The North Equatorial Countercurrent and heat storage in the western Pacific Ocean during 1982–83

Abstract

A sequence of extreme climate anomalies known as an El Niño Southern Oscillation episode was observed in the tropical Pacific Ocean during 1982–83^1,2. Models suggest that oceanic circulation has an important role in the formation of such anomalies^1,3,4 by altering the pattern of sea-surface temperature through advection. The baroclinic structure of the upper 500 m of the ocean has been monitored routinely in the western Pacific since 1979, providing indirect current measurements by the geostrophic method. These observations, reported here, show large changes in the near-equatorial currents during 1982–83 which are consistent with currents observed in the central and eastern Pacific^5,6. In particular, the North Equatorial Countercurrent (NECC) flowed with 25–50% increased strength during the early phase, then weakened almost to zero flow. The West Pacific heat pool cooled by more than 1 °C. Observed changes in circulation were large enough to alter surface heat storage by advection, although other potentially important processes may not be negligible.