Sea surface temperature budget in Indonesian seas: the role of vertical turbulent flux and its east–west variations

Abstract

Abstract The vertical turbulent flux, which comprises heat flux and vertical mixing, is one of key processes governing seawater temperature changes in the vertical direction. In this study, the influence of vertical turbulent flux on sea surface temperature (represented by a layer between the free-surface and approximately 20 m depth) in Indonesian seas was diagnosed from an eddy-permitting ocean modeling experiment result. The heat flux, as the sum of the net heat flux at the surface and penetrative shortwave radiation at the base of the surface layer, induced a net cooling tendency in both eastern and western Indonesia (represented by the Java Sea and Banda Sea, respectively). The cooling tendency due to the heat flux was opposed by the warming tendency induced by vertical mixing at the base of the surface layer, preventing excessive heat loss in the surface layer. An exception occurred during the Boreal Autumn in the Banda Sea, when the heat flux and vertical mixing resulted in warming and cooling tendencies, respectively. It was further found that the effect of vertical mixing on the surface layer heat budget was sensitive to the selection of the base layer depth, highlighting the mixing-related dynamic variation within the water column. In summary, this study provides additional insights into the near-surface dynamics that govern sea surface temperature seasonality in Indonesian Seas.