Tuesday, December 30, 2008
Wednesday, December 24, 2008
Pacific indicators point to la nina: bureau
December 23, 2008, Weekly Times
A CONTINUED cooling of the equatorial Pacific in the past two weeks raises the possibility of indicators reaching levels of a la nina, often associated with above-average rainfall in Australia, the Bureau of Meteorlogy says.
If a la nina develops, summer crops such as sorghum and cotton in northeast Australia might experience several rainfall events in the coming months, potentially boosting production. Already, these cropping areas in northern New South Wales and southern Queensland received above-average November rainfall. "Given current conditions and recent trends, the development of a la nina during the southern summer can't be ruled out. However, the majority of climate models forecast neutral conditions, with a cooler than normal Pacific, during the first quarter of 2009," the bureau said in a regular review of Pacific conditions. The bureau also cited persistently stronger than normal trade winds for some months in the western Pacific and cloudiness suppressed along much of the central and eastern equatorial Pacific.
Its Southern Oscillation Index has remained strongly positive since late August. The value of the SOI in the 30 days ended December 21 was +13, falling a little from +17 in November. Sustained positive values of the SOI are associated with a la nina. Historically, it is unusual for la nina thresholds to be reached during the southern summer, though this did occur as recently as the summer of 1999/2000, it said.
The bureau also reiterated the Indian Ocean Dipole is neutral and is expected to remain neutral through summer. The bureau previously identified a positive mode for the IOD as a key influence for a drought in 2007 that wrecked winter crops including wheat in southeast Australia. A positive mode for the IOD is an effect that often hinders the formation of the northwest cloudbands that are an important source of winter/spring rainfall in southeast Australia.