Multivariate ENSO index

[2] While the National Oceanic and Atmospheric Administration (NOAA) has recorded MEI values from 1950 to the present, various researchers have cited the need for data before 1950 in order to better characterize typical ENSO behavior versus unusual occurrences that may be a result of climate change.

Plots comparing MEI and MEI.ext values have shown that data from both methods are highly correlated, supporting the accuracy and effectiveness of MEI.ext.

[3] The Southern Oscillation Index (SOI) is calculated based on the sea level pressure difference between Tahiti and Darwin, Australia.

[5] Developed by Braganza, et al., 2009, this index uses coral, tree ring and ice core data to characterize ENSO events from 1525 – 1982.

Although the proxy ENSO index covers a large time scale of over four centuries, it shows high correlation (> 40%) with the SOI, Niño 3.4 SST and CEI, indicating its accuracy and utility.