As we shall later see, a certain amount of salt enters the atmosphere as a result of the 

 freezing process when ice crystals are separated and blown off the surface of sea ice. 



The evaporation is especially complicated by the processes that accompany the phenomenon, 

 and therefore, not only are theoretical investigations of it extremely difficult, but also direct 

 measurements. Indeed, it is impossible to construct instruments which would completely repeat 

 the natural conditions. This explains, among other things, the numerous empirical formulae sug- 

 gested for evaporation and the diverse calculation of results based on them. 



UTERATURE: 62, 77, 108. 



Section 16. Evaporation of Snow 



In table 13 are presented data calculated by Schaffernak for the evaporation of snow and 

 water; the calculation was carried out in 1914 in Munchen in similar climatic conditions. The 

 evaporation of water and snow is expressed in millimeters of water column. It is seen from the 

 table that the evaporation of snow is more than twice greater than that of water. 



TABLE 13. EVAPORATION OF SNOW AND WATER IN IDENTICAL CLIMATIC 



CONDITIONS IN JANUARY 1914 (EVAPORATION EST MM OF WATER 

 COLUMN) 



It is evident that snow evaporates in any season of the year when its temperature, for one or 

 another reason, is higher than the temperature of the air stratum contiguous to it. A moisture 

 deficit and convection are then created in the air that is heated by snow, which leads to evaporation. 

 This is, as always, intensified by wind. The evaporation reaches high values when thaw or a sharp 

 rise of snow temperature is followed by cold weather and the air is little saturated with moisture. 

 In such cases, the radiational fog resulting from intense evaporation is frequent. It is evident that 

 evaporation diminishes as the surface of snow is cooled by evaporation, convection and reradiation. 



The evaporation of snow is of special significance in spring and summer during stabilized 

 anticyclonic weather. Dispite its high albedo, snow is continually heated by incident and diffuse 

 solar radiation, through which the temperature difference needed for evaporation is preserved. At 

 night, with the cessation of solar radiation, the evaporation ceases. Before the simrise, such 

 cases, especially in calm weather, are characterized by using radiational fog which may sometimes 

 completely disappear during the day. 



LITERATURE: 62, 77, 140. 



34 



