Figure 3-9. — Fog trails. 



open water or to obscure landmarks along the airlines. Over the 

 Arctic Ocean they serve the very important purpose of advising 

 the traveler of the presence of open water. They are most notice- 

 able when the temperature contrast between water and air is the 

 greatest, i. e., at extremely low temperatures. In some places 

 steam fogs are so frequent during cold weather as to be a natural 

 part of the landscape. For example, Reykjavik, meaning "Smoky 

 Bay," derives its name from the fact that steam fogs arise from 

 the abnormally warm waters of the bay during extremely cold 

 weather. 



Of special interest is the fact that fog trails are left by airplanes 

 when traveling through the very cold atmosphere of arctic regions. 

 Canadian fliers have reported fog trails 18 miles long in the lower 

 Mackenzie district. Various factors enter into the formation of 

 these fog trails : the amount of condensation nuclei in the exhaust 

 gases; the formation of water vapor in the exhaust gases; the 

 lower pressures set up by the airfoils; and the turbulence set up 

 by the rapidly moving airplanes. It is possible for one airplane 

 to follow another by means of its fog trail. 



The summer sea fogs occur most frequently with easterly winds 

 over the portions of the Arctic north of the Siberian coast. The 

 explanation may be offered that the stable condition necessary for 

 fog formation exists with easterly winds. It was noted from the 

 upper air observations taken on the Maud that the temperature 

 inversion aloft existed most frequently with easteVly winds and 

 that warm air aloft was carried over the arctic seas in a southeast- 

 erly current. The westerly winds were generally uniformly cold 

 at all levels. During the summer, fog occurred most frequently at 

 all but two of the stations with winds from the north to east. The 

 two exceptions were the stations on Great Liakhov Island and 

 Bulun. The latter is an interior station and the former showed 

 considerable variability due to the adjacent land masses. 



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