The Reorganized Turbulent Eddies Over Ocean Surface Waves

Abstract The drag coefficient C dN is a key parameter for accurately modeling atmospheric and upper ocean dynamics. However, the scattering of C dN has confused us for several decades. To better understand the mechanism behind the scattering of C dN , the turbulent theory, which considers the momentum flux carried by the eddies that have vertical size s z and horizontal size s x , is used. By adding the wave coherent (WC) stress to the turbulent kinetic energy (TKE) budget, this study models the turbulent eddies reorganized by the waves. The result shows that the reorganized turbulent eddies affect the dimensionless wind gradient, leading to different roughness lengths z 0 derived from different levels of wave‐affected wind speed and further resulting in the scatter of C dN . Two experiments from a fixed platform located in the South China Sea, one is a regular observation, and the other is outside the periphery of typhoons, demonstrate the above finding. The observation shows that ratios of z 0 derived from different levels of wind rely on the proportion of WC stress to total wind stress, and the horizontal integral length scales of eddies are stretched while the vertical sizes of eddies are shrunk. This study indicates that, to reduce the scatter of C dN , the wave‐affected wind should be considered.