资源环境科技发展态势分析平台

Buoy observations from a 1999 Gulf of Mexico field program (GOM99) are used to investigate the relationships among friction velocity u_*, wind speed U, and amount of swell present. A U–u_*sea parameterization is developed for the case of pure wind sea (denoted by u_*sea), which is linear in U over the range of available winds (2–16 m s⁻¹). The curve shows no sign of an inflection point near 7–8 m s⁻¹ as suggested in a 2012 paper by Andreas et al. on the basis of a transition from smooth to rough flow. When observations containing more than minimal swell energy are included, a different U–u_* equation for U < 8 m s⁻¹ is found, which would intersect the pure wind-sea curve about 7–8 m s⁻¹. These two relationships yield a bilinear curve similar to Andreas et al. with an apparent inflection near 7–8 m s⁻¹. The absence of the inflection in the GOM99 experiment pure wind-sea curve and the similarity of the GOM99 swell-dominated low wind speed to Andreas et al.’s low wind speed relationship suggest that the inflection may be due to the effect of swell and not a flow transition. Swell heights in the range of only 25–50 cm may be sufficient to impact stress at low wind speeds.