FY 1990

Variability in the eastern equatorial Pacific Ocean during 1986–1988

McPhaden, M.J., and S.P. Hayes

J. Geophys. Res., 95(C8), 13,195–13,208, doi: 10.1029/JC095iC08p13195 (1990)

We examine variability in the eastern equatorial Pacific during 1986–1988 using conductivity-temperature-depth data, velocity and temperature data from equatorial moorings between 110°W and 140°W, and wind data from a basin scale zonal array of islands and moorings between 110°W and 165°E. The period studied coincides with the El Niño/Southern Oscillation (ENSO) event of 1986–1987 and a subsequent cold event in 1988. Weak warm sea surface temperature anomalies first appeared in the eastern equatorial Pacific in mid-1986 and increased to >1°C in September-November 1986 in association with a 30 cm s^-1 weakening of the South Equatorial Current and a 20- to 40-m depression of the thermocline. These warm anomalies lasted until early 1988, after which a large-scale shoaling of the thermocline led to sea surface temperatures more than 3°C colder than climatology. Year-to-year fluctuations in the eastern Pacific were related primarily to zonal wind variations in the central and western Pacific. Westerly wind stress anomalies of 0.02–0.05 N m^-2 were observed between 140°W and 165°E from the latter half of 1986 until the end of 1987; these were replaced by easterly wind anomalies of similar magnitude between 157°W and 165°E in 1988. Energetic intraseasonal fluctuations with periods of 2–3 months were also prominent in zonal current, temperature, and dynamic height time series. These fluctuations propagate eastward at approximately first baroclinic mode Kelvin wave phase speeds and are forced west of the date line by episodes of westerly winds. Extrema in several oceanic variables occurred in association with these waves, though their precise dynamical link to the ENSO cycle is unclear from our data. Sea surface temperature and thermocline depth anomalies at 0°, 110°W were less pronounced during the 1986–87 ENSO than during the 1982–83 ENSO; the Equatorial Undercurrent, though weaker than normal in early 1987, did not disappear as it did in early 1983.