This is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. Sustained negative values of the SOI often indicate El Niño episodes. Positive values of the SOI are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia, popularly known as a La Niña episode ( BoM 2002).
The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. Click here for more information
( SOI) is the difference between the seasonally normalized sea level pressures of Darwin, Australia and Tahiti. A negative SOI (also called "low index") usually relates to a weakening of the Trade Winds and a resulting warm event. Conversely a positive SOI ("high index") usually relates to an increase in the Trades and a resulting cool event. [ Table, Plot
An index calculated from anomalies in the pressure difference between Tahiti and Darwin. Low negative values of this index correspond to El Niño conditions, and high positive SOI values coincide with La Niña episodes.
An index that represents the strength of the Southern Oscillation, generally taken as the normalized SLP at Tahiti minus that at Darwin. It is highly correlated with time series of ENSO. During a warm event, mean sea level pressures will tend to be below normal at Tahiti and above normal at Darwin, Australia. Hence, the SOI would be negative.
An index calculated from the pressure difference between Darwin and Tahiti. Abbreviates to SOI.
A measure of the state of the Southern Oscillation. A common index used for this purpose is the sea level pressure at Tahiti minus the sea level pressure at Darwin, Australia, divided by the standard deviation of that quantity. It is closely associated with El Niño and is thus often referred to as ENSO (El Niño–Southern Oscillation).