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 Niņa.
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 Niņo.
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.
'Godzilla El Nino' intensifying: Drought, heatwaves and heightened bushfire risk expected this summer
With Australia in the grip of an extreme El Nino weather event, more heatwaves and a heightened bushfire risk are expected this summer.
Adelaide has recorded one of its hottest October days in 70 years, with the temperature reaching 35.6 degrees Celsius, as Country Fire Service (CFS) crews battle blazes across the state.
Monday was the earliest October day to surpass 30 degrees Celsius in Canberra since records began in 1939.