4 Discussion 



The primary purpose of this report is to elucidate the directional distri- 

 butions of nearshore wind wave energy in the context of evolving storms. 

 With the illustrations in Appendix A for guidance, some fundamental proper- 

 ties of storm wave fields can be identified. 



A primary question is whether a storm wave field can, in any sense, be 

 reasonably approximated as unidirectional and monochromatic, or, perhaps, as 

 corresponding to simple models of deep-ocean wave fields. A quick perusal 

 of Appendix A shows, in a few observations, that a unidirectional, monochro- 

 matic model may be appropriate for some applications (examine, e.g., Event 

 R and conditions near the peaks of Events V and W), but such conditions are 

 relatively rare. Furthermore, narrow spreads of naturally occurring spectral 

 energy in frequency and direction do not mean the waves are unidirectional 

 and monochromatic. Real ocean waves are invariably groupy and subject to 

 nonlinear interactions. These dynamically important properties can not be 

 represented by unidirectional, monochromatic wave models, and the utility of 

 such models is thereby somewhat restricted. 



The wave fields of Appendix A do not appear to conform to models and 

 observations of deep-ocean wave fields, either. For example, papers by 

 Mitsuyasu et al. (1975) and Mitsuyasu and Uji (1989) indicate that S(f,6) in 

 the deep ocean is characterized by narrower directional spreads near the spec- 

 tral peak frequency than in the spectral tails. Spectra shown in Appendix A 

 appear generally to have maximum spreads near spectral peak frequencies. 

 These observations mean that neither a single-wave-train model nor deep- 

 ocean wave behavior is appropriate to characterize nearshore storm waves. 



While the spectra of storm wave fields at the FRF are complicated, they 

 are not without a remarkable similarity in structure that can be described, at 

 least qualitatively. In this part of the report, these structural similarities are 

 discussed, and some of the consequent research questions are posited. 



Of the 29 storm events identified in this report, 25 have S(f,6) with com- 

 mon structural features (described qualitatively below) through the progress of 

 a storm. Four events, E, P, Q, and R, do not follow this pattern. Of these 

 four, waves in Events P and Q are associated with Hurricanes Gabrielle and 

 Hugo, respectively, both of which passed several hundred kilometers away 



16 



Chapter 4 Discussion 



