RAS question
The monsoon trough is a:
Correct answer: (B) Low pressure zone over the Indo-Gangetic Plain.
The monsoon trough is an east-west low-pressure zone over the Indo-Gangetic Plain, extending from the Thar Desert towards the Bay of Bengal.
Explanation
The monsoon trough is not a barrier or a front; it is a low-pressure belt linked with the northward shift of the ITCZ during the southwest monsoon. NCERT describes the July ITCZ over the Gangetic plain as the monsoon trough and says that this trough encourages thermal low pressure over north and northwest India. It has an east-west alignment from the Thar Desert towards the Bay of Bengal across the Indo-Gangetic Plain. Its position matters because rain-bearing storms along the trough influence rainfall distribution; when such storms are not frequent over northern India, monsoon breaks can occur.
Why the other options are wrong
- (A) A high-pressure area in the Arabian Sea does not match the monsoon trough, which NCERT identifies with a low-pressure zone over the Gangetic plain and north-west India.
- (C) A mountain barrier describes the role of ranges such as the Himalayas, while the monsoon trough is a pressure zone, not a physical obstruction.
- (D) A cold front in the Himalayas is a temperate-weather feature, whereas the monsoon trough is tied to the monsoon-season ITCZ and low pressure over northern India.
Concept
This tests the Indian monsoon mechanism, especially the seasonal shift of the ITCZ and its control over rainfall. It recurs in RAS because monsoon behaviour explains Rajasthan's rainfall variability and north-west India's summer low-pressure conditions.