longer, and between 12.5 and 14,5 seconds for the longest periods 

 of waves present. 



To present a simple interpretation it seems that two or three 

 frequency bands could be defined as characterizing the observed data 

 in the case where the sea was generated by a quasistationary and quasi- 

 homogeneous wind field. Hence the usual conclusions drawn from the 

 observations would be that the sea surface roughness pattern con- 

 sists of discrete bands which indicate dominating periods in the com- 

 posite wave motion. 



It may be pointed out here that a nearly continuous distribution 

 of observed periods is found in series of observations under more 

 complicated wind conditions; for example, where a stronger wind at 

 the windward part of the fetch generates a fully arisen sea, while 

 the wind decreases to the leeward, where the sea is observed (see 

 page 26). 



The prediction of certain characteristics of period patterns 

 may be based on the prediction of the distribution function for in- 

 dividual wave periods. Statistical data for individual wave periods 

 at given wind velocities indicate regularities in the distribution, 

 namely, the range of characteristic periods, the most frequent per- 

 iods, and the asymmetry of the distribution. Some examples for 

 fully developed sea are presented in figure 4, covering the range 

 of wind velocities between 5.5-6.4 m/sec, 7.5-8.4 m/sec, 10.5-11.4 

 m/sec, 11.5-12.4 m/sec, and 14.5-15.4 m/sec, respectively. In 

 these distribution graphs all data are collected from observations 

 at fully developed sea within the given wind velocity interval. The 

 graphs show the percentages of observed characteristic periods at 



15 



