Evaporation from the Surface of the Sea and the Water Budget of the Earth 225 



could give only an estimated value for the heat contribution to be ascribed to convective 

 processes, v^hich was based principally on Angstrom's investigation. This quantity 

 was finally assumed to be about one-tenth of the heat available for evaporation, so that 

 a heat amount of about 0-119 g cal cm~^ min"^ must be available for evaporation. 

 The estimation of the convectional flow discussed on p. 92 led to a value of 

 about 20gcalcm-2day"^, i.e., about 0014 g cal cm-^min-^ The agreement 

 with the value assumed by Mosby is rather good, but this estimate applies 

 only to temperate latitudes and the value should be increased for warmer 

 climates to 0-030 g cal cm ~-min~^ Choosing a mean value of about 0-022 

 g cal cm"2 min-^ then the amount of heat available for evaporation will be 0-1 II 

 g cal cm~2 min~^. Since the evaporation of 1 cm^ of water requires approximately 

 590 g/cal this latter value gives a mean evaporation of 97 cm a year, while Mosby's 

 value is 106 cm a year. The accuracy here is also scarcely more than 10%. These 

 values are in good agreement and within the limits of uncertainty of the value derived 

 by Wiist. 



Another possibility for determining the value of R was pointed out by Bowtn 

 (1926). For identical eddy coefficients for the diffusion of water vapour and the turbu- 

 lent conductivity of heat, the upward flux of the latent energy of water vapour and 

 heat are given by 



0-621 de ^ d§ 



Q, = -L -y- A -j-_ and Qn = -c^ A ^- 



(see p. 92 concerning the latter equation). 

 From these equations it follows that 



O, 0-62 IL dejdz ' 



Putting p = 1000 mb and L = 585 and replacing the differentials by corresponding 

 finite differences the Bowen ratio is obtained: 



R = 0-64 -^ 



es - ea 



where t?, and '&a denote the temperatures of water and air and e^ is the maximum 

 vapour pressure of water at temperature 'Og and e„ is the actual vapour pressure in the 

 air. Jacobs (1942, 1943) has determined the dependence of the Bowen ratio on latitude 

 in the North Atlantic and the North Pacific and found that R decreases with latitude. 

 The following values were found as the mean for both oceans: 



The northward increase is an effect of the continents from which the cold air flows out 

 over the warm sea in the winter. In the Southern Hemisphere this effect is missing 

 so that R may increase only to about 0-25 at 70° S. 



By making proper use of all observations and methods which were more or less 

 independent on each other, WiJST (1954) has evaluated a mean meridional distribution 



