Southern Oscillation Index
The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.
A strongly and consistently positive SOI pattern (e.g. consistently above about +6 over a two month period) is related to a high probability of above the long-term average (median) rainfall for many areas of Australia, especially areas of eastern Australia (including northern Tasmania) - La Niña.
Conversely, a 'deep' and consistently negative SOI pattern (less than about minus 6 over a two month period, with little change over that period) is related to a high probability of below median rainfall for many areas of Australia at certain times of the year - El Niño.
However, it is important to remember that the pattern of relationship between SOI and rainfall (and temperature) can vary depending on the particular season and region. Additionally, the change in SOI over a specified period can be as important in understanding relationships between SOI and rainfall as is the absolute value in SOI.
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Weather News
West Australian farmers grow feed in refrigerated cabinet to keep stock fed during dry winter conditions
09:06 EST
Farmers in Western Australia's eastern wheatbelt are trying to drought proof their farm by growing sheep feed in large refrigerated cabinets on farm.
Winter takes a break in Qld, NSW
17:03 EST
It was a spring-like day in parts of Queensland and NSW today, although a return of wintry weather is just around the corner.
Another turbulent day in South Australia
14:11 EST
Strong winds continue to buffet South Australia today following the heaviest rain in more than a year in some parts of the state.
