The southwest monsoon is a seasonal wind system that brings heavy rainfall to the Indian subcontinent.

 The southwest monsoon is a seasonal wind system that brings heavy rainfall to the Indian subcontinent. It's primarily caused by the differential heating of land and water, with the landmass of India heating up faster than the surrounding seas and creating a low-pressure area. This low pressure draws in moist winds from the Arabian Sea and Bay of Bengal, leading to widespread rainfall. 

Here's a more detailed explanation:

1. Differential Heating: During the summer months, the Indian subcontinent heats up more intensely than the Arabian Sea and Bay of Bengal. This creates a low-pressure zone over the landmass. 

2. Low-Pressure Zone: The heated landmass creates a low-pressure area, drawing in air from surrounding high-pressure areas, specifically from the Arabian Sea and Bay of Bengal.

3. Moisture-laden Winds: These incoming winds from the Arabian Sea and Bay of Bengal are moist and laden with water vapor. 

4. Onset and Impact: The sudden onset of the southwest monsoon brings a significant drop in temperature and a rise in humidity, marking the beginning of the rainy season for most of India.

5. Branches: The southwest monsoon has two main branches: the Arabian Sea branch and the Bay of Bengal branch. These branches converge and cause rainfall across various regions of India.