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摘要

HSSR suggested that, for global mapping of the air-sea momentum exchange using the inverse wave age, the parameter U_(10)/c_p should be used. Because the wave growth rate is determined mainly by the wind in the wave direction, the momentum flux varies as the angle between the wind and the waves varies; therefore, we have argued that U_(10) cosθ)/c_p is a better parameter to use. We have shown here that the main conclusions from HBS—(i) that the local wind and waves are often in a state of nonequilibrium with remotely generated swell generally present, (ii) that the waves are most strongly coupled to the local wind in the midlatitude storm tracks and (iii) that upward momentum transfer is most likely to occur in the tropical eastern ocean basins—are robust to the definition chosen for the inverse wave age. Finally we note that, as discussed in section 3, a more precise climatology would require calculation of the exchange of momentum between the wind and waves by integrating over the entire wave spectrum. It might be that separating the wave spectrum into two parts, one characterizing the swell and another characterizing the wind sea, as suggested by HSSR, provides a useful simplification. However, the effectiveness of this simplification remains to be demonstrated. It seems likely that more precise calculations of the momentum exchange will enable better interpretation of the specific case studies, such as those presented in HSSR.