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.
The cold fronts that have frozen southeastern Australia haven't had the gas to push far enough north to cool Darwin, with heat records for the NT capital.
As residents in New South Wales emerge from under the rug after their , the question on the blue lips of many is what's the best way to stay warm? While many may feel their insides are rapidly chilling, Dr Ollie Jay from the University of Sydney said little was happening to our bodies internally and the cold was all due to "perception".
So far this winter Western Australia has been divided, unseasonably cold in the south and hot in the north.