Madden-Julian Oscillation (MJO)

Context: IMD has reported that the Madden Julian Oscillation (MJO) is very likely to remain over Maritime Continent with weak amplitude during next 15 days.


Madden-Julian Oscillation, or MJO

  • The Madden–Julian Oscillation (MJO), as it’s called, is a moving band of rain clouds that travels around the globe spanning 12,000–20,000 km across the tropical oceans.
  • In its journey, it interacts with surface waters of the Indo-Pacific ocean, the largest pool of warm water in the globe, and due to this — the authors say — the lifecycle of the MJO gets affected.
  • Unlike ENSO (El Nino and Southern Oscillation together sometimes called ENSO)which is stationary, the MJO is an eastward moving disturbance of clouds, rainfall, winds, and pressure that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days, on average. This atmospheric disturbance is distinct from ENSO
  • There can be multiple MJO events within a season, and so the MJO is best described as intra-seasonal tropical climate variability (i.e. varies on a week-to-week basis).

Fig: MJO movement and its phases/parts – The surface and upper-atmosphere structure of the MJO for a period when the enhanced convective phase (thunderstorm cloud) is centered across the Indian Ocean and the suppressed convective phase is centered over the west-central Pacific Ocean. The entire system shifts eastward over time, eventually circling the globe and returning to its point of origin. 

  • The MJO consists of two parts, or phases: one is the enhanced rainfall (or convective) phase and the other is the suppressed rainfall phase.
  • Strong MJO activity often dissects the planet into halves: one half within the enhanced convective phase and the other half in the suppressed convective phase. These two phases produce opposite changes in clouds and rainfall and this entire dipole (i.e., having two main opposing centers of action) propagates eastward. 
  • For the MJO to be considered active, this dipole of enhanced/suppressed convective phases must be present and shifting eastward with time. 
  • In the enhanced convective phase, winds at the surface converge, and air is pushed up throughout the atmosphere. At the top of the atmosphere, the winds reverse (i.e., diverge). Such rising air motion in the atmosphere tends to increase condensation and rainfall.
  • In the suppressed convective phase, winds converge at the top of the atmosphere, forcing air to sink and, later, to diverge at the surface. As air sinks from high altitudes, it warms and dries, which suppresses rainfall.
  • It is this entire dipole structure, illustrated in above Figure, that moves west to east with time in the Tropics, causing more cloudiness, rainfall, and even storminess in the enhanced convective phase, and more sunshine and dryness in the suppressed convective phase.  
  • The changes in rainfall and winds described above impact both the Tropics and the Extratropics, which makes the MJO important for extended-range weather and climate prediction over the U.S. and many other areas.

Effects of MJO on global weather phenomenon

  • It can modulate the timing and strength of monsoons.
  • It Influences tropical cyclone numbers and strength in nearly all ocean basins.
  • It can result in jet stream changes that can lead to cold air outbreaks, extreme heat events, and flooding rains over the United States and North America.

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