Sea level variability in the eastern tropical Pacific as observed by TOPEX and Tropical OceanGlobal Atmosphere Tropical AtmosphereOcean Experiment

Sea surface height measurements from the TOPEX altimeter and dynamic height from Tropical Ocean-Global Atmosphere Tropical Atmosphere-Ocean (TOGA TAO) moorings are used to explore sea level variability in the northeastern tropical Pacific Ocean. After the annual harmonic is removed, there are two distinct bands of variability: one band is centered at 5øN to 7øN and extends from 165øW to 110øW, and the other band is centered at 10øN to 12øN and extends from 120øW to the coast of Central America. The correspondence between the two independent observation data sets at 5øN is excellent with correlations of about 90%. The variability at 5ø-7øN is identified as instability waves formed just south of the North Equatorial Countercurrent during the months of July through March. Wave amplitudes are largest in the range of longitudes 160ø-140øW, where they can exceed 10 cm. The waves disappear when the equatorial current system weakens, during the months of March through May. The variability at 11øN in 1993 has the form of anticyclonic eddies. These eddies propagate westward at a speed of about 17 cm s-1 consistent with the dispersion characteristics of free Rossby waves. The eddies are shown to have their origin near the coast of Central America during northern fall and winter. Their formation seems to result from intense wind bursts across the Gulfs of Tehuantepec and Papagayo which generate strong anticyclonic ocean eddies. The disappearance of the eddies in the summer of 1993 coincides with the seasonal intensification of equatorial currents. Thus the variability at 11øN has very little overlap in time with the variability at 5øN.