Wind-Induced Rainfall and Surface Temperature Anomalies in the Australian Region

Abstract

An extended coupled atmosphere?ocean model simulation has been analyzed to explore the relationship between Australian rainfall and regional surface temperature anomalies. The interannual variability of seasonal rainfall in the model (which has a weak El Niño) was generally similar to that from a simulation by the atmospheric model with SSTs specified to follow a repeated annual cycle, suggesting that much of the variability is generated internally to the atmosphere. Given the expected role of winds, rotated principal component analyses of both January and July regional 800-hPa wind anomalies from the coupled model were performed. In each season, two wind patterns correlated with realistic rainfall patterns: a monsoon surge pattern brought rainfall to northern Australia in January; a northwesterly flow induced winter rainfall along a band extending to the southeast; and a pattern including northerlies along the east coast brought rainfall to eastern Australia, in both winter and summer. The wind patterns also induced significant surface temperature anomalies over both land and sea. Correlations between the wind-related rainfall indices and seasonal SSTs produced regional SST patterns with much in common to those observed. In particular, the northwesterly rainfall coincided with an eastern Indian Ocean dipole pattern. Aside from the monsoon surge, there is little long-term precursor to these wind anomalies in the model, however, and hence little predictability of the rainfall patterns via the SSTs. Clearly, substantial seasonal rainfall?SST relationships do not necessarily result from forcing of wind anomalies by SSTs, and, excepting El Niño, much of the Australian relationship may, evidently, be unforced.