LRT and COT vary by similar to 1 km (similar to 2 K), 0.5 km (similar to 1.8 K) and 1.3 km (similar to 6 K), respectively. CPT and LRT show highly similar seasonal behaviour, with higher and colder values during winter and lower and warmer values during monsoon months, whereas COT exhibits a different pattern of seasonal behaviour with higher variability. The thickness of the TTL varies from a minimum of 4.2 km in July to a maximum of 6 km in March. Further, the impact of deep convection on the tropopause was analysed by collocating the radiosonde observations with the deep convection based on infrared brightness temperature (IRBT) data of Indian geostationary satellites, INSAT-3D and Kalpana-1. The anomalies of temperature profiles and tropopause parameters (altitude and temperature) are estimated during deep convection categorized by IRBT values into three groups designated as DC1 (< 220 K), DC2 (220-235 K) and DC3 (235-245 K). The analysis reveals cooling within the TTL and warming in the middle troposphere which are enhanced with the deepening of convection. The TTL cooling (mid-tropospheric warming) peaks near 16 km (10 km) altitude and varies as -1.1 K (1.2 K), -0.8 K (0.9 K) and -0.6 K (0.4 K) for DC1, DC2 and DC3, respectively. The tropopause anomalies show that the CPT and LRT descend while the COT ascends during deep convection. The thickness of the TTL decreases due to the combined effect of the descent of the CPT and ascent of the COT, but the main contribution is the elevation of the COT. The TTL narrows as the convection deepens, and shrinks most (similar to 1 km) during deepest convection (DC1).