GEOSAT AND ADVANCED VERY HIGH-RESOLUTION RADIOMETER OBSERVATIONS OF OCEANIC PLANETARY-WAVES ADJACENT TO THE HAWAIIAN-ISLANDS

Geosat observations of the central North Pacific Ocean show westward propagating mesoscale features with length scales (>500 km), time scales (105-155 days), and observed zonal phase speeds commensurate with those of nearly nondispersive baroclinic Rossby waves. Advanced very high resolution radiometer-derived sea surface temperatures observed during April 1988 showed a cusp-shaped pattern north of the Hawaiian Islands congruent with concurrent Geosat-derived sea level height anomalies. It is believed that the cusp-shaped pattern is the surface manifestation of a baroclinic Rossby wave. The observed wavelength of the cusp-shaped pattern was 560 km. It had an observed meridional extent (horizontal amplitude) of 200-300 km and an inferred zonal propagation speed of 0.052 m s-1. The westward propagating sea level height structure was observed to amplify as it approached 150-degrees-W reaching amplitudes of 0.06-0.08 m in the vicinity of the cusp-shaped feature. These waves are believed to be locally forced by the topography, either as the result of eastward flow over the submerged island ridge or as a result of baroclinic instability during periods of westward flow.