La Niña Modoki impacts Australia autumn rainfall variability

Abstract

Both El Niño-Southern Oscillation (ENSO) and ENSO Modoki affect Australian rainfall but the commonalities and contrasts of their impacts have not been fully explored. We show that both types feature a strong asymmetry between impacts of La Niña and El Niño in austral autumn (March-May); the La Niña-Australian rainfall teleconnection is statistically significant, whereas the El Niño-Australian rainfall relationship is not. A La Niña Modoki cold anomaly near the Dateline is effective in shining convection westward, causing an autumn rainfall increase over northwestern Australia extending to the northern Murray-Darling Basin, rather than over the east as in a conventional La Niña. During an El Niño Modoki, the tendency for lower Australian rainfall is far weaker. The asymmetry explains the strong inter-ENSO variations in rainfall anomalies, including 1983, when a strong El Niño residual was associated with a wet autumn. Our results highlight the importance of considering the influence from La Niña Modoki in predicting ENSO's impacts. Copyright 2009 by the American Geophysical Union.