AN EXAMINATION OF THE NORTH PACIFIC-OCEAN IN THE SPECTRAL-DOMAIN USING GEOSAT ALTIMETER DATA AND A NUMERICAL OCEAN MODEL

The sea surface height (SSH) variations of the North Pacific ocean and the Kuroshio Extension region, in particular, are examined by frequen cy and wavenumber decompositions of a 1/8 degrees, six-layer primitive equation Pacific Ocean model and of the Geosat Exact Repeat Mission ( ERM) data. Both data sets exhibit peaks in variability at 1 and 2 cycl es per year over much of the Kuroshio Extension region. This study is restricted to these two frequencies. Annual variations of equatorial c urrents in both data sets are similar in both space and time, with the variations in the South Equatorial Current appearing as annual westwa rd propagations. Annual variations in the strength of the Kuroshio Ext ension are manifested mainly through changes in the strength of the re circulation gyres on the southern side of the current. Annual transpor t maxima for the Kuroshio Extension occur around late October for both the model and Geosat. Large-scale variations (length scales greater t han 1000 km) of the model and Geosat have comparable amplitudes. The m ain differences between the model SSH and the Geosat ERM data occur ov er regions where seasonal steric variations are significant (from 20 d egrees N to 30 degrees N). Wavenumber spectra over the Kuroshio Extens ion region reveal similar dynamics in both data sets. Much of the ener gy in wavenumber spectra appears as westward propagating SSH anomalies near the theoretical Rossby wave dispersion relations. As the Rossby wave dispersion relation changes with latitude (shifting to shorter wa velengths with higher latitudes), the peaks in the wavenumber decompos itions follow. Thus the dynamics are generally consistent with quasige ostrophic dynamics in both the model and altimeter data. Wavelengths o f propagating SSH anomalies which have spectral peaks near the Rossby dispersion curve are longer in the Geosat and model than wavelengths i ndicated by theory. In the semiannual frequency below 35 degrees N, we stward propagation dominates over eastward propagation in both Geosat and the model. Most differences in the dynamics' of the model and Geos at occur at shorter length and timescales, with Geosat showing higher amplitudes at the shorter scales than the model.