2. Snow density 



The factor next in importance to snow thickness In determining ice 

 thickness growth with time is snow density,, In Figure 4 the initial 

 ice thickness is 4$. 7 cm«, the ice increment 22.8 em., snow thickness 

 7.6 cm. and snow density varies from 0.2 to 0,8. Curve (l) of Figure 

 4 shows the time required to add this ice thickness increment of 22.8 

 cm. with varying snow density. The time diminishes rapidly at a non- 

 linear rate up to a density of 0.5» where it becomes more nearly linear 

 and diminishes slowly up to the maximum density of 0.8s, In going from 

 a density of 0.2 to one of 0.5 the time diminishes from about 35 days 

 to 16 days to add on the ice increment of 22.8 cm. When the density 

 changes from 0.5 to 0.8, the time drops only about 2 days, from 16 to 14 



Curve (2) shows the amount of time that is added by the snow layer 

 alone. This curve shows that the snow contributes a much higher per- 

 centage of the total time at low snow densities than at high densities. 

 At low snow densities the snow layer contributes about 63$ of the total 

 time while at high snow densities it contributes only about 10$ of the 

 total time. 



3. Air and Equivalent Temperatures 



The next meteorological factor to consider is 0-Te+2E /cc c$ which 

 is the sum of the air temperature and the net temperature change due to 

 the heat exchange at the surface of the snow or ice. The quantity 5E G J/£ C 

 is analyzed and derived above. Figure 5 shows the effect of a change c 

 in © } both for ice formation in salt water (curve 1) (equation 22) and 

 in fresh water (curve 2). Curve 3 indicates the change in time for ice 

 growth in fresh water due to changes .in snow thickness^ The vertical 

 scale indicates the time in days required to add ice thickness increments 

 of 2 centimeters. 



Curve 1 indicates the nonlinear nature of the variation of time with 

 ice thickness for different values of snow thickness on salt water ice. 

 The slope shows a definite Increase with increasing thickness of ice. 

 It requires approximately 35 days to add 14 cm. of ice under the indicated 

 conditions with © ■« -10°C, and approximately 12 days with - -30° C. 

 Curve 2 indicates the variation for fresh water under the same conditions. 

 It is seen that the growth of ice in fresh water requires slightly less 

 time than in salt water under the same conditions. Curv e 3 indicates) the 

 variation in time for ice growth in fresh water for different ' snow thick- 

 nesses. 



4. Initial Ice Thickness 



The next parameter to consider is that of initial ice thickness (£ ), 

 Figure 6 shows that the variation in ice thickness growth with time is 

 linear for constant values of initial ice thickness. Greater values of 

 ice increment result from lower initial ice thicknesses. The relative 



16 



