SEA-LEVEL VARIABILITY IN THE EASTERN TROPICAL PACIFIC AS OBSERVED BY TOPEX AND TROPICAL OCEAN-GLOBAL ATMOSPHERE TROPICAL ATMOSPHERE-OCEAN 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 5 degrees N to 7 degrees N and extends from 165 degrees W to 110 degrees W, and the other band is centered at 10 degrees N to 12 degrees N and extends from 120 degrees W to the coast of Central America. The correspondence between the two independent observation data sets at 5 degrees N is excellent with correlations of about 90%. The variability at 5 degrees-7 degrees N 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 160 degrees-140 degrees W, 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 11 degrees N 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 11 degrees N has very little overlap in time with the variability at 5 degrees N.