then, where greater accuracy is required than is available in Figure 13a, 

 recourse must be made to computation. This is not a difficult process, 

 however, using equation (22). As pointed out previously, it is only nec- 

 essary to evaluate first the left and then the right sides of the equa- 

 tion by means of the given meteorological and oceanographic factors, and 

 then divide the left by the right side of the equation to find the time 

 expressed in units of a 24-hour day. 



That this process yields accurate results can be shown by the fol- 

 lowing examples: The observed growth of the ice at Archangel averaged 

 over a 12-year period is shown in Figure 14 and the computed growth for 

 the same period in the same figure. The close agreement is immediately 

 evident. It is to be noted that the meteorological parameters used in 

 the computation of Figure 9 are the same as the observed values and that 

 the air temperature was -20°C„ and the effective temperature -25°C» 



Similarly, the observed ice thickness growth observed on the Denmark 

 Expedition from November 1, 1906, to February 8, 1907, is shown in Figure 

 15 and the ice growth computed by equation 22 is shown on the same figure. 

 Complete meteorological data including humidity, cloud cover and type of 

 cloud, and snow density were not available from the records, but probable, 

 reasonable values were used which resulted in good agreement with the 

 observed ice thickness data. 



More recent ice observation data is that for Padloping Island showing 

 the observed and computed ice growth for January 1949 and January 1950. 

 The observed ice thickness data for this station is shown in curve 1 on 

 Figures 16 and 17. This station is located off Baffin Island, Davis Strait 

 at about 67°N. The weather data for this station were obtained from the 

 Padloping Island Ice Observer's Log, and the snow and ice data from the 

 weather summary. The computed ice growth is indicated in curve 2. The 

 agreement between the observed and computed ice thickness is quite close. 

 The weather, snow and ice data from which the computations were made are 

 indicated on the figures. 



G. EMPIRICAL FORMULAS FOR ICE GROWTH PREDICTION 



Perhaps one of the best known empirical formulas for ice accretion 

 as it varies with time is that of Zubov (1938). It is of the form: 



£ 2 + 50 £ = 8 IT ( 



(26) 



where £ = ice thickness and 

 T = air temperature. 



This expression was obtained by the use of observed data from a particular 

 location with particular average values of the various parameters involved. 



Comparing the results obtained from the use of this equation with 

 observed results obtained at Archangel, averaged for a 12-year period, the 



25 



