A linearized model with two vertical modes has been developed to understand observed characteristics of monthly variability in the Equatorial Pacific from TOPEX/POSEIDON measurements of Sea. Surface Height. (SSH). The 2-mode model is obtained from an equatorial beta plane model that has been linearized about a geostrophically balanced mean flow with the state variables projected onto the first 2 baroclinic vertical eigenfunctions. Because in situ measurements of currents in the equatorial Pacific are not available with adequate spatial and temporal resolution, the mean current structure used in the 2-mode model was obtained from the Parallel Ocean Climate Model (POCM). POCM was chosen because the monthly variability in the model SSH fields closely resembles that of TOPEX/POSEIDON in dispersion characteristics and cross-equatorial structure. The sensitivity of the 2-mode projection model to the mean equatorial currents is examined by individually increasing and decreasing the various components of the equatorial current system. The eigenvectors and cigenvalues from this range of current structures are able to reproduce many of the characteristics (phase, amplitude, period, wavenumber and ineridional structure) observed in TOPEX/POSEIDON and POCM. The most surprising result is that the latitudinal structure of the eigenvector amplitudes south of the equator depends only on the strength of the northern equatorial current system.
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