Estimates of Turbulent Heat Flux and Heat Budget in the Upper Layer of the Western Equatorial Pacific Ocean

Abstract

Estimates of turbulent heat flux and heat budget in a time-dependent mixed layer and a surface slab layer are presented using the microstructure data measured during the cruise of the R/V Hakuho-maru at the fixed location of 0°, 156°E. Repeated profilings of the microstructure measurements with 3- or 6-hour intervals were carried out from November 12 to 27 in 1992.
The maximum turbulent heat flux at the bottom of the time-dependent mixed layer, which was determined as the depth with temperature difference of 0.1° from temperature at 5m layer, is 239.1W/m² downward. Mean heat flux at the bottom of the time-dependent mixed layer averaged over the analyzed period of eleven days, however, was only 31.4W/m² downward. Heat budget in the time-dependent mixed layer is greatly affected by advective heat flux, which reaches more than 50 percent of the net heat stored in the layer.
On the other hand, accumulated heat budget in the surface slab layer (surface layer) about 70m thick, defined as the layer between sea surface and 28°C isotherm, is also evaluated. Accumulated net heat input estimated from the surface meteorological data for eleven days is 80MJ/m². The maximum components of turbulent heat flux in the surface layer were 50W/m² upward and 250W/m² downward. However, the mean flux for eleven days averaged over the surface layer was only 9.1W/m². The total heat flow at the bottom of the surface layer for eleven days was 9.3MJ/m² downward. Therefore, if we neglect the advective heat, the residue of 70.7MJ/m² could contribute to a rise in temperature of the surface layer. The net heat input estimated from mean temperature change in the surface layer was 84MJ/m². The difference of 13.3MJ/m² could be attributed to advective heat, which corresponds to 16 percent of the surface net heat input.