The Combined Effect of Initial Error and Model Error on ENSO Prediction Uncertainty Generated by the Zebiak-Cane Model

Abstract

Initial errors and model errors are the source of prediction errors. In this study, the authors compute the conditional nonlinear optimal perturbation (CNOP)-type initial errors and nonlinear forcing singular vector (NFSV)- type tendency errors of the Zebiak-Cane model with re- spect to El Nino events and analyze their combined effect on the prediction errors for El Nino events. The CNOP- type initial error (NFSV-type tendency error) represents the initial errors (model errors) that have the largest effect on prediction uncertainties for El Nino events under the perfect model (perfect initial conditions) scenario. How- ever, when the CNOP-type initial errors and the NFSV- type tendency errors are simultaneously considered in the model, the prediction errors caused by them are not am- plified as the authors expected. Specifically, the predic- tion errors caused by the combined mode of CNOP-type initial errors and NFSV-type tendency errors are a little larger than those caused by the NFSV-type tendency er- rors. This fact emphasizes a need to investigate the opti- mal combined mode of initial errors and tendency errors that cause the largest prediction error for El Nino events.  Keywords: predictability, initial error, model error, opti- mal perturbation Citation: Zhao, P., and W.-S. Duan, 2014: The combined effect of initial error and model error on ENSO prediction uncertainty generated by the Zebiak-Cane model, Atmos. Oceanic Sci. Lett., 7, 447-452, doi:10.3878/j.issn.1674- 2834.14.0034.