were determined quantitatively. These define also the sum 



S. + S but the further separation into the individual 

 in as ' ^ 



contributions S. and S, shown in Fig. 8 is somewhat specu- 

 lative. Fortunately, the ambiguity is somewhat restricted in 

 this case by the side condition that the total momentum trans- 

 ferred from the atmosphere to the wave field cannot exceed the 

 total momentum transferred across the air-sea interface, which 

 is reasonably well known from flux measurements in the atmos- 

 pheric boundary layer (also made during JONSWAP). Assuming 

 negligible energy dissipation in the main part of the spec- 

 trum, as in Fig. 8, the net transfer of momentum from the 

 atmosphere to the wave field is found to account for 50% ±30% 

 of the total momentum lost from the atmosphere. (Since the 

 ratio of momentum to energy for each wave component is equal 

 to k/co , the spectral momentum transfer to the waves is 

 given by S^ 'k/cu • A cos ^ 9 angular distribution was 

 assumed in carrying out the integration.) Dobson (1971) and 

 Synder (personal communication) also found that a major part 

 of the momentum lost by the atmosphere enters the wave field. 

 If dissipation is added to the energy balance, the atmospheric 

 input has to be increased accordingly in order for the sum 



S. + S, to remain constant. Clearly, a very large dissi- 

 m ds ' ° 



pation is not acceptable within the limitations set by the 

 total transfer across the air-sea interface. 



25-23 



