Section 17. The Effect of Evaporation and Condensation 

 on Sea Temperature 



Evaporation is accompanied by an increase in salinity and a drop in temperature of the sea 

 surface. Condensation is accompanied by dilution and a rise of temperature. * 



It is evident that the role of evaporation and condensation in the heat balance is considerably 

 increased if it is associated with individual areas. Especially for the arctic the processes are of 

 paramount significance. 



In this connection it is necessary to examine at the beginning the local processes of evapora- 

 tion and condensation, i.e. , the processes occurring without heat exchange with the adjacent 

 areas . It was stated above that equilibrium cannot exist in areas where the water and ice come in 

 contact. Evaporation prevails all the time above the water, and condensation above the ice. In 

 consequence, fog is found more frequently over areas of scattered ice and here the fog is denser 

 than over areas with open water or over concentrated ice. The local evaporation and condensation 

 further, evidently, the cooling and heating of the sea and the destruction and melting of ice, but the 

 amount of heat is not changed. The advective heat brought into the arctic from the adjacent land 

 and sea areas is of great significance in this respect. 



Indeed, when warm and moist air is brought into the cold arctic areas, notably in areas that 

 are covered by ice, large quantities of heat which have been accumulated in lower latitudes at 

 evaporation are liberated in the process of condensation. 



The statement can be confirmed by the following example. In order to cool 1 m^ of air 

 saturated with moisture, the initial temperature of which was 10° to 0°, it is necessary to 

 obtain 5, 850 g-cal from the air, which suffices to diminish the thickness of 1 m^ of ice by 

 more than 1/2 cm. 



It is evident that the warmer and moister the air, and the stronger the wind, the more in- 

 tense is the heating of the sea and the melting of ice . 



If the qualitative aspect of the influence of evaporation and condensation on the regimen of the 

 arctic is indubitable, then the quantitative calculations can hardly be carried out at the present 

 time, first, due to the absence of sufficiently dependable formulae and, secondly, due to the ab- 

 sence of pertinent observations in open portions of the sea. 



Personally, I assume that the following formula can be used for an approximate evaluation 

 of evaporation in the sea. ** 



£=0.1(^^ — Ow. 

 where E = evaporation in 24 hours expressed in mm. 



*The change of salinity caused by evaporation is considerable in certain sea areas, for in- 

 stance, in the Mediterranean and Black Seas. However, the effect of these changes can in no way 

 be compared to the heat value of evaporation and condensation for the regime of the World Ocean 

 and for the climate of the earth. 



**This formula was derived by a rough simplification of the theoretical formula by Sverdrup 

 and by a few calculations . 



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