Summary

Impacts of the Madden–Julian Oscillation on wintertime Australian minimum temperatures and Southern Hemisphere circulation.

Increasing the accuracy of multiweek forecasts would assist farmers by providing increased lead time to prepare for extreme events. Bureau of Meteorology researchers investigated using the Madden-Julian Oscillation (MJO) to predict winter temperatures in Australia several weeks in advance. The MJO is a large-scale climate driver influencing rainfall and temperature in northern Australia in summer. It also drives atmospheric winds to move in north and south meandering waves (Rossby waves). These Rossby waves impact mid-latitudes across winter, spring, and summer. Changes in the MJO occur on an intra-seasonal time scale (typically recurring every 30-60 days), so the data can be used to inform multi-week forecasts.

Based on data from 1990 to 2012, specific phases of the MJO were associated with lower minimum temperatures in much of northern Australia. During these phases, the enhanced MJO convection was to the north of Australia. The phases are associated with a strong anticyclonic anomaly over Australia with the Rossby waves largely fixed in space. The chances of an extreme weekly mean minimum temperature at least doubled during these states of the MJO. However, effects on mean maximum weekly temperature were negligible. This is due to weather patterns that promote dry and clear conditions.

Going forward, researchers intend adding this relationship to the existing sub-seasonal and seasonal forecast system to see if it improves prediction of minimum temperatures.