Southern Oscillation Index

Southern Oscillation Index since 1876

The Southern Oscillation Index ( SOI ) is the normalized air pressure differential between Tahiti (Central Pacific ) and Darwin  (Northern Australia). It indicates the state of the Southern Oscillation , specifically the relative strength or weakness of the Walker circulation .

The index goes back to Gilbert Walker , who calculated correlations between numerous meteorological time series in the 1920s and 30s and, based on this, created complex formulas for predicting the strength of the Indian monsoon . The motive was to predict droughts due to the absence of monsoons.

To form the SOI, the measured values ​​are averaged (quarterly by Walker, now monthly), adjusted for their annual variation and their difference is scaled to a standard deviation of 10. If the result clearly tends in one direction over several months,> 7 or <−7, this is considered a La Niña or El Niño event, see El Niño-Southern Oscillation .

Web links

• NOAA Climate Prediction Center
• Commonwealth Bureau of Meteorology, Climate Information

Individual evidence

1. ^ Donald R. Mock (NOAA): The Southern Oscillation: Historical Origins. May 1981.
2. ↑ International Research Institute for Climate and Society ( IRI ): Walker: Identifying the Southern Oscillation. Retrieved May 13, 2018.