TABLE 5 



Statistics for Log-Normal Distributions Computed from Wave Observations 

 Made in North Atlantic Ocean 



Ocean 

 Station 



Latitude 

 deg, min 



Longitude 

 deg, min 



Characteristic Wave Heights 



Characteristic Wave Periods 



Dates of 

 Observations 



Number of 

 Observations 



Median Value of 

 Characteristic 



Wave Height 

 ft 



Mean Value of 

 Logarithm of 



Characteristic 

 Wave Height 



Variance (o- 2 ) of 

 Logarithm of 

 Characteristic 

 Wave Height 



Period 

 of Records 



Number of 

 Observations 



Mean Value of 

 Characteristic 

 Wave Period 



Mean Value of 

 Logarithm of 



Characteristic 

 Wave Period 



Variance (r, 2 ) of 

 Logarithm of 

 Characteristic 

 Wave Period 



A 



62°00'H 



33°00'W 



1/49- 6/54 



12,691 



6.34 



1.847 



0.4524 



1/49- 6/54 



12,342 



6.30 



1.840 



0.0935 



B 



56°39'N 



51°00'W 



1/49-12/54 



15,547 



6.59 



1.886 



0.4434 



1/49- 6/55 



16.0 60 



6.40 



1.857 



0.0748 



C 



52°45'N 



35°30'W 



1/49-12/54 



16,857 



6.75 



1.910 



0.3763 



1/49- 6/55 



17,471 



6.48 



1'.869 



0.0873 



D 



44°00'N 



41°00'W 



1/49-12/54 



16.804 



6.26 



1.834 



0.3843 



1/49- 6/55 



17,310 



6.24 



1.831 



0.0800 



E 



35°00'N 



48°00'W 



1/49-12/54 



16,777 



4.56 



1.516 



0.3765 



1/49- 6/55 



16,896 



5.86 



1.768 



0.0939 



H 



36°00'N 



70°00'W 



1/49- 6/54 



14,607 



5.08 



1.625 



0.4237 



5/49- 6/54 



13,647 



5.92 



1.779 



0.0643 



1 



61°00'N 



15°20"W 



1/47- 6/53 



11,274 



7.36 



1.996 



0.3747 



1/49-12/51 

 1/53-12/54 



12,142 



7.02 



1.348 



0.0546 



J 



52°30'N 



20°00'W 



'1/47- 6/53 



12,016 



7.40 



2.002 



0.3863 



1/49-12/51 

 1/53-12/54 



11,593 



7.29 



1.986 



0.0423 



K 



45°00'N 



16°00'W 



1/49-12/53 



11,182 



6.20 



1.824 



0.3033 



6/49-12/53 



11.906 



8.30 



2.117 



0.0548 



M 



66°00'N 



02°00'W 



1/49-12/53 



14,324 



4.99 



1.608 



0.2344 



1/49-12/53 



14,188 



6.99 



1.946 



0.0676 



Note: The statistical computations are based on truncated data. The truncation point is 2.5 ft for wave heights and 5 sec for wave periods. 



SUMMARY 



Frequency distribution patterns of wave heights and wave periods may be approximated 

 by a one-parameter type of distribution function when the environmental conditions are steady, 

 whereas they will tend to follow the two-parameter logarithmically normal distribution when 

 the environmental conditions are allowed to vary over a wide range. It should be emphasized 

 that the log-normal distributions in Figures 9 through 30 are influenced much more by the 

 usual sea conditions than by the rare occurrences of very high or very low seas. Thus one 

 should expect greater deviations from the fitted line for very small and very large wave heights 

 and wave periods than for those heights and periods which occur more frequently. It is con- 

 cluded that the long-term distributions of wave height and wave period may be approximated 

 by the log-normal distribution. 



Reasonably accurate visual estimates of wave height can be obtained from trained ob- 

 servers, provided a number of independent estimates are averaged. A single estimate may be 

 considerably in error. 



ACKNOWLEDGMENTS 



This work would not have been possible without the cooperation of many persons on 

 board the VALLEY FORGE and UNIMAK, on the Coast Guard and Navy staffs, in the Weather 

 Bureau, at the Hydrographic Office, at the Naval Photographic Interpretation Center, and at 

 the Taylor Model Basin. 



15 



