VARIABILITY IN THE CENTRAL EQUATORIAL PACIFIC, 1985-1989

We describe variability in the equatorial Pacific Ocean near 160 degrees W during the 5-year period 1985-1989, encompassing ''normal'', El Nino, and La Nina conditions. This description is based on conductivity-temperature-depth and acoustic Doppler current profiler data acquired during five cruises between 21 degrees N and 4 degrees S and on dynamic-height time series from an array based mainly on the Line Islands. At Jarvis Island, near the equator, the time series of dynamic height and near-surface temperature go back to 1981 and show the 1986-1987 El Nino anomalies starting later in the year and having longer duration than those of the 1982-1983 El Nino. Dynamic-height anomaly was less strong for the 1986-1987 event, but the near-surface temperature anomaly was of similar magnitude for the two El Ninos. The Jarvis near-surface temperature drop from 1986-1987 El Nino maximum to 1988-1989 La Nina minimum was 8 degrees C. Empirical orthogonal function analysis of the time series shows that interannual and interseasonal variability in dynamic height was dominated by a mode with meridional form similar to a first-vertical-mode Kelvin wave, while intraseasonal variability had a primary mode with a single peak at 6 degrees N and a secondary mode with peak at 6 degrees N and trough at 2 degrees N. While the equatorial thermocline deepened to the east and shoaled to the west during the 1986-1987 El Nino, at 160 degrees W it did not change depth during either this El Nino or the subsequent La Nina. Nevertheless, just before El Nino and just after La Nina, the thermocline was observed to be about 50 m deeper than at other times. The South Equatorial Current and North Equatorial Countercurrent had markedly reduced (increased) transports during this El Nino (La Nina). However, the Northern Tsuchiya Jet strengthened during El Nino and weakened during La Nina.