Development of a New Technique to Evaluate Surface Winds from Routine Buoy Observation of Ocean Waves

本研究的目的是探索一种利用简单浮标系统从日常海浪观测中评估空气摩擦速度u_*（海面风应力的量度）、10米风速u_ <10>和风向的新技术。从初步研究中发现，从波浪资料中估计u_*，利用波浪谱高频部分的平衡范围是最有希望的，在大风海况下，利用3/2-幂律结合有效波高和有效波周期也是可行的。从U_ *估计U_<10>时，由于风应力取决于风海条件，因此有必要建立最合适的阻力系数或海面粗糙度参数z_0公式，其中应适当考虑风海条件参数。因此，获得z_<10>的最相关公式是第一优先事项。当风浪在近乎稳定的风力条件下发展时，z_0的平均变化量为Toba-Koga公式z_0 sigma_p/u_* = gamma，其中gamma = 0.015。然而，由于几分钟至一小时时间尺度上的风的波动，数据点在无量纲粗糙度参数—波龄图上显示出明显的波动，其方向与平均变化方向相反。z_0的变化直接反映了风浪谱高频范围的过饱和或欠饱和程度。实际使用的表示上述三角形面积的折衷公式是gz_0/u_*^2 = 0.020 (sigma_pu_*/g) ^<-0.5>。

The objective of this study is to pursue a new technique to evaluate the air friction velocity u_* which is a measure of the sea-surface wind stress, the 10-m wind speed U_<10> and the wind direction from routine observation of ocean waves by using a simple buoy system.From preliminary investigations, it has been found that for the estimation of u_* from wave data, the use of the equilibrium range of the high frequency part of the wave spectra is most promising, and that use of the 3/2-power law together with the significant wave height and period is also available for high wind sea conditions. For the estimation of U_<10> from u_* , it is necessary to establish the most pertinent formula for the drag coefficient or the sea-surface roughness parameter z_0 in which parameters of wind sea conditions are properly included, since the wind stress depends on conditions of the wind sea. Consequently, the first priority has been placed on obtaining the most pertinent formulas for z_<10>.In the conditions when wind waves are developing under nearly steady wind conditions, the averaged variation of z_0 is that given by the Toba-Koga formula z_0 sigma_p/u_* = gamma with gamma = 0.015. However, as a result of the fluctuation of wind of the time scales of several minutes to an hour, data points show a conspicuous fluctuation on the nondimensional roughness parameter -- wave age diagram, in the direction transverse to the averaged variation. The variation of z_0 directly reflects the degree of over - or under-saturation of the high frequency range of the wind-wave spectra. A compromise formula for practical uses to represent the above triangle area is gz_0/u_*^2 = 0.020 (sigma_pu_*/g) ^<-0.5>.