in midsummer. Those localities under the influence of th'e ad- 

 jacent continents will have the maximum cloudiness in early- 

 autumn, with a secondary maximum in early summer. 



In the warmer months of the year cloudiness shows a maximum 

 during the daylight hours and a minimum during the night hours. 

 In some months the trend may be reversed and the maximum 

 cloudiness will occur at night. This may be due to the occurrence 

 of fog at night, but further observations are necessary to verify 

 the present data — observations taken over wide areas simultane- 

 ously. During the winter half-year the observed diurnal varia- 

 tion is largely due to conditions of the light, more clouds being ob- 

 served in the daytime or twilight hours than are observed at night. 



The character of the cloud deck is quite different over the Arctic 

 Ocean than over more temperate latitudes. Stratus clouds are by 

 far the most frequent type observed. They cover the sky com- 

 pletely and seem to merge with the snow or ice-covered landscape 

 at the skyline. In the summer and fall the stratus clouds will con- 

 stitute from 70 percent to 80 percent of all clouds observed. In 

 the winter and spring they are not quite so frequent, making from 

 45 percent to 60 percent of all cloud types observed. These pro- 

 portions apply only to conditions over the Arctic Ocean or adjacent 

 seas. Along the coast lines the stratus clouds are slightly less 

 frequent and have a tendency to be more broken up by convective 

 currents, with an increase in the percentage of stratocumulus type 

 of cloud being reported. In the winter, altostratus and cirro- 

 stratus clouds are frequently recorded. At this season the clouds 

 are thin ; during daylight hours the disk of the sun can frequently 

 be observed through the clouds. 



Cloudless days are uncommon in the Arctic. Days with zero- 

 to two-tenths coverage usually occur with the greatest frequency 

 during February and March, although the number of such days in 

 a winter period will total no more than 3 to 10. The greater 

 number of clear days will naturally occur over those areas where 

 anticyclonic conditions are most likely to prevail. Thus the ex- 

 pectancy of clear days is greatest over the interior of the arctic 

 basin, with the lower Mackenzie valley and the lower Lena and 

 Yana River valleys running second. Clear days are least fre- 

 quent over the Barents and Kara Seas and relatively infrequent 

 over the Chukchi Sea. Cloudy days, those with eight- to ten-tenths 

 coverage, are most frequent over the arctic basin in summer. 

 From May to October they will run between 18 and 24 a month 

 over most of the area. There are a few more cloudy days over 



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