What is latitudinal zonation? How does it manifest itself? Natural zoning. Latitudinal and altitudinal zoning
Latitudinal (geographical, landscape) zoning means a natural change various processes, phenomena, individual geographical components and their combinations (systems, complexes) from the equator to the poles. Zoning in its elementary form was known to scientists Ancient Greece, but the first steps in the scientific development of the theory of world zoning are associated with the name of A. Humboldt, who in early XIX V. substantiated the idea of the climatic and phytogeographic zones of the Earth. At the very end of the 19th century. V.V. Dokuchaev elevated latitudinal (in his terminology, horizontal) zoning to the rank of a world law.
For the existence of latitudinal zonality, two conditions are sufficient: the presence of a flow solar radiation and the sphericity of the Earth. Theoretically, the flow of this flow to the earth's surface decreases from the equator to the poles in proportion to the cosine of latitude (Fig. 3). However, the actual amount of insolation reaching the earth's surface is also influenced by some other factors that are also of an astronomical nature, including the distance from the Earth to the Sun. As you move away from the Sun, the flow of its rays becomes weaker, and at a sufficiently long distance the difference between the polar and equatorial latitudes loses its significance; Thus, on the surface of the planet Pluto, the estimated temperature is close to -230 °C. When you get too close to the Sun, on the contrary, all parts of the planet become too hot. In both extreme cases, the existence of water in the liquid phase, life, is impossible. The Earth is thus most “successfully” located in relation to the Sun.
The inclination of the earth's axis to the ecliptic plane (at an angle of about 66.5°) determines the uneven supply of solar radiation over the seasons, which significantly complicates the zonal distribution.
heat loss and intensifies zonal contrasts. If the earth's axis were perpendicular to the plane of the ecliptic, then each parallel would receive almost the same amount of solar heat throughout the year and there would be practically no seasonal changes in phenomena on Earth. The daily rotation of the Earth, which causes the deviation of moving bodies, including air masses, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, introduces additional complications into the zonation scheme.
The mass of the Earth also influences the nature of zonation, although indirectly: it allows the planet (unlike, for example, “light-
171 koi" of the Moon) to retain the atmosphere, which serves as an important factor in transformation and redistribution solar energy.
With a homogeneous material composition and the absence of irregularities, the amount of solar radiation on the earth's surface would vary strictly along latitude and would be the same at the same parallel, despite the complicating influence of the listed astronomical factors. But in the complex and heterogeneous environment of the epigeosphere, the flow of solar radiation is redistributed and undergoes various transformations, which leads to a violation of its mathematically correct zoning.
Since solar energy is practically the only source of physical, chemical and biological processes that underlie the functioning of geographical components, latitudinal zonality must inevitably appear in these components. However, these manifestations are far from unambiguous, and the geographical mechanism of zoning turns out to be quite complex.
Already passing through the thickness of the atmosphere, the sun's rays are partially reflected and also absorbed by clouds. Because of this, the maximum radiation reaching the earth's surface is observed not at the equator, but in the zones of both hemispheres between the 20th and 30th parallels, where the atmosphere is most transparent to sunlight (Fig. 3). Over land, the contrasts in atmospheric transparency are more significant than over the Ocean, which is reflected in the drawing of the corresponding curves. The curves of the latitudinal distribution of the radiation balance are somewhat smoother, but it is clearly visible that the surface of the Ocean is characterized by higher values than the land. The most important consequences of the latitudinal-zonal distribution of solar energy include zonality of air masses, atmospheric circulation and moisture circulation. Under the influence of uneven heating, as well as evaporation from the underlying surface, four main zonal types of air masses are formed: equatorial (warm and humid), tropical (warm and dry), boreal, or temperate masses (cool and wet), and Arctic, and in Southern Hemisphere Antarctic (cold and relatively dry).
The difference in the density of air masses causes disturbances in thermodynamic equilibrium in the troposphere and mechanical movement (circulation) of air masses. Theoretically (without taking into account the influence of the Earth’s rotation around its axis), air flows from heated equatorial latitudes should have risen and spread to the poles, and from there cold and heavier air would have returned in the surface layer to the equator. But the deflecting effect of the planet’s rotation (Coriolis force) introduces significant amendments to this scheme. As a result, several circulation zones or belts are formed in the troposphere. For the equator
The 172 al zone is characterized by low atmospheric pressure, calms, rising air currents, for tropical - high pressure, winds with an eastern component (trade winds), for moderate - low pressure, westerly winds, for polar - low pressure, winds with an eastern component. In summer (for the corresponding hemisphere), the entire atmospheric circulation system shifts towards “its” pole, and in winter - towards the equator. Therefore, in each hemisphere, three transition zones are formed - subequatorial, subtropical and subarctic (subantarctic), in which the types of air masses change according to the seasons. Thanks to atmospheric circulation, zonal temperature differences on the earth's surface are somewhat smoothed out, however, in the Northern Hemisphere, where the land area is much larger than in the Southern, the maximum heat supply is shifted to the north, to approximately 10 - 20 ° N. w. Since ancient times, it has been customary to distinguish five heat zones on Earth: two cold and temperate and one hot. However, such a division is purely conditional; it is extremely schematic and its geographical significance is small. The continuous nature of changes in air temperature near the earth's surface makes it difficult to distinguish between thermal zones. Nevertheless, using the latitudinal-zonal change in the main types of landscapes as a complex indicator, we can propose the following series of thermal zones, replacing each other from the poles to the equator:
1) polar (Arctic and Antarctic);
2) subpolar (subarctic and subantarctic);
3) boreal (cold-temperate);
4) subboreal (warm-temperate);
5) pre-subtropical;
6) subtropical;
7) tropical;
8) subequatorial;
9) equatorial.
The zonality of atmospheric circulation is closely related to the zonality of moisture circulation and humidification. A peculiar rhythmicity is observed in the distribution of precipitation by latitude: two maxima (the main one at the equator and a secondary one at boreal latitudes) and two minima (at tropical and polar latitudes) (Fig. 4). The amount of precipitation, as is known, does not yet determine the conditions of moisture and moisture supply of landscapes. To do this, it is necessary to correlate the amount of annual precipitation with the amount that is necessary for the optimal functioning of the natural complex. The best integral indicator of the need for moisture is the value of evaporation, i.e., the maximum evaporation theoretically possible given the climatic (and above all temperature)
nyh) conditions. G.N. Vysotsky first used this ratio back in 1905 to characterize the natural zones of European Russia. Subsequently, N. N. Ivanov, independently of G. N. Vysotsky, introduced an indicator into science that became known as humidification coefficient Vysotsky - Ivanov:
K=g/E,
Where G- annual precipitation; E- annual evaporation value 1.
1 For comparative characteristics of atmospheric humidification, the dryness index is also used RfLr, proposed by M.I.Budyko and A.A. Grigoriev: where R- annual radiation balance; L- latent heat of evaporation; G- annual amount of precipitation. In its physical meaning, this index is close to the inverse indicator TO Vysotsky-Ivanov. However, its use gives less accurate results.
In Fig. Figure 4 shows that latitudinal changes in precipitation and evaporation do not coincide and, to a large extent, even have the opposite character. As a result, on the latitude curve TO in each hemisphere (for land) two critical points are distinguished, where TO passes through 1. Value TO- 1 corresponds to the optimum atmospheric humidification; at K> 1 moisture becomes excessive, and when TO< 1 - insufficient. Thus, on the surface of the land itself general view One can distinguish an equatorial belt of excess moisture, two belts of insufficient moisture located symmetrically on both sides of the equator in low and middle latitudes, and two belts of excess moisture in high latitudes (see Fig. 4). Of course, this is a highly generalized, averaged picture that does not reflect, as we will see later, gradual transitions between belts and significant longitudinal differences within them.
The intensity of many physical-geographical processes depends on the ratio of heat supply and moisture. However, it is easy to notice that latitudinal-zonal changes in temperature conditions and moisture have different directions. If solar heat reserves generally increase from the poles to the equator (although the maximum is somewhat shifted to tropical latitudes), then the humidification curve has a pronounced wave-like character. Without touching on methods for quantitatively assessing the ratio of heat supply and humidification, we will outline the most general patterns changes in this ratio along latitude. From the poles to approximately the 50th parallel, an increase in heat supply occurs under conditions of constant excess moisture. Further, as one approaches the equator, an increase in heat reserves is accompanied by a progressive increase in dryness, which leads to frequent changes in landscape zones, the greatest diversity and contrast of landscapes. And only in a relatively narrow strip on both sides of the equator is there a combination of large heat reserves with abundant moisture.
To assess the influence of climate on the zonation of other components of the landscape and the natural complex as a whole, it is important to take into account not only the average annual values of heat and moisture supply indicators, but also their regime, i.e. intra-annual changes. Thus, temperate latitudes are characterized by seasonal contrast in thermal conditions with a relatively uniform intra-annual distribution of precipitation; in the subequatorial zone, with small seasonal differences in temperature conditions, the contrast between dry and wet seasons etc.
Climatic zoning is reflected in all other geographical phenomena - in the processes of runoff and hydrological regime, in the processes of waterlogging and the formation of groundwater.
175 waters, the formation of weathering crust and soils, in the migration of chemical elements, as well as in the organic world. Zoning is also clearly evident in the surface layer of the World Ocean. A particularly vivid, to a certain extent integral expression geographical zonation found in vegetation and soils.
Separately, it should be said about the zonality of the relief and the geological foundation of the landscape. In the literature one can find statements that these components do not obey the law of zonation, i.e. azonal. First of all, it should be noted that it is unlawful to divide geographical components into zonal and azonal, because in each of them, as we will see, the influence of both zonal and azonal patterns is manifested. The relief of the earth's surface is formed under the influence of so-called endogenous and exogenous factors. The first include tectonic movements and volcanism, which are of an azonal nature and create morphostructural features of the relief. Exogenous factors are associated with the direct or indirect participation of solar energy and atmospheric moisture, and the sculptural relief forms they create are distributed zonally on Earth. It is enough to recall the specific forms of the glacial relief of the Arctic and Antarctic, thermokarst depressions and heaving mounds of the Subarctic, ravines, gullies and subsidence depressions of the steppe zone, aeolian forms and drainless saline depressions of the desert, etc. In forest landscapes, thick vegetation cover restrains the development of erosion and determines the predominance of “soft” weakly dissected relief. The intensity of exogenous geomorphological processes, for example, erosion, deflation, karst formation, significantly depends on latitudinal and zonal conditions.
The structure of the earth's crust also combines azonal and zonal features. If igneous rocks are undoubtedly of azonal origin, then the sedimentary layer is formed under the direct influence of climate, the life activity of organisms, and soil formation and cannot but bear the stamp of zonality.
All along geological history Sedimentation (lithogenesis) proceeded differently in different zones. In the Arctic and Antarctic, for example, unsorted clastic material (moraine) accumulated, in the taiga - peat, in deserts - clastic rocks and salts. For each specific geological era, it is possible to reconstruct the picture of the zones of that time, and each zone will have its own types of sedimentary rocks. However, throughout geological history, the system of landscape zones has undergone repeated changes. Thus, the results of lithogenesis were superimposed on the modern geological map
176 all geological periods, when the zones were completely different from what they are now. Hence the external diversity of this map and the absence of visible geographical patterns.
From the above it follows that zonation cannot be considered as some simple imprint of the modern climate in earthly space. Essentially, landscape zones are space-time formations, they have their own age, their own history and are changeable both in time and space. The modern landscape structure of the epigeosphere developed mainly in the Cenozoic. The equatorial zone is distinguished by the greatest antiquity; as one moves towards the poles, the zonation experiences increasing variability, and the age modern zones decreases.
The last significant restructuring of the world zonation system, which mainly affected high and moderate latitudes, is associated with continental glaciations of the Quaternary period. Oscillatory zone displacements continue here in post-glacial times. In particular, over the past millennia there has been at least one period when the taiga zone in some places advanced to the northern edge of Eurasia. The tundra zone within its modern boundaries arose only after the subsequent retreat of the taiga to the south. The reasons for such changes in the position of zones are associated with rhythms of cosmic origin.
The effect of the law of zoning is most fully reflected in the relatively thin contact layer of the epigeosphere, i.e. in the landscape sector itself. As one moves away from the surface of land and ocean to the outer boundaries of the epigeosphere, the influence of zonality weakens, but does not completely disappear. Indirect manifestations of zonality are observed at great depths in the lithosphere, almost throughout the entire stratisphere, i.e., thicker than sedimentary rocks, the connection of which with zonality has already been discussed. Zonal differences in the properties of artesian waters, their temperature, mineralization, and chemical composition can be traced to a depth of 1000 m or more; fresh horizon groundwater in zones of excessive and sufficient moisture it can reach a thickness of 200-300 and even 500 m, while in arid zones the thickness of this horizon is insignificant or completely absent. On the ocean floor, zoning is indirectly manifested in the nature of bottom silts, which have predominantly organic origin. We can assume that the law of zonality applies to the entire troposphere, since its most important properties are formed under the influence of the subaerial surface of the continents and the World Ocean.
In Russian geography, the importance of the law of zonation for human life and social production has long been underestimated. V.V. Dokuchaev’s judgments on this topic are assessed
177 were exaggerated and a manifestation of geographical determinism. The territorial differentiation of population and economy has its own patterns, which cannot be completely reduced to action natural factors. However, to deny the influence of the latter on the processes occurring in human society would be a gross methodological error, fraught with serious socio-economic consequences, as all historical experience and modern reality convince us of.
Various aspects of the manifestation of the law of latitudinal zonation in the sphere of socio-economic phenomena are discussed in more detail in Chapter. 4.
The law of zonation finds its most complete, complex expression in the zonal landscape structure of the Earth, i.e. in the existence of the system landscape areas. The system of landscape zones should not be imagined as a series of geometrically regular continuous stripes. Even V.V. Dokuchaev did not imagine zones as an ideal belt shape, strictly delimited by parallels. He emphasized that nature is not mathematics, and zoning is just a diagram or law. As the landscape zones were further explored, it was discovered that some of them were broken, some zones (for example, the zone deciduous forests) are developed only in the peripheral parts of the continents, others (deserts, steppes), on the contrary, gravitate towards inland areas; the boundaries of the zones deviate to a greater or lesser extent from parallels and in some places acquire a direction close to the meridional; in the mountains, latitudinal zones seem to disappear and are replaced by altitudinal zones. Similar facts gave rise in the 30s. XX century some geographers claim that latitudinal zoning is not at all universal law, but only a special case characteristic of the large plains, and that its scientific and practical significance is exaggerated.
In reality, various kinds of violations of zonality do not refute its universal significance, but only indicate that it manifests itself differently in different conditions. Every natural law operates differently in different conditions. This also applies to such simple physical constants as the freezing point of water or the magnitude of the acceleration of gravity: they are not violated only under the conditions of a laboratory experiment. In the epigeosphere, many natural laws operate simultaneously. Facts that at first glance do not fit into the theoretical model of zonation with its strictly latitudinal continuous zones indicate that zonation is not the only geographical pattern and it is impossible to explain the whole complex nature territorial physical-geographical differentiation.
178 pressure maximums. In the temperate latitudes of Eurasia, differences in average January air temperatures on the western periphery of the continent and in its inner extreme continental part exceed 40 °C. In summer, it is warmer in the interior of the continents than on the periphery, but the differences are not so great. A generalized idea of the degree of oceanic influence on the temperature regime of continents is given by indicators of climate continentality. Exist various ways calculations of such indicators based on taking into account the annual amplitude of average monthly temperatures. The most successful indicator, taking into account not only the annual amplitude of air temperatures, but also the daily one, as well as the lack of relative humidity in the driest month and the latitude of the point, was proposed by N.N. Ivanov in 1959. Taking the average planetary significance indicator for 100%, the scientist broke down the entire series of values he obtained for different points globe, for ten continental zones (the numbers in brackets are given as percentages):
1) extremely oceanic (less than 48);
2) oceanic (48 - 56);
3) temperate oceanic (57 - 68);
4) marine (69 - 82);
5) weak sea (83-100);
6) weakly continental (100-121);
7) moderate continental (122-146);
8) continental (147-177);
9) sharply continental (178 - 214);
10) extremely continental (more than 214).
In the diagram of a generalized continent (Fig. 5), the continental climate zones are located in the form of concentric stripes irregular shape around the extreme continental cores in each hemisphere. It is easy to notice that at almost all latitudes continentality varies widely.
About 36% atmospheric precipitation that fall onto the land surface are of oceanic origin. As they move inland, sea air masses lose moisture, leaving most it is found on the periphery of continents, especially on the slopes of mountain ranges facing the Ocean. The greatest longitudinal contrast in the amount of precipitation is observed in tropical and subtropical latitudes: heavy monsoon rains on the eastern periphery of the continents and extreme aridity in the central, and partly in the western regions, exposed to the influence of the continental trade wind. This contrast is aggravated by the fact that evaporation sharply increases in the same direction. As a result, on the Pacific periphery of the tropics of Eurasia, the humidification coefficient reaches 2.0 - 3.0, while in most of the space tropical zone it does not exceed 0.05,
The landscape and geographical consequences of the continental-oceanic circulation of air masses are extremely diverse. In addition to heat and moisture, various salts come from the Ocean with air currents; this process, called impulverization by G.N. Vysotsky, serves the most important reason salinization of many arid regions. It has long been noted that as one moves away from the ocean coasts into the interior of the continents, there is a natural change in plant communities, animal populations, and soil types. In 1921, V.L. Komarov called this pattern meridional zoning; he believed that on each continent three meridional zones should be distinguished: one inland and two oceanic. In 1946, this idea was concretized by the Leningrad geographer A.I. Yaunputnin. In his
181 physical-geographical zoning of the Earth, he divided all continents into three longitudinal sectors- western, eastern and central and for the first time noted that each sector is distinguished by its own set of latitudinal zones. However, the predecessor of A.I. Jaunputnin should be considered the English geographer A.J. Herbertson, who back in 1905 divided the land into natural zones and in each of them identified three longitudinal segments - western, eastern and central.
With a subsequent, deeper study of the pattern, which became commonly called longitudinal sectoring, or simply sectorality, It turned out that the three-member sector division of the entire landmass is too schematic and does not reflect the full complexity of this phenomenon. The sector structure of the continents has a clearly expressed asymmetrical character and is not the same in different latitudinal zones. Thus, in tropical latitudes, as already noted, a two-member structure is clearly outlined, in which the continental sector dominates, and the western sector is reduced. In polar latitudes, sectoral physical-geographical differences are weak due to the dominance of fairly homogeneous air masses, low temperatures and excess moisture. In the bo-real belt of Eurasia, where the land has the greatest (almost 200°) longitude extent, on the contrary, not only are all three sectors clearly expressed, but there is also a need to establish additional, transitional steps between them.
The first detailed scheme of sector division of land, implemented on the maps of the “Physical-geographical Atlas of the World” (1964), was developed by E. N. Lukashova. There are six physical-geographical (landscape) sectors in this scheme. The use of quantitative indicators as criteria for sectoral differentiation - humidification coefficients and continental ™, and as a complex indicator - the boundaries of distribution of zonal types of landscapes made it possible to detail and clarify E. N. Lukashova’s scheme.
Here we come to the essential question of the relationship between zonality and sectorization. But first it is necessary to pay attention to a certain duality in the use of terms zone And sector. In a broad sense, these terms are used as collective, essentially typological concepts. Thus, when saying “desert zone” or “steppe zone” (in the singular), they often mean the entire set of territorially isolated areas with similar zonal landscapes, which are scattered in different hemispheres, on different continents and in different sectors of the latter. Thus, in such cases, the zone is not conceived as a single integral territorial block, or region, i.e. cannot be considered as a zoning object. But at the same time the same ter-
182 mines may refer to specific, integral, territorially isolated units that correspond to the idea of the region, for example Desert zone of Central Asia, Steppe zone of Western Siberia. In this case, we are dealing with objects (taxa) of zoning. In the same way, we have the right to speak, for example, of the “western oceanic sector” in the broadest sense of the word as global phenomenon, uniting a number of specific territorial areas on different continents - in the Atlantic part of Western Europe and the Atlantic part of the Sahara, along the Pacific slopes of the Rocky Mountains, etc. Each similar piece of land is an independent region, but they are all analogues and are also called sectors, but understood in a narrower sense of the word.
Zone and sector in the broad sense of the word, which has a clearly typological connotation, should be interpreted as a common noun and, accordingly, their names should be written with a lowercase letter, while the same terms in the narrow (i.e. regional) sense and included in the proper geographical name, - capitalized. Options are possible, for example: Western European Atlantic sector instead of Western European Atlantic sector; Eurasian steppe zone instead of Steppe zone of Eurasia (or Steppe zone of Eurasia).
There are complex relationships between zoning and sectoring. Sector differentiation largely determines the specific manifestations of the law of zoning. Longitudinal sectors (in the broad sense) are, as a rule, extended across the strike of latitudinal zones. When moving from one sector to another, each landscape zone undergoes a more or less significant transformation, and for some zones, the boundaries of sectors turn out to be completely insurmountable barriers, so that their distribution is limited to strictly defined sectors. For example, the Mediterranean zone is confined to the western oceanic sector, and the subtropical moist forest zone is confined to the eastern oceanic sector (Table 2 and Fig. b) 1 . The reasons for such apparent anomalies should be sought in zonal-sectoral laws.
1 In Fig. 6 (as in Fig. 5) all continents are brought together in strict accordance with the latitudinal distribution of land, observing a linear scale along all parallels and the axial meridian, i.e. in the Sanson equal-area projection. This conveys the actual ratio of all contours by area. A similar, widely known and included in textbooks scheme by E. N. Lukashova and A. M. Ryabchikov was built without observing the scale and therefore distorts the proportions between the latitudinal and longitudinal extent of a conventional land mass and the areal relationships between individual contours. The essence of the proposed model is more accurately expressed by the term generalized continent instead of the frequently used ideal continent.
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the distribution of solar energy and, in particular, atmospheric humidification.
The main criteria for diagnosing landscape zones are objective indicators of heat supply and moisture. It has been established experimentally that among the many possible indicators for our purpose, the most acceptable
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rows of landscape zones analogues in terms of heat supply." I - polar; II - subpolar; III - boreal; IV - subboreal; V - pre-subtropical; VI - subtropical; VII - tropical and subequatorial; VIII - equatorial; rows of landscape analogue zones for moisture: A - extra-arid; B - arid; B - semiarid; G - semihumid; D - humid; 1 - 28 - landscape zones (explanations in Table 2); T- the sum of temperatures for the period with average daily air temperatures above 10 °C; TO- moisture coefficient. Scales - logarithmic
It should be noted that each such series of analogue zones fits into a certain range of values of the accepted heat supply indicator. Thus, the zones of the subboreal series lie in the range of sum temperatures 2200-4000 "C, subtropical - 5000 - 8000 "C. Within the accepted scale, less clear thermal differences are observed between the zones of the tropical, subequatorial and equatorial zones, but this is quite natural, since in this case the determining factor of zonal differentiation is not heat supply, but humidification 1 .
If the series of analogous zones in terms of heat supply generally coincide with the latitudinal zones, then the series of humidification have a more complex nature, containing two components - zonal and sectoral, and their territorial change is not unidirectional. Differences in atmospheric humidification cause
1 Due to this circumstance, as well as due to the lack of reliable data in table. 2 and in Fig. The 7th and 8th tropical and subequatorial belts are combined and the analogous zones related to them are not delimited.
187 are caught both by zonal factors during the transition from one latitudinal zone to another, and by sectoral factors, i.e., longitudinal moisture advection. Therefore, the formation of analogue zones in terms of moisture in some cases is associated primarily with zonality (in particular, taiga and equatorial forest in the humid series), in others - sectorality (for example, subtropical wet forest in the same series), and in others - a coinciding effect both patterns. The latter case includes zones of subequatorial wet forests and forest savannas.
The surface of our planet is heterogeneous and is conventionally divided into several belts, which are also called latitudinal zones. They naturally replace each other from the equator to the poles. What is latitudinal zonation? What does it depend on and how does it manifest itself? We'll talk about all this.
What is latitudinal zonation?
In certain parts of our planet, natural complexes and components differ. They are distributed unevenly and may seem chaotic. However, they have certain patterns, and they divide the Earth's surface into so-called zones.
What is latitudinal zonation? This is the distribution natural ingredients and physical-geographical processes in belts parallel to the equator line. It is manifested by differences in the average annual amount of heat and precipitation, the change of seasons, plant and soil cover, as well as representatives of the animal world.
In each hemisphere, the zones replace each other from the equator to the poles. In areas where there are mountains, this rule changes. Here, natural conditions and landscapes change from top to bottom, relative to absolute height.
Both latitudinal and altitudinal zoning are not always expressed equally. Sometimes they are more noticeable, sometimes less. The features of the vertical change of zones largely depend on the distance of the mountains from the ocean and the location of the slopes in relation to passing air flows. Most brightly altitudinal zone expressed in the Andes and Himalayas. What is latitudinal zoning is best seen in lowland regions.
What does zoning depend on?
The main reason for all the climatic and natural features of our planet is the Sun and the position of the Earth relative to it. Due to the fact that the planet is spherical in shape, solar heat is distributed unevenly over it, heating some areas more, others less. This, in turn, contributes to unequal heating of the air, which is why winds arise, which also participate in climate formation.
The natural features of individual areas of the Earth are also influenced by the development of the river system in the area and its regime, the distance from the ocean, the level of salinity of its waters, sea currents, the nature of the relief and other factors.
Manifestation on continents
On land, latitudinal zonation is more clearly visible than in the ocean. It manifests itself in the form of natural zones and climatic zones. In the Northern and Southern Hemispheres, the following zones are distinguished: equatorial, subequatorial, tropical, subtropical, temperate, subarctic, arctic. Each of them has its own natural zones (deserts, semi-deserts, arctic deserts, tundra, taiga, evergreen forest, etc.), of which there are much more.
On which continents is latitudinal zoning pronounced? It is best observed in Africa. Quite clearly visible on the plains North America and Eurasia (Russian Plain). In Africa, latitudinal zonation is clearly visible due to the small number of high mountains. They do not create a natural barrier for air masses, so climate zones replace each other without breaking the pattern.
The equator line crosses the African continent in the middle, so its natural areas are distributed almost symmetrically. Yes, wet equatorial forests transition to savannas and woodlands subequatorial belt. This is followed by tropical deserts and semi-deserts, which give way to subtropical forests and shrubs.
Interesting zoning manifests itself in North America. In the north, it is standardly distributed by latitude and is expressed by Arctic tundra and subarctic taiga. But below the Great Lakes, the zones are distributed parallel to the meridians. The high Cordilleras in the west block the winds from Pacific Ocean. Therefore, natural conditions change from west to east.
Zoning in the ocean
Changes in natural zones and zones also exist in the waters of the World Ocean. It is visible at a depth of up to 2000 meters, but is very clearly visible at a depth of 100-150 meters. It manifests itself in various components of the organic world, the salinity of water, as well as its chemical composition, and temperature differences.
The belts of the World Ocean are almost the same as those on land. Only instead of arctic and subarctic there is subpolar and polar, since the ocean reaches directly to the North Pole. In the lower layers of the ocean, the boundaries between the belts are stable, but in the upper layers they can shift depending on the season.
Latitudinal zonation
Regional and local differentiation of the epigeosphere
Latitudinal zonation
The differentiation of the epigeosphere into geosystems of different orders is determined by the unequal conditions of its development in different parts. As already noted, there are two main levels of physical-geographical differentiation - regional and local (or topological), which are based on deeply different reasons.
Regional differentiation is determined by the relationship between the two main energy factors external to the epigeosphere - radiant energy of the Sun and internal energy of the Earth. Both factors manifest themselves unevenly both in space and time. The specific manifestations of both in the nature of the epigeosphere determine the two most general geographical patterns - zoning And azonality.
Under latitudinal (geographical, landscape)zonality 1
implied natural change in physical-geographical processes, components and complexes (geosystems) from the equator To poles. The primary cause of zonality is the uneven distribution of short-wave radiation from the Sun across latitude due to the sphericity of the Earth and changes in the angle of incidence sun rays to the earth's surface. For this reason, the amount of radiant energy from the Sun varies per unit area depending on latitude. Consequently, for the existence of zonality, two conditions are sufficient - the flow of solar radiation and the sphericity of the Earth, and theoretically, the distribution of this flow over the earth's surface should have the form of a mathematically correct curve (Fig. 5, Ra). In reality, however, the latitudinal distribution of solar energy also depends on some other factors, which also have an external, astronomical nature. One of them is the distance between the Earth and the Sun.
As you move away from the Sun, the flow of its rays becomes weaker, and you can imagine a distance (for example, how far away the planet Pluto is from the Sun) at which the difference
Rice. 5. Zonal distribution of solar radiation:
Ra - radiation at the upper boundary of the atmosphere; total radiation: Rcc- on. land surface, Rco - on the surface of the World Ocean, Rcз - average for the surface of the globe; radiation balance: Rc- on the land surface, Ro- on the surface of the ocean, Rз - average for the surface of the globe
between the equatorial and polar latitudes, in relation to insolation, it loses its significance - it will be equally cold everywhere (on the surface of Pluto, the estimated temperature is about - 230 ° C). If we were too close to the Sun, on the contrary, all parts of the planet would be excessively hot. In both extreme cases, the existence of neither water in the liquid phase nor life is possible. The Earth turned out to be the most “successfully” located planet in relation to the Sun.
The mass of the Earth also affects the nature of zonation, although
This is true: it allows our planet (unlike, for example, the “light” Moon) to retain an atmosphere, which serves as an important factor in the transformation and redistribution of solar energy.
The inclination of the earth’s axis to the ecliptic plane (at an angle of about 66.5°) plays a significant role; the uneven supply of solar radiation over the seasons depends on this, which greatly complicates the zonal distribution of heat, and
also moisture and exacerbates zonal contrasts. If the earth's axis were
perpendicular to the ecliptic plane, then each parallel would receive almost the same amount of solar heat throughout the year and there would be practically no seasonal change in phenomena on Earth.
The daily rotation of the Earth, which causes the deviation of moving bodies, including air masses, to the right in the northern hemisphere and to the left in the southern, also introduces additional complications into the zonation scheme.
If the earth's surface were composed of any one substance and did not have irregularities, the distribution of solar radiation would remain strictly zonal, i.e., despite the complicating influence of the listed astronomical factors, its amount would vary strictly along latitude and at one parallel would be the same. But the heterogeneity of the surface of the globe - the presence of continents and oceans, the diversity of relief and rocks, etc. - causes a violation of the mathematically regular distribution of the flow of solar energy. Since solar energy is practically the only source of physical, chemical and biological processes on the earth's surface, these processes must inevitably have a zonal character. The mechanism of geographic zonation is very complex; it manifests itself far from unambiguously in different “environments”, in different components, processes, as well as in different parts of the epigeosphere. The first direct result of the zonal distribution of the solar radiant energy is the zonality of the radiation balance of the earth's surface. However, already in the distribution of incoming radiation we
We observe a clear violation of strict correspondence with latitude. In Fig. 51it is clearly seen that the maximum of the total radiation arriving at the earth's surface is not observed at the equator, which should be expected theoretically,
and in the space between the 20th and 30th parallels in both hemispheres -
northern and southern. The reason for this phenomenon is that at these latitudes the atmosphere is most transparent to the sun's rays (above the equator there are many clouds in the atmosphere that reflect the sun's rays).
1B SI energy is measured in joules, but until recently thermal energy It was customary to measure it in calories. Since many published geographical works indicators of radiation and thermal regimes are expressed in calories (or kilocalories), we present the following ratios: 1 J = 0.239 cal; 1 kcal = 4.1868*103J; 1 kcal/cm2= 41.868
rays, scatter and partially absorb them). Over land, the contrasts in atmospheric transparency are especially significant, which is clearly reflected in the shape of the corresponding curve. Thus, the epigeosphere does not passively, automatically respond to the influx of solar energy, but redistributes it in its own way. The curves of the latitudinal distribution of the radiation balance are somewhat smoother, but they are not a simple copy of the theoretical graph of the distribution of the flux of solar rays. These curves are not strictly symmetrical; It is clearly visible that the surface of the oceans is characterized by higher numbers than land. This also indicates an active reaction of the epigeosphere substance to external energy influences (in particular, due to the high reflectivity of the land, it loses significantly more radiant energy from the Sun than the ocean).
Radiant energy received by the earth's surface from the Sun and converted into heat is spent mainly on evaporation and heat transfer to the atmosphere, and the magnitude of these expenditure items is
radiation balance and their ratios change quite complexly according to
latitude And here we do not observe curves that are strictly symmetrical for land and
ocean (Fig. 6).
The most important consequences of uneven latitudinal heat distribution are
zonality of air masses, atmospheric circulation and moisture circulation. Under the influence of uneven heating, as well as evaporation from the underlying surface, air masses are formed that differ in their temperature properties, moisture content, and density. There are four main zonal types of air masses: equatorial (warm and humid), tropical (warm and dry), boreal or temperate masses (cool and wet), and Arctic, and in the southern hemisphere, Antarctic (cold and relatively dry). Uneven heating and, as a result, different densities of air masses (different atmospheric pressure) cause a violation of thermodynamic equilibrium in the troposphere and the movement (circulation) of air masses.
If the Earth did not rotate around its axis, air flows in the atmosphere would have a very simple character: from the heated equatorial latitudes, the air would rise up and spread to the poles, and from there it would return to the equator in the surface layers of the troposphere. In other words, the circulation should have had a meridional character and northern winds would constantly blow near the earth's surface in the northern hemisphere, and southern winds in the southern hemisphere. But the deflecting effect of the Earth's rotation introduces significant amendments to this scheme. As a result, several circulation zones are formed in the troposphere (Fig. 7). The main ones correspond to four zonal types of air masses, so in each hemisphere there are four of them: equatorial, common for the northern and southern hemispheres (low pressure, calms, rising air currents), tropical (high pressure, easterly winds), moderate
Rice. 6. Zonal distribution of radiation balance elements:
1 - the entire surface of the globe, 2 - land, 3 - ocean; LE- heat costs for
evaporation, R - turbulent heat transfer to the atmosphere
(low pressure, westerly winds) and polar (low pressure, eastern winds). In addition, there are three transition zones - subarctic, subtropical and subequatorial, in which the types of circulation and air masses change seasonally due to the fact that in summer (for the corresponding hemisphere) the entire atmospheric circulation system shifts to its “own” pole, and in winter - To equator (and opposite pole). Thus, seven circulation zones can be distinguished in each hemisphere.
Atmospheric circulation is a powerful mechanism for the redistribution of heat and moisture. Thanks to it, zonal temperature differences on the earth's surface are smoothed out, although the maximum still occurs not at the equator, but at slightly higher latitudes of the northern hemisphere (Fig. 8), which is especially clearly expressed on the land surface (Fig. 9).
The zonality of solar heat distribution has found its expression
Rice. 7. Scheme of general atmospheric circulation:
tion in the traditional concept of the Earth's thermal belts. However, the continuous nature of changes in air temperature near the earth's surface does not allow us to establish a clear system of zones and justify the criteria for their delimitation. Typically, the following zones are distinguished: hot (with an average annual temperature above 20 ° C), two moderate (between the annual isotherm of 20 ° C and the isotherm of the warmest month of 10 ° C) and two cold (with the temperature of the warmest month below 10 ° C); inside the latter, “regions of eternal frost” are sometimes distinguished (with the temperature of the warmest month below 0 ° C). This scheme, like some of its variants, is purely conventional in nature, and its landscape significance is small due to its extreme schematism. So, temperate zone covers a huge temperature range within which it fits the whole winter landscape zones - from tundra to desert. Note that such temperature zones do not coincide with circulation ones,
The zonality of atmospheric circulation is closely related to the zonality of moisture circulation and humidification. This is clearly manifested in the distribution of precipitation (Fig. 10). Zoning distribution
Rice. 8. Zonal distribution of air temperature on the surface of the globe: I- January, VII - July
Rice. 9. Zonal distribution of heat in the mind -
Renno continental sector of the northern hemisphere:
t- average air temperature in July,
sum of temperatures for a period with average daily
with temperatures above 10° C
The precipitation pattern has its own specificity, a peculiar rhythm: three maxima (the main one at the equator and two minor ones in temperate latitudes) and four minima (in polar and tropical latitudes). The amount of precipitation in itself does not determine the conditions of moisture or moisture supply of natural processes and the landscape as a whole. In the steppe zone, with 500 mm of annual precipitation, we are talking about insufficient moisture, and in the tundra, with 400 mm, we are talking about excess moisture. To judge moisture, you need to know not only the amount of moisture entering the geosystem annually, but also the amount that is necessary for its optimal functioning. The best indicator of moisture requirements is volatility, i.e., the amount of water that can evaporate from the earth's surface under given climatic conditions, assuming that moisture reserves are unlimited. Volatility is a theoretical value. Her
Rice. 10. Zonal distribution of precipitation, evaporation and coefficient
moisture content on the land surface:
1 - average annual precipitation, 2 - average annual evaporation, 3 - excess of precipitation over evaporation,
4 - excess of evaporation over precipitation, 5 - humidification coefficient (according to Vysotsky - Ivanov)
should be distinguished from evaporation, i.e., actually evaporating moisture, the amount of which is limited by the amount of precipitation. On land, evaporation is always less than evaporation.
In Fig. 10 it is clear that latitudinal changes in precipitation and evaporation do not coincide with each other and, to a large extent, even have the opposite character. Ratio of annual precipitation to
annual evaporation value can serve as an indicator of climatic
hydration. This indicator was first introduced by G. N. Vysotsky. Back in 1905, he used it to characterize the natural zones of European Russia. Subsequently, the Leningrad climatologist N.N. Ivanov built isolines of this relationship, which he called humidification coefficient(K), for the entire landmass of the Earth and showed that the boundaries of landscape zones coincide with certain values of K: in the taiga and tundra it exceeds 1, in the forest-steppe it is equal
1.0-0.6, in the steppe - 0.6 - 0.3, in the semi-desert - 0.3 - 0.12, in the desert -
less than 0.12 1.
In Fig. Figure 10 schematically shows the change in average values of the humidification coefficient (on land) by latitude. There are four critical points on the curve where K passes through 1. A value of 1 means that moisture conditions are optimal: precipitation can (theoretically) completely evaporate, doing useful “work”; if they
“pass” through plants, they will ensure maximum biomass production. It is no coincidence that in those zones of the Earth where K is close to 1, the highest productivity of vegetation is observed. The excess of precipitation over evaporation (K > 1) means that the moisture is excessive: the precipitation cannot completely return to the atmosphere, it flows along the earth's surface, fills depressions, and causes waterlogging. If precipitation is less than evaporation (K< 1), увлажнение недостаточное; в этих условиях обычно отсутствует лесная растительность, биологическая продуктивность низка, резко падает величина стока,.в почвах развивается засоление.
It should be noted that the amount of evaporation is determined primarily by heat reserves (as well as air humidity, which, in turn, also depends on thermal conditions). Therefore, the ratio of precipitation to evaporation can to a certain extent be considered as an indicator of the ratio of heat and moisture, or the conditions of heat and water supply of a natural complex (geosystem). There are, however, other ways of expressing the relationships between heat and moisture. The best known is the dryness index proposed by M. I. Budyko and A. A. Grigoriev: R/Lr, where R is the annual radiation balance, L
- latent heat of vaporization, r- annual amount of precipitation. Thus, this index expresses the ratio of the “useful reserve” of radiative heat to the amount of heat that must be expended to evaporate all precipitation in a given place.
In its physical meaning, the radiation dryness index is close to the Vysotsky-Ivanov humidification coefficient. If in the expression R/Lr divide the numerator and denominator by L, then we will get nothing more than
ratio of the maximum possible under given radiation conditions
evaporation (evaporation rate) to the annual amount of precipitation, i.e., a kind of inverted Vysotsky-Ivanov coefficient - a value close to 1/K. True, an exact match is not possible, since R/L does not fully correspond to evaporation, and for some other reasons related to the peculiarities of the calculations of both indicators. In any case, the isolines of the dryness index also generally coincide with the boundaries of landscape zones, but in excessively wet zones the index value is less than 1, and in arid zones it is more than 1.
1See: Ivanov N. N. Landscape and climatic zones of the globe // Notes
Geogr. Society of the USSR. New series. T. 1. 1948.
The intensity of many other physical-geographical processes depends on the ratio of heat and moisture. However, zonal changes in heat and moisture have different directions. If heat reserves generally increase from the poles to the equator (although the maximum is slightly shifted from the equator by tropical latitudes), then the moisture changes as if rhythmically, forming “waves” on the latitudinal curve (see Fig. 10). As a very primary scheme, we can outline several main climatic zones according to the ratio of heat supply and moisture: cold humid (north and south of 50°), warm (hot) dry (between 50° and 10°) and hot humid (between 10° N latitude and 10° S latitude).
Zoning is expressed not only in the average annual amount of heat and moisture, but also in their regime, that is, in intra-annual changes. It is common knowledge that equatorial zone distinguished by the most even temperature conditions, for temperate latitudes four thermal seasons are typical, etc. The zonal types of precipitation regime are varied: in the equatorial zone precipitation falls more or less evenly, but with two maximums, in subequatorial latitudes the summer maximum is pronounced, in the Mediterranean zone there is a winter maximum, for temperate latitudes are characterized by a uniform distribution with a summer maximum, etc. Climatic zoning is reflected in all other geographical phenomena - in the processes of runoff and hydrological regime, in the processes of swamping and the formation of groundwater, the formation of weathering crust and soils, in migration chemical elements, in the organic world. Zoning is clearly evident in the surface layer of the ocean (Table 1). Geographical zoning finds vivid expression in the organic world. It is no coincidence that landscape zones received their names mostly from characteristic types of vegetation. No less expressive is the zonality of the soil cover, which served as V.V. Dokuchaev’s starting point for developing the doctrine of natural zones, for defining zonality as
"world law".
Sometimes there are also statements that zonality does not appear in the relief of the earth’s surface and the geological foundation of the landscape, and these components are called “azonal”. Divide geographical components into
“zonal” and “azonal” are illegal, because in any of them, as we will see later, both zonal and azonal features are combined (we are not yet touching on the latter). Relief is no exception in this regard. As is known, it is formed under the influence of so-called endogenous factors, which are typically azonal in nature, and exogenous, associated with the direct or indirect participation of solar energy (weathering, the activity of glaciers, wind, flowing waters, etc.). All processes of the second group are zonal in nature, and the relief forms they create, called sculptural
Latitudinal (geographical, landscape) zoning means a natural change in various processes, phenomena, individual geographic components and their combinations (systems, complexes) from the equator to the poles. Zoning in its elementary form was known to the scientists of Ancient Greece, but the first steps in the scientific development of the theory of world zoning are associated with the name of A. Humboldt, who at the beginning of the 19th century. substantiated the idea of the climatic and phytogeographic zones of the Earth. At the very end of the 19th century. V.V. Dokuchaev elevated latitudinal (in his terminology, horizontal) zoning to the rank of a world law.For the existence of latitudinal zonality, two conditions are sufficient - the presence of a flux of solar radiation and the sphericity of the Earth. Theoretically, the flow of this flow to the earth's surface decreases from the equator to the poles in proportion to the cosine of latitude (Fig. 1). However, the actual amount of insolation reaching the earth's surface is also influenced by some other factors that are also of an astronomical nature, including the distance from the Earth to the Sun. As you move away from the Sun, the flow of its rays becomes weaker, and at a sufficiently long distance the difference between the polar and equatorial latitudes loses its significance; Thus, on the surface of the planet Pluto, the estimated temperature is close to -230°C. When you get too close to the Sun, on the contrary, all parts of the planet become too hot. In both extreme cases, the existence of water in the liquid phase, life, is impossible. The Earth is thus most “successfully” located in relation to the Sun.
The inclination of the earth's axis to the ecliptic plane (at an angle of about 66.5°) determines the uneven supply of solar radiation over the seasons, which significantly complicates the zonal distribution of heat and exacerbates zonal contrasts. If the earth's axis were perpendicular to the plane of the ecliptic, then each parallel would receive almost the same amount of solar heat throughout the year and there would be practically no seasonal changes in phenomena on Earth. The daily rotation of the Earth, which causes the deviation of moving bodies, including air masses, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, introduces additional complications into the zonation scheme.
Rice. 1. Distribution of solar radiation by latitude:
Rc - radiation at the upper boundary of the atmosphere; total radiation: 
- on the surface of the land, 
- on the surface of the World Ocean; 
- average for the surface of the globe; radiation balance: Rc - on the land surface, Ro - on the ocean surface, R3 - on the surface of the globe (average value)
The mass of the Earth also affects the nature of zonation, although indirectly: it allows the planet (unlike, for example, the “light” Moon) to retain an atmosphere, which serves as an important factor in the transformation and redistribution of solar energy.
With a homogeneous material composition and the absence of irregularities, the amount of solar radiation on the earth's surface would vary strictly along latitude and would be the same at the same parallel, despite the complicating influence of the listed astronomical factors. But in the complex and heterogeneous environment of the epigeosphere, the flow of solar radiation is redistributed and undergoes various transformations, which leads to a violation of its mathematically correct zoning.
Since solar energy is practically the only source of physical, chemical and biological processes that underlie the functioning of geographical components, latitudinal zonality must inevitably appear in these components. However, these manifestations are far from unambiguous, and the geographical mechanism of zoning turns out to be quite complex.
Already passing through the thickness of the atmosphere, the sun's rays are partially reflected and also absorbed by clouds. Because of this, the maximum radiation reaching the earth's surface is observed not at the equator, but in the zones of both hemispheres between the 20th and 30th parallels, where the atmosphere is most transparent to sunlight (Fig. 1). Over land, the atmospheric transparency contrasts are more significant than over the ocean, which is reflected in the drawing of the corresponding curves. The curves of the latitudinal distribution of the radiation balance are somewhat smoother, but it is clearly visible that the ocean surface is characterized by higher values than the land. The most important consequences of the latitudinal-zonal distribution of solar energy include zonality of air masses, atmospheric circulation and moisture circulation. Under the influence of uneven heating, as well as evaporation from the underlying surface, four main zonal types of air masses are formed: equatorial (warm and humid), tropical (warm and dry), boreal, or masses of temperate latitudes (cool and wet), and arctic, and in Southern Hemisphere Antarctic (cold and relatively dry).
The difference in the density of air masses causes disturbances in thermodynamic equilibrium in the troposphere and mechanical movement (circulation) of air masses. Theoretically (without taking into account the influence of the Earth’s rotation around its axis), air currents from the heated equatorial latitudes should have risen and spread to the poles, and from there cold and heavier air would have returned in the surface layer to the equator. But the deflecting effect of the planet’s rotation (Coriolis force) introduces significant amendments to this scheme. As a result, several circulation zones or belts are formed in the troposphere. The equatorial belt is characterized by low atmospheric pressure, calms, rising air currents, for the tropical - high pressure, winds with an eastern component (trade winds), for moderate - low pressure, westerly winds, for the polar - low pressure, winds with an eastern component. In summer (for the corresponding hemisphere), the entire atmospheric circulation system shifts to “its” pole, and in winter - to the equator. Therefore, in each hemisphere, three transition zones are formed - subequatorial, subtropical and subarctic (subantarctic), in which the types of air masses change according to the seasons. Thanks to atmospheric circulation, zonal temperature differences on the earth's surface are somewhat smoothed out, however, in the Northern Hemisphere, where the land area is much larger than in the Southern, the maximum heat supply is shifted to the north, to approximately 10-20° N latitude. Since ancient times, it has been customary to distinguish five heat zones on Earth: two cold and temperate and one hot. However, such a division is purely conditional; it is extremely schematic and its geographical significance is small. The continuous nature of changes in air temperature near the earth's surface makes it difficult to distinguish between thermal zones. Nevertheless, using the latitudinal-zonal change in the main types of landscapes as a complex indicator, we can propose the following series of thermal zones, replacing each other from the poles to the equator:
1) polar (Arctic and Antarctic);
2) subpolar (subarctic and subantarctic);
3) boreal (cold-temperate);
4) subboreal (warm-temperate);
5) pre-subtropical;
6) subtropical;
7) tropical;
8) subequatorial;
9) equatorial.
The zonality of atmospheric circulation is closely related to the zonality of moisture circulation and humidification. A peculiar rhythmicity is observed in the distribution of precipitation by latitude: two maxima (the main one at the equator and a secondary one at boreal latitudes) and two minima (at tropical and polar latitudes) (Fig. 2). The amount of precipitation, as is known, does not yet determine the conditions of moisture and moisture supply of landscapes. To do this, it is necessary to correlate the amount of annual precipitation with the amount that is necessary for the optimal functioning of the natural complex. The best integral indicator of moisture demand is the evaporation value, i.e. maximum evaporation theoretically possible under given climatic (and above all temperature) conditions. G.N. Vysotsky first used this ratio back in 1905 to characterize natural areas European Russia. Subsequently N.N. Ivanov, independently of G.N. Vysotsky introduced into science an indicator that became known as the Vysotsky-Ivanov humidification coefficient:
K = r / E,
where r is the annual amount of precipitation; E - annual evaporation value1.
Figure 2 shows that latitudinal changes in precipitation and evaporation do not coincide and, to a large extent, even have the opposite character. As a result, two critical points are identified on the latitudinal curve K in each hemisphere (for land), where K passes through 1. The value K = 1 corresponds to the optimum of atmospheric moisture; at K >1, moisture becomes excessive, and at K< 1 - недостаточным. Таким образом, на поверхности суши в самом общем виде можно выделить экваториальный пояс избыточного увлажнения, два симметрично расположенных по обе стороны от экватора пояса недостаточного увлажнения в низких и средних широтах и два пояса избыточного увлажнения в высоких широтах (рис. 2). Разумеется, это сильно генерализованная, осреднённая картина, не отражающая, как мы увидим в дальнейшем, постепенных переходов между поясами и существенных долготных различий внутри них.
Rice. 2. Distribution of precipitation, evaporation
And the moisture coefficient by latitude on the land surface:
1 - average annual precipitation; 2 - average annual evaporation;
3 - excess of precipitation over evaporation; 4 - excess
Evaporation over precipitation; 5 - moisture coefficient
The intensity of many physical-geographical processes depends on the ratio of heat supply and moisture. However, it is easy to notice that latitudinal-zonal changes in temperature conditions and moisture have different directions. If solar heat reserves generally increase from the poles to the equator (although the maximum is somewhat shifted to tropical latitudes), then the humidification curve has a pronounced wave-like character. Without touching on methods for quantitatively assessing the ratio of heat supply and humidification, we will outline the most general patterns of changes in this ratio along latitude. From the poles to approximately the 50th parallel, an increase in heat supply occurs under conditions of constant excess moisture. Further, as one approaches the equator, an increase in heat reserves is accompanied by a progressive increase in dryness, which leads to frequent changes in landscape zones, the greatest diversity and contrast of landscapes. And only in a relatively narrow strip on both sides of the equator is there a combination of large heat reserves with abundant moisture.
To assess the influence of climate on the zonation of other components of the landscape and the natural complex as a whole, it is important to take into account not only the average annual values of heat and moisture supply indicators, but also their regime, i.e. intra-annual changes. Thus, temperate latitudes are characterized by seasonal contrast in thermal conditions with a relatively uniform intra-annual distribution of precipitation; in the subequatorial zone, with small seasonal differences in temperature conditions, the contrast between the dry and wet seasons is sharp, etc.
Climatic zonality is reflected in all other geographical phenomena - in the processes of runoff and hydrological regime, in the processes of swamping and the formation of groundwater, the formation of weathering crust and soils, in the migration of chemical elements, as well as in the organic world. Zoning is clearly manifested in the surface thickness of the World Ocean. Geographic zoning finds a particularly vivid and, to a certain extent, integral expression in vegetation cover and soils.
Separately, it should be said about the zonality of the relief and the geological foundation of the landscape. In the literature one can find statements that these components do not obey the law of zonation, i.e. azonal. First of all, it should be noted that it is unlawful to divide geographical components into zonal and azonal, because in each of them, as we will see, the influence of both zonal and azonal patterns is manifested. The relief of the earth's surface is formed under the influence of so-called endogenous and exogenous factors. The first include tectonic movements and volcanism, which are of an azonal nature and create morphostructural features of the relief. Exogenous factors are associated with the direct or indirect participation of solar energy and atmospheric moisture, and the sculptural relief forms they create are distributed zonally on Earth. It is enough to recall the specific forms of the glacial relief of the Arctic and Antarctic, thermokarst depressions and heaving mounds of the Subarctic, ravines, gullies and subsidence depressions of the steppe zone, aeolian forms and drainless saline depressions of the desert, etc. In forest landscapes, a thick vegetation cover restrains the development of erosion and determines the predominance of “soft” weakly dissected relief. The intensity of exogenous geomorphological processes, such as erosion, deflation, karst formation, significantly depends on latitudinal and zonal conditions.
The structure of the earth's crust also combines azonal and zonal features. If igneous rocks are undoubtedly of azonal origin, then the sedimentary layer is formed under the direct influence of climate, the life activity of organisms, and soil formation and cannot but bear the stamp of zonality.
Throughout geological history, sedimentation (lithogenesis) occurred differently in different zones. In the Arctic and Antarctic, for example, unsorted clastic material (moraine) accumulated, in the taiga - peat, in deserts - clastic rocks and salts. For each specific geological era, it is possible to reconstruct the picture of the zones of that time, and each zone will have its own types of sedimentary rocks. However, throughout geological history, the system of landscape zones has undergone repeated changes. Thus, the results of lithogenesis of all geological periods, when the zones were completely different from what they are now, are superimposed on the modern geological map. Hence the external diversity of this map and the absence of visible geographical patterns.
From the above it follows that zonation cannot be considered as some simple imprint of the modern climate in earthly space. Essentially, landscape zones are spatiotemporal formations; they have their own age, their own history and are variable both in time and space. The modern landscape structure of the epigeosphere developed mainly in the Cenozoic. The equatorial zone is distinguished by the greatest antiquity; as we move towards the poles, zonality experiences increasing variability, and the age of modern zones decreases.
The last significant restructuring of the world zonation system, which mainly affected high and moderate latitudes, is associated with continental glaciations of the Quaternary period. Oscillatory zone displacements continue here in post-glacial times. In particular, over the past millennia there has been at least one period when the taiga zone in some places advanced to the northern edge of Eurasia. The tundra zone within its modern boundaries arose only after the subsequent retreat of the taiga to the south. The reasons for such changes in the position of zones are associated with rhythms of cosmic origin.
The effect of the law of zoning is most fully reflected in the relatively thin contact layer of the epigeosphere, i.e. in the landscape sector itself. As one moves away from the surface of land and ocean to the outer boundaries of the epigeosphere, the influence of zonality weakens, but does not completely disappear. Indirect manifestations of zoning are observed at great depths in the lithosphere, practically throughout the stratosphere, i.e. thicker than sedimentary rocks, the connection of which with zonation has already been discussed. Zonal differences in the properties of artesian waters, their temperature, mineralization, and chemical composition can be traced to a depth of 1000 m or more; The horizon of fresh groundwater in zones of excessive and sufficient moisture can reach a thickness of 200-300 and even 500 m, while in arid zones the thickness of this horizon is insignificant or completely absent. On the ocean floor, zonation is indirectly manifested in the nature of bottom silts, which are predominantly of organic origin. It can be considered that the law of zonation applies to the entire troposphere, since its most important properties are formed under the influence of the subaerial surface of the continents and the World Ocean.
In Russian geography, the importance of the law of zonation for human life and social production has long been underestimated. Judgments V.V. Dokuchaev on this topic was regarded as an exaggeration and a manifestation of geographical determinism. The territorial differentiation of population and economy has its own patterns, which cannot be completely reduced to the action of natural factors. However, to deny the influence of the latter on the processes occurring in human society would be a gross methodological mistake, fraught with serious socio-economic consequences, as all historical experience and modern reality convince us of.
The law of zonation finds its most complete, complex expression in the zonal landscape structure of the Earth, i.e. in the existence of a system of landscape zones. The system of landscape zones should not be imagined as a series of geometrically regular continuous strips. Also V.V. Dokuchaev did not imagine the zones as an ideal belt shape, strictly delimited by parallels. He emphasized that nature is not mathematics, and zoning is just a pattern or a law. As we further studied the landscape zones, it was discovered that some of them were broken, some zones (for example, the zone of broad-leaved forests) were developed only in the peripheral parts of the continents, others (deserts, steppes), on the contrary, gravitated towards inland areas; the boundaries of the zones deviate to a greater or lesser extent from parallels and in some places acquire a direction close to the meridional; in the mountains, latitudinal zones seem to disappear and are replaced by altitudinal zones. Similar facts gave rise in the 30s. XX century some geographers argue that latitudinal zoning is not a universal law at all, but only special case, characteristic of the great plains, and that its scientific and practical significance exaggerated.
In reality, various kinds of violations of zonality do not refute its universal significance, but only indicate that it manifests itself differently in different conditions. Every natural law operates differently in different conditions. This also applies to such simple physical constants as the freezing point of water or the magnitude of the acceleration of gravity. They are not violated only in conditions laboratory experiment. In the epigeosphere, many natural laws operate simultaneously. Facts that at first glance do not fit into the theoretical model of zonality with its strictly latitudinal continuous zones indicate that zonality is not the only geographical pattern and it alone cannot explain the entire complex nature of territorial physical-geographic differentiation.
The surface of our planet is heterogeneous and is conventionally divided into several belts, which are also called latitudinal zones. They naturally replace each other from the equator to the poles. What is latitudinal zonation? What does it depend on and how does it manifest itself? We'll talk about all this.
What is latitudinal zonation?
In certain parts of our planet, natural complexes and components differ. They are distributed unevenly and may seem chaotic. However, they have certain patterns, and they divide the Earth's surface into so-called zones.
What is latitudinal zonation? This is the distribution of natural components and physical-geographical processes in belts parallel to the equator line. It is manifested by differences in the average annual amount of heat and precipitation, the change of seasons, plant and soil cover, as well as representatives of the animal world.
In each hemisphere, the zones replace each other from the equator to the poles. In areas where there are mountains, this rule changes. Here, natural conditions and landscapes change from top to bottom, relative to absolute height.
Both latitudinal and altitudinal zoning are not always expressed equally. Sometimes they are more noticeable, sometimes less. The features of the vertical change of zones largely depend on the distance of the mountains from the ocean and the location of the slopes in relation to passing air flows. Altitudinal zonation is most clearly expressed in the Andes and Himalayas. What latitudinal zonation is is best seen in lowland regions.
What does zoning depend on?
The main reason for all the climatic and natural features of our planet is the Sun and the position of the Earth relative to it. Due to the fact that the planet has a spherical shape, the sun's heat is distributed unevenly across it, heating some areas more and others less. This, in turn, contributes to unequal heating of the air, which is why winds arise, which also participate in climate formation.
The natural features of individual areas of the Earth are also influenced by the development of the river system in the area and its regime, the distance from the ocean, the salinity level of its waters, sea currents, the nature of the relief and other factors.
Manifestation on continents
On land, latitudinal zonation is more clearly visible than in the ocean. It manifests itself in the form of natural zones and climatic zones. In the Northern and Southern Hemispheres, the following zones are distinguished: equatorial, subequatorial, tropical, subtropical, temperate, subarctic, arctic. Each of them has its own natural zones (deserts, semi-deserts, arctic deserts, tundra, taiga, evergreen forest, etc.), of which there are many more.
On which continents is latitudinal zoning pronounced? It is best observed in Africa. It can be seen quite well on the plains of North America and Eurasia (Russian Plain). In Africa, latitudinal zonation is clearly visible due to the small number of high mountains. They do not create a natural barrier for air masses, so climate zones replace each other without breaking the pattern.
The equator line crosses the African continent in the middle, so its natural areas are distributed almost symmetrically. Thus, humid equatorial forests transform into savannas and open forests of the subequatorial belt. This is followed by tropical deserts and semi-deserts, which give way to subtropical forests and shrubs.
Interesting zoning manifests itself in North America. In the north, it is standardly distributed by latitude and is expressed by Arctic tundra and subarctic taiga. But below the Great Lakes, the zones are distributed parallel to the meridians. The high Cordilleras in the west block the winds from the Pacific Ocean. Therefore, natural conditions change from west to east.
Zoning in the ocean
Changes in natural zones and zones also exist in the waters of the World Ocean. It is visible at a depth of up to 2000 meters, but is very clearly visible at a depth of 100-150 meters. It manifests itself in various components of the organic world, the salinity of water, as well as its chemical composition, and temperature differences.
The belts of the World Ocean are almost the same as those on land. Only instead of arctic and subarctic there is subpolar and polar, since the ocean reaches directly to the North Pole. In the lower layers of the ocean, the boundaries between the belts are stable, but in the upper layers they can shift depending on the season.