INTERACTION BETWEEN THE ATMOSPHERE AND THE OCEANS 227 



from the west carrying cold continental air, whereas on a western coast 

 the winds, while also blowing from the west, carry relatively warm 

 maritime air. Thus, in middle latitudes, the waters off the continental 

 east coast are in winter much warmer than the air, but off the west 

 coast the waters may be colder. Consequently, one must expect that in 

 winter the evaporation in middle latitudes is localized, taking place 

 primarily off the eastern coasts of the continents. The above reasoning 

 applies equally well to the amounts of sensible heat given off from the 

 ocean; that is, in middle latitudes, in winter, heat is conducted from the 

 oceans to the atmosphere mainly off the east coasts of the continents. 

 The condensation of water vapor in the atmosphere is one of the major 

 sources of heat supply to the atmosphere as a whole (p. 5), and in 

 middle and high latitudes is probably the major one, particularly in 

 winter. Since evaporation is localized, it seems reasonable that conden- 

 sation is also localized, so that the regional heat supply to the atmosphere 

 depends upon the interaction between the sea and the atmosphere. 

 Both the major features and the details of the atmospheric circulation 

 are dependent upon where the supply of energy takes place, and it 

 follows therefore that the weather over wide oceanic areas and on coasts 

 and even over inland areas must reflect the results of the interaction. 



The conclusions as to the localization of the regions of maximum 

 evaporation and heat transfer have been confirmed by Jacobs for the 

 North Atlantic and the North Pacific. It was shown (p. 61) that both 

 evaporation and heat transfer can be computed from meteorological data 

 and sea surface temperatures, provided that certain results in fluid 

 mechanics are applicable to the air flow directly over the sea, and that 

 the results of a few measurements of humidity gradients over the sea 

 can be generalized. The evaporation, E, can be derived by the 

 formula 



E = k{e,o - ea)W, 



where e-w is the vapor pressure at the sea surface, Ca is the vapor pressure 

 in the air, and W is the wind velocity. 



The evaporation can be expressed as the thickness of the water 

 layer which evaporates in a given length of time, such as centimeters of 

 water per day, or in units of heat required for the evaporation from a 

 given area in a given time, such as gram calories per square centimeter 

 per minute or per day. If the evaporation is expressed as heat, Qe, the 

 corresponding amount of heat given off to the atmosphere, Qh, is (p. 63) 



e^v — Ca lUUU 



where ??„, is the surface temperature of the water, d-a is the temperature 



