Seasonal climate Summary southern hemisphere (autumn 2011): One of the strongest la Niña events on record begins to decline

Abstract

Southern hemisphere circulation patterns and associated anomalies for the austral autumn 2011 are reviewed, with emphasis given to the Pacific Basin climate indicators and Australian rainfall and temperature patterns. Early autumn saw the continuation of the strong La Niña conditions that had been evident during the latter half of 2010. ENSO indices during March and April showed a strong La Niña signature prior to a rapid decline to neutral conditions in May. The April Southern Oscillation Index value was the second-highest for any month since November 1973. Averaged nationally over the Australian continent and Tasmania, rainfall for autumn was the fourth-highest on record and highest since 2000, with falls over the Northern Territory exceeding the previous highest area-averaged total. In contrast, there were continuing rainfall deficiencies over the western half of Western Australia. Australia-wide mean temperatures were lowest on record, as were mean temperatures for the Northern Territory, and for Queensland as a whole.