Aiv-Sea Interaotions ; Program at IMST 



Fig. 3. Relative vertical variation of the turbulent heat flux, for 

 various atmospheric situations 



4. Water Vapor Turbulence and Its Measurement 



The turbulent transfer of humidity in the lowest atnnospheric 

 layers is, as mentioned earlier, one of the principal mechanisms 

 for the exchange of energy between air and sea. In addition, this 

 process governs the mean distribution and turbulent structure of 

 specific humidity in the lower levels, and thus exerts an essential 

 influence on electromagnetic wave propagation. Therefore, the 

 contemplated studies require the measurement of humidity fluctu- 

 ations , whose levels and scales have to be estimated to delineate 

 suitable measuring devices. 



This estimation has been obtained by: a) studying the equa- 

 tions governing the mean distributions, turbulent fluxes and levels 

 of fluctuations of humidity b) examining the known experimental 

 data; and c) predicting the form of the spectrum from the Kolmogorov- 

 Obukhov theory (Coantic and Leducq [ 1969]). Figure 4 compares the 

 predicted spectral behavior of turbulent humidity fluctuations (after 

 some shift towards lower frequencies), and recent measurennents by 

 Miyake and McBean [ 1970] . Considering the experiinental under- 

 estimation of the high frequency part of the spectrum, the overall 

 agreement is not too bad. 



Once the estimate is made, it is then possible to define 

 specifications for devices nneasuring humidity turbulence, for use 

 either in the field or in the laboratory (see VI. 3). 



43 



