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File: ClimateDashboard-variability-Southern-Oscillation-Index-graph-20211004-1400px.jpg

Graph of SOI index since 1950

Image caption

Monthly surface pressure anomalies—differences from the 1981-2010 average—in Darwin, Australia, compared to Tahiti. Positive values indicate a strong Walker Circulation, which occurs during La Niña. Negative values indicate a weak or disrupted Walker Circulation, which occurs during El Niño. NOAA Climate.gov image, based on data from the Climate Prediction Center.