Trenberth Southern Oscillation Index (SOI) from NCAR

The Southern Oscillation Index (SOI) at NCAR is computed using monthly mean sea level pressures at Tahiti (T) and Darwin (D). The SOI [T-D] is an optimal index that combines the Southern Oscillation into one series. These SOI values are slightly different than those calculated by the Climate Prediction Center ("cpc.ncep.noaa.gov/") due to the normalization used.

The [T+D] series is a measure of small scale and/or transient phenomena that are not part of the large scale Southern Oscillation. To access the SOI data at NCAR, see: "cgd.ucar.edu/cas/catalog/climind/soi.html" or "ftp://ftp.cgd.ucar.edu/pub/shea/soi_dir/"