资源环境科技发展态势分析平台

Balloon-borne cryogenic frost-point hygrometer (CFH) observations conducted over three stations Trivandrum, Hyderabad and Kolkata in the Indian region during the period 2014–2017 are used to study the influence of deep convection and monsoon dynamics on the distribution of water vapour in the upper troposphere and lower stratosphere (UTLS) and to quantify the amount of water vapour transported to the lower stratosphere (LS) during summer-monsoon (June to September). In summer monsoon season, CFH observations show a water vapour enhancement of ~40–250% in the upper troposphere (UT) and 0.5–1 ppmv (10–40%) in the LS compared to pre-monsoon. In this season, the spatial pattern of Microwave Limb Sounder (MLS) derived water vapour mixing ratio (WVMR) at 100 hPa peaks north of the deep convection core over the head Bay of Bengal (BoB). In the LS, the water vapour maximum shows a south westward shift with altitude in accordance with the anticyclonic circulation flow. The maximum altitude of deep convective cloud top increases north eastward in accordance with the peak in tropical easterly jet (TEJ) causing the altitudinal shift in water vapour enhancement in the UT. The probability of dehydration (WVMR<3 ppmv) maximizes west of the deep convective core over Head BoB. During summer-monsoon, the day-to-day variability of water vapour in the tropical tropopause layer (TTL) is mainly controlled by the dehydration of air due to freeze drying (temperature dependent) and rehydration due to recurrent overshooting deep convections. Direct injection of water vapour into the LS region is probable when the tropopause is relatively warm (>192 K).