Multidecadal simulations of Australian rainfall variability: The role of SSTs

Australian rainfall variability and its relationship with the Southern Osci llation index (SOI) and global sea surface temperature (SST) variability is considered in both observational datasets and ensembles of multidecadal si mulations using two different atmospheric general circulation models forced by observed SSTs and sea ice extent, Monthly and seasonal time series have been constructed to examine the observed and modeled relationships, The models show some success in the Australian region, largely reproducing the observed relationships between rainfall, the SOI, and global SSTs, albe it better in some seasons and geographical regions than others. A partition of the rainfall variance into components due to SST forcing and internal v ariability, suggests that both models have too much internal variability ov er the central eastern half of the continent, especially during austral win ter and spring. Consequently, the strength of the SOI and SST relationships tend to be underestimated in this region. The largest impact of SST forcin g is seen over the tropical and western parts of the continent. A principal component analysis reveals two dominant rotated modes of rainfa ll variability that are very similar in both the observed and modeled cases . One of these modes is significantly correlated with SST anomalies to the north-northwest of Australia (in the case of the models) and the SST gradie nt between the Indonesian archepelago and the central Indian Ocean (in the observed case). The other mode is significantly correlated with the typical SST anomaly pattern associated with the Ei Nino-Southern Oscillation. Corr elative maps between the principal component time series and the modeled MS LP, 700-hPa, and 300-hPa geopotential heights are used to explore the under lying physical processes associated with these statistical relationships.