Influence of the Madden-Julian Oscillation on Multiweek Prediction of Australian Rainfall Extremes using the ACCESS-S1 Prediction System

Scientific journal article


The MJO is a large-scale eastward moving 'pulse' of cloud and rainfall near the equator typically recurring every 30 to 60 days. Its position in relation to Australia, both in terms of the latitude of the eastward moving winds and the location of the cloud and rainfall pulse, influences Australia’s climate. The MJO particularly affects the tropical regions of Australia during summer where it can impact the timing and intensity of active monsoon periods. Researchers from the Bureau of Metrology have investigated the predictability of the MJO and associated Australian weather using the seasonal climate model, ACCESS-S1.

Data from 1990 to 2012 demonstrate that the MJO is a driver of rainfall variation across Australia. For instance, the chances of extreme rainfall in northern Australia increased when the active phases of the MJO are present in the area. The MJO also impacted extreme rainfall in more southern locations due to the impact the MJO has on circulation patterns in the atmosphere.

The analysis demonstrated that ACCESS-S1 can predict the MJO up 28 days in advance, and the model did a reasonable job of simulating the changes in extremes of weekly rainfall for different phases of the MJO across seasons. This allows for predictability 2 to 3 weeks in advance during spring and summer in eastern and southern Australia when the MJO is strong. However, this is not the case for forecasting for central and far north Australia in summer. During autumn and winter, the strength of the MJO has negligible impacts on forecast skill. Thus, the skill of ACCESS-S1 is greatest in regions where the MJO has little influence on rainfall variation.

There are ongoing efforts to improve the depiction of the MJO and its connections to Australian weather patterns in ACCESS-S1. Improvements to ACCESS-S1 based on this study would be particularly helpful to regions that with large variations in rainfall due to the phase of the MJO.