RAS question
Western disturbances that bring winter rainfall to northern India originate from:
Correct answer: (D) Mediterranean Sea region.
Western disturbances that bring winter rainfall to northern India originate in the Mediterranean Sea region as extratropical cyclones.
Explanation
Western disturbances are extratropical cyclones that originate in the Mediterranean Sea region and move eastwards through Iran, Afghanistan and Pakistan towards the Indian subcontinent. According to the India Meteorological Department, they are non-monsoonal weather systems driven by the westerlies and carry moisture in the upper layers of the atmosphere. When they reach the Himalayan region, this moisture falls as rain or snow. Consequently, winter and early spring precipitation in north-western areas such as Punjab, Haryana and Jammu and Kashmir comes from western disturbances rather than from the summer monsoon. This precipitation is especially important for rabi crops such as wheat, which depend on cool-season moisture.
Why the other options are wrong
- (A) The Pacific Ocean is associated with ENSO, whereas western disturbances are extratropical cyclones that originate in the Mediterranean Sea region and move eastwards towards India.
- (B) The Bay of Bengal is associated with the northeast monsoon, whereas western disturbances are westerly, non-monsoonal systems that originate in the Mediterranean Sea region.
- (C) The Arabian Sea supplies moisture to the southwest monsoon, whereas western disturbances originate as extratropical cyclones in the Mediterranean Sea region.
Concept
This tests the Indian climatology concept of non-monsoonal winter rainfall. It recurs in RAS because western disturbances link their Mediterranean origin and eastward movement with westerly circulation, Himalayan precipitation and rabi agriculture in north-western India.