Role of stratospheric tropospheric exchange in influencing precipitation associated with western disturbances over North India during winter

The NCEP/NCAR final analysis data set of 1° × 1° resolution from the Research Data Archive and the gridded rainfall data provided by the India Meteorological Department was used to identify the western disturbances (WDs) which resulted in precipitation over North India during the winter season between 2009 and 2018. Variation in potential vorticity (PV), tropopause undulations and changes in ozone mixing ratio were investigated over North India and neighbourhood. The changes in these parameters were then related to the nature of precipitation associated with WD when they affect North India. It was observed that there is a fall in the tropopause height over North India as a WD approached. The lowest tropopause height of (6000–10,000 gpm) was seen close to the system centre at 500 hPa. A positive potential vorticity anomaly (PVAn) was observed at upper tropospheric levels with peak value observed at 300 hPa. Positive potential vorticity advection (PVA) was also resulted in changes to the PV value, which was lesser by a factor of 10 compared to the role played by intrusion of the stratospheric air mass to the upper troposphere. Fall in tropopause height occurred concurrently with increase in the ozone mixing ratio in the upper troposphere, while WDs affected North India. The study highlights the importance of stratospheric-tropospheric exchange in influencing the intensity of precipitation resulting from WDs over North India.