533 



£ 

 o 



10 



20 



30 



U). (cm 



s-^) 



FIGURE 6. The phase speed of the initial wavelets C 

 as a function of u*. Theoretical values correspond to 

 those for waves of the maximum growth rate. The theo- 

 retical values were calculated by use of the observed 

 velocity profiles in the water at the critical time of 

 the first appearance of the initial wavelets. The ob- 

 served values for higher three wind speeds were deter- 

 mined at the critical time, whereas that for the lowest 

 wind speed was determined about 3.5 s after the critical 

 time because of the experimental difficulty, and this 

 delay may presumably explain the observed higher value 

 than the theoretical ones. [Cited from Kawai (1977).] 



f(H2) 



FIGURE 7. An example of minute inspection of the ob- 

 served time series of the spectral peak for the initial 

 stage of the generation of wind waves. The lapse of 

 time is indicated in alphabetical order, the interval 

 between successive points being 0.32 s. After the growth 

 of regular initial wavelets at a constant frequency of 

 about 15 Hz, the spectral peak shows an irregular mo- 

 tion corresponding to the transition to irregular wind 

 waves. [Cited from Kawai (1977).) 



-lao -BO 





 Phase 



FIGURE 8. Observed values of the 

 local shearing stress along the 

 surface of representative wind 

 waves. The abscissa is the phase 

 relative to the peak point of the 

 crest and the ordinate is ex- 

 pressed as the square of the fric- 

 tion velocity of the water. The 

 wind speed was 6.2 m/s and the 

 fetch was 2.85 m. [Cited from 

 Okuda et al. (1977) .] 



