The Earth's atmosphere is heterogeneous: at different altitudes there are different air densities and pressures, temperature and gas composition changes. Based on the behavior of the ambient air temperature (i.e., the temperature increases or decreases with height), the following layers are distinguished in it: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The boundaries between layers are called pauses: there are 4 of them, because the upper boundary of the exosphere is very blurred and often refers to near space. The general structure of the atmosphere can be found in the attached diagram.
Fig.1 The structure of the Earth's atmosphere. Credit: website
The lowest atmospheric layer is the troposphere, the upper boundary of which, called the tropopause, varies depending on the geographic latitude and ranges from 8 km. in the polar up to 20 km. in tropical latitudes. In middle or temperate latitudes, its upper limit lies at altitudes of 10-12 km. During the year, the upper limit of the troposphere experiences fluctuations depending on the influx of solar radiation. Thus, as a result of sounding at the South Pole of the Earth by the US meteorological service, it was revealed that from March to August or September there is a steady cooling of the troposphere, as a result of which for a short period in August or September its boundary rises to 11.5 km. Then, in the period from September to December, it quickly decreases and reaches its lowest position - 7.5 km, after which its height remains virtually unchanged until March. Those. The troposphere reaches its greatest thickness in summer and its thinnest in winter.
It is worth noting that, in addition to seasonal ones, there are also daily fluctuations in the height of the tropopause. Also, its position is influenced by cyclones and anticyclones: in the first, it falls, because The pressure in them is lower than in the surrounding air, and secondly, it rises accordingly.
The troposphere contains up to 90% of the total mass of earth's air and 9/10 of all water vapor. Turbulence is highly developed here, especially in the near-surface and highest layers, clouds of all levels develop, cyclones and anticyclones form. And thanks to the accumulation of greenhouse gases (carbon dioxide, methane, water vapor) reflected from the Earth’s surface sun rays the greenhouse effect develops.
The greenhouse effect is associated with a decrease in air temperature in the troposphere with height (since the heated Earth gives off more heat to the surface layers). The average vertical gradient is 0.65°/100 m (i.e., the air temperature decreases by 0.65° C for every 100 meters of rise). So, if the average annual air temperature at the surface of the Earth near the equator is +26°, then at the upper boundary it is -70°. Temperature near the tropopause above north pole throughout the year it varies from -45° in summer to -65° in winter.
With increasing altitude, air pressure also decreases, amounting to only 12-20% of the near-surface level at the upper boundary of the troposphere.
At the boundary of the troposphere and the overlying layer of the stratosphere lies a layer of the tropopause, 1-2 km thick. The lower boundaries of the tropopause are usually taken to be a layer of air in which the vertical gradient decreases to 0.2°/100 m versus 0.65°/100 m in the underlying regions of the troposphere.
Within the tropopause, air flows of a strictly defined direction are observed, called high-altitude jet streams or “jet streams”, formed under the influence of the rotation of the Earth around its axis and heating of the atmosphere with the participation of solar radiation. Currents are observed at the boundaries of zones with significant temperature differences. There are several centers of localization of these currents, for example, arctic, subtropical, subpolar and others. Knowledge of the localization of jet streams is very important for meteorology and aviation: the first uses streams for more accurate weather forecasting, the second for constructing aircraft flight routes, because At the boundaries of the flows, there are strong turbulent vortices, similar to small whirlpools, called “clear-sky turbulence” due to the absence of clouds at these altitudes.
Under the influence of high-altitude jet currents, breaks often form in the tropopause, and at times it disappears altogether, although it then forms anew. This is especially often observed in subtropical latitudes, which are dominated by a powerful subtropical high-altitude current. In addition, the difference in tropopause layers in ambient temperature leads to the formation of gaps. For example, a large gap exists between the warm and low polar tropopause and the high and cold tropopause of tropical latitudes. IN Lately The tropopause layer of temperate latitudes also stands out, which has breaks with the previous two layers: polar and tropical.
The second layer of the earth's atmosphere is the stratosphere. The stratosphere can be roughly divided into two regions. The first of them, lying up to altitudes of 25 km, is characterized by almost constant temperatures, which are equal to the temperatures of the upper layers of the troposphere over a particular area. The second region, or inversion region, is characterized by an increase in air temperature to altitudes of approximately 40 km. This occurs due to the absorption of solar ultraviolet radiation by oxygen and ozone. In the upper part of the stratosphere, thanks to this heating, the temperature is often positive or even comparable to the temperature of the surface air.
Above the inversion region there is a layer of constant temperatures, which is called the stratopause and is the boundary between the stratosphere and mesosphere. Its thickness reaches 15 km.
Unlike the troposphere, turbulent disturbances are rare in the stratosphere, but there are strong horizontal winds or jet streams blowing in narrow zones along the boundaries of temperate latitudes facing the poles. The position of these zones is not constant: they can shift, expand, or even disappear altogether. Often jet streams penetrate into the upper layers of the troposphere, or, conversely, air masses from the troposphere penetrate into the lower layers of the stratosphere. Such mixing of air masses is especially typical in areas of atmospheric fronts.
There is little water vapor in the stratosphere. The air here is very dry, and therefore few clouds form. Only at altitudes of 20-25 km, being in high latitudes You can see very thin pearlescent clouds consisting of supercooled water droplets. During the day, these clouds are not visible, but with the onset of darkness they seem to glow due to the illumination of them by the Sun, which has already set below the horizon.
At the same altitudes (20-25 km) in the lower stratosphere there is the so-called ozone layer - the area with the highest content of ozone, which is formed under the influence of ultraviolet solar radiation (you can find out more about this process on the page). The ozone layer or ozonosphere is of extreme importance for maintaining the life of all organisms living on land, absorbing deadly ultraviolet rays with a wavelength of up to 290 nm. It is for this reason that living organisms do not live above the ozone layer; it is the upper limit of the distribution of life on Earth.
Under the influence of ozone, magnetic fields also change, atoms and molecules disintegrate, ionization occurs, and new formation of gases and other chemical compounds occurs.
The layer of the atmosphere lying above the stratosphere is called the mesosphere. It is characterized by a decrease in air temperature with height with an average vertical gradient of 0.25-0.3°/100 m, which leads to severe turbulence. At the upper boundaries of the mesosphere, in the region called the mesopause, temperatures down to -138°C were recorded, which is the absolute minimum for the entire Earth's atmosphere as a whole.
Here, within the mesopause, lies the lower boundary of the region of active absorption of X-ray and short-wave ultraviolet radiation from the Sun. This energy process is called radiant heat transfer. As a result, the gas is heated and ionized, which causes the atmosphere to glow.
At altitudes of 75-90 km at the upper boundaries of the mesosphere, special clouds were noted, occupying vast areas in the polar regions of the planet. These clouds are called noctilucent because of their glow at dusk, which is caused by the reflection of sunlight from the ice crystals of which these clouds are composed.
Air pressure within the mesopause is 200 times less than at the earth's surface. This suggests that almost all the air in the atmosphere is concentrated in its 3 lower layers: the troposphere, stratosphere and mesosphere. The overlying layers, the thermosphere and exosphere, account for only 0.05% of the mass of the entire atmosphere.
The thermosphere lies at altitudes from 90 to 800 km above the Earth's surface.
The thermosphere is characterized by a continuous increase in air temperature to altitudes of 200-300 km, where it can reach 2500°C. The temperature rises due to the absorption of X-rays and short-wavelength ultraviolet radiation from the Sun by gas molecules. Above 300 km above sea level, the temperature increase stops.
Simultaneously with the increase in temperature, the pressure and, consequently, the density of the surrounding air decreases. So if at the lower boundaries of the thermosphere the density is 1.8 × 10 -8 g/cm 3, then at the upper boundaries it is already 1.8 × 10 -15 g/cm 3, which approximately corresponds to 10 million - 1 billion particles per 1 cm 3.
All characteristics of the thermosphere, such as the composition of air, its temperature, density, are subject to strong fluctuations: depending on the geographical location, season of the year and time of day. Even the location of the upper boundary of the thermosphere changes.
The uppermost layer of the atmosphere is called the exosphere or scattering layer. Its lower limit is constantly changing within very wide limits; The average height is taken to be 690-800 km. It is installed where the probability of intermolecular or interatomic collisions can be neglected, i.e. the average distance that a chaotically moving molecule will cover before colliding with another similar molecule (the so-called free path) will be so great that in fact the molecules will not collide with a probability close to zero. The layer where the described phenomenon occurs is called thermal pause.
The upper boundary of the exosphere lies at altitudes of 2-3 thousand km. It is greatly blurred and gradually turns into a near-space vacuum. Sometimes, for this reason, the exosphere is considered part of outer space, and its upper limit is taken to be a height of 190 thousand km, at which the influence of solar radiation pressure on the speed of hydrogen atoms exceeds the gravitational attraction of the Earth. This is the so-called the earth's crown, consisting of hydrogen atoms. The density of the earth's corona is very small: only 1000 particles per cubic centimeter, but this number is more than 10 times higher than the concentration of particles in interplanetary space.
Due to the extreme rarefaction of the air in the exosphere, particles move around the Earth in elliptical orbits without colliding with each other. Some of them, moving along open or hyperbolic trajectories at cosmic speeds (hydrogen and helium atoms), leave the atmosphere and go into outer space, which is why the exosphere is called the scattering sphere.
The stratosphere is one of the upper layers air envelope of our planet. It begins at an altitude of approximately 11 km above the ground. Passenger aircraft no longer fly here and clouds rarely form. The Earth's ozone layer is located in the stratosphere - a thin shell that protects the planet from the penetration of harmful ultraviolet radiation.
The air envelope of the planet
The atmosphere is the gaseous shell of the Earth, adjacent with its inner surface to the hydrosphere and the earth's crust. Its outer boundary gradually passes into outer space. The composition of the atmosphere includes gases: nitrogen, oxygen, argon, carbon dioxide, and so on, as well as impurities in the form of dust, water droplets, ice crystals, and combustion products. The ratio of the main elements of the air shell remains constant. The exceptions are carbon dioxide and water - their amount in the atmosphere often changes.
Layers of gas shell
The atmosphere is divided into several layers, located one above the other and having the following features:
boundary layer - directly adjacent to the surface of the planet, extending to a height of 1-2 km;
troposphere - the second layer, the outer boundary is located on average at an altitude of 11 km, almost all the water vapor of the atmosphere is concentrated here, clouds form, cyclones and anticyclones arise, and as the altitude increases, the temperature rises;
tropopause - a transition layer characterized by the cessation of temperature decrease;
the stratosphere is a layer that extends to a height of 50 km and is divided into three zones: from 11 to 25 km the temperature changes slightly, from 25 to 40 - the temperature rises, from 40 to 50 - the temperature remains constant (stratopause);
the mesosphere extends to a height of 80-90 km;
the thermosphere reaches 700-800 km above sea level, here at an altitude of 100 km is the Karman line, which is taken as the boundary between the Earth’s atmosphere and space;
The exosphere is also called the scattering zone; particles of matter are greatly lost here, and they fly off into space.
Temperature changes in the stratosphere
So, the stratosphere is the part of the gas shell of the planet that follows the troposphere. Here the air temperature, constant throughout the tropopause, begins to change. The height of the stratosphere is approximately 40 km. The lower limit is 11 km above sea level. Starting from this point, the temperature undergoes slight changes. At an altitude of 25 km, the heating rate begins to slowly increase. At 40 km above sea level, the temperature rises from -56.5º to +0.8ºС. Then it remains close to zero degrees up to an altitude of 50-55 km. The zone between 40 and 55 kilometers is called the stratopause because the temperature does not change here. It is a transition zone from the stratosphere to the mesosphere.
Features of the stratosphere
The Earth's stratosphere contains about 20% of the mass of the entire atmosphere. The air here is so rarefied that it is impossible for a person to stay without a special spacesuit. This fact is one of the reasons why flights into the stratosphere began to be carried out only relatively recently.
Another feature of the gaseous shell of the planet at an altitude of 11-50 km is the very small amount of water vapor. For this reason, clouds almost never form in the stratosphere. There is simply no building material for them. However, it is rarely possible to observe the so-called mother-of-pearl clouds with which the stratosphere is “decorated” (photo below) at an altitude of 20-30 km above sea level. Thin formations, as if glowing from within, can be observed after sunset or before sunrise. The shape of nacreous clouds is similar to cirrus or cirrocumulus.
Earth's ozone layer
The main distinguishing feature of the stratosphere is the maximum concentration of ozone in the entire atmosphere. It is formed under the influence of sunlight and protects all life on the planet from their destructive radiation. The Earth's ozone layer is located at an altitude of 20-25 km above sea level. O 3 molecules are distributed throughout the stratosphere and even exist near the surface of the planet, but at this level their highest concentration is observed.
It should be noted that the Earth's ozone layer is only 3-4 mm. This will be its thickness if particles of this gas are placed under conditions normal pressure, for example, near the surface of the planet. Ozone is formed as a result of the breakdown of an oxygen molecule under the influence of ultraviolet radiation into two atoms. One of them combines with a “full” molecule and ozone is formed - O 3.
Dangerous Defender
Thus, today the stratosphere is a more explored layer of the atmosphere than at the beginning of the last century. However, the future of the ozone layer, without which life on Earth would not have arisen, remains not very clear. While countries are reducing freon production, some scientists say that this will not bring much benefit, at least at this rate, while others say that it is not necessary at all, since the bulk of the harmful substances are formed naturally. Time will judge who is right.
The atmosphere began to form along with the formation of the Earth. During the evolution of the planet and as its parameters approached modern values, fundamentally qualitative changes occurred 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 formed as a solid body. This milestone is taken as the beginning of the geological chronology. From that time on, the slow evolution of the atmosphere began. Some geological processes (for example, lava outpourings during volcanic eruptions) were accompanied by the release of gases from the bowels of the Earth. They included nitrogen, ammonia, methane, water vapor, CO oxide and carbon dioxide CO 2. Under the influence of solar ultraviolet radiation, water vapor decomposed into hydrogen and oxygen, but the released oxygen reacted with carbon monoxide to form carbon dioxide. Ammonia decomposed into nitrogen and hydrogen. During the process of diffusion, hydrogen rose upward and left the atmosphere, and heavier nitrogen could not evaporate 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, which resulted in the formation of organic substances, in particular amino acids. 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 layers of the atmosphere, began to protect its lower layers and the surface of the Earth from life-threatening ultraviolet and X-ray radiation. According to theoretical estimates, the oxygen content, 25,000 times less than now, could already lead to the formation of an ozone layer with only half the concentration than now. However, this is already enough to provide very significant protection of organisms from the destructive effects of ultraviolet rays.
It is likely that the primary atmosphere contained a lot of carbon dioxide. It was used up during photosynthesis, and its concentration must have decreased as the plant world evolved and also due to absorption during certain 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 reasons for such large-scale climate change in the history of the Earth, 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 during radioactive decay an electric charge is neither formed nor destroyed, with the formation of each a-particle two electrons appear, which, recombining with the a-particles, form neutral helium atoms. Radioactive elements are contained in minerals dispersed in rocks, so a significant part of the helium formed as a result of radioactive decay is retained in them, escaping very slowly into the atmosphere. A certain amount of helium rises upward 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 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 approximately ten billion times higher than on Earth, krypton - ten million times, and xenon - a million times. It follows that the concentration of these inert gases, apparently initially present in the Earth’s atmosphere and not replenished during chemical reactions, decreased greatly, probably even at the stage of the Earth’s loss of its primary atmosphere. An exception is the inert gas argon, since in the form of the 40 Ar isotope it is still formed during the 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, at sea level is approximately 11 t/m 2 = 1.1 kg/cm 2. Pressure equal to P 0 = 1033.23 g/cm 2 = 1013.250 mbar = 760 mm Hg. Art. = 1 atm, taken as the standard average atmospheric pressure. For the atmosphere in a state of hydrostatic equilibrium we have: d P= –rgd h, this means that in the height interval from h before h+ d h occurs equality between the change in atmospheric pressure d P and the weight of the corresponding element of the atmosphere with unit area, density r and thickness d h. As a relationship between pressure R and temperature T The equation of state of an ideal gas with density r, which is quite applicable to 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. Its inverse value H is called the atmospheric altitude scale.
When integrating this equation for an isothermal atmosphere ( T= const) or for its part where such an approximation is permissible, the barometric law of pressure distribution with height is obtained: P = P 0 exp(– h/H 0), where the height reference h produced from ocean level, where the standard mean pressure is P 0 . Expression H 0 = R T/ mg, is called the altitude 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 integration must take into account the change in temperature with height, and the parameter N– some local characteristic of atmospheric layers, depending on their temperature and the properties of the environment.
Standard atmosphere.
Model (table of values of the main parameters) corresponding to standard pressure at the base of the atmosphere R 0 and chemical composition is called a standard atmosphere. More precisely, this is a conditional model of the atmosphere, for which the average values of temperature, pressure, density, viscosity and other characteristics of air at altitudes from 2 km below sea level to the outer boundary of the earth’s atmosphere are specified for latitude 45° 32ў 33І. The parameters of the middle atmosphere at all altitudes were calculated using the equation of state of an ideal gas and the barometric law assuming that at sea level the pressure is 1013.25 hPa (760 mm Hg) 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 linear function height. In the lowest layer - the troposphere (h Ј 11 km) the temperature drops by 6.5 ° C with each kilometer of rise. On 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 altitude.
The standard atmosphere is a periodically updated, legalized standard, issued in the form of tables.
| Table 1. STANDARD MODEL OF THE EARTH'S ATMOSPHERE. The table shows: h– height from sea level, R- pressure, T– temperature, r – density, N– number of molecules or atoms per unit volume, H– height scale, l– free path length. Pressure and temperature at an altitude of 80–250 km, obtained from rocket data, have lower values. Values for altitudes greater than 250 km obtained by extrapolation 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 most dense 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 the polar and middle latitudes to altitudes 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, and various meteorological phenomena, fog and precipitation occur. These layers of the earth's atmosphere are in convective equilibrium and, thanks 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) caused by the transfer of heat from warmer land through the infrared radiation of the earth's surface, which is absorbed in the troposphere, mainly by vapors 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 temperature drop with height of approximately 6.5 K/km.
The wind speed in the surface boundary layer initially increases rapidly with height, and above it continues to increase by 2–3 km/s per kilometer. Sometimes narrow planetary flows (with a speed of more than 30 km/s) appear in the troposphere, western in the middle latitudes, and eastern 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 located above it. The thickness of the tropopause ranges 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 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 tropopause breaks are possible.
Water in the Earth's atmosphere.
The most important feature of the Earth's atmosphere is the presence significant amount 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 scale of 10 or as a percentage, is called cloudiness. The shape of clouds is determined according to 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 ground 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 together (mixed clouds). As droplets and crystals become larger, they fall out of the clouds in the form of precipitation. Clouds form mainly in the troposphere. They arise as a result of 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 ranges from fractions to several grams per m3. Clouds are classified by height: According to the international classification, there are 10 types of clouds: cirrus, cirrocumulus, cirrostratus, altocumulus, altostratus, nimbostratus, stratus, stratocumulus, cumulonimbus, cumulus.
Pearlescent clouds are also observed in the stratosphere, and noctilucent clouds are observed in the mesosphere.
Cirrus clouds are transparent clouds in the form of thin white threads or veils with a silky sheen that do not provide shadows. Cirrus clouds consist of ice crystals and form in the upper layers of the troposphere at very high temperatures. 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 are a whitish translucent veil in the upper troposphere, usually fibrous, sometimes blurry, consisting of small needle-shaped or columnar ice crystals.
Altocumulus clouds are white, gray or white-gray clouds in the lower and middle layers of the troposphere. Altocumulus clouds have the appearance of layers and ridges, as if built from plates, rounded masses, shafts, flakes lying on top of each other. Altocumulus clouds form during intense convective activity and usually consist of supercooled water droplets.
Altostratus clouds are grayish or bluish clouds with a fibrous or uniform structure. Altostratus clouds are observed in the middle troposphere, extending several kilometers in height and sometimes thousands of kilometers in the horizontal direction. Typically, altostratus clouds are part of frontal cloud systems associated with upward movements of air masses.
Nimbostratus clouds are a low (from 2 km and above) amorphous layer of clouds, uniformly gray giving rise to continuous rain or snow. Nimbostratus clouds are highly developed vertically (up to several km) and horizontally (several thousand km), consist of supercooled water droplets mixed with snowflakes, usually associated with atmospheric fronts.
Stratus clouds are 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. Occasionally, 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. Typically, cumulus clouds arise as convection clouds in cold air masses.
Stratocumulus clouds are 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 produce light precipitation.
Cumulonimbus clouds are powerful and dense clouds with strong vertical development (up to a height of 14 km), producing heavy rainfall with thunderstorms, hail, and squalls. Cumulonimbus clouds develop from powerful cumulus clouds, differing from them top 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 altitudes of about 20 km, it is isothermal (temperature about 220 K). It then 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 significantly less water vapor in the stratosphere. Still, thin translucent pearlescent clouds are sometimes observed, occasionally appearing in the stratosphere at an altitude of 20–30 km. Pearlescent clouds are visible in the dark sky after sunset and before sunrise. In shape, nacreous clouds resemble cirrus and cirrocumulus clouds.
Middle atmosphere (mesosphere).
At an altitude of about 50 km, the mesosphere begins from the peak of the broad 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
O 2 + hv® O + O and the subsequent reaction of a triple collision of an oxygen atom and molecule with some third molecule M.
O + O 2 + M ® O 3 + M
Ozone voraciously absorbs ultraviolet radiation in the region from 2000 to 3000 Å, and this radiation heats the atmosphere. Ozone, located in the upper atmosphere, serves as a kind of shield that protects us from the effects 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 atmospheric temperature decreases to its minimum value of about 180 K at the upper boundary of the mesosphere (called mesopause, altitude 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 may appear, observed in the form of a beautiful spectacle of noctilucent clouds shortly after sunset.
In the mesosphere, small solid meteorite particles that fall on the Earth, causing the phenomenon of meteors, mostly burn up.
Meteors, meteorites and fireballs.
Flares and other phenomena in the upper atmosphere of the Earth caused by the intrusion of solid cosmic particles or bodies into it at a speed of 11 km/s or higher are called meteoroids. An observable bright meteor trail appears; the most powerful phenomena, often accompanied by the fall of meteorites, are called fireballs; the appearance of meteors is associated with meteor showers.
Meteor shower:
1) the phenomenon of multiple falls of meteors over several hours or days from one radiant.
2) a swarm of meteoroids moving in the same orbit around the Sun.
The systematic appearance of meteors in a certain area of the sky and on certain days of the year, caused by the intersection of the Earth's orbit with the common orbit of many meteorite bodies moving at approximately the same and identically directed speeds, due to which their paths in the sky appear to emerge from the same common point(radiant). They are named after the constellation where the radiant is located.
Meteor showers make a deep impression with their light effects, but individual meteors are rarely visible. Much more numerous are invisible meteors, too small to be visible when they are absorbed into the atmosphere. Some of the smallest meteors probably do not heat up at all, but are only captured by the atmosphere. These small particles with sizes ranging from a few millimeters to ten thousandths of a millimeter are called micrometeorites. The amount of meteoric matter entering the atmosphere every day ranges from 100 to 10,000 tons, with the majority of this material coming from micrometeorites.
Since meteoric matter partially burns in the atmosphere, its gas composition is replenished with traces of various chemical elements. For example, rocky meteors introduce lithium into the atmosphere. The combustion of metal meteors leads to the formation of tiny spherical iron, iron-nickel and other droplets that pass through the atmosphere and settle 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 meteor particles entering the atmosphere settle within approximately 30 days. Some scientists believe that this cosmic dust plays an important role in the formation of atmospheric phenomena such as rain because it serves as condensation nuclei for water vapor. Therefore, it is assumed that precipitation is statistically related to large meteor showers. However, some experts believe that since the total supply of meteoric material is many tens of times greater than that of even the largest meteor shower, the change in the total amount of this material resulting from one such rain 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 heating it. This is one of the minor components heat balance atmosphere.
A meteorite is a naturally occurring solid body that fell to the surface of the Earth from space. Usually a distinction is made between stony, stony-iron and iron meteorites. The latter mainly consist of iron and nickel. Among the meteorites found, most weigh from a few 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 bolide is a very bright meteor, sometimes visible 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, first slowly and then quickly begins to rise again. The reason is the absorption of ultraviolet radiation from the Sun at altitudes of 150–300 km, due to the ionization of atomic oxygen: O + hv® O + + e.
In the thermosphere, the temperature continuously increases to an altitude of about 400 km, where it reaches 1800 K during the day during the epoch of maximum solar activity. During the epoch of minimum solar activity, this limiting temperature can be less than 1000 K. Above 400 km, the atmosphere turns into an isothermal exosphere. The critical level (the base of the exosphere) is at an altitude of about 500 km.
Polar lights 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 a few 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 spectrum of auroras consists of emission lines and bands. Some of the night sky emissions are enhanced in the aurora spectrum, primarily the green and red lines l 5577 Å and l 6300 Å oxygen. It happens that one of these lines is many times more intense than the other, and this determines visible color aurora: green or red. Magnetic field disturbances are also accompanied by disruptions in radio communications in the polar regions. The cause of the disruption is changes in the ionosphere, which mean that during magnetic storms there is a powerful source of ionization. It has been established that strong magnetic storms occur when there are large groups of sunspots near the center of the solar disk. Observations have shown that storms are not associated with the sunspots themselves, but with solar flares that appear during the development of a group of sunspots.
Auroras are a range of light of varying intensity with rapid movements observed in high latitude regions of the Earth. The visual aurora contains green (5577Å) and red (6300/6364Å) atomic oxygen emission lines and molecular N2 bands, which are excited by energetic particles of solar and magnetospheric origin. These emissions usually appear at altitudes of about 100 km and above. The term optical aurora is used to refer to visual auroras and their emission spectrum from the infrared to the ultraviolet region. The radiation energy in the infrared part of the spectrum significantly exceeds the energy in the visible region. When auroras appeared, emissions were observed in the ULF range (
The actual forms of auroras are difficult to classify; The most commonly used terms are:
1. Calm, uniform arcs or stripes. The arc typically extends ~1000 km in the direction of the geomagnetic parallel (toward the Sun in polar regions) and has a width of one to several tens of kilometers. A stripe is a generalization of the concept of an arc; it usually does not have a regular arc-shaped shape, but bends in the form of the letter S or in the form of spirals. Arcs and stripes are located at altitudes of 100–150 km.
2. Rays of the aurora . This term refers to an auroral structure elongated along magnetic field lines, with a vertical extent of several tens to several hundred kilometers. The horizontal extent of the rays is small, from several tens of meters to several kilometers. The 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 connected to each other.
4. Veil. Unusual shape aurora, which is a uniform glow that covers large areas of the sky.
According to their structure, auroras are divided into homogeneous, hollow 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 the entire part is red (6300–6364 Å). They usually appear at altitudes of 300–400 km with high geomagnetic activity.
Aurora type IN colored red in the lower part and associated with the glow of the bands of the first positive system N 2 and the first negative system O 2. Such forms of auroras appear during the most active phases of auroras.
Zones polar lights – These are the zones of maximum frequency 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 geomagnetic local time, occurs in oval-like belts (oval auroras), 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 geometric locus of the points of the oval’s midnight region in latitude – longitude coordinates. The oval belt is located approximately 23° from the geomagnetic pole in the night sector and 15° in the daytime sector.
Aurora oval and aurora zones. The location of the aurora oval depends on geomagnetic activity. The oval becomes wider at high geomagnetic activity. Auroral zones or auroral oval boundaries are better represented by L 6.4 than by dipole coordinates. Geomagnetic field lines at the boundary of the daytime sector of the aurora oval coincide with magnetopause. A change in the position of the aurora oval is observed 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 precipitation of particles (electrons and protons) of certain energies. Its position can be independently determined from data on Kaspakh on the dayside and in the tail of the magnetosphere.
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 the daily variations is preserved. On the polar side of the oval, the frequency of auroras decreases gradually and is characterized by complex diurnal changes.
Intensity of auroras.
Aurora intensity determined by measuring the apparent surface brightness. Luminosity surface I aurora in a certain direction is determined by the total emission of 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 when studying auroras. The usual unit for measuring total emission is Rayleigh (Rl) equal to 10 6 photons/(cm 2 column s). More practical units of auroral intensity are determined by the emissions of an individual line or band. For example, the intensity of auroras is determined by the international brightness coefficients (IBRs) according to the intensity of the green line (5577 Å); 1 kRl = I MKY, 10 kRl = II MKY, 100 kRl = III MKY, 1000 kRl = IV MKY (maximum intensity of the aurora). This classification cannot be used for red auroras. One of the discoveries of the era (1957–1958) was the establishment of the spatiotemporal distribution of auroras in the form of an oval, shifted relative to the magnetic pole. From simple ideas about the circular shape of the distribution of auroras relative to the magnetic pole there was The transition to modern physics of the magnetosphere has been completed. The honor of the discovery belongs to O. Khorosheva, and the intensive development of ideas for the auroral oval was carried out by G. Starkov, Y. Feldstein, S. I. Akasofu and a number of other researchers. The auroral oval is the region of the most intense influence of the solar wind on the Earth's upper atmosphere. The intensity of the aurora is greatest in the oval, and its dynamics are continuously monitored using satellites.
Stable auroral red arcs.
Steady auroral red arc, otherwise called mid-latitude red arc or M-arc, is a subvisual (below the limit of sensitivity of the eye) wide arc, stretching from east to west for thousands of kilometers and possibly encircling the entire Earth. The latitudinal length of the arc is 600 km. The emission of 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) were also reported. Sustained 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 (typical value 6 kRl). The sensitivity threshold of the eye at this wavelength is about 10 kRl, so arcs are rarely observed visually. However, observations have shown that their brightness is >50 kRL on 10% of nights. The usual lifespan of arcs is about one day, and they rarely appear in subsequent days. Radio waves from satellites or radio sources crossing persistent auroral red arcs are subject to scintillation, indicating the existence of electron density inhomogeneities. The theoretical explanation for red arcs is that the heated electrons of the region F The ionosphere causes an increase in oxygen atoms. Satellite observations show an increase in electron temperature along geomagnetic field lines that intersect persistent auroral red arcs. The intensity of these arcs is positively correlated with geomagnetic activity (storms), and the frequency of occurrence of arcs is positively correlated with sunspot activity.
Changing aurora.
Some forms of auroras experience quasi-periodic and coherent temporal variations in intensity. These auroras with approximately 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 aurora shape. 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 from 0.01 to 10 Hz of low intensity (1–2 kRl). Most auroras R 1 – these are spots or arcs that pulsate with a period of several seconds.
R 2 (fiery aurora). The term is usually used to refer to movements like flames filling the sky, rather than to describe a distinct form. The auroras have the shape of arcs and usually move upward from a height of 100 km. These auroras are relatively rare and occur more often outside the aurora.
R 3 (shimmering aurora). These are auroras with rapid, irregular or regular variations in brightness, giving the impression of flickering flames in the sky. They appear shortly before the aurora disintegrates. Typically observed frequency of variation 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 quickly horizontally in auroral arcs and streaks.
The changing aurora is one of the solar-terrestrial phenomena that accompany 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 high intensity of the band of the first negative system N + 2 (l 3914 Å). Typically, 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 ranges from 0.1 to 10 kRl (usually 1–3 kRl). During these auroras, which appear during periods of PCA, a uniform glow covers the entire polar cap up to a geomagnetic latitude of 60° at altitudes of 30 to 80 km. It is generated predominantly by solar protons and d-particles with energies of 10–100 MeV, creating a maximum ionization at these altitudes. There is another type of glow in aurora zones, called mantle aurora. For this type of auroral glow, the daily maximum intensity, occurring in the morning hours, is 1–10 kRL, and the minimum intensity is five times weaker. Observations of mantle auroras are few and far between; their intensity depends on geomagnetic and solar activity.
Atmospheric glow is defined as radiation produced and emitted by a planet's atmosphere. This is 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 (nightglow, twilight glow and dayglow). Atmospheric glow constitutes only a portion of the light available in the atmosphere. Other sources include starlight, zodiacal light, and daytime diffuse light from the Sun. At times, the atmospheric glow can be up to 40% total number Sveta. Atmospheric glow occurs in atmospheric layers of varying height and thickness. The atmospheric glow spectrum covers wavelengths from 1000 Å to 22.5 microns. The main emission line in the atmospheric glow is l 5577 Å, appearing at an altitude of 90–100 km in a layer 30–40 km thick. The appearance of luminescence is due to the Chapman mechanism, based on the recombination of oxygen atoms. Other emission lines are l 6300 Å, appearing in the case of dissociative recombination of O + 2 and emission NI l 5198/5201 Å and NI l 5890/5896 Å.
The intensity of airglow is measured in Rayleigh. Brightness (in Rayleigh) is equal to 4 rv, where b is the angular surface brightness of the emitting layer in units of 10 6 photons/(cm 2 ster·s). The intensity of the glow depends on latitude (different for different emissions), and also varies throughout the day with a maximum near midnight. A positive correlation was noted for airglow in the l 5577 Å emission with the number of sunspots and solar radiation flux at a wavelength of 10.7 cm. Airglow is observed during satellite experiments. From outer space, it appears as a ring of light around the Earth and has a greenish color.
Ozonosphere.
At altitudes of 20–25 km, the maximum concentration of an insignificant amount of ozone O 3 is reached (up to 2×10 –7 of the oxygen content!), which arises under the influence of solar ultraviolet radiation at altitudes of approximately 10 to 50 km, 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 deposit all the molecules to the base of the atmosphere, you will 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 individual atoms, which, ionized under the influence of hard radiation from the Sun, form the ionosphere. The pressure and density of air in the Earth's atmosphere decrease with altitude. Depending on the temperature distribution, the Earth's atmosphere is divided into the troposphere, stratosphere, mesosphere, thermosphere and exosphere. .
At an altitude of 20–25 km there is ozone layer. Ozone is formed due to the breakdown of oxygen molecules when absorbing ultraviolet radiation from the Sun with wavelengths shorter than 0.1–0.2 microns. Free oxygen combines with O 2 molecules and forms ozone O 3, which greedily absorbs all ultraviolet radiation shorter than 0.29 microns. O3 ozone molecules are easily destroyed by short-wave radiation. Therefore, despite its rarefaction, the ozone layer effectively absorbs ultraviolet radiation from the Sun that has passed through 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.
Radiation from the sun 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, sequential processes of dissociation of various molecules and subsequent ionization of various atoms and ions occur. These are mainly molecules of oxygen O 2, nitrogen N 2 and their atoms. Depending on the intensity of these processes, the 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 achieved at altitudes of 300–400 km.
History of the study of the ionosphere.
The hypothesis about the existence of a conducting 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 to explain the propagation of radio waves over long distances it was necessary to assume the existence of regions of 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, English researchers Appleton and Barnett, as well as Breit and Tuve, first experimentally proved the existence of regions that reflect radio waves, and laid the foundation for their systematic study. Since that time, a systematic study has been carried out of the properties of these layers, generally called the ionosphere, which play 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 for ensuring 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 pulse probing were created. Many general properties of the ionosphere, heights and electron concentration of its main layers were studied.
At altitudes of 60–70 km layer D is observed, at altitudes of 100–120 km layer 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. | ||||||
| Ionospheric region | Maximum height, km | T i , K | Day | Night n e , cm –3 | a΄, ρm 3 s – 1 | |
| min n e , cm –3 | Max n e , 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 |
| n e– electron concentration, e – electron charge, T i– ion temperature, a΄ – recombination coefficient (which determines the value n e and its change over time) | ||||||
Average values are given because they vary at different latitudes, depending on the time of day and seasons. Such data is necessary to ensure long-distance radio communications. They are used in selecting operating frequencies for various shortwave radio links. Knowledge of their changes depending on the state of the ionosphere at different times of the day and in different seasons extremely important to ensure reliable 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 ultraviolet and X-ray radiation from the Sun, which occurs mainly in the solar chromosphere and corona. In addition, the degree of ionization upper atmosphere influenced by solar corpuscular streams that occur during solar flares, as well as cosmic rays and meteor particles.
Ionospheric layers
- these are areas in the atmosphere in which maximum concentrations 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 atoms of atmospheric gases, interacting with radio waves (i.e., electromagnetic oscillations), can change their direction, reflecting or refracting them, and absorb their energy. As a result of this, when receiving distant radio stations, various effects may occur, for example, fading of radio communications, increased audibility of remote stations, blackouts and so on. phenomena.
Research methods.
Classical methods of studying the ionosphere from Earth come down to pulse sounding - sending radio pulses and observing their reflections from various layers of the ionosphere, measuring the delay time and studying the intensity and shape of the reflected signals. By measuring the heights of reflection of radio pulses at various frequencies, determining the critical frequencies of various areas (the critical frequency is the carrier frequency of a radio pulse, for which a given region of the ionosphere becomes transparent), it is possible to determine the value of the electron concentration in the layers and the effective heights for given frequencies, and select 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 near-Earth space plasma, the lower part of which is the ionosphere.
Measurements of electron concentration, carried out on board specially launched rockets and along satellite flight paths, confirmed and clarified data previously obtained by ground-based methods on the structure of the ionosphere, the distribution of electron concentration with height above various regions of the Earth and made it possible to obtain electron concentration values above the main maximum - the layer F. Previously, this was impossible to do using sounding methods based on observations of reflected short-wave radio pulses. It has been discovered that in some areas of the globe there are quite stable areas with a reduced electron concentration, 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 particularly highly sensitive receiving devices made it possible to receive pulse signals partially reflected from the lowest regions of the ionosphere (partial reflection stations) at ionospheric pulse sounding stations. The use of powerful pulsed installations in the meter and decimeter wavelength ranges with the use of antennas that allow for a high concentration of emitted energy made it possible to observe signals scattered by the ionosphere at various altitudes. 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 quite transparent for the frequencies used.
The concentration of electric charges (the electron concentration is equal to the ion concentration) in the earth's ionosphere at an altitude of 300 km is about 10 6 cm –3 during the day. Plasma of such density reflects radio waves with a length of more than 20 m, and transmits shorter ones.
Typical vertical distribution of electron concentration in the ionosphere for day and night conditions.
Propagation of radio waves in the ionosphere.
Stable reception of long-distance 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 travel 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 the plates of a huge capacitor, acting on them like the effect of mirrors on light. Reflecting from them, radio waves can travel many thousands of kilometers, circling 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 20s of the last century, 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-distance reception of short waves across the Atlantic between Europe and America were carried out by English physicist Oliver Heaviside and American electrical engineer Arthur Kennelly. Independently of each other, they suggested that somewhere around the Earth there is an ionized layer of the atmosphere capable of reflecting radio waves. It was called the Heaviside-Kennelly layer, and then the ionosphere.
According to modern ideas 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 ionization of neutral gas atoms by solar X-rays and ultraviolet radiation. In order to ionize an atom, it is necessary to impart ionization energy to it, the main source of which for the ionosphere is ultraviolet, x-ray and corpuscular radiation from the Sun.
Bye gas envelope The Earth is illuminated by the Sun, more and more electrons are continuously being formed in it, but at the same time some of the electrons, colliding with ions, recombine, again forming neutral particles. After sunset, the formation of new electrons almost stops, and the number of free electrons begins to decrease. The more free electrons there are in the ionosphere, the better high-frequency waves are reflected from it. With a decrease in 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 altitudes from 50 to 400 km there are several layers or regions of increased electron concentration. These areas smoothly transition into one another and have different effects on the propagation of HF radio waves. The upper layer of the ionosphere is designated by the letter F. Here 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-distance propagation of high-frequency HF radio waves. In the summer months, region F splits into two layers - F 1 and F 2. Layer F1 can occupy heights from 200 to 250 km, and 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 the layer F 2 remains, slowly losing up to 60% of its degree of ionization. Below layer F at altitudes from 90 to 150 km there is a layer E ionization of which 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 in the low-frequency HF ranges of 31 and 25 m occurs when signals are reflected from the layer E. Typically these are stations located at a distance of 1000–1500 km. At night in the layer E Ionization decreases sharply, but even at this time it continues to play a significant role in the reception of signals from stations on the 41, 49 and 75 m ranges.
Of great interest for receiving signals of high-frequency HF ranges of 16, 13 and 11 m are those arising in the area E layers (clouds) of highly 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 is designated 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 mid-latitudes 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 in high latitudes it usually appears at night. Sometimes, during years of low solar activity, when there is no transmission on the high-frequency HF bands, distant stations suddenly appear on the 16, 13 and 11 m bands with good volume, the signals of which are reflected many times 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 the area D Long and medium waves are well reflected, and signals from 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. Individual layers of the ionosphere play an important role in the propagation of HF radio signals. The effect on radio waves occurs mainly due to the presence of free electrons in the ionosphere, although the mechanism of radio wave propagation is associated with the presence of large ions. The latter are also of interest when studying 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 using geophysical rockets and satellites have provided a wealth of new information, indicating that 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, which has a shorter wavelength and higher energy than violet light rays, is emitted by hydrogen in the Sun's inner atmosphere (the chromosphere), and X-rays, which have even higher energy, are emitted by gases in the Sun's outer shell (the corona).
The normal (average) state of the ionosphere is due to constant powerful radiation. Regular changes occur in the normal ionosphere due to 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 International Geophysical Year (IGY) program 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 to two hours. During the flare, solar plasma (mostly protons and electrons) is erupted, and elementary particles rush into outer space. Electromagnetic and corpuscular radiation from the Sun during such flares has a strong impact on the Earth's atmosphere.
The initial reaction is observed 8 minutes after the flare, when intense ultraviolet and X-ray radiation reaches the Earth. As a result, ionization increases sharply; 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”). The additional absorption of radiation causes the gas to heat up, 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 occurs and an electric current is created. Such currents can, in turn, cause noticeable disturbances in the magnetic field and manifest themselves in the form of magnetic storms.
The structure and dynamics of the upper atmosphere are significantly determined by non-equilibrium processes in the thermodynamic sense associated with ionization and dissociation by solar radiation, chemical processes, excitation of molecules and atoms, their deactivation, collisions 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 higher, the degree of nonequilibrium for many characteristics of the upper atmosphere is quite small, which makes it possible to use classical and hydromagnetic hydrodynamics, taking into account 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
Materials on the Internet: http://ciencia.nasa.gov/
The structure of the Earth's atmosphere
The atmosphere is the gaseous shell of the Earth with the aerosol particles it contains, moving together with the Earth in space as a single whole and at the same time taking part in the rotation of the Earth. Most of our life takes place at the bottom of the atmosphere.
Almost all of our planets have their own atmospheres. solar system, but only the earth's atmosphere is capable of supporting life.
When our planet formed 4.5 billion years ago, it was apparently devoid of an atmosphere. The atmosphere was formed as a result of volcanic emissions of water vapor mixed with carbon dioxide, nitrogen and other chemicals from the interior of the young planet. But the atmosphere can contain a limited amount of moisture, so its excess as a result of condensation gave rise to the oceans. But then the atmosphere was devoid of oxygen. The first living organisms that originated and developed in the ocean, as a result of the photosynthesis reaction (H 2 O + CO 2 = CH 2 O + O 2), began to release small portions of oxygen, which began to enter the atmosphere.
The formation of oxygen in the Earth's atmosphere led to the formation of the ozone layer at altitudes of approximately 8 – 30 km. And, thus, our planet has acquired protection from the harmful effects of ultraviolet study. This circumstance served as an impetus for the further evolution of life forms on Earth, because As a result of increased photosynthesis, the amount of oxygen in the atmosphere began to grow rapidly, which contributed to the formation and maintenance of life forms, including on land.
Today our atmosphere consists of 78.1% nitrogen, 21% oxygen, 0.9% argon, and 0.04% carbon dioxide. Very small fractions compared to the main gases are neon, helium, methane, and krypton.
The gas particles contained in the atmosphere are affected by the force of gravity of the Earth. And, given that air is compressible, its density gradually decreases with height, passing into outer space without a clear boundary. Half of the total mass of the earth's atmosphere is concentrated in the lower 5 km, three quarters in the lower 10 km, nine tenths in the lower 20 km. 99% of the mass of the Earth's atmosphere is concentrated below an altitude of 30 km, which is only 0.5% of the equatorial radius of our planet.
At sea level, the number of atoms and molecules per cubic centimeter of air is about 2 * 10 19, at an altitude of 600 km only 2 * 10 7. At sea level, an atom or molecule travels approximately 7 * 10 -6 cm before colliding with another particle. At an altitude of 600 km this distance is about 10 km. And at sea level, about 7 * 10 9 such collisions occur every second, at an altitude of 600 km - only about one per minute!
But not only pressure changes with altitude. The temperature also changes. For example, at the foot of a high mountain it can be quite hot, while the top of the mountain is covered with snow and the temperature there is at the same time below zero. And if you take a plane to an altitude of about 10-11 km, you can hear a message that it is -50 degrees outside, while at the surface of the earth it is 60-70 degrees warmer...
Initially, scientists assumed that the temperature decreases with height until it reaches absolute zero (-273.16°C). But that's not true.
The Earth's atmosphere consists of four layers: troposphere, stratosphere, mesosphere, ionosphere (thermosphere). This division into layers was also adopted based on data on temperature changes with height. The lowest layer, where air temperature decreases with height, is called the troposphere. The layer above the troposphere, where the temperature drop stops, is replaced by isotherm, and finally the temperature begins to rise, is called the stratosphere. The layer above the stratosphere in which the temperature rapidly drops again is the mesosphere. And finally, the layer where the temperature begins to rise again is called the ionosphere or thermosphere.
The troposphere extends on average to the lower 12 km. This is where our weather is formed. The highest clouds (cirrus) form in the uppermost layers of the troposphere. The temperature in the troposphere decreases adiabatically with height, i.e. The temperature change occurs due to the decrease in pressure with height. The temperature profile of the troposphere is largely determined by solar radiation reaching the Earth's surface. As a result of the heating of the Earth's surface by the Sun, convective and turbulent flows are formed, directed upward, which form the weather. It is worth noting that the influence of the underlying surface on the lower layers of the troposphere extends to a height of approximately 1.5 km. Of course, excluding mountainous areas.
The upper boundary of the troposphere is the tropopause - an isothermal layer. Remember characteristic appearance thunderclouds whose top is a “burst” of cirrus clouds called an “anvil.” This “anvil” just “spreads” under the tropopause, because due to isotherm, the ascending air currents are significantly weakened, and the cloud stops developing vertically. But in special, rare cases, the tops of cumulonimbus clouds can invade the lower layers of the stratosphere, breaking the tropopause.
The height of the tropopause depends on latitude. Thus, at the equator it is located at an altitude of approximately 16 km, and its temperature is about –80°C. At the poles, the tropopause is located lower, at approximately 8 km altitude. In summer the temperature here is –40°C, and –60°C in winter. Thus, despite higher temperatures at the Earth's surface, the tropical tropopause is much colder than at the poles.
The atmosphere is one of the most important components of our planet. It is she who “shelters” people from the harsh conditions of outer space, such as solar radiation and space debris. However, many facts about the atmosphere are unknown to most people.
1. True color of the sky
Although it's hard to believe, the sky is actually purple. When light enters the atmosphere, air and water particles absorb the light, scattering it. In this case, most of all dissipates purple That's why people see blue skies.
2. An exclusive element in the Earth's atmosphere
As many remember from school, the Earth's atmosphere consists of approximately 78% nitrogen, 21% oxygen and small amounts of argon, carbon dioxide and other gases. But few people know that our atmosphere is the only one so far discovered by scientists (besides comet 67P) that has free oxygen. Because oxygen is a highly reactive gas, it often reacts with other chemicals in space. Its pure form on Earth makes the planet habitable.
3. White stripe in the sky
Surely, some people have sometimes wondered why a white stripe remains in the sky behind a jet plane. These white trails, known as contrails, form when hot, humid exhaust gases from a plane's engine mix with cooler outside air. Water vapor from the exhaust freezes and becomes visible.
4. Main layers of the atmosphere
The Earth's atmosphere consists of five main layers, which make life on the planet possible. The first of these, the troposphere, extends from sea level to an altitude of about 17 km at the equator. Most weather events occur here.
5. Ozone layer
The next layer of the atmosphere, the stratosphere, reaches an altitude of approximately 50 km at the equator. It contains the ozone layer, which protects people from dangerous ultraviolet rays. Even though this layer is above the troposphere, it may actually be warmer due to the energy absorbed from the sun's rays. Most jet planes and weather balloons fly in the stratosphere. Airplanes can fly faster in it because they are less affected by gravity and friction. Weather balloons can provide a better picture of storms, most of which occur lower in the troposphere.6. Mesosphere
The mesosphere is the middle layer, extending to a height of 85 km above the surface of the planet. Its temperature hovers around -120 °C. Most meteors that enter the Earth's atmosphere burn up in the mesosphere. The last two layers that extend into space are the thermosphere and exosphere.
7. Disappearance of the atmosphere
The Earth most likely lost its atmosphere several times. When the planet was covered in oceans of magma, massive interstellar objects crashed into it. These impacts, which also formed the Moon, may have formed the planet's atmosphere for the first time.
8. If there were no atmospheric gases...
Without the various gases in the atmosphere, the Earth would be too cold for human existence. Water vapor, carbon dioxide and other atmospheric gases absorb heat from the sun and “distribute” it across the planet's surface, helping to create a habitable climate.
9. Formation of the ozone layer
The notorious (and essential) ozone layer was created when oxygen atoms reacted with ultraviolet light from the sun to form ozone. It is ozone that absorbs most of the harmful radiation from the sun. Despite its importance, the ozone layer was formed relatively recently after enough life arose in the oceans to release into the atmosphere the amount of oxygen needed to create a minimum concentration of ozone
10. Ionosphere
The ionosphere is so called because high-energy particles from space and the sun help form ions, creating an "electric layer" around the planet. When there were no satellites, this layer helped reflect radio waves.
11. Acid rain
Acid rain, which destroys entire forests and devastates aquatic ecosystems, forms in the atmosphere when sulfur dioxide or nitrogen oxide particles mix with water vapor and fall to the ground as rain. These chemical compounds are also found in nature: sulfur dioxide is produced during volcanic eruptions, and nitrogen oxide is produced during lightning strikes.
12. Lightning power
Lightning is so powerful that just one bolt can heat the surrounding air up to 30,000°C. The rapid heating causes an explosive expansion of nearby air, which is heard as a sound wave called thunder.
Aurora Borealis and Aurora Australis (northern and southern auroras) are caused by ion reactions occurring in the fourth level of the atmosphere, the thermosphere. When highly charged particles from the solar wind collide with air molecules above the planet's magnetic poles, they glow and create dazzling light shows.
14. Sunsets
Sunsets often look like the sky is on fire as small atmospheric particles scatter the light, reflecting it in orange and yellow hues. The same principle underlies the formation of rainbows.
In 2013, scientists discovered that tiny microbes can survive many kilometers above the Earth's surface. At an altitude of 8-15 km above the planet, microbes were discovered that destroy organic chemicals and float in the atmosphere, “feeding” on them.
Adherents of the theory of the apocalypse and various other horror stories will be interested in learning about.