the wind velocity. 



But, in fact roservations show that longer waves with (T > v 

 are generated in the wind region (see [23]). Probably these waves 

 have been generated under conditions not covered in the analysis 

 of Schaaf and Sauer. Special attention must be called again to the 

 fact that our knowledge of the actual distribution of "V . (and 'C ) , 

 or of the actual difference of wind velocity-water particle velocity 

 at the real ocean surface with its complicated wave pattern is too 

 meager, and it seems very difficult at present to estimate the effect 

 of normal stress components and tangential stress components separ- 

 ately. The actual rough sea surface may offer entirely different 

 conditions than are assumed in mathematical treatments of the prob- 

 lem, where only a simple sine-wave profile and simple water particle 

 displacements are considered. 



A special mechanism therefore may be considered in this con- 

 nection, which probably plays no unimportant part in the generation 

 of long waves which are faster than the wind. The idea is that 

 short period waves in the generating area may disappear, transfer- 

 ring their energy to other waves. This special kind of energy trans- 

 fer seems to be possible only in complex wave motion, and its mech- 

 anism perhaps may be explained in the following way. 



Consider the fully arisen steep "sea" or p -wave traveling always 

 with ^<v, and constantly overtaken by flat disturbances traveling 

 in the same or nearly the same direction but with a phase velocity, 

 (T = V or 6" > v. Every time the low crest of the long wave disturb- 

 ance overtakes a crest of the steep p -wave, the water particle 

 velocities of both wave motions are added, and according to the di- 

 mensions of the two waves, the horizontal particle speed will increase 



87 



