of the nonlinear source function directly beneath the 

 spectral maximum, causing the peak to grow. As the peak 

 develops, the positive lobe moves towards the forward face 

 of the spectrum until a stage is reached, corresponding 

 roughly to the mean JONSWAP spectrum, where the peak no 

 longer grows but merely shifts towards lower frequencies 

 without appreciable change in shape (2nd panel). For a still 

 sharper peak, shown in the third example, the source function 

 develops two positive lobes immediately adjacent to a strong 

 negative lobe beneath the spectral maximum, and the peak 

 broadens again. 



The evolution of this self-stabilizing spectral shape 

 does not appear to be affected qualitatively by the details 

 of the energy input from the atmosphere or the dissipation; 

 these determine the energy level of the spectrum and the rate 

 at which the nonlinear transfer causes the neak to wander 

 towards lower frequencies, but not the basic form of the 

 energy distribution resulting from the combination of the 

 three source terms. 



The probable decomposition of the net source function 

 S into its three constituents S^n ? Str and S^s 

 is shown in Fig. 8. Of the four terms in the equation 



only the terms s (measured) and S^-^ (computec 



25-22 



