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climate,average condition of the atmosphere near the earth's surface over a long period of time, taking into account temperature, precipitation (see rainrain,
precipitation in liquid form. It consists of drops of water falling from clouds; if the drops are very small, they are collectively termed drizzle. Rain plays a key role in the hydrologic, or water, cycle in which moisture from the oceans evaporates, condenses into clouds,
..... Click the link for more information. ), humidityhumidity,
moisture content of the atmosphere, a primary element of climate. Humidity measurements include absolute humidity, the mass of water vapor per unit volume of natural air; relative humidity (usually meant when the term humidity
..... Click the link for more information. , windwind,
flow of air relative to the earth's surface. A wind is named according to the point of the compass from which it blows, e.g., a wind blowing from the north is a north wind.
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Primary Influence on Climate
The major influence governing the climate of a region is its latitude. A broad latitudinal division of the earth's surface into climatic zones based on global winds includes the equatorial zone, or doldrumsdoldrums
or equatorial belt of calms,
area around the earth centered slightly north of the equator between the two belts of trade winds. The large amount of solar radiation that arrives at the earth in this area causes intense heating of the land and ocean.
..... Click the link for more information. , characterized by high temperatures with small seasonal and diurnal change and heavy rainfall; the subtropical, including the trade-wind belts and the horse latitudeshorse latitudes,
two belts of latitude where winds are light and the weather is hot and dry. They are located mostly over the oceans, at about 30° lat. in each hemisphere, and have a north-south range of about 5° as they follow the seasonal migration of the sun.
..... Click the link for more information. , a dry region with uniformly mild temperatures and little wind; the intermediate, the region of the prevailing westerlies that, because of several secondary influences, displays wide temperature ranges and marked changeability of weather; and the polar, a region of short summers and long winters, where the ground is generally perpetually frozen (see permafrostpermafrost,
permanently frozen soil, subsoil, or other deposit, characteristic of arctic and some subarctic regions; similar conditions are also found at very high altitudes in mountain ranges.
..... Click the link for more information. ). The transitional climate between those of the subtropical and intermediate zones, known as the Mediterranean type, is found in areas bordering the Mediterranean Sea and on the west coasts of continents. It is characterized by mild temperatures with moderate winter rainfall under the influence of the moisture-laden prevailing westerlies and dry summers under the influence of the horse latitudes or the trade winds.
Secondary Influences on Climate
The influence of latitude on climate is modified by one or more secondary influences including position relative to land and water masses, altitude, topographytopography
, description or representation of the features and configuration of land surfaces. Topographic maps use symbols and coloring, with particular attention given to the shape and elevations of terrain.
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interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other in most cases by the continental masses. See also oceanography.
..... Click the link for more information. currents, and prevalence of cyclonic storms. Climatic types combining the basic factor of latitude with one or more secondary influences include the continental and the marine. Except in the equatorial region, the continental type is marked by dry, sunny weather with low humidity and seasonal extremes in temperature; noteworthy are the Sahara and Siberia. Marine climates are characterized by small annual and diurnal temperature variation and by copious rainfall on the windward side of coastal highlands and mountainous islands; notable is the mean annual precipitation of 451 in. (1146 cm) at Mt. Waialeale, Hawaii.
The coastal, or littoral, climate is one in which the direction of the prevailing winds plays a dominant role—the east coasts having generally the heavier rainfall in the trade-wind belts, the west coasts in westerly belts. Both coasts have a climate resembling the continental during the season when the wind is blowing from the interior of the continent. An instance of the coastal type, in which the precipitation is accentuated by the nearness of a mountain barrier, is the west coast of North America from Alaska to Oregon, where the mean annual precipitation averages 80 to 100 in. (203 to 254 cm), almost all of it falling during the winter months. Elevation is the dominant factor in mountain and plateau climates, with the temperature decreasing about 3°F; per 1,000 ft (1.7°C; per 305 m) of ascent and rainfall increasing with altitude up to about 6000 ft (1829 m), then decreasing with further elevation.
Climatology and Climatic Change
Climatology, the science of climate and its relation to plant and animal life, is important in many fields, including agriculture, aviation, medicine, botany, zoology, geology, and geography. Changes in climate affect, for example, the plant and animal life of a given area. The presence of coal beds in North America and Europe along with evidence of glaciation in these same areas indicates that they must have experienced alternately warmer and colder climates than they now possess.
Despite yearly fluctuations of climatic elements, there was, apparently, comparatively little overall change during the period of recorded history prior to the Industrial Revolution. Numerous climatic cycles (variations in weather elements that recur with considerable regularity) have been claimed to exist, including an 11-year cycle related to sunspot activity, but these are generally difficult to confirm. There is currently much concern about how human activities since the Industrial Revolution are changing the earth's climate, and how the global warmingglobal warming,
the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution. Global warming and its effects, such as more intense summer and winter storms, are also referred to as climate
..... Click the link for more information. that has occurred as a result will alter the natural and human environment. Computer models of climate changes have been developed in recent years; some examine potential parameters that effect global warmingglobal warming,
the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution. Global warming and its effects, such as more intense summer and winter storms, are also referred to as climate
..... Click the link for more information. or cooling.
See H. H. Lamb, Climate History and the Future (1985); J. R. Herman and R. A. Sun, Weather and Climate (1985).
long-term weather conditions peculiar to a given place on earth and one of its geographical characteristics. The phrase “long-term conditions” refers to the aggregate of all the weather conditions in a given place over a period of dozens of years, to the typical annual succession of these conditions and possible deviations from it in individual years, and to the combination of weather conditions typical of various anomalies (droughts, rainy periods, drops in temperature). About the middle of the 20th century, the concept of climate, which was once applied only to conditions at the earth’s surface, was extended to the upper layers of the atmosphere.
Main characteristics of climate. Long-term series of meteorological observations are needed to discover the distinctive features of the climate, both typical and rare. In the temperate zone 25– to 50–year series are used; they may be shorter in the tropics. Sometimes (for example, for the antarctic or the upper atmosphere) one has to rely on briefer observations, keeping in mind that subsequent experience may introduce greater accuracy into preliminary concepts.
In studying the climate of oceans, besides observations on islands, use is made of information obtained at different times on ships in some part of the water area and of regular observations made on weather ships.
Climatic features are statistical conclusions drawn from long-term series of observations chiefly on the following principal meteorological elements: atmospheric pressure, wind velocity and direction, air temperature and humidity, cloudiness, and atmospheric precipitation. Other factors taken into account include the duration of solar radiation, range of visibility, temperature of the upper layers of soil and of bodies of water, evaporation of water from the earth’s surface into the atmosphere, height and condition of the snow cover, various atmospheric phenomena, and ground hydrometeors (dew, glaze ice, fogs, thunderstorms, snowstorms). In the 20th century, the elements of the heat balance at the earth’s surface, such as total solar radiation, radiation balance, magnitude of heat exchange between the earth’s surface and the atmosphere, and expenditures of heat on evaporation, were included among the climatic features.
The features of the climate of the free atmosphere include primarily atmospheric pressure, wind, air temperature and humidity, and data on radiation.
The mean long-term values of meteorological elements (annual, seasonal, monthly, daily), their totals, frequency, and so forth are called climatic norms; the corresponding quantities for individual days, months, years, and so forth are regarded as deviations from these norms. Complex parameters, that is, functions of several elements, are also used to characterize the climate, including various coefficients, factors, and indexes—for example, of continentality, aridity, and moisture.
Special parameters of the climate are used in applied branches of climatology—for example, the totals of temperatures during the growing season in agroclimatology, effective temperatures in bioclimatology and industrial climatology, and degree-days in calculations for designing heating systems.
Ideas were advanced in the 20th century concerning the microclimate, the climate of the layer of air near the ground, local climate, and macroclimate—the climate of regions on a planetary scale. There are also concepts of “soil climate” and “plant climate” (phytoclimate) that characterize the habitat of plants. Such terms as “city climate” have gained wide popularity because the modern large city has a significant effect on its own climate.
Main processes that form the climate. Climatic conditions on earth are created as a result of the following principal interrelated cycles of geophysical processes operating on a global scale: thermal cycle, hydrologic cycle, and general circulation of the atmosphere.
The thermal cycle consists of (1) the influx of electromagnetic solar radiation, whose radiant energy is converted into heat during the absorption of radiation in the atmosphere and on the earth’s surface; (2) exchange of heat between the atmosphere and the earth’s surface by long-wave radiation, thermal conductivity, and phase transformations of water (expenditures of heat by soil and bodies of water on evaporation of water and release of the latent heat of vaporization during condensation in the atmosphere); (3) redistribution of heat on the earth through transport by air and ocean currents; and (4) emission of both reflected and scattered solar radiation and of the earth’s own long-wave radiation and atmospheric radiation into outer space.
The hydrologic cycle consists of (1) the evaporation of water into the atmosphere from bodies of water and land, including plant transpiration, (2) transport of water vapor to the upper atmosphere and transport by air currents of the general atmospheric circulation, (3) condensation of water vapor in the form of clouds and fogs, (4) transport of clouds by air currents and the falling of precipitation from them, and (5) runoff of precipitation and its evaporation again.
The general circulation of the atmosphere is largely responsible for wind conditions. The global transfer of heat and moisture is connected with the transport of air masses of the general circulation. Local atmospheric circulations (breezes, mountain-valley winds) generate the transport of air only over limited areas of the earth’s surface. This process is superposed on the general circulation, and it influences the climatic conditions in these areas.
Influence of geographic factors on climate. The climate-forming processes take place under the influence of several geographic factors, the most important of which are as follows:
(1) GEOGRAPHIC LATITUDE. Geographic latitude determines zonation and seasonality in the distribution of the solar radiation reaching the earth and with it the air temperature, atmospheric pressure, and so forth. Latitude also affects wind conditions directly because the deflecting force of the earth’s rotation depends on it.
(2) ALTITUDE ABOVE SEA LEVEL. Climatic conditions in the free atmosphere and in the mountains vary with altitude. Comparatively small differences in altitude, measured in hundreds and thousands of meters, are equivalent in their effect on the climate to latitudinal distances of thousands of kilometers. Thus, altitudinal climatic zones can be distinguished in mountains.
(3) DISTRIBUTION OF LAND AND SEA. Differences arise between the climate of continents and oceans because of differences in the conditions under which heat spreads in the upper layers of the soil and water and because of differences in their absorptive capacity. The general circulation of the atmosphere causes the conditions of the marine climate to be extended deep into the continents by air currents and causes the conditions of the continental climate to be extended to the adjacent sections of the oceans.
(4) OROGRAPHY. Mountain ranges and massifs with different exposures of the slopes create major disturbances in the distribution of air currents, air temperature, clouds, precipitation, and so forth.
(5) OCEAN CURRENTS. When warm currents reach the high latitudes, they release heat into the atmosphere; cold currents moving to the low latitudes cool the atmosphere. The currents also affect the hydrologic cycle, by promoting or preventing the formation of clouds and fogs, and the atmospheric circulation because it is dependent on temperature conditions.
(6) NATURE OF THE SOIL. The nature of the soil, especially its reflective power (albedo) and moisture, is another geographic factor that influences climate.
(7) VEGETATION. To some extent, vegetation affects the absorption and emission of radiation, humidification, and wind.
(8) SNOW AND ICE COVER. Seasonal snow cover on land, ice in the sea, permanent ice and snow cover in places like Greenland and Antarctica, and névé fields and glaciers in mountains significantly affect the temperature regime, wind conditions, cloudiness, and humidification.
(9) COMPOSITION OF AIR. Over short periods of time the composition of air does not change substantially under natural conditions except in the case of sporadic volcanic eruptions or forest fires. However, in industrial regions the amount of carbon dioxide increases as a result of the combustion of fuel and the air is polluted by the gaseous and aerosol waste products of industry and transport.
Climate and man. The types of climate and their global distribution have a profound effect on the water regime, soil, vegetation, and animals as well as on the geographical range and yield of crops. To some extent climate influences the dispersal of population, location of industry, people’s living conditions, and their health. Therefore, a correct estimation of the features and effects of the climate is essential not only for agriculture but also for the location, planning, construction, and operation of hydroelectric and industrial plants and in urban development, the transportation network, public health (network of health resorts, climatotherapy, control of epidemics, social hygiene), tourism, and sports. The agencies of the Hydrometeorological Service of the USSR study climatic conditions in general and from the standpoint of specific needs of the economy and generalize and disseminate data on the climate for practical purposes.
Man is still unable to modify the climate significantly by directly changing the physical mechanisms regulating the climate-forming processes. Man’s active physicochemical intervention in the formation of clouds and precipitation is now a reality, but it has no climatic significance because of its spatial limitation. The industrial activity of human society is increasing the amount of carbon dioxide, industrial gases, and aerosol admixtures in the air. This affects not only the people’s living conditions and health but also the absorption of radiation in the atmosphere and, consequently, the air temperature. The flow of heat into the atmosphere is steadily increasing as a result of the combustion of fuel. These anthropogenic changes in the climate are particularly noticeable in large cities, but they are still insignificant on a global scale. However, they can be expected to intensify considerably in the near future. Moreover, by acting on this or that geographic factor of the climate, that is, by altering the environment in which the climate-forming processes take place, people out of ignorance or indifference have changed the climate for the worse since ancient times by irrational cutting down of forests and by predatory plowing up of land. On the other hand, the carrying out of rational irrigation measures and creation of oases in deserts has improved the climate in the regions affected. The question of deliberate, planned improvement of the climate has been raised chiefly with respect to the microclimate and local climate. This can be realistically and safely accomplished by a deliberate expansion of activities designed to alter the soil and vegetation (planting shelterbelts, irrigation, drainage of land).
Climatic changes. Studies of sedimentary deposits, fossil remains of the flora and fauna, radioactivity of rocks, and so forth have shown that the earth’s climate changed significantly in different eras. The earth appears to have been warmer during the last hundreds of millions of years (until the Anthropogene) than it is now: the temperature in the tropics was close to that of the present day, but it was much higher in the middle and high latitudes than it is now. At the beginning of the Paleogene (about 70 million years ago), the temperature contrasts between the equatorial and polar regions started to increase, but until the beginning of the Anthropogene they were smaller than they are now. The temperature in the high latitudes dropped sharply in the Anthropogene, and polar glaciations occurred. The last shrinking of the glaciers in the northern hemisphere appears to have ended about 10,000 years ago, after which permanent ice sheets remained chiefly in the Arctic Ocean, on Greenland and other arctic islands, and in the southern hemisphere in Antarctica.
There is an abundance of data obtained by paleogeographic research methods (dendrochronology and palynological analysis, for example) to characterize the climate that has prevailed in the last few millennia. Study of archaeological finds, folklore and literary monuments, and, more recently, chronicles has also provided information. It is reasonable to conclude that the climate of Europe and neighboring regions (and probably of the entire earth as well) during the last 5,000 years fluctuated within comparatively narrow limits. Dry and warm periods gave way several times to wetter and cooler ones. Precipitation increased perceptibly in about 500 B.C. and the climate became cooler. At the beginning of the Common Era it was similar to that of the present day. The climate in the 12th and 13th centuries was milder and drier than at the beginning of the Common Era, but it again became much cooler and the amount of ice in the seas increased in the 15th and 16th centuries. More and more data have been collected in the last three centuries from worldwide instrumental meteorological observations. The climate remained cold and wet from the 17th to the mid-19th century and the glaciers advanced. A new warming trend began in the second half of the 19th century; it was particularly pronounced in the arctic, but it embraced almost the entire earth. This modern warming trend continued until the mid-20th century. Short-term fluctuations with smaller amplitudes took place against a background of climatic fluctuations lasting hundreds of years. Thus, climatic changes exhibit a rhythmic and oscillating character.
The climatic regime that prevailed until the Anthropogene— warm with small temperature contrasts and absence of polar glaciations—was stable. The climate of the Anthropogene and recent climate with glaciations and their pulsations and sharp fluctuations in atmospheric conditions, on the other hand, are unstable. M. I. Budyko has concluded that even a very slight rise in the mean temperatures of the earth’s surface and atmosphere could lead to a decrease in polar glaciation and that the resulting changes in the reflective power (albedo) of the earth would cause further warming and shrinking of the ice sheets until they disappeared completely.
The climatic conditions on earth are closely related to geographic latitude. Accordingly, it was believed even in ancient times that there are climatic (temperature) zones whose boundaries coincide with the tropics and polar circles. The sun is at the zenith twice a year in the tropical belt (between the northern and southern tropics); there are 12 hours of daylight at the equator throughout the year, but the daylight period varies from 11 to 13 hours within the tropics. In the temperate zones (between the tropics and the polar circles) the sun rises and sets every day but does not reach the zenith. Its midday height in summer is much greater than in winter, as is the duration of daylight, and these seasonal differences increase as one approaches the poles. Beyond the polar circles the sun does not set in summer, and it does not rise in winter for a period of time, the length of which varies with the latitude of the place. At the poles, the year is divided into a six-month day and a six-month night.
The solar radiation flux at the upper boundary of the atmosphere in different latitudes and at different moments and times of the year (the solar climate) is determined by the visible motion of the sun. The solar radiation flux at the boundary of the atmosphere in the tropical zone has an annual cycle with a small amplitude and two maximums during the year. In the temperate zones, the solar radiation flux on a horizontal surface at the boundary of the atmosphere in summer differs comparatively little from the flux in the tropics: the lower height of the sun is compensated for by the longer day. But in winter the radiation flux decreases quickly with latitude. The summer radiation flux is also great in the polar latitudes with a long continuous day. On the day of the summer solstice, the pole receives at the boundary of the atmosphere even more radiation on a horizontal surface than does the equator. In the winter half of the year, on the other hand, there is no radiation flux at all at the pole. Thus, the solar radiation flux at the boundary of the atmosphere varies only with the geographic latitude and with the time of year, and it is strictly zonal.
Within the atmosphere solar radiation experiences nonzonal influences due to differences in the amount of water vapor and dust, cloudiness, and other distinctive features of the gaseous and colloidal state of the atmosphere. The complex distribution of the quantities of radiation reaching the earth’s surface reflects these influences. Many geographic factors affecting the climate (distribution of land and sea, orography, ocean currents) are also nonzonal in character. Therefore, in the complex distribution of climatic features at the earth’s surface, zonality is only a background that shows more or less clearly through nonzonal influences.
The climatic regionalization of the earth is based on a division of the land into belts, zones, and regions with more or less similar climatic conditions. The boundaries of the climatic belts and zones not only do not coincide with the latitudinal circles, but they also do not always extend around the earth (the zones in such cases are split into regions that do not meet). Regionalization can be based either on strictly climatic features (for example, distribution of mean air temperatures and total atmospheric precipitation according to W. Köppen) or on other groups of climatic characteristics, as well as on the distinctive features of the general atmospheric circulation with which the types of climate are associated (for example, B. P. Alisov’s classification) or on the nature of the geographic landscapes determined by the climate (L. S. Berg’s classification). The characterization of the earth’s climates given below largely corresponds to B. P. Alisov’s regionalization (1952).
The profound effect of the distribution of land and sea on the climate can be seen by comparing the conditions prevailing in the northern hemisphere with those in the southern hemisphere. The main land masses are concentrated in the northern hemisphere and, consequently, its climatic conditions are more continental than those in the southern hemisphere. The mean ground air temperatures are 8°C in January and 22°C in July in the northern hemisphere and 17°C and 10°C, respectively, in the southern. The mean temperature over the entire earth is 14°C (12°C in January and 16°C in July). The earth’s warmest parallel, the thermal equator, with a temperature of 27°C, coincides with the geographic equator only in January. It shifts to 20° N lat. in July, and its mean annual position is about 10° N lat. The temperature drops from the thermal equator to the poles by 0.5°–0.6°C on the average for each degree of latitude (very slowly in the tropics, more rapidly in nontropical latitudes). Moreover, the air temperature within the continents is higher in summer and lower in winter than over the oceans, especially in the temperate regions. This statement does not apply to the climate over the ice plateaus of Greenland and Antarctica where the air is much colder the year round than it is over the adjacent oceans. (The mean annual air temperatures drop to —35°C or —45°C.)
The mean annual total precipitation is highest in the latitudes near the equator (1,500–1,800 mm). It decreases toward the subtropics to 800 mm, increases again in the temperate regions to 900–1,200 mm, and decreases sharply in the polar regions (to 100 mm or less).
Equatorial climate. The equatorial climate embraces a low-pressure band (the equatorial trough) extending 5°–10° north and south of the equator. It has a very uniform temperature regime with high air temperatures throughout the year (usually fluctuating between 24°C and 28°C; the temperature amplitudes on land do not exceed 5°C, but on the sea they can be less than 1°C). Humidity is always high, and the total annual precipitation varies from 1,000 to 3,000 mm a year and in some places on land from 6,000 to 10,000 mm. The precipitation is usually in the form of heavy showers which, as a rule, are evenly distributed throughout the year, especially in the intertropical convergence zone that separates the trade winds of the two hemispheres. Cloudiness is substantial. Equatorial rain forests are the dominant natural landscapes on dry land.
Trade-wind climate. A trade-wind climate with a stable easterly wind regime, moderate cloudiness, and fairly dry weather prevails on both sides of the equatorial trough, in high-pressure areas, and in the tropics over the oceans. The mean summer and winter temperatures are 20°–27°C and 10°–15°C, respectively. The total annual precipitation is about 500 mm. The amount increases sharply on the slopes of mountainous islands facing the trade wind and during the comparatively rare tropical cyclones.
Tropical desert climate. The regions of oceanic trade winds correspond to land areas with a tropical desert climate, which have an exceptionally hot summer. (The mean temperature of the warmest month in the northern hemisphere is about 40°C; in Australia, as high as 34°C.) The absolute temperature maximums are 57°–58°C in North Africa and the interior of California and as high as 55°C in Australia (the highest air temperatures on earth). The mean winter temperatures range from 10° to 15°C. The daily temperature amplitudes are great (more than 40°C in some places). Precipitation is low (usually less than 250 mm, often less than 100 mm a year).
Tropical monsoon climate. The trade-wind climate is replaced by a tropical monsoon climate in some tropical regions (equatorial Africa, South and Southeast Asia, northern Australia). In summer the intertropical convergence zone here shifts far from the equator, and instead of an easterly trade wind between it and the equator there develops a westerly air transport (summer monsoon) that brings most of the precipitation. Almost as much rain falls on the average as in an equatorial climate. (In Calcutta, for example, there is 1,630 mm of precipitation a year with 1,180 mm of it falling during the four months of the summer monsoon.) On mountain slopes exposed to the summer monsoon the amount of precipitation that falls is a record for the corresponding regions; the maximum amount of precipitation on earth falls in northeastern India (Cherrapunji), about 12,000 mm a year on the average. The summers are hot (the mean air temperature is over 30°C), and the warmest month usually precedes the onset of the summer monsoon. The highest mean annual temperatures on earth (30°–32°C) occur in the tropical monsoon zone, East Africa, and Southwest Asia. In some regions the winters are cool. The mean January temperature is 25°C in Madras and 16°C in Varanasi, but only 3°C in Shanghai.
Mediterranean climate. The climate in the western parts of the continents in subtropical latitudes (25°–40° N lat. and S lat.) is characterized by high atmospheric pressure in summer (subtropical anticyclones) and cyclonic activity in winter when the anticyclones shift slightly toward the equator. These conditions give rise to a Mediterranean climate, which, in addition to the Mediterranean region, is also found on the southern coast of the Crimea, in western California, southern Africa, and southwestern Australia. The summers are hot, almost cloudless, and dry; the winters are cool and rainy. The amount of precipitation is usually small, and some regions with this climate are semiarid. The temperature ranges from 20° to 25°C in summer and from 5° to 10°C in winter; the total annual precipitation is usually 400–600 mm.
Dry subtropical climate. High atmospheric pressure prevails within the continents in the subtropical latitudes in winter and summer. The result is a dry subtropical climate, hot and almost cloudless in summer and cool in winter. In Turkmenia, for example, the summer temperatures on some days rise to 50°C and freezing temperatures down to –10° or –20°C are possible in winter. The total annual precipitation amounts to only 120 mm in some places.
Cold desert climate. The uplands of Asia (Pamirs, Tibet) have a cold desert climate with cool summers, very cold winters, and meager precipitation. For example, in Murgab in the Pamirs, the temperature may rise to 14°C in July and drop to – 18°C in January, and precipitation is about 80 mm a year.
Monsoon subtropical climate. A monsoon subtropical climate prevails in the eastern parts of the continents in the subtropical latitudes (eastern China, southeastern United States, countries of the Paraná basin in South America). The temperature conditions are similar to those in regions with a Mediteranean climate, but the precipitation is more abundant and it falls mostly in summer with the oceanic monsoon. (In Peking, for example, of 640 mm of annual precipitation, 260 mm falls in July and only 2 mm in December.)
The temperate regions are characterized by intensive cyclonic activity that produces frequent and drastic changes in pressure and air temperature. Westerly winds prevail (especially over the oceans and in the southern hemisphere). The transitional seasons (fall, spring) are long and distinct.
Marine climate. A marine climate with cool summers, warm (for the particular latitudes) winters, and a moderate amount of precipitation (in Paris, for example, the temperature rises to 18°C in July and drops to 2°C in January, and annual precipitation is 490 mm) without a stable snow cover prevails in the western parts of the continents (chiefly Eurasia and North America). The precipitation increases markedly on windward slopes of mountains. For example, in Bergen (in the western foothills of the Scandinavian mountains) the annual precipitation is more than 2,500 mm, but it is only 540 mm in Stockholm (east of the Scandinavian mountains). The effect of the orography on precipitation is even more pronounced in North America where the mountain ranges stretch north and south. A total of 3,000–6,000 mm of precipitation falls in some places on the western slopes of the Cascade Range, but behind the range precipitation is about 500 mm or less.
Intracontinental climate of the temperate regions. The intracontinental climate of the temperate regions in Eurasia and North America has a more or less stable high-pressure regime, especially in winter, warm summers, and cold winters with a stable snow cover. The annual temperature amplitudes are great and they increase toward the interior of the continents (chiefly due to the increasingly severe winters). In Moscow, for example, the temperature is 17°C in July and – 10°C in January; annual precipitation is about 600 mm. The corresponding values in Novosibirsk are 19°, – 19°C, and 410 mm. (Everywhere the maximum precipitation falls in the summer.) The aridity of the climate increases in the southern part of the temperate zone within Eurasian regions, and there are steppe, semisteppe, and desert landscapes; the snow cover is unstable. The most continental climate is found in the northeastern regions of Eurasia. The Verkhoiansk-Oimiakon region in Yakutia is one of the winter poles of cold in the northern hemisphere. The mean January temperature here drops to – 50°C, and the absolute minimum temperature is about – 70°C. In the northern hemisphere the winters are very harsh and almost snowless in the mountains and on the high plateaus in the interior of continents. Anticyclonic weather prevails, summers are hot, and there is comparatively little precipitation, which falls mainly in summer. (In Ulan Bator, for example, the temperature is 17°C in July and – 24°C in January; annual precipitation is 240 mm.) An intracontinental climate did not develop in the southern hemisphere owing to the limited area of the continents at the corresponding latitudes.
Monsoon climate of the temperate regions. The monsoon climate of the temperate regions forms at the eastern edges of Eurasia. It is characterized by almost cloudless and cold winters with prevailing southwesterly winds, warm or moderately warm summers with southeasterly and southerly winds, and adequate or even abundant summer precipitation. (In Khabarovsk, for example, the temperature rises to 23°C in July and drops to – 20°C in January; annual precipitation is 560 mm, of which only 74 mm falls in the cold months.) The winters are much milder in Japan and on Kamchatka and there is a great deal of precipitation both in winter and in summer. A deep snow cover forms on Kamchatka, Sakhalin, and the island of Hokkaido.
Subarctic climate. A subarctic climate prevails at the northern edges of Eurasia and North America. The winters are long and harsh. The mean temperature of the warmest month is no higher than 12°C; annual precipitation is less than 300 mm, and it is even less than 100 mm in southeastern Siberia. With cold summers and permafrost, even a little precipitation creates excess moisture and causes the soil to become waterlogged in many areas. A similar climate is found in the southern hemisphere only on subantarctic islands and Graham Land.
Intense cyclonic activity with windy, cloudy weather and abundant precipitation prevails over the oceans of both hemispheres in the temperate and subpolar regions.
Arctic basin climate. The climate of the Arctic basin is bleak. The mean monthly temperatures vary from 0°C in summer to –40°C in winter and from –15° to –50°C on the Greenland plateau; the absolute minimum is close to – 70°C. The mean annual air temperature is below – 30°C. There is little precipitation (less than 100 mm a year on most of Greenland). The Atlantic regions of the European arctic have a comparatively mild and humid climate because they are frequently reached by warm air masses from the Atlantic Ocean. (In Spitsbergen the temperature is –16°C in January and 5°C in July, and there is about 320 mm of precipitation a year.) Sudden warm spells sometimes occur even at the north pole. The climate is harsher in the Asian-American sector of the arctic.
Antarctic climate. The climate of Antarctica is the bleakest on earth. The winds that blow along the coasts are fierce because of the continuous cyclones that pass over the surrounding ocean and because of the cold air flowing from the central regions of the continent down the slopes of the ice shield. The mean temperature in Mirnyi is –2°C in January and December and – 18°C in August and September. Annual precipitation totals 300–700 mm. High atmospheric pressure prevails almost constantly in eastern Antarctica on the highy icy plateau; the winds are weak and there is little cloudiness. The mean temperature is about –30°C in summer and about –70°C in winter. The absolute minimum at Vostok Station is close to –90°C (the coldest spot on earth). Less than 100 mm of precipitation falls a year. The climate is somewhat milder in western Antarctica and at the south pole.
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S. P. KHROMOV