Pierson, Tick, and Baer 



S(f) 



030 0.040 0.060 0.080 0.100 



frequency (sec"') 



0.120 



0.140 



0.160 



Fig. 2 - Spectral growth for 40 knots with a white noise 

 background present 



growth scheme, the original scheme without dissipation, and the growth scheme 

 of Inoue (18), to be described later. 



There is another aspect of wave theory that might possibly play a role in the 

 modification of the spectrum of a wind sea. It consists of the theory given by 

 Phillips (19) on third-order interactions for intersecting trains of gravity waves 

 and the extension by Hasselman (20). Pierson (21) has prepared a technical re- 

 port that attempts to show that these theories are not fully substantiated. It is 

 the opinion of Pierson that these third-order nonlinear interactions are not a 

 feature of nature and that they are not necessary to forecast the correct shape 

 of wave spectra on the open sea. We understand that certain computer tech- 

 niques are being employed in an attempt to find out whether or not changes in 

 the spectrum due to such interactions can explain what is observed. A number 

 of laboratory experiments are also being planned that may answer some crucial 

 questions. However, it is important to point out that energy cannot be destroyed 

 in such a process if it exists; it must reappear at some other frequency. Unless 

 after it reappears at some other frequency, it is then removed by the process of 

 wave breaking, there is the tendency to make the directional spectrum nearly 

 isotropic, and this is not an observed condition on the open ocean. 



504 



