Thermodynamic coupling and predictability of tropical sea surface temperature

Air-sea coupling involves the exchange of both momentum and heat between the atmosphere and the ocean. Dynamic coupling, which relates to the momentum exchange, is believed to play the dominant role in the tropics, especially in phenomena such as the El Nino-Southern Oscillation in the tropical Pacific. However, thermodynamic heat exchange between the atmosphere and the ocean also plays a significant role in tropical air-sea coupling. This is,especially true in the tropical Atlantic, where dynamic coupling may be of secondary importance. In this study, we analyze the role of thermodynamic air-sea coupling using an atmospheric general circulation model coupled to a slab ocean model. Predictability experiments using observed sea surface temperature (SST) initial conditions show that thermodynamic coupling plays a significant role in enhancing the persistence of SST anomalies, both in the tropical Pacific and in the tropical Atlantic. Thermodynamic coupling is also sufficient to provide fairly accurate forecasts of tropical Atlantic SST in the boreal spring that are significantly better than persistence forecasts.