which will follow. 



H, U. Sverdrup and W. H. Munk compute the work done by wind 

 to waves ("significant waves") by normal pressures and tangential 

 stresses separately. But there are some uncertainties in their as- 

 sumptions and the forthcoming calculations seem inconsistent with 

 the degree of accuracy which is required in the energy balance, when 

 considering the growth of ocean wave motion under the action of wind. 

 For estimating the tangential stresses and the work done by this 

 wind force component on the wave motion, Sverdrup-Munk had to assume 

 a "resistance coefficient," y > which was constant at all wind velo- 

 cities, although they mentioned that this would not be true in the 



case where the wind velocity differs too much from the wave velocity. 



2 

 Under these conditions the value of y would probably be greater. 



In the present state of our Icnowledge we have to take into account 



2 

 the fact that there is really substantial evidence that y varies 



with the wind velocity ([8], [13]) and with the stage of wave de- 



2 

 velopment. The assumption of a constant y -value is only a rough 



approximation. A similarly insufficient approximation is represented 



by the assumption that the tangential stress (drag) over the wave 



profile is constant at different parts of the wave even if we assume 



2 

 a constant resistance-(drag-) coefficient y over the wave. 



Besides these important questions of energy transfer from wind 

 to waves, which in the meantime were also discussed by Schaaf and 

 Sauer [15] with respect to the tangential transfer, it must be mention- 

 ed that Sverdrup-Munk do not include the dissipated energy in the 

 energy budget of growing and f Tilly risen waves. After mentioning 

 the idea, they disregard turbulent friction, arguing that txirbulent 



41 



