Temperate Zone

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Temperate Zone

those parts of the earth's surface lying between the Arctic Circle and the tropic of Cancer and between the Antarctic Circle and the tropic of Capricorn

Temperate Zone

 

either of the two latitudinal belts of the earth that lie between approximately 40° and 65° N lat. in the northern hemisphere and between 42° and 58° S lat. in the southern hemisphere. The belts are referred to as the north temperate zone and the south temperate zone, respectively.

The temperate zones occupy one-fourth of the earth’s surface, an area considerably greater than that of the other geographic zones. Approximately 55 percent of the north temperate zone is land, and approximately 98 percent of the south temperate zone is ocean. The temperate zones have characteristic, well-marked seasonal variations in temperature, which determine the periodic character of climatic, hydrologic, geomorphological, and biological processes. Thermal conditions permit woody vegetation to grow throughout the zones, but the severe winters prevent the growth of broad-leaved woody evergreens. The lack of moisture in certain regions gives rise to unforested landscapes. The temperate zones, especially vast territories in the northern hemisphere, are marked by an exceptionally diverse natural environment, a result of large areal heat and moisture gradients.

Total annual radiation in the temperate zones ranges from 70–80 to 140–160 kilocalories (kcal) per cm2. The annual radiation balance for the land areas is 20–40 kcal/cm2 for the northern hemisphere and 30–40 kcal/cm2 for the southern hemisphere; the corresponding ranges for the oceans are 20–60 and 30–60 kcal/cm2. During the summer, total radiation varies only slightly with latitude, because the day is longer at higher latitudes. In winter, the total radiation diminishes rapidly with increased latitude, and the radiation balance is negative. Throughout the year there is a westerly transfer of air masses throughout the troposphere over the temperate zones; combined with intense cyclonic activity, this movement of air masses helps transport moisture from the oceans to the continents and promotes the interlatitudinal exchange of heat. Mean air temperatures in the coldest months range from 6° to – 50°C over land in the north temperate zone and from 2° to 8°C over land in the south temperate zone; the corresponding ranges over the oceans are from 10° to –8° and from 2° to 10°C. Mean temperatures in the warmest months range from 10° to 28°C over land in the north temperate zone and from 8° to 20°C over land in the south temperate zone; the corresponding ranges over the oceans are from 8° to 20°C and from 8° to 16°C.

Total annual precipitation in most of the region of the temperate zones ranges from 500 to 800 mm, increasing to 1,000–2,000 mm on the continental borders; it diminishes to 100–200 mm in the southern intracontinental regions, where cyclonic circulation becomes weaker. The land areas of the temperate zones have considerable surface flow and rapidly moving streams that result in extensive dissection of the surface. In the north temperate zone, the amount of runoff decreases toward the southern regions, which have large basins with subsurface flow. The temperate zones have more lakes than the other geographic zones, with lakes of glacial origin constituting a clearly defined group.

Soil formation is generally marked by leaching and the intensive mineralization of organic matter; podzolic and various podzolized soils are widespread. In the warmer and more humid regions, active formation of secondary minerals and argillation of the soils occur. Sod formation predominates in moderately humid regions, and salinization is predominant in arid temperate regions. Podzolic, brown, and gray forest soils cover large areas in the temperate zones; chernozem, chestnut, and other soils are less extensive.

The most widespread types of vegetation are forests: taiga (swampy over large areas), mixed coniferous and broad-leaved, and summer green broad-leaved. Among fauna, forest animals that primarily lead a settled mode of life are the most common; animals that inhabit unforested areas are rarer. Many mammals hibernate in the winter or resort to other adaptive means to survive unfavorable periods.

The land of the temperate zones is divided into the western coastal, intracontinental, and eastern coastal sectors. The boundaries between the sectors are indistinct; therefore transitional sectors between the interior and the coasts are sometimes specified. In the western coastal sectors, a mild, humid climate with intense cyclonic circulation prevails. The water balance is sufficient, or there is a water overbalance; the snow cover is of short duration or entirely absent; and rivers are persistently flowing. Mesophyllic broad-leaved or coniferous forests and brown forest or sod-podzolic soils predominate. The mountain regions of this sector exhibit the forest-meadow spectrum of altitudinal zones.

The intracontinental sectors of the north temperate zone have a continental climate with the greatest seasonal temperature differences of the temperate zones. Winters are cold and, especially in the north, snowy; summers are relatively warm in the north and hot in the south. Tracts of permafrost have developed over large areas. The northern parts of the sectors have a water overbalance; in the middle belt the water balance is sufficient, and in the south it is deficient. As radiation increases and moisture decreases, the following succession of landscapes is typical for the intracontinental sectors: forest zones, forest-steppe zones, temperate steppe zones, semidesert zones, and desert zones. The steppe and forest-steppe zones are concentrically disposed.

In the eastern coastal sectors, forest-zone landscapes are typical; they develop in areas with a monsoon-cyclonic climate and appear most clearly in Eastern Asia. In the plains and on the low mountains, dark coniferous, mixed, and (in the south) broad-leaved forests predominate on sod-podzolic and brown forest soils. Landscapes of the forest-tundra complex are found on the high mountains.

The spectrum of landscape and altitudinal zones appears at its fullest in Eurasia and North America. There, the largest areas are occupied by forest zones and, in the mountains, by forest-tundra (in the north) and forest-meadow types of altitudinal zonality. In the coastal sectors the zonation of landscapes is abbreviated as a result of the decreased areal variation in the amplitude of the water balance: the desert and semidesert zones disappear, and the forest-steppe and steppe zones appear only fragmentally. Subdivision into zones is less clearly marked in South America and on Tasmania, owing to regional characteristics of the land and the circulation of air masses.

The land of the temperate zones has undergone varied economic development. The most highly developed areas are in the Atlantic coastal sectors of Europe and North America, where industrial anthropogenic landscapes are widespread. The steppe and forest-steppe regions of the intracontinental sectors are also highly developed; they are dominated by agricultural anthropogenic landscapes. The northern taiga zone and the deserts are the least developed.

The oceans of the temperate zones are characterized by the year-round transfer of surface layers of water toward the east as a result of prevailing westerly winds; they show greater annual fluctuations of temperature, salinity, and other hydrologic indexes than the oceans of the other zones. In addition, the surface waters of the temperate zones surpass those of all other zones in density of plankton. The benthic fauna is extremely rich, and, as a result, many oceanic regions in the temperate zones serve as feeding grounds for commercially valuable fish. The oceans of the temperate zones produce more than two-thirds of the world catch of ocean fish, including herring, cod, haddock, pollack, halibut, flounder, and, in the warmer regions, sardines, mullet, and mackerel.

REFERENCES

Ivanov, N. N. Landshaftno-klimaticheskie zony zemnogo shara. Moscow-Leningrad, 1948.
Grigor’ev, A. A., and M. I. Budyko. “O periodicheskom zakone geograficheskoi zonal’nosti.” Dokl. AN SSSR, vol. 110, 1956, no. 1.
Kalesnik, S. V. Obshchie geograficheskie zakonomernosti Zemli. Moscow, 1970.

R. A. ERAMOV

Temperate Zone

[′tem·prət ‚zōn]
(climatology)
Either of the two latitudinal zones on the earth's surface which lie between 23°27′ and 66°32′ N and S (the North Temperate Zone and South Temperate Zone, respectively).
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