In News:

In 2025, the early onset of the southwest monsoon in Kerala (May 24) and Mumbai (May 26—the earliest on record) was significantly influenced by the Madden-Julian Oscillation (MJO), as reported by the India Meteorological Department (IMD).

What is the MJO?

• The Madden-Julian Oscillation (MJO) is a large-scale atmospheric phenomenon observed in the tropical belt (30°N to 30°S).
• It is an eastward-moving disturbance involving winds, clouds, pressure, and rainfall that circles the globe every 30 to 60 days (occasionally up to 90 days).
• Identified in 1971 by Roland Madden and Paul Julian, it differs from ENSO (El Niño–Southern Oscillation) in being intra-seasonal and transient.

Phases of MJO:

• Enhanced Convective Phase:
  • Associated with increased cloudiness, low pressure, and above-normal rainfall.
  • Characterized by rising air and moisture convergence.
• Suppressed Convective Phase:
  • Brings clearer skies and reduced rainfall due to subsiding dry air.

• These phases shift eastward and influence weather globally, including India.

Formation and Movement:

• Triggered by surface wind convergence that causes upward motion, cloud formation, and upper-level wind divergence.
• Travels at 4–8 m/s, completing a global circuit roughly every 30–60 days.

MJO’s Impact on Indian Monsoon:

• MJO in active phase over the Indian Ocean can:
  • Trigger early monsoon onset, as seen in 2024 and 2025.
  • Enhance cyclogenesis and monsoon depressions.
  • Improve intra-seasonal rainfall variability.
• May 2025 Event:
  • The MJO was in Phase 4 with amplitude >1, indicating strong activity conducive to rainfall.
  • This condition, along with favorable local and oceanic factors, supported early monsoon advancement in India.

Global Influence of MJO:

• Cyclone Modulation: Alters frequency and intensity of tropical cyclones.
• Weather Extremes: Affects jet streams, triggering cold surges, heatwaves, or floods in mid-latitudes (e.g., U.S., Europe, Australia).
• Interaction with ENSO: While not always directly linked, MJO can amplify or be influenced by El Niño conditions.