3. The resonance process is most efficient in the case of a modulation 

 which travels in the same direction as the carrier wave (the main constituent) of 

 a swell. The creation of internal waves of this type is strongly dependent on the 

 stratification of the water. 



4. Preliminary evaluations of temperature and swell records from the NEL 

 Tower show good agreement between periods of swell modulation and internal 

 wave periods. 



5. It is likely that internal waves are created on the entire continental 

 shelf off Southern California during times of favorable stratification. This de- 

 pends on tide and wind. 



RECOMMENDATIONS 



1. Verify, with additional measurements at the NEL Tower, the theory that 

 internal waves are produced by swell. 



2. Acquire, for complete analysis, long records of temperature fluctuations 

 and surface waves in order to compute spectra with high resolution and statistical 

 confidence. 



3. Check, by measurements of surface waves at two positions, and slick 

 observations, the result that internal waves travel in the direction of the swell 

 modulation. 



REFERENCES 



Navy Electronics Laboratory Report 937, Slicks and Temperature Structure 



in the Sea , by E. C. LaFond, 2 November 1959. 

 LaFond, E.C., "Internal Waves," p.731-751 in M.N. Hill, The Sea , v.l, 



Interscience, 1962. 

 Navy Electronics Laboratory Report 1342, The U. S. Navy Electronics 



Laboratory's Oceanographic Research Tower; Its Development and 



Utilization , by E.C. LaFond. 22 December 1965 

 Lee, O.S., "Observations on Internal Waves in Shallow Water," Limnology 



and Oceanography , v. 6, p. 312-321, July 1961 

 Cairns, J.L. and LaFond, E.C, "Periodic Motions of the Seasonal Thermo- 



cline Along the Southern California Coast," Journal of Geophysical 



Research , v.71, p. -3903-3915, 15 August 1966 

 Ufford, C.W., "Internal Waves Measured at Three Stations," American 



Geophysical Union. Transactions , v. 28, p. 87-95, February 1947 

 Ewing, G., "Slicks, Surface Films and Internal Waves," Journal of Marine 



Research, v. 9, p. 161-187, 1950 



27 



