Southern Oscillation Index (SOI) and Equatorial SOI

This plot shows time series of the three-month running average of the Equatorial Southern Oscillation Index (EQ_SOI; in red) and the three-month running average of the Southern Oscillation Index (SOI; in blue) for the past 20 years.

In this plot the Equatorial SOI is calculated as the standardized anomaly of the difference between the area-average monthly sea level pressure in an area of the eastern equatorial Pacific (80°W - 130°W, 5°N - 5°S) and an area over Indonesia (90°E - 140°E, 5°N - 5°S). The SOI is calculated as the standardized difference between standardized Tahiti monthly average sea level pressure anomalies and standardized Darwin monthly average sea level pressure anomalies. The base period used for calculating the anomalies is January 1991 to December 2020.

Dataset Documentation

Equatorial SOI Data

Data

NCEP/NCAR Reanalysis monthly sea level pressure on a 2.5° lat/lon grid

Data Source

NOAA National Centers for Environmental Prediction (NCEP) (NCEP/NCAR Reanalysis)

Analysis

Three-month running average of the standardized anomaly of the difference between the area-average monthly sea level pressure in an area of the eastern equatorial Pacific (80°W - 130°W, 5°N - 5°S) and an area over Indonesia (90°E - 140°E, 5°N - 5°S).

SOI Data

Data

Standardized Difference of Standardized Tahiti minus Standardized Darwin Sea Level Pressure Anomalies

Data Source

NOAA National Centers for Environmental Prediction (NCEP) Climate Prediction Center (CPC) (Monthly Atmospheric and SST Indices: Southern Oscillation Index (SOI))

Analysis

Three-month running average of the standardized difference of standardized Tahiti sea level pressure anomalies minus standardized Darwin sea level pressure anomalies, with 1991-2020 used as the climatological base period.

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