The first principal component of the Southern Oscillation Index (SOI) is used as the intensity of annual SO.

用南方涛动指数(SOI)的第一主成分表示年涛动强度。

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But by the Berkeley team's analysis, the global temperature correlates more closely with the state of the Atlantic Multidecadal Oscillation (AMO) index - a measure of sea surface temperature in the north Atlantic.

BBC: Global warming 'confirmed' by independent study

To explore this they used an index of weather severity called the North Atlantic oscillation.

ECONOMIST: Evolution and climate change