TM No. 377 



The small phase shifts of one orthogonal velocity component with respect 

 to the other are associated with orbits corresponding to a sloped ellipse 

 (with the semi -major axis in the vertical., tipped backwards), This configuration 

 was shown by Starr to suggest a mechanism for the downward transfer of horizontal 

 wind imparted momentum , 



A few additional words should be said regarding the apparently exceedingly 

 large Reynolds stresses observed within the waves , Values of wind stress on the 

 water (usually an order of magnitude smaller than the ones reported here) have 

 been inferred by many authors > even though no direct measurements have thus far 

 been made. In general;, one chooses some value of mean stress appropriate for 

 the particular ocean circulation model under ex ami nation. A stress value of 

 one dyne cm" 2 is often used (e.g., Stommel, 1958, page 90) . If this is the 

 value estimated for a large ocean area> it seems plausible that, since sea 

 surface stress is a vector quantity having both magnitude and direction (which 

 is that of the local wind),, spatially and vectorially averaged values must be 

 quite dependent on the direction of the stress vector at each point, Thus, the 

 averaged vector magnitude may not be indicative of local magnitude. Furthermore, 

 stress is generally associated with the approximate square of the wind speed* 

 In local regions of high winds, there may be a disproportionately large contri- 

 bution of stress (from these relatively small areas of ocean) to the mean wind 

 stress over the whole ocean. 



With regard to theories of wind-driven ocean circulation models, the wind 

 stress is that which drives the ocean currents * It is possible that a consider- 

 able fraction of the wi.nd=induced stress applied at the sea surface is utilized 

 in wave generation and turbulent diffusion. 



Although the reported stresses in the waves seem large, the vagaries 

 inherent in this subject preclude sound justification for doubting these values 

 at this time e 



Future Studies 



The following suggested future studies should prove of significant value to 

 the investigations of turbulent processes in the ocean, 



lo As previously mentioned,, improved calibration procedures must be utilized, 

 which will remove many of the -uncertainties pertaining to the potential biasing 

 of the wave meters,, A new (OMDUM IV) system having a threshold velocity of less 

 than 2 cm sec"- would allow more precise examination of wave motions associated 

 with higher frequencies and smaller velocity amplitudes. 



The use of arrays of ducted meters could provide a much clearer picture of 

 the instantaneous field of motion within the waves. With improved instrument 

 suspension^ more extreme wave conditions could be examined with regard to 

 variance and auto-spectra distribution with depth, and estimates could be made 

 of total wave kinetic energy <, 



166 



