Observations and Measurements of Ocean Waves 



45 



of the wind velocity and the corresponding maximum and minimum wave 

 height. From this table it is easy to see that the deviation is quite large for 

 each group. Figure 27 is a graphic presentation of these average values and 

 the values given by Cornish in Table 5. Cornish's values are distributed 



1 + V. Cornish 



• *•— E. Zimmerman 



Fig. 27. Relationship between wave height h and wind velocity w for well-developed ocean 



waves __| \. f according to Cornish; , according to Zimmermann (averaged 



from observations); , 6=1/3 v. 



along a straight line which passes through the origin. The inclination coeffici- 

 ent is about 48 and a little larger than the average value given by Cornish 

 previously. The heavy solid line corresponds to the equation h = \i\ which 

 can be used for wind velocities below 6 Beaufort. Similar values were observed 

 in the Baltic (Bruns, 1936). 



A distinct effect of the thermal stratification on the waves has been found 

 in wave measurements on ocean weather ships (Roll, 1952; Brown, 1953), 

 at lakes (Burling, 1955) as well as in laboratory experiments (Francis, 1954). 

 Appreciable temperature differences between air and water (e.g. the air 6°C 

 colder than the water) are connected with greater wave heights (approx. 22 %) 

 and greater wave lengths (approx. 15%) as compared to equal temperature 

 conditions in both layers, with the same wind velocity. These differences 

 are certainly caused by the unstable stratification of the air above the water, 

 giving rise to strong turbulence and small vertical wind shear. Thus, the 

 wind forces can exercise a greater influence on the surface of the sea. 



