Wave decay 
In the Sverdrup Munk theory the decrease in wave height due 
to the travel of the waves into the area of decay is ascribed 
to selective attenuation of the waves against the atmosphere. 
The forecasting diagrams in figures 15 and 16, show that the square 
of the wave record averaged over time decreases with the band 
width of the filter. Therefore for a disturbance of finite dur- 
ation over a fetch of finite length, the wave amplitudes die down 
essentially like 1//’x simply due to the properties of dispersion. 
This amount is not quite enough to fit the empirical forecasting 
graphs of Sverdrup and Munk as revised by Arthur [1948, 1949], 
but another factor approximately equal to 1//x will result from 
consideration of short crested waves. It will eventually be shown 
in this paper that wave decay can be explained without friction 
effects. At this point, reference is made to figure 8 in the 
paper by Donn [1949]. Although the spectrum shown is not a power 
spectrum, (and the # axis is plotted backwards), this figure 
already shows remarkable agreement with figure 16. 
Comparison with the models of Chapter 6 
The models studied in this chapter are far more realistic 
than the models studied in Chapter 6. In the first place, wave 
records appear to be actually Gaussian to a very good degree of 
approximation even if the records are swell records. Secondly, 
the models in this chapter provide for a smooth continuously 
varying record at large decay distances, whereas all of the models 
in Chapter 6 required discrete jumps in wave amplitude at distant 
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