Warm Pool SST Variability in Relation to the Surface Energy Balance

Abstract

The warm tropical oceans underlie the most convective regions on earth and are a critical component of the earth’s climate, yet there are differing opinions on the processes that control warm pool SST. The Indo–Pacific warm pool is characterized by large-scale variations in SST approaching 30°C on intraseasonal timescales. In this study, surface heat flux anomalies associated with composite warm episodes over three spatial scales in both the Pacific and Indian Ocean basins are examined. The current study benefits from the recently available National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset that enables the examination of variability in surface evaporation with moderate confidence. Solar flux estimates from the reanalysis are somewhat less reliable than evaporation estimates, however, and two techniques that infer surface shortwave radiation from satellite retrievals of cloud properties are considered. Error in all measurements is quantified. Both shortwave and evaporative flux variability play significant roles in modifying the temperature of the warm pool, though the relative importance of individual flux anomalies depends on SST tendency and geographical location. There also exist differences in the relative heating roles of the flux anomalies among episodes within a fixed location, though in instances the resolved differences are less than likely flux estimation error. Differences also exist between the ocean basins. A more pronounced annual cycle exists in the eastern Indian Ocean, and SST there is less sensitive to surface thermal forcing. Finally, the analysis offers evidence that SST is not regulated by a simple atmospheric thermodynamic response to the surface. Instead, the relationship between warm pool variability and large-scale dynamical features of the Tropics (e.g., intraseasonal oscillation and the seasonal monsoon) is demonstrated. The conclusions are shown to be robust to spatial scale and are consistent with a recent analysis of Tropical Oceans and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment observations.