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Difficulty: MediumClimate, Weather Systems, and Monsoon of India

During the summer season in India, the Inter-Tropical Convergence Zone (ITCZ) shifts northward to lie over the Indo-Gangetic Plain, creating the ITCZ monsoon trough. Which of the following atmospheric conditions is a direct consequence of this northward shift?

  1. Development of a thermal low-pressure trough over northern India that attracts the cross-equatorial south-west trade windsAnswer
  2. B
    Permanent anchoring of the Subtropical Westerly Jet Stream south of the Himalayan mountain barrier
  3. C
    Intensification of dry north-east continental trade winds blowing across the Bay of Bengal
  4. D
    Establishment of an intense atmospheric high-pressure cell over the Chota Nagpur Plateau

Answer

Development of a thermal low-pressure trough over northern India that attracts the cross-equatorial south-west trade winds
The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure zone located at the thermal equator where trade winds converge. In summer, intense heating of the Indian subcontinent shifts the ITCZ northward over the Ganga plain. This monsoon trough creates a strong pressure gradient that pulls moist air masses across the equator into the Indian subcontinent as the South-West Monsoon.

Step-by-Step Solution

1
Analyze the position and behavior of the ITCZ during summer.
In July, the ITCZ shifts northward over the Ganga plain (around 20°N–25°N), commonly called the monsoon trough.
Solar insolation heats the landmass of northern India intensely, shifting the thermal equator northward.
2
Determine the atmospheric pressure change resulting from this shift.
An elongated low-pressure area forms over northern and north-western India.
Rising warm air creates surface convergence and low atmospheric pressure.
3
Connect pressure gradients to wind circulation.
South-East trade winds from the Southern Hemisphere cross the Equator, deflect right due to Coriolis force, and enter the subcontinent as moist South-West monsoon winds.
Wind moves down the pressure gradient from the high-pressure southern Indian Ocean toward the low-pressure Indian monsoon trough.

Key Concept

Role of the ITCZ and Monsoonal Trough in South-West Monsoon Mechanics
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Topics

Climate, Weather Systems, and Monsoon of India

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