The subtropical jet stream plays a critical role in the withdrawal of the monsoon by which of the following?

Correct option is B

Correct Answer: (B) Inducing subsidence over land

Explanation:

• The subtropical jet stream plays a critical role in the withdrawal of the monsoon by inducing subsidence (downward motion of air) over the land. This subsidence causes a decrease in cloud formation and rainfall, signaling the retreat of the monsoon.
• During the monsoon season, the jet stream remains to the north of the Indian subcontinent. As the monsoon begins to withdraw, the jet stream shifts southward, leading to increased subsidence, which reduces atmospheric moisture and ends the monsoon rains.

Information Booster:

• Subtropical Jet Stream: The subtropical jet stream is a fast-moving air current found at higher altitudes (around 200-300 mb) in the atmosphere, primarily between 20° and 30° latitude in both hemispheres.
• Withdrawal of Monsoon: As the subtropical jet stream moves southward, it helps in weakening the monsoon winds, reduces the upward motion of moist air, and causes dry conditions that mark the end of the monsoon season.

Other Options:

• A (Replacing tropical easterlies): The tropical easterlies are typical of the monsoon phase, and while the jet stream interacts with them, it does not replace them directly during monsoon withdrawal.
• C (Triggering cold air advection): While cold air advection occurs in some atmospheric systems, it is not the primary mechanism driving the monsoon withdrawal in this context.
• D (Intensifying the ITCZ): The Inter-Tropical Convergence Zone (ITCZ) is important during the monsoon onset, but the subtropical jet stream contributes to the withdrawal by inducing subsidence rather than intensifying the ITCZ.