Role of Madden-Julian Oscillation (MJO)

It is an oceanic-atmospheric phenomenon which affects weather activities across the globe. It brings major fluctuation in tropical weather on weekly to monthly timescales.

The MJO can be defined as a disturbance of clouds, wind and pressure, moving eastward at a speed of 4-8 metres per second, MJO goes around the globe in 30-60 days on average. Sometimes, it can take 90 days. It’s a traversing phenomenon and is most prominent over the Indian and Pacific Oceans.

As it moves, strong MJO activity often splits the planet in to two halves— one in which the MJO is in active phase or enhanced rainfall or convective phase, and the other in which it suppresses rainfall phase.

      • Enhanced rainfall (or convective) phase: In this phase, wind converges at the surface, and ascends throughout the atmosphere and diverges at the top of atmosphere. The rising air motion in the atmosphere tends to increase condensation and, thereby, rainfall.
      • Suppressed rainfall phase: In this phase, winds converge at the top of the atmosphere, forcing air to descend and, then, it diverges at the surface. As air descends from high altitudes, its temperature increases and humidity decreases. This leads to decrease in rainfall.

The journey of MJO goes through eight phases. When it is over the Indian Ocean during the Monsoon season, it brings good rainfall over the Indian subcontinent. On the other hand, when it witnesses a longer cycle and stays over the Pacific Ocean, MJO brings bad news for the Indian Monsoon.

Indian Monsoon

Fig 9: Madden-Julian Oscillation

Note: In this graphic, the MJO is not one thunderstorm that covers an entire ocean. Such a thing doesn’t exist! Rather, in the region represented by the cloud, MJO favors the development of more thunderstorms than normal