COMMON CHARACTERISTICS 



Regardless of the criteria used for the various definitions, there 

 are certain characteristics common to the region. These are : 



1. Short cool summers. 



2. Long cold winters. 



3. Low annual mean temperature (23° F. or minus 5° C). 



4. Long periods of semi-darkness. 



5. Periods of continual daylight and darkness. 



6. Absence of forests. 



7. Freezing in winter of lakes, rivers, bays, and parts of the sea. 



8. Scant precipitation. 



9. Low absolute humidity. 



10. Low evaporation rate. 



11. Moist soils when thawed. 



12. Presence of permanently frozen ground. 



13. High windchill factor. 



14. High latitude position. 



Other phenomena found in the Arctic include the aurora bore- 

 alis, mirage, increased visual and auditory perception, glare, fog, 

 and the magnetic pole. 



In the matter of darkness it should be noted that, although there 

 is no direct sunshine in the winter above 74° N. latitude, there 

 are long periods of moonlight, with the snow and ice acting as 

 good reflectors for the light from stars, the aurora, and the mioon. 

 However, the reflected light is diffused and as there are no clear 

 shadows it is difficult to judge size and shape of objects. Under 

 such conditions, fliers have trouble in judging the surface of 

 the ground. 



The aurora borealis is a useful source of winter light but it is 

 not regular and dependable. The area of maximum frequency 

 is oval-shaped around the northern geographical and magnetic 

 poles. Discussion of the effect of aurora upon communications 

 is included in chapter 3, Part IL 



The long summer daylight does not mean that there is good 

 visibility. Fog is especially prevalent in the spring and summer. 

 The fog is mainly along the coasts where the warmer continental 

 air passes over the cold arctic waters, and is frequently concen- 

 trated in the lower levels, a few feet above the surface. Fog is 

 also produced by communities and encampments of men, by power 

 plants and airplanes. In the Mackenzie delta area, the black fog 

 occurs, especially in March, making flying very hazardous. Some 



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