Abstract
This study investigates impacts of two types of La Niña events, eastern Pacific ( EP ) La Niña and central Pacific ( CP ) La Niña, on Australian summer rainfall during 1951–2009. Results show that Australian summer rainfall is sensitive to the change in the location of sea surface temperature ( SST ) anomalies in equatorial Pacific. During CP La Niña, maximum cold SST anomaly is located in the equatorial CP west of 150°W, and significant northeasterly wind anomalies tend to prevail over northeastern Australia during austral summer. This brings more moist and warm flow from the tropics to Australia and leads to significant positive rainfall anomalies over northern and eastern Australia. In contrast, during EP La Niña, maximum cold SST anomaly is confined to equatorial EP east of 150°W and atmospheric circulation anomalies tend to be weak. As a result, rainfall anomalies are generally weak over Australia in EP La Niña. The differences in the Australian summer rainfall anomalies between CP La Niña and EP La Niña are attributed to the differences in atmospheric circulation anomalies. Specifically, the atmospheric circulation anomalies over tropical Pacific tend to be stronger and located more westward in CP La Niña. Higher climatological SST in the equatorial CP than equatorial EP , larger magnitude and westward shift of cold SST anomaly centre in CP La Niña than EP Niña may explain stronger and westward shift of the atmospheric anomalies in CP La Niña. Atmospheric model numerical experiments confirm the contribution of stronger circulation response in CP La Niña to the positive rainfall anomalies in Australia. Results in this study suggest that it is important to classify the La Niña events into different types when predicting Australian summer rainfall.