Spatial Patterns

In January, representing winter conditions, the spatial distribution of cloudiness shows greater variation than in summer. The zone with highest cloudiness (> 80%) spreads from the Norwegian Sea to Novaya Zemlya, covering a large part of the Barents Sea and even the southern part of Spitsbergen (Figure 5.4). Cloudiness above 60% occurs in the whole Atlantic region and in the south-eastern part of the Baffin Bay region. The lowest cloudiness (< 40%) includes the belt spreading from the central part of the Siberian region through the North Pole to Greenland and the eastern part of the Canadian Arctic. In this area the absolute minimum occurs over the plateau of the Greenland Ice Sheet and in the Arctic Ocean from the Siberian side (Figure 5.4). In Arctic areas with the highest winter cloudiness on the one hand, as well as in the Arctic Ocean from the Canadian and Greenland side on the other hand, the low clouds dominate. In the rest of the Arctic the middle and high clouds are more common (see Vowinckel 1962 or Vowinckel and Orvig 1970).

From January to July, the most dramatic change in cloudiness (from 35% to more than 90%) occurs in the central part of the Arctic Ocean (Figure 5.4). Very high cloudiness (even greater than in winter) is still observed in the Atlantic region. The cloudiness between the northern part of Norway and Greenland, similar to that of the central Arctic, exceeds 90%. A likely reason for this may be the fact that a slight reduction in cloudiness connected with only slightly lower cyclonic activity can be fully compensated for by more cloudy air masses inflowing from the Arctic Ocean in this season than in winter. The lowest cloudiness (< 60%) occurs on the Greenland Ice Sheet, with a minimum in its north-eastern part (< 50%).

Figure 5.4. Spatial distributions of mean monthly (January and July) total cloud amounts (in %) in (he Arctic (after Vowinckel 1962),

The numbers of clear (0-3 degree in 0-10 scale) and cloudy (7-10 degree) days in the sea area of the Arctic for February and August arc shown in Figure 5.5. There are a significantly greater number of clear days in wintertime. In February there is a clear day every other day over most of the Arctic Ocean (Figure 5.5c). The largest number of clear days occurs in the southwestern part of the Canadian Arctic Archipelago (> 60%). The clear days are a very rare phenomenon (< 10-20%) in most parts of the Atlantic region and in the southern part of the Baffin Bay region, i.e., in the areas strongly influenced by vigorous cyclonic activity. In summer (August) sunny weather occurs very rarely (Figure 5.5d). In most areas there is a chance of less than 10% frequency. Only on coastal areas of Greenland and Ellesmere Island can clear days occur with a 20-30% frequency.

Figure 5.5. Frequency of occurrence (in %) of cloudy sky (7-10 tenths) and clear sky (0-3 tenths) days in February (a and c, respectively) and in August (b and d, respectively) in the Arctic (after Gorshkov 1980).

Cloudy days in summer occur with greater frequency than in winter over almost the entire Arctic (compare Figures 5.5a and 5.5b). The large difference can be seen mainly in the part of the Arctic with a high degree of climate continentality. Cloudy days are almost constant (> 90%) in the central part of the Arctic Ocean and between Spitsbergen, Bjórnoya, and Jan Mayen. In the rest of the Arctic (excluding the waters near Greenland, Baffin Bay, the whole Canadian Arctic, and the southern parts of the Barents Sea), cloudy days occur with a frequency of 80-90%. The frequency of cloudy days below 60% occurs only near Greenland and Hllesmere Island. In winter, in the entire Arctic (except the Atlantic and the Baffin Bay regions) the frequency of cloudy days is about two times lower. On the other hand, in the Atlantic region and the northern part of the Baffin Bay region, the frequency is generally 10-20% lower. Only in a small area between Greenland and the Labrador Peninsula may a greater amount of cloudiness be noted in winter than in summer.

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