Thermal belts of the Earth

Uneven heating of the earth's surface causes different air temperatures at different latitudes. Latitudinal bands with certain air temperatures are called thermal zones. The belts differ in the amount of heat coming from the Sun. Their stretching depending on the distribution of temperatures is well illustrated by isotherms (from the Greek "iso" - the same, "therma" - heat). These are lines on a map that connect points with the same temperature.

hot belt located along the equator, between the Northern and Southern tropics. It is limited on both sides of the 20 0 C isotherms. It is interesting that the boundaries of the belt coincide with the boundaries of the distribution of palm trees on land and corals in the ocean. Here the earth's surface receives the greatest solar heat. Twice a year (December 22 and June 22) at noon, the sun's rays fall almost vertically (at an angle of 90 0). The air from the surface gets very hot. Therefore, it is hot there throughout the year.

temperate zones(In both hemispheres) are adjacent to the hot belt. They stretched in both hemispheres between the Arctic Circle and the tropic. The sun's rays there fall on the earth's surface with a certain slope. Moreover, the further north, the greater the slope. Therefore, the sun's rays heat the surface less. As a result, the air heats up less. That is why temperate zones are colder than hot ones. The sun is never at its zenith there. Clearly defined seasons: winter, spring, summer, autumn. Moreover, the closer to the Arctic Circle, the longer and colder the winter. The closer to the tropic, the longer and warmer the summer. The temperate zones from the side of the poles are limited by the isotherm of the warm month of 10 0 C. It is the limit of the spread of forests.

cold belts(Northern and southern) of both hemispheres lie between the isotherms 10 0 C and 0 0 C of the warmest month. The sun there in winter for several months does not appear above the horizon. And in the summer, although it does not go beyond the horizon for months, it is very low above the horizon. Its rays only glide over the surface of the Earth and heat it weakly. The Earth's surface not only heats but also cools the air. Therefore, the temperatures there are low. Winters are cold and harsh, while summers are short and cool.

Two belts of eternal cold(northern and southern) are surrounded by an isotherm with temperatures of all months below 0 0 C. This is the kingdom of eternal ice.

So, the heating and lighting of each locality depends on the position in the thermal zone, that is, on the geographical latitude. The closer to the equator, the greater the angle of incidence of the sun's rays, the more the surface heats up and the air temperature rises. Conversely, with distance from the equator to the poles, the angle of incidence of the rays decreases, respectively, the air temperature decreases.

Belts of illumination and their characteristics.

Moderate

Cold

It is located between the tropic and the polar circle inside the hemisphere.

The sun is never at its zenith

During the year, the angle of incidence of the sun's rays varies greatly, therefore, the thermal seasons of the year (summer, autumn, winter, spring) are distinguished. Summer and winter temperatures are very different. For example, at a latitude of 50

t° summer≈ +20°С

t° winters≈ -10°С

Located between the northern and southern tropics.

The sun is at its zenith twice a year. The surface warms up very well all year round, there is no difference between summer and winter temperatures, there are no thermal seasons of the year, the average annual t o \u003d + 25 o C. During the year, the daylight hours change slightly. Approximate day=night=12 hours. Twilight is virtually non-existent.

It is located inside the polar circle of each hemisphere.

In winter, the Sun does not rise above the horizon at all - the phenomenon of the Polar Night. In summer, the Sun, on the contrary, does not set below the horizon - the phenomenon of the Polar Day. The angle of incidence of sunlight even in summer is very small, so the heating of the surface is very weak. Summer temperatures usually do not exceed +10°C. In the long polar night, a strong cooling occurs, because. no heat gain at all.

Illumination belts are parts of the Earth's surface bounded by the tropics and the polar circles and differing in illumination conditions.

As a first approximation, it is enough to distinguish three zones in each hemisphere: 1) tropical, limited by the tropics, 2) temperate, going to the Arctic Circle, and 3) polar. The first is characterized by the presence of the Sun at the zenith at each latitude twice a year (on the tropic one) and a small difference in the length of the day by month. The second is characterized by a large seasonal difference in the height of the Sun and the length of the day. The third is characterized by polar night and polar day, the longitude of which depends on the geographical latitude. North of the Arctic Circle and south of the Antarctic Circle, polar day (summer) and polar night (winter) are observed. The area from the Arctic Circle to the Pole in both hemispheres is called the Arctic.
The polar day is the period when the Sun at high latitudes does not fall below the horizon around the clock. The duration of the polar day is longer, the farther to the pole from the Arctic Circle. In the polar circles, the Sun does not set only on the day of the solstice, at 68 ° latitude the polar day lasts about 40 days, at the North Pole 189 days, at the South it is somewhat less, due to the unequal speed of the Earth's orbit in the winter and summer half-years.
The polar night is the period when the Sun does not rise above the horizon at high latitudes around the clock - a phenomenon opposite to the polar day is observed simultaneously with it at the corresponding latitudes of the other hemisphere. In fact, the polar night is always shorter than the polar day due to the fact that the Sun, when it is not much below the horizon, illuminates the atmosphere and there is no complete darkness (twilight).
However, the division of the Earth into such large belts cannot satisfy practical needs.

On the days of the equinoxes, the height of the midday Sun above the horizon h for different latitudes f is easily determined by the formula: h = 90 ° -f.
So, in St. Petersburg (φ = 60°) on March 21 and September 23 at noon the Sun is at a height of 90°-60° = 30°. It heats the Earth for 12 hours. In the summer of each hemisphere, when the Sun is above the corresponding tropic, its height at noon increases by 23 ° 27 ":
A \u003d 90 ° -f + 23 ° 27 ".
For St. Petersburg, for example, on June 21, the height of the Sun is: 90 ° -60 ° + 23 ° 27 "= 53 ° 27". The day lasts 18.5 hours.

In winter, when the Sun moves to the opposite hemisphere, its height decreases accordingly and reaches a minimum on the days of the solstices. Then it should be reduced by 23°27".
On the Leningrad parallel on December 22, the Sun is at an altitude of 90°-60° -23°27" = 6°33" and illuminates the earth's surface for only 5.5 hours.

The described conditions of illumination of the globe, due to the inclination of the earth's axis, represent the radiative, associated with the sun's rays, the basis for the change of seasons.

Not only solar radiation, but also many telluric (terrestrial) factors take part in the formation of the weather, and thus the seasons, so in reality both the seasons and their change are a complex phenomenon.



Thermal belts- These are different areas of the globe that receive an unequal amount of heat from the Sun. There are five thermal zones on the globe: one hot, two temperate and two cold.

In the hot zone, the sun stands overhead, its rays fall down almost vertically, the duration of day and night is approximately the same throughout the year. In the cold zone, the sun never rises high, its rays almost glide over the surface of the earth, the winter day is very short. The temperate zone lies between hot and cold. In the summer in the temperate zone, the sun shines high in the sky, the day is long. In winter, the days are short, the sun does not rise high and almost does not warm the earth.

Most solar heat is received by the area located on both sides of the Equator, between the North and South tropics. It is hot there all year round, and snow never falls on the plains. This territory, stretching from north to south for more than 5 thousand km, is called hot belt.material from the site

Significantly less solar heat is received by the regions of the globe north of the Arctic Circle and south of the Antarctic Circle. It is cold here all year round, and in a short summer the snow and ice do not even have time to melt. The sun does not appear at all for several months, and in summer it is so low that its rays seem to glide over the surface of the Earth (Fig. 129). The area north of the Arctic Circle is called northern cold belt, and south of the Antarctic Circle - southern cold belt.

Between the Arctic Circle and the Northern Tropic stretches northern temperate zone. In the southern hemisphere between the Antarctic Circle and the Tropic of the South is southern temperate zone.

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The main pattern in the distribution of heat on Earth - its zoning - allows us to distinguish thermal, or temperature, belts. They do not coincide with the illumination belts formed according to astronomical laws, since the thermal regime depends not only on illumination, but also on a number of telluric factors.

On either side of the equator, up to approximately 30° N. sh. and yu. sh. is hot belt, bounded by an annual isotherm 20°C. Within these limits, wild palm trees and coral buildings are common.

In the middle latitudes are moderate temperature zones. They are limited to 10 isotherms ° Since the warmest month. These isotherms coincide with the boundary of the distribution of woody plants (the lowest average temperatures at which the seeds of trees ripen, 10 ° C; with a lower monthly amount of heat, forests do not regenerate).

In subpolar latitudes stretch cold belts, the polar boundaries of which are the 0°C isotherms of the warmest month. They generally coincide with the tundra zones.

Around the poles are belts of eternal frost, where the temperature of any month is below 0°C. Here lies the eternal snow and ice.

The hot belt, despite its large area, is thermally quite homogeneous. The average temperature of the year varies from 26°C at the equator to 20°C at the tropical limits. Annual and daily amplitudes are insignificant. Thermally relatively homogeneous are the cold and eternal frost belts due to their narrowness. The temperate belts, covering latitudes from subtropical to subpolar, are thermally very heterogeneous. Here, the annual temperature at some latitudes reaches 20°C, while at others even the temperature of the warmest month does not exceed 10°C. Latitudinal differentiation of temperate zones is revealed. The northern temperate zone, due to its continentality, is also differentiated in the longitudinal direction: in the annual course of temperatures, the coastal and inland positions clearly affect.

In the temperate zones, in the most nervous approximation, subtropical latitudes are distinguished, the temperature regime of which ensures the growth of subtropical vegetation, moderately warm latitudes, where heat ensures the existence of broad-leaved forests and steppes, and boreal latitudes with a sum of heat sufficient only for the growth of coniferous and small-leaved trees.

With the general similarity of the temperature zones of both hemispheres, the thermal dissymmetry of the Earth with respect to the equator clearly stands out. The thermal equator is shifted to the north relative to the geographic one, the northern hemisphere is warmer than the southern, in the south the course of temperature is oceanic, in the north - continental, the Arctic is warmer than the Antarctic.

The thermal conditions of the belts naturally disturb the mountainous countries. Due to the decrease in temperature with height in them

The largest annual amplitudes from 23 to 32 ° C are characteristic of the middle zone of the largest area of ​​the continents, in which different heating and cooling of the continents and oceans, the formation of positive and negative temperature anomalies cause different temperature patterns on the ocean and in the depths of the continents.

During the day, the air temperature changes. The lowest temperature is observed before sunrise, the highest - at 14-15 hours.

To determine average daily temperature it is necessary to measure the temperature four times a day: at 1 am, at 7 am, at 1 pm, at 7 pm. The arithmetic mean of these measurements is the average daily temperature.

The air temperature changes not only during the day, but also throughout the year (Fig. 138).

Rice. 138. Head change in air temperature at a latitude of 62 ° N. latitude: 1 - Torshavn Denmark (marine tyne), average annual temperature 6.3 °C; 2- Yakutsk (continental type) - 10.7 ° С

Average annual temperature is the arithmetic average of temperatures for all months of the year. It depends on the geographic latitude, the nature of the underlying surface, and the transfer of heat from low to high latitudes.

The Southern Hemisphere is generally colder than the Northern Hemisphere due to the ice and snow covered Antarctica.

The warmest month of the year in the Northern Hemisphere is July, while the coldest month is January.

Lines on maps connecting places with the same air temperature are called isotherms(from the Greek isos - equal and therme - heat). Their complex location can be judged from the maps of January, July and annual isotherms.

The climate at the corresponding parallels of the Northern Hemisphere is warmer than the corresponding parallels of the Southern Hemisphere.

The highest annual temperatures on Earth are observed on the so-called thermal equator. It does not coincide with the geographic equator and is located at 10 ° N. sh. This is due to the fact that in the Northern Hemisphere a large area is occupied by land, and in the Southern Hemisphere, on the contrary, there are oceans that spend heat on evaporation, and besides this, the influence of ice-covered Antarctica affects. The average annual temperature at the parallel is 10° N. sh. is 27 °C.

Isotherms do not coincide with parallels despite the fact that solar radiation is distributed zonally. They bend, moving from the mainland to the ocean, and vice versa. So, in the Northern Hemisphere in January over the mainland isotherms deviate to the south, and in July - to the north. This is due to the unequal conditions for heating land and water. In winter, land cools, and in summer it heats up faster than water.

If we analyze isotherms in the Southern Hemisphere, then in temperate latitudes their course is very close to parallels, since there is little land there.

In January, the highest air temperature is observed at the equator - 27 ° C, in Australia, South America, central and southern parts of Africa. The lowest temperature in January was recorded in the northeast of Asia (Oymyakon, -71 °С) and at the North Pole -41 °С.

The "warmest parallel of July" is the parallel of 20°N. with a temperature of 28 ° C, and the coldest place in July is the south pole with an average monthly temperature of -48 ° C.

The absolute maximum air temperature was registered in North America (+58.1 °С). The absolute minimum air temperature (-89.2 °C) was recorded at the Vostok station in Antarctica.

Observations revealed the existence of daily and annual fluctuations in air temperature. The difference between the highest and lowest air temperatures during the day is called daily range, and during the year annual temperature range.

The daily temperature amplitude depends on a number of factors:

  • latitude of the area - decreases when moving from low to high latitudes;
  • the nature of the underlying surface - it is higher on land than over the ocean: over the oceans and seas, the daily temperature amplitude is only 1-2 ° C, and over the steppes and deserts it reaches 15-20 ° C, since the water heats up and cools down more slowly than land ; in addition, it increases in areas with bare soil;
  • terrain - due to lowering into the valley of cold air from the slopes;
  • cloud cover - with its increase, the daily temperature amplitude decreases, since clouds do not allow the earth's surface to become very hot during the day and cool at night.

The magnitude of the daily amplitude of air temperature is one of the indicators of the continentality of the climate: in deserts, its value is much greater than in areas with a maritime climate.

Annual temperature amplitude has patterns similar to the daily temperature amplitude. It depends mainly on the latitude of the area and the proximity of the ocean. Over the oceans, the annual temperature amplitude most often does not exceed 5-10 °C, and over the interior regions of Eurasia - up to 50-60 °C. Near the equator, average monthly air temperatures differ little from each other throughout the year. At higher latitudes, the annual temperature amplitude increases, and in the Moscow region it is 29 °C. At the same latitude, the annual temperature amplitude increases with distance from the ocean. In the equatorial zone above the ocean, the annual temperature amplitude is only G, and over the continents - 5-10 °.

The different conditions for heating water and land are explained by the fact that the heat capacity of water is twice that of land, and with the same amount of heat, land heats up twice as fast as water. On cooling, the opposite happens. In addition, when heated, water evaporates, while a significant amount of heat is consumed. It is also important that on land heat is distributed practically only in the upper soil layer, and only a small part of it is transferred to the depth. In the seas and oceans, a considerable thickness is being heated. This is facilitated by vertical mixing of water. As a result, oceans accumulate heat much more than land, retain it longer and spend it more evenly than land. The oceans heat up more slowly and cool more slowly.

The annual temperature amplitude in the Northern Hemisphere is 14 °С, and in the Southern - 7 °С. For the globe, the average annual air temperature near the earth's surface is 14 °C.

Thermal belts

The uneven distribution of heat on the Earth, depending on the latitude of the place, allows us to distinguish the following thermal belts, whose boundaries are isotherms (Fig. 139):

  • the tropical (hot) zone is located between the annual isotherms + 20 °С;
  • temperate zones of the Northern and Southern hemispheres - between the annual isotherms +20 °С and the isotherm of the warmest month +10 °С;
  • the polar (cold) belts of both hemispheres are located between the isotherms of the warmest month +10 °С and О °С;
  • the belts of eternal frost are limited by the 0°C isotherm of the warmest month. This is the realm of eternal snow and ice.

Rice. 139. Thermal belts of the Earth

The heating of the soil and the illumination of any territory are directly dependent on the thermal zone in which it is located. This, in turn, is affected by geographic latitude.

What are thermal belts?

Solar heat arrives at high and low latitudes differently. This is due to the fact that the angles of inclination of the rays of our star to the surface of the Earth differ. This is where the concept of climate comes from. The further north a territory is located, the less heat it receives per unit of surface. This is due to the lower rise of the sun at noon.

The very word "climate" in Greek means "slope". It depends on the geographical location of a particular area and is determined by atmospheric pressure, humidity and average air temperature throughout the year.
There are three thermal zones on Earth. It is temperate, hot and cold. Each of them has its own distinctive features.

Cold climate zone

It is located in the region of the Arctic Circle, located both in the North and South Poles of our planet, as far as possible from the equator, and in connection with this, the sun sends only oblique rays to them. That is why in these areas the earth heats up very weakly.

Winters in these areas are long and harsh, while summers are short and cool. There are several months of the year when the sun's rays do not reach the Arctic Circle at all. This period is the polar night. The temperature at this time here can drop to eighty-nine degrees.

Temperate zone

These thermal zones are also located in two hemispheres. In their territories, oblique sun rays slightly warm the earth in winter. In summer, the sun illuminates them more intensively. There are moderate thermal zones between the Arctic Circle and the two parallels. To the north is Cancer and to the south is the Tropics of Capricorn.

The sun in these belts is never at its zenith. Therefore, it does not heat the soil and air very much. Temperate thermal zones are characterized by a clear delineation of seasons. Winter, summer, autumn and spring are observed here. At the same time, the temperature character of these seasons is not the same. The closer an area is to the Arctic Circle, the colder the winter on its territory. Conversely, summers are warmer and longer as the territory approaches the tropics.

hot belt

Above this zone, the sun always rises high and sends direct rays to it. That is why there is always a high temperature here. The dominance of this belt is observed in the tropics. The winter period in this area is the rainy season, and the summer is characterized by drought.

The hot thermal belt of the Earth is located between the South and along the equator. Twice during the year, namely at noon on June 22 and December 22, the sun's rays fall in this zone almost vertically, that is, at an angle of ninety degrees. The air warms up from the surface of the soil. That is why this area is hot all year round. Palm trees grow only within this belt.

Thus, the thermal belts of the world are represented by five zones. They include two cold, two moderate and one hot. Sometimes in cold thermal zones a region of eternal frost is isolated. It is located directly near the poles, and the average annual temperature here does not rise above zero.

The thermal zones of Russia are cold and temperate. The north of the country is characterized by a harsh climate. At the same time, a change of polar winter and polar summer is observed. The more southern territories have a mild climate and pronounced seasonality.

The nature of the cold thermal zone

The polar zones of our planet are constantly covered with snow and ice. These are the coldest places on earth. The Arctic, which belongs to the polar zone, passes through Alaska. It includes the island of Greenland. Located in the polar zone north of Canada and Russia.

Antarctica, located in the Southern Hemisphere, is the southern polar zone. The continent of Antarctica is located there.

The cold thermal zone, which is characterized by a lack of heat, does not have forests. The soil in these areas is swampy. In some places you can find areas of permafrost. The most severe climate is observed at the poles. There are sea or continental ice. Vegetation is usually absent or represented by lichens and moss.

Mostly migratory birds live in the cold zone. Especially a lot of them on the islands of the Arctic Ocean. There are also animals in this area. They migrate from more southerly areas during the summer season. The fauna is represented by owls and arctic foxes, polar mice and polar bears, walruses, seals and penguins.

The nature of the temperate thermal zone

The territories of these climatic zones receive more light and heat. It's not such a harsh winter here. Summer in the temperate zone is not very hot. The sun is never at its zenith over these areas. Therefore, the climate of the temperate zones is mild, and its changes from warm to cold occur gradually. There are four seasons in these zones: summer, spring, winter and autumn.

The temperate thermal zone passes through the territory of Great Britain, Europe. It contains North Asia and North America. In the Southern Hemisphere, the temperate zone is located on the waters of three oceans. Thus, 98% of its area is occupied by water. The temperate zone in the Southern Hemisphere runs through Australia and New Zealand. It covers southern South Africa and South America.

The nature of this thermal zone is very diverse. These are taiga, semi-deserts and deserts, as well as steppes.

The animal world is quite homogeneous. It is mainly represented by forest animals that lead a sedentary lifestyle. To a lesser extent, representatives of the fauna of open areas - steppes and deserts.

The nature of the hot thermal zone

Most of Africa is located in this zone. In the hot zone is the south of India and Asia. This zone includes Central America, New Guinea, northern Australia and northern South America.

There is no seasonality near the equator. Throughout the year, these areas are very warm and humid.

The hot thermal zone is characterized by savannahs, evergreens and light forests. Some areas are semi-deserts and deserts.
The animal world is remarkable for its extraordinary diversity. These are birds of prey and running, hippos and antelopes, elephants and zebras, buffaloes, etc.