Extended Abstract (124K)2A.2
Air-sea momentum flux at high winds
Tetsu Hara, University of Rhode Island, Narragansett, RI; and S. E. Belcher, I. Ginis, and I. J. Moon
The mean wind profile and the Charnock coefficient, or drag coefficient, over mature, growing, and complex seas are investigated. We develop a model of the wave boundary layer, which consists of the lowest part of the atmospheric boundary layer that is influenced by surface waves, based on the conservation of momentum and energy. Energy conservation is cast as a bulk constraint, integrated across the depth of the wave boundary layer, and the turbulence closure is achieved by parameterizing the dissipation rate of turbulent kinetic energy. Over mature seas, momentum conservation is accounted for using an analytical model of the equilibrium surface wave spectra. This allows us to obtain analytical expressions of the Charnock coefficient, and to examine the results in terms of key nondimensional parameters. In particular, simple expressions are obtained in the asymptotic limit that effects of viscosity and surface tension are small and majority of the stress is supported by wave drag. This analytical model allows us to identify the conditions necessary for the Charnock coefficient to be a true constant, an assumption routinely made in existing bulk parameterizations. The drag coefficient is also estimated over growing and complex seas, such as under hurricane wind forcing, by combining the numerical wave model. At higher wind forcing the effect of breaking waves on the drag coefficient is investigated in detail.
Session 2A, CBLAST II
Monday, 3 May 2004, 10:45 AM-12:00 PM, Le Jardin Room
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