in the total radiation due to the mean cloudiness, and n is the average 

 cloudiness in percentage. Assigned values of c are .86 for nirabo stratus, 

 stratus and stratocumulus clouds, .77 for altocumulus, and .20 for 

 clrrostratus clouds, from the study of Efimov (1939). The reflection 

 coefficient is taken as a constant equal to 0.65. 



E. EFFECT OF CHANGES IN METEOROLOGICAL AND 0CEAN0GRAPHIC PARAMETERS ON 

 ICE THICKNESS 



1. Snow Thickness 



The factor having the most pronounced influence on the rate of ice 

 growth is the blanketing effect of a layer of snow on the ice surface. 

 A quantitative graphical evaluation of this effect is presented in Figure 

 3. The parameters have been given the following values: 



Initial ice thickness (^) = 15 cm. 



Snow density ( /°o ) - 0.3 

 Wind velocity (v ) « 4.5 m/sec. 

 Air temperature (T ) ■ -20° C. 

 Equivalent temperature (©) = -25°C. 



The rate of growth of the ice for snow thickness § of 0, 10, 20, 30, 40, 

 and 50 cm. is indicated. The following facts are evident from the figure: 



The most rapid ice growth takes place with an Ice surface free from 

 snow. For this surface the most rapid growth takes place with the lesser 

 ice thicknesses. Here a decreasing rate with increasing ice thickness is 

 evident. Upon reaching a thickness of approximately 50 cm. the rate of 

 growth becomes essentially linear but at a much lower rate than in the 

 initial stages. To add this 50 cm. of ice requires about 18 days with an 

 average temperature of -20°C. From this point on, the rate of growth is 

 essentially linear at the rate of about 10 cm, in 8 days. 



A snow layer only 10 cm. thick makes a marked change in the charac- 

 teristics of the rate of growth. To reach a thickness of 50 cm. now takes 

 about 48 days. The ice thickness increase is essentially linear with time, 

 requiring approximately 8 days to produce an increase of 10 cm. in thick- 

 ness. 



With increasing thickness of snow, the ice thickness increase remains 

 essentially linear but with progressively decreasing slope; with 20 cm. of 

 snow it requires about 14 days to add a thickness of 10 cm.} with 40 cm. 

 of snow about 20 days are required to add 10 cm. 5 and with 50 cm. of snow 

 about 32 days are needed to add 10 cm. to the ice thickness. 



14 



