La Nina Modoki impacts Australia autumn rainfall variability

Both El Nino-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 Nina and El Nino in austral autumn (March May); the La Nina-Australian rainfall teleconnection is statistically significant, whereas the El Nino-Australian rainfall relationship is not. A La Nina Modoki cold anomaly near the Dateline is effective in shifting 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 Nina. During an El Nino 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 Nino residual was associated with a wet autumn. Our results highlight the importance of considering the influence from La Nina Modoki in predicting ENSO's impacts. Citation: Cai, W., and T. Cowan (2009), La Nina Modoki impacts Australia autumn rainfall variability, Geophys. Res. Lett., 36, L12805, doi:10.1029/2009GL037885.