Question

Which one of the following causes rainfall during winter in the north western part of India?
a)Cyclonic depression
b)Western disturbances
c)Retreating monsoon
d)South west monsoon

Answer 1

Hint: During Winter, there is rainfall in the North Western part of India due to Western disturbances. Westerlies drive the pattern of these non-monsoonal precipitation. Western disturbances are essential for the development of rabi crops in the northern subcontinent. For example, the most important staple wheat.

Complete answer: Western disturbances is an extratropical storm that originates from the Mediterranean region and brings sudden winter rain to North-Western part of Indian subcontinent. This precipitation pattern is derived by Westerlies. These extratropical storms are a global phenomenon where the moisture is generally carried in the upper atmosphere. Whereas the tropical counterparts carry moisture in lower atmosphere. When these storms encounter the natural barrier in the Himalayas, moisture is sometimes shed in the form of rain in the North Western Indian subcontinent.
Formation of western Disturbances:
The extra tropical cyclones originate from Mediterranean region. There is a high pressure belt over Ukraine and neighboring countries. This causes intrusion of cold air from the polar region towards the warm region with high moisture. This generates favourable conditions for cyclogenesis in the upper atmosphere promoting the formation of an eastward moving extratropical depression in the sea. They gradually travel across Middle East Iran, Afghanistan, Pakistan before entering the Indian Subcontinent.

Looking at the options given:
Option A: Cyclonic depression on reaching land loses its source of energy and eventually dies out. This is an incorrect answer.
Option B: Western disturbances cause rainfall during winter in the north western part of India. This is the correct answer.
Option C: Retreating monsoon causes rainfall in south eastern coasts. This is an incorrect answer.
Option D: Southwest monsoon causes rainfall during June to October. This is an incorrect answer.

Thus, Option ‘B’ is correct.

Note: It plays an important role in bringing moderate to heavy rain in low-lying areas and huge snow in mountainous regions on Indian Subcontinent. Due to these disturbances there is usually a cloudy sky, high night temperature and unusual rain. This precipitation is very significant for agriculture, especially rabi crops.