k8 



height, since the high-frequency waves which determine the form drag reach 

 their final state much more rapidly than the low-frequency waves dominating 

 the wave amplitude . 



For the composite wind stress, which is composed of the tangential 

 stress and the form drag, Munk obtained a cubic relationship with the wind 

 speed. This would imply that the total drag coefficient increases linearly 

 with wind si)eed. (The cornresponding straight line is entered in Figure 7-) 

 Thus, at least some theoretical support is provided for this kind of 

 variation of the drag coefficient with wind speed. 



On the whole, however, the state reached is far from being satisfactory. 

 There is a distinct gap between empirical and theoretical work . On one side, 

 theory is not yet able to interpret empirical findings sufficiently. On 

 the other hand, theoreticians penetrate with their reasoning into regions 

 which are not yet accessible to measuring. In the latter respect, I am 

 thinking of quite a number of important papers concerned with the problem of 

 wave generation (e.g. those published by Phillips (1957> 1958, 1962), Miles 

 (1957? 1959, 1962) Hasselmann (1960), and others) which cannot be discussed 

 here. The same is true with regard to the theoretical work recently done 

 by Schmitz (1962) who studied the transfer of mechanical energy at the sea 

 surface. He found for instance, that the equality of the vectors of mean 

 flow on both sides of the sea surface is not a necessary condition (but, of 

 course, a sufficient one) for the continuous transfer of mechanical energy, 

 as it is usually thought. This can also be fulfilled if the mean values of 

 flow in air and water immediately at the surface differ from each other, 

 i.e. if the air glides over the water. 



Thus, a concentrated effort, made both by experimenters and theoreticians; 

 is needed in order to clarify the complicated process of riechenical 'nter- 

 action at the sea surface . 



THE RADIATIVE INTERACTION 



Passing now to a short treatment of the radiative processes in the 

 marine boundary layer we enter a region which can perhaps be characterized 

 best by the statement that here the importance of the subject is only sur- 

 passed by the imperfection and incompleteness of our knowledge about it. 

 Although radiation forms the primary energy source of all processes in 

 atmosphere and ocean, there is an almost complete lack of data measured in 

 the boundary layer air-sea which however are indispensable when the radiative 

 interaction between both media shall be studied. First we need a sufficient 

 coverage of the oceans with climatological radiation data, but in addition 

 to that some current information on radiation for the study of synoptic- 

 scale processes will be necessary, because the empirical formula describing 

 e.g. the effect of cloudiness on the different components of the radiative 

 budget deviate substantially from each other. Laevastu (196O), has certainly 

 taken great care in checking the diverse empiricfil relationships but finally 

 it results that he gets a higher net radiation for the cloudiness of i4-/lO 

 than for a cloudless sky. This is caused by the fact that he assumes a 



