Thermal structure of hot events and their possible role in maintaining the warm isothermal layer in the Western Pacific warm pool

Abstract

The short-lived events of high SST are called hot events (HEs) and can only be generated under the conditions of large daily heat gain due to strong solar radiation and weak wind. We investigated the thermal structure below HEs in the western equatorial Pacific by using in situ data obtained from TAO/TRITON buoys. We found that the occurrence of HEs can be identified by the typical vertical thermal structure within the isothermal layer. During the development stage of a HE, heat is accumulated in the surface layer due to strong solar radiation and weak wind, increasing temperature and creating strong stratification in the upper layer. During the decay stage, strong westerly winds induce current convergence which transports the heat from the upper layer to the deeper layer. Thus, temperature decreases at the surface and increases in the deeper layer. Furthermore, this mechanism indicates the important role of HEs in maintaining the warm isothermal layer in the western Pacific warm pool. The more HEs occur, the more heat in the surface layer gained from solar radiation is transported to the deeper layer. This process makes areas of frequent HE occurrences coincident with areas of warm pool. Since surface winds control the heat accumulation and heat transport in the isothermal layer by influencing current divergence and latent heat flux, surface winds become the key factor for the occurrence of HEs and the formation of the thermal structure in the Pacific warm pool.