Impact of Subsurface Entrainment on ENSO Prediction: 1997-98 El Nino

Twenty-one-year hindcasts of sea surface temperature (SST) anomalies in the tropical Pacific were performed to validate the influence of ocean subsurface entrainment on SST prediction. A new hybrid coupled model was used that considered the entrainment of subsurface temperature anomalies into the sea surface. The results showed that predictions were improved significantly in the new coupled model. The predictive correlation skill increased by about 0.2 at a lead time of 9 months, and the root-mean-square (RMS) errors were decreased by nearly 0.2°C in general. A detailed analysis of the 199798 El Niño hindcast showed that the new model was able to predict the onset, peak (both time and amplitude), and decay of the 199798 strong El Niño event up to a lead time of one year, factors that are not represented well by many other forecast systems. This implies, in terms of prediction, that subsurface anomalies and their impact on the SST are one of the controlling factors in ENSO cycles. Improving the presentation of such effects in models would increase the forecast skill.