CHAPTER X 



Interaction Between the Atmosphere and the Oceans 



Character of Interaction 



From the preceding discussions of the heat budget of the oceans and 

 the relationship between the prevaiUng winds and the ocean currents, 

 it is evident that the oceans must exercise a profound influence upon the 

 climates of the world and upon the larger and smaller features of the 

 atmospheric circulation which together determine the weather, and that, 

 conversely, the atmosphere controls to a great extent the oceanic circula- 

 tion. The interaction, however, is so complicated that it is as yet 

 impossible to separate cause and effect. 



The ocean currents are closelj^ related to the prevailing winds, and the 

 energy needed for maintaining the currents is derived from the stresses 

 that the winds exert on the sea surface. However, the currents would 

 alter the distribution of density if this distribution were not also controlled 

 by exchange of heat with the atmosphere and by processes of evaporation, 

 precipitation, and radiation. Thus, the approximately stationary dis- 

 tribution of density in the oceans represents a state of dynamic equilib- 

 rium in which changes induced by the action of the winds are balanced by 

 changes related to the processes of heat conduction, evaporation, pre- 

 cipitation, and radiation, all of which are closely related to the state of the 

 atmosphere. It might appear, therefore, as if the oceanic circulation and 

 the distribution of temperature and salinity in the oceans are caused by 

 the atmospheric processes, but such a conclusion would be erroneous, 

 because the energy that maintains the atmospheric circulation is to a 

 great extent supplied by the oceans. It will be shown that this energy 

 supply is very localized, owing to the character of the ocean currents, and 

 that therefore the circulation of the atmosphere, which depends upon 

 where energy is supplied, must be influenced by the oceanic circulation. 

 The reasoning leads to the conclusion that one cannot deal independently 

 with the atmosphere or the oceans, but must deal with the complete 

 system, atmosphere-oceans. This fact has been recognized in oceanog- 

 raphy, where one gets nowhere by neglecting the relation to the atmos- 

 phere, but in meterorology it has not yet received sufficient attention. 



When dealing with the entire system the processes at the boundary 

 between atmosphere and ocean — that is, at the sea surface — must be fully 



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