What is Madden-Julian Oscillation (MJO)?

According to the UK’s Met Office, Madden-Julian Oscillation (MJO) is characterised by an eastward spread of large regions of enhanced and suppressed tropical rainfall, mainly observed over the Indian and Pacific Ocean.

How does MJO work?

An area of enhanced tropical rainfall is first apparent over the Western Indian Oceans, which spreads eastwards into the warm waters of the tropical Pacific. This pattern of tropical rainfall tends to lose its identity as it moves over the cooler waters of the Eastern Pacific, before reappearing at some point over the Indian Ocean again.

A wet phase of enhanced convection (rainfall) is followed by a dry phase, where thunderstorm activity is suppressed (no rainfall). Each cycle lasts approximately 30-60 days and there are eight phases, it says.

Following are the phases of MJO, according to the Met Office of the UK.

Phase 1 – Enhanced convection (rainfall) develops over the Western Indian Ocean.

Phase 2 and 3 – Enhanced convection (rainfall) moves slowly eastwards over Africa, the Indian Ocean and parts of the Indian Subcontinent. 

Phase 4 and 5 – Enhanced convection (rainfall) reaches the Maritime Continent (Indonesia and West Pacific)

Phase 6, 7 and 8 – Enhanced rainfall moves further eastward over the Western Pacific, eventually dying out in the central Pacific.

The next MJO cycle begins.