Climatic Research Unit : Data

Southern Oscillation Index (SOI)


The SOI is defined as the normalized pressure difference between Tahiti and Darwin. There are several slight variations in the SOI values calculated at various centres. Here we calculate the SOI based on the method given by Ropelewski and Jones (1987). It uses a second normalization step, and was the Climate Analysis Centre's standard method in 1987. The reader is also referred to Allan et al. (1991) and Können et al. (1998) for details of the early pressure sources and methods used to compile the series from 1866 onwards.

File format (SOI)
for year = 1866 to endyear
  format(i5,12f7.2,f8.2) year, 12 * monthly value, annual value
Missing values represented by -99.99 and -10.00

File format (Station pressure)
for year = 1855 to endyear
  format(i5,12i6) year, 12 * monthly value
Missing values represented by -989, -990 and -10
Divide by 10 for millibars

Filename SizeDescription
soi.dat 14 kilobytesSOI
soi_dar.dat 12 kilobytesPressure data for Darwin
soi_tah.dat 12 kilobytesPressure data for Tahiti


Last updated: January 2010, Phil Jones & Mike Salmon

These datasets are made available under the Open Database License.
Any rights in individual contents of the datasets are licensed under the
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Please use the attribution Climatic Research Unit, University of East Anglia