Study on Environmental and Thermodynamic Factors that influence Precipitation associated with Western Disturbances over North India during Winter

A diagnostic investigation of extreme rainfall episodes associated with western disturbances that occurred during winter in recent years between 2009 and 2018 over North India is carried out using data from a suite of surface observations and reanalysis datasets. Observations indicate the source of the moisture flux as advection from the adjoining Arabian Sea. The dynamical and thermodynamical contributions are evaluated based on atmospheric instability analysis. The rise and fall of the isotherm level in the upper and lower troposphere indicates warming and cooling at the respective levels. The increase in horizontal temperature gradient and vertical wind shear demonstrates the role of baroclinic instability in the development of western disturbances. The equivalent potential temperature and the temperature profile indicate that the atmosphere is conditionally stable in the lower and mid-tropospheric layer. Increase in convective available potential energy explains convective precipitation only over certain regions, whereas lowering of lifting condensation level could be associated with all forms of precipitation events related to western disturbances. Significant precipitation events that occur under the influence of western disturbances could be associated with a rise in total precipitable water to beyond 20 g kg(-1) and rise in specific humidity in the lower troposphere.