From these data the ice potential has been calculated by the method of 

 Defant and the results shown in Table 2A, Finally, the ic® potential 

 curve for Station 37 is shown in Figure 2„ It will be noted that the 

 ice potential curve is by no means a straight line or a smooth curve. 

 In fact, for this station, the heat loss necessary to form a given 

 amount of ice varies considerably. For this reason, the actual fore- 

 casting for this station is difficult, for a small additional heat loss 

 at about 2 kg. cal. causes the formation of a large amount of ice. In 

 this respect the example shown is not typical of may stations where 

 the ice potential curve is quite regular and smooth j however., it is 

 included to illustrate the kind of difficulties encountered in practice. 

 In addition, the curve is atypical because Q , the heat loss necessary 

 to bring about formation of ice was found exactly at 25 meters when the 

 temperature of the completely mixed layer (1-4, Table 2B) first dropped 

 to -1.8° C. In general, Q cannot be so easily determined. 



C* METHOD OF COMPUTING DATE OF ICE FORMATION 



There are two acceptable methods of computing the date of ice 

 formation. Since the amount of heat that must be lost before ice is 

 formed is known from the ice potential computations, it is only necessary 

 to compute the time required to lose this heat. One method is to make 

 actual observations of the heat loss per day per square cm, and thus to 

 find the mean heat loss which is representative of a given area. The 

 other method is to compute the total heat loss by consideration of the 

 climatological data, the sun's altitude, and oceanographic data. For 

 this purpose the only known formulas are those of Jacobs (1942), which 

 yield rates of heat loss of the right order of magnitude in the Arctic, 

 although they were specifically derived for middle latitudes. 



Jacobs' formulas for computing heat losses aret 



Q ab = .025 a [.29 +.71 (!-_£_)] ft- r)t,t in minutes (4) 



Qb= .94 [eff. Qb U- .0083c}] 

 Q e = 145.4 w(e w -e a )| j+ #0 1 



u 



t in minutes (5) 



fTw- 



Jkllt , t in days, ( 6 ) 



*■ "w ™ 



@oiJ 



where 



2 



Q . = total Incoming radiation- in gm, cal/cm, 

 ab ? 



Q. - total back radiation in gra. cal/cm. ~ 



q - total heat loss due to evaporation in gm, cal/cn 



cc a mean altitude of the sun in degress, 



c «■ mean cloud amount in percent, 



W ■ mean wind velocity in knots, 



