资源环境科技发展态势分析平台

The spring predictability barrier (SPB) is a well-known characteristic of ENSO prediction, which has been widely studied for El Nino events. However, due to the nonlinearity of the coupled ocean-atmosphere system and the asymmetries between El Nino and La Nina, it is worthy to investigate the SPB for La Nina events and reveal their differences with El Nino. This study investigates the season-dependent predictability of sea surface temperature (SST) for La Nina events by exploring initial error growth in a perfect model scenario within the Community Earth System Model. The results show that for the prediction through the spring season, the prediction errors caused by initial errors have a season-dependent evolution and induce an SPB for La Nina events. Two types of initial errors that often yield the SPB phenomenon are identified: the first are type-1 initial errors showing positive SST errors in the central-eastern equatorial Pacific accompanied by a large positive error in the upper layers of the eastern equatorial Pacific. The second are type-2 errors presenting an SST pattern with positive errors in the southeastern equatorial Pacific and a west-east dipole pattern in the subsurface ocean. The type-1 errors exhibit an evolving mode similar to the growth phase of an El Nino-like event, while the type-2 initially experience a La Nina-like decay and then a transition to the growth phase of an El Nino-like event. Both types of initial errors cause positive prediction errors for Nino3 SST and under-predict the corresponding La Nina events. The resultant prediction errors of type-1 errors are owing to the growth of the initial errors in the upper layers of the eastern equatorial Pacific. For the type-2 errors, the prediction errors originate from the initial errors in the subsurface layers of the western equatorial Pacific. These two regions may represent the sensitive areas of targeted observation for La Nina prediction. In addition, the type-2 errors in the equatorial regions are enlarged by the recharge process from 10 degrees N in the central Pacific during the eastward propagation. Therefore, the off-equatorial regions around 10 degrees N in the central Pacific may represent another sensitive area of La Nina prediction. Additional observations may be prioritized in these identified sensitive areas to better predict La Nina events.