SEA-LEVEL FROM TEMPERATURE PROFILES IN THE TROPICAL PACIFIC-OCEAN, 1975-1982

We investigate how well the 1975-1992 sea level interannual variabilit y in the tropical Pacific is captured by dynamic height from temperatu re profiles. For each temperature profile, a surface dynamic height re lative to 300 m is estimated, assuming a constant temperature-salinity relationship. After multiplication by a latitudinally varying factor and the removal of a seasonal cycle, the dynamic height deviations fit the tide gauge sea level variability to within the sampling errors, e xcept at a few sites near the equator west of the date line, where sur face salinity variability is large. The dynamic height data are assimi lated into a wind-forced linear numerical model of the sea level in th e tropical Pacific, applying a Kalman filter in a space of reduced dim ension. A limited number of empirical orthogonal functions of the unfi ltered run (1975-1992) define the reduced space, into which the Kalman Filter covariance evolution calculation is done [Cane et at, 1996]. E xperiments indicate that results are better with 32 functions than wit h a smaller number but are not improved by retaining more functions. T he resulting analyzed fields of sea level are compared to withheld dyn amic height estimates from moorings, sea level data from tide gauges, and sea level analyses made with the same Kalman filter formalism appl ied to tide gauge measurements. The comparisons to observations sugges t that the temperature profiles were usually sufficient to constrain t he monthly analyzed fields to be close to the observed sea level with errors typically less than 3 cm neat the equator. The comparison to ti de gauge sea level reveals that this analysis is often more accurate t han the analysis of tide gauge sea level data with which it shares man y characteristics. Near the equator west of the date line, salinity va riations ate large and their neglect in estimating dynamic height has a negative impact on the analysis. The analyzed signal is underestimat ed in the southwest Pacific and at more than 20 degrees off the equato r. The reanalysis of the temperature data done with a primitive equati on model at the National Meteorological Center (NMC) [Ji et at, 1995; Enfield and Harris, 1995] does not share this problem. On the other ha nd, NMC reanalysis (RA4) departs more from the observations elsewhere, although more data were included than in our analysis.