Strong Coupling of Wind and Wind Waves
Observational evidence is presented that the wind and the wind waves are in strong coupling in their fluctuations. In this strong coupling the wave breaking should play an essential role. A 4.5-hour time series of wind profile and wind-wave statistics, obtained at an oceanographic tower station under a winter monsoon wind, were reanalyzed. The main part of the equilibrium range of wind-wave spectra always follows the σ=4-slope, though the energy level fluctuates following the fluctuating wind speed. The time scale of the adjustment of the energy level to the fluctuation of the wind is of the order of ten minutes, and within this time scale over- and under-saturation of the energy level occurs. During this time scale, there is significant energy transfer between the waves in the equilibrium range and those at the spectral peak, involving both upward and downward cascading of the wave energy. The variation of z0 directly reflects the degree of over- and under-saturation of the level of the equilibrium range.
KeywordsRoughness Length Wind Wave Wave Breaking Equilibrium Range Fluctuate Wind Speed
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