Several questions remain unanswered In this descrip- 

 tion. Although the Inferred momentum transfer rate from 

 the atmosphere to the wave field can be shown to scale In 

 accordance with a linear process [53, as predicted by the 

 majority of wave-generation theories, and yields a drag 

 coefficient Independent of wind and fetch, as generally 

 observed, the actual mechanism of wave generation by wind 

 has not been determined. The existence of an asymptotic, 

 fully developed spectrum at very large fetches Is another 

 open point. Without some mechanism for extracting energy 

 from very long waves, the nonlinear transfer would continue 

 to generate longer and longer waves Indefinitely. Possible 

 candidates for a long-wave energy sink are the attenuation 

 by the wind of waves traveling at phase speeds exceeding 

 the wind speed, which has found some support In recent 

 laboratory experiments [51], or the transfer of energy from 

 long waves to very short waves (which lie beyond the range 

 of resonant-Interaction theory) via WKBJ interactions [24]. 

 The latter process Is also relevant for a third unresolved 

 problem, the form of the energy balance at high wavenumbers. 

 Since 70% ±20% of the momentum flux to the waves is trans- 

 ferred to short waves via the long waves and wave-wave 

 interactions, a significant energy and momentum sink is 

 needed at high wavenumbers. Valenzuela (1971) has shown 



25-26 



