Context

Madden-Julian Oscillation (MJO): A Key
Tropical Phenomenon
The Madden-Julian Oscillation (MJO) is an equatorial, eastward-moving system of
atmospheric disturbances characterized by alternating wet and dry phases. It influences global
weather and oceanic patterns, particularly across the Indian and Pacific Oceans, with
occasional reach into the Atlantic.

  Fundamental Characteristics 

• Scale & Duration: Planetary-scale phenomenon with 30–60 day cycles.
• Movement: Propagates eastward along the equator at about 5 m/s (11 mph).
• Phases: Alternates between enhanced (wet) and suppressed (dry) convective phases.
• Measurement: Monitored using outgoing longwave radiation—lower values indicate
  stronger convection (i.e. more rainfall). MJO Dynamics and Dipole Behaviour
  Convective (Enhanced Rainfall) Phase
• Surface winds converge and push moist air upwards.
• Air cools and condenses into clouds, producing heavy rainfall.
• At upper levels, winds diverge, supporting continued uplift.
  Suppressed Rainfall Phase
• Upper-level winds converge, causing dry air to descend.
• Descending air warms, drying the atmosphere and suppressing rain.
• Surface winds diverge, reducing moisture availability.
  Dipole Nature
• The MJO often divides the tropics into two contrasting zones:
  o One half experiences enhanced convection and rainfall.
  o The other sees suppressed activity and dryness.
• For an MJO to be considered active, this dipole must be distinct and propagating
  eastward. MJO’s Influence on the Indian Monsoon
• Onset & Breaks: The MJO strongly affects the timing, intensity, and intra-seasonal
  variability of the Indian monsoon.
• Rainfall Boost: Enhanced convection from the MJO leads to increased rainfall in
  India within 5–10 days of sea surface warming.
• Break Periods: When the MJO’s active phase moves away from the Indian
  subcontinent, monsoon breaks (especially in July) tend to occur. Impact on Tropical Cyclones
• Storm Formation: Ascending motion during the active phase creates a favorable
  environment for cyclogenesis.
• Suppression: Descending motion during the suppressed phase discourages cyclone
  development.
• Regional Shifts: As the MJO advances, cyclone-prone zones move from:
  Western Pacific → Central Pacific → Atlantic
• Inversion Pattern: Cyclone activity often shows a reverse trend between the North
  Pacific and North Atlantic, depending on MJO phases. Favorable Atmospheric Conditions

Low Pressure over Arabian Sea:
o A developing cyclonic system led to heavy pre-monsoon showers and
accelerated the monsoon’s northward advance.

Active MJO (Phase 4):
o High amplitude phase 4 created ideal conditions for rain enhancement over the
Indian Ocean and western Pacific.
o Southwest India benefited from a significant rainfall boost.

Strong Cross-Equatorial Moisture Flow:
o Intensified moisture transport across the equator fueled cloud formation.