The air shell that surrounds our planet and rotates with it is called the atmosphere. Half of the total mass of the atmosphere is concentrated in the lower 5 km, and three-quarters of the mass in the lower 10 km. Above, the air is much rarefied, although its particles are found at an altitude of 2000-3000 km above the earth's surface.

The air we breathe is a mixture of gases. Most of all it contains nitrogen - 78% and oxygen - 21%. Argon is less than 1% and 0.03% is carbon dioxide. Numerous other gases, such as krypton, xenon, neon, helium, hydrogen, ozone and others, make up thousandths and millionths of a percent. The air also contains water vapor, particles of various substances, bacteria, pollen and cosmic dust.

The atmosphere is made up of several layers. The lower layer up to a height of 10-15 km above the Earth's surface is called the troposphere. It heats up from the Earth, so the air temperature here with height drops by 6 ° C per 1 kilometer of ascent. Almost all water vapor is in the troposphere and almost all clouds are formed - note .. The height of the troposphere over different latitudes of the planet is not the same. It rises up to 9 km above the poles, up to 10-12 km over temperate latitudes, and up to 15 km over the equator. The processes occurring in the troposphere - the formation and movement of air masses, the formation of cyclones and anticyclones, the appearance of clouds and precipitation - determine the weather and climate near the earth's surface.

Above the troposphere is the stratosphere, which extends up to 50-55 km. The troposphere and stratosphere are separated by a transition layer called the tropopause, 1–2 km thick. In the stratosphere at an altitude of about 25 km, the air temperature gradually begins to rise and reaches + 10 +30 °С at 50 km. Such an increase in temperature is due to the fact that there is a layer of ozone in the stratosphere at altitudes of 25-30 km. At the surface of the Earth, its content in the air is negligible, and at high altitudes, diatomic oxygen molecules absorb ultraviolet solar radiation, forming triatomic ozone molecules.

If ozone were located in the lower layers of the atmosphere, at a height with normal pressure, the thickness of its layer would be only 3 mm. But even in such a small amount, it plays a very important role: it absorbs part of the solar radiation harmful to living organisms.

Above the stratosphere, up to about 80 km, the mesosphere extends, in which the air temperature drops with height to several tens of degrees below zero.

The upper part of the atmosphere is characterized by very high temperatures and is called the thermosphere - note .. It is divided into two parts - the ionosphere - up to a height of about 1000 km, where the air is highly ionized, and the exosphere - over 1000 km. In the ionosphere, atmospheric gas molecules absorb ultraviolet radiation from the Sun, and charged atoms and free electrons are formed. Auroras are observed in the ionosphere.

The atmosphere plays a very important role in the life of our planet. It protects the Earth from strong heating by the sun's rays during the day and from hypothermia at night. Most meteorites burn up in the atmospheric layers before reaching the surface of the planet. The atmosphere contains oxygen, necessary for all organisms, an ozone shield that protects life on Earth from the harmful part of the ultraviolet radiation of the Sun.

ATMOSPHERES OF THE PLANETS OF THE SOLAR SYSTEM

The atmosphere of Mercury is so rarefied that, one might say, it is practically non-existent. The air envelope of Venus consists of carbon dioxide (96%) and nitrogen (about 4%), it is very dense - the atmospheric pressure near the surface of the planet is almost 100 times greater than on Earth. The Martian atmosphere also consists mainly of carbon dioxide (95%) and nitrogen (2.7%), but its density is about 300 times less than that of the earth, and its pressure is almost 100 times less. The visible surface of Jupiter is actually the top layer of a hydrogen-helium atmosphere. The air shells of Saturn and Uranus are the same in composition. The beautiful blue color of Uranus is due to the high concentration of methane in the upper part of its atmosphere - approx .. Neptune, shrouded in hydrocarbon haze, has two main layers of clouds: one consists of frozen methane crystals, and the second, located below, contains ammonia and hydrogen sulfide.

STRUCTURE OF THE ATMOSPHERE

Atmosphere(from other Greek ἀτμός - steam and σφαῖρα - ball) - a gaseous shell (geosphere) surrounding the planet Earth. Its inner surface covers the hydrosphere and partially the earth's crust, while its outer surface borders on the near-Earth part of outer space.

Physical Properties

The thickness of the atmosphere is about 120 km from the Earth's surface. The total mass of air in the atmosphere is (5.1-5.3) 10 18 kg. Of these, the mass of dry air is (5.1352 ± 0.0003) 10 18 kg, the total mass of water vapor is on average 1.27 10 16 kg.

The molar mass of clean dry air is 28.966 g/mol, the air density at the sea surface is approximately 1.2 kg/m 3 . The pressure at 0 °C at sea level is 101.325 kPa; critical temperature - -140.7 ° C; critical pressure - 3.7 MPa; C p at 0 °C - 1.0048 10 3 J/(kg K), C v - 0.7159 10 3 J/(kg K) (at 0 °C). The solubility of air in water (by mass) at 0 ° C - 0.0036%, at 25 ° C - 0.0023%.

For "normal conditions" at the Earth's surface are taken: density 1.2 kg / m 3, barometric pressure 101.35 kPa, temperature plus 20 ° C and relative humidity 50%. These conditional indicators have a purely engineering value.

The structure of the atmosphere

The atmosphere has a layered structure. The layers of the atmosphere differ from each other in air temperature, its density, the amount of water vapor in the air and other properties.

Troposphere(ancient Greek τρόπος - "turn", "change" and σφαῖρα - "ball") - the lower, most studied layer of the atmosphere, 8-10 km high in the polar regions, up to 10-12 km in temperate latitudes, at the equator - 16-18 km.

When rising in the troposphere, the temperature drops by an average of 0.65 K every 100 m and reaches 180-220 K in the upper part. This upper layer of the troposphere, in which the decrease in temperature with height stops, is called the tropopause. The next layer of the atmosphere above the troposphere is called the stratosphere.

More than 80% of the total mass of atmospheric air is concentrated in the troposphere, turbulence and convection are highly developed, the predominant part of water vapor is concentrated, clouds arise, atmospheric fronts also form, cyclones and anticyclones develop, as well as other processes that determine weather and climate. The processes occurring in the troposphere are primarily due to convection.

The part of the troposphere within which glaciers can form on the earth's surface is called the chionosphere.

tropopause(from the Greek τροπος - turn, change and παῦσις - stop, cessation) - the layer of the atmosphere in which the decrease in temperature with height stops; transition layer from troposphere to stratosphere. In the earth's atmosphere, the tropopause is located at altitudes from 8-12 km (above sea level) in the polar regions and up to 16-18 km above the equator. The height of the tropopause also depends on the time of year (the tropopause is higher in summer than in winter) and cyclonic activity (it is lower in cyclones and higher in anticyclones)

The thickness of the tropopause ranges from several hundred meters to 2-3 kilometers. In the subtropics, tropopause ruptures are observed due to powerful jet streams. The tropopause over certain areas is often destroyed and re-formed.

Stratosphere(from Latin stratum - flooring, layer) - a layer of the atmosphere, located at an altitude of 11 to 50 km. A slight change in temperature in the 11-25 km layer (the lower layer of the stratosphere) and its increase in the 25-40 km layer from -56.5 to 0.8 °C (the upper stratosphere layer or inversion region) are typical. Having reached a value of about 273 K (almost 0 °C) at an altitude of about 40 km, the temperature remains constant up to an altitude of about 55 km. This region of constant temperature is called the stratopause and is the boundary between the stratosphere and the mesosphere. The density of air in the stratosphere is tens and hundreds of times less than at sea level.

It is in the stratosphere that the ozonosphere layer ("ozone layer") is located (at an altitude of 15-20 to 55-60 km), which determines the upper limit of life in the biosphere. Ozone (O 3 ) is formed as a result of photochemical reactions most intensively at an altitude of ~30 km. The total mass of O 3 at normal pressure would be a layer 1.7-4.0 mm thick, but even this is enough to absorb the solar ultraviolet radiation that is harmful to life. The destruction of O 3 occurs when it interacts with free radicals, NO, halogen-containing compounds (including "freons").

Most of the short-wavelength part of ultraviolet radiation (180-200 nm) is retained in the stratosphere and the energy of short waves is transformed. Under the influence of these rays, magnetic fields change, molecules break up, ionization, new formation of gases and other chemical compounds occur. These processes can be observed in the form of northern lights, lightning and other glows.

In the stratosphere and higher layers, under the influence of solar radiation, gas molecules dissociate - into atoms (above 80 km, CO 2 and H 2 dissociate, above 150 km - O 2, above 300 km - N 2). At an altitude of 200-500 km, ionization of gases also occurs in the ionosphere; at an altitude of 320 km, the concentration of charged particles (O + 2, O - 2, N + 2) is ~ 1/300 of the concentration of neutral particles. In the upper layers of the atmosphere there are free radicals - OH, HO 2, etc.

There is almost no water vapor in the stratosphere.

Flights into the stratosphere began in the 1930s. The flight on the first stratospheric balloon (FNRS-1), which Auguste Picard and Paul Kipfer made on May 27, 1931 to a height of 16.2 km, is widely known. Modern combat and supersonic commercial aircraft fly in the stratosphere at altitudes generally up to 20 km (although the dynamic ceiling can be much higher). High-altitude weather balloons rise up to 40 km; the record for an unmanned balloon is 51.8 km.

Recently, in the military circles of the United States, much attention has been paid to the development of layers of the stratosphere above 20 km, often called the "prespace" (Eng. « near space» ). It is assumed that unmanned airships and solar-powered aircraft (like NASA Pathfinder) will be able to stay at an altitude of about 30 km for a long time and provide observation and communication for very large areas, while remaining vulnerable to air defense systems; such devices will be many times cheaper than satellites.

Stratopause- the layer of the atmosphere, which is the boundary between two layers, the stratosphere and the mesosphere. In the stratosphere, temperature rises with altitude, and the stratopause is the layer where the temperature reaches its maximum. The temperature of the stratopause is about 0 °C.

This phenomenon is observed not only on Earth, but also on other planets with an atmosphere.

On Earth, the stratopause is located at an altitude of 50 - 55 km above sea level. Atmospheric pressure is about 1/1000 of the pressure at sea level.

Mesosphere(from the Greek μεσο- - “middle” and σφαῖρα - “ball”, “sphere”) - the layer of the atmosphere at altitudes from 40-50 to 80-90 km. It is characterized by an increase in temperature with height; the maximum (about +50°C) temperature is located at an altitude of about 60 km, after which the temperature begins to decrease to −70° or −80°C. Such a decrease in temperature is associated with the energetic absorption of solar radiation (radiation) by ozone. The term was adopted by the Geographical and Geophysical Union in 1951.

The gas composition of the mesosphere, as well as those of the lower atmospheric layers, is constant and contains about 80% nitrogen and 20% oxygen.

The mesosphere is separated from the underlying stratosphere by the stratopause, and from the overlying thermosphere by the mesopause. The mesopause basically coincides with the turbopause.

Meteors begin to glow and, as a rule, burn up completely in the mesosphere.

Noctilucent clouds may appear in the mesosphere.

For flights, the mesosphere is a kind of "dead zone" - the air here is too rarefied to support airplanes or balloons (at an altitude of 50 km, the air density is 1000 times less than at sea level), and at the same time too dense for artificial flights. satellites in such a low orbit. Direct studies of the mesosphere are carried out mainly with the help of suborbital meteorological rockets; in general, the mesosphere has been studied worse than other layers of the atmosphere, in connection with which scientists called it the “ignorosphere”.

mesopause

mesopause The layer of the atmosphere that separates the mesosphere and thermosphere. On Earth, it is located at an altitude of 80-90 km above sea level. In the mesopause, there is a temperature minimum, which is about -100 ° C. Below (starting from a height of about 50 km) the temperature drops with height, above (up to a height of about 400 km) it rises again. The mesopause coincides with the lower boundary of the region of active absorption of the X-ray and the shortest wavelength ultraviolet radiation of the Sun. Silvery clouds are observed at this altitude.

The mesopause exists not only on Earth, but also on other planets with an atmosphere.

Karman Line- height above sea level, which is conventionally accepted as the boundary between the Earth's atmosphere and space.

As defined by the Fédération Aéronautique Internationale (FAI), the Karman Line is at an altitude of 100 km above sea level.

The height was named after Theodor von Karman, an American scientist of Hungarian origin. He was the first to determine that at about this altitude the atmosphere becomes so rarefied that aeronautics becomes impossible, since the speed of the aircraft, necessary to create sufficient lift, becomes greater than the first cosmic speed, and therefore, to achieve higher altitudes, it is necessary to use the means of astronautics.

The Earth's atmosphere continues beyond the Karman line. The outer part of the earth's atmosphere, the exosphere, extends to an altitude of 10,000 km or more, at such an altitude the atmosphere consists mainly of hydrogen atoms that can leave the atmosphere.

Reaching the Karman Line was the first condition for the Ansari X Prize, as this is the basis for recognizing the flight as a space flight.

ATMOSPHERE
gaseous envelope surrounding a celestial body. Its characteristics depend on the size, mass, temperature, rotation speed and chemical composition of a given celestial body, and are also determined by the history of its formation from the moment of its birth. Earth's atmosphere is made up of a mixture of gases called air. Its main constituents are nitrogen and oxygen in a ratio of approximately 4:1. A person is affected mainly by the state of the lower 15-25 km of the atmosphere, since it is in this lower layer that the bulk of the air is concentrated. The science that studies the atmosphere is called meteorology, although the subject of this science is also the weather and its effect on humans. The state of the upper layers of the atmosphere, located at altitudes from 60 to 300 and even 1000 km from the Earth's surface, is also changing. Strong winds, storms develop here, and such amazing electrical phenomena as auroras appear. Many of these phenomena are associated with fluxes of solar radiation, cosmic radiation, and the Earth's magnetic field. The high layers of the atmosphere are also a chemical laboratory, since there, under conditions close to vacuum, some atmospheric gases, under the influence of a powerful flow of solar energy, enter into chemical reactions. The science that studies these interrelated phenomena and processes is called the physics of the high layers of the atmosphere.
GENERAL CHARACTERISTICS OF THE EARTH'S ATMOSPHERE
Dimensions. Until sounding rockets and artificial satellites explored the outer layers of the atmosphere at distances several times greater than the radius of the Earth, it was believed that as you move away from the earth's surface, the atmosphere gradually becomes more rarefied and smoothly passes into interplanetary space. It has now been established that energy flows from the deep layers of the Sun penetrate into outer space far beyond the Earth's orbit, up to the outer limits of the Solar System. This so-called. The solar wind flows around the Earth's magnetic field, forming an elongated "cavity" within which the Earth's atmosphere is concentrated. The Earth's magnetic field is noticeably narrowed on the day side facing the Sun and forms a long tongue, probably extending beyond the orbit of the Moon, on the opposite, night side. The boundary of the Earth's magnetic field is called the magnetopause. On the day side, this boundary passes at a distance of about seven Earth radii from the surface, but during periods of increased solar activity it is even closer to the Earth's surface. The magnetopause is at the same time the boundary of the earth's atmosphere, the outer shell of which is also called the magnetosphere, since it contains charged particles (ions), the movement of which is due to the earth's magnetic field. The total weight of atmospheric gases is approximately 4.5*1015 tons. Thus, the "weight" of the atmosphere per unit area, or atmospheric pressure, is approximately 11 tons/m2 at sea level.
Significance for life. It follows from the above that the Earth is separated from interplanetary space by a powerful protective layer. Outer space is permeated with powerful ultraviolet and X-ray radiation from the Sun and even harder cosmic radiation, and these types of radiation are detrimental to all living things. At the outer edge of the atmosphere, the radiation intensity is lethal, but a significant part of it is retained by the atmosphere far from the Earth's surface. The absorption of this radiation explains many properties of the high layers of the atmosphere, and especially the electrical phenomena that occur there. The lowest, surface layer of the atmosphere is especially important for a person who lives at the point of contact of the solid, liquid and gaseous shells of the Earth. The upper shell of the "solid" Earth is called the lithosphere. About 72% of the Earth's surface is covered by the waters of the oceans, which make up most of the hydrosphere. The atmosphere borders both the lithosphere and the hydrosphere. Man lives at the bottom of the air ocean and near or above the level of the water ocean. The interaction of these oceans is one of the important factors that determine the state of the atmosphere.
Compound. The lower layers of the atmosphere consist of a mixture of gases (see table). In addition to those listed in the table, other gases are also present in the form of small impurities in the air: ozone, methane, substances such as carbon monoxide (CO), nitrogen and sulfur oxides, ammonia.

COMPOSITION OF THE ATMOSPHERE

In the high layers of the atmosphere, the composition of the air changes under the influence of hard radiation from the Sun, which leads to the breakdown of oxygen molecules into atoms. Atomic oxygen is the main component of the high layers of the atmosphere. Finally, in the most distant layers of the atmosphere from the surface of the Earth, the lightest gases, hydrogen and helium, become the main components. Since the bulk of matter is concentrated in the lower 30 km, changes in air composition at altitudes above 100 km do not have a noticeable effect on the overall composition of the atmosphere.
Energy exchange. The sun is the main source of energy coming to the Earth. Being at a distance of approx. 150 million km from the Sun, the Earth receives about one two billionth of the energy it radiates, mainly in the visible part of the spectrum, which man calls "light". Most of this energy is absorbed by the atmosphere and lithosphere. The earth also radiates energy, mostly in the form of far infrared radiation. Thus, a balance is established between the energy received from the Sun, the heating of the Earth and the atmosphere, and the reverse flow of thermal energy radiated into space. The mechanism of this balance is extremely complex. Dust and gas molecules scatter light, partially reflecting it into the world space. Clouds reflect even more of the incoming radiation. Part of the energy is absorbed directly by gas molecules, but mostly by rocks, vegetation and surface waters. Water vapor and carbon dioxide present in the atmosphere transmit visible radiation but absorb infrared radiation. Thermal energy accumulates mainly in the lower layers of the atmosphere. A similar effect occurs in a greenhouse when the glass lets light in and the soil heats up. Since glass is relatively opaque to infrared radiation, heat accumulates in the greenhouse. The heating of the lower atmosphere due to the presence of water vapor and carbon dioxide is often referred to as the greenhouse effect. Cloudiness plays a significant role in the conservation of heat in the lower layers of the atmosphere. If the clouds dissipate or the transparency of the air masses increases, the temperature will inevitably decrease as the surface of the Earth freely radiates thermal energy into the surrounding space. Water on the surface of the Earth absorbs solar energy and evaporates, turning into a gas - water vapor, which carries a huge amount of energy into the lower atmosphere. When water vapor condenses and forms clouds or fog, this energy is released in the form of heat. About half of the solar energy reaching the earth's surface is spent on the evaporation of water and enters the lower atmosphere. Thus, due to the greenhouse effect and the evaporation of water, the atmosphere warms up from below. This partly explains the high activity of its circulation in comparison with the circulation of the World Ocean, which warms up only from above and is therefore much more stable than the atmosphere.
See also METEOROLOGY AND CLIMATOLOGY. In addition to the general heating of the atmosphere by solar "light", significant heating of some of its layers occurs due to ultraviolet and X-ray radiation from the Sun. Structure. Compared to liquids and solids, in gaseous substances, the force of attraction between molecules is minimal. As the distance between molecules increases, gases are able to expand indefinitely if nothing prevents them. The lower boundary of the atmosphere is the surface of the Earth. Strictly speaking, this barrier is impenetrable, since gas exchange occurs between air and water and even between air and rocks, but in this case these factors can be neglected. Since the atmosphere is a spherical shell, it has no side boundaries, but only a lower boundary and an upper (outer) boundary open from the side of interplanetary space. Through the outer boundary, some neutral gases leak out, as well as the flow of matter from the surrounding outer space. Most of the charged particles, with the exception of high-energy cosmic rays, are either captured by the magnetosphere or repelled by it. The atmosphere is also affected by the force of gravity, which keeps the air shell at the surface of the Earth. Atmospheric gases are compressed by their own weight. This compression is maximum at the lower boundary of the atmosphere, and therefore the air density is the highest here. At any height above the earth's surface, the degree of air compression depends on the mass of the overlying air column, so the air density decreases with height. The pressure, equal to the mass of the overlying air column per unit area, is directly related to the density and, therefore, also decreases with height. If the atmosphere were an "ideal gas" with a constant composition independent of height, a constant temperature, and a constant force of gravity acting on it, then the pressure would decrease by a factor of 10 for every 20 km of altitude. The real atmosphere slightly differs from the ideal gas up to about 100 km, and then the pressure decreases more slowly with height, as the composition of the air changes. Small changes in the described model are also introduced by a decrease in the force of gravity with distance from the center of the Earth, amounting to approx. 3% for every 100 km of altitude. Unlike atmospheric pressure, temperature does not decrease continuously with altitude. As shown in fig. 1, it decreases to approximately 10 km and then begins to rise again. This occurs when oxygen absorbs ultraviolet solar radiation. In this case, ozone gas is formed, the molecules of which consist of three oxygen atoms (O3). It also absorbs ultraviolet radiation, and therefore this layer of the atmosphere, called the ozonosphere, heats up. Higher, the temperature drops again, since there are much fewer gas molecules, and the energy absorption is correspondingly reduced. In even higher layers, the temperature rises again due to the absorption of the shortest wavelength ultraviolet and X-ray radiation from the Sun by the atmosphere. Under the influence of this powerful radiation, the atmosphere is ionized, i.e. A gas molecule loses an electron and acquires a positive electric charge. Such molecules become positively charged ions. Due to the presence of free electrons and ions, this layer of the atmosphere acquires the properties of an electrical conductor. It is believed that the temperature continues to rise to heights where the rarefied atmosphere passes into interplanetary space. At a distance of several thousand kilometers from the surface of the Earth, temperatures from 5000 ° to 10,000 ° C probably prevail. Although molecules and atoms have very high speeds of movement, and therefore a high temperature, this rarefied gas is not "hot" in the usual sense. . Due to the meager number of molecules at high altitudes, their total thermal energy is very small. Thus, the atmosphere consists of separate layers (i.e., a series of concentric shells, or spheres), the selection of which depends on which property is of greatest interest. Based on the average temperature distribution, meteorologists have developed a scheme for the structure of an ideal "middle atmosphere" (see Fig. 1).

Troposphere - the lower layer of the atmosphere, extending to the first thermal minimum (the so-called tropopause). The upper limit of the troposphere depends on the geographical latitude (in the tropics - 18-20 km, in temperate latitudes - about 10 km) and the time of year. The US National Weather Service conducted soundings near the South Pole and revealed seasonal changes in the height of the tropopause. In March, the tropopause is at an altitude of approx. 7.5 km. From March to August or September there is a steady cooling of the troposphere, and its boundary rises for a short period in August or September to a height of approximately 11.5 km. Then from September to December it drops rapidly and reaches its lowest position - 7.5 km, where it remains until March, fluctuating within only 0.5 km. It is in the troposphere that the weather is mainly formed, which determines the conditions for human existence. Most of the atmospheric water vapor is concentrated in the troposphere, and therefore clouds form mainly here, although some of them, consisting of ice crystals, are also found in the higher layers. The troposphere is characterized by turbulence and powerful air currents (winds) and storms. In the upper troposphere, there are strong air currents of a strictly defined direction. Turbulent eddies, like small whirlpools, are formed under the influence of friction and dynamic interaction between slow and fast moving air masses. Since there is usually no cloud cover in these high layers, this turbulence is referred to as "clear air turbulence".
Stratosphere. The upper layer of the atmosphere is often erroneously described as a layer with relatively constant temperatures, where the winds blow more or less steadily and where the meteorological elements change little. The upper layers of the stratosphere heat up as oxygen and ozone absorb solar ultraviolet radiation. The upper boundary of the stratosphere (stratopause) is drawn where the temperature rises slightly, reaching an intermediate maximum, which is often comparable to the temperature of the surface air layer. Based on observations made with airplanes and balloons adapted to fly at a constant altitude, turbulent disturbances and strong winds blowing in different directions have been established in the stratosphere. As in the troposphere, powerful air vortices are noted, which are especially dangerous for high-speed aircraft. Strong winds, called jet streams, blow in narrow zones along the borders of temperate latitudes facing the poles. However, these zones can shift, disappear and reappear. Jet streams usually penetrate the tropopause and appear in the upper troposphere, but their speed decreases rapidly with decreasing altitude. It is possible that part of the energy entering the stratosphere (mainly spent on the formation of ozone) affects the processes in the troposphere. Particularly active mixing is associated with atmospheric fronts, where extensive flows of stratospheric air were recorded significantly below the tropopause, and tropospheric air was drawn into the lower layers of the stratosphere. Significant progress has been made in the study of the vertical structure of the lower layers of the atmosphere in connection with the improvement of the technique of launching radiosondes to altitudes of 25-30 km. The mesosphere, located above the stratosphere, is a shell in which, up to a height of 80-85 km, the temperature drops to the minimum for the atmosphere as a whole. Record low temperatures down to -110°C were recorded by meteorological rockets launched from the US-Canadian installation at Fort Churchill (Canada). The upper limit of the mesosphere (mesopause) approximately coincides with the lower limit of the region of active absorption of the X-ray and the shortest wavelength ultraviolet radiation of the Sun, which is accompanied by heating and ionization of the gas. In the polar regions in summer, cloud systems often appear in the mesopause, which occupy a large area, but have little vertical development. Such clouds glowing at night often make it possible to detect large-scale undulating air movements in the mesosphere. The composition of these clouds, sources of moisture and condensation nuclei, dynamics and relationship with meteorological factors are still insufficiently studied. The thermosphere is a layer of the atmosphere in which the temperature rises continuously. Its power can reach 600 km. The pressure and, consequently, the density of a gas constantly decrease with height. Near the earth's surface, 1 m3 of air contains approx. 2.5x1025 molecules, at a height of approx. 100 km, in the lower layers of the thermosphere - approximately 1019, at an altitude of 200 km, in the ionosphere - 5 * 10 15 and, according to calculations, at an altitude of approx. 850 km - approximately 1012 molecules. In interplanetary space, the concentration of molecules is 10 8-10 9 per 1 m3. At a height of approx. 100 km, the number of molecules is small, and they rarely collide with each other. The average distance traveled by a randomly moving molecule before colliding with another similar molecule is called its mean free path. The layer in which this value increases so much that the probability of intermolecular or interatomic collisions can be neglected is located on the boundary between the thermosphere and the overlying shell (exosphere) and is called the thermal pause. The thermopause is located approximately 650 km from the earth's surface. At a certain temperature, the speed of a molecule's movement depends on its mass: lighter molecules move faster than heavier ones. In the lower atmosphere, where the free path is very short, there is no noticeable separation of gases according to their molecular weight, but it is expressed above 100 km. In addition, under the influence of ultraviolet and X-ray radiation from the Sun, oxygen molecules break up into atoms, the mass of which is half the mass of the molecule. Therefore, as we move away from the Earth's surface, atomic oxygen becomes increasingly important in the composition of the atmosphere and at an altitude of approx. 200 km becomes its main component. Higher, at a distance of about 1200 km from the Earth's surface, light gases - helium and hydrogen - predominate. They are the outer layer of the atmosphere. This separation by weight, called diffuse separation, resembles the separation of mixtures using a centrifuge. The exosphere is the outer layer of the atmosphere, which is isolated on the basis of changes in temperature and the properties of neutral gas. Molecules and atoms in the exosphere revolve around the Earth in ballistic orbits under the influence of gravity. Some of these orbits are parabolic and similar to the trajectories of projectiles. Molecules can revolve around the Earth and in elliptical orbits, like satellites. Some molecules, mainly hydrogen and helium, have open trajectories and escape into outer space (Fig. 2).

SOLAR-TERRESTRIAL RELATIONSHIPS AND THEIR INFLUENCE ON THE ATMOSPHERE
atmospheric tides. The attraction of the Sun and the Moon causes tides in the atmosphere, similar to the terrestrial and sea tides. But atmospheric tides have a significant difference: the atmosphere reacts most strongly to the attraction of the Sun, while the earth's crust and ocean - to the attraction of the Moon. This is explained by the fact that the atmosphere is heated by the Sun and, in addition to the gravitational tide, a powerful thermal tide arises. In general, the mechanisms of formation of atmospheric and sea tides are similar, except that in order to predict the reaction of air to gravitational and thermal effects, it is necessary to take into account its compressibility and temperature distribution. It is not entirely clear why semidiurnal (12-hour) solar tides in the atmosphere predominate over diurnal solar and semidiurnal lunar tides, although the driving forces of the latter two processes are much more powerful. Previously, it was believed that a resonance occurs in the atmosphere, which amplifies precisely the oscillations with a 12-hour period. However, observations carried out with the help of geophysical rockets indicate that there are no temperature reasons for such a resonance. In solving this problem, one should probably take into account all the hydrodynamic and thermal features of the atmosphere. At the earth's surface near the equator, where the influence of tidal fluctuations is maximum, it provides a change in atmospheric pressure by 0.1%. The speed of the tidal winds is approx. 0.3 km/h. Due to the complex thermal structure of the atmosphere (especially the presence of a temperature minimum in the mesopause), tidal air currents intensify, and, for example, at an altitude of 70 km, their speed is about 160 times higher than at the earth's surface, which has important geophysical consequences. It is believed that in the lower part of the ionosphere (layer E) tidal oscillations move the ionized gas vertically in the Earth's magnetic field, and therefore, electric currents arise here. These constantly emerging systems of currents on the surface of the Earth are established by perturbations of the magnetic field. The diurnal variations of the magnetic field are in good agreement with the calculated values, which convincingly testifies in favor of the theory of tidal mechanisms of the "atmospheric dynamo". Electric currents arising in the lower part of the ionosphere (layer E) must move somewhere, and, therefore, the circuit must be closed. The analogy with the dynamo becomes complete if we consider the oncoming movement as the work of the engine. It is assumed that the reverse circulation of the electric current is carried out in a higher layer of the ionosphere (F), and this counter flow can explain some of the peculiar features of this layer. Finally, the tidal effect must also generate horizontal currents in the E layer and, consequently, in the F layer.
Ionosphere. Trying to explain the mechanism of the occurrence of auroras, scientists of the 19th century. suggested that in the atmosphere there is a zone with electrically charged particles. In the 20th century Convincing evidence was obtained experimentally for the existence of a layer reflecting radio waves at altitudes from 85 to 400 km. It is now known that its electrical properties are the result of atmospheric gas ionization. Therefore, this layer is usually called the ionosphere. The impact on radio waves is mainly due to the presence of free electrons in the ionosphere, although the propagation mechanism of radio waves is associated with the presence of large ions. The latter are also of interest in the study of the chemical properties of the atmosphere, since they are more active than neutral atoms and molecules. Chemical reactions occurring in the ionosphere play an important role in its energy and electrical balance.
normal ionosphere. Observations carried out with the help of geophysical rockets and satellites have given a lot of new information, indicating that the ionization of the atmosphere occurs under the influence of broad-spectrum solar radiation. Its main part (more than 90%) is concentrated in the visible part of the spectrum. Ultraviolet radiation with a shorter wavelength and more energy than violet light rays is emitted by the hydrogen of the inner part of the Sun's atmosphere (chromosphere), and X-ray radiation, which has even higher energy, is emitted by the gases of the Sun's outer shell (corona). The normal (average) state of the ionosphere is due to constant powerful radiation. Regular changes occur in the normal ionosphere under the influence of the daily rotation of the Earth and seasonal differences in the angle of incidence of the sun's rays at noon, but unpredictable and abrupt changes in the state of the ionosphere also occur.
Disturbances in the ionosphere. As is known, powerful cyclically repeating perturbations arise on the Sun, which reach a maximum every 11 years. Observations under the program of the International Geophysical Year (IGY) coincided with the period of the highest solar activity for the entire period of systematic meteorological observations, i.e. from the beginning of the 18th century During periods of high activity, some areas on the Sun increase in brightness several times, and they send out powerful pulses of ultraviolet and X-ray radiation. Such phenomena are called solar flares. They last from several minutes to one or two hours. During a flare, solar gas (mostly protons and electrons) erupts, and elementary particles rush into outer space. The electromagnetic and corpuscular radiation of the Sun at the moments of such flares has a strong effect on the Earth's atmosphere. The initial reaction is observed 8 minutes after the flash, when intense ultraviolet and X-ray radiation reaches the Earth. As a result, ionization sharply increases; x-rays penetrate the atmosphere to the lower boundary of the ionosphere; the number of electrons in these layers increases so much that the radio signals are almost completely absorbed ("extinguished"). Additional absorption of radiation causes heating of the gas, which contributes to the development of winds. Ionized gas is an electrical conductor, and when it moves in the Earth's magnetic field, a dynamo effect appears and an electric current is generated. Such currents can, in turn, cause noticeable perturbations of the magnetic field and manifest themselves in the form of magnetic storms. This initial phase takes only a short time, corresponding to the duration of a solar flare. During powerful flares on the Sun, a stream of accelerated particles rushes into outer space. When it is directed towards the Earth, the second phase begins, which has a great influence on the state of the atmosphere. Many natural phenomena, among which the auroras are best known, indicate that a significant number of charged particles reach the Earth (see also POLAR LIGHTS). Nevertheless, the processes of separation of these particles from the Sun, their trajectories in interplanetary space, and the mechanisms of interaction with the Earth's magnetic field and the magnetosphere are still insufficiently studied. The problem became more complicated after the discovery in 1958 by James Van Allen of shells held by the geomagnetic field, consisting of charged particles. These particles move from one hemisphere to another, rotating in spirals around the magnetic field lines. Near the Earth, at a height depending on the shape of the lines of force and on the energy of the particles, there are "points of reflection", in which the particles change their direction of motion to the opposite (Fig. 3). Since the strength of the magnetic field decreases with distance from the Earth, the orbits along which these particles move are somewhat distorted: electrons deviate to the east, and protons to the west. Therefore, they are distributed in the form of belts around the globe.

Some consequences of the heating of the atmosphere by the Sun. Solar energy affects the entire atmosphere. We have already mentioned the belts formed by charged particles in the Earth's magnetic field and revolving around it. These belts are closest to the earth's surface in the circumpolar regions (see Fig. 3), where auroras are observed. Figure 1 shows that the auroral regions in Canada have significantly higher thermospheric temperatures than those in the US Southwest. It is likely that the trapped particles give up some of their energy to the atmosphere, especially when colliding with gas molecules near the reflection points, and leave their former orbits. This is how the high layers of the atmosphere are heated in the aurora zone. Another important discovery was made while studying the orbits of artificial satellites. Luigi Iacchia, an astronomer at the Smithsonian Astrophysical Observatory, believes that the small deviations of these orbits are due to changes in the density of the atmosphere as it is heated by the Sun. He suggested the existence of a maximum electron density in the ionosphere at an altitude of more than 200 km, which does not correspond to solar noon, but under the influence of friction forces lags with respect to it by about two hours. At this time, the values ​​of the atmospheric density, typical for an altitude of 600 km, are observed at a level of approx. 950 km. In addition, the maximum electron density experiences irregular fluctuations due to short-term flashes of ultraviolet and X-ray radiation from the Sun. L. Yakkia also discovered short-term fluctuations in air density, corresponding to solar flares and magnetic field disturbances. These phenomena are explained by the intrusion of particles of solar origin into the Earth's atmosphere and the heating of those layers where satellites orbit.
ATMOSPHERIC ELECTRICITY
In the surface layer of the atmosphere, a small part of the molecules undergo ionization under the influence of cosmic rays, radiation from radioactive rocks and decay products of radium (mainly radon) in the air itself. In the process of ionization, an atom loses an electron and acquires a positive charge. A free electron quickly combines with another atom, forming a negatively charged ion. Such paired positive and negative ions have molecular dimensions. Molecules in the atmosphere tend to cluster around these ions. Several molecules combined with an ion form a complex commonly referred to as a "light ion". The atmosphere also contains complexes of molecules, known in meteorology as condensation nuclei, around which, when the air is saturated with moisture, the condensation process begins. These nuclei are particles of salt and dust, as well as pollutants released into the air from industrial and other sources. Light ions often attach to such nuclei to form "heavy ions". Under the influence of an electric field, light and heavy ions move from one area of ​​the atmosphere to another, transferring electric charges. Although the atmosphere is not generally considered to be an electrically conductive medium, it does have a small amount of conductivity. Therefore, a charged body left in the air slowly loses its charge. Atmospheric conductivity increases with height due to increased cosmic ray intensity, reduced ion loss under lower pressure conditions (and hence longer mean free path), and due to fewer heavy nuclei. The conductivity of the atmosphere reaches its maximum value at a height of approx. 50 km, so-called. "compensation level". It is known that between the Earth's surface and the "compensation level" there is always a potential difference of several hundred kilovolts, i.e. constant electric field. It turned out that the potential difference between a certain point in the air at a height of several meters and the Earth's surface is very large - more than 100 V. The atmosphere has a positive charge, and the earth's surface is negatively charged. Since the electric field is an area, at each point of which there is a certain potential value, we can talk about a potential gradient. In clear weather, within the lower few meters, the electric field strength of the atmosphere is almost constant. Due to differences in the electrical conductivity of air in the surface layer, the potential gradient is subject to diurnal fluctuations, the course of which varies significantly from place to place. In the absence of local sources of air pollution - over the oceans, high in the mountains or in the polar regions - the daily course of the potential gradient in clear weather is the same. The magnitude of the gradient depends on the universal, or Greenwich Mean Time (UT) and reaches a maximum at 19:00 E. Appleton suggested that this maximum electrical conductivity probably coincides with the greatest thunderstorm activity on a planetary scale. Lightning discharges during thunderstorms carry a negative charge to the Earth's surface, since the bases of the most active cumulonimbus thunderclouds have a significant negative charge. The tops of thunderclouds have a positive charge, which, according to the calculations of Holzer and Saxon, flows from their tops during thunderstorms. Without constant replenishment, the charge on the earth's surface would be neutralized by the conductivity of the atmosphere. The assumption that the potential difference between the earth's surface and the "compensation level" is maintained due to thunderstorms is supported by statistical data. For example, the maximum number of thunderstorms is observed in the valley of the river. Amazons. Most often, thunderstorms occur there at the end of the day, i.e. OK. 19:00 Greenwich Mean Time, when the potential gradient is at its maximum anywhere in the world. Moreover, the seasonal variations in the shape of the curves of the diurnal variation of the potential gradient are also in full agreement with the data on the global distribution of thunderstorms. Some researchers argue that the source of the Earth's electric field may be of external origin, since electric fields are believed to exist in the ionosphere and magnetosphere. This circumstance probably explains the appearance of very narrow elongated forms of auroras, similar to backstage and arches.
(see also POLAR LIGHTS). Due to the potential gradient and conductivity of the atmosphere between the "compensation level" and the Earth's surface, charged particles begin to move: positively charged ions - towards the earth's surface, and negatively charged - upwards from it. This current is approx. 1800 A. Although this value seems large, it must be remembered that it is distributed over the entire surface of the Earth. The current strength in an air column with a base area of ​​1 m2 is only 4 * 10 -12 A. On the other hand, the current strength during a lightning discharge can reach several amperes, although, of course, such a discharge has a short duration - from fractions of a second to a whole second or a little more with repeated discharges. Lightning is of great interest not only as a peculiar phenomenon of nature. It makes it possible to observe an electric discharge in a gaseous medium at a voltage of several hundred million volts and a distance between the electrodes of several kilometers. In 1750, B. Franklin proposed to the Royal Society of London that they experiment with an iron rod fixed on an insulating base and mounted on a high tower. He expected that when a thundercloud approaches the tower, a charge of the opposite sign will be concentrated at the upper end of the initially neutral rod, and a charge of the same sign as at the base of the cloud will be concentrated at the lower end. If the strength of the electric field during a lightning discharge increases sufficiently, the charge from the upper end of the rod will partially drain into the air, and the rod will acquire a charge of the same sign as the base of the cloud. The experiment proposed by Franklin was not carried out in England, but it was set up in 1752 in Marly near Paris by the French physicist Jean d'Alembert. He used an iron rod 12 m long inserted into a glass bottle (which served as an insulator), but did not place it on the tower. May 10 his assistant reported that when a thundercloud was over a rod, sparks were produced when a grounded wire was brought to it.Franklin himself, unaware of the successful experience realized in France, in June of that year conducted his famous experiment with a kite and observed electric sparks at the end of a wire tied to it.The following year, while studying the charges collected from a rod, Franklin found that the bases of thunderclouds are usually negatively charged.More detailed studies of lightning became possible in the late 19th century due to improvements in photographic methods, especially after the invention of the apparatus with rotating lenses, which made it possible to fix rapidly developing processes. Such a camera was widely used in the study of spark discharges. It was found that there are several types of lightning, with the most common being linear, flat (intra-cloud) and globular (air discharges). Linear lightning is a spark discharge between a cloud and the earth's surface, following a channel with downward branches. Flat lightning occurs inside a thundercloud and looks like flashes of scattered light. Air discharges of ball lightning, starting from a thundercloud, are often directed horizontally and do not reach the earth's surface.

A lightning discharge usually consists of three or more repeated discharges - impulses following the same path. The intervals between successive pulses are very short, from 1/100 to 1/10 s (this is what causes lightning to flicker). In general, the flash lasts about a second or less. A typical lightning development process can be described as follows. First, a weakly luminous discharge-leader rushes from above to the earth's surface. When he reaches it, a brightly glowing reverse, or main, discharge passes from the earth up the channel laid by the leader. The discharge-leader, as a rule, moves in a zigzag manner. The speed of its propagation ranges from one hundred to several hundred kilometers per second. On its way, it ionizes air molecules, creating a channel with increased conductivity, through which the reverse discharge moves upward at a speed of about a hundred times greater than that of the leader discharge. It is difficult to determine the size of the channel, but the diameter of the leader discharge is estimated at 1–10 m, and that of the reverse discharge, several centimeters. Lightning discharges create radio interference by emitting radio waves in a wide range - from 30 kHz to ultra-low frequencies. The greatest radiation of radio waves is probably in the range from 5 to 10 kHz. Such low-frequency radio interference is "concentrated" in the space between the lower boundary of the ionosphere and the earth's surface and is capable of propagating to distances of thousands of kilometers from the source.
CHANGES IN THE ATMOSPHERE
Impact of meteors and meteorites. Although sometimes meteor showers make a deep impression with their lighting effects, individual meteors are rarely seen. Far more numerous are invisible meteors, too small to be seen at the moment they are swallowed up by the atmosphere. Some of the smallest meteors probably do not heat up at all, but are only captured by the atmosphere. These small particles ranging in size from a few millimeters to ten-thousandths of a millimeter are called micrometeorites. The amount of meteoric matter entering the atmosphere every day is from 100 to 10,000 tons, with most of this matter being micrometeorites. Since meteoric matter partially burns up in the atmosphere, its gas composition is replenished with traces of various chemical elements. For example, stone meteors bring lithium into the atmosphere. The combustion of metallic meteors leads to the formation of tiny spherical iron, iron-nickel and other droplets that pass through the atmosphere and are deposited on the earth's surface. They can be found in Greenland and Antarctica, where ice sheets remain almost unchanged for years. Oceanologists find them in bottom ocean sediments. Most of the meteor particles entering the atmosphere are deposited within approximately 30 days. Some scientists believe that this cosmic dust plays an important role in the formation of atmospheric phenomena such as rain, as it serves as the nuclei of water vapor condensation. Therefore, it is assumed that precipitation is statistically associated with large meteor showers. However, some experts believe that since the total input of meteoric matter is many tens of times greater than even with the largest meteor shower, the change in the total amount of this material that occurs as a result of one such shower can be neglected. However, there is no doubt that the largest micrometeorites and, of course, visible meteorites leave long traces of ionization in the high layers of the atmosphere, mainly in the ionosphere. Such traces can be used for long-distance radio communications, as they reflect high-frequency radio waves. The energy of meteors entering the atmosphere is spent mainly, and perhaps completely, on its heating. This is one of the minor components of the heat balance of the atmosphere.
Carbon dioxide of industrial origin. In the Carboniferous period, woody vegetation was widespread on Earth. Most of the carbon dioxide absorbed by plants at that time was accumulated in coal deposits and in oil-bearing deposits. People have learned to use the huge reserves of these minerals as a source of energy and are now rapidly returning carbon dioxide to the circulation of substances. The fossil is probably ca. 4*10 13 tons of carbon. Over the past century, mankind has burned so much fossil fuel that approximately 4 * 10 11 tons of carbon has again entered the atmosphere. There are currently approx. 2 * 10 12 tons of carbon, and in the next hundred years this figure may double due to the burning of fossil fuels. However, not all carbon will remain in the atmosphere: some of it will dissolve in the waters of the ocean, some will be absorbed by plants, and some will be bound in the process of weathering of rocks. It is not yet possible to predict how much carbon dioxide will be in the atmosphere or what effect it will have on the world's climate. Nevertheless, it is believed that any increase in its content will cause warming, although it is not at all necessary that any warming will significantly affect the climate. The concentration of carbon dioxide in the atmosphere, according to the results of measurements, is noticeably increasing, albeit at a slow pace. Climate data for Svalbard and Little America station on the Ross Ice Shelf in Antarctica indicate an increase in average annual temperatures over a period of approximately 50 years by 5° and 2.5°C, respectively.
The impact of cosmic radiation. When high-energy cosmic rays interact with individual components of the atmosphere, radioactive isotopes are formed. Among them, the 14C carbon isotope, which accumulates in plant and animal tissues, stands out. By measuring the radioactivity of organic substances that have not exchanged carbon with the environment for a long time, their age can be determined. The radiocarbon method has established itself as the most reliable method for dating fossil organisms and objects of material culture, the age of which does not exceed 50 thousand years. Other radioactive isotopes with long half-lives could be used to date materials that are hundreds of thousands of years old if the fundamental problem of measuring extremely low levels of radioactivity is solved.
(see also RADIOCARBON DATING).
ORIGIN OF THE EARTH'S ATMOSPHERE
The history of the formation of the atmosphere has not yet been restored absolutely reliably. Nevertheless, some probable changes in its composition have been identified. The formation of the atmosphere began immediately after the formation of the Earth. There are fairly good reasons to believe that in the process of the evolution of the Pra-Earth and its acquisition of close to modern dimensions and mass, it almost completely lost its original atmosphere. It is believed that at an early stage the Earth was in a molten state and ca. 4.5 billion years ago, it took shape in a solid body. This milestone is taken as the beginning of the geological chronology. Since that time there has been a slow evolution of the atmosphere. Some geological processes, such as eruptions of lava during volcanic eruptions, were accompanied by the release of gases from the bowels of the Earth. They probably included nitrogen, ammonia, methane, water vapor, carbon monoxide and carbon dioxide. Under the influence of solar ultraviolet radiation, water vapor decomposed into hydrogen and oxygen, but the released oxygen reacted with carbon monoxide to form carbon dioxide. Ammonia decomposed into nitrogen and hydrogen. Hydrogen in the process of diffusion rose up and left the atmosphere, while heavier nitrogen could not escape and gradually accumulated, becoming its main component, although some of it was bound during chemical reactions. Under the influence of ultraviolet rays and electrical discharges, a mixture of gases, probably present in the original atmosphere of the Earth, entered into chemical reactions, as a result of which organic substances, in particular amino acids, were formed. Consequently, life could originate in an atmosphere fundamentally different from the modern one. With the advent of primitive plants, the process of photosynthesis began (see also PHOTOSYNTHESIS), accompanied by the release of free oxygen. This gas, especially after diffusion into the upper atmosphere, began to protect its lower layers and the Earth's surface from life-threatening ultraviolet and X-ray radiation. It is estimated that as little as 0.00004 of today's volume of oxygen could lead to the formation of a layer with half the current ozone concentration, which nevertheless provided very significant protection from ultraviolet rays. It is also likely that the primary atmosphere contained a lot of carbon dioxide. It was consumed during photosynthesis, and its concentration must have decreased as the plant world evolved, and also due to absorption during some geological processes. Since the greenhouse effect is associated with the presence of carbon dioxide in the atmosphere, some scientists believe that fluctuations in its concentration are one of the important causes of large-scale climatic changes in the history of the Earth, such as ice ages. The helium present in the modern atmosphere is probably mostly a product of the radioactive decay of uranium, thorium, and radium. These radioactive elements emit alpha particles, which are the nuclei of helium atoms. Since no electrical charge is created or destroyed during radioactive decay, there are two electrons for every alpha particle. As a result, it combines with them, forming neutral helium atoms. Radioactive elements are contained in minerals dispersed in the thickness of rocks, so a significant part of the helium formed as a result of radioactive decay is stored in them, volatilizing very slowly into the atmosphere. A certain amount of helium rises up into the exosphere due to diffusion, but due to the constant influx from the earth's surface, the volume of this gas in the atmosphere is unchanged. Based on the spectral analysis of starlight and the study of meteorites, it is possible to estimate the relative abundance of various chemical elements in the Universe. The concentration of neon in space is about ten billion times higher than on Earth, krypton - ten million times, and xenon - a million times. It follows that the concentration of these inert gases, which were originally present in the Earth's atmosphere and were not replenished in the course of chemical reactions, greatly decreased, probably even at the stage of the Earth's loss of its primary atmosphere. An exception is the inert gas argon, since it is still formed in the form of the 40Ar isotope in the process of radioactive decay of the potassium isotope.
OPTICAL PHENOMENA
The variety of optical phenomena in the atmosphere is due to various reasons. The most common phenomena include lightning (see above) and the very picturesque aurora borealis and aurora borealis (see also POLAR LIGHTS). In addition, the rainbow, gal, parhelion (false sun) and arcs, crown, halos and ghosts of Brocken, mirages, St. Elmo's fires, luminous clouds, green and twilight rays are of particular interest. Rainbow is the most beautiful atmospheric phenomenon. Usually this is a huge arch, consisting of multi-colored stripes, observed when the Sun illuminates only part of the sky, and the air is saturated with water droplets, for example, during rain. The multi-colored arcs are arranged in a spectrum sequence (red, orange, yellow, green, cyan, indigo, violet), but the colors are almost never pure because the bands overlap. As a rule, the physical characteristics of rainbows vary significantly, and therefore they are very diverse in appearance. Their common feature is that the center of the arc is always located on a straight line drawn from the Sun to the observer. The main rainbow is an arc consisting of the brightest colors - red on the outside and purple on the inside. Sometimes only one arc is visible, but often a secondary one appears on the outside of the main rainbow. It has not as bright colors as the first one, and the red and purple stripes in it change places: red is located on the inside. The formation of the main rainbow is explained by double refraction (see also OPTICS) and single internal reflection of sunlight rays (see Fig. 5). Penetrating inside a drop of water (A), a ray of light is refracted and decomposed, as when passing through a prism. Then it reaches the opposite surface of the drop (B), is reflected from it and exits the drop to the outside (C). In this case, the beam of light, before reaching the observer, is refracted a second time. The initial white beam is decomposed into rays of different colors with a divergence angle of 2°. When a secondary rainbow is formed, double refraction and double reflection of the sun's rays occur (see Fig. 6). In this case, the light is refracted, penetrating inside the drop through its lower part (A), and reflected from the inner surface of the drop, first at point B, then at point C. At point D, the light is refracted, leaving the drop towards the observer.

At sunrise and sunset, the observer sees the rainbow in the form of an arc equal to half a circle, since the axis of the rainbow is parallel to the horizon. If the Sun is higher above the horizon, the arc of the rainbow is less than half a circle. When the Sun rises above 42° above the horizon, the rainbow disappears. Everywhere, except at high latitudes, a rainbow cannot appear at noon when the Sun is too high. It is interesting to estimate the distance to the rainbow. Although it seems that the multi-colored arc is located in the same plane, this is an illusion. In fact, the rainbow has great depth, and it can be represented as the surface of a hollow cone, at the top of which is the observer. The axis of the cone connects the Sun, the observer and the center of the rainbow. The observer looks, as it were, along the surface of this cone. Two people can never see exactly the same rainbow. Of course, one can observe the same effect in general, but the two rainbows are in different positions and are formed by different water droplets. When rain or mist forms a rainbow, the full optical effect is achieved by the combined effect of all the water droplets crossing the surface of the rainbow's cone with the observer at the apex. The role of each drop is fleeting. The surface of the rainbow cone consists of several layers. Quickly crossing them and passing through a series of critical points, each drop instantly decomposes the sun's ray into the entire spectrum in a strictly defined sequence - from red to purple. Many drops cross the surface of the cone in the same way, so that the rainbow appears to the observer as continuous both along and across its arc. Halo - white or iridescent light arcs and circles around the disk of the Sun or Moon. They are caused by the refraction or reflection of light by ice or snow crystals in the atmosphere. The crystals that form the halo are located on the surface of an imaginary cone with the axis directed from the observer (from the top of the cone) to the Sun. Under certain conditions, the atmosphere is saturated with small crystals, many of whose faces form a right angle with the plane passing through the Sun, the observer, and these crystals. Such facets reflect the incoming light rays with a deviation of 22 °, forming a halo that is reddish on the inside, but it can also consist of all colors of the spectrum. Less common is a halo with an angular radius of 46°, located concentrically around a 22-degree halo. Its inner side also has a reddish tint. The reason for this is also the refraction of light, which occurs in this case on the crystal faces that form right angles. The ring width of such a halo exceeds 2.5°. Both 46-degree and 22-degree halos tend to be brightest at the top and bottom of the ring. The rare 90-degree halo is a faintly luminous, almost colorless ring that has a common center with the other two halos. If it is colored, it has a red color on the outside of the ring. The mechanism of the appearance of this type of halo has not been fully elucidated (Fig. 7).

Parhelia and arcs. Parhelic circle (or circle of false suns) - a white ring centered at the zenith point, passing through the Sun parallel to the horizon. The reason for its formation is the reflection of sunlight from the edges of the surfaces of ice crystals. If the crystals are sufficiently evenly distributed in the air, a full circle becomes visible. Parhelia, or false suns, are brightly luminous spots resembling the Sun, which form at the points of intersection of the parhelic circle with the halo, having angular radii of 22°, 46° and 90°. The most frequently formed and brightest parhelion forms at the intersection with a 22-degree halo, usually colored in almost all colors of the rainbow. False suns at intersections with 46- and 90-degree halos are observed much less frequently. Parhelia that occur at intersections with 90-degree halos are called paranthelia, or false countersuns. Sometimes an antelium (counter-sun) is also visible - a bright spot located on the parhelion ring exactly opposite the Sun. It is assumed that the cause of this phenomenon is the double internal reflection of sunlight. The reflected beam follows the same path as the incident beam, but in the opposite direction. The circumzenithal arc, sometimes incorrectly referred to as the upper tangent arc of the 46-degree halo, is an arc of 90° or less centered on the zenith point and approximately 46° above the Sun. It is rarely visible and only for a few minutes, has bright colors, and the red color is confined to the outer side of the arc. The circumzenithal arc is notable for its coloration, brightness, and clear outlines. Another curious and very rare optical effect of the halo type is the Lovitz arc. They arise as a continuation of parhelia at the intersection with the 22-degree halo, pass from the outer side of the halo and are slightly concave towards the Sun. Pillars of whitish light, as well as various crosses, are sometimes visible at dawn or dusk, especially in the polar regions, and can accompany both the Sun and the Moon. At times, lunar halos and other effects similar to those described above are observed, with the most common lunar halo (ring around the Moon) having an angular radius of 22°. Like false suns, false moons can arise. Crowns, or crowns, are small concentric colored rings around the Sun, Moon or other bright objects that are observed from time to time when the light source is behind translucent clouds. The corona radius is smaller than the halo radius and is approx. 1-5°, the blue or violet ring is closest to the Sun. A corona is formed when light is scattered by small water droplets of water that form a cloud. Sometimes the crown looks like a luminous spot (or halo) surrounding the Sun (or Moon), which ends with a reddish ring. In other cases, at least two concentric rings of larger diameter, very weakly colored, are visible outside the halo. This phenomenon is accompanied by iridescent clouds. Sometimes the edges of very high clouds are painted in bright colors.
Gloria (halos). Under special conditions, unusual atmospheric phenomena occur. If the Sun is behind the observer, and its shadow is projected onto nearby clouds or a curtain of fog, under a certain state of the atmosphere around the shadow of a person's head, you can see a colored luminous circle - a halo. Usually such a halo is formed due to the reflection of light by dew drops on a grassy lawn. Glorias are also quite common to be found around the shadow that the plane casts on the underlying clouds.
Ghosts of the Brocken. In some regions of the globe, when the shadow of an observer on a hill, at sunrise or sunset, falls behind him on clouds located at a short distance, a striking effect is revealed: the shadow acquires colossal dimensions. This is due to the reflection and refraction of light by the smallest water droplets in the fog. The described phenomenon is called the "ghost of the Brocken" after the peak in the Harz mountains in Germany.
Mirages- an optical effect due to the refraction of light when passing through layers of air of different densities and is expressed in the appearance of a virtual image. In this case, distant objects may turn out to be raised or lowered relative to their actual position, and may also be distorted and acquire irregular, fantastic shapes. Mirages are often observed in hot climates, such as over sandy plains. Inferior mirages are common, when the distant, almost flat desert surface takes on the appearance of open water, especially when viewed from a slight elevation or simply above a layer of heated air. A similar illusion usually occurs on a heated paved road that looks like a water surface far ahead. In reality, this surface is a reflection of the sky. Below eye level, objects, usually upside down, may appear in this "water". An "air puff cake" is formed above the heated land surface, and the layer closest to the earth is the most heated and so rarefied that light waves passing through it are distorted, since their propagation speed varies depending on the density of the medium. Superior mirages are less common and more scenic than inferior mirages. Distant objects (often below the sea horizon) appear upside down in the sky, and sometimes a direct image of the same object also appears above. This phenomenon is typical for cold regions, especially when there is a significant temperature inversion, when a warmer layer of air is above the colder layer. This optical effect is manifested as a result of complex patterns of propagation of the front of light waves in air layers with a non-uniform density. Very unusual mirages occur from time to time, especially in the polar regions. When mirages occur on land, trees and other landscape components are upside down. In all cases, objects in the upper mirages are more clearly visible than in the lower ones. When the boundary of two air masses is a vertical plane, side mirages are sometimes observed.
Saint Elmo's fire. Some optical phenomena in the atmosphere (for example, glow and the most common meteorological phenomenon - lightning) are electrical in nature. Much less common are the fires of St. Elmo - luminous pale blue or purple brushes from 30 cm to 1 m or more in length, usually on the tops of masts or the ends of the yards of ships at sea. Sometimes it seems that the entire rigging of the ship is covered with phosphorus and glows. Elmo's fires sometimes appear on mountain peaks, as well as on spiers and sharp corners of tall buildings. This phenomenon is brush electric discharges at the ends of electrical conductors, when the electric field strength is greatly increased in the atmosphere around them. Will-o'-the-wisps are a faint bluish or greenish glow that is sometimes seen in swamps, cemeteries, and crypts. They often appear as a calmly burning, non-heating, candle flame raised about 30 cm above the ground, hovering over the object for a moment. The light seems to be completely elusive and, as the observer approaches, it seems to move to another place. The reason for this phenomenon is the decomposition of organic residues and the spontaneous combustion of swamp gas methane (CH4) or phosphine (PH3). Wandering lights have a different shape, sometimes even spherical. Green beam - a flash of emerald green sunlight at the moment when the last ray of the Sun disappears below the horizon. The red component of sunlight disappears first, all the others follow in order, and the emerald green remains last. This phenomenon occurs only when only the very edge of the solar disk remains above the horizon, otherwise there is a mixture of colors. Crepuscular rays are diverging beams of sunlight that become visible when they illuminate dust in the high atmosphere. Shadows from the clouds form dark bands, and rays propagate between them. This effect occurs when the Sun is low on the horizon before dawn or after sunset.

Atmosphere

The atmosphere is the gaseous shell that surrounds the Earth. It is held in place by the force of gravity of the Earth, under the influence of which most of the gases accumulate above the surface of the earth - in the lowest layer of the atmosphere - the troposphere.

We live in the lowest layer of the atmosphere. Planes fly in a layer called the atmosphere. Phenomena such as auroras in the northern and southern hemispheres originate in the thermosphere. Above is space.

Layers of the atmosphere

How many layers are there in the atmosphere?

There are five main layers of the atmosphere. The lowest layer, the troposphere, is 18 km above the earth's surface. The next layer - the stratosphere - extends to a height of 50 km, above - the mesosphere - about 80 km above the earth. The topmost layer is called the thermosphere. The higher you go, the less dense the atmosphere becomes; above 1000 km, the earth's atmosphere almost disappears, and the exosphere (a very rarefied fifth layer) passes into a vacuum.

How does the atmosphere protect us?

The stratosphere contains a layer of ozone (a compound of three oxygen atoms) that forms a protective shield that keeps most of the harmful ultraviolet radiation out. At the edge of the atmosphere there are two radiation zones, known as the Van Allen belts, which also reflect cosmic rays like a shield.

Why is the sky blue?

Light from the sun travels through the atmosphere and is scattered, reflecting off small particles of dust and water vapor in the air. This is how white sunlight is broken down into spectral parts - the colors of the rainbow. Blue rays scatter faster than the rest. As a result, we see more blue than any other color in the solar spectrum, which is why the sky appears blue.

Clouds change shape all the time. The reason for this is the wind. Some rise in huge masses, others resemble light feathers. Sometimes clouds completely cover the sky above us.

Earth's atmosphere is the gaseous envelope of our planet. Its lower boundary passes at the level of the earth's crust and hydrosphere, and the upper one passes into the near-Earth region of outer space. The atmosphere contains about 78% nitrogen, 20% oxygen, up to 1% argon, carbon dioxide, hydrogen, helium, neon and some other gases.

This earth shell is characterized by clearly defined layering. The layers of the atmosphere are determined by the vertical distribution of temperature and the different density of gases at its different levels. There are such layers of the Earth's atmosphere: troposphere, stratosphere, mesosphere, thermosphere, exosphere. The ionosphere is distinguished separately.

Up to 80% of the total mass of the atmosphere is the troposphere - the lower surface layer of the atmosphere. The troposphere in the polar zones is located at a level of up to 8-10 km above the earth's surface, in the tropical zone - up to a maximum of 16-18 km. Between the troposphere and the overlying stratosphere is the tropopause - the transition layer. In the troposphere, temperature decreases as altitude increases, and atmospheric pressure decreases with altitude. The average temperature gradient in the troposphere is 0.6°C per 100 m. The temperature at different levels of this shell is determined by the absorption of solar radiation and the efficiency of convection. Almost all human activity takes place in the troposphere. The highest mountains do not go beyond the troposphere, only air transport can cross the upper boundary of this shell to a small height and be in the stratosphere. A large proportion of water vapor is contained in the troposphere, which determines the formation of almost all clouds. Also, almost all aerosols (dust, smoke, etc.) that form on the earth's surface are concentrated in the troposphere. In the boundary lower layer of the troposphere, daily fluctuations in temperature and air humidity are expressed, the wind speed is usually reduced (it increases with altitude). In the troposphere, there is a variable division of the air column into air masses in the horizontal direction, which differ in a number of characteristics depending on the zone and the area of ​​their formation. At atmospheric fronts - the boundaries between air masses - cyclones and anticyclones are formed, which determine the weather in a certain area for a specific period of time.

The stratosphere is the layer of the atmosphere between the troposphere and the mesosphere. The limits of this layer range from 8-16 km to 50-55 km above the Earth's surface. In the stratosphere, the gas composition of air is approximately the same as in the troposphere. A distinctive feature is a decrease in the concentration of water vapor and an increase in the ozone content. The ozone layer of the atmosphere, which protects the biosphere from the aggressive effects of ultraviolet light, is at a level of 20 to 30 km. In the stratosphere, the temperature rises with height, and the temperature values ​​​​are determined by solar radiation, and not by convection (movements of air masses), as in the troposphere. The heating of the air in the stratosphere is due to the absorption of ultraviolet radiation by ozone.

The mesosphere extends above the stratosphere up to a level of 80 km. This layer of the atmosphere is characterized by the fact that the temperature decreases from 0 ° C to - 90 ° C as the height increases. This is the coldest region of the atmosphere.

Above the mesosphere is the thermosphere up to a level of 500 km. From the border with the mesosphere to the exosphere, the temperature varies from approximately 200 K to 2000 K. Up to a level of 500 km, the air density decreases by several hundred thousand times. The relative composition of the atmospheric components of the thermosphere is similar to the surface layer of the troposphere, but with increasing altitude, more oxygen passes into the atomic state. A certain proportion of molecules and atoms of the thermosphere is in an ionized state and distributed in several layers, they are united by the concept of the ionosphere. The characteristics of the thermosphere vary over a wide range depending on the geographic latitude, the amount of solar radiation, the time of year and day.

The upper layer of the atmosphere is the exosphere. This is the thinnest layer of the atmosphere. In the exosphere, the mean free paths of particles are so huge that particles can freely escape into interplanetary space. The mass of the exosphere is one ten millionth of the total mass of the atmosphere. The lower boundary of the exosphere is the level of 450-800 km, and the upper boundary is the area where the concentration of particles is the same as in outer space - several thousand kilometers from the Earth's surface. The exosphere is made up of plasma, an ionized gas. Also in the exosphere are the radiation belts of our planet.

Video presentation - layers of the Earth's atmosphere:

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