Climate and the tropical oceans

An attempt is made to determine the role of the ocean in establishing the m ean tropical climate and its sensitivity to radiative perturbations. A simp le two-box energy balance model is developed that includes ocean heat trans ports as an interactive component of the tropical climate system. It is fou nd that changes in the zonal mean ocean heat transport can have a considera ble affect on the mean tropical sea surface temperature (SST) through their effect on the properties of subtropical marine stratus clouds or on the wa ter vapor greenhouse effect of the tropical atmosphere. The way that the tr opical climate adjusts to changes in the ocean heat transport is primarily through the atmospheric heat transport, without changing the net top of the atmosphere radiative balance. Thus, the total amount of low-latitude polew ard heat transport is invariant with respect to changes in ocean circulatio n in this model. These results are compared with analogous experiments with general circulation models. Doubled CO2 experiments are performed with different values of ocean heat t ransport. It is found that the sensitivity of the mean tropical SST to doub led CO2 depends on the strength of the ocean heat transport due to feedback s between the ocean and subtropical marine stratus clouds and the water vap or greenhouse effect, In this model, the results are the same whether the o cean heat transports are determined interactively or are fixed, Some recent studies have suggested that an increased meridional overturning in the ocean due to changes in the zonally asymmetric circulation can redu ce the sensitivity of the tropical climate to increased CO2. It is found th at, in equilibrium, this is not that case, but rather an increase in ocean heat transport, which involves increased equatorial upwelling, actually war ms the tropical climate.