Influence of sea surface temperatures on air temperatures in the tropics

Abstract

Interannual variations of tropical tropospheric temperatures are closely related to sea surface temperature (SST) changes in the tropical eastern Pacific (TEP). This study investigated the physical mechanisms for such an air-sea interrelationship. SSTs and latent heat flux were analyzed to find the unique properties of their variations during El Nino. A Gill-type model was used to investigate how a local heat source communicates with the entire tropics. Radiative fluxes in the tropics were evaluated to search for the factors limiting air temperature increases when warm SSTs remain in the TEP. We found that interannual variabilities of SST and latent heat flux are dominated by the variations in the TEP region. The SST variations there have three unique properties that allow the ocean to influence the atmosphere effectively: large magnitude, long persistence, and spatial coherence. The Gill-type model shows that a local heat source can warm the entire tropical troposphere when the heat source is near the equator. Released latent heat in the heat source region and forced adiabatic subsidence elsewhere in the tropics warm the atmosphere. As a result, a local heat source warms the entire tropical strip. The forced subsidence depresses clouds, allowing more infrared radiation to leave the atmosphere and preventing further atmospheric warming when warm SSTs remain in the TEP. This finding is verified by reanalysis data from the National Centers for Environmental Prediction.