The name of the rivers in the world. The wealth of the waterway of our country: the name of the rivers of Russia
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 formed as a solid body about 4.5 billion years ago. 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 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. Because 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 no electric charge is 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 occurs 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 d log 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 for the latitude 45° 32° 33І are given for temperature, pressure, density, viscosity, and other air characteristics 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 cloud layer of a uniform gray color giving rise to heavy 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 a 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 range 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 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 quickly 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 in the presence near the center of the solar disk large groups spots. 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. unusual shape 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 A. 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 IN 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 the 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 present moment geomagnetic local 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 auroral 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 discovery belongs to O. Khorosheva, and the intensive development of the ideas of the aurora oval was carried out by G. Starkov, J. Feldshtein, S. I. Akasof and a number of other researchers. 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 the 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 at 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 influenced by solar corpuscular streams that occur during solar flares, as well as cosmic rays and meteor particles.
Ionospheric layers
are areas in the atmosphere where maximum values concentration of free electrons (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 and so on. 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 critical), 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 with the advent of the space age of artificial Earth satellites (AES) and other spacecraft, it became possible to directly measure the parameters of near-Earth space plasma, bottom 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 wave bands with the use of antennas that make it possible to carry out 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 the 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 1 . 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, on the bands of 16, 13 and 11 m, distant stations suddenly appear with good loudness, 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 gases in 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 quite 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/
And impurities (aerosols). In terms of composition, the air near the earth's surface contains 78% nitrogen (N 2) and about 21% oxygen (O 2), i.e. these two elements account for about 99% of the volume of air. A significant proportion belongs to argon (Ar) - 0.9%. Important components of the atmosphere are ozone (O 3), carbon dioxide (CO 2), and water vapor. The significance of these gases is determined primarily by the fact that they very strongly absorb radiant energy and thus have a significant effect on the temperature regime of the earth's surface and atmosphere.
Carbon dioxide is one of the most important components of plant nutrition. It enters the atmosphere as a result of the processes of combustion, respiration of living organisms and decay, but is consumed in the process of assimilation by plants.
Ozone, most of which is concentrated in the so-called ozone layer (), serves as a natural absorber of ultraviolet, which is harmful to living organisms.
The composition also includes numerous solid and liquid impurities suspended in it - the so-called aerosols. They are of natural and artificial (anthropogenic) origin (dust, soot, ash, ice and sea salt crystals, water droplets, microorganisms, etc.).
A characteristic property of the atmosphere is that the content of at least the main gases (N 2 , O 2 , Ar) changes slightly with height. So, at an altitude of 65 km in the atmosphere, the content of nitrogen is 86%, oxygen - 19, argon - 0.91, and at an altitude of 95 km - 77, 21.3 and 0.82%, respectively. The constancy of the composition of atmospheric air both vertically and horizontally is maintained by its mixing.
The modern composition of the Earth's air was established at least several hundred million years ago and remained unchanged until the industrial activity of man increased sharply. In the current century, there has been an increase in the content of CO 2 around the globe by about 10 - 12%.
The atmosphere has a complex structure. In accordance with the change in temperature with height, four layers are distinguished: the troposphere (up to 12 km), the stratosphere (up to 50 km), the upper ones, which include the mesosphere (up to 80 km) and the thermosphere, gradually turning into interplanetary space. In the troposphere and mesosphere, it decreases with height, while in the stratosphere and thermosphere, on the contrary, it increases.
Troposphere - the lower layer of the atmosphere, the height of which varies from 8 km above the poles to 17 km (average 12 km). It contains up to 4/5 of the entire mass of the atmosphere and almost all of the water vapor. Air is dominated by nitrogen, oxygen, argon and carbon dioxide. The air of the troposphere is heated from the earth's surface - the surface of water and land. The air in the troposphere is constantly churning. Water vapor condenses, and forms, rains fall, and storms occur. The temperature decreases with height by an average of 0.6°C for every 100 m, and at the upper limit it is — 70°C at the equator and -65°C over the North Pole.
The stratosphere is the second layer of the atmosphere above the troposphere. It extends up to a height of 50 km. Gases in the stratosphere are constantly mixed, in its lower part there are stable so-called jet streams of air with a speed of up to 300 km/h. The color of the sky in the stratosphere does not seem blue, as in the troposphere, but purple. This is due to the rarefaction of the air, as a result of which the sun's rays almost do not scatter. There is very little water vapor in the stratosphere, and there are no active processes of cloud formation and precipitation. Occasionally, in the stratosphere at an altitude of » 30 km in high latitudes, thin bright clouds appear, called mother-of-pearl. It is in the stratosphere, approximately at an altitude of 20-30 km, that a layer of maximum ozone concentration is released - the ozone layer (ozone screen, ozonosphere). Thanks to ozone, the temperature in the stratosphere and at the upper boundary is within +50 +55°C.
Above the stratosphere are the high layers of the atmosphere - the mesosphere and the thermosphere.
Mesosphere - the middle sphere extends from 40-45 to 80-85 km. The color of the sky in the mesosphere appears black, day and night bright non-flickering stars are visible. The temperature drops to 75-90°C below zero.
The thermosphere extends from the mesosphere and above. Its upper limit is supposed to be at an altitude of 800 km. It mainly consists of ions formed under the influence of cosmic rays, the action of which on gas molecules leads to their decay into charged particles of atoms. The layer of ions in the thermosphere is called the ionosphere, which is characterized by high electrification and from which, like a mirror, long and medium radio waves are reflected. In the ionosphere arise - the glow of rarefied gases under the influence of electrically charged particles flying from the Sun.
The thermosphere is characterized by an increasing increase in temperature: at an altitude of 150 km it reaches 220-240°C; at an altitude of 500-600 km it exceeds 1500°C.
Above the thermosphere (i.e., above 800 km) is the outer sphere, the sphere of dispersion is the exosphere, which extends up to several thousand kilometers.
It is conditionally considered that the atmosphere extends up to an altitude of 3000 km.
Atmosphere- this is the air shell that surrounds the Earth and the force of gravity associated with it. The atmosphere is involved in the daily rotation and annual movement of our planet. Atmospheric air is a mixture of gases in which liquid (water droplets) and solid particles (smoke, dust) are suspended. The gas composition of the atmosphere is unchanged up to a height of 100-110 km, which is due to the balance in nature. The volume fractions of gases are: nitrogen - 78%, oxygen - 21%, inert gases (argon, xenon, krypton) - 0.9%, carbon - 0.03%. In addition, water vapor is always present in the atmosphere.
In addition to biological processes, oxygen, nitrogen and carbon are actively involved in the chemical weathering of rocks. The role of ozone 03 is very important, absorbing most of the ultraviolet radiation of the Sun, in large doses it is dangerous for living organisms. Solid particles, which are especially abundant above cities, serve as condensation nuclei (water drops and snowflakes form around them).
Height, boundaries and structure of the atmosphere
The upper boundary of the atmosphere is conditionally drawn at an altitude of about 1000 km, although it can be traced much higher - up to 20,000 km, but there it is very rarefied.
Through the different nature of changes in air temperature with altitude, other physical properties in the atmosphere, several parts are distinguished, which are separated from each other by transitional layers.
The troposphere is the lowest and densest layer of the atmosphere. Its upper boundary is drawn at an altitude of 18 km above the equator and 8-12 km above the poles. The temperature in the troposphere decreases by an average of 0.6 ° C for every 100 m. It is characterized by significant horizontal differences in the distribution of temperature, pressure, wind speed, as well as the formation of clouds and precipitation. In the troposphere there is an intense vertical movement of air - convection. It is in this lower layer of the atmosphere that the weather is mainly formed. Almost all of the water vapor in the atmosphere is concentrated here.
The stratosphere extends mainly up to a height of 50 km. The ozone concentration at an altitude of 20-25 km reaches its highest values, forming an ozone screen. The air temperature in the stratosphere, as a rule, increases with height by an average of 1-2 ° C per 1 km, reaching 0 ° C and higher at the upper limit. This is due to the absorption of solar energy by ozone. There is almost no water vapor and clouds in the stratosphere, and hurricane-force winds blow at speeds up to 300-400 km/h.
In the mesosphere, the air temperature drops to -60 ... - 100 ° C, intensive vertical and horizontal air movements occur.
In the upper layers of the thermosphere, where the air is highly ionized, the temperature rises again to 2000 ° C. Here, auroras and magnetic storms are observed.
The atmosphere plays a big role in the life of the Earth. It prevents excessive heating of the earth's surface during the day and its cooling at night, redistributes moisture on the Earth, protects its surface from meteorite impacts. The presence of an atmosphere is an indispensable condition for the existence of organic life on our planet.
Solar radiation. Heating of the atmosphere
The sun radiates a huge amount of energy, only a small fraction of which is received by the Earth.
The emission of light and heat from the Sun is called solar radiation. Solar radiation travels a long way in the atmosphere before reaching the earth's surface. Overcoming it, it is largely absorbed and dissipated by the air shell. Radiation that directly reaches the earth's surface in the form of direct rays is called direct radiation. Part of the radiation that is scattered in the atmosphere also reaches the Earth's surface in the form of scattered radiation.
The combination of direct and diffuse radiation entering a horizontal surface is called total solar radiation. The atmosphere absorbs about 20% of the solar radiation entering its upper boundary. Another 34% of the radiation is reflected from the Earth's surface and atmosphere (reflected radiation). 46% of solar radiation is absorbed by the earth's surface. Such radiation is called absorbed (absorbed).
The ratio of the intensity of the reflected solar radiation to the intensity of all the radiant energy of the Sun entering the upper boundary of the atmosphere is called the Earth's albedo and is expressed as a percentage.
So, the albedo of our planet, together with its atmosphere, averages 34%. The albedo value at different latitudes has significant differences associated with the color of the surface, vegetation, cloudiness, and the like. A surface area covered with fresh snow reflects 80-85% of radiation, grass vegetation and sand - respectively 26% and 30%, and water - only 5%.
The amount of solar energy received by individual parts of the Earth depends primarily on the angle of incidence of the sun's rays. The straighter they fall (i.e., the greater the height of the Sun above the horizon), the greater the amount of solar energy per unit area.
The dependence of the total radiation on the angle of incidence of rays is due to two reasons. Firstly, the smaller the angle of incidence of the sun's rays, the larger the area distributed this flux of light and the less energy per unit surface. Secondly, the smaller the angle of incidence, the longer the path of the beam in the atmosphere.
The amount of solar radiation that hits the earth's surface is affected by the transparency of the atmosphere, especially cloudiness. The dependence of solar radiation on the angle of incidence of solar rays and the transparency of the atmosphere determines the zonal nature of its distribution. Differences in the amount of total solar radiation at the same latitude are mainly caused by cloudiness.
The amount of heat entering the earth's surface is determined in calories per unit area (1 cm) per unit time (1 year).
The absorbed radiation is spent on heating the thin near-surface layer of the Earth and water evaporation. The heated earth's surface transfers heat to the environment through radiation, conduction, convection and condensation of water vapor.
Changes in air temperature depending on the geographical latitude of the place and on the height above sea level
The total radiation decreases from the equatorial-tropical latitudes to the poles. It is maximum - about 850 J / m2 per year (200 kcal / cm2 per year) - in tropical deserts, where direct solar radiation through the high altitude of the Sun and a cloudless sky is intense. In the summer half of the year, the differences in the total solar radiation inflow between low and high latitudes are smoothed out. This is due to the longer duration of solar illumination, especially in the polar regions, where the polar day lasts even half a year.
Although the total solar radiation entering the earth's surface is partially reflected by it, however, most of it is absorbed by the earth's surface and converted into heat. Part of the total radiation that remains after its costs for reflection and for thermal radiation of the earth's surface is called the radiation balance (residual radiation). In general, for the year it is positive everywhere on Earth, with the exception of the high ice deserts of Antarctica and Greenland. The radiation balance naturally decreases in the direction from the equator to the poles, where it is close to zero.
Accordingly, the air temperature is distributed zonal, that is, it decreases in the direction from the equator to the poles. .Air temperature also depends on the height of the area above sea level: the higher the area, the lower the temperature.
Significant influence on air temperature distribution of land and water. The surface of the land heats up quickly, but quickly cools, and the surface of the water heats up more slowly, but retains heat longer and releases it more slowly into the air.
As a result of the different intensity of heating and cooling of the Earth's surface day and night, in the warm and cold seasons, the air temperature changes during the day and year.
Thermometers are used to measure air temperature. it is measured 8 times a day and the average is taken per day. At the average daily temperature, monthly averages are calculated. It is they who, as a rule, are shown on climate maps by isotherms (lines that connect points with the same temperature over a certain period of time). To characterize temperatures, average monthly January and July indicators are most often taken, less often annual ones. ,
Blue planet...
This topic was supposed to appear on the site one of the first. After all, helicopters are atmospheric aircraft. Earth's atmosphere- their, so to speak, habitat :-). A physical properties of air just determine the quality of this habitat :-). So that's one of the basics. And the basis is always written first. But I just realized this now. However, it is better, as you know, late than never ... Let's touch on this issue, but without getting into the wilds and unnecessary difficulties :-).
So… Earth's atmosphere. This is the gaseous shell of our blue planet. Everyone knows this name. Why blue? Simply because the “blue” (as well as blue and violet) component of sunlight (spectrum) is most well scattered in the atmosphere, thus coloring it in bluish-bluish, sometimes with a hint of violet (on a sunny day, of course :-)) .
Composition of the Earth's atmosphere.
The composition of the atmosphere is quite wide. I will not list all the components in the text, there is a good illustration for this. The composition of all these gases is almost constant, with the exception of carbon dioxide (CO 2 ). In addition, the atmosphere necessarily contains water in the form of vapors, suspended droplets or ice crystals. The amount of water is not constant and depends on temperature and, to a lesser extent, on air pressure. In addition, the Earth's atmosphere (especially the current one) contains and a certain amount of I would say "any nasty things" :-). These are SO 2, NH 3, CO, HCl, NO, in addition there are mercury vapors Hg. True, all this is there in small quantities, thank God :-).
Earth's atmosphere It is customary to divide into several zones following each other in height above the surface.
The first, closest to the earth, is the troposphere. This is the lowest and, so to speak, the main layer for life. different kind. It contains 80% of the mass of all atmospheric air (although by volume it makes up only about 1% of the entire atmosphere) and about 90% of all atmospheric water. The bulk of all winds, clouds, rains and snows 🙂 come from there. The troposphere extends to heights of about 18 km in tropical latitudes and up to 10 km in polar latitudes. The air temperature in it drops with a rise of about 0.65º for every 100 m.
atmospheric zones.
The second zone is the stratosphere. I must say that another narrow zone is distinguished between the troposphere and stratosphere - the tropopause. It stops the temperature drop with height. The tropopause has an average thickness of 1.5-2 km, but its boundaries are indistinct and the troposphere often overlaps the stratosphere.
So the stratosphere has an average height of 12 km to 50 km. The temperature in it up to 25 km remains unchanged (about -57ºС), then somewhere up to 40 km it rises to about 0ºС and further up to 50 km it remains unchanged. The stratosphere is a relatively quiet part of the earth's atmosphere. There are practically no adverse weather conditions in it. It is in the stratosphere that the famous ozone layer is located at altitudes from 15-20 km to 55-60 km.
This is followed by a small boundary layer stratopause, in which the temperature remains around 0ºС, and then the next zone is the mesosphere. It extends to altitudes of 80-90 km, and in it the temperature drops to about 80ºС. In the mesosphere, small meteors usually become visible, which begin to glow in it and burn out there.
The next narrow gap is the mesopause and beyond it the thermosphere zone. Its height is up to 700-800 km. Here the temperature again begins to rise and at altitudes of about 300 km it can reach values of the order of 1200ºС. Thereafter, it remains constant. The ionosphere is located inside the thermosphere up to a height of about 400 km. Here, the air is strongly ionized due to exposure to solar radiation and has a high electrical conductivity.
The next and, in general, the last zone is the exosphere. This is the so-called scatter zone. Here, mainly very rarefied hydrogen and helium (with a predominance of hydrogen) are present. At altitudes of about 3000 km, the exosphere passes into the near space vacuum.
It's like that somewhere. Why about? Because these layers are rather conditional. Various changes in altitude, composition of gases, water, temperature, ionization, and so on are possible. In addition, there are many more terms that define the structure and state of the earth's atmosphere.
For example homosphere and heterosphere. In the first, the atmospheric gases are well mixed and their composition is quite homogeneous. The second is located above the first and there is practically no such mixing there. The gases are separated by gravity. The boundary between these layers is located at an altitude of 120 km, and it is called turbopause.
Let's finish with the terms, but I will definitely add that it is conventionally accepted that the boundary of the atmosphere is located at an altitude of 100 km above sea level. This border is called the Karman Line.
I will add two more pictures to illustrate the structure of the atmosphere. The first, however, is in German, but it is complete and easy enough to understand :-). It can be enlarged and well considered. The second shows the change in atmospheric temperature with altitude.
The structure of the Earth's atmosphere.
Change in air temperature with height.
Modern manned orbital spacecraft fly at altitudes of about 300-400 km. However, this is no longer aviation, although the area, of course, is in a certain sense closely related, and we will certainly talk about it again :-).
The aviation zone is the troposphere. Modern atmospheric aircraft can also fly in the lower layers of the stratosphere. For example, the practical ceiling of the MIG-25RB is 23000 m.
Flight in the stratosphere.
And exactly physical properties of air tropospheres determine how the flight will be, how effective the aircraft control system will be, how the turbulence in the atmosphere will affect it, how the engines will work.
The first main property is air temperature. In gas dynamics, it can be determined on the Celsius scale or on the Kelvin scale.
Temperature t1 at a given height H on the Celsius scale is determined:
t 1 \u003d t - 6.5N, Where t is the air temperature at the ground.
Temperature on the Kelvin scale is called absolute temperature Zero on this scale is absolute zero. At absolute zero, the thermal motion of molecules stops. Absolute zero on the Kelvin scale corresponds to -273º on the Celsius scale.
Accordingly, the temperature T on high H on the Kelvin scale is determined:
T \u003d 273K + t - 6.5H
Air pressure. Atmosphere pressure measured in Pascals (N / m 2), in the old system of measurement in atmospheres (atm.). There is also such a thing as barometric pressure. This is the pressure measured in millimeters of mercury using a mercury barometer. Barometric pressure (pressure at sea level) equal to 760 mm Hg. Art. called standard. In physics, 1 atm. just equal to 760 mm Hg.
Air density. In aerodynamics, the most commonly used concept is the mass density of air. This is the mass of air in 1 m3 of volume. The density of air changes with height, the air becomes thinner.
Air humidity. Shows the amount of water in the air. There is a concept " relative humidity". This is the ratio of the mass of water vapor to the maximum possible at a given temperature. The concept of 0%, that is, when the air is completely dry, can exist in general only in the laboratory. On the other hand, 100% humidity is quite real. This means that the air has absorbed all the water it could absorb. Something like an absolutely "full sponge". High relative humidity reduces air density, while low relative humidity increases it accordingly.
Due to the fact that aircraft flights take place under different atmospheric conditions, their flight and aerodynamic parameters in one flight mode may be different. Therefore, for a correct assessment of these parameters, we introduced International Standard Atmosphere (ISA). It shows the change in the state of the air with the rise in altitude.
The main parameters of the state of air at zero humidity are taken as:
pressure P = 760 mm Hg. Art. (101.3 kPa);
temperature t = +15°C (288 K);
mass density ρ \u003d 1.225 kg / m 3;
For the ISA, it is assumed (as mentioned above :-)) that the temperature drops in the troposphere by 0.65º for every 100 meters of altitude.
Standard atmosphere (example up to 10000 m).
ISA tables are used for calibrating instruments, as well as for navigational and engineering calculations.
Physical properties of air also include such concepts as inertness, viscosity and compressibility.
Inertia is a property of air that characterizes its ability to resist changes in the state of rest or uniform rectilinear motion. . The measure of inertia is the mass density of air. The higher it is, the higher the inertia and drag force of the medium when the aircraft moves in it.
Viscosity. Determines the frictional resistance against air as the aircraft moves.
Compressibility measures the change in air density as pressure changes. At low speeds of the aircraft (up to 450 km/h), there is no change in pressure when the air flow flows around it, but at high speeds, the effect of compressibility begins to appear. Its influence on supersonic is especially pronounced. This is a separate area of aerodynamics and a topic for a separate article :-).
Well, it seems that's all for now ... It's time to finish this slightly tedious enumeration, which, however, cannot be dispensed with :-). Earth's atmosphere, its parameters, physical properties of air are as important for the aircraft as the parameters of the apparatus itself, and it was impossible not to mention them.
For now, until the next meetings and more interesting topics 🙂 …
P.S. For dessert, I suggest watching a video filmed from the cockpit of a MIG-25PU twin during its flight into the stratosphere. Filmed, apparently, by a tourist who has money for such flights :-). Filmed mostly through the windshield. Notice the color of the sky...
The gaseous envelope that surrounds our planet Earth, known as the atmosphere, consists of five main layers. These layers originate on the surface of the planet, from sea level (sometimes below) and rise to outer space in the following sequence:
- Troposphere;
- Stratosphere;
- Mesosphere;
- Thermosphere;
- Exosphere.
Diagram of the main layers of the Earth's atmosphere
In between each of these main five layers are transitional zones called "pauses" where changes in air temperature, composition and density occur. Together with pauses, the Earth's atmosphere includes a total of 9 layers.
Troposphere: where the weather happens
Of all the layers of the atmosphere, the troposphere is the one with which we are most familiar (whether you realize it or not), since we live at its bottom - the surface of the planet. It envelops the surface of the Earth and extends upwards for several kilometers. The word troposphere means "change of the ball". A very appropriate name, as this layer is where our daily weather happens.
Starting from the surface of the planet, the troposphere rises to a height of 6 to 20 km. The lower third of the layer closest to us contains 50% of all atmospheric gases. It is the only part of the entire composition of the atmosphere that breathes. Due to the fact that the air is heated from below by the earth's surface, which absorbs the thermal energy of the Sun, the temperature and pressure of the troposphere decrease with increasing altitude.
At the top is a thin layer called the tropopause, which is just a buffer between the troposphere and stratosphere.
Stratosphere: home of ozone
The stratosphere is the next layer of the atmosphere. It extends from 6-20 km to 50 km above the earth's surface. This is the layer in which most commercial airliners fly and balloons travel.
Here, the air does not flow up and down, but moves parallel to the surface in very fast air currents. Temperatures increase as you ascend, thanks to an abundance of naturally occurring ozone (O3), a by-product of solar radiation, and oxygen, which has the ability to absorb the sun's harmful ultraviolet rays (any rise in temperature with altitude is known in meteorology as an "inversion") .
Because the stratosphere has warmer temperatures at the bottom and cooler temperatures at the top, convection (vertical movements of air masses) is rare in this part of the atmosphere. In fact, you can view a storm raging in the troposphere from the stratosphere, because the layer acts as a "cap" for convection, through which storm clouds do not penetrate.
The stratosphere is again followed by a buffer layer, this time called the stratopause.
Mesosphere: middle atmosphere
The mesosphere is located approximately 50-80 km from the Earth's surface. Upper area The mesosphere is the coldest natural place on Earth, where temperatures can drop below -143°C.
Thermosphere: upper atmosphere
The mesosphere and mesopause are followed by the thermosphere, located between 80 and 700 km above the surface of the planet, and containing less than 0.01% of the total air in the atmospheric shell. Temperatures here reach up to +2000° C, but due to the strong rarefaction of the air and the lack of gas molecules to transfer heat, these high temperatures are perceived as very cold.
Exosphere: the boundary of the atmosphere and space
At an altitude of about 700-10,000 km above the earth's surface is the exosphere - the outer edge of the atmosphere, bordering space. Here meteorological satellites revolve around the Earth.
How about the ionosphere?
The ionosphere is not a separate layer, and in fact this term is used to refer to the atmosphere at an altitude of 60 to 1000 km. It includes the uppermost parts of the mesosphere, the entire thermosphere and part of the exosphere. The ionosphere gets its name because in this part of the atmosphere, the Sun's radiation is ionized when it passes the Earth's magnetic fields at and . This phenomenon is observed from the earth as the northern lights.
