PART VIII: PEAK DIRECTION AND SPREAD AT THE FREQUENCY LEVEL 



214. Of interest in directional analysis at the frequency -by -frequency 

 level are the peak direction and directional spread. This section considers 

 the distributions of peak direction ^p^, and directional spread Ad^ (from 

 Equation 17) for each of the 28 frequencies f„ in the observed frequency- 

 direction spectra. In light of the modality discussion above, the distribu- 

 tions are done both for all (1,046) cases and for just unimodal cases (number 

 varies with frequency) . The distinction is made to see if multimodality has 

 any effect on distributions of these parameters. Of particular interest is 

 directional spread which, at the frequency level, is based on an integral 

 across all modes in a directional distribution. 



Peak Direction 



case where all data are considered, and one distribution is computed for each 

 frequency. In Figure 25, frequency and number of cases are noted in the upper 

 right corner of each subplot. The lowest frequency is in the upper left 

 subplot. Frequency increases across, then down the page. Note that the scale 

 for the percent of cases is different for the top row of subplots . 



216. Figure 25 shows that the low-frequency distributions (top row) all 

 have peak directions ranging from about shore -normal (0 deg) to slightly south 

 of shore-normal (about -20 deg) , consistent with the refraction arguments 

 given earlier for long waves originating in the open, deep Atlantic. As 

 frequency increases, the distributions become wider, suggesting a reduced 

 effect of refraction and an increase in dominance of other wave processes and 

 local wind as wave generating and transforming mechanisms. At high frequen- 

 cies (bottom row), peak directions range from about 70 to -80 deg, almost 

 across the whole horizon. 



217. When directional distributions identified as multimodal are 

 removed, the set of distributions of peak direction become those shown in 

 Figure 26. Since most of the low-frequency distributions are unimodal (from 

 Figure 23) , the results are little changed from Figure 25 for these frequen- 

 cies. In fact, little significant change is seen at all except at the highest 

 frequencies (bottom row). In these cases, the number of samples has dropped 



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