13. (Concluded). 



Bulk directional characteristics are deduced from a spread parameter, 

 based on the angular arc which subtends the central half of the area under a 

 wave energy directional distribution, and an asymmetry parameter, which 

 indicates how evenly energy is distributed about the peak of a directional 

 distribution. The spread parameter for energy integrated across all 

 frequencies ranges from 20 to 60 deg with a distinct maximum occurrence near 

 40 deg. Unidirectional sea states do not exist in this data set. The same 

 general behavior is found when data are evaluated frequency by frequency. The 

 tendency for spread to be near 40 deg appears to occur under all conditions, 

 being nearly independent of conventional sea state descriptors such as 

 characteristic wave height, peak period, peak direction, and bulk steepness. 



Multiple modes (distinct peaks in a directional distribution at a given 

 frequency) occur in about one-third of the observations. Where multimodal 

 distributions exist, energy tends to be evenly distributed among modes. 

 Causes and effects of this feaure of wave climate are subjects for future 

 research. 



An indication of ordered structure in directional distributions at 

 individual frequencies is apparent when select distributions are classed by 

 ranges of spread and asymmetry parameter and then averaged to find mean 

 shapes. Select distributions are those which are unimodal and contain enough 

 wave energy to avoid noise contamination. The shapes thus found can be used 

 as structural elements with which to constitute a complete sea state in 

 numerical models or in signal generation algorithms for directional physical 

 models. Only about one-third of all distributions are found to be symmetric. 

 Sjmmietry is a common assumption in specifying analytic functions with which 

 to model directionally distributed wave energy. The remaining two-thirds of 

 observations are strongly asymmetric, a feature which is sure to have im- 

 portant consequences in wave dynamics inshore of the observation site. 



