Representation of the Australian sub-tropical ridge in the CMIP3 models

This study examines the representation of one of the key drivers of southeastern Australian rainfall, the sub-tropical ridge (STR) in mean sea level pressure, in the World Climate Research Programme's Coupled Model Intercomparison Project phase 3 multi-model dataset. In particular, the mean state and variability of the ridge's intensity and position is diagnosed and compared to observations for the 20th Century. The mean annual cycle of the STR intensity and position are found to be moderately well represented compared to two observational datasets. The models project that STR intensity will increase over the 21st Century whilst its mean position will be further south. Given the historical relationship between the STR and rainfall, this suggests that southeastern Australia will most likely be drier in the future. Most models fail to reproduce the spatial pattern of correlation between the STR intensity and precipitation but some models show a correlation (significant in some cases) between high rainfall and a weaker STR intensity. However, these correlations are much weaker than the observations. Given that the annual cycle of the STR has significant implications for rainfall in southeastern Australia, this is of some concern and leads to questions about which processes are driving rainfall in the models. Copyright (C) 2011 Royal Meteorological Society