Large-scale dynamics of western disturbances caused extreme precipitation on 24–27 January 2017 over Jammu and Kashmir, India

Abstract

Western Himalaya receives heavy precipitation due to western disturbances embedded in the eastward moving upper tropospheric Rossby wave train, especially in the winter months. The interaction of intricate topography and large-scale atmospheric dynamics plays an essential role in determining the amount of precipitation over this region. The cold air intrusion causes the middle troposphere to be baroclinically unstable and develop a sharp gradient of potential temperature which in turn is responsible for non-conservation of Ertel potential vorticity. Baroclinic instability provided energy of the disturbance (latent heating) by strengthening the influence of baroclinicity on the vertical component of relative vorticity causing intense convection. The increase in the baroclinic influence on the vertical component of relative vorticity in the moist middle and upper troposphere led to extreme precipitation over Jammu and Kashmir region during 24–27 January 2017 and can be considered as one of the prognostic parameters for predictions of such event. Extreme precipitation over western Himalayan regions in the winter months is generally attributed to the passage of western disturbance. In this paper, we investigated large-scale atmospheric influences which are responsible for the occurrence of such extreme precipitation. Our results indicated that the cold air intrusion from the northern latitudes into the core of western disturbances causes modulation of the density field, which in turn causes middle troposphere of this region to become baroclinically unstable. The influence of baroclinicity on the vertical component of relative vorticity and non-convergence of Ertel potential vorticity led to the development of intense convection and heavy precipitation over Jammu and Kashmir region of India.