Parameterization of Sea Surface Drag Coefficient for All Wind Regimes Using 11 Aircraft Eddy-Covariance Measurement Databases

The drag coefficient is essential for calculating the aerodynamic friction between air and sea. In this study, we regress a set of relationships between the drag coefficient and the wind speed for different wind ranges using an observational dataset that consists of 5941 estimates of the mean flow and fluxes from 11 aircraft turbulent measurements over the sea surface. Results show that: (1) the drag coefficient is a power function of wind speed over smooth sea surface when it is no greater than 4.5 ms⁻¹, and the drag coefficient decreases with the increase of wind speed; and (2) for rough sea surface, when the wind speed is greater than 4.5 ms⁻¹ and less than or equal to 10.5 ms⁻¹, the drag coefficient increases linearly with the increase of horizontal wind speed; when the wind speed is greater than 10.5 ms⁻¹ and less than or equal to 33.5 ms⁻¹, the drag coefficient changes parabolically with the increase of wind speed; when the wind speed is greater than 33.5 ms⁻¹, the drag coefficient is constant. Additionally, regressed from drag coefficient, the saturated wind speed threshold is 23 ms⁻¹. Parameterizations of turbulent heat transfer coefficient ($C_h$) and water vapor transfer coefficient ($C_e$) are also investigated.