52 



there is a clear relation between wind shear and wind speed but I am not 

 sure that it is a linear one. In addition, there is also a substantial 

 scatter caused by the thermal stratification as is indicated by the different 

 notations. Under stable conditions, the wind shear recorded with a certain 

 wind speed is distinctly greater than with adiabatic or unstable stratifica- 

 tion. Thus, for the height level z = a, we may write 



9u/az = f,(u ,Ae ) 



a 1 a a 



(6) 



if we try to be exact. Replacing the wind shear simply by the wind speed 



as it is usually done, would introduce an error which depends on stability. 



To avoid it, we must determine the function f (il F ) 



1 a a 



Similar relationships can be found for the potential temperature 

 and the humidity of the air. Figure 9 provides some evidence on the relation 

 between temperature gradient and temperature difference air-sea. Again a 

 definite - certainly non-linear - functional relationship is indicated, 



fi,-«. 



Figure 9. Vertical differences in potential air temperature 10~ 1 

 between the 10 m and 1 m levels as a function of potential temperature 

 difference air-sea AG and grouped according to the wind speed ui, measured 

 at )+ m height (from Brocks, 1963). f q. 



