Abstract

An intermediate ocean-atmosphere coupled model of the tropical Pacific is used to investigate the sensitivity of the seasonal forecasts to the configuration of the oceanic vertical structure. The models consist in a three baroclinic mode tropical Pacific Ocean model and a Gill (1980)'s tropical atmosphere. The predictive skill of the model using a simple nudging method for the initialization is first presented from 1970 and compared to the results of other prediction system of similar complexity, which emphasizes the modulation of the skill on decadal timescales. It is then demonstrated that the skill is critically dependant on the energy distribution on the baroclinic mode, higher-order mode contributions being favored at some period and not at others. Linear Green's function are used to assimilate satellite observations (SST and wind) and derive the optimized set of parameters that determines the vertical structure in the model for a particular period of time. The scheme is first tested for the period prior to the development of the 1997 El Ni