Madden Julian Oscillation

Background

The Madden Julian Oscillation (MJO), or 40 day wave as it is sometimes called, was first discovered by Madden and Julian in the early 1970s. The MJO can be observed as a band of low atmospheric pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events across much of tropical Australia, including parts of Queensland.

During summer/early autumn the MJO can also intensify the monsoon season as well as help trigger cyclones if there are any existing low-pressure systems in the Coral Sea. There is also the potential for it to create westerly wind bursts in the central Pacific after it has passed over Australia. From late summer through to late winter westerly wind bursts in the Pacific can help trigger an El Nino event.

Tracking and using the MJO

It is important to realise that all methods of tracking or forecasting the MJO are still experimental.

Bureau of Meteorology

This method we are going to show you has been developed by Matthew Wheeler from the Bureau of Meteorology Research Centre and it lets you view the passage of the MJO as it propagates along the equator.

An example of the MJO over a 40 day period is as follows:

The diagram is split into 8 sections, or "phases". These phases represent the different location of the MJO as it moves along the equator. The cycle usually starts on the east coast of central Africa (Phases 8 and 1). From there the MJO passes through the Indian Ocean (Phases 2 and 3), across the top of Australia (Phases 4 and 5) and through the Pacific Ocean (Phases 6 and 7). The influence on Australian rainfall is different depending on the location of the MJO in each phase.

The coloured lines on the diagram represent the passage of the MJO. The green line represents the passage of the MJO through April and the blue line represents its passage through May. The numbered dots along each line represent the days of each month.

If the MJO is inside of the circle, which is in the centre of the diagram, the MJO is classed as 'weak' while the further out it is from the circle the 'stronger' the MJO cycle is. Generally, the influence of the MJO is greater when it is stronger. When it is 'weak', it should not be used as a forecasting guide.