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Southern Oscillation Index

Key Finding

A strong El Niño occurred from mid-2015 to early 2016, followed by predominantly ENSO-neutral conditions.

The Southern Oscillation Index (SOI) is based on pressure differences between Tahiti and Darwin, and is the key atmospheric indicator of the El Niño-Southern Oscillation (ENSO).

ENSO is a coupled atmospheric and oceanic phenomenon which fluctuates between its El Niño and La Niña phases, and has wide-ranging effects on seasonal conditions in Queensland.

The SOI and Pacific Ocean sea surface temperature (SST) anomalies are used to assess the presence of El Niño and La Niña and the likelihood of drier or wetter than normal conditions.

El Niño is characterised by warmer than average waters in the central tropical Pacific, and sustained negative values of the SOI. For Queensland, El Niño is often, but not always, associated with below average rainfall.

A strong El Niño prevailed from mid-2015 through early 2016, over which time the 6-month average value of the SOI fell to -16 and seasonal rainfall was below average in parts of northern and central Queensland.

La Niña is characterised by the reverse conditions, often shifting tropical weather systems closer to Queensland. The shift in weather systems increases the likelihood of above average summer rainfall, floods and tropical cyclones.

A strong La Niña occurred from late 2010 through early 2011, over which time the 6-month average value of the SOI rose to +22 and spring through summer rainfall was extremely high across most of the state.

More information:

Relevant Sustainable Development Goals’ targets


Download data from Queensland Government data


The Southern Oscillation Index (SOI) data were taken from the Longpaddock website. The data were current as at February 2020. The Longpaddock SOI data were computed using air pressure data at Darwin (obtained from the Australian Bureau of Meteorology) and air pressure data at Tahiti (obtained from Meteo France).