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ENSO Prediction by Coupled Ocean-Atmosphere Models
Jin, E.K., Kinter III, J.L., Wang, B., Park, C.-K., Kang, I.-S., Kirtman, B.P., Kug, J.-S., Kumar, A., Luo, J.-J., Schemm, J., Shukla, J. and Yamagata, T. 2008. Current status of ENSO prediction skill in coupled ocean-atmosphere models. Climate Dynamics 31: 647-664.

What was done
The authors investigated the overall skill of El Niņo Southern Oscillation (ENSO) prediction in retrospective forecasts made with ten different state-of-the-art ocean-atmosphere coupled general circulation models (CGCMs) -- which they describe as "coupled ocean-land-atmosphere dynamical seasonal prediction systems" -- with respect to their ability to "hindcast" real-world observations for the 22 years from 1980 to 2001.

What was learned
The twelve US, South Korean and Japanese researchers report that almost all models have problems simulating the mean equatorial sea surface temperature (SST) and its annual cycle. In fact, they say that "none of the models we examined attain good performance in simulating the mean annual cycle of SST, even with the advantage of starting from realistic initial conditions," while noting that "with increasing lead time, this discrepancy gets worse," and stating that "the phase and peak amplitude of westward propagation of the annual cycle in the eastern and central equatorial Pacific are different from those of observed." What is more, they find that "ENSO-neutral years are far worse predicted than growing warm and cold events," and they write that "the skill of forecasts that start in February or May drops faster than that of forecasts that start in August or November," which behavior they and others refer to as "the spring predictability barrier," which designation gives an indication of the difficulty of what they are attempting to do.

What it means
Jin et al. conclude that "accurately predicting the strength and timing of ENSO events continues to be a critical challenge for dynamical models of all levels of complexity."

We concur. It is clear that even the best ocean-atmosphere CGCMs of the day are "not there yet," when it comes to making reasonably accurate predictions of ENSO occurrence and behavior; and it would appear that they still have a long way to go before they arrive at their desired destination.

Reviewed 4 February 2009