Y 2 may be a constant for different wind speeds. However, in the 

 case of the sea surface, the "roughness" is given by the composite 

 wave motion. Since the wave motion is a function of the wind speed, 

 W, (and of the state of wave development), y will probably also be 

 a function of the wind speed. (In the case of stable stratified 

 air, y also depends on the stability of the air stratification.) 



The results obtained by the author in 1948 indicate that under 



normal conditions (with an adiabatic lapse rate in the lowest layers) 



p 

 Y varies inversely proportional to the square root of W, and 



r 2 = 9.0 x 10-3 ( 1 [cm/sec 3 N ^ 



v W .[cm/sec]' 



for winds from 1 to 40 m/sec. Thus, the wind stress at the sea 

 surface (for a fully arisen sea) can be represented by 



T= p» x 0.009 x W 3//2 [dyne/cm 2 ] , (33) 



where W is to be inserted in centimeters per second. 



A comparison of (32) with the corresponding resistance co- 

 efficients obtained from wind profile measurements was made in 

 1951? and the results are reproduced in figure 7> where more recent 



cup anemometer measurements by U. Roll (1948) show again the char- 



2 

 acteristic discrepancy between the y values as derived from "slope" 



observations and from wind profile observations. By disregarding 



the results based on "slope" observations at wind speeds of less 



than 10 m/sec, and replacing them by the results of the inadequate 



2 

 cup anemometer measurements, a "jump" of y from low to high values 



appears erroneously at 10 m/sec wind velocity. 



A critical review of the accuracy and a summary of the results 



obtained by different methods, including wind slope observations 



in wind tunnels has been recently made by R. B. Montgomery (1952). 



39 



