During the fall and winter, the fogs appeared to occur most 

 frequently with south or southwest winds. This would indicate 

 that the stable conditions in which the fog occurs are associated 

 more frequently in this portion of the arctic region with the great 

 Asiatic Anticyclone than with the Arctic Anticyclone. However, 

 considerable variability may be expected from year to year with 

 the varying strength of the two anticyclonic systems. 



Fogs are not to be expected in summer with offshore winds, 

 as a rule. The offshore winds are generally dry and are not cooled 

 sufficiently to cause the formation of fog. 



Summer fogs are most frequent with light winds, but may occur 

 with winds of high velocity under favorable conditions. Since 

 they are advection fogs, they do not form readily in calm weather. 

 The opposite is true of the mists or frost fogs of the winter season. 

 These latter are radiation fogs and form most readily in calm 

 weather or with very light winds. High winds are very unfavor- 

 able for the formation or continuation of fog in the colder months 

 of the year. 



Fogs in the arctic region are more frequent in the late night 

 and early morning hours than at any other time. In discussing 

 the fogs of the Kara Sea region, Vize has noted that the maximum 

 frequency of fogs occurs at midnight or in the hours immediately 

 following, and that the minimum frequency occurs at noon or in 

 the hours immediately following. This agrees closely with ex- 

 perience of the Maud in the East Siberian Sea. 



Data on the diurnal distribution of mist, or frost fogs, are not 

 so conclusive, but indicate a similar distribution to the summer 

 advection fogs. The data from Aklavik indicate that frost fogs 

 are much more frequent in the early morning than at noon or in 

 the evening. It is the common practice in these regions to limit 

 aviation activities to the late morning or afternoon hours. It is 

 particularly important that all flights terminating in the lower 

 Mackenzie, the Yukon, or the Lower Lena River valleys during 

 the winter season be so planned that they are completed at midday 

 or in the afternoon. 



CLOUDINESS 



In general, cloudiness over the arctic regions is greatest in 

 summer and fall and least in winter and spring. This statement 

 should be modified slightly when dealing with specific locations. 

 Those localities in the Arctic Ocean or under the immediate in- 

 fluence of the ocean circulation will have the maximum cloudiness 



117 



