Air-Sea Intevaotions ; Pvogram at IMST 



As discussed in our previous publications (Coantic [ 1968] , Coantic 

 et al. [ 1969]), and in Part III of the present paper, the preceeding 

 considerations have been the basis for the settling of our research 

 program and the design of our simulation facility. Some aspects of 

 the problem are already being the subject of theoretical investigations, 

 which we shall now mention shortly. 



2. Wave and Current Generation by Wind 



The transfer of mechanical energy from air to sea has two 

 main consequences: the development of currents and turbulence in 

 the upper ocean, and the generation and amplification of waves. This 

 latter process can be broadly described as follows: the turbulent 

 atmospheric boundary layer exerts on the water surface normal and 

 tangential stresses, with steady, periodic and random components. 

 As a consequence of these stresses and of the gravity and capillarity 

 restoring forces, motions of a wavy character are generated at the 

 interface. As soon as their amplitude becomes appreciable, non- 

 linear effects are developed, which result In a modification of the 

 airflow structure and, hence, of the applied stresses, the existence 

 of a continuous wave spectrum and the production of turbulent energy 

 In the sea. The wave amplitude Is then limited by the dlsslpatlve 

 action of turbulence and viscosity. 



As mentioned earlier, the understanding of this complex 

 mechanism Is essential to elucidate, not onlv the dynamical, but 

 also the thermodynamical aspects of air-sea interactions. A careful 

 study has, accordingly, been undertaken (Ramamonjlarlsoa [ 1969, 

 1970] ) , first of existing theories (based on models proposed by 

 Miles and Phillips) and later on of more recent developments In the 

 researches of Stewart, Mollo-Chrlstensen, Longuet-Hlgglns , 

 Hasselmann and Reynolds, among others. This helped us In Identify- 

 ing some points that have to be subjected to experimental study, 

 namely: the existence of separation after the wave crests, the phase 

 shift between surface pressure and elevation, the spatial and temporal 

 variations of Reynolds stresses, and of the turbulent structure of the 

 flow in general. Our future measurement program has been estab- 

 lished In consequence, taking advantage of the possible use of the 

 space-time correlation technique, and of numerical data processing 

 methods to separate the "mean, " the "phase average" and the "tur- 

 bulent" parts of each variable. 



3. Interaction of Turbulent and Radiative Transfers 



Another typical example of reciprocal interactions between 

 the various modes of energy transfer near the air-sea Interface Is 

 the simultaneous transport of sensible enthalpy by turbulent con- 

 vection, and by infrared radiation. The turbulent heat flux Is 

 usually assumed constant with height In the atmospheric surface 

 layer. However, the validity of this hypothesis Is known to be 

 questionable, due to a possible vertical variation of the Infrared 



41 



