II. INTERCHANGE OF PROPERTIES BETWEEN 



SEA AND AIR 



3. SMALL-SCALE INTERACTIONS 



E. L. Deacon and E. K. Webb 



A knowledge of the rates of exchange of energy between sea and atmosphere 

 is a fundamental requirement for a proper understanding of the general circula- 

 tion of atmosphere and ocean, and of the way in which air- and water-masses 

 undergo modification of their characteristics in moving about the globe. One of 

 the main objectives is to arrive at relationships which would permit computa- 

 tion of the transfer rates of sensible heat, latent heat and momentum from the 

 meteorological elements routinely recorded on board ship, that is, from air 

 temperature and humidity, wind velocity and sea-surface temperature. 

 Fortunately this is a practicable objective, whereas over land the complexities 

 of surface conditions and topography are such that the simple meteorological 

 elements are much less informative. The fact that the observations at sea have 

 this great utility additional to their normal meteorological significance makes 

 it necessary to strive for continued improvement in the standard of accuracy of 

 observations at sea. 



The methods by which the transfers may be measured and the main results 

 so far obtained are outlined in the following pages. The accent is placed here 

 on small-scale interactions, i.e. events taking place in the layers from sea surface 

 to some 10 or 15 m height. Although, as will be seen, useful progress has been 

 made in recent years, much remains to be done to establish relationships of 

 satisfactory precision. 



Considerations of the heat income available for evaporation and sensible- 

 heat transfer applied to suitable large oceanic areas have given a foundation on 

 which it has been possible to build useful first approximations to the geo- 

 graphical distributions of these transfers and their seasonal variations (see e.g. 

 Jacobs, 1951, 1951a). Further progress in this direction awaits more detailed 

 knowledge of transfer processes as well as more accurate measurement of the 

 radiant energy income of the sea. The work considered in the following pages 

 has all been directed to the problem of steady-state wind and sea conditions ; 

 unsteady conditions are not dealt with, not because they are unimportant, but 

 because they have not as yet been studied. 



1. General Considerations of Transfer 



The transfer of such an entity as heat from the sea surface to the atmosphere 

 is effected in the first place by purely molecular diffusion through a film of air 



[MS received Juhj, 1960] 43 



