An ocean dynamical thermostat

Abstract

The role of ocean dynamics in the regulation of tropical sea surface temperatures (SSTs) is investigated using the Zebiak-Cane coupled ocean-atmosphere model. The model is forced with a uniform heating, or cooling, varying between ±40 W m-2 into the ocean surface. A new climatological SST pattern is established for which the area-averaged temperature change is smaller in magnitude than the imposed forcing. The forcing is balanced almost equally by a change in the heat flux out of the ocean and by vertical advection of heat in the ocean through anomalous equatorial ocean upwelling. The generation of anomalous upwelling is identified here as a possible mechanism capable of regulating tropical SSTs. This ocean dynamical thermostat mechanism has a seasonally varying efficiency that causes amplification (weakening) of the seasonal cycle for the heating (cooling). The interannual variability also changes under the imposed forcing. These results suggest that the role of ocean dynamics should be included in any discussion of the regulation of the tropical climate.