The longitudinal differences in mid-latitude climates persist into the northern polar margins, giving rise to maritime and continental subtypes, modified by the extreme radiation conditions in winter and summer. For example, radiation receipts in summer along the Arctic coast of Siberia compare favourably, by virtue of the long daylight, with those in lower mid-latitudes.
The maritime type is found in coastal Alaska, Iceland, northern Norway and adjoining parts of Russia. Winters are cold and stormy, with very short days. Summers are cloudy but mild with mean temperatures of about 10°C. For example, Vard0 in northern Norway (70°N, 31°E) has monthly mean temperatures of -6°C in January and 9°C in July, while Anchorage in Alaska (61°N, 150°W) records -11°C and 14°C, respectively. Annual precipitation is generally between 60 and 125 cm, with a cool season maximum and about six months of snow cover.
The weather is controlled mainly by depressions, which are weakly developed in summer. In winter, the Alaskan area is north of the main depression tracks and occluded fronts and upper troughs are prominent, whereas northern Norway is affected by frontal depressions moving into the Barents Sea. Iceland is similar to Alaska, although depressions often move slowly over the area and occlude, whereas others moving northeastward along the Denmark Strait bring mild, rainy weather.
The interior, cold-continental climates have much more severe winters, although precipitation amounts are smaller. At Yellowknife (62°N, 114°W), for instance, the mean January temperature is only -28°C. In these regions, permafrost (permanently frozen ground) is widespread and often of great depth. In summer, only the top 1 to 2 m of ground thaw and, as the water cannot drain away readily this 'active layer' often remains waterlogged. Although frost may occur in any month, the long summer days usually give three months with mean temperatures above 10°C, and at many stations extreme maxima reach 32°C or more (see Figure 10.17). The Barren Grounds of Keewatin, however, are much cooler in summer due to the extensive areas of lake and muskeg; only July has a mean daily temperature of 10°C. Labrador-Ungava to the east, between 52° and 62°N, is rather similar with very high cloud amounts and maximum precipitation in June to September (Figure 10.36). In winter, conditions fluctuate between periods of very cold, dry, high-pressure weather and spells of dull, bleak, snowy weather as depressions move eastward or occasionally northward over the area. In spite of the very low mean temperatures in winter, there have been occasions when maxima
have exceeded 4°C during incursions of maritime Atlantic air. Such variability is not found in eastern Siberia, which is intensely continental, apart from the Kamchatka Peninsula, with the northern hemisphere's cold pole located in the remote northeast (see Figure 3.11A). Verkhoyansk and Oimyakon have a January mean of -50°C, and both have recorded an absolute minimum of -67.7°C. Stations located in the valleys of northern Siberia record, on average, strong to extreme frosts 50 per cent of the time during six months of the year, but very warm summers (Figure 10.37).
Continue reading here: The polar regions
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