It is concluded on the basis of the foregoing discussion that the visual estimates by 

 Weather Bureau personnel of sea state, reported as a "characteristic" wave height, may be 

 used with confidence in establishing distribution patterns such as are given in the following 

 section. 



DISTRIBUTION PATTERNS OF WAVE HEIGHTS AND WAVE PERIODS 

 FROM ANALYSIS OF U.S. WEATHER BUREAU DATA 



Cumulative long-term distribution patterns of the characteristic wave heights and 

 periods are given in Figures 9 through 30 for the ten ocean stations shown in Figure 1. For 

 each station the odd-numbered figure gives the wave height distribution and the even-numbered 

 figure gives the corresponding wave period distribution. Methods for fitting a log-normal dis- 

 tribution to the data are given in Reference 11. In Appendix C a sample calculation illustrates 

 the method used for deriving Figures 9 through 30 from the data (Tables 1 and 2) furnished 

 by the Weather Bureau. 



The rather good fit of the computed lines to the plotted data, in Figures 9 through 30, 

 suggests that a log-normal distribution is a good approximation to the distribution pattern of 

 characteristic wave heights and periods for values above the truncation point.* 



Distribution patterns for wave length can be derived from the data for wave periods by 

 applying an approximate conversion** 



Wave Length = 5.1 (Wave Period) 2 



This conversion has been made for all the weather stations. It is apparent that the distribu- 

 tion of wave lengths will be log-normal if that for the periods is log-normal, since the conver- 

 sion involves only a change in mean value and slope from the distribution of the periods. See 

 Figure 16 for an illustration of the conversion to wave length. 



In Table 5 mean values and variances are given for the wave height and period data 

 reported from each ocean station. Also the latitudes, longitudes, and observation periods 

 over which the data were collected are shown. 



*The truncation point is that value of wave height or period below which no observations are available or are 

 utilized. In this report only wave periods above 5 sec and wave heights above 2.5 ft were used. 



**This conversion is applicable to gravity waves in deep water. The numerical value of the factor, 5.1 in this 

 case, does not affect the type of distribution; it only changes the value of the median. 



14 



