Recent unprecedented skewness towards positive Indian Ocean Dipole occurrences and its impact on Australian rainfall

Is the recent high frequency of positive Indian Ocean Dipole (pIOD) events a consequence of global warming? Using available observations and reanalyses, we show that the pIOD occurrences increase from about four per 30 years early in the 20th century to about 10 over the last 30 years; by contrast, the number of negative Indian Ocean Dipole (nIOD) events decreases from about 10 to two over the same periods, respectively. A skewness measure, defined as the difference in occurrences of pIODs and nIODs, illustrates a systematic trend in this parameter commencing early in the 20th century. After 1950, there are more pIODs than nIODs, with consistent mean circulation changes in the pIOD-prevalent seasons. Over southeastern Australia (SEA), these changes potentially account for much of the observed austral winter and spring rainfall reduction since 1950. These features are consistent with projected future climate change and hence with what is expected from global warming. Citation: Cai, W., T. Cowan, and A. Sullivan (2009), Recent unprecedented skewness towards positive Indian Ocean Dipole occurrences and its impact on Australian rainfall, Geophys. Res. Lett., 36, L11705, doi: 10.1029/2009GL037604.