Impact of sea level assimilation on salinity variability in the western equatorial Pacific

In the primitive equation model for the tropical Pacific at the National Ce nters for Environmental Prediction, subsurface temperature observations are assimilated. The addition of TOPEX/Poseidon sea level observations to the NCEP assimilation scheme has resulted in large differences in sea level dur ing 1996. These differences are suggested to be related to salinity variabi lity. A bivariate assimilation scheme is presented that corrects both temperature and salinity. The method is tested with synthetic data in an identical tri plets experiment, in which a westerly wind burst is simulated. In this expe riment, the correction of salinity improves the density simulation and atte nuates errors in salinity. A four-year assimilation experiment with real da ta is performed to test the system's performance for 1993-96. In this exper iment. the assimilation of TOPEX/Poseidon observations improves dynamic hei ght simulation without degrading the temperature held. This application of altimetry improves the mean salinity in the western equatorial Pacific and leads to a more pronounced salinity variability in the ocean model.