SPINDEL: PHASE FLUCTUATIONS, COHERENCE AND INTERNAL WAVES 



January 1974 did not show any effect of the Vaisala frequency, and 

 all measurements since January 1974 have shown sharp cutoffs. Very 

 curious discontinuity. 



There at least we do know the answer other than people finding 

 what is fashionable at the moment. Those before were moored measure- 

 ments, and the whole field was convected past the fixed transducers, 

 so that to some extent you got a mixture of the spatial as well as 

 the temporal variation. And there is no cutoff in the spatial vari- 

 ation at high wave number. 



So you might think of that as a Doppler shift or a Doppler smear 

 cutoff. If the tides convect your whole field by variable speed, it 

 is certainly going to blur and maybe even eliminate the cutoff. 



When people went to other kinds of instrumentations, like 

 capsules that yo-yoed but stayed with the water column, then all of 

 a sudden the cutoff did, thank heaven, appear. It was a 20 dB cutoff 

 and was very pretty. 



And I am hoping against hope somehow that in some future experi- 

 ments in acoustics suddenly a sharp Vaisala cutoff will appear. I 

 do not know how. 



Dr. Clark: Where would you expect that, Walter? 



Dr. Munk: At the local Vaisala — I don't know. That is a good 

 point. There is, of course, great smearing if you have rays which 

 have gone through the whole water column. I hadn't thought of that. 

 And that really in a way changes the situation from the internal 

 wave experiment I mentioned. 



Dr. Clark: In that data that I gave you, you will find a knee 

 at about one cycle per hour. 



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