k2. 



checked every possible influence carefully, stated that this deviation was 

 not caused hy any instrumental or observational error. They were led to 

 believe that the structure of the air flow over the undulating sea surface 

 is different from that over land or along a solid wall. Theoretical argu- 

 ments (Miles, 1957; Stewart, 196I) also suggest the existence of a critical 

 layer in the wind profile over waves where the wind speed is equal to the 

 phase velocity of the waves. Stewart predicts a nonturbulent, organized 

 and wave-like motion below that level which is connected with a reduction 

 of the turbulent stress and wind shear. At present it is yst too early to 

 interpret the kink recently found in vertical wind profiles over the sea by 

 referring to Miles' and Stewart's critical level. A systematic investiga- 

 tion of the fluctuations of flow, both immediately above the sea surface 

 and at it, is necessary in order to bring this problem nearer to solution. 



Before leaving this subject of vertical wind profiles over water let 

 us cast a short glance at a diagram ( Figure 6) which summarizes the results 

 obtained from log-profiles by applying the turbulent boundary layer concept. 

 Under adiabatic conditions those profiles yield corresponding values for 

 the aerodynamic roughness Zq and for the friction velocity u* which is 

 defined as the square root of the ratio surface wind stress t by air 

 density p . 



In the diagram zq is plotted as a function of u^. We are confronted 

 with a very confusing result, because some evidence for a decrease of zq 

 with growing u^<. can be found as well as some proof for its increase with 

 growing u* or its constancy. Thus we must state that this relationship 

 is by no means well understood at present. Even the physical meaning of 

 the so-called roughness parameter Zq is obscure. In the boundary layer 

 theory Zq describes the scale of turbulence at the level where the mean 

 wind speed u is equal to zero. Remember the well-known log-profile of 

 wind speed 



u z + z 



* In 



F" Zq 



(1) 



where u = for z = and the turbulence present at this level is described 

 by the mixing length 1 = k zq (k = von Karman constant). At sea there is, 

 in general, no level at which the mean wind velocity u = 0, since the water 

 surface itself may move with appreciable speed (by about h percent of the 

 wind speed taken at 10 m) . Thus, the boundary layer model needs considerable 

 amendment and refinement in order to be applicable to the complicated 

 mechanism of air-sea interaction. 



The results presented so far referred to the adiabatic wind profile. 

 Regarding the wind profile i:mder nonadiabatic stratification very little 

 evidence is available from the sea which can be compared with the theoretical 

 approaches given by Monin and Obukhov {iS^h) , Ellison (1957), Yamamoto (1959), 

 and Panofsky, Blackadar and McVehil (196O). The reason for this is that, 

 in order to be able to apply these theories, data on the vertical heat flux 

 are needed apart from the simultaneous measurement of the vertical momentum 

 flux and wind profile. It is very difficult to get reliable information 



