Variation of the western equatorial Pacific Ocean, 1986–1988

Abstract

Twenty‐one oceanographic sections made along 165°E during 1984–1988 provide a unique picture of the 1986–1987 El Niño and the subsequent La Niña in the western equatorial Pacific. The mean of six cruises from January 1984 through June 1986, a relatively normal period, provides a reference with which the later sections are compared. The net warm water transport across 165°E within 10° of the equator was small in this mean reference section: 7 × 106 m3 s−1 to the east. In December 1986, strong westerly winds at and to the west of 165°E increased the net eastward transport of warm water to 88 × 106 m3 s−1, and the 1986–1987 El Niño was underway. During the following 2 years the net transport varied widely and rapidly; the extrema were 56 × 106 m3 s−1 to the east and 58 × 106 m3 s−1 to the west. Changes in the stratification along 165°E were correspondingly large, reflecting both the geostrophic balance of the strong zonal currents and the changes in the volume of warm water in the western equatorial Pacific. The anomaly of warm water volume corresponded closely to the time integral of the warm water transport across 165°E. Local wind forcing and remotely forced waves were both important causes of the transport fluctuations. Winds, precipitation, and currents were all important factors determining the depth of the surface mixed layer and the thickness of the underlying barrier layer. The way in which these factors interact is a strong function of latitude.