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?1) were observed by means of a thin capacitance-type wave gage. 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 sublayer when the wind speed exceeds 3 m sec?1. The values of the roughness Reynolds number, hpu*/v, 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?5 saturation relation of Phillips at frequencies in the range 10?250 rad sec?1. Moreover, the departure increases with wind speed indicating that a saturation limit does not seem to exist for the capillary range.