THE PROBLEM 



Investigate oceanographic factors which may be pertinent to the behavior of 

 underw^ater sound. In particular investigate the vertical fluctuations of temperature 

 and their relation to sea surface slicks. 



RESULTS 



1. The depth of isotherms in the shallow summer thermocline fluctuates virtually 

 all the time. At Mission Beach, California, of the significant vertical oscillations 

 of a central isotherm in the thermocline, half were greater than 7.2 feet and half 

 had periods greater than 7.6 seconds. Because the internal waves were refracted, 

 they usually proceeded in a general shoreward direction at the measurement site 

 where they had an average speed of 0.31 knot. 



2. Every large internal wave of height greater than 14 feet had a sea surface slick 

 associated with it for the thermocline depths observed. 



3. In accordance with wave motion theory of simple internal waves, an aaive 

 convergence circulation occurs over the descending slope of an internal wave. In 

 85 cases out of 105 at the measurement site, the slick occurred between the crest 

 and the following trough. The relationship was sufficiently reliable to provide 

 an approximate prediction of the subsurface thermal topography from a knowl- 

 edge of the distribution and movement of the slicks. 



RECOMMENDATIONS 



Continue the general study of the near-shore and near-surface environmental 

 characteristics which aff'ect acoustic transmission. Give special emphasis to long 

 duration waves and to the geographical distribution of internal waves. Study 

 acoustical transmission through internal waves. 



ADMINISTRATIVE INFORMATION 



The work reported here was carried on in the Signal Propagation Division under 

 lO 15401, NE 120221-847.13 (NEL L4-1) during the period June 1958 and July 

 1959 and was approved for publication 2 November 1959. 



Many of the sea measurements were made by O. S. Lee, C. D. Curtis, J. C. Roque, 

 and J. S. Black. Much of the data processing was done by A. L. Moore. The 

 bridge circuits and compensating resistor circuit in the thermistor line were 

 designed by A. T. Burke, the thermistor mountings were designed by J. C. Roque, 

 and the beads were cast in plastic by R. L. Arthur. Helpful suggestions were made 

 by G. H. Curl. 



The bridge system was built by Hartley Herman of Kahl Scientific Instrument 

 Company, El Cajon, California. 



WIBL/WHOI 



D D301 ODHDSBt, T 



