High-frequency components of ocean waves and their relation to the aerodynamic roughness

Abstract

Ocean waves of high frequency (from about 10 to 200 rad/sec) were observed by means of a thin capacitance-type wave gauge. The representative rms height, hp, of the sea-surface irregularities associated with the high-frequency waves is less than the thickness of the laminar sub-layer under light winds, but increases with wind speed and exceeds the thickness of the laminar sub-layer when the wind speed exceeds 3 m/sec. The values of the roughness Reynolds number, which delineate the upper limit of the smooth surface regime and the lower limit of the fully rough regime are found to be about 6 and 67, respectively. Power spectra vs frequency n from the present field observations indicate a significant departure from the n SUP-5 saturation relation of Phillips at frequencies in the range 10-250 rad/sec. Moreover, the departure increases with wind speed indicating that a saturation limit does not seem to exsit for the capillary range