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.
The clean-up is continuing after a severe storm hit the New South Wales North Coast on Sunday afternoon leaving thousands without power and displacing some patients at Lismore Base Hospital.
Hot, windy weather could pose a danger on the fire ground in South Australia's lower north today, authorities have warned.
More than a dozen homes have lost their roofs and about 20,000 properties were left without power after very dangerous thunderstorms tore across south-east Queensland on Sunday afternoon.