WIND-FORCED VARIATIONS IN SEA-SURFACE HEIGHT IN THE NORTHEAST PACIFIC-OCEAN

Sea surface height (SSH) anomalies from the Geosat altimeter for the n ortheast Pacific Ocean were analyzed to determine their annual and int erannual fluctuations over a 2.5-year period. The interannual anomalie s suggested large-scale changes in the intensity of the California and Alaska currents, with a weak California Current for the first year (1 986-1987), which strengthened during the second year, partly by a dive rsion of flow from the Alaskan gyre into the California Current and pa rtly by a decrease in SSH along the coast. In the California Current b etween about 36-degrees and 46-degrees-N, the annual fluctuations in S SH showed westward phase propagation. These observations were modeled using a linearized potential vorticity equation with one active layer, forced by realistic wind stress curl, which resembled a standing wave . The annual fluctuations in SSH were produced primarily by Ekman pump ing, because Rossby waves are coastally trapped poleward of about 37-d egrees-N. The predicted response had excellent phase agreement with th e data but underestimated the magnitude of the observations by nearly a factor of 2. This simple analysis suggests that the California Curre nt core propagates offshore during the year not due to Rossby waves bu t rather due to a combination of spatial variations in the wind stress curl field and the meridional variation of the Coriolis parameter. So me qualifications to these conclusions are discussed along with an exa mination of errors in both SSH and wind stress.