THE HEAT BUDGET OF THE OCEANS 



69 



center in 47° N and 12° W. The radiation income in that area can be 

 obtained from Kimball's data, and the back radiation can be found by- 

 means of the diagram in fig. 1 1 ; in this region the transport by currents, 

 q^, can be neglected. In fig. 14A are represented the annual variation 

 of the net surplus of radiation, qr, the annual variation of the amount of 

 heat used for changing the temperature of the water, q^, and the difference 

 between these two amounts, qa, which represents the total amount of 

 heat given off to the atmosphere. The greater part of the last amount is 

 used for evaporation, and therefore the curve marked qa represents 

 approximately the annual variation of the evaporation, which shows a 

 maximum in the fall and early winter, a secondary minimum in February, 

 followed by a secondary maximum in March, and a low minimum in 

 In June and July no evaporation takes place. 



summer. 



A B 



Fig. 14. Left: Annual variation in the total amount of heat, ^o, given off to the 

 atmosphere in an area of the North Atlantic (about 47°N, 12° W). Right: Corre- 

 sponding diurnal variation near the Equator in the Atlantic Ocean. For explanation 

 of symbols, see text. 



This example illustrates the method of approach which may be 

 applied, but so far the necessary data for a more complete study are 

 lacking. The result that the evaporation is at a minimum in summer 

 and at a maximum in fall and early winter is in agreement with the con- 

 clusions that were drawn when discussing the process of evaporation in 

 general. 



Diurnal Variation of Evaporation. The diurnal variation of 

 evaporation can be examined in a similar manner, but at the present time 

 suitable data are available only at four Meteor stations near the Equator 

 in the Atlantic Ocean. In fig. 14B the curves marked g^ and q^ corre- 

 spond to the similar curves in fig. 14A, and the difference between these, 

 qa, shows the amount of heat lost during 24 hours, which is approxi- 

 mately proportional to the evaporation. The diurnal variation of 

 evaporation in the Tropics appears to have considerable similarity to 

 the annual variation in middle latitudes, and is characterized by a 

 double period with maxima in the late forenoon and the early part of the 



