Recent trends in the UTLS temperature and tropical tropopause parameters over tropical South Indian region

Abstract

The Upper Troposphere and Lower Stratosphere (UTLS) region plays an important role in the climate system. Quantifying the processes that control UTLS represents a crucial task. We assess UTLS trends and associated tropopause parameters (Cold Point Tropopause temperature/altitude (CPT/CPH), Lapse Rate Tropopause temperature/altitude (LRT/LRH), Convective outflow level temperature/altitude (COT/COH) and Tropical Tropopause Layer (TTL) thickness). This study is based on high-resolution daily radiosonde data from 2006 to 2018 over a tropical station Gadanki in south India supported by satellite measurements. The results show an increase of CPH (LRH) of ~0.06 km (~0.10 km), decrease of CPT (LRT) of ~1.09 K (1.16 K), increase of COH of ~0.29 km and decrease of TTL thickness of ~0.23 km in the recent decade. The vertical temperature trends show a strong cooling trend at lower stratosphere (17–19 km) with a maximum cooling rate of 1.3 ± 0.86 K per decade at 19.4 km altitude unlike reported recently using global radiosonde network. A warming trend is observed in the entire troposphere (0–15 km) with maximum warming rate of 0.44 ± 0.55 K at 11.6 km during the last decade. Distinct variability in the temperature is noticed below and above the tropopause with the strong seasonal change above the tropical tropopause (18 and 19 km) compared to the below the tropopause (15–17 km). The observed trends are explained in relation to the ozone (O3) and water vapor (WV) trends over Gadanki. Compare to the ozone changes, the WV increasing trend was found strongly influencing the LS cooling trend in the recent decade over Indian monsoon region.