Seasonal climate summary southern hemisphere (autumn 2008): a return to neutral ENSO conditions in the tropical Pacific

Abstract

Southern hemisphere circulation patterns and associated anomalies for the austral autumn 2008 are reviewed, with emphasis given to the Pacific Basin climate indicators and Australian rainfall and temperature patterns. Autumn 2008 saw the decay of a La Niña event. The La Niña peaked in February 2008 and was the strongest since 1988 by most measures. The Pacific Ocean surface and subsurface gradually warmed through autumn. By the end of May, although some cool anomalies were still present in the central Pacific, most ocean indices were within the El Niño-Southern Oscillation (ENSO) neutral range. In addition, the Southern Oscillation Index (SOI) also fell with each autumn month, reaching a neutral −4.3 in May. In the extra-tropics, the positive phase of the Southern Annular Mode (SAM) that dominated summer 2007–08 switched to a weak negative phase in autumn. The mean sea level pressure (MSLP) and geopotential height patterns that are typical of a negative SAM were evident over the Antarctic region as well as the mid-latitudes of the southern Indian and Atlantic Oceans. In the Indian Ocean, a positive Indian Ocean Dipole sea surface temperature (SST) pattern started to establish itself during May. In the Australian region, the most significant climatic feature for autumn was exceptionally low rainfall. Averaged across the continent Australia had its driest May on record