Pierson, Tick, and Baer 



GRID POINT 



OBSERVED (OWS) 



72 



73 



84 



85 



00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 12 

 DEC 16 DEC 17 DEC 18 DEC 19 DEC 20 DEC 21 DEC 22 DEC 23 DEC 24 DEC 25 DEC 26 DEC 27 DEC 28 



Fig. 5 - Observed and computed significant wave heights based on 

 the same wind fields, dissipation and propagation as Fig. 3 but 

 with Eqs. (7), (8), and (9) describing the wave growth 



Finally, the character of the turbulence in the wind over the ocean should 

 play an important part in determining the rate of growth of the waves. A great 

 deal of new theoretical work on turbulence is becoming available in the litera- 

 ture. These results suggest that the drag coefficient, and the roughness length, 

 depend on atmospheric stability and on the height of the sea present in that par- 

 ticular area. It would be highly desirable to develop a better way to modify the 

 growth of a wave spectrum on the basis of how high the waves are at the time of 

 the observation and on the basis of the stability of the air over the water. Miles' 

 theory states that the rate of growth of a particular spectral component is deter- 

 mined by the ratio of the curvature of the wind profile to the slope of the wind 

 profiled at that elevation above the sea surface where the phase speed of the 

 waves equals the wind speed. Since the phase speeds observed in fully developed 

 seas are considerably in excess of the winds measured 19.5 meters above the 

 surface, this means that knowledge of the wind profile over the water must ex- 

 tend both theoretically and observationally to elevations well over 70 meters. 

 Also, since the wind profile changes its character as a function of stability, the 

 rate of growth of different spectral components will be quite different depending 

 upon how the particular ratio mentioned above compares to the ratio that would 

 exist under neutral conditions. 



A COMPUTER-BASED GLOBAL PROCEDURE 



A procedure for hindcasting and forecasting wave spectra over the world 

 ocean is under development. It will include many of the results described above 



506 



