V 



Symbol 



Location 



No. of Cases 



« 







8 



I 





Michigan Clty(Buoy) 

 Michigan City (Pressure) 



246 

 127 



T 



A 





 







e 







Presque Isle (Buoy) 



no 



» 



t 







.2 7 



• 





Presque Isle (Pressure) 



119 



f 







a 









Huntington Beach 



746 



T 









X 



C^6 









Pt. Mugu 



799 



T 



01 



c 



□ 

 X 















01 



















T 



t 











• 









•y 



i 





















ax 





O 3 4 











t 





xo 





«o •? 











off 



X 



'o" • 





°;:3 



Normo 



lized Gaussian Oisfribution 



, ,fl X 



□ 











OA X Of 



— T-U 







•"*~ 





•1 ° 







fa * 







• 







'm 





X 



« T 



• 

 • 



• 









£ 2 



- 

































t 

 n 



■ 



1 



1 1 1 



1 1 



. 1 





1 



.. -L., ., 



99.9 99 



90 70 50 30 10 

 Cumulative Percent 



0.1 



Figure 26. 



Cumulative probability distribution functions for kurtosis 

 of sea-surface elevation distribution function at Great 

 Lakes and Pacific coast locations. 



locations. The Great Lakes locations and Pt. Mugu tend to have the 

 lowest skewness values. The Michigan City locations and the Presque 

 Isle buoy gage show a tendency for occasional very high kurtosis values 

 which are associated with very low significant wave heights. Although 

 several kurtosis values greater than nine occurred for the Michigan City 

 locations and Pt. Mugu, the values are omitted from Figures 25 and 26. 

 The Presque Isle pressure gage shows a tendency for exceptionally low 

 kurtosis values. A section of pen-and-ink record for a case with high 

 kurtosis (equal to 8.0) was shown in Figure 11. 



Some of the kurtosis values in Figures 25 and 26 are questionably 

 high. Since kurtosis is based on the fourth power of the deviation of 

 sea-surface elevations from the mean (i.e., n = 4 in eq. 6), it is more 

 affected by a few elevations far from the mean than any other parameters 

 considered in this report. Noise or momentary signal losses in a record 

 which are comparable to the size of the largest waves will pass uncor- 

 rected through the editing process described earlier. These bad data 

 points usually have little effect on the spectrum but they can have a 

 significant effect on the kurtosis of the distribution of sea-surface 

 elevations. 



Another factor which leads to questionably high values of kurtosis 

 is the occasional tendency of the step-resistance gage to become elec- 

 trically shorted at a particular elevation, often by marine growth, and 

 to produce wave records in which the troughs are unrealistically flat. 

 Because kurtosis is especially sensitive to these problems (known to 

 have occurred intermittently in the data considered in this report) , 



53 



