Fairfax Media Network

Agriculture Weather

Southern Oscillation Index

  • location
  • Aus

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.

Southern Oscillation Index


Nino3.4 Index

Display Your Local Weather

Weather News

Reduced market options for wheaten hay: exporter

16:14 EDT

Farmers across of Australia have been forced to cut areas of their cereal crops for wheaten hay, despite the product's lack of appeal on international markets.

Healthy rain along the QLD coast

15:23 EDT

Parts of coastal QLD received their heaviest October rain in five years.

Sunset Strip residents plan open day to beat population drought

14:41 EDT

Residents of Sunset Strip southeast of Broken Hill are gearing up to host the town's first open day this weekend, aimed at pitching the lakeside settlement to prospective home buyers.