Prediction of the dry and wet spell of the Australian monsoon

This study is a sequel to two recent studies on the monsoonal dry and wet spells. The previous studies addressed the dry and wet spells of the monsoon over India and China on the intraseasonal time‐scales. The present study is intended to provide an outlook for the occurrence of dry and wet spells in reference to the Australian monsoon, within roughly a 1 ‐month period from the time of start of the forecast with a global model. In the global model, the definition of a time mean state and an intraseasonal component are retained. The high‐frequency component is viewed as one where inclusion in the initial state can contribute to a degradation of month long forecasts and hence is excluded initially. Sea‐surface temperature anomalies on intraseasonal time‐scales are included in this analysis. The prediction of the wet spells of the monsoon is assessed from the superposition of the predicted intraseasonal cyclonic circulation anomaly on top of the climatological cyclonic anomaly. The dry spell is assessed from an inverse superposition. We consider here a specific period, i.e. March 1992. The early part of this month was characterized by a wet spell over Northern Australia. A dry spell prevailed during the middle of this month and was followed by a wet spell during the latter part of the month. The prediction experiments with a prescribed and a modelled sea‐surface temperature anomaly successfully demonstrated the passage of the intraseasonal anomaly, with the superposition of the geometries of the intraseasonal and the climatic components favouring the wet and the dry spell during different periods of the month.