RAS question
Which jet stream plays a crucial role in the onset of the Indian monsoon?
Correct answer: (A) Tropical Easterly Jet (TEJ).
The Tropical Easterly Jet is the upper-air jet stream that plays a crucial role in the onset and advancement of the Indian monsoon.
Explanation
The Tropical Easterly Jet is central to the Indian summer monsoon because it appears as an important upper-air easterly circulation over the Indian region after the Subtropical Westerly Jet shifts north of the Himalayas. IMD describes it as a strong easterly airflow centred near 15°N and extending across the Indian Ocean and south Indian peninsula. Summer heating of the Tibetan Plateau helps the TEJ develop, and the jet supports the monsoon's advance. The Subtropical Westerly Jet's withdrawal from north India is a prerequisite, but the upper-air stream that aids monsoon progression is the Tropical Easterly Jet.
Why the other options are wrong
- (B) The Somali Jet is a low-level jet that helps moisture transport, whereas the upper-air jet stream linked with monsoon onset and advancement is the Tropical Easterly Jet.
- (C) The Polar Jet Stream is associated with higher-latitude weather systems, not the Indian summer monsoon mechanism over the Indian region.
- (D) The Subtropical Westerly Jet must shift away from north India before the monsoon sets in, but that withdrawal is a prerequisite, not the jet that aids the monsoon's advancement.
Concept
Upper-air circulation is a key physical geography concept in the Indian monsoon system. Monsoon onset is not just a rainfall event; it depends on linked circulation changes such as the retreat of the Subtropical Westerly Jet and the development of the Tropical Easterly Jet.