Sensitivity of Australian rainfall to inter-El Nino variations

Australia typically experiences drought during El Nino, especially across the eastern two- thirds of the continent during austral spring ( September - November). There have, however, been some interesting departures from this paradigm. For instance, the near- record- strength El Nino of 1997 was associated with near- normal rainfall. In contrast, eastern Australia experienced near- record drought during the modest El Nino of 2002. This stark contrast raises the issue of how the magnitude of the drought is related to the character and magnitude of El Nino, for instance as measured by the broadscale sea surface temperature ( SST) anomaly in the equatorial eastern Pacific. Internal ( unpredictable) atmospheric noise is one plausible explanation for this contrasting behavior during these El Nino events. Here, the authors suggest that Australian rainfall is sensitive to the zonal distribution of SST anomalies during El Nino and, in particular, the greatest sensitivity is to the SST variations on the eastern edge of the Pacific warm pool rather than in the eastern Pacific where El Nino variations are typically largest. Positive SST anomalies maximized near the date line in 2002, but in 1997 maximum anomalies were shifted well into the eastern Pacific, where their influence on Australian rainfall appears to be less. These findings provide a plausible physical basis for the view that forecasting the strength of El Nino is not sufficient to accurately predict rainfall variations across Australia during El Nino.