Vertical Changes in the Storm Tracks and Dynamics of Western Disturbances

Abstract

This study investigates the long-term horizontal and vertical changes of the storm tracks for all the boreal seasons (Northern Hemisphere) during the period (1979-2014). To perform the analysis, we considered ERA Interim reanalysis dataset and utilised a cyclone tracking algorithm. During winter, the Atlantic and Pacific storm tracks are stronger and remain circumpolar. These winter storm tracks extend meridionally from polar region to 30°N, and vertically extend from the lower troposphere to the lower stratosphere. Characteristically, baroclinic instability is a common mechanism of generation associated with storm tracks and western disturbances (WDs), which often occur in northern parts of India, mostly in fall and winter. We found that observed WDs are generated by moist baroclinic instability of westerlies over Indian longitudes as their characteristics agree well with theoretically and numerically deduced ones. Indeed, these WDs observed during the boreal fall and winter seasons are ingredients of the storm tracks in the northern hemisphere, with strengthened relative vorticity at 500 hPa and moving zonally eastward towards the north Indian region triggering extreme precipitation. Thus, WDs over northern India is of great interest in the fall and winter seasons.