Climates of this group, located at high latitude, are controlled largely by polar and arctic air masses. They have low temperatures, usually low precipitation, and low evapotranspiration.
(1) Continental sub arctic climate (Dc, Dfd, Dwc, Dwd)
In the two great landmasses of North America and Eurasia, a vast expanse of interior continental area lies between 50° and 70° N lat. Here are the source regions for the continental polar air masses.
In winter, when excessive heat loss by radiation has resulted in the formation of the prevailing Siberian and Canadian highs, severely cold air temperatures develop over snow-covered surfaces, forming a cold, dense air mass. Typically, a severe temperature inversion prevails in winter, so that the air at, say, 5000 ft (1500 m) may be 10° F (5°C) warmer than air at the ground level. Low in moisture content, this air mass is stable and normally clear.
In summer, the source region is shifted farther north; air mass temperatures rise to moderately high levels, but the moisture content, although much greater in summer, is still small by comparison with that of maritime tropical air masses.
We might expect, therefore, a climate type showing very great seasonal temperature range, with extremely severe winters and a small annual total precipitation concentrated in the warm months. This climate, called here the continental sub arctic climate, includes four of Koppen's climate types. The largest area, including belts from Alaska to Labrador and from Scandinavia to Siberia, is classified as Dfc, a cold, snowy forest climate, moist all year, with cool, short summers. Less than four months of the year have averages over 50°F (10°C). A still colder climate, Dfd, found in northern Siberia only, has very cold winters in which the average of the coldest months is below -36.4°F (-38°C). Climates Dwe and Dwd are also cold, snowy forest climates, but with a dry winter. They are found only in northeastern Asia. The letters c and d denote a cool summer and a very cold winter, respectively.
The continental sub arctic climate (Dfc) is well illustrated. The annual range of 74°F (41°C) is remarkable enough, but it is greatly exceeded by that of Ykutsk, USSR, lying in the Dwd climate type. The annual temperature range of the continental sub arctic climate is the greatest of any on earth, reaching 110°F (61°C) in Siberia. Even in central Antarctica, which has the lowest temperatures on earth, the annual range is not over 70°F (39°C).
Absolute minimum temperatures of -70° to -80°F (-57° to -62°C) are recorded in northwestern Canada, the lowest being -81.4°F(-63°C) at Snag, Yukon on February 3, 1947. Perhaps the coldest place in the northern hemisphere is Verkhoyansk, USSR, which lies in this climate zone and has a January mean of -59°F (-5l°C) and an absolute minimum recorded temperature of -93°F (-69°C).
Summer in the sub arctic climate regions is very short. The warmest month average may not greatly exceed 50°F(10°C), and frosts can occur at any time during the summer. Daily maximum temperatures, however, commonly reach 70°F(21°C). At these high latitudes the sun is above the horizon. Condition of perennially frozen ground, or permafrost, prevails over large parts of this and the tundra regions to the north. Seasonal thaw penetrates from 2 to 14 ft (0.6-4m), depending on location and nature of the ground. This shallow zone of alternate freeze and thaw is termed the active zone.
"The world is a book, and those who do not travel read only a page", St. Augustine said. Here at www.travel-university.org we believe that every page must be read and explored. Travel is an avenue of learning that no text or classroom can teach. The world is a living classroom and you the student. We invite you to the www.travel-university.org library where you can read general interest and detail oriented articles.
