The atmosphere began to form along with the formation of the Earth. In the course of the evolution of the planet and as its parameters approached modern values, there were fundamentally qualitative changes in its chemical composition and physical properties. According to the evolutionary model, at an early stage, the Earth was in a molten state and about 4.5 billion years ago was formed as a solid body. This milestone is taken as the beginning of the geological chronology. Since that time, the slow evolution of the atmosphere began. Some geological processes (for example, outpourings of lava during volcanic eruptions) were accompanied by the release of gases from the bowels of the Earth. They included nitrogen, ammonia, methane, water vapor, CO2 oxide and CO2 carbon dioxide. Under the influence of solar ultraviolet radiation, water vapor decomposed into hydrogen and oxygen, but the released oxygen reacted with carbon monoxide, forming 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 the main component, although some of it was bound into molecules as a result of chemical reactions ( cm. CHEMISTRY OF THE ATMOSPHERE). Under the influence of ultraviolet rays and electrical discharges, a mixture of gases that were 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. With the advent of primitive plants, the process of photosynthesis began, accompanied by the release of 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. According to theoretical estimates, the oxygen content, which is 25,000 times lower than now, could already lead to the formation of an ozone layer with only half as much as it is now. However, this is already enough to provide a very significant protection of organisms from the damaging effects of ultraviolet rays.
It is 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. Insofar as the greenhouse effect associated with the presence of carbon dioxide in the atmosphere, fluctuations in its concentration are one of the important causes of such large-scale climatic changes in the history of the Earth, such as ice ages.
The helium present in the modern atmosphere is mostly a product of the radioactive decay of uranium, thorium and radium. These radioactive elements emit a-particles, which are the nuclei of helium atoms. Since an electric charge is not formed and does not disappear during radioactive decay, with the formation of each a-particle, two electrons appear, which, recombining with a-particles, form 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 remains almost 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 from this that the concentration of these inert gases, apparently originally present in the Earth's atmosphere and 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 40 Ar isotope in the process of radioactive decay of the potassium isotope.
Barometric pressure distribution.
The total weight of atmospheric gases is approximately 4.5 10 15 tons. Thus, the "weight" of the atmosphere per unit area, or atmospheric pressure, is approximately 11 t / m 2 = 1.1 kg / cm 2 at sea level. Pressure equal to P 0 \u003d 1033.23 g / cm 2 \u003d 1013.250 mbar \u003d 760 mm Hg. Art. = 1 atm, taken as the standard mean atmospheric pressure. For an atmosphere in hydrostatic equilibrium, we have: d P= -rgd h, which means that on the interval of heights from h before h+d h takes place equality between atmospheric pressure change d P and the weight of the corresponding element of the atmosphere with unit area, density r and thickness d h. As a ratio between pressure R and temperature T the equation of state of an ideal gas with density r, which is quite applicable for the earth's atmosphere, is used: P= r R T/m, where m is the molecular weight, and R = 8.3 J/(K mol) is the universal gas constant. Then dlog P= – (m g/RT)d h= -bd h= – d h/H, where the pressure gradient is on a logarithmic scale. The reciprocal of H is to be called the scale of the height of the atmosphere.
When integrating this equation for an isothermal atmosphere ( T= const) or for its part, where such an approximation is acceptable, the barometric law of pressure distribution with height is obtained: P = P 0 exp(- h/H 0), where the height reading h produced from ocean level, where the standard mean pressure is P 0 . Expression H 0=R T/ mg, is called the height scale, which characterizes the extent of the atmosphere, provided that the temperature in it is the same everywhere (isothermal atmosphere). If the atmosphere is not isothermal, then it is necessary to integrate taking into account the change in temperature with height, and the parameter H- some local characteristic of the layers of the atmosphere, depending on their temperature and the properties of the medium.
Standard atmosphere.
Model (table of values of the main parameters) corresponding to the standard pressure at the base of the atmosphere R 0 and chemical composition is called the standard atmosphere. More precisely, this is a conditional model of the atmosphere, for which the average values of temperature, pressure, density, viscosity, and other air characteristics for a latitude of 45° 32° 33І are set at altitudes from 2 km below sea level to the outer boundary of the earth's atmosphere. The parameters of the middle atmosphere at all altitudes were calculated using the ideal gas equation of state and the barometric law assuming that at sea level the pressure is 1013.25 hPa (760 mmHg) and the temperature is 288.15 K (15.0°C). According to the nature of the vertical temperature distribution, the average atmosphere consists of several layers, in each of which the temperature is approximated by a linear function of height. In the lowest of the layers - the troposphere (h Ј 11 km), the temperature drops by 6.5 ° C with each kilometer of ascent. At high altitudes, the value and sign of the vertical temperature gradient change from layer to layer. Above 790 km, the temperature is about 1000 K and practically does not change with height.
The standard atmosphere is a periodically updated, legalized standard, issued in the form of tables.
| Table 1. STANDARD EARTH ATMOSPHERE MODEL. The table shows: h- height from sea level, R- pressure, T– temperature, r – density, N is the number of molecules or atoms per unit volume, H- height scale, l is the length of the free path. Pressure and temperature at an altitude of 80–250 km, obtained from rocket data, have lower values. Extrapolated values for heights greater than 250 km are not very accurate. | ||||||
| h(km) | P(mbar) | T(°C) | r (g / cm 3) | N(cm -3) | H(km) | l(cm) |
| 0 | 1013 | 288 | 1.22 10 -3 | 2.55 10 19 | 8,4 | 7.4 10 -6 |
| 1 | 899 | 281 | 1.11 10 -3 | 2.31 10 19 | 8.1 10 -6 | |
| 2 | 795 | 275 | 1.01 10 -3 | 2.10 10 19 | 8.9 10 -6 | |
| 3 | 701 | 268 | 9.1 10 -4 | 1.89 10 19 | 9.9 10 -6 | |
| 4 | 616 | 262 | 8.2 10 -4 | 1.70 10 19 | 1.1 10 -5 | |
| 5 | 540 | 255 | 7.4 10 -4 | 1.53 10 19 | 7,7 | 1.2 10 -5 |
| 6 | 472 | 249 | 6.6 10 -4 | 1.37 10 19 | 1.4 10 -5 | |
| 8 | 356 | 236 | 5.2 10 -4 | 1.09 10 19 | 1.7 10 -5 | |
| 10 | 264 | 223 | 4.1 10 -4 | 8.6 10 18 | 6,6 | 2.2 10 -5 |
| 15 | 121 | 214 | 1.93 10 -4 | 4.0 10 18 | 4.6 10 -5 | |
| 20 | 56 | 214 | 8.9 10 -5 | 1.85 10 18 | 6,3 | 1.0 10 -4 |
| 30 | 12 | 225 | 1.9 10 -5 | 3.9 10 17 | 6,7 | 4.8 10 -4 |
| 40 | 2,9 | 268 | 3.9 10 -6 | 7.6 10 16 | 7,9 | 2.4 10 -3 |
| 50 | 0,97 | 276 | 1.15 10 -6 | 2.4 10 16 | 8,1 | 8.5 10 -3 |
| 60 | 0,28 | 260 | 3.9 10 -7 | 7.7 10 15 | 7,6 | 0,025 |
| 70 | 0,08 | 219 | 1.1 10 -7 | 2.5 10 15 | 6,5 | 0,09 |
| 80 | 0,014 | 205 | 2.7 10 -8 | 5.0 10 14 | 6,1 | 0,41 |
| 90 | 2.8 10 -3 | 210 | 5.0 10 -9 | 9 10 13 | 6,5 | 2,1 |
| 100 | 5.8 10 -4 | 230 | 8.8 10 -10 | 1.8 10 13 | 7,4 | 9 |
| 110 | 1.7 10 -4 | 260 | 2.1 10 –10 | 5.4 10 12 | 8,5 | 40 |
| 120 | 6 10 -5 | 300 | 5.6 10 -11 | 1.8 10 12 | 10,0 | 130 |
| 150 | 5 10 -6 | 450 | 3.2 10 -12 | 9 10 10 | 15 | 1.8 10 3 |
| 200 | 5 10 -7 | 700 | 1.6 10 -13 | 5 10 9 | 25 | 3 10 4 |
| 250 | 9 10 -8 | 800 | 3 10 -14 | 8 10 8 | 40 | 3 10 5 |
| 300 | 4 10 -8 | 900 | 8 10 -15 | 3 10 8 | 50 | |
| 400 | 8 10 -9 | 1000 | 1 10 –15 | 5 10 7 | 60 | |
| 500 | 2 10 -9 | 1000 | 2 10 -16 | 1 10 7 | 70 | |
| 700 | 2 10 –10 | 1000 | 2 10 -17 | 1 10 6 | 80 | |
| 1000 | 1 10 –11 | 1000 | 1 10 -18 | 1 10 5 | 80 | |
Troposphere.
The lowest and densest layer of the atmosphere, in which the temperature decreases rapidly with height, is called the troposphere. It contains up to 80% of the total mass of the atmosphere and extends in polar and middle latitudes up to heights of 8–10 km, and in the tropics up to 16–18 km. Almost all weather-forming processes develop here, heat and moisture exchange occurs between the Earth and its atmosphere, clouds form, various meteorological phenomena occur, fogs and precipitation occur. These layers of the earth's atmosphere are in convective equilibrium and, due to active mixing, have a homogeneous chemical composition, mainly from molecular nitrogen (78%) and oxygen (21%). The vast majority of natural and man-made aerosol and gas air pollutants are concentrated in the troposphere. The dynamics of the lower part of the troposphere up to 2 km thick strongly depends on the properties of the underlying surface of the Earth, which determines the horizontal and vertical movements of air (winds) due to the transfer of heat from a warmer land through the IR radiation of the earth's surface, which is absorbed in the troposphere, mainly by vapor water and carbon dioxide (greenhouse effect). The temperature distribution with height is established as a result of turbulent and convective mixing. On average, it corresponds to a drop in temperature with height of about 6.5 K/km.
The wind speed in the surface boundary layer first increases rapidly with height, and higher it continues to increase by 2–3 km/s per kilometer. Sometimes in the troposphere there are narrow planetary streams (with a speed of more than 30 km/s), western ones in middle latitudes, and eastern ones near the equator. They are called jet streams.
tropopause.
At the upper boundary of the troposphere (tropopause), the temperature reaches its minimum value for the lower atmosphere. This is the transition layer between the troposphere and the stratosphere above it. The thickness of the tropopause is from hundreds of meters to 1.5–2 km, and the temperature and altitude, respectively, range from 190 to 220 K and from 8 to 18 km, depending on the geographic latitude and season. In temperate and high latitudes, in winter it is 1–2 km lower than in summer and 8–15 K warmer. In the tropics, seasonal changes are much less (altitude 16–18 km, temperature 180–200 K). Above jet streams possible rupture of the tropopause.
Water in the Earth's atmosphere.
The most important feature of the Earth's atmosphere is the presence of a significant amount of water vapor and water in droplet form, which is most easily observed in the form of clouds and cloud structures. The degree of cloud coverage of the sky (at a certain moment or on average over a certain period of time), expressed on a 10-point scale or as a percentage, is called cloudiness. The shape of the clouds is determined by the international classification. On average, clouds cover about half of the globe. Cloudiness is an important factor characterizing weather and climate. In winter and at night, cloudiness prevents a decrease in the temperature of the earth's surface and the surface layer of air, in summer and during the day it weakens the heating of the earth's surface by the sun's rays, softening the climate inside the continents.
Clouds.
Clouds are accumulations of water droplets suspended in the atmosphere (water clouds), ice crystals (ice clouds), or both (mixed clouds). As drops and crystals become larger, they fall out of the clouds in the form of precipitation. Clouds form mainly in the troposphere. They result from the condensation of water vapor contained in the air. The diameter of cloud drops is on the order of several microns. The content of liquid water in clouds is from fractions to several grams per m3. Clouds are distinguished by height: According to the international classification, there are 10 genera of clouds: cirrus, cirrocumulus, cirrostratus, altocumulus, altostratus, stratonimbus, stratus, stratocumulus, cumulonimbus, cumulus.
Mother-of-pearl clouds are also observed in the stratosphere, and noctilucent clouds in the mesosphere.
Cirrus clouds - transparent clouds in the form of thin white threads or veils with a silky sheen, not giving a shadow. Cirrus clouds are made up of ice crystals and form in the upper troposphere at very low temperatures. Some types of cirrus clouds serve as harbingers of weather changes.
Cirrocumulus clouds are ridges or layers of thin white clouds in the upper troposphere. Cirrocumulus clouds are built from small elements that look like flakes, ripples, small balls without shadows and consist mainly of ice crystals.
Cirrostratus clouds - a whitish translucent veil in the upper troposphere, usually fibrous, sometimes blurry, consisting of small needle or columnar ice crystals.
Altocumulus clouds are white, gray or white-gray clouds of the lower and middle layers of the troposphere. Altocumulus clouds look like layers and ridges, as if built from plates lying one above the other, rounded masses, shafts, flakes. Altocumulus clouds form during intense convective activity and usually consist of supercooled water droplets.
Altostratus clouds are grayish or bluish clouds of a fibrous or uniform structure. Altostratus clouds are observed in the middle troposphere, extending several kilometers in height and sometimes thousands of kilometers in a horizontal direction. Usually, altostratus clouds are part of frontal cloud systems associated with ascending movements of air masses.
Nimbostratus clouds - a low (from 2 km and above) amorphous layer of clouds of a uniform gray color, giving rise to overcast rain or snow. Nimbostratus clouds - highly developed vertically (up to several km) and horizontally (several thousand km), consist of supercooled water drops mixed with snowflakes, usually associated with atmospheric fronts.
Stratus clouds - clouds of the lower tier in the form of a homogeneous layer without definite outlines, gray in color. The height of stratus clouds above the earth's surface is 0.5–2 km. Occasional drizzle falls from stratus clouds.
Cumulus clouds are dense, bright white clouds during the day with significant vertical development (up to 5 km or more). The upper parts of cumulus clouds look like domes or towers with rounded outlines. Cumulus clouds usually form as convection clouds in cold air masses.
Stratocumulus clouds - low (below 2 km) clouds in the form of gray or white non-fibrous layers or ridges of round large blocks. The vertical thickness of stratocumulus clouds is small. Occasionally, stratocumulus clouds give light precipitation.
Cumulonimbus clouds are powerful and dense clouds with strong vertical development (up to a height of 14 km), giving heavy rainfall with thunderstorms, hail, squalls. Cumulonimbus clouds develop from powerful cumulus clouds, differing from them in the upper part, consisting of ice crystals.
Stratosphere.
Through the tropopause, on average at altitudes from 12 to 50 km, the troposphere passes into the stratosphere. In the lower part, for about 10 km, i.e. up to heights of about 20 km, it is isothermal (temperature about 220 K). Then it increases with altitude, reaching a maximum of about 270 K at an altitude of 50–55 km. Here is the boundary between the stratosphere and the overlying mesosphere, called the stratopause. .
There is much less water vapor in the stratosphere. Nevertheless, thin translucent mother-of-pearl clouds are occasionally observed, occasionally appearing in the stratosphere at a height of 20–30 km. Mother-of-pearl clouds are visible in the dark sky after sunset and before sunrise. In shape, mother-of-pearl clouds resemble cirrus and cirrocumulus clouds.
Middle atmosphere (mesosphere).
At an altitude of about 50 km, the mesosphere begins with the peak of a wide temperature maximum. . The reason for the increase in temperature in the region of this maximum is an exothermic (i.e., accompanied by the release of heat) photochemical reaction of ozone decomposition: O 3 + hv® O 2 + O. Ozone arises as a result of the photochemical decomposition of molecular oxygen O 2
About 2+ hv® O + O and the subsequent reaction of a triple collision of an atom and an oxygen molecule with some third molecule M.
O + O 2 + M ® O 3 + M
Ozone greedily absorbs ultraviolet radiation in the region from 2000 to 3000Å, and this radiation heats up the atmosphere. Ozone, located in the upper atmosphere, serves as a kind of shield that protects us from the action of ultraviolet radiation from the sun. Without this shield, the development of life on Earth in its modern forms would hardly have been possible.
In general, throughout the mesosphere, the temperature of the atmosphere decreases to its minimum value of about 180 K at the upper boundary of the mesosphere (called the mesopause, height is about 80 km). In the vicinity of the mesopause, at altitudes of 70–90 km, a very thin layer of ice crystals and particles of volcanic and meteorite dust can appear, observed in the form of a beautiful spectacle of noctilucent clouds. shortly after sunset.
In the mesosphere, for the most part, small solid meteorite particles that fall on the Earth are burned, causing the phenomenon of meteors.
Meteors, meteorites and fireballs.
Flares and other phenomena in the upper atmosphere of the Earth caused by the intrusion into it at a speed of 11 km / s and above solid cosmic particles or bodies are called meteoroids. There is an observed bright meteor trail; the most powerful phenomena, often accompanied by the fall of meteorites, are called fireballs; meteors are associated with meteor showers.
meteor shower:
1) the phenomenon of multiple meteor falls over several hours or days from one radiant.
2) a swarm of meteoroids moving in one orbit around the Sun.
The systematic appearance of meteors in a certain region of the sky and on certain days of the year, caused by the intersection of the Earth's orbit with a common orbit of many meteorite bodies moving at approximately the same and equally directed speeds, due to which their paths in the sky seem to come out of one common point (radiant) . They are named after the constellation where the radiant is located.
Meteor showers make a deep impression with their lighting effects, but 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 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.
A meteorite is a solid body of natural origin that fell to the surface of the Earth from space. Usually distinguish stone, iron-stone and iron meteorites. The latter are mainly composed of iron and nickel. Among the found meteorites, most have a weight of several grams to several kilograms. The largest of those found, the Goba iron meteorite weighs about 60 tons and still lies in the same place where it was discovered, in South Africa. Most meteorites are fragments of asteroids, but some meteorites may have come to Earth from the Moon and even from Mars.
A fireball is a very bright meteor, sometimes observed even during the day, often leaving behind a smoky trail and accompanied by sound phenomena; often ends with the fall of meteorites.
Thermosphere.
Above the temperature minimum of the mesopause, the thermosphere begins, in which the temperature, at first slowly, and then quickly, begins to rise again. The reason is the absorption of ultraviolet, solar radiation at altitudes of 150–300 km, due to the ionization of atomic oxygen: O + hv® O + + e.
In the thermosphere, the temperature continuously rises to a height of about 400 km, where it reaches 1800 K in the daytime during the epoch of maximum solar activity. In the epoch of minimum, this limiting temperature can be less than 1000 K. Above 400 km, the atmosphere passes into an isothermal exosphere. The critical level (the base of the exosphere) is located at an altitude of about 500 km.
Auroras and many orbits of artificial satellites, as well as noctilucent clouds - all these phenomena occur in the mesosphere and thermosphere.
Polar Lights.
At high latitudes, auroras are observed during magnetic field disturbances. They may last for several minutes, but are often visible for several hours. Auroras vary greatly in shape, color and intensity, all of which sometimes change very rapidly over time. The aurora spectrum consists of emission lines and bands. Some of the emissions from the night sky are enhanced in the aurora spectrum, primarily the green and red lines of l 5577 Å and l 6300 Å of oxygen. It happens that one of these lines is many times more intense than the other, and this determines the visible color of the radiance: green or red. Disturbances in the magnetic field are also accompanied by disruptions in radio communications in the polar regions. The disruption is caused by changes in the ionosphere, which means that during magnetic storms a powerful source of ionization operates. It has been established that strong magnetic storms occur when there are large groups of spots near the center of the solar disk. Observations have shown that storms are associated not with the spots themselves, but with solar flares that appear during the development of a group of spots.
The auroras are a range of light of varying intensity with rapid movements observed in the high latitude regions of the Earth. The visual aurora contains green (5577Å) and red (6300/6364Å) emission lines of atomic oxygen and N 2 molecular bands, which are excited by energetic particles of solar and magnetospheric origin. These emissions are usually displayed at an altitude of about 100 km and above. The term optical aurora is used to refer to the visual auroras and their infrared to ultraviolet emission spectrum. The radiation energy in the infrared part of the spectrum significantly exceeds the energy of the visible region. When auroras appeared, emissions were observed in the ULF range (
The actual forms of auroras are difficult to classify; The following terms are most commonly used:
1. Calm uniform arcs or stripes. The arc usually extends for ~1000 km in the direction of the geomagnetic parallel (toward the Sun in the polar regions) and has a width from one to several tens of kilometers. A strip is a generalization of the concept of an arc, it usually does not have a regular arcuate shape, but bends in the form of an S or in the form of spirals. Arcs and bands are located at altitudes of 100–150 km.
2. Rays of aurora . This term refers to an auroral structure stretched along magnetic field lines with a vertical extension from several tens to several hundreds of kilometers. The length of the rays along the horizontal is small, from several tens of meters to several kilometers. Rays are usually observed in arcs or as separate structures.
3. Stains or surfaces . These are isolated areas of glow that do not have a specific shape. Individual spots may be related.
4. Veil. An unusual form of aurora, which is a uniform glow that covers large areas of the sky.
According to the structure, the auroras are divided into homogeneous, polish and radiant. Various terms are used; pulsating arc, pulsating surface, diffuse surface, radiant stripe, drapery, etc. There is a classification of auroras according to their color. According to this classification, auroras of the type BUT. The upper part or completely are red (6300–6364 Å). They usually appear at altitudes of 300–400 km during high geomagnetic activity.
Aurora type AT are colored red in the lower part and are associated with the luminescence of the bands of the first positive N 2 system and the first negative O 2 system. Such forms of aurora appear during the most active phases of auroras.
Zones auroras – these are zones of maximum frequency of occurrence of auroras at night, according to observers at a fixed point on the Earth's surface. The zones are located at 67° north and south latitude, and their width is about 6°. The maximum occurrence of auroras, corresponding to a given moment of local geomagnetic time, occurs in oval-like belts (aurora oval), which are located asymmetrically around the north and south geomagnetic poles. The aurora oval is fixed in latitude-time coordinates, and the aurora zone is the locus of points in the midnight region of the oval in latitude-longitude coordinates. The oval belt is located approximately 23° from the geomagnetic pole in the night sector and 15° in the day sector.
Auroral oval and aurora zones. The location of the aurora oval depends on geomagnetic activity. The oval becomes wider at high geomagnetic activity. Aurora zones or aurora oval boundaries are better represented by L 6.4 than by dipole coordinates. The geomagnetic field lines at the boundary of the daytime sector of the aurora oval coincide with magnetopause. There is a change in the position of the aurora oval depending on the angle between the geomagnetic axis and the Earth-Sun direction. The auroral oval is also determined on the basis of data on the precipitation of particles (electrons and protons) of certain energies. Its position can be independently determined from data on caspakh on the dayside and in the magnetotail.
The daily variation in the frequency of occurrence of auroras in the aurora zone has a maximum at geomagnetic midnight and a minimum at geomagnetic noon. On the near-equatorial side of the oval, the frequency of occurrence of auroras sharply decreases, but the shape of diurnal variations is retained. On the polar side of the oval, the frequency of occurrence of auroras decreases gradually and is characterized by complex diurnal changes.
Intensity of auroras.
Aurora Intensity determined by measuring the apparent luminance surface. Brightness surface I auroras in a certain direction is determined by the total emission 4p I photon/(cm 2 s). Since this value is not the true surface brightness, but represents the emission from the column, the unit photon/(cm 2 column s) is usually used in the study of auroras. The usual unit for measuring total emission is Rayleigh (Rl) equal to 10 6 photon / (cm 2 column s). A more practical unit of aurora intensity is determined from the emissions of a single line or band. For example, the intensity of the auroras is determined by the international brightness coefficients (ICF) according to the green line intensity data (5577 Å); 1 kRl = I MKH, 10 kRl = II MKH, 100 kRl = III MKH, 1000 kRl = IV MKH (maximum aurora intensity). This classification cannot be used for red auroras. One of the discoveries of the epoch (1957–1958) was the establishment of the spatial and temporal distribution of auroras in the form of an oval displaced relative to the magnetic pole. From simple ideas about the circular shape of the distribution of auroras relative to the magnetic pole, the transition to modern physics of the magnetosphere was completed. The honor of the discovery belongs to O. Khorosheva, and G. Starkov, J. Feldshtein, S-I. The aurora oval is the region of the most intense impact of the solar wind on the Earth's upper atmosphere. The intensity of auroras is greatest in the oval, and its dynamics are continuously monitored by satellites.
Stable auroral red arcs.
Steady auroral red arc, otherwise called the mid-latitude red arc or M-arc, is a subvisual (below the sensitivity limit of the eye) wide arc, stretched from east to west for thousands of kilometers and encircling, possibly, the entire Earth. The latitudinal extent of the arc is 600 km. The emission from the stable auroral red arc is almost monochromatic in the red lines l 6300 Å and l 6364 Å. Recently, weak emission lines l 5577 Å (OI) and l 4278 Å (N + 2) have also been reported. Persistent red arcs are classified as auroras, but they appear at much higher altitudes. The lower limit is located at an altitude of 300 km, the upper limit is about 700 km. The intensity of the quiet auroral red arc in the l 6300 Å emission ranges from 1 to 10 kRl (a typical value is 6 kRl). The sensitivity threshold of the eye at this wavelength is about 10 kR, so arcs are rarely observed visually. However, observations have shown that their brightness is >50 kR on 10% of nights. The usual lifetime of the arcs is about one day, and they rarely appear in the following days. Radio waves from satellites or radio sources crossing stable auroral red arcs are subject to scintillations, indicating the existence of electron density inhomogeneities. The theoretical explanation of the red arcs is that the heated electrons of the region F ionospheres cause an increase in oxygen atoms. Satellite observations show an increase in electron temperature along geomagnetic field lines that cross stable auroral red arcs. The intensity of these arcs correlates positively with geomagnetic activity (storms), and the frequency of occurrence of arcs correlates positively with solar sunspot activity.
Changing aurora.
Some forms of auroras experience quasi-periodic and coherent temporal intensity variations. These auroras, with a roughly stationary geometry and rapid periodic variations occurring in phase, are called changing auroras. They are classified as auroras forms R according to the International Atlas of Auroras A more detailed subdivision of the changing auroras:
R 1 (pulsating aurora) is a glow with uniform phase variations in brightness throughout the form of the aurora. By definition, in an ideal pulsating aurora, the spatial and temporal parts of the pulsation can be separated, i.e. brightness I(r,t)= I s(r)· I T(t). In a typical aurora R 1, pulsations occur with a frequency of 0.01 to 10 Hz of low intensity (1–2 kR). Most auroras R 1 are spots or arcs that pulsate with a period of several seconds.
R 2 (fiery aurora). This term is usually used to refer to movements like flames filling the sky, and not to describe a single form. The auroras are arc-shaped and usually move upward from a height of 100 km. These auroras are relatively rare and occur more often outside of the auroras.
R 3 (flickering aurora). These are auroras with rapid, irregular or regular variations in brightness, giving the impression of a flickering flame in the sky. They appear shortly before the collapse of the aurora. Commonly observed variation frequency R 3 is equal to 10 ± 3 Hz.
The term streaming aurora, used for another class of pulsating auroras, refers to irregular variations in brightness moving rapidly horizontally in arcs and bands of auroras.
The changing aurora is one of the solar-terrestrial phenomena accompanying pulsations of the geomagnetic field and auroral X-ray radiation caused by the precipitation of particles of solar and magnetospheric origin.
The glow of the polar cap is characterized by a high intensity of the band of the first negative N + 2 system (λ 3914 Å). Usually, these N + 2 bands are five times more intense than the green line OI l 5577 Å; the absolute intensity of the polar cap glow is from 0.1 to 10 kRl (usually 1–3 kRl). With these auroras, which appear during PCA periods, a uniform glow covers the entire polar cap up to the geomagnetic latitude of 60° at altitudes of 30 to 80 km. It is generated mainly by solar protons and d-particles with energies of 10–100 MeV, which create an ionization maximum at these heights. There is another type of glow in the aurora zones, called mantle auroras. For this type of auroral glow, the daily intensity maximum in the morning hours is 1–10 kR, and the intensity minimum is five times weaker. Observations of mantle auroras are few and their intensity depends on geomagnetic and solar activity.
Atmospheric glow is defined as radiation produced and emitted by a planet's atmosphere. This is the non-thermal radiation of the atmosphere, with the exception of the emission of auroras, lightning discharges and the emission of meteor trails. This term is used in relation to the earth's atmosphere (night glow, twilight glow and day glow). Atmospheric glow is only a fraction of the light available in the atmosphere. Other sources are starlight, zodiacal light, and daytime scattered light from the sun. At times, the glow of the atmosphere can be up to 40% of the total amount of light. Airglow occurs in atmospheric layers of varying height and thickness. The atmospheric glow spectrum covers wavelengths from 1000 Å to 22.5 µm. The main emission line in the airglow is l 5577 Å, which appears at a height of 90–100 km in a layer 30–40 km thick. The appearance of the glow is due to the Champen mechanism based on the recombination of oxygen atoms. Other emission lines are l 6300 Å, appearing in the case of dissociative O + 2 recombination and emission NI l 5198/5201 Å and NI l 5890/5896 Å.
The intensity of atmospheric glow is measured in Rayleighs. The brightness (in Rayleighs) is equal to 4 rb, where c is the angular surface of the luminance of the emitting layer in units of 10 6 photon/(cm 2 sr s). The glow intensity depends on latitude (differently for different emissions), and also varies during the day with a maximum near midnight. A positive correlation was noted for the airglow in the l 5577 Å emission with the number of sunspots and the flux of solar radiation at a wavelength of 10.7 cm. The airglow was observed during satellite experiments. From outer space, it looks like a ring of light around the Earth and has a greenish color.
Ozonosphere.
At altitudes of 20–25 km, the maximum concentration of a negligible amount of ozone O 3 (up to 2×10–7 of the oxygen content!), which occurs under the action of solar ultraviolet radiation at altitudes of about 10 to 50 km, is reached, protecting the planet from ionizing solar radiation. Despite the extremely small number of ozone molecules, they protect all life on Earth from the harmful effects of short-wave (ultraviolet and X-ray) radiation from the Sun. If you precipitate all the molecules to the base of the atmosphere, you get a layer no more than 3–4 mm thick! At altitudes above 100 km, the proportion of light gases increases, and at very high altitudes, helium and hydrogen predominate; many molecules dissociate into separate atoms, which, being ionized under the influence of hard solar radiation, form the ionosphere. The pressure and density of air in the Earth's atmosphere decrease with height. Depending on the distribution of temperature, the Earth's atmosphere is divided into the troposphere, stratosphere, mesosphere, thermosphere and exosphere. .
At an altitude of 20-25 km is located ozone layer. Ozone is formed due to the decay of oxygen molecules during the absorption of solar ultraviolet radiation with wavelengths shorter than 0.1–0.2 microns. Free oxygen combines with O 2 molecules and forms O 3 ozone, which greedily absorbs all ultraviolet light shorter than 0.29 microns. Ozone molecules O 3 are easily destroyed by short-wave radiation. Therefore, despite its rarefaction, the ozone layer effectively absorbs the ultraviolet radiation of the Sun, which has passed through the higher and more transparent atmospheric layers. Thanks to this, living organisms on Earth are protected from the harmful effects of ultraviolet light from the Sun.
Ionosphere.
Solar radiation ionizes the atoms and molecules of the atmosphere. The degree of ionization becomes significant already at an altitude of 60 kilometers and steadily increases with distance from the Earth. At different altitudes in the atmosphere, successive processes of dissociation of various molecules and subsequent ionization of various atoms and ions occur. Basically, these are oxygen molecules O 2, nitrogen N 2 and their atoms. Depending on the intensity of these processes, various layers of the atmosphere lying above 60 kilometers are called ionospheric layers. , and their totality is the ionosphere . The lower layer, the ionization of which is insignificant, is called the neutrosphere.
The maximum concentration of charged particles in the ionosphere is reached at altitudes of 300–400 km.
History of the study of the ionosphere.
The hypothesis of the existence of a conductive layer in the upper atmosphere was put forward in 1878 by the English scientist Stuart to explain the features of the geomagnetic field. Then in 1902, independently of each other, Kennedy in the USA and Heaviside in England pointed out that in order to explain the propagation of radio waves over long distances, it is necessary to assume the existence of regions with high conductivity in the high layers of the atmosphere. In 1923, Academician M.V. Shuleikin, considering the features of the propagation of radio waves of various frequencies, came to the conclusion that there are at least two reflective layers in the ionosphere. Then, in 1925, the English researchers Appleton and Barnet, as well as Breit and Tuve, experimentally proved for the first time the existence of regions that reflect radio waves, and laid the foundation for their systematic study. Since that time, a systematic study of the properties of these layers, generally called the ionosphere, has been carried out, playing a significant role in a number of geophysical phenomena that determine the reflection and absorption of radio waves, which is very important for practical purposes, in particular, to ensure reliable radio communications.
In the 1930s, systematic observations of the state of the ionosphere began. In our country, on the initiative of M.A. Bonch-Bruevich, installations for its pulsed sounding were created. Many general properties of the ionosphere, heights and electron density of its main layers were investigated.
At altitudes of 60–70 km, the D layer is observed; at altitudes of 100–120 km, the E, at altitudes, at altitudes of 180–300 km double layer F 1 and F 2. The main parameters of these layers are given in Table 4.
| Table 4 | ||||||
| Ionosphere region | Maximum height, km | T i , K | Day | Night ne , cm -3 | a΄, ρm 3 s – 1 | |
| min ne , cm -3 | Max ne , cm -3 | |||||
| D | 70 | 20 | 100 | 200 | 10 | 10 –6 |
| E | 110 | 270 | 1.5 10 5 | 3 10 5 | 3000 | 10 –7 |
| F 1 | 180 | 800–1500 | 3 10 5 | 5 10 5 | – | 3 10 -8 |
| F 2 (winter) | 220–280 | 1000–2000 | 6 10 5 | 25 10 5 | ~10 5 | 2 10 –10 |
| F 2 (summer) | 250–320 | 1000–2000 | 2 10 5 | 8 10 5 | ~3 10 5 | 10 –10 |
| ne is the electron concentration, e is the electron charge, T i is the ion temperature, a΄ is the recombination coefficient (which determines the ne and its change over time) | ||||||
Averages are given as they vary for different latitudes, times of day and seasons. Such data is necessary to ensure long-range radio communications. They are used in selecting operating frequencies for various shortwave radio links. Knowing their change depending on the state of the ionosphere at different times of the day and in different seasons is extremely important for ensuring the reliability of radio communications. The ionosphere is a collection of ionized layers of the earth's atmosphere, starting from altitudes of about 60 km and extending to altitudes of tens of thousands of km. The main source of ionization of the Earth's atmosphere is the ultraviolet and X-ray radiation of the Sun, which occurs mainly in the solar chromosphere and corona. In addition, the degree of ionization of the upper atmosphere is affected by solar corpuscular streams that occur during solar flares, as well as cosmic rays and meteor particles.
Ionospheric layers
are areas in the atmosphere in which the maximum values of the concentration of free electrons are reached (i.e. their number per unit volume). Electrically charged free electrons and (to a lesser extent, less mobile ions) resulting from the ionization of atmospheric gas atoms, interacting with radio waves (i.e. electromagnetic oscillations), can change their direction, reflecting or refracting them, and absorb their energy. As a result, when receiving distant radio stations, various effects may occur, for example, radio fading, increased audibility of distant stations, blackouts etc. phenomena.
Research methods.
The classical methods of studying the ionosphere from the Earth are reduced to pulse sounding - sending radio pulses and observing their reflections from various layers of the ionosphere with measuring the delay time and studying the intensity and shape of the reflected signals. By measuring the heights of reflection of radio pulses at different frequencies, determining the critical frequencies of various regions (the carrier frequency of the radio pulse for which this region of the ionosphere becomes transparent is called the critical frequency), it is possible to determine the value of the electron density in the layers and the effective heights for given frequencies, and choose the optimal frequencies for given radio paths. With the development of rocket technology and the advent of the space age of artificial Earth satellites (AES) and other spacecraft, it became possible to directly measure the parameters of the near-Earth space plasma, the lower part of which is the ionosphere.
Electron density measurements carried out from specially launched rockets and along satellite flight paths confirmed and refined data previously obtained by ground-based methods on the structure of the ionosphere, the distribution of electron density with height over different regions of the Earth, and made it possible to obtain electron density values above the main maximum - the layer F. Previously, it was impossible to do this by sounding methods based on observations of reflected short-wavelength radio pulses. It has been found that in some regions of the globe there are fairly stable regions with low electron density, regular “ionospheric winds”, peculiar wave processes arise in the ionosphere that carry local ionospheric disturbances thousands of kilometers from the place of their excitation, and much more. The creation of especially highly sensitive receiving devices made it possible to carry out at the stations of pulsed sounding of the ionosphere the reception of pulsed signals partially reflected from the lowest regions of the ionosphere (station of partial reflections). The use of powerful pulse installations in the meter and decimeter wavelength ranges with the use of antennas that allow for a high concentration of radiated energy made it possible to observe signals scattered by the ionosphere at various heights. The study of the features of the spectra of these signals, incoherently scattered by electrons and ions of the ionospheric plasma (for this, stations of incoherent scattering of radio waves were used) made it possible to determine the concentration of electrons and ions, their equivalent temperature at various altitudes up to altitudes of several thousand kilometers. It turned out that the ionosphere is sufficiently transparent for the frequencies used.
The concentration of electric charges (the electron density is equal to the ion one) in the earth's ionosphere at a height of 300 km is about 106 cm–3 during the day. A plasma of this density reflects radio waves longer than 20 m, while transmitting shorter ones.
Typical vertical distribution of electron density in the ionosphere for day and night conditions.
Propagation of radio waves in the ionosphere.
The stable reception of long-range broadcasting stations depends on the frequencies used, as well as on the time of day, season and, in addition, on solar activity. Solar activity significantly affects the state of the ionosphere. Radio waves emitted by a ground station propagate in a straight line, like all types of electromagnetic waves. However, it should be taken into account that both the surface of the Earth and the ionized layers of its atmosphere serve as a kind of plates of a huge capacitor, acting on them like the action of mirrors on light. Reflected from them, radio waves can travel many thousands of kilometers, bending around the globe in huge leaps of hundreds and thousands of kilometers, reflecting alternately from a layer of ionized gas and from the surface of the Earth or water.
In the 1920s, it was believed that radio waves shorter than 200 m were generally not suitable for long-distance communications due to strong absorption. The first experiments on long-range reception of short waves across the Atlantic between Europe and America were carried out by the English physicist Oliver Heaviside and the American electrical engineer Arthur Kennelly. Independently of each other, they suggested that somewhere around the Earth there is an ionized layer of the atmosphere that can reflect radio waves. It was called the Heaviside layer - Kennelly, and then - the ionosphere.
According to modern concepts, the ionosphere consists of negatively charged free electrons and positively charged ions, mainly molecular oxygen O + and nitric oxide NO + . Ions and electrons are formed as a result of the dissociation of molecules and the ionization of neutral gas atoms by solar X-ray and ultraviolet radiation. In order to ionize an atom, it is necessary to inform it of ionization energy, the main source of which for the ionosphere is the ultraviolet, X-ray and corpuscular radiation of the Sun.
As long as the gas shell of the Earth is illuminated by the Sun, more and more electrons are continuously formed in it, but at the same time, some of the electrons, colliding with ions, recombine, again forming neutral particles. After sunset, the production of new electrons almost stops, and the number of free electrons begins to decrease. The more free electrons in the ionosphere, the better high-frequency waves are reflected from it. With a decrease in the electron concentration, the passage of radio waves is possible only in low-frequency ranges. That is why at night, as a rule, it is possible to receive distant stations only in the ranges of 75, 49, 41 and 31 m. Electrons are distributed unevenly in the ionosphere. At an altitude of 50 to 400 km, there are several layers or regions of increased electron density. These areas smoothly transition into one another and affect the propagation of HF radio waves in different ways. The upper layer of the ionosphere is denoted by the letter F. Here is the highest degree of ionization (the fraction of charged particles is about 10–4). It is located at an altitude of more than 150 km above the Earth's surface and plays the main reflective role in the long-range propagation of radio waves of high-frequency HF bands. In the summer months, the F region breaks up into two layers - F 1 and F 2. The F1 layer can occupy heights from 200 to 250 km, and the layer F 2 seems to “float” in the altitude range of 300–400 km. Usually layer F 2 is ionized much stronger than the layer F one . night layer F 1 disappears and layer F 2 remains, slowly losing up to 60% of its degree of ionization. Below the F layer, at altitudes from 90 to 150 km, there is a layer E, whose ionization occurs under the influence of soft X-ray radiation from the Sun. The degree of ionization of the E layer is lower than that of the F, during the day, reception of stations of low-frequency HF bands of 31 and 25 m occurs when signals are reflected from the layer E. Usually these are stations located at a distance of 1000–1500 km. At night in a layer E ionization sharply decreases, but even at this time it continues to play a significant role in the reception of signals from stations in the bands 41, 49 and 75 m.
Of great interest for receiving signals of high-frequency HF bands of 16, 13 and 11 m are those arising in the area E interlayers (clouds) of strongly increased ionization. The area of these clouds can vary from a few to hundreds of square kilometers. This layer of increased ionization is called the sporadic layer. E and denoted Es. Es clouds can move in the ionosphere under the influence of wind and reach speeds of up to 250 km/h. In summer, in the middle latitudes during the daytime, the origin of radio waves due to Es clouds occurs 15–20 days per month. Near the equator, it is almost always present, and at high latitudes it usually appears at night. Sometimes, in the years of low solar activity, when there is no passage to the high-frequency HF bands, distant stations suddenly appear with good loudness on the bands of 16, 13 and 11 m, the signals of which were repeatedly reflected from Es.
The lowest region of the ionosphere is the region D located at altitudes between 50 and 90 km. There are relatively few free electrons here. From area D long and medium waves are well reflected, and the signals of low-frequency HF stations are strongly absorbed. After sunset, ionization disappears very quickly and it becomes possible to receive distant stations in the ranges of 41, 49 and 75 m, the signals of which are reflected from the layers F 2 and E. Separate layers of the ionosphere play an important role in the propagation of HF radio signals. 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 hydrogen in 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 manifestations of activity occur 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, the brightness of some areas on the Sun increases several times, and the power of ultraviolet and X-ray radiation increases sharply. Such phenomena are called solar flares. They last from several minutes to one or two hours. During a flare, solar plasma erupts (mainly protons and electrons), 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 noted 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.
The structure and dynamics of the upper atmosphere is essentially determined by thermodynamically nonequilibrium processes associated with ionization and dissociation by solar radiation, chemical processes, excitation of molecules and atoms, their deactivation, collision, and other elementary processes. In this case, the degree of nonequilibrium increases with height as the density decreases. Up to altitudes of 500–1000 km, and often even higher, the degree of nonequilibrium for many characteristics of the upper atmosphere is sufficiently small, which allows one to use classical and hydromagnetic hydrodynamics with allowance for chemical reactions to describe it.
The exosphere is the outer layer of the Earth's atmosphere, starting at altitudes of several hundred kilometers, from which light, fast-moving hydrogen atoms can escape into outer space.
Edward Kononovich
Literature:
Pudovkin M.I. Fundamentals of solar physics. St. Petersburg, 2001
Eris Chaisson, Steve McMillan Astronomy today. Prentice Hall Inc. Upper Saddle River, 2002
Online materials: http://ciencia.nasa.gov/
The atmosphere extends upward for many hundreds of kilometers. Its upper boundary, at an altitude of about 2000-3000 km, to a certain extent conditional, since the gases that make up it, gradually rarefied, pass into the world space. The chemical composition of the atmosphere, pressure, density, temperature and its other physical properties change with height. As mentioned earlier, the chemical composition of air up to a height of 100 km does not change significantly. Somewhat higher, the atmosphere also consists mainly of nitrogen and oxygen. But at altitudes 100-110 km, Under the influence of ultraviolet radiation from the sun, oxygen molecules are split into atoms and atomic oxygen appears. Above 110-120 km almost all of the oxygen becomes atomic. It is assumed that above 400-500 km the gases that make up the atmosphere are also in the atomic state.
Air pressure and density decrease rapidly with height. Although the atmosphere extends upwards for hundreds of kilometers, most of it is located in a rather thin layer adjacent to the earth's surface in its lowest parts. So, in the layer between sea level and altitudes 5-6 km half of the mass of the atmosphere is concentrated in layer 0-16 km-90%, and in the layer 0-30 km- 99%. The same rapid decrease in air mass occurs above 30 km. If weight 1 m 3 air at the earth's surface is 1033 g, then at a height of 20 km it is equal to 43 g, and at a height of 40 km only 4 years
At an altitude of 300-400 km and above, the air is so rarefied that during the day its density changes many times. Studies have shown that this change in density is related to the position of the Sun. The highest air density is around noon, the lowest at night. This is partly explained by the fact that the upper layers of the atmosphere react to changes in the electromagnetic radiation of the Sun.
The change in air temperature with height is also uneven. According to the nature of the change in temperature with height, the atmosphere is divided into several spheres, between which there are transitional layers, the so-called pauses, where the temperature changes little with height.
Here are the names and main characteristics of spheres and transition layers.
Let us present the basic data on the physical properties of these spheres.
Troposphere. The physical properties of the troposphere are largely determined by the influence of the earth's surface, which is its lower boundary. The highest height of the troposphere is observed in the equatorial and tropical zones. Here it reaches 16-18 km and relatively little subject to daily and seasonal changes. Above the polar and adjacent regions, the upper boundary of the troposphere lies on average at a level of 8-10 km. In mid-latitudes, it ranges from 6-8 to 14-16 km.
The vertical power of the troposphere depends significantly on the nature of atmospheric processes. Often during the day, the upper boundary of the troposphere over a given point or area drops or rises by several kilometers. This is mainly due to changes in air temperature.
More than 4/5 of the mass of the earth's atmosphere and almost all of the water vapor contained in it are concentrated in the troposphere. In addition, from the earth's surface to the upper limit of the troposphere, the temperature drops by an average of 0.6° for every 100 m, or 6° for 1 km uplift . This is due to the fact that the air in the troposphere is heated and cooled mainly from the surface of the earth.
In accordance with the influx of solar energy, the temperature decreases from the equator to the poles. Thus, the average air temperature near the earth's surface at the equator reaches +26°, over the polar regions -34°, -36° in winter, and about 0° in summer. Thus, the temperature difference between the equator and the pole is 60° in winter and only 26° in summer. True, such low temperatures in the Arctic in winter are observed only near the surface of the earth due to cooling of the air over the ice expanses.
In winter, in Central Antarctica, the air temperature on the surface of the ice sheet is even lower. At Vostok station in August 1960, the lowest temperature on the globe was recorded -88.3°, and most often in Central Antarctica it is -45°, -50°.
From a height, the temperature difference between the equator and the pole decreases. For example, at height 5 km at the equator the temperature reaches -2°, -4°, and at the same height in the Central Arctic -37°, -39° in winter and -19°, -20° in summer; therefore, the temperature difference in winter is 35-36°, and in summer 16-17°. In the southern hemisphere, these differences are somewhat larger.
The energy of atmospheric circulation can be determined by equator-pole temperature contracts. Since the temperature contrasts are greater in winter, atmospheric processes are more intense than in summer. This also explains the fact that the prevailing westerly winds in the troposphere in winter have higher speeds than in summer. In this case, the wind speed, as a rule, increases with height, reaching a maximum at the upper boundary of the troposphere. Horizontal transport is accompanied by vertical air movements and turbulent (disordered) movement. Due to the rise and fall of large volumes of air, clouds form and disperse, precipitation occurs and stops. The transition layer between the troposphere and the overlying sphere is tropopause. Above it lies the stratosphere.
Stratosphere extends from heights 8-17 to 50-55 km. It was opened at the beginning of our century. In terms of physical properties, the stratosphere differs sharply from the troposphere in that the air temperature here, as a rule, rises by an average of 1 - 2 ° per kilometer of elevation and at the upper boundary, at a height of 50-55 km, even becomes positive. The increase in temperature in this area is caused by the presence of ozone (O 3) here, which is formed under the influence of ultraviolet radiation from the Sun. The ozone layer covers almost the entire stratosphere. The stratosphere is very poor in water vapor. There are no violent processes of cloud formation and no precipitation.
More recently, it was assumed that the stratosphere is a relatively calm environment, where air mixing does not occur, as in the troposphere. Therefore, it was believed that the gases in the stratosphere are divided into layers, in accordance with their specific gravity. Hence the name of the stratosphere ("stratus" - layered). It was also believed that the temperature in the stratosphere is formed under the influence of radiative equilibrium, i.e., when the absorbed and reflected solar radiation are equal.
New data from radiosondes and meteorological rockets have shown that the stratosphere, like the upper troposphere, is subject to intense air circulation with large variations in temperature and wind. Here, as in the troposphere, the air experiences significant vertical movements, turbulent movements with strong horizontal air currents. All this is the result of a non-uniform temperature distribution.
The transition layer between the stratosphere and the overlying sphere is stratopause. However, before proceeding to the characteristics of the higher layers of the atmosphere, let's get acquainted with the so-called ozonosphere, the boundaries of which approximately correspond to the boundaries of the stratosphere.
Ozone in the atmosphere. Ozone plays an important role in creating the temperature regime and air currents in the stratosphere. Ozone (O 3) is felt by us after a thunderstorm when we inhale clean air with a pleasant aftertaste. However, here we will not talk about this ozone formed after a thunderstorm, but about the ozone contained in the layer 10-60 km with a maximum at a height of 22-25 km. Ozone is produced by the action of the ultraviolet rays of the sun and, although its total amount is insignificant, plays an important role in the atmosphere. Ozone has the ability to absorb the ultraviolet radiation of the sun and thereby protects the animal and plant world from its harmful effects. Even that tiny fraction of ultraviolet rays that reaches the surface of the earth burns the body badly when a person is excessively fond of sunbathing.
The amount of ozone is not the same over different parts of the Earth. There is more ozone in high latitudes, less in middle and low latitudes, and this amount changes depending on the change of seasons of the year. More ozone in spring, less in autumn. In addition, its non-periodic fluctuations occur depending on the horizontal and vertical circulation of the atmosphere. Many atmospheric processes are closely related to the ozone content, since it has a direct effect on the temperature field.
In winter, during the polar night, at high latitudes, the ozone layer emits and cools the air. As a result, in the stratosphere of high latitudes (in the Arctic and Antarctic) a cold region is formed in winter, a stratospheric cyclonic eddy with large horizontal temperature and pressure gradients, which causes westerly winds over the middle latitudes of the globe.
In summer, under conditions of a polar day, at high latitudes, the ozone layer absorbs solar heat and warms the air. As a result of the temperature increase in the stratosphere of high latitudes, a heat region and a stratospheric anticyclonic vortex are formed. Therefore, over the average latitudes of the globe above 20 km in summer, easterly winds prevail in the stratosphere.
Mesosphere. Observations with meteorological rockets and other methods have established that the overall temperature increase observed in the stratosphere ends at altitudes of 50-55 km. Above this layer, the temperature drops again and near the upper boundary of the mesosphere (about 80 km) reaches -75°, -90°. Further, the temperature rises again with height.
It is interesting to note that the decrease in temperature with height, characteristic of the mesosphere, occurs differently at different latitudes and throughout the year. At low latitudes, the temperature drop occurs more slowly than at high latitudes: the average vertical temperature gradient for the mesosphere is, respectively, 0.23° - 0.31° per 100 m or 2.3°-3.1° per 1 km. In summer it is much larger than in winter. As shown by the latest research in high latitudes, the temperature at the upper boundary of the mesosphere in summer is several tens of degrees lower than in winter. In the upper mesosphere at a height of about 80 km in the mesopause layer, the decrease in temperature with height stops and its increase begins. Here, under the inversion layer at twilight or before sunrise in clear weather, brilliant thin clouds are observed, illuminated by the sun below the horizon. Against the dark background of the sky, they glow with a silvery-blue light. Therefore, these clouds are called silvery.
The nature of noctilucent clouds is not yet well understood. For a long time it was believed that they were composed of volcanic dust. However, the absence of optical phenomena characteristic of real volcanic clouds led to the rejection of this hypothesis. Then it was suggested that noctilucent clouds are composed of cosmic dust. In recent years, a hypothesis has been proposed that these clouds are composed of ice crystals, like ordinary cirrus clouds. The level of location of noctilucent clouds is determined by the delay layer due to temperature inversion during the transition from the mesosphere to the thermosphere at a height of about 80 km. Since the temperature in the subinversion layer reaches -80°C and lower, the most favorable conditions are created here for the condensation of water vapor, which enters here from the stratosphere as a result of vertical movement or by turbulent diffusion. Noctilucent clouds are usually observed in the summer, sometimes in very large numbers and for several months.
Observations of noctilucent clouds have established that in summer at their level the winds are highly variable. Wind speeds vary widely: from 50-100 to several hundred kilometers per hour.
Temperature at altitude. A visual representation of the nature of the temperature distribution with height, between the earth's surface and altitudes of 90-100 km, in winter and summer in the northern hemisphere, is given in Figure 5. The surfaces separating the spheres are depicted here by bold dashed lines. At the very bottom, the troposphere stands out well, with a characteristic decrease in temperature with height. Above the tropopause, in the stratosphere, on the contrary, the temperature increases with height in general and at heights of 50-55 km reaches + 10°, -10°. Let's pay attention to an important detail. In winter, in the stratosphere of high latitudes, the temperature above the tropopause drops from -60 to -75 ° and only above 30 km rises again to -15°. In summer, starting from the tropopause, the temperature increases with height and by 50 km reaches + 10°. Above the stratopause, the temperature again begins to decrease with height, and at a level of 80 km it does not exceed -70°, -90°.
From figure 5 it follows that in layer 10-40 km the air temperature in winter and summer in high latitudes is sharply different. In winter, during the polar night, the temperature here reaches -60°, -75°, and in summer a minimum of -45° is near the tropopause. Above the tropopause, the temperature increases and at altitudes of 30-35 km is only -30°, -20°, which is caused by the heating of the air in the ozone layer during the polar day. It also follows from the figure that even in one season and at the same level, the temperature is not the same. Their difference between different latitudes exceeds 20-30°. In this case, the inhomogeneity is especially significant in the low-temperature layer (18-30 km) and in the layer of maximum temperatures (50-60 km) in the stratosphere, as well as in the layer of low temperatures in the upper mesosphere (75-85km).
The mean temperatures shown in Figure 5 are based on observations in the northern hemisphere, but according to the available information, they can also be attributed to the southern hemisphere. Some differences exist mainly at high latitudes. Over Antarctica in winter, the air temperature in the troposphere and lower stratosphere is noticeably lower than over the Central Arctic.
Winds on high. The seasonal distribution of temperature determines a rather complex system of air currents in the stratosphere and mesosphere.
Figure 6 shows a vertical section of the wind field in the atmosphere between the earth's surface and a height of 90 km winter and summer over the northern hemisphere. The isolines show the average speeds of the prevailing wind (in m/s). It follows from the figure that the wind regime in winter and summer in the stratosphere is sharply different. In winter, both in the troposphere and in the stratosphere, westerly winds prevail with maximum speeds equal to about
100 m/s at a height of 60-65 km. In summer, westerly winds prevail only up to heights of 18-20 km. Higher they become eastern, with maximum speeds up to 70 m/s at a height of 55-60km.
In summer, above the mesosphere, the winds become westerly, and in winter, they become easterly.
Thermosphere. Above the mesosphere is the thermosphere, which is characterized by an increase in temperature with height. According to the data obtained, mainly with the help of rockets, it was found that in the thermosphere it is already at the level of 150 km the air temperature reaches 220-240°, and at the level of 200 km over 500°. Above, the temperature continues to rise and at the level of 500-600 km exceeds 1500°. On the basis of data obtained during launches of artificial earth satellites, it has been found that in the upper thermosphere the temperature reaches about 2000° and fluctuates significantly during the day. The question arises how to explain such a high temperature in the high layers of the atmosphere. Recall that the temperature of a gas is a measure of the average velocity of molecules. In the lower, densest part of the atmosphere, the gas molecules that make up the air often collide with each other when moving and instantly transfer kinetic energy to each other. Therefore, the kinetic energy in a dense medium is on average the same. In high layers, where the air density is very low, collisions between molecules located at large distances occur less frequently. When energy is absorbed, the speed of molecules in the interval between collisions changes greatly; in addition, the molecules of lighter gases move at a higher speed than the molecules of heavy gases. As a result, the temperature of the gases can be different.
In rarefied gases, there are relatively few molecules of very small sizes (light gases). If they move at high speeds, then the temperature in a given volume of air will be high. In the thermosphere, each cubic centimeter of air contains tens and hundreds of thousands of molecules of various gases, while at the surface of the earth there are about a hundred million billion of them. Therefore, excessively high temperatures in the high layers of the atmosphere, showing the speed of movement of molecules in this very thin medium, cannot cause even a slight heating of the body located here. Just as a person does not feel heat when dazzling electric lamps, although the filaments in a rarefied medium instantly heat up to several thousand degrees.
In the lower thermosphere and mesosphere, the main part of meteor showers burns out before reaching the earth's surface.
Available information about atmospheric layers above 60-80 km are still insufficient for final conclusions about the structure, regime and processes developing in them. However, it is known that in the upper mesosphere and lower thermosphere, the temperature regime is created as a result of the transformation of molecular oxygen (O 2) into atomic oxygen (O), which occurs under the action of ultraviolet solar radiation. In the thermosphere, the temperature regime is greatly influenced by corpuscular, X-ray, and radiation. ultraviolet radiation from the sun. Here, even during the day, there are sharp changes in temperature and wind.
Atmospheric ionization. The most interesting feature of the atmosphere above 60-80 km is her ionization, i.e., the process of formation of a huge number of electrically charged particles - ions. Since the ionization of gases is characteristic of the lower thermosphere, it is also called the ionosphere.
The gases in the ionosphere are mostly in the atomic state. Under the influence of ultraviolet and corpuscular radiation of the Sun, which have high energy, the process of splitting off electrons from neutral atoms and air molecules occurs. Such atoms and molecules, having lost one or more electrons, become positively charged, and a free electron can reattach to a neutral atom or molecule and endow them with its negative charge. These positively and negatively charged atoms and molecules are called ions, and the gases ionized, i.e., having received an electric charge. At a higher concentration of ions, gases become electrically conductive.
The ionization process occurs most intensively in thick layers limited by heights of 60-80 and 220-400 km. In these layers, there are optimal conditions for ionization. Here, the air density is noticeably higher than in the upper atmosphere, and the influx of ultraviolet and corpuscular radiation from the Sun is sufficient for the ionization process.
The discovery of the ionosphere is one of the most important and brilliant achievements of science. After all, a distinctive feature of the ionosphere is its influence on the propagation of radio waves. In the ionized layers, radio waves are reflected, and therefore long-range radio communication becomes possible. Charged atoms-ions reflect short radio waves, and they again return to the earth's surface, but already at a considerable distance from the place of radio transmission. Obviously, short radio waves make this path several times, and thus long-range radio communication is ensured. If not for the ionosphere, then for the transmission of radio station signals over long distances it would be necessary to build expensive radio relay lines.
However, it is known that sometimes shortwave radio communications are disrupted. This occurs as a result of chromospheric flares on the Sun, due to which the ultraviolet radiation of the Sun sharply increases, leading to strong disturbances of the ionosphere and the Earth's magnetic field - magnetic storms. During magnetic storms, radio communication is disrupted, since the movement of charged particles depends on the magnetic field. During magnetic storms, the ionosphere reflects radio waves worse or passes them into space. Mainly with a change in solar activity, accompanied by an increase in ultraviolet radiation, the electron density of the ionosphere and the absorption of radio waves in the daytime increase, leading to disruption of short-wave radio communications.
According to new research, in a powerful ionized layer there are zones where the concentration of free electrons reaches a slightly higher concentration than in neighboring layers. Four such zones are known, which are located at altitudes of about 60-80, 100-120, 180-200 and 300-400 km and are marked with letters D, E, F 1 and F 2 . With increasing radiation from the Sun, charged particles (corpuscles) under the influence of the Earth's magnetic field are deflected towards high latitudes. Upon entering the atmosphere, corpuscles intensify the ionization of gases to such an extent that their glow begins. This is how auroras- in the form of beautiful multi-colored arcs that light up in the night sky, mainly in the high latitudes of the Earth. Auroras are accompanied by strong magnetic storms. In such cases, the auroras become visible in the middle latitudes, and in rare cases even in the tropical zone. Thus, for example, the intense aurora observed on January 21-22, 1957, was visible in almost all the southern regions of our country.
By photographing the auroras from two points located at a distance of several tens of kilometers, the height of the aurora is determined with great accuracy. Auroras are usually located at an altitude of about 100 km, often they are found at an altitude of several hundred kilometers, and sometimes at a level of about 1000 km. Although the nature of auroras has been elucidated, there are still many unresolved issues related to this phenomenon. The reasons for the diversity of forms of auroras are still unknown.
According to the third Soviet satellite, between heights 200 and 1000 km during the day, positive ions of split molecular oxygen, i.e., atomic oxygen (O), predominate. Soviet scientists are studying the ionosphere with the help of artificial satellites of the Kosmos series. American scientists are also studying the ionosphere with the help of satellites.
The surface separating the thermosphere from the exosphere fluctuates depending on changes in solar activity and other factors. Vertically, these fluctuations reach 100-200 km and more.
Exosphere (scattering sphere) - the uppermost part of the atmosphere, located above 800 km. She is little studied. According to the data of observations and theoretical calculations, the temperature in the exosphere increases with height presumably up to 2000°. In contrast to the lower ionosphere, in the exosphere the gases are so rarefied that their particles, moving at tremendous speeds, almost never meet each other.
Until relatively recently, it was assumed that the conditional boundary of the atmosphere is located at an altitude of about 1000 km. However, based on the deceleration of artificial Earth satellites, it has been established that at altitudes of 700-800 km in 1 cm 3 contains up to 160 thousand positive ions of atomic oxygen and nitrogen. This gives grounds to assume that the charged layers of the atmosphere extend into space for a much greater distance.
At high temperatures, at the conditional boundary of the atmosphere, the velocities of gas particles reach approximately 12 km/s At these velocities, the gases gradually leave the region of the earth's gravity into interplanetary space. This has been going on for a long time. For example, particles of hydrogen and helium are removed into interplanetary space over several years.
In the study of the high layers of the atmosphere, rich data were obtained both from satellites of the Kosmos and Elektron series, and geophysical rockets and space stations Mars-1, Luna-4, etc. Direct observations of astronauts were also valuable. So, according to photographs taken in space by V. Nikolaeva-Tereshkova, it was found that at an altitude of 19 km there is a dust layer from the Earth. This was also confirmed by the data obtained by the crew of the Voskhod spacecraft. Apparently, there is a close relationship between the dust layer and the so-called mother-of-pearl clouds, sometimes observed at altitudes of about 20-30km.
From the atmosphere to outer space. Previous assumptions that outside the Earth's atmosphere, in the interplanetary
space, gases are very rarefied and the concentration of particles does not exceed several units in 1 cm 3, were not justified. Studies have shown that near-Earth space is filled with charged particles. On this basis, a hypothesis was put forward about the existence of zones around the Earth with a markedly increased content of charged particles, i.e. radiation belts- internal and external. New data helped to clarify. It turned out that there are also charged particles between the inner and outer radiation belts. Their number varies depending on geomagnetic and solar activity. Thus, according to the new assumption, instead of radiation belts, there are radiation zones without clearly defined boundaries. The boundaries of radiation zones change depending on solar activity. With its intensification, i.e., when spots and jets of gas appear on the Sun, ejected over hundreds of thousands of kilometers, the flow of cosmic particles increases, which feed the radiation zones of the Earth.
Radiation zones are dangerous for people flying on spacecraft. Therefore, before a flight into space, the state and position of the radiation zones are determined, and the spacecraft's orbit is chosen in such a way that it passes outside the regions of increased radiation. However, the high layers of the atmosphere, as well as outer space close to the Earth, have not yet been studied enough.
In the study of the high layers of the atmosphere and near-Earth space, rich data obtained from satellites of the Kosmos series and space stations are used.
The high layers of the atmosphere are the least studied. However, modern methods of studying it allow us to hope that in the coming years a person will know many details of the structure of the atmosphere at the bottom of which he lives.
In conclusion, we present a schematic vertical section of the atmosphere (Fig. 7). Here, the altitudes in kilometers and air pressure in millimeters are plotted vertically, and the temperature is plotted horizontally. The solid curve shows the change in air temperature with height. At the corresponding heights, the most important phenomena observed in the atmosphere, as well as the maximum heights reached by radiosondes and other means of sounding the atmosphere, were noted.
Its upper limit is at an altitude of 8-10 km in polar, 10-12 km in temperate and 16-18 km in tropical latitudes; lower in winter than in summer. The lower, main layer of the atmosphere. It contains more than 80% of the total mass of atmospheric air and about 90% of all water vapor present in the atmosphere. Turbulence and convection are strongly developed in the troposphere, clouds appear, cyclones and anticyclones develop. Temperature decreases with altitude with an average vertical gradient of 0.65°/100 m
For "normal conditions" at the Earth's surface are taken: density 1.2 kg/m3, barometric pressure 101.35 kPa, temperature plus 20 °C and relative humidity 50%. These conditional indicators have a purely engineering value.
Stratosphere
The layer of the atmosphere located at an altitude of 11 to 50 km. A slight change in temperature in the 11-25 km layer (lower layer of the stratosphere) and its increase in the 25-40 km layer from −56.5 to 0.8 ° (upper stratosphere or inversion region) are characteristic. 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.
Stratopause
The boundary layer of the atmosphere between the stratosphere and the mesosphere. There is a maximum in the vertical temperature distribution (about 0 °C).
Mesosphere
mesopause
Transitional layer between mesosphere and thermosphere. There is a minimum in the vertical temperature distribution (about -90°C).
Karman Line
Altitude above sea level, which is conventionally accepted as the boundary between the Earth's atmosphere and space.
Thermosphere
The upper limit is about 800 km. The temperature rises to altitudes of 200-300 km, where it reaches values of the order of 1500 K, after which it remains almost constant up to high altitudes. Under the influence of ultraviolet and x-ray solar radiation and cosmic radiation, air is ionized ("polar lights") - the main regions of the ionosphere lie inside the thermosphere. At altitudes above 300 km, atomic oxygen predominates.
Exosphere (scattering sphere)
Up to a height of 100 km, the atmosphere is a homogeneous, well-mixed mixture of gases. In higher layers, the distribution of gases in height depends on their molecular masses, the concentration of heavier gases decreases faster with distance from the Earth's surface. Due to the decrease in gas density, the temperature drops from 0 °C in the stratosphere to -110 °C in the mesosphere. However, the kinetic energy of individual particles at altitudes of 200–250 km corresponds to a temperature of ~1500°C. Above 200 km, significant fluctuations in temperature and gas density are observed in time and space.
At an altitude of about 2000-3000 km, the exosphere gradually passes into the so-called near space vacuum, which is filled with highly rarefied particles of interplanetary gas, mainly hydrogen atoms. But this gas is only part of the interplanetary matter. The other part is composed of dust-like particles of cometary and meteoric origin. In addition to extremely rarefied dust-like particles, electromagnetic and corpuscular radiation of solar and galactic origin penetrates into this space.
The troposphere accounts for about 80% of the mass of the atmosphere, the stratosphere accounts for about 20%; the mass of the mesosphere is no more than 0.3%, the thermosphere is less than 0.05% of the total mass of the atmosphere. Based on the electrical properties in the atmosphere, the neutrosphere and ionosphere are distinguished. It is currently believed that the atmosphere extends to an altitude of 2000-3000 km.
Depending on the composition of the gas in the atmosphere, they emit homosphere and heterosphere. heterosphere- this is an area where gravity affects the separation of gases, since their mixing at such a height is negligible. Hence follows the variable composition of the heterosphere. Below it lies a well-mixed, homogeneous part of the atmosphere, called the homosphere. The boundary between these layers is called turbopause, it lies at an altitude of about 120 km.
Physical properties
The thickness of the atmosphere is approximately 2000 - 3000 km from the Earth's surface. The total mass of air - (5.1-5.3)? 10 18 kg. The molar mass of clean dry air is 28.966. Pressure at 0 °C at sea level 101.325 kPa; critical temperature ?140.7 °C; critical pressure 3.7 MPa; C p 1.0048?10? J / (kg K) (at 0 °C), C v 0.7159 10? J/(kg K) (at 0 °C). Solubility of air in water at 0°С - 0.036%, at 25°С - 0.22%.
Physiological and other properties of the atmosphere
Already at an altitude of 5 km above sea level, an untrained person develops oxygen starvation and, without adaptation, a person's performance is significantly reduced. This is where the physiological zone of the atmosphere ends. Human breathing becomes impossible at an altitude of 15 km, although up to about 115 km the atmosphere contains oxygen.
The atmosphere provides us with the oxygen we need to breathe. However, due to the drop in the total pressure of the atmosphere as you rise to a height, the partial pressure of oxygen also decreases accordingly.
The human lungs constantly contain about 3 liters of alveolar air. The partial pressure of oxygen in the alveolar air at normal atmospheric pressure is 110 mm Hg. Art., pressure of carbon dioxide - 40 mm Hg. Art., and water vapor - 47 mm Hg. Art. With increasing altitude, the oxygen pressure drops, and the total pressure of water vapor and carbon dioxide in the lungs remains almost constant - about 87 mm Hg. Art. The flow of oxygen into the lungs will completely stop when the pressure of the surrounding air becomes equal to this value.
At an altitude of about 19-20 km, the atmospheric pressure drops to 47 mm Hg. Art. Therefore, at this height, water and interstitial fluid begin to boil in the human body. Outside the pressurized cabin at these altitudes, death occurs almost instantly. Thus, from the point of view of human physiology, "space" begins already at an altitude of 15-19 km.
Dense layers of air - the troposphere and stratosphere - protect us from the damaging effects of radiation. With sufficient rarefaction of air, at altitudes of more than 36 km, ionizing radiation, primary cosmic rays, has an intense effect on the body; at altitudes of more than 40 km, the ultraviolet part of the solar spectrum, which is dangerous for humans, operates.
As we rise to an ever greater height above the Earth's surface, gradually weaken, and then completely disappear, such phenomena that are familiar to us observed in the lower layers of the atmosphere, such as the propagation of sound, the occurrence of aerodynamic lift and resistance, heat transfer by convection, etc.
In rarefied layers of air, the propagation of sound is impossible. Up to altitudes of 60-90 km, it is still possible to use air resistance and lift for controlled aerodynamic flight. But starting from altitudes of 100-130 km, the concepts of the M number and the sound barrier familiar to every pilot lose their meaning, there passes the conditional Karman Line, beyond which the sphere of purely ballistic flight begins, which can only be controlled using reactive forces.
At altitudes above 100 km, the atmosphere is also deprived of another remarkable property - the ability to absorb, conduct and transfer thermal energy by convection (i.e., by means of air mixing). This means that various elements of equipment, equipment of the orbital space station will not be able to be cooled from the outside in the way it is usually done on an airplane - with the help of air jets and air radiators. At such a height, as in space in general, the only way to transfer heat is thermal radiation.
Composition of the atmosphere
The Earth's atmosphere consists mainly of gases and various impurities (dust, water drops, ice crystals, sea salts, combustion products).
The concentration of gases that make up the atmosphere is almost constant, with the exception of water (H 2 O) and carbon dioxide (CO 2).
| Gas | Content by volume, % |
Content by weight, % |
|---|---|---|
| Nitrogen | 78,084 | 75,50 |
| Oxygen | 20,946 | 23,10 |
| Argon | 0,932 | 1,286 |
| Water | 0,5-4 | - |
| Carbon dioxide | 0,032 | 0,046 |
| Neon | 1.818×10 −3 | 1.3×10 −3 |
| Helium | 4.6×10 −4 | 7.2×10 −5 |
| Methane | 1.7×10 −4 | - |
| Krypton | 1.14×10 −4 | 2.9×10 −4 |
| Hydrogen | 5×10 −5 | 7.6×10 −5 |
| Xenon | 8.7×10 −6 | - |
| Nitrous oxide | 5×10 −5 | 7.7×10 −5 |
In addition to the gases indicated in the table, the atmosphere contains SO 2, NH 3, CO, ozone, hydrocarbons, HCl, vapors, I 2, as well as many other gases in small quantities. In the troposphere there is constantly a large amount of suspended solid and liquid particles (aerosol).
History of the formation of the atmosphere
According to the most common theory, the Earth's atmosphere has been in four different compositions over time. Initially, it consisted of light gases (hydrogen and helium) captured from interplanetary space. This so-called primary atmosphere(about four billion years ago). At the next stage, active volcanic activity led to the saturation of the atmosphere with gases other than hydrogen (carbon dioxide, ammonia, water vapor). This is how secondary atmosphere(about three billion years before our days). This atmosphere was restorative. Further, the process of formation of the atmosphere was determined by the following factors:
- leakage of light gases (hydrogen and helium) into interplanetary space;
- chemical reactions occurring in the atmosphere under the influence of ultraviolet radiation, lightning discharges and some other factors.
Gradually, these factors led to the formation tertiary atmosphere, characterized by a much lower content of hydrogen and a much higher content of nitrogen and carbon dioxide (formed as a result of chemical reactions from ammonia and hydrocarbons).
Nitrogen
The formation of a large amount of N 2 is due to the oxidation of the ammonia-hydrogen atmosphere by molecular O 2, which began to come from the surface of the planet as a result of photosynthesis, starting from 3 billion years ago. N 2 is also released into the atmosphere as a result of the denitrification of nitrates and other nitrogen-containing compounds. Nitrogen is oxidized by ozone to NO in the upper atmosphere.
Nitrogen N 2 enters into reactions only under specific conditions (for example, during a lightning discharge). Oxidation of molecular nitrogen by ozone during electrical discharges is used in the industrial production of nitrogen fertilizers. It can be oxidized with low energy consumption and converted into a biologically active form by cyanobacteria (blue-green algae) and nodule bacteria that form rhizobial symbiosis with legumes, the so-called. green manure.
Oxygen
The composition of the atmosphere began to change radically with the advent of living organisms on Earth, as a result of photosynthesis, accompanied by the release of oxygen and the absorption of carbon dioxide. Initially, oxygen was spent on the oxidation of reduced compounds - ammonia, hydrocarbons, the ferrous form of iron contained in the oceans, etc. At the end of this stage, the oxygen content in the atmosphere began to grow. Gradually, a modern atmosphere with oxidizing properties formed. Since this caused serious and abrupt changes in many processes occurring in the atmosphere, lithosphere and biosphere, this event was called the Oxygen Catastrophe.
Carbon dioxide
The content of CO 2 in the atmosphere depends on volcanic activity and chemical processes in the earth's shells, but most of all - on the intensity of biosynthesis and decomposition of organic matter in the Earth's biosphere. Almost the entire current biomass of the planet (about 2.4 × 10 12 tons) is formed due to carbon dioxide, nitrogen and water vapor contained in the atmospheric air. Buried in the ocean , swamps and forests , organic matter turns into coal , oil and natural gas . (see Geochemical carbon cycle)
noble gases
Air pollution
Recently, man has begun to influence the evolution of the atmosphere. The result of his activities was a constant significant increase in the content of carbon dioxide in the atmosphere due to the combustion of hydrocarbon fuels accumulated in previous geological epochs. Huge amounts of CO 2 are consumed during photosynthesis and absorbed by the world's oceans. This gas enters the atmosphere due to the decomposition of carbonate rocks and organic substances of plant and animal origin, as well as due to volcanism and human production activities. Over the past 100 years, the content of CO 2 in the atmosphere has increased by 10%, with the main part (360 billion tons) coming from fuel combustion. If the growth rate of fuel combustion continues, then in the next 50 - 60 years the amount of CO 2 in the atmosphere will double and may lead to global climate change.
Fuel combustion is the main source of polluting gases (СО,, SO 2). Sulfur dioxide is oxidized by atmospheric oxygen to SO 3 in the upper atmosphere, which in turn interacts with water vapor and ammonia, and the resulting sulfuric acid (H 2 SO 4) and ammonium sulfate ((NH 4) 2 SO 4) return to the surface of the Earth in the form of a so-called. acid rain. The use of internal combustion engines leads to significant air pollution with nitrogen oxides, hydrocarbons and lead compounds (tetraethyl lead Pb (CH 3 CH 2) 4)).
Aerosol pollution of the atmosphere is caused both by natural causes (volcanic eruption, dust storms, entrainment of sea water droplets and plant pollen, etc.) and by human economic activity (mining of ores and building materials, fuel combustion, cement production, etc.). Intense large-scale removal of solid particles into the atmosphere is one of the possible causes of climate change on the planet.
Literature
- V. V. Parin, F. P. Kosmolinsky, B. A. Dushkov "Space biology and medicine" (2nd edition, revised and enlarged), M.: "Prosveshchenie", 1975, 223 pages.
- N. V. Gusakova "Environmental Chemistry", Rostov-on-Don: Phoenix, 2004, 192 s ISBN 5-222-05386-5
- Sokolov V. A. Geochemistry of natural gases, M., 1971;
- McEwen M., Phillips L.. Atmospheric Chemistry, M., 1978;
- Wark K., Warner S., Air pollution. Sources and control, trans. from English, M.. 1980;
- Monitoring of background pollution of natural environments. in. 1, L., 1982.
see also
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Earth's atmosphere |
The composition of the earth. Air
Air is a mechanical mixture of various gases that make up the Earth's atmosphere. Air is essential for the respiration of living organisms and is widely used in industry.
The fact that air is a mixture, and not a homogeneous substance, was proved during the experiments of the Scottish scientist Joseph Black. During one of them, the scientist discovered that when white magnesia (magnesium carbonate) is heated, "bound air", that is, carbon dioxide, is released, and burnt magnesia (magnesium oxide) is formed. In contrast, when limestone is fired, “bound air” is removed. Based on these experiments, the scientist concluded that the difference between carbonic and caustic alkalis is that the former includes carbon dioxide, which is one of the components of air. Today we know that in addition to carbon dioxide, the composition of the earth's air includes:
The ratio of gases in the earth's atmosphere indicated in the table is typical for its lower layers, up to a height of 120 km. In these areas lies a well-mixed, homogeneous region, called the homosphere. Above the homosphere lies the heterosphere, which is characterized by the decomposition of gas molecules into atoms and ions. The regions are separated from each other by a turbopause.
The chemical reaction in which, under the influence of solar and cosmic radiation, molecules decompose into atoms, is called photodissociation. During the decay of molecular oxygen, atomic oxygen is formed, which is the main gas of the atmosphere at altitudes above 200 km. At altitudes above 1200 km, hydrogen and helium, which are the lightest of the gases, begin to predominate.
Since the bulk of the air is concentrated in the 3 lower atmospheric layers, changes in the air composition at altitudes above 100 km do not have a noticeable effect on the overall composition of the atmosphere.
Nitrogen is the most common gas, accounting for more than three-quarters of the earth's air volume. Modern nitrogen was formed when the early ammonia-hydrogen atmosphere was oxidized by molecular oxygen, which is formed during photosynthesis. Currently, a small amount of nitrogen enters the atmosphere as a result of denitrification - the process of reduction of nitrates to nitrites, followed by the formation of gaseous oxides and molecular nitrogen, which is produced by anaerobic prokaryotes. Some nitrogen enters the atmosphere during volcanic eruptions.
In the upper atmosphere, when exposed to electrical discharges with the participation of ozone, molecular nitrogen is oxidized to nitrogen monoxide:
N 2 + O 2 → 2NO
Under normal conditions, the monoxide immediately reacts with oxygen to form nitrous oxide:
2NO + O 2 → 2N 2 O
Nitrogen is the most important chemical element in the earth's atmosphere. Nitrogen is part of proteins, provides mineral nutrition to plants. It determines the rate of biochemical reactions, plays the role of an oxygen diluent.
Oxygen is the second most abundant gas in the Earth's atmosphere. The formation of this gas is associated with the photosynthetic activity of plants and bacteria. And the more diverse and numerous photosynthetic organisms became, the more significant the process of oxygen content in the atmosphere became. A small amount of heavy oxygen is released during degassing of the mantle.
In the upper layers of the troposphere and stratosphere, under the influence of ultraviolet solar radiation (we denote it as hν), ozone is formed:
O 2 + hν → 2O
As a result of the action of the same ultraviolet radiation, ozone decays:
O 3 + hν → O 2 + O
O 3 + O → 2O 2
As a result of the first reaction, atomic oxygen is formed, as a result of the second - molecular oxygen. All 4 reactions are called the Chapman mechanism, after the British scientist Sidney Chapman who discovered them in 1930.
Oxygen is used for the respiration of living organisms. With its help, the processes of oxidation and combustion occur.
Ozone serves to protect living organisms from ultraviolet radiation, which causes irreversible mutations. The highest concentration of ozone is observed in the lower stratosphere within the so-called. ozone layer or ozone screen lying at altitudes of 22-25 km. The ozone content is small: at normal pressure, all the ozone of the earth's atmosphere would occupy a layer only 2.91 mm thick.
The formation of the third most common gas in the atmosphere, argon, as well as neon, helium, krypton and xenon, is associated with volcanic eruptions and the decay of radioactive elements.
In particular, helium is a product of the radioactive decay of uranium, thorium and radium: 238 U → 234 Th + α, 230 Th → 226 Ra + 4 He, 226 Ra → 222 Rn + α (in these reactions, the α-particle is a helium nucleus, which in in the process of energy loss captures electrons and becomes 4 He).
Argon is formed during the decay of the radioactive isotope of potassium: 40 K → 40 Ar + γ.
Neon escapes from igneous rocks.
Krypton is formed as the end product of the decay of uranium (235 U and 238 U) and thorium Th.
The bulk of atmospheric krypton was formed in the early stages of the Earth's evolution as a result of the decay of transuranium elements with a phenomenally short half-life or came from space, the content of krypton in which is ten million times higher than on Earth.
Xenon is the result of the fission of uranium, but most of this gas is left over from the early stages of the Earth's formation, from the primary atmosphere.
Carbon dioxide enters the atmosphere as a result of volcanic eruptions and in the process of decomposition of organic matter. Its content in the atmosphere of the middle latitudes of the Earth varies greatly depending on the seasons of the year: in winter, the amount of CO 2 increases, and in summer it decreases. This fluctuation is connected with the activity of plants that use carbon dioxide in the process of photosynthesis.
Hydrogen is formed as a result of the decomposition of water by solar radiation. But, being the lightest of the gases that make up the atmosphere, it constantly escapes into outer space, and therefore its content in the atmosphere is very small.
Water vapor is the result of the evaporation of water from the surface of lakes, rivers, seas and land.
The concentration of the main gases in the lower layers of the atmosphere, with the exception of water vapor and carbon dioxide, is constant. In small quantities, the atmosphere contains sulfur oxide SO 2, ammonia NH 3, carbon monoxide CO, ozone O 3, hydrogen chloride HCl, hydrogen fluoride HF, nitrogen monoxide NO, hydrocarbons, mercury vapor Hg, iodine I 2 and many others. In the lower atmospheric layer of the troposphere, there is constantly a large amount of suspended solid and liquid particles.
Sources of particulate matter in the Earth's atmosphere are volcanic eruptions, plant pollen, microorganisms, and, more recently, human activities such as the burning of fossil fuels in manufacturing processes. The smallest particles of dust, which are the nuclei of condensation, are the causes of the formation of fogs and clouds. Without solid particles constantly present in the atmosphere, precipitation would not fall on the Earth.
