Standing Rossby waves associated with anomalously warm sea surface temperatures in the tropical Indian Ocean have been linked to Australian spring maximum temperature extremes. These Rossby waves were suggested to contribute to the anomalously high 200hPa geopotential height that helped develop the observed heat in recent springs. This study aims to better understand the dynamics of the teleconnection between the tropical Indian Ocean and Australia during austral spring months by taking advantage of the ensemble member spread in a seasonal prediction system. A tropical Indian Ocean teleconnection could lead to more skilful prediction of future monthly and seasonal heat extremes across Australia.

We use Rossby wave analysis techniques, including wave source and activity flux at 200hPa, and linear regression analysis techniques. We use the ERA-Interim reanalysis dataset and POAMA, one of the Bureau of Meteorology’s seasonal forecasting systems, and compare ensemble member forecasts of the recent Australian spring heat events to see whether the members that best capture the heat also capture conditions over the Indian Ocean. POAMA experimental forecasts with climatological sea surface temperatures in the Indian Ocean are also examined.

Results from the reanalysis suggest that the influence of the tropical Indian Ocean on Australia varies over the individual months of spring. Early season Rossby waves appear to have mid-latitude origins, however, a greater amount of activity flux develops out of the tropical Indian Ocean as spring progresses. This is partly reflected in the hotter POAMA ensemble members, with better performing members capturing some of this activity flux pattern, particularly in late spring. It appears that Rossby waves are emitted from the tropical Indian Ocean and propagate towards Australia later in spring and may provide predictability of extreme temperatures in this period.