I WARM AIR+ COLD S U R F A C E = A D V E C T I N FOG 



Figure 3-7. — Advection fogs. 



able heights, obscuring buildings, radio masts, and other high 

 objects. With high winds all traffic becomes impossible. The 

 driven snow penetrates all types of buildings and equipment. 

 The natives remain in their huts until the urga, as the blizzards 

 are known, have blown over. These storms explain the poor 

 visibility recorded at Chelyuskin in the colder months. The loca- 

 tion of this station exposes it to frequent winds of sufficient veloc- 

 ity to cause almost continually blowing snow. 



FOG 



In many respects fog is the most important of the weather ele- 

 ments limiting aviation in the arctic regions. Over a large por- 

 tion of the northern seas, fog may be expected to occur 90 or more 

 days each year, and over small areas as many as 180 or more days 

 each year. Any analysis of fog in the Arctic is rendered difficult 

 due to the carelessness in defining and recording fog and to the 

 lack of observational reports over large areas. 



Two types of fog are frequent in the Arctic. The most com- 

 mon type is advection fog, formed when relatively warm air moves 

 over a cold surface. A further condition is a fairly stable strati- 

 fication of the air which would limit the increment of visible 

 water vapor to the lowest layers of the atmosphere. Turbulence, 

 whether convective or frontal in nature, is conducive to the forma- 

 tion of clouds but not of fog. The areas where conditions are 

 most favorable for the formation of advection fog are the open 

 waters of the Kara, Laptev, East Siberian, and Chukchi Seas dur- 

 ing the summer. Fifteen to 20 days monthly with sea fog dur- 



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