PROBLEM 



In general, investigate oceanographic factors pertinent to 

 the behavior of underwater sound; in particular, study vertical 

 fluctuations in thermocline depth. Specifically, study the thermal 

 structure of the upper 750 feet of the ocean utilizing the towed 

 thermistor chain and thereby gain a predictive understanding of 

 these fluctuations and their distribution in time and space. 

 Finally, incorporate the findings in an improved acoustic model 

 that can be used in critical areas of the ocean. 



RESULTS 



1. Time -dependent vertical -temperature fluctuations in the 

 thermocline were found to exist in all areas of the ocean examined 

 with the NEL Thermistor Chain. 



2. Time -dependent horizontal-temperature gradients were com- 

 puted from continuous cross sections of the upper 750 feet of the 

 ocean in 17 geographical areas of the eastern North Pacific. The 

 horizontal -gradient field alternates in sign with a regularity that 

 implies a dominant frequency of internal waves or convection 

 cells. The corresponding wavelength is 0. 72 nautical mile with 



a standard deviation of 0. 16 mile. 



3. The vertical -temperature gradient in the thermocline is gen- 

 erally of the order 10~ 2 °C/ft, but ranges between 10 and 10 -3 



C/ft. The corresponding horizontal-temperature gradient is 

 generally of the order 10 C/ft, but ranges between 10~ 3 and 

 10 -5 C/ft. The slopes of isothermal surfaces are of the order 

 10~ 2 . Thus, the vertical and horizontal gradients normally differ 

 by two orders of magnitude. The horizontal gradient in the 

 thermocline can be predicted within useful limits from the measured 

 vertical -temperature gradient by means of the equation 



dT /dT^ °- 71 



— = 0.0047 I — 

 dx \ dz 



MBL/WHOI 



0301 00M0511 M 



