at X = with a temperature probe at say, z = -50 meters, then 

 the instrument would record undulations of temperature as the 

 subsurface levels oscillated in response to the surface wave motions. 

 Even if one considered the averaging that is usually applied to data, 

 these effects need not necessarily average out since the wave con- 

 ditions at any given point on the surface are continually changing. 

 This effect may account for much of the apparent thermal unrest in 

 the oceans. 



REMARKS 



The estimates of mean Stokes' velocity are, of course, only as 

 good as the approximations and spectra that produced them. At the 

 present time, it is still not possible to verify directly a directional 

 spectrum. One can, however, verify the significant height and 

 the frequency spectrum against actual observations of wave elevation 

 as a function of time. Bunting and Moskowitz (1969) have provided 

 the authors with an advance copy of significant height verification 

 statistics for spectra similar to those used in the above calculations. 

 The bias is on the order of -0.9 ft and the RMS deviation is about 

 ±5.0 ft. These are well within the present state of the art. 



It should be pointed out at this juncture that all the spectra 

 used in the computations were not fully developed. For a fully de- 

 veloped local wind sea, the mean Stokes' velocity increases with 

 wind speed as shown in Figure 6. 



In order to compare the resultant drift magnitudes with Ekman 

 magnitudes, the empirical equations of Durst and Thorade (as given 

 by Neumann and Pier son, 1966) were applied to the 4 March wind 

 field. The Durst magnitudes ranged from 0.3 to 20.7 cm/sec. The 

 Thorade magnitudes ranged from 2.5 to 33.0 cm /sec. The drift 

 magnitudes went from to 19.0 cm/sec. Further examination 

 shows that these values are not always proportionally related. At 

 times, the drift maybe comparable to or greater than the steady state 

 Ekman velocity. 



A convenient check on the magnitude of the drift was provided 

 by comparing the long and short crested results. For instance, in 

 the test calculation at 5 = -40 meters, the long-crested model showed 

 that the ensemble of particles had drifts ranging from 1.96 to 1.99 

 cm/sec with an average of 1.98 cm/sec. The short-crested model 

 produced a mean velocity of 1.61 cm/sec. The latter should be ex- 

 pected to be lower than the former due to the effect of the short- 

 crestedness. 



The use of a ratio statistic in this context was found to be of 

 only limited significance, especially in the westerlies. In those 

 regions, one should resort to the spectral techniques to compute 

 drift. 



405 



