Understanding and predicting the strong Southern Annular Mode and its impact on the record wet east Australian spring 2010
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In 2010 eastern Australia experienced its wettest spring on record, which has been largely attributed to a strong La Niña event in conjunction with an extraordinary positive excursion of the Southern Annular Mode (SAM). La Niña impacts would be expected to have been predictable months in advance, but predictability of the occurrence of the strong SAM is less known. We explore the predictability of the strong SAM in austral spring 2010 and its contribution to the extreme wet conditions in eastern Australia, using the Australian Bureau of Meteorology’s dynamical seasonal forecast system (POAMA2). Seasonal forecasts from POAMA2 were skilful in predicting the wet conditions over eastern Australia at up to 2 month lead time as a result of a good prediction of the impacts of the ongoing La Niña and the development of a strong positive excursion of the SAM. Forecast sensitivity experiments on initial conditions demonstrate that (1) the strong La Niña was a necessary condition for promoting the positive phase of SAM (high SAM) and the anomalous wet conditions over eastern Australia during October to November 2010; but (2) internal atmospheric processes were important for producing the moderate strength of the high SAM in September 2010 and for amplifying the strength of the high SAM forced by La Niña in October to November 2010; and (3) the strong high SAM was an important factor for the extremity of the Australian rainfall in late spring 2010. Therefore, high quality atmosphere and ocean initial conditions were both essential for the successful prediction of the extreme climate during austral spring 2010.
KeywordsLa Niña 2010 Southern Annular Mode 2010 Australian rainfall extreme 2010 Seasonal forecasts
This research was supported in part by the Victorian Climate Initiative (VicCI). The authors thank Dr. Guo Liu in CAWCR for his technical support in conducting the forecast sensitivity experiments and Drs. Debra Hudson, Julie Arblaster and Tom Beer in CAWCR and two anonymous reviewers for providing constructive comments. Hurrell et al. (2008) SST data and ERA-Interim data used in this study have been provided by NCAR/UCAR and ECMWF, respectively.
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