An ENSO model has been developed by Paul Pukite and Paul has given me a copy of his spreadsheet. The spreadsheet was designed to find a best model fit to the Southern Oscillation using one of the Southern Oscillation indexes (SOI); Paul was using the NINO34 index.
I decided to expand the choice of index to include all that I could find on the web. I found 10 in total. Five that stretch all the way back to 1880 and five from 1950 to the present. The five that go back to 1880 are the NINO34 index, the 'Cold Tongue Index,' the SOI_signal index, the SOI_noise index, and the SOI_boma (Bureau of Meteorology - Australia).
I trained the model on the period from 1885 - 1935 using the CTI dataset. I then calculated the correlation coefficients for the Model output versus the various datasets over various time periods. Here are the results.
This result was not wholly unexpected the different ENSO datasets are highly correlated - except for one outlier in each group.