A large sample of tropical Pacific SSTA forecasts using the COLA global anomaly coupled prediction system is diagnosed in terms of the evolution of ENSO events. The systematic errors in the evolution of the ENSO events include: (1) SSTA that are too narrowly confined to the equator, (2) SSTA that extend too far into the western Pacific, (3) relatively weak SSTA in the eastern Pacific, and (4) an excessively fast transition between the warm and cold states. These errors are part of the initialization shock associated with the coupled predictions, and are, in part, due to the fact that the model climate differs from observed initial states.

It is hypothesized that a significant component of these errors and initialization shock could be due to systematic errors in the structure of the atmospheric wind stress anomalies, which are then amplified via coupled feedbacks.

Here we have developed an empirical correction to the spatial structure of the wind stress that improves the evolution of the ENSO events in long simulations and in coupled forecasts leading to improved prediction skill. The reduction of the initialization shock and the improved simulation is diagnosed in terms of equatorial wave dynamics.