HAMILTON: TIME VARIATIONS OF SOUND SPEED OVER LONG PATHS IN THE OCEAN 



Mr. M. A. Pedersen (Naval Undersea Center) : I have several 

 comments on this particular presentation. I have worked up a number 

 of Pacific profiles for which the slowest arrival is not the axial 

 arrival. It seems that the slowest arrival is associated with the 

 steepness of the thermocline. That is, in one case I worked out the 

 slowest ray formed was about a yard-per-second slower than the axial 

 speed. And it corresponded to a ray which is turning around in the 

 steep thermocline portion. 



Mr. Hamilton : Figure D-1 shows a comparison of some typical pro- 

 files and their SOFAR signals. For the Sargasso Sea profile from 

 the western North Atlantic, the slowest SOFAR arrival travels along 

 the sound-channel axis. The resulting signal is in the lower left. 

 In the typical Eastern Atlantic profile the Mediterranean outflow 

 broadens the sound-speed minimum and increases its value, so the 

 slowest arrival travels in the surface and bottom grazing ray paths. 

 This SOFAR signal is on the lower right. In the Pacific profile, 

 the SOFAR signal is shorter as shown in the middle bottom trace. 

 It is actually quite similar to what a western North Atlantic SOFAR 

 signal looks like if you eliminate the rays that penetrate the 18 C 

 Sargasso water. In the Atlantic where you have the Sargasso water 

 in the surface 500 meters, this high sound speed near surface 

 water gives the early SOFAR arrivals in the lower left SOFAR signal. 



I ran into the Eastern Atlantic SOFAR signals a few years ago. 

 When I saw these signals, I assumed they were from surface shots and 

 made some stupid statements to that effect. I then realized that 

 the Eastern Atlantic was a different ocean entirely with this entirely 

 different profile, that it just reverses the SOFAR signal completely 

 from the classical one Dr. Worzel published, 25 years ago. 



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