Daily News Analysis ‘Monsoon Mechanisms’ : 14 May

The India Meteorological Department (IMD) has launched a new granular forecast system to provide block-level monsoon arrival estimates across 3,196 blocks in 15 States.

Thermal Contrast: The primary driver is the differential heating of the Indian landmass and the surrounding Indian Ocean during summer.
ITCZ Shift: The Inter-Tropical Convergence Zone (ITCZ) shifts northward over the Indo-Gangetic plain in summer, creating a low-pressure trough that draws in moisture-laden winds.
Pressure Gradient: The Mascarene High (a high-pressure area near Madagascar) pushes winds toward the low-pressure center over Northwest India.
Coriolis Effect: As these winds cross the equator, they are deflected to the right by the Coriolis force, becoming the Southwest Monsoon.
Jet Streams:
- STWJ: The withdrawal of the Sub-Tropical Westerly Jet from the north of the Himalayas is a prerequisite for monsoon onset.
- TEJ: The Tropical Easterly Jet, established over the peninsula, helps in the sudden “burst” of the monsoon.
Branches: The monsoon enters India in two branches: the Arabian Sea Branch and the Bay of Bengal Branch.
Unique Points:
- Orographic Lift: Most of India’s monsoon rain is orographic, caused by mountains like the Western Ghats and Himalayas forcing air upwards.
- Break in Monsoon: Periods of little or no rain during the monsoon season are caused by the shifting of the monsoon trough or unfavorable tropical depressions.