Madden-Julian Oscillation (MJO)

Monsoon arrived two weeks early in Mumbai, shattering all-time records. As per India Meteorological Department (IMD) records (since 1950), this is Mumbai’s earliest monsoon onset ever. Previous record: May 29 (in 1971, 1962, 1956)

• Normal onset: June 11
• The early arrival caused severe waterlogging, traffic jams, and disruption to train services across the city.

Why Did It Happen? The Role of the MJO

• Madden-Julian Oscillation (MJO) played a major role in this year’s unusual onset.
• What is MJO?
  • A large, eastward-moving system of clouds, winds, and pressure that affects global weather.
  • Moves at 4–8 m/s, circling the globe in 30–60 days.
• How MJO influences the monsoon:
  • In its favourable (active) phase, MJO boosts cloud formation and rainfall.
  • Enhances monsoon strength when located over the Indian Ocean.

Why This Matters:

• Mumbai’s early monsoon in May is a rare event, attributed to dynamic climate and ocean-atmosphere interactions.
• Such events highlight the increasing complexity and variability of monsoons, which are vital to India’s agriculture, economy, and daily life.

(Source: IE)