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Difficulty: MediumClimate, Weather Systems, and Monsoon of India

The seasonal withdrawal of the South-West monsoon from North-Western India, which typically begins in early September, is primarily driven by which of the following atmospheric changes?

  1. A
    The northward shift of the Subtropical Westerly Jet Stream over the Tibetan Plateau
  2. The southward retreat of the Inter-Tropical Convergence Zone (ITCZ) accompanied by the weakening of the intense heat low over North-West IndiaAnswer
  3. C
    The sudden strengthening of the Somalian Jet Stream across the equatorial Indian Ocean
  4. D
    The persistent formation of tropical easterly waves over the Arabian Sea

Answer

The southward retreat of the Inter-Tropical Convergence Zone (ITCZ) accompanied by the weakening of the intense heat low over North-West India.
Monsoon withdrawal begins when solar insolation over the northern sub-continent decreases in late autumn. This causes the Inter-Tropical Convergence Zone (ITCZ) to migrate southwards. As a result, the intense thermal low over North-West India breaks down, allowing land-to-sea pressure gradients to form and triggering clear skies and retreating wind patterns.

Step-by-Step Solution

1
Analyze the solar movement and surface pressure conditions in late summer
By September, the Sun's apparent movement shifts southward toward the equator, reducing solar insolation over the Northern Hemisphere.
Solar declination change alters thermal contrast between the Indian landmass and the ocean.
2
Trace the movement of the low-pressure system (ITCZ)
The trough of low pressure (Monsoon Trough/ITCZ) over North-West India weakens and shifts southward.
Without the thermal low driving the pressure gradient, moisture-bearing south-westerly winds lose momentum.
3
Evaluate the wind pattern reversal leading to withdrawal
Clear skies and rising pressure establish north-easterly flow, marking the systematic retreat of the monsoon from Punjab and Rajasthan.
The change in atmospheric driving forces leads to the onset of the retreat phase.

Key Concept

Mechanisms of South-West Monsoon Withdrawal and ITCZ Migration
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Topics

Climate, Weather Systems, and Monsoon of India

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