A numerical study on the coupling between sea surface temperature and surface evaporation

Abstract

The feedback between sea surface temperature (SST) and surface evaporation is an important issue in the study of climate change. To understand this feedback and its interaction with surface wind in the tropical Pacific Ocean (30°N – 30°S), and in particular over the warm pool region, a dynamic tropical atmospheric circulation model is used. The model consists of a two‐layer free troposphere and a well‐mixed boundary layer. It involves active interactions between the boundary layer flow, forced by an SST gradient, and the free atmospheric flow, forced by SST. Various SST fields (representing climatology, El Niño, and La Niña conditions) are used to drive the model. It is found that the binned averages of evaporation and wind speed increase with SST for up to about 300–301 K. From that point on they decrease with SST. In addition, negative SST anomalies correspond to excess latent heat flux and wind speed. These results are in agreement with relevant observations. To understand the thermodynamic versus dynamic effects of SST on surface evaporation, in one of the experiments we impose a sudden positive SST perturbation on the climatological SST field during the model integration. It is shown that while surface evaporation is initially enhanced in response to the SST change, as the atmospheric circulation gradually “feels” the SST perturbation, its dynamic effect through the circulation change becomes more apparent over the SST perturbation region. Overall, the results of our study show that in the low SST regime the behavior of evaporation is dictated by thermodynamics, whereas in the high SST regime it is dictated by atmospheric dynamic considerations.