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 Nino Southern Oscillation episode was observed in the tropical Pacific Ocean during 1982–831,2. Models suggest that oceanic circulation has an important role in the formation of such anomalies1,3,4 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 Pacific5,6. 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.