Studies on western disturbances affecting North India during winter

Abstract

The term Western Disturbance (WD) in general is applied to a low or trough either at the surface or in the upper air in the region of westerly wind regime (North of 20º N), newlineusually giving rise to change in pressure, wind and temperature fields accompanied newlineby cloudiness but with or without precipitation. When two or more closed isobars at newline2 hPa interval can be drawn on the sea level chart, the disturbance is described as newlinewestern depression. In cases where the surface systems are complex and feeble but newlinewith marked upper air systems then the upper air features are only described, newlinespecifying the level/levels where these are seen. Features at level 500 hPa and above newlineare described as troughs in westerlies. These systems often originate in West Atlantic newlineor Mediterranean region and they belong to the extra tropical cyclone families. newlineWestern disturbances are the major synoptic system that influence the rainfall during newlinethe winter months of January and February over the northern parts of India. This newlinerainfall contributes substantially towards the economy of various states viz, Jammu and newlineKashmir, Punjab, UP, Rajasthan, Haryana and Uttaranchal. Western disturbances are newlinemainly confined to the period between December and May. But they may also travel newlineacross the region to the north of the sub-continent in the other months of the year and newlineinfluence the weather over North West Indian region. About 6-7 western disturbances newlineaffect North India during each of the winter months and about 1-2 of them result in newlinesignificant activity in the form of precipitation. The precipitation caused by the WDs newlinecontributes significantly to the Northern Indian winter rainfall and thus has major newlineconsequences throughout the region. The importance of the hydrological cycle, with newlineprecipitation as its main components, is immeasurable. The system that affects newlineLadakh and Kashmir are referred to as primary western disturbances and those newlinedeveloping south of latitude 30º N as induced lows.