Seasonal climate summary southern hemisphere (winter 2011): a dry season in the lull between La Niña events

Abstract

Southern hemisphere circulation patterns and associated anomalies for the austral winter 2011 are reviewed, with emphasis given to the Pacific Basin climate indicators and Australian rainfall and temperature patterns. Winter 2011 saw a brief period of neutral El Niño – Southern Oscillation (ENSO) conditions following the 2010–11 La Niña’s conclusion in the preceding autumn, before the equatorial Pacific was again dominated by cooling leading into the formation of the 2011–12 La Niña during spring. Most ENSO indicators were consistent with this, with values generally on the cool side of neutral, but not yet showing a consistent La Niña signal, despite the substantial volume of cooler-than-usual water present below the surface of the central and eastern equatorial Pacific by late winter. The Indian Ocean Dipole entered a positive phase from late winter 2011, with surface temperatures in the Arabian Sea generally warmer than average, while water off the coast of Sumatra was cooler than average. Averaged over Australia, winter rainfall was slightly below average. Maximum temperatures were above to very much above average across southern Australia, while minimum temperatures were below to very much below average across most of the north and above to very much above average for Tasmania, the southern half of Western Australia, and coastal areas of the southeastern mainland. For maximum temperatures, winter 2011 was in the top five warmest winters on record for South Australia and the southeastern states.