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.
With another earthquake of 5.7 magnitude being recorded today near off the southern Queensland coast, meteorologists and oceanographers are keeping a wary eye on the potential for tsunamis.
A series of strong cold fronts which are moving in quick succession over southeastern parts of Australia threaten to bring low level snow over the coming days to parts of Tasmania.
Adelaide has recorded its chilliest July in close to 20 years, with both maximum and minimum temperatures colder than average.