Seasonal Prediction of Australian Summer Monsoon Rainfall

Abstract

Seasonal prediction of Australian summer monsoon rainfall is reviewed. Due to the strong influence of EI Nino, rainfall in the pre-monsoon season (late austral spring) is highly predictable using both statistical forecast schemes and dynamical coupled models. Although of far lesser magnitude than rainfall during the monsoon, prediction of pre-monsoon rainfall has great economic value. Even though EI Nino persists and typically peaks during austral summer, seasonal rainfall during the monsoon is shown to be far less predictable than in the pre-monsoon using both statistical models and dynamical coupled models. We review here the basis for skilful prediction of pre-monsoon rainfall and the lack of skill during the monsoon. We postulate that local air-sea interaction tends to promote predictability in the pre-monsoon and to degrade predictability during the monsoon. Although predictive skill with our dynamical coupled models is hampered by model bias and error, the seasonality of the local air-sea interaction is well depicted in the model, thus suggesting the lower skill during the monsoon is a reflection of intrinsically lower predictability than in the pre-monsoon.