SAM and why Western Australia missed out on rain

The Southern Annular Mode (SAM) was positive from March 2010 until February 2011. Record high positive monthly values were observed in 2010 for June, July and November, while August and October were the second-highest on record. The SAM appears to have a weak but discernible relationship with La Niña and El Niño in summer. Hence the positive SAM values in late 2010 may well have been enhanced by the La Niña event.

For southwest Western Australia, 2010 was the driest year on record, continuing and worsening the long drying trend that has affected the southwest since the late 1960s. At least partly as a result of climate change, there has been a change in the dominant weather systems over the region, including a weakening of storms and southwards movement of storm tracks and cold fronts, leading to a reduction in rainfall.

The persistently strong SAM during 2010 meant that high-pressure anomalies dominated parts of southern Australia for most of the southern hemisphere winter–spring. The dominance of the SAM over southern Australia is likely to have contributed to dry conditions in southwest Western Australia during winter and spring.

SAM event

The strong positive SAM event during 2010 is likely to have contributed to the dry conditions in southwest Western Australia.