Evidence for decadal variability in southern Australian rainfall and relationships with regional pressure and sea surface temperature

A study of decadal variability in winter rainfall over various areas in sou thern Australia and possible links with regional mean sea level pressure (M SLP) and sea surface temperature (SST) is presented. Newly released histori cal data sets (GISST 3 and GMSLP 2.1f) are used for this purpose. Emphasis is placed upon southwest Western Australia (SW WA), since this region has a pparently experienced a significant winter rainfall decline since the mid-1 960s. Cross-spectral, empirical orthogonal function (EOF) and correlation techniq ues are used to show that there is a statistically significant inverse rela tionship between regional MSLP and SW WA rainfall on a time scale of 8-9 ye ars. EOF analysis of winter averaged MSLP revealed a mode prominent between Australia and New Zealand and extending into the high southern latitudes, which explained 19.5% of the variance. This pattern appears to reflect a st rengthening of the sub-tropical high pressure belt and a shift of the Circu mpolar Trough and was found to be significantly correlated with SW WA winte r rainfall. Based on the premise that the MSLP-rainfall relationship involves changes t o the strength and track of the mid-latitude depressions and associated fro ntal systems that provide the bulk of SW WA winter rainfall, an investigati on into coastal regions downstream (Tasmania and coastal South Australia (S A)) was also performed, This also showed a significant relationship between rainfall and regional MSLP on time scales of about 8-9 years. Links between rainfall in these regions and Indo-Pacific Ocean SST were als o investigated but found to be less prominent than those for MSLP. This fin ding is consistent with previous work and possibly reflects the mid-latitud e location of the regions considered and the likelihood that winter depress ions are more sensitive to the large scale atmospheric circulation than the y are to the underlying SST field. Copyright (C) 2000 Royal Meteorological Society.