Convective Transport Theory for Surface Fluxes Tested over the Western Pacific Warm Pool

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Abstract
Turbulent flux measurements from five flights of the National Center for Atmospheric Research Electra aircraft during the Tropical Oceans and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) are used to test convective transport theory (CTT) for a marine boundary layer. Flights during light to moderate winds and under the clearest sky conditions available were chosen. Fluxes of heat, moisture, and momentum were observed by the eddy-correlation method. Mean kinematic values for the observed sensible and latent heat fluxes and momentum flux were 0.0061 K m s−1, 0.0313 g kg−1 m s−1, and 0.0195 m2 s−2, respectively. For the range of mixed-layer wind speeds (0.8–8.4 m s−1) studied here, the version of CTT that includes the mixed effects of buoyant and shear-driven transport give a better fit to the observations than either the COARE bulk algorithm or the pure free-convection version of CTT. This is to be expected because both of those latter parameterizations were designed for light winds (−1 approximately). The CTT empirical coefficients listed in Table 3 exhibited slight sensitivity to the COARE light flux conditions, compared to their previous estimates during larger fluxes over land. For example, COARE heat fluxes were roughly 10 times smaller than previous land-based flux measurements used to calculate CTT coefficients, but the corresponding empirical mixed-layer transport coefficients were only 3% smaller. COARE momentum fluxes were also roughly 10 times smaller, but the CTT coefficients were about four times smaller. The greater variation in momentum coefficient may be due, in part, to insufficient flight-leg length used to compute momentum fluxes, to uncertainties in the effects of the ocean surface current and waves, or perhaps to roughness differences.

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