Question.
Which type(s) of cyclones cause rainfall in north-western India during winter? Where do they originate?
(Chapter-4 Climate, Class 11 NCERT geography "India Physical Environment")
Answer.
Northwest India receives rainfall during winter due to western disturbances. These cyclones originate in the Mediterranean Sea or the Caspian Sea.
A Western Disturbance is an extra-tropical cyclone or a temperate cyclone. Due to western disturbances, there is non-monsoon rainfall in the winter season in North-West India and it provides rain to the farmers planting Rabi crops in North-West India. Since the temperate cyclones come from the north-western part of the country and disturb the pleasant climate of the northern plain, hence it is called a Western Disturbance.
The Western Disturbance originates near the Mediterranean Sea or the Caspian Sea and moves eastwards through West Asia, Iran, Afghanistan, and Pakistan and then enters India.
There are two reasons for the arrival of Western Disturbances in India:
The Gangetic plains have lower atmospheric pressure than the Mediterranean Sea and the Caspian Sea during winter. Therefore winds move from high atmospheric pressure (the Mediterranean Sea) to low atmospheric pressure (the Gangetic plains).
In the upper atmospheric circulation, during the winter season, the western jet stream moves from the Mediterranean Sea towards the Indus-Gangetic plains. The western jet stream helps in the arrival of Western Disturbances in India.
The Caspian Sea and the Persian Gulf are the major moisture providers of Western Disturbances that cause rainfall over the Indian subcontinent.
During winter, the night temperature rises before the arrival of the Northern Plains Western Disturbance, indicating the onset of Western Disturbances.
Implication (Effect ) of Western Disturbance in India:
The cold increases in the northern plains.
Winter rains are beneficial for Rabi crops like wheat, gram, peas, potatoes, etc.
Snowfall occurs in the mountainous regions of the Himalayas like Jammu and Kashmir, Himachal Pradesh, Ladakh, Uttarakhand, etc.
The Western Disturbance brings with it rain as well as dust particles, which increases the smoke and fog in the area around Delhi.
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