RAS question
Jet streams over India are important because:
Correct answer: (D) The sub-tropical westerly jet influences winter weather; its northward shift triggers monsoon onset.
Jet streams over India are important because the sub-tropical westerly jet influences winter weather, and its withdrawal north of the Himalayas allows the easterly jet to set in and trigger the burst of the monsoon.
Explanation
Upper-air circulation shifts seasonally over India. In winter, the sub-tropical westerly jet lies over north India and helps steer western disturbances, so it has a direct bearing on winter weather. NCERT links the monsoon mechanism to the withdrawal of this westerly jet from north India, south of the Himalayas. Only after that withdrawal does the easterly jet stream set in near 15 degrees N; NCERT holds this easterly jet responsible for the burst of the monsoon in India. The Tropical Easterly Jet over peninsular India then strengthens the monsoon. Jet streams matter not as a side topic of aviation, but as a core part of India's winter-weather and monsoon-onset mechanism.
Why the other options are wrong
- (A) Earthquakes arise from tectonic processes, while jet streams influence winter weather and the monsoon mechanism.
- (B) NCERT explicitly connects jet-stream shifts with the burst of the monsoon, so jet streams have a major weather impact over India.
- (C) Aviation may be affected by jet streams, but over India their climatic importance lies especially in western disturbances and monsoon onset.
Concept
The Indian monsoon mechanism depends on upper-air circulation, especially in winter weather and monsoon onset. RAS climate questions often ask how pressure, winds, ITCZ movement and jet streams combine rather than testing a single isolated term.