On the signatures of local and regional dynamics in the distribution of lower stratospheric water vapour over Indian region using balloon-borne and satellite observations

Balloon-borne cryogenic frost-point hygrometer (CFH) observations over two tropical stations Trivandrum (8.53° N, 76.87° E) and Hyderabad (17.47° N, 78.58° E) [2014–2017] along with Microwave Limb Sounder (MLS) observations [2011–2017] are used to examine the signatures of local and regional dynamics in the distribution of lower stratospheric water vapour over the Indian region. The column-integrated water vapour in the lower stratosphere (IWV LS ) varies in the range 2.5–5 g/m 2 with low values during winter and high values during summer monsoon and post monsoon seasons. About 50–75% of IWV LS lies in the lower regime of the lower stratosphere, the region from cold point tropopause (CPT) to 21 km (LS1). Hygropause is very near to the CPT in winter and pre-monsoon and 2–3 km above the CPT in summer-monsoon and post-monsoon. The CPT and the minimum in saturated mixing ratio (SMR min ) altitudes show a positive correlation, with SMR min mostly occurring below the CPT. Though water vapour mixing ratio (WVMR) at CPT increases with increase in SMR min , it is mostly less than the corresponding SMR min value. CFH observations showed that the tape recorder signal in the LS1 is disturbed by the local/regional dynamics. While the amount of water vapour entering the lower stratosphere is higher over Hyderabad in winter and summer monsoon, it is higher over Trivandrum in the other two seasons. Hydration at the tropopause level is mainly determined by the overshooting/deep convection, monsoon dynamics and horizontal transport and dehydration is determined by temperature variations in the tropical tropopause layer (TTL).