wind speed increases from east to west across the area under study. A 

 possible effect of the shear would be to produce the skewness in the angular 

 variation as indicated^ At some future time it may be possible to extend 

 the concepts of wave theory to permit a representation of the local wave 

 spectrum as a function of wind velocity and wind direction locally and as a 

 function of the change of wind direction up wind and the shear in wind velO' 

 city cross wind. To do this would require a greater number of degrees of 

 freedom than this study has obtained, several different spectra for different 

 wind conditions,; and a very detailed study of the wind fields. 



An idealized directional spectrum 



For the present purpose, however, it is desirable to attempt to ideal* 

 ize the results obtained so as to reflect the three results pointed out above and 

 so as to eliminate sanapling variation and the effects of changing wind direction 

 and wind shear. It will therefore be assumed that \Mv-t 9)] is an even func- 

 tion about the local wind direction and that its peak value falls at 9=0. The 

 values of cjdo.) as tabulated above thus determine the amplitude of the cos 20 

 terna and ^i (jx) is assumed to be zero. (This implies a rotation of -30 for 

 the axes in the figures given above if it is desired to approximate the peak 

 of the spectrum. ) 



After considerable subjective curve fitting and trying a nurnber of pos- 

 sible functions which did not do as well, it was found that cj could be approxi- 

 mated by the following function of frequency and wind speed -wiiere the values 



are in c, g. s,. units and v is (18.7 x 51- 5) cm/sec. 



235 



