Madden-Julian Oscillation Helped Trigger the Early Onset of the Monsoon

Syllabus: GS1/ Geography

Context

• The early onset of the southwest monsoon over Kerala this year has caught the attention of meteorologists.
  • According to the India Meteorological Department (IMD), the Madden-Julian Oscillation (MJO) played a significant role in this development.

What is Madden-Julian Oscillation (MJO)

• The MJO is a moving system of winds, clouds, and pressure that brings rain as it circles around the equator. 
• It was discovered in 1971 by Roland Madden and Paul Julian.
• The system travels eastward at 4–8 m/s and circles the globe typically every 30–60 days, though it can take up to 90 days.
• As it moves, strong MJO activity often splits the planet into two parts — one in which the MJO is in active phase and brings rainfall, and the other in which it suppresses rainfall.

Geographical Influence

• The effect of the MJO is witnessed mainly in the tropical region, in the band between 30 degrees North and 30 degrees South of the equator, even though the mid-latitude regions in both hemispheres also feel its impact.
  • It also includes India, making it a crucial player in the South Asian monsoon system.
• During an active MJO phase, regions within its influence experience above-average rainfall, often due to increased cloud formation, convection, and cyclonic activity.

Contribution of MJO to the Early Monsoon

• This year, the MJO was observed in Phase 4 with an amplitude greater than 1 around May 22, originating in the Indian Ocean.
• Phase 4 with strong amplitude is indicative of intense rainfall and storm systems, conducive for monsoon initiation.
• This setup contributed to frequent cyclonic activity and cloud build-up over the Bay of Bengal, helping trigger the early arrival of the monsoon over Kerala.

Other reasons for Early Monsoon

• Transition to La Niña: In early 2025, global climate models indicated El Niño weakening and possible La Niña development — a pattern historically associated with stronger and earlier monsoon seasons in India.
• Stronger-than-usual cross-equatorial winds: During May, winds from the southern hemisphere begin to blow across the equator and enter the Arabian Sea.
  • When these winds are stronger and more organised, they push moisture-laden air toward the Indian coast more quickly, hastening the monsoon’s arrival.
• Above-normal sea surface temperatures:  Warmer-than-usual waters in the Arabian Sea and Bay of Bengal fuel intense convection, which helps develop cloud bands and low-pressure systems needed for monsoon formation.
  • In 2025, sea surface temperatures in the region were higher than average, aiding early cloud development.

Concluding remarks

• While the early onset of the monsoon offers critical advantages for agriculture and water resource management, it also intensifies climate-related vulnerabilities.
• As monsoon patterns become increasingly erratic under climate change, strengthening early warning systems and forecasting models remains essential for safeguarding lives, livelihoods, and ecosystems.

Source: IE