Section 69. Radiation Properties 



The ice crystals are uniaxial and positive. Therefore, the speed of extraordinary rays in ice 

 is greater than the speed of ordinary rays and hence the coefficients of refraction are greater. * 



The coefficients of refraction of ice are very close to the coefficients of refraction of water. 

 Water and ice also differ only slightly in their absorption coefficients and because of this, ice is 

 very similar to water in its optical properties . 



Other radiation properties of snow and ice are more important. 



The great ability of snow to reflect radiant energy (albedo) has already been noted. This is of 

 especially great significance to ice cover inasmuch as the latter is always covered on top by a more 

 or less thick layer of snow. Kalitin's special investigations show that the reflecting ability of snow 

 is greater, the more pure and fine the snow is and the lower its temperature. Thus, the albedo of 

 newly fallen pure snow attains 90 per cent and the albedo of melted and granular snow (after a warm 

 spell) decreases to 52 percent and lower. 



Recently many observations of the albedo of sea ice, snow, and on the penetration of solar 

 radiation have been conducted under natural conditions at different polar stations of the soviet sec- 

 tor of the arctic, namely at: Uedineniie Island, Cape Cheliuskin, Tiksi Bay, Tikhaia Bay, and Cape 

 Schmidt. 



As a result of a breakdown of these observations, Chernigovskii gives the following table of 

 albedo for snow cover and ice, free of snow, by months, for the northern latitudes from 69° to 

 80° (table 53) . 



TABLE 53. THE APPARENT VALUE OF SNOW AND ICE 

 ALBEDO IN ARCTIC SEAS IN PER CENT 



Month 



March 

 April . 

 May . . 



June . . 

 July . . 



Snow 



87 

 87 

 83 



80 

 60 



Ice 



40 

 45 

 Along an offshore strip the albedo of 

 45 I snow cover is about 70 per cent in 

 50 I June and about 50 per cent in July. 



Kalitin conducted investigations of the passage of radiant energy through snow covers of 

 various thicknesses. Figure 59 shows the results of these investigations. The upper curve deals 

 with snow having a temperature below 0°, i. e. , with dry snow. The lower curve deals with melting 

 snow, soaked with water. Both curves are constructed taking into consideration the reflecting 

 ability of the snow, in other words, taking into consideration only the radiant energy which had 



*In uniaxial crystals (into which category fall ice crystals) , the incident ray is divided into 

 2 rays during refraction; the ordinary — in which the ratio of the sine of the angles of incidents and 

 refraction is equal to the refractive index, and the extraordinary— for which this ratio has no 

 physical significance. When the index of refraction of an extraordinary ray is mentioned, it is 

 understood to mean the maximum deflection of an extraordinary ray. 



175 



