Characteristics of Western Disturbance intensification and associated induced circulations over the Indian Region

Western Disturbances (WD) are significantly important weather systems causing precipitation in the Western Himalayan region during Indian Winter months. WDs have two major components-the eastward propagating upper-level trough originating in the mid-latitudes and the low-level Induced Circulation (IC) prevailing over the Northern Indo-Pak region. The present work aims to study the genesis and movement of these upper-level systems using composite analysis of 10 WD events during the Indian winter season that caused extreme precipitation over the western Himalayan region with emphasize on associative mechanisms leading to the IC. Further, we find that the Meridional Temperature Gradient (MTG) is responsible for the development of extra-tropical storms initiated by frontal genesis over the mid-latitude regions. The frontal genesis occurs due to the polar cold air outbreak (CAO) over higher latitudes, causing meandering of the jet stream and leading to the development of the upper-level perturbation that intensifies into a trough. Prior to the IC intensification, the upper-level moisture transport dominates, and during the intensification process, the combined effect of the upper-level trough and IC facilitates a drastic increase in moisture flux from the Arabian Sea at the lower levels. The moisture transport from the Arabian Sea is, therefore, a primary precursor to heavy precipitation in the Himalayan vicinity due to rapid vertical ascent and intense cloud formation because of orographic effects.