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 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

Display Your Local Weather

Weather News

Cyclone Marcus 'a real wake-up call' for complacent Territorians, NT Police say

00:15 EDT

The damage wrought by Tropical Cyclone Marcus is a "real wake-up call" for Darwin residents lulled into a false sense of security when it comes to cyclone safety, emergency services say.

Cyclone Marcus: What you need to know at a glance

00:15 EDT

Tropical Cyclone Marcus passed over Darwin as a category two system just before midday on Saturday.

Fire risks as Victorians warned of severe weather conditions

15:47 EDT

It's hot and windy across Victoria and if a fire starts up, it will be very hard to stop, warns Victoria's Emergency Management Commissioner.