TM No. 377 



Several series of wave observations were made, which demonstrated the 

 applicability of the wave meters to the following important studies . 



1. The determination of the auto-spectra of wave particle motions - 

 Auto-spectra were obtained for various wave conditions and showed similar- 

 ities to free surface motion auto-spectra observed, with energy peaks di- 

 rectly associated with the wave frequencies. 



2. The decrease of wave energy with depth - The variances of the wave 

 motions showed an exponential decrease with depth and were compared to theo- 

 retical waves obtained from a classical wave model. Estimates of the total 

 kinetic energy of the waves (obtained by vertical . integration of the variances 

 of the motions ) showed a realistic amount of wave energy when compared to 

 estimated wave potential energy. 



3- Short term variations of wave energy - Observations showed changes 

 in both auto-spectra and variance distributions. These changes were associ- 

 ated with variations of the weather conditions over a twenty-four hour period. 



h. The "equilibrium range" of wave spectra - The slopes of the higher 

 frequency range of the auto -spectra of the motions appeared to follow the 

 "minus -fifth power" law attributed to free surface spectra. 



5- Reynolds stresses in waves - Covariances and cross -spectra are esti- 

 mated for the u and w observations, giving values of the order of -25 cm^ 

 sec"2. However, spurious values range from +28 to -162 cm.2 sec~2. The larger 

 covariances could be produced by instrument bias. Co-spectra indicate the 

 covariance contributions are largely caused by correlations in the band of 

 wind wave frequencies. Simple wave models are presented which contain the 

 covariance and cross spectral properties observed in the real data. Dis- 

 cussion is also presented on ways which instrument bias could occur. 



From observed mean shear of horizontal velocities, estimates are made 

 of the dissipation of turbulent wave energy to mean flow. 



This study provides evidence that the complex motions at the sea sur- 

 face can and should be measured. With the relatively crude instrumentation, 

 measurements were obtained which provided meaningful information on the mo- 

 mentum and energy transfer within the sea surface layer. Improvement of 

 instruments and techniques can only result in a better understanding of the 

 energetics of the ocean surface layer. 



IV 



