Circulation of air begins to set in around this trough.
Explanation
During the summer months, intense solar heating over the Indian subcontinent, particularly the Thar Desert and the northwestern plains, leads to the development of a strong thermal low-pressure area. This elongated low-pressure zone is often referred to as the Monsoon Trough.
Detailed Analysis:
- It repels the monsoon winds. is Incorrect: A low-pressure area acts as a vacuum that attracts air masses from high-pressure zones. Consequently, the low pressure over the Thar Desert attracts the moisture-laden Southwest Monsoon winds from the Indian Ocean rather than repelling them.
- It causes the withdrawal of the monsoon. is Incorrect: The development and intensification of this low-pressure area facilitate the onset and advancement of the monsoon. The withdrawal of the monsoon is associated with the weakening of this low-pressure system and the southward shift of the Inter-Tropical Convergence Zone (ITCZ) as winter approaches.
- Circulation of air begins to set in around this trough. is Correct: As the low-pressure area intensifies, a circulation of air sets in around this trough. This cyclonic circulation creates a pressure gradient that pulls the Southeast Trade Winds across the equator. Upon crossing the equator, these winds deflect towards the right (due to the Coriolis force) and enter the Indian subcontinent as the Southwest Monsoon, establishing the seasonal atmospheric circulation pattern.
- It causes snowfall in the Himalayas. is Incorrect: Snowfall in the Himalayas is typically associated with Western Disturbances during the winter season. The summer low pressure brings rainfall (liquid precipitation) to the region, not snow.
Key Takeaway:
The intense low-pressure system formed over the Thar Desert in summer is the primary driver that attracts the Southwest Monsoon winds, establishing the atmospheric circulation required for the rainy season in India.