The Madden-Julian Oscillation (MJO) has become active over Australia – but what is the MJO and what does it mean?

The MJO is an eastward-moving pulse of tropical activity. When it is active, it brings an increase in rainfall, thunderstorms and tropical cyclones to the region it is in.

The MJO gets the most attention during the summer months, as it tends to bring the monsoon trough to northern Australia, although it has an impact on Australia all year round.

Over the last few months, the MJO has been weak, but over the last week, it has become active over the Maritime Continent (i.e. Indonesia and the surrounds) and is continuing to strengthen.

Given the time of year, it’s still a bit too early for the monsoon to arrive over northern Australia, but it is delivering copious amounts of moisture to both sides of the equator.

Image: Himawari-8 Satellite showing the vast amount of cloud extending over the equator and surrounds from the MJO 

In Australia, a northwest cloudband has tapped into the MJO, stretching from WA to Tasmania and delivering record-breaking rainfall to the southeast.

In the Northern Hemisphere, a train of tropical depressions and lows has formed east and west of the Philippines. A broad area of rain and thunderstorms is stretching over 10,000 km from southern India to the middle of the Pacific (just west of Hawaii). This enormous band covers about one-quarter of the entire length of the equator!

Image: Tropical depressions and lows of note for possible Tropical Cyclone/Typhoon development. Source: JTWC 

Over the next few weeks, the MJO will stay active over Australian longitudes as it slowly tracks east. Like the current system, this will allow troughs for the next few weeks the opportunity to tap into an abundant source of tropical moisture and deliver heavier rain to the continent.

When the MJO keeps its strength, it tends to circle the globe in about 4-8 weeks, meaning the next time it arrives over Australia it is a good chance to bring the monsoon with it.