Evaluation of Drag Coefficient over the Ocean Surface Based on Wave-Field Conditions

Abstract

Estimations of the drag coefficient over the ocean surface were made by means of the eddy correlation and inertial dissipation methods. The variation of the drag coefficient with the wave age and swell conditions was investigated by using data set, showing good agreements between both methods. On the basis of directional wave spectra, we classified swell conditions into five groups, i.e., Pure windsea, Swell-dominated sea, Cross, Following and Counter swells. The present data show that the drag coefficient increases obviously with decreasing the wave age under same wind speeds, whereas the dependence of the drag coefficient on the swell conditions is unclear in comparison with that on the wave age. This suggests that the drag coefficient depends strongly on microstructures of the wave field, not lower-frequency structures for swells.