day-to-day, deep-ocean background swell. At high energy, peak directions are 

 more shore normal, suggesting the influence of refraction on the low- 

 frequency, energetic waves in well -developed seas. In terms of peak period, 

 short-period (high-frequency) wave fields tend to arrive from the northeast 

 quadrant, consistent with patterns of predominant local wave -generating winds. 

 Long-period wind waves which are likely from distant sources tend to arrive 

 from shore normal to slightly south of shore normal. 



255. The observed range of peak directions is about 70 deg on either 

 side of shore normal. Characteristic wave heights range from about 0.3 to 

 4.4 m. Peak periods cover the full range allowed in the effective filtering 

 by the Fourier analysis used here, from about 3.1 to 18.5 sec. As a whole, 

 the data set is dominated by day-to-day low-energy observations. Fewer than 

 10 percent of observations represent storms. 



256. One of the most important results of this study is the behavior of 

 the new parameter characterizing directional spread. It was found never to be 

 small (no unidirectional wave fields) . The range was from about 20 to 50 deg. 

 For the data set as a whole, there was a well-defined peak in the spread 

 parameter at about 40 deg. This peak appeared to occur in all sea states, 

 being nearly independent (statistically) of energy level, peak period, peak 

 direction, or bulk steepness (as a dimensionless combination of wave height 

 and wavelength deduced from peak period) . Given the sensitivity of system 

 response to directional spread deduced in the laboratory studies of Vincent 

 and Briggs (1989) and Kaihatu and Briggs (in preparation), this result is a 

 strong indication that directional spread must be taken into account in sea 

 state description. 



257. Frequency-by- frequency examination of the data indicates that 

 roughly a third of all directional distributions are multimodal. Where 

 multimodal distributions occur, the tendency is for energy to be evenly 

 distributed among the modes. Though some multimodal distributions at high 

 frequencies may be attributable to noise contamination, the occurrence is too 

 high at intermediate frequencies to ignore. This means that multimodal 

 distributions are a very important aspect of wave directionality. Ignoring 

 secondary modes in an attempt to simplify the problem is highly likely to give 

 a poor representation of wave energy. This result indicates that further 

 study is required concerning this aspect of wave directionality. 



124 



