> Southern Oscillation Index based upon annual standardization, Climate Analysis Section, NCAR/UCAR. This includes links to monthly sea level pressure anomalies in Darwin and Tahiti, in either ASCII format (click the second two links) or netCDF format (click the first one and read the explanation).

Which data sets are being used here? There are several at [http://www.cgd.ucar.edu/cas/catalog/climind/soiAnnual.html#download](http://www.cgd.ucar.edu/cas/catalog/climind/soiAnnual.html#download). The links in the blog post are to `darwin.ascii` and `tahiti.ascii`. From just looking at the numbers, these do not seem to be seasonally adjusted and they do look positively correlated. They both go up around July and down around January.