Internal Wave Interactions 



In the paper, I considered the steady motion as the limit of a zero frequency in- 

 ternal wave. In an internal gravity wave in a uniformly stratified fluid, the 

 magnitude of the variations in density op and velocity 5u are intimately related: 



I I I Su I 3/0 

 N 3z ' 



and this relation is preserved as the frequency approaches zero. Consequently, 

 in the analysis that I presented, there are coupled vertical variations in both the 

 density gradient and the horizontal velocity field. In Dr. Benjamin's analysis, 

 only velocity variations are considered. In actual fact, either or both can occur 

 independently; it will be of interest to see how the two effects separately influ- 

 ence the nature of the trapping. Preliminary results indicate that Dr. Benja- 

 min's result can be recovered when the density gradient is uniform and that the 

 results presented in the paper appear when the variations in density and velocity 

 are related according to the equation above. These further results will be pre- 

 sented in the literature in due course. 



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