OBSERVED SEA-SURFACE HEIGHT AND MODELED DYNAMIC HEIGHT ANOMALY DEPARTURES IN THE TROPICAL PACIFIC-OCEAN - 1986-1989

Observations of sea surface height departure (SSH') from November 1986 through September 1989 in the tropical Pacific from the improved (T2) GEOSAT data set (Cheney et al., 1991) are compared with monthly mean dynamic height anomaly departure (Delta D') from the ''second reanalys is'' using the NOAA ocean analysis system (Ji et al., 1994, 1995). For comparisons, Delta D' is calculated by removing north-south tilt and bias as in SSH orbit error removal, giving standard deviation fields s igma(SSH') and sigma(Delta D') that quantitatively reproduce variabili ty of the North Equatorial Current (NEC)/North Equatorial Countercurre nt (NECC)/South Equatorial Current (SEC) system between El Nino and no n-El Nino years. Hovmoller diagrams of SSH' and Delta D' variability a t 110 degrees W, 140 degrees W, 170 degrees W, and 165 degrees E betwe en 20 degrees S and 20 degrees N, and along the equator from 120 degre es E to 80 degrees W, display the amplitude and phase of the 1986-1987 El Nino-Southern Oscillation (ENSO) event as distinguished from the y ears following, with the NECC significantly weakened in 1987 as compar ed to 1988. Cross-correlations (r) between Delta D' and SSH' are highe st near the Equator in the vicinity of the TOGA-TAO (Hayes et al., 199 1; McPhaden, 1993) in situ mooring arrays, with values above r = 0.7 i n much of the region +/- 7 degrees of the Equator across about half of the Pacific basin. Differences between Delta D' and SSH' are typicall y less than +/- 5 cm RMS in this same equatorial band, but there are t wo regions of differences in excess of +/- 15 cm RMS: off Central Amer ica and east of New Guinea. The reason for these large RMS differences is uncertain, but it is inferred from Lagrangian buoy data that inten se eddy activity is unresolved in the model as compared to GEOSAT. For the 35 monthly realizations, the ensemble cross correlation r = 0.5 h as +/- 7 cm RMS within +/- 15 degrees of the Equator, and peaks in 198 8 with decay towards the end of the GEOSAT Exact Repeat Mission (ERM) in September 1989. Seasonally, both SSH' and Delta D' show that the bo real winter (DJF) of 1987 is dominated by the ENSO-related sea level m aximum in mid-basin, which is absent in the following two winters; spr ing (MAM) and summer (JJA) of all three years have little resemblance to each other, with 1987 and 1989 being more similar than 1988; autumn (SON) of 1988 shows a well developed NECC across much of the eastern Pacific centered at similar to 7 degrees N. The ERM altimeter data and the model calculations of the annual cycle both show east-west height amplitude maxima along 5 degrees N and 10 degrees N that explain more than 50% of the variance for a substantial portion of the central Pac ific Ocean. Concurrent drogued buoy tracks show more eddies centered a long similar to 5 degrees N in the eastern Pacific in 1988 as compared to 1987 or 1989, but Delta D' is unable to resolve these features.