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Southern Oscillation Index

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Aus

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Weekly
Monthly

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.

Southern Oscillation Index

Nino3.4 Index

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Increasing signs a positive IOD could develop this winter

12:48 AEST There are increasing signs that a positive Indian Ocean Dipole could develop this winter, increasing the chance of abnormally dry and warm weather in some parts of Australia over the coming months. What is the Indian Ocean Dipole? The Indian Ocean Dipole (IOD) is an index that measures the difference between sea surface temperatures on the eastern and western sides of the Indian Ocean.