tlon directions yields the one-dimensional frequency spec- 

 trum E(f) = / E2(fie)d9 



-IT •' 



Since each "wave packet" of the spectrum propagates 



with a group velocity appropriate to its wavenumber k , 

 densities at different times t and positions x in 

 the ocean are Interrelated through the spectral energy bal- 

 ance or radiative transfer equation (neglecting refractive 

 effects) 



dF(k;x,t) = F^^.^p^s . (1) 



at t. ~ 



The left-hand side of the equation expresses the conserva- 

 tion of spectral energy density along the path of a wave 

 group, in accordance with the conservation of energy of 

 individual wave packets as given by the linear, free-wave 

 theory, while the right hand side S represents the net 

 change in energy of the component k due to all dynami- 

 cal processes not included in the linear theory. The source 

 function can be represented generally as a superposition 



of the input Sj_^ due to air-sea interactions, a transfer 

 term S^ representing a redistribution of energy v;ithin 

 the spectrum conserving total wave energy and momentum, and 

 a dissipation term S^ 



Once the dependence of S on the wave spectrum and 



25-8 



