The surface-layer heat balance in the equatorial Pacific Ocean. Part I: Mean seasonal cycle

The surface-layer heat balance in the equatorial Pacific is examined in ord er to determine the processes responsible for the mean seasonal cycle of se a surface temperature (SST). Principal datasets include multiyear time seri es of surface winds, upper-ocean temperature, and velocity obtained from Tr opical Atmosphere Ocean (TAO) buoy array at four locations along the equato r in the western (165 degrees E), central (170 degrees W), and eastern (140 degrees and 110 degrees W) Pacific. A blended satellite-in situ SST produc t and climatological surface heat fluxes based on the Comprehensive Ocean-A tmosphere Data Set are also used. Changes in heat storage, horizontal heat advection. and hear fluxes at the surface are estimated directly from data; vertical fluxes of heat out of the base of the mixed layer are calculated as a residual. Results indicate that, of the terms that can be directly est imated, the net surface heat flux is generally the largest term in heat bal ance. Zonal heat advection is important at all locations and is generally a cooling term except in the eastern Pacific where the springtime reversal o f the South Equatorial Current leads to warming. Meridional heat advection is largest in the eastern Pacific where it is dominated by seasonally varyi ng tropical instability waves, which tend to warm the equator. The inferred vertical heat fluxes out the base of the mixed layer are comparable in mag nitude to the surface fluxes, except in the western Pacific where they are close to zero. From these inferred vertical fluxes, the authors estimate th e mean seasonal cycles in vertical eddy diffusivities and entrainment veloc ities, which, in the eastern Pacific, mimic the mean seasonal cycle of the surface winds, implications for modeling and predicting SST are addressed.