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25 Jul 2008

Recent trends in the Southern Oscillation Index (SOI) can be used to calculate more accurately the probabilities of receiving particular amounts of rainfall at a particular location; over the next few months.The phases of the SOI were defined by Dr Roger Stone then of QDPI, who used a statistical technique (cluster analysis) to group all sequential two-month pairs of the SOI (from 1882 to 1991) into five clusters (see legend below & help on use of trends in the SOI).

By using this information we have constructed maps of future rainfall probability.

Reference for the SOI Phase system: Stone, R.C., Hammer, G.L and Marcussen, T. (1996) Prediction of global rainfall probabilities using phases of the Southern Oscillation Index. Nature, 384, 252-255.

Phases of the Southern Oscillation Index
	Consistently negative (phase 1)
	Consistently positive (phase 2)
	Rapidly falling (phase 3)
	Rapidly rising (phase 4)
	Consistently near zero (phase 5)

Maps for the all five SOI phases:

Maps for the current three month period using the latest phase:

phase 4

Chance of exceeding median rainfall in the period from July through September based on a Rapidly rising SOI phase over May and June

Graphics in GIF format, each image will appear in a new window.

Acrobat document(s). You may need to download the free Adobe Acrobat Reader.

Years in history with the same SOI phase over May-Jun:

1879, 1884, 1887, 1889, 1897, 1900, 1901, 1909, 1910, 1920, 1922, 1929, 1934, 1945, 1947, 1950, 1951, 1953, 1957, 1958, 1966, 1967, 1970, 1973, 1986, 1996, 1998, 2001, 2005, 2007, 2008