Western Disturbance

Western Disturbance is the term used in India, Pakistan, Bangladesh and Nepal to describe an extratropical storm originating in the Mediterranean, that brings sudden winter rain and snow to the northwestern parts of the Indian subcontinent.[1][2] This is a non-monsoonal precipitation pattern driven by the Westerlies. The moisture in these storms usually originates over the Mediterranean Sea and the Atlantic Ocean. Extratropical storms are a global, rather than a localized, phenomena with moisture usually carried in the upper atmosphere (unlike tropical storms where it is carried in the lower atmosphere). In the case of the subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.

Western Disturbances are important to the development of the Rabi crop in the northern subcontinent, which includes the locally important staple wheat.[3][4]

References

  1. ^ J. S. Lall, A. D. Moddie (1981), The Himalaya, aspects of change, India International Centre, http://books.google.com/books?id=b94GAAAAYAAJ, "... The onset of a western disturbance is heralded by dense thunder clouds accompanied by heavy rain or snow. The weather conditions during winter are generally influenced by the distribution pattern of pressure in Central and West Asia. In winter, due to the shifting of the pressure belts, the westerlies blow from 20°N to 50°N latitude and Northern India comes under the influence of the winds and cyclones rising from the Mediterranean Sea. In the wake of the disturbance comes cold air often accompanied by strong winds ..." 
  2. ^ D. K. Majumdar. "Irrigation water management: principles and practice". PHI Learning Pvt. Ltd., 2004. ISBN 9788120317291. http://books.google.com/books?id=hf1j9v4v3OEC. "... Rains during winter months in north India are due to occurrence of low pressure system called western disturbances. This moves from the west to the east causing snow fall in the high ranges in the Himalayas and rains in sub-mountainous tracts and adjoining areas ..." 
  3. ^ "Social Science (A Textbook in Geography Part II) Class X". FK Publications. http://books.google.com/books?id=yl5I2Vp5YCgC. "... These states are: Punjab, Haryana, Himachal Pradesh, Jammu & Kashmir, Uttarakhand and Uttar Pradesh. These states receive some rainfall (precipitation) during the rabi season, brought about by western disturbances, which originate in the Mediterranean region. These showers are very beneficial for rabi crops ..." 
  4. ^ J.E. Parkinson, R. H. Whitehouse. "Proceedings". Printed at the Mufid-i-'Am Press, 1927. http://books.google.com/books?id=c56gAAAAMAAJ. "... In northern India rainfall occurs again during the year in connection with the Western Disturbances which are of great agricultural importance to north-west India as they occur chiefly during the Rabi ..." 

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