2. There are two situations in which the normally prevalent low 

 stratus can be expected to be absent. One is on the front side, 

 near the middle of high pressure ridges, where there is marked 

 divergent circulation. The other, less frequent, is in the relatively 

 dry continental arctic air moving southeast from the Beaufort Sea 

 area, prior to its picking up moisture in the maritime archipelago. 

 This second situation is due partly to divergence, although the lack 

 of moisture in the air mass in general is the major factor. 



3. Broken layers of altocumulus clouds, usually mixed with much 

 altostratus, are present a long distance behind fronts in the arctic 

 areas. This is due to the usual shallowness and great homo- 

 geneity of the air masses behind the fronts in the Arctic. The 

 broken layers of clouds are connected either with cold fronts or 

 occlusions that are part of the systems that stagnate in the Baffin 

 Bay area in summer. In autumn they lie to the north of the cold 

 fronts that develop between the polar air masses of central Canada 

 and the arctic air masses formed over the ice pack to the north 

 and west of Canada. The distance behind fronts to which the 

 middle clouds extend varies greatly, and no definite statement can 

 be made without further observation. 



4. Very low stratus, only a few hundred feet above sea level, 

 forms on the sides of hills, due to the radiation effect in combina- 

 tion with the high moisture content of the air near the surface. 

 Moisture is supplied during the summer months by the continuous 

 melting of the top of the permafrost layer. Since continuous 

 observations could not be made in any of the areas where this 

 stratus formed, it was not possible to establish any criteria for 

 the formation and dissipation of these clouds. 



PRECIPITATION AND FOG 



1. Throughout July, and until the latter part of August, drizzle 

 type rain was the prevailing form of precipitation encountered. 

 Commencing in the latter part of August, and from then on until 

 completion of the operation, as the warming effect of the sun les- 

 S3ned and the autumn season replaced summer, temperatures de- 

 creased and snow, instead of rain, become the common form of 

 precipitation. 



2. The type of precipitation experienced was largely in the form 

 of intermittent drizzle, and in almost all cases precipitation was 



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