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WIND STRESS AND SURFACE ROUGHNESS AT AIR-SEA INTERFACE
HYDRONAUTICS INC LAUREL MD
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Based on the compiled data of thirty independent observations, the report presents the wind-stress coefficient, the surface roughness and the boundary layer flow regime at the air-sea interface under various wind conditions. Both the wind-stress coefficient and the surface roughness are found to increase with the wind velocity when U10 is less than 15 msec and reach a saturated value for U10 greater than 15 msec. Based on the oceanic wave observations, it states that this discontinuity at U10 15 msec is due to an increase in the wind velocity measured at the significant wave amplitude above the mean water level beyond the average wave phase velocity. This finding provides a well-defined separation for the often quoted terms light and strong winds, and also explains the existence of the so-called critical wind velocity. It also shows that the surface roughness is governed by the amplitude of the short gravity waves rather than the mean square surface slope. Charnocks relationship is shown to be applicable to most of the data and Charnocks proportionality constant is determined. Finally, two approximate formulae for the wind-stress coefficient, one for light wind and the other for strong wind are suggested.
APPROVED FOR PUBLIC RELEASE