On the variability of the Charnock constant and the functional dependence of the drag coefficient on wind speed: Part II-Observations

• Published in: Ocean dynamics Vol. 64; no. 7; pp. 969 - 974
• Main Authors: Bye, John A. T., Wolff, Jörg-Olaf, Lettmann, Karsten A.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2014; Springer Nature B.V
• Subjects: Atmospheric Sciences; Boundary layers; Earth and Environmental Science; Earth Sciences; Fluid- and Aerodynamics; Geophysics/Geodesy; Interfaces; Monitoring/Environmental Analysis; Oceanic analysis; Oceanography; Velocity; Wave power; Wind; Wind speed; Air-sea momentum exchange; Inertial coupling; Charnock constant
• ISSN: 1616-7341; 1616-7228
• DOI: 10.1007/s10236-014-0735-4

An analytical expression for the 10 m drag law in terms of the 10 m wind speed at the maximum in the 10 m drag coefficient, and the Charnock constant is presented, which is based on the results obtained from a model of the air-sea interface derived in Bye et al. ( 2010 ). This drag law is almost independent of wave age and over the mid-range of wind speeds (5−17 ms −1 ) is very similar to the drag law based on observed data presented in Foreman and Emeis ( 2010 ). The linear fit of the observed data which incorporates a constant into the traditional definition of the drag coefficient is shown to arise to first-order as a consequence of the momentum exchange across the air-sea boundary layer brought about by wave generation and spray production which are explicitly represented in the theoretical model.