meteoroid(meteor body) - a celestial body intermediate in size between interplanetary dust and an asteroid.
Here we need to understand a little terminology. Flying at great speed into the Earth's atmosphere, due to friction, it heats up and burns out, turning into a luminous meteor, or a fireball, which can be seen as shooting star. The visible trace of a meteoroid entering the Earth's atmosphere is called meteor, and a meteoroid that fell to the surface of the Earth - meteorite.
The solar system is full of these small space debris, which are called meteoroids. It can be dust particles from comets, large boulders, or even fragments of broken asteroids.
According to the official definition of the International Meteor Organization (IMO), meteoroid is a solid object moving in interplanetary space, the size is significantly smaller than an asteroid but much larger than an atom. The British Royal Astronomical Society put forward another formulation, according to which a meteoroid is a body with a diameter of 100 microns to 10 m.
is not an object, but phenomenon, i.e. glowing trace of a meteoroid. Regardless of whether it flies out of the atmosphere back into outer space, whether it burns up in the atmosphere or falls to Earth as a meteorite, this phenomenon is called a meteor.
The distinctive characteristics of a meteor, in addition to mass and size, are its speed, ignition height, track length (visible path), brightness of the glow and chemical composition (affects the color of combustion).
Meteors often cluster into meteor showers- constant masses of meteors that appear at a certain time of the year, in a certain side of the sky. The meteor showers Leonids, Quadrantids and Perseids are known. All meteor showers are generated by comets as a result of destruction during the melting process during the passage of the inner part of the solar system.
The trail of a meteor usually disappears in a matter of seconds, but can sometimes remain for minutes and move under the influence of the wind at the height of the meteor. Sometimes the Earth crosses the orbits of meteoroids. Then, passing through the earth's atmosphere and warming up, they flare up with bright stripes of light, which are called meteors, or shooting stars.
On a clear night, you can see several meteors in an hour. And when the Earth passes through a stream of dust particles left behind by a passing comet, dozens of meteors can be seen every hour.
Pieces of meteoroids that survived after passing through the atmosphere as meteors and fell to the ground in the form of charred stones are sometimes found. They are usually dark in color and very heavy. Sometimes they look rusty. It happens that meteorites break through the roofs of houses or fall near the house. But the danger of being hit by a meteorite for a person is negligible. The only documented case of a meteorite hitting a person occurred on November 30, 1954 in the state of Alabama. A meteorite weighing about 4 kg broke through the roof of the house and ricocheted Anna Elizabeth Hodges on the arm and thigh. The woman received bruises.
In addition to visual and photographic methods for studying meteors, electron-optical, spectrometric, and especially radar methods have recently developed, based on the property of a meteor trail to scatter radio waves. Radio meteor sounding and the study of the movement of meteor trails provide important information about the state and dynamics of the atmosphere at altitudes of about 100 km. It is possible to create meteor radio channels.
A body of cosmic origin that fell onto the surface of a large celestial object.
Most meteorites found have a weight of several grams to several kilograms. The largest meteorite ever found Goba(weight about 60 tons). It is believed that 5-6 tons of meteorites fall on Earth per day, or 2 thousand tons per year.
The Russian Academy of Sciences now has a special committee that manages the collection, study and storage of meteorites. The committee has a large meteorite collection.
At the site of the fall of a large meteorite, crater(astrobleme). One of the most famous craters in the world - Arizona. It is assumed that the largest meteorite crater on Earth - Wilkes Land crater in Antarctica(diameter about 500 km).
How does this happen
A meteor enters the Earth's atmosphere at a speed of 11 to 72 km/s. At this speed, it begins to warm up and glow. at the expense ablation(burning and blowing away by the oncoming flow of particles of the substance of the meteoric body), the mass of the body that reached the surface may be less, and in some cases significantly less than its mass at the entrance to the atmosphere. For example, a small body that enters the Earth's atmosphere at a speed of 25 km/s or more burns out almost completely. At such a rate of entry into the atmosphere, out of tens and hundreds of tons of initial mass, only a few kilograms or even grams of matter reach the surface. Traces of the combustion of a meteoroid in the atmosphere can be found throughout almost the entire trajectory of its fall.
If the meteor body did not burn up in the atmosphere, then as it decelerates, it loses the horizontal component of velocity. This leads to a change in the trajectory of the fall. As the meteorite slows down, the glow of the meteorite falls, it cools down (it is often indicated that the meteorite was warm, not hot, during the fall).
In addition, the destruction of the meteoroid into fragments may occur, which leads to a meteor shower.
Large meteorites discovered in Russia
Tunguska meteorite(at the moment it is unclear exactly the meteorite origin of the Tunguska phenomenon). Fell June 30, 1908 in the basin of the Podkamennaya Tunguska River in Siberia. The total energy is estimated at 40-50 megatons of TNT.
Tsarevsky meteorite(meteor Rain). Fell December 6, 1922 near the village of Tsarev, Volgograd region. This is a stone meteorite. The total mass of the collected fragments is 1.6 tons over an area of about 15 square meters. km. The weight of the largest fallen fragment was 284 kg.
Sikhote-Alin meteorite(the total mass of fragments is 30 tons, the energy is estimated at 20 kilotons). It was an iron meteorite. Fell in the Ussuri taiga on February 12, 1947.
Vitim fireball. Fell near the villages of Mama and Vitimsky, Mamsko-Chuysky district, Irkutsk region, on the night of September 24-25, 2002. The total energy of the meteorite explosion, apparently, is relatively small (200 tons of TNT, with an initial energy of 2.3 kilotons), the maximum the initial mass (before combustion in the atmosphere) is 160 tons, and the final mass of fragments is about several hundred kilograms.
Although meteorites fall to Earth often, the discovery of a meteorite is a rather rare occurrence. The meteoritics laboratory reports: “In total, only 125 meteorites have been found on the territory of the Russian Federation in 250 years.”
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 that were present in the original atmosphere of the Earth entered into chemical reactions, as a result of which organic substances, in particular amino acids, were formed. With the advent of primitive plants, the process of photosynthesis began, accompanied by the release of oxygen. This gas, especially after diffusion into the upper atmosphere, began to protect its lower layers and the Earth's surface from life-threatening ultraviolet and X-ray radiation. According to theoretical estimates, the oxygen content, which is 25,000 times lower than now, could already lead to the formation of an ozone layer with only half as much as it is now. However, this is already enough to provide a very significant protection of organisms from the damaging effects of ultraviolet rays.
It is likely that the primary atmosphere contained a lot of carbon dioxide. It was consumed during photosynthesis, and its concentration must have decreased as the plant world evolved, and also due to absorption during some geological processes. Insofar as the greenhouse effect associated with the presence of carbon dioxide in the atmosphere, fluctuations in its concentration are one of the important causes of such large-scale climatic changes in the history of the Earth, such as ice ages.
The helium present in the modern atmosphere is mostly a product of the radioactive decay of uranium, thorium and radium. These radioactive elements emit a-particles, which are the nuclei of helium atoms. Since an electric charge is not formed and does not disappear during radioactive decay, with the formation of each a-particle, two electrons appear, which, recombining with a-particles, form neutral helium atoms. Radioactive elements are contained in minerals dispersed in the thickness of rocks, so a significant part of the helium formed as a result of radioactive decay is stored in them, volatilizing very slowly into the atmosphere. A certain amount of helium rises up into the exosphere due to diffusion, but due to the constant influx from the earth's surface, the volume of this gas in the atmosphere remains almost unchanged. Based on the spectral analysis of starlight and the study of meteorites, it is possible to estimate the relative abundance of various chemical elements in the Universe. The concentration of neon in space is about ten billion times higher than on Earth, krypton - ten million times, and xenon - a million times. It follows from this that the concentration of these inert gases, apparently originally present in the Earth's atmosphere and not replenished in the course of chemical reactions, greatly decreased, probably even at the stage of the Earth's loss of its primary atmosphere. An exception is the inert gas argon, since it is still formed in the form of the 40 Ar isotope in the process of radioactive decay of the potassium isotope.
Barometric pressure distribution.
The total weight of atmospheric gases is approximately 4.5 10 15 tons. Thus, the "weight" of the atmosphere per unit area, or atmospheric pressure, is approximately 11 t / m 2 = 1.1 kg / cm 2 at sea level. Pressure equal to P 0 \u003d 1033.23 g / cm 2 \u003d 1013.250 mbar \u003d 760 mm Hg. Art. = 1 atm, taken as the standard mean atmospheric pressure. For an atmosphere in hydrostatic equilibrium, we have: d P= -rgd h, which means that on the interval of heights from h before h+d h takes place equality between atmospheric pressure change d P and the weight of the corresponding element of the atmosphere with unit area, density r and thickness d h. As a ratio between pressure R and temperature T the equation of state of an ideal gas with density r, which is quite applicable for the earth's atmosphere, is used: P= r R T/m, where m is the molecular weight, and R = 8.3 J/(K mol) is the universal gas constant. Then dlog P= – (m g/RT)d h= -bd h= – d h/H, where the pressure gradient is on a logarithmic scale. The reciprocal of H is to be called the scale of the height of the atmosphere.
When integrating this equation for an isothermal atmosphere ( T= const) or for its part, where such an approximation is acceptable, the barometric law of pressure distribution with height is obtained: P = P 0 exp(- h/H 0), where the height reading h produced from ocean level, where the standard mean pressure is P 0 . Expression H 0=R T/ mg, is called the height scale, which characterizes the extent of the atmosphere, provided that the temperature in it is the same everywhere (isothermal atmosphere). If the atmosphere is not isothermal, then it is necessary to integrate taking into account the change in temperature with height, and the parameter H- some local characteristic of the layers of the atmosphere, depending on their temperature and the properties of the medium.
Standard atmosphere.
Model (table of values of the main parameters) corresponding to the standard pressure at the base of the atmosphere R 0 and chemical composition is called the standard atmosphere. More precisely, this is a conditional model of the atmosphere, for which the average values of temperature, pressure, density, viscosity, and other air characteristics for a latitude of 45° 32° 33І are set at altitudes from 2 km below sea level to the outer boundary of the earth's atmosphere. The parameters of the middle atmosphere at all altitudes were calculated using the ideal gas equation of state and the barometric law assuming that at sea level the pressure is 1013.25 hPa (760 mmHg) and the temperature is 288.15 K (15.0°C). According to the nature of the vertical temperature distribution, the average atmosphere consists of several layers, in each of which the temperature is approximated by a linear function of height. In the lowest of the layers - the troposphere (h Ј 11 km), the temperature drops by 6.5 ° C with each kilometer of ascent. At high altitudes, the value and sign of the vertical temperature gradient change from layer to layer. Above 790 km, the temperature is about 1000 K and practically does not change with height.
The standard atmosphere is a periodically updated, legalized standard, issued in the form of tables.
| Table 1. STANDARD EARTH ATMOSPHERE MODEL. The table shows: h- height from sea level, R- pressure, T– temperature, r – density, N is the number of molecules or atoms per unit volume, H- height scale, l is the length of the free path. Pressure and temperature at an altitude of 80–250 km, obtained from rocket data, have lower values. Extrapolated values for heights greater than 250 km are not very accurate. | ||||||
| h(km) | P(mbar) | T(°C) | r (g / cm 3) | N(cm -3) | H(km) | l(cm) |
| 0 | 1013 | 288 | 1.22 10 -3 | 2.55 10 19 | 8,4 | 7.4 10 -6 |
| 1 | 899 | 281 | 1.11 10 -3 | 2.31 10 19 | 8.1 10 -6 | |
| 2 | 795 | 275 | 1.01 10 -3 | 2.10 10 19 | 8.9 10 -6 | |
| 3 | 701 | 268 | 9.1 10 -4 | 1.89 10 19 | 9.9 10 -6 | |
| 4 | 616 | 262 | 8.2 10 -4 | 1.70 10 19 | 1.1 10 -5 | |
| 5 | 540 | 255 | 7.4 10 -4 | 1.53 10 19 | 7,7 | 1.2 10 -5 |
| 6 | 472 | 249 | 6.6 10 -4 | 1.37 10 19 | 1.4 10 -5 | |
| 8 | 356 | 236 | 5.2 10 -4 | 1.09 10 19 | 1.7 10 -5 | |
| 10 | 264 | 223 | 4.1 10 -4 | 8.6 10 18 | 6,6 | 2.2 10 -5 |
| 15 | 121 | 214 | 1.93 10 -4 | 4.0 10 18 | 4.6 10 -5 | |
| 20 | 56 | 214 | 8.9 10 -5 | 1.85 10 18 | 6,3 | 1.0 10 -4 |
| 30 | 12 | 225 | 1.9 10 -5 | 3.9 10 17 | 6,7 | 4.8 10 -4 |
| 40 | 2,9 | 268 | 3.9 10 -6 | 7.6 10 16 | 7,9 | 2.4 10 -3 |
| 50 | 0,97 | 276 | 1.15 10 -6 | 2.4 10 16 | 8,1 | 8.5 10 -3 |
| 60 | 0,28 | 260 | 3.9 10 -7 | 7.7 10 15 | 7,6 | 0,025 |
| 70 | 0,08 | 219 | 1.1 10 -7 | 2.5 10 15 | 6,5 | 0,09 |
| 80 | 0,014 | 205 | 2.7 10 -8 | 5.0 10 14 | 6,1 | 0,41 |
| 90 | 2.8 10 -3 | 210 | 5.0 10 -9 | 9 10 13 | 6,5 | 2,1 |
| 100 | 5.8 10 -4 | 230 | 8.8 10 -10 | 1.8 10 13 | 7,4 | 9 |
| 110 | 1.7 10 -4 | 260 | 2.1 10 –10 | 5.4 10 12 | 8,5 | 40 |
| 120 | 6 10 -5 | 300 | 5.6 10 -11 | 1.8 10 12 | 10,0 | 130 |
| 150 | 5 10 -6 | 450 | 3.2 10 -12 | 9 10 10 | 15 | 1.8 10 3 |
| 200 | 5 10 -7 | 700 | 1.6 10 -13 | 5 10 9 | 25 | 3 10 4 |
| 250 | 9 10 -8 | 800 | 3 10 -14 | 8 10 8 | 40 | 3 10 5 |
| 300 | 4 10 -8 | 900 | 8 10 -15 | 3 10 8 | 50 | |
| 400 | 8 10 -9 | 1000 | 1 10 –15 | 5 10 7 | 60 | |
| 500 | 2 10 -9 | 1000 | 2 10 -16 | 1 10 7 | 70 | |
| 700 | 2 10 –10 | 1000 | 2 10 -17 | 1 10 6 | 80 | |
| 1000 | 1 10 –11 | 1000 | 1 10 -18 | 1 10 5 | 80 | |
Troposphere.
The lowest and densest layer of the atmosphere, in which the temperature decreases rapidly with height, is called the troposphere. It contains up to 80% of the total mass of the atmosphere and extends in polar and middle latitudes up to heights of 8–10 km, and in the tropics up to 16–18 km. Almost all weather-forming processes develop here, heat and moisture exchange occurs between the Earth and its atmosphere, clouds form, various meteorological phenomena occur, fogs and precipitation occur. These layers of the earth's atmosphere are in convective equilibrium and, due to active mixing, have a homogeneous chemical composition, mainly from molecular nitrogen (78%) and oxygen (21%). The vast majority of natural and man-made aerosol and gas air pollutants are concentrated in the troposphere. The dynamics of the lower part of the troposphere up to 2 km thick strongly depends on the properties of the underlying surface of the Earth, which determines the horizontal and vertical movements of air (winds) due to the transfer of heat from a warmer land through the IR radiation of the earth's surface, which is absorbed in the troposphere, mainly by vapor water and carbon dioxide (greenhouse effect). The temperature distribution with height is established as a result of turbulent and convective mixing. On average, it corresponds to a drop in temperature with height of about 6.5 K/km.
The wind speed in the surface boundary layer first increases rapidly with height, and higher it continues to increase by 2–3 km/s per kilometer. Sometimes in the troposphere there are narrow planetary streams (with a speed of more than 30 km / s), western ones in middle latitudes, and eastern ones near the equator. They are called jet streams.
tropopause.
At the upper boundary of the troposphere (tropopause), the temperature reaches its minimum value for the lower atmosphere. This is the transition layer between the troposphere and the stratosphere above it. The thickness of the tropopause is from hundreds of meters to 1.5–2 km, and the temperature and altitude, respectively, range from 190 to 220 K and from 8 to 18 km, depending on the geographic latitude and season. In temperate and high latitudes, in winter it is 1–2 km lower than in summer and 8–15 K warmer. In the tropics, seasonal changes are much less (altitude 16–18 km, temperature 180–200 K). Above jet streams possible rupture of the tropopause.
Water in the Earth's atmosphere.
The most important feature of the Earth's atmosphere is the presence of a significant amount of water vapor and water in droplet form, which is most easily observed in the form of clouds and cloud structures. The degree of cloud coverage of the sky (at a certain moment or on average over a certain period of time), expressed on a 10-point scale or as a percentage, is called cloudiness. The shape of the clouds is determined by the international classification. On average, clouds cover about half of the globe. Cloudiness is an important factor characterizing weather and climate. In winter and at night, cloudiness prevents a decrease in the temperature of the earth's surface and the surface layer of air, in summer and during the day it weakens the heating of the earth's surface by the sun's rays, softening the climate inside the continents.
Clouds.
Clouds are accumulations of water droplets suspended in the atmosphere (water clouds), ice crystals (ice clouds), or both (mixed clouds). As drops and crystals become larger, they fall out of the clouds in the form of precipitation. Clouds form mainly in the troposphere. They result from the condensation of water vapor contained in the air. The diameter of cloud drops is on the order of several microns. The content of liquid water in clouds is from fractions to several grams per m3. Clouds are distinguished by height: According to the international classification, there are 10 genera of clouds: cirrus, cirrocumulus, cirrostratus, altocumulus, altostratus, stratonimbus, stratus, stratocumulus, cumulonimbus, cumulus.
Mother-of-pearl clouds are also observed in the stratosphere, and noctilucent clouds in the mesosphere.
Cirrus clouds - transparent clouds in the form of thin white threads or veils with a silky sheen, not giving a shadow. Cirrus clouds are made up of ice crystals and form in the upper troposphere at very low temperatures. Some types of cirrus clouds serve as harbingers of weather changes.
Cirrocumulus clouds are ridges or layers of thin white clouds in the upper troposphere. Cirrocumulus clouds are built from small elements that look like flakes, ripples, small balls without shadows and consist mainly of ice crystals.
Cirrostratus clouds - a whitish translucent veil in the upper troposphere, usually fibrous, sometimes blurry, consisting of small needle or columnar ice crystals.
Altocumulus clouds are white, gray or white-gray clouds of the lower and middle layers of the troposphere. Altocumulus clouds look like layers and ridges, as if built from plates lying one above the other, rounded masses, shafts, flakes. Altocumulus clouds form during intense convective activity and usually consist of supercooled water droplets.
Altostratus clouds are grayish or bluish clouds of a fibrous or uniform structure. Altostratus clouds are observed in the middle troposphere, extending several kilometers in height and sometimes thousands of kilometers in a horizontal direction. Usually, altostratus clouds are part of frontal cloud systems associated with ascending movements of air masses.
Nimbostratus clouds - a low (from 2 km and above) amorphous layer of clouds of a uniform gray color, giving rise to overcast rain or snow. Nimbostratus clouds - highly developed vertically (up to several km) and horizontally (several thousand km), consist of supercooled water drops mixed with snowflakes, usually associated with atmospheric fronts.
Stratus clouds - clouds of the lower tier in the form of a homogeneous layer without definite outlines, gray in color. The height of stratus clouds above the earth's surface is 0.5–2 km. Occasional drizzle falls from stratus clouds.
Cumulus clouds are dense, bright white clouds during the day with significant vertical development (up to 5 km or more). The upper parts of cumulus clouds look like domes or towers with rounded outlines. Cumulus clouds usually form as convection clouds in cold air masses.
Stratocumulus clouds - low (below 2 km) clouds in the form of gray or white non-fibrous layers or ridges of round large blocks. The vertical thickness of stratocumulus clouds is small. Occasionally, stratocumulus clouds give light precipitation.
Cumulonimbus clouds are powerful and dense clouds with strong vertical development (up to a height of 14 km), giving heavy rainfall with thunderstorms, hail, squalls. Cumulonimbus clouds develop from powerful cumulus clouds, differing from them in the upper part, consisting of ice crystals.
Stratosphere.
Through the tropopause, on average at altitudes from 12 to 50 km, the troposphere passes into the stratosphere. In the lower part, for about 10 km, i.e. up to heights of about 20 km, it is isothermal (temperature about 220 K). Then it increases with altitude, reaching a maximum of about 270 K at an altitude of 50–55 km. Here is the boundary between the stratosphere and the overlying mesosphere, called the stratopause. .
There is much less water vapor in the stratosphere. Nevertheless, thin translucent mother-of-pearl clouds are occasionally observed, occasionally appearing in the stratosphere at a height of 20–30 km. Mother-of-pearl clouds are visible in the dark sky after sunset and before sunrise. In shape, mother-of-pearl clouds resemble cirrus and cirrocumulus clouds.
Middle atmosphere (mesosphere).
At an altitude of about 50 km, the mesosphere begins with the peak of a wide temperature maximum. . The reason for the increase in temperature in the region of this maximum is an exothermic (i.e., accompanied by the release of heat) photochemical reaction of ozone decomposition: O 3 + hv® O 2 + O. Ozone arises as a result of the photochemical decomposition of molecular oxygen O 2
About 2+ hv® O + O and the subsequent reaction of a triple collision of an atom and an oxygen molecule with some third molecule M.
O + O 2 + M ® O 3 + M
Ozone greedily absorbs ultraviolet radiation in the region from 2000 to 3000Å, and this radiation heats up the atmosphere. Ozone, located in the upper atmosphere, serves as a kind of shield that protects us from the action of ultraviolet radiation from the sun. Without this shield, the development of life on Earth in its modern forms would hardly have been possible.
In general, throughout the mesosphere, the temperature of the atmosphere decreases to its minimum value of about 180 K at the upper boundary of the mesosphere (called the mesopause, height is about 80 km). In the vicinity of the mesopause, at altitudes of 70–90 km, a very thin layer of ice crystals and particles of volcanic and meteorite dust can appear, observed in the form of a beautiful spectacle of noctilucent clouds. shortly after sunset.
In the mesosphere, for the most part, small solid meteorite particles that fall on the Earth are burned, causing the phenomenon of meteors.
Meteors, meteorites and fireballs.
Flares and other phenomena in the upper atmosphere of the Earth caused by the intrusion into it at a speed of 11 km / s and above solid cosmic particles or bodies are called meteoroids. There is an observed bright meteor trail; the most powerful phenomena, often accompanied by the fall of meteorites, are called fireballs; meteors are associated with meteor showers.
meteor shower:
1) the phenomenon of multiple meteor falls over several hours or days from one radiant.
2) a swarm of meteoroids moving in one orbit around the Sun.
The systematic appearance of meteors in a certain region of the sky and on certain days of the year, caused by the intersection of the Earth's orbit with a common orbit of many meteorite bodies moving at approximately the same and equally directed speeds, due to which their paths in the sky seem to come out of one common point (radiant) . They are named after the constellation where the radiant is located.
Meteor showers make a deep impression with their lighting effects, but individual meteors are rarely seen. Far more numerous are invisible meteors, too small to be seen at the moment they are swallowed up by the atmosphere. Some of the smallest meteors probably do not heat up at all, but are only captured by the atmosphere. These small particles ranging in size from a few millimeters to ten-thousandths of a millimeter are called micrometeorites. The amount of meteoric matter entering the atmosphere every day is from 100 to 10,000 tons, with most of this matter being micrometeorites.
Since meteoric matter partially burns up in the atmosphere, its gas composition is replenished with traces of various chemical elements. For example, stone meteors bring lithium into the atmosphere. The combustion of metallic meteors leads to the formation of tiny spherical iron, iron-nickel and other droplets that pass through the atmosphere and are deposited on the earth's surface. They can be found in Greenland and Antarctica, where ice sheets remain almost unchanged for years. Oceanologists find them in bottom ocean sediments.
Most of the meteor particles entering the atmosphere are deposited within approximately 30 days. Some scientists believe that this cosmic dust plays an important role in the formation of atmospheric phenomena such as rain, as it serves as the nuclei of water vapor condensation. Therefore, it is assumed that precipitation is statistically associated with large meteor showers. However, some experts believe that since the total input of meteoric matter is many tens of times greater than even with the largest meteor shower, the change in the total amount of this material that occurs as a result of one such shower can be neglected.
However, there is no doubt that the largest micrometeorites and visible meteorites leave long traces of ionization in the high layers of the atmosphere, mainly in the ionosphere. Such traces can be used for long-distance radio communications, as they reflect high-frequency radio waves.
The energy of meteors entering the atmosphere is spent mainly, and perhaps completely, on its heating. This is one of the minor components of the heat balance of the atmosphere.
A meteorite is a solid body of natural origin that fell to the surface of the Earth from space. Usually distinguish stone, iron-stone and iron meteorites. The latter are mainly composed of iron and nickel. Among the found meteorites, most have a weight of several grams to several kilograms. The largest of those found, the Goba iron meteorite weighs about 60 tons and still lies in the same place where it was discovered, in South Africa. Most meteorites are fragments of asteroids, but some meteorites may have come to Earth from the Moon and even from Mars.
A fireball is a very bright meteor, sometimes observed even during the day, often leaving behind a smoky trail and accompanied by sound phenomena; often ends with the fall of meteorites.
Thermosphere.
Above the temperature minimum of the mesopause, the thermosphere begins, in which the temperature, at first slowly, and then quickly, begins to rise again. The reason is the absorption of ultraviolet, solar radiation at altitudes of 150–300 km, due to the ionization of atomic oxygen: O + hv® O + + e.
In the thermosphere, the temperature continuously rises to a height of about 400 km, where it reaches 1800 K in the daytime during the epoch of maximum solar activity. In the epoch of minimum, this limiting temperature can be less than 1000 K. Above 400 km, the atmosphere passes into an isothermal exosphere. The critical level (the base of the exosphere) is located at an altitude of about 500 km.
Auroras and many orbits of artificial satellites, as well as noctilucent clouds - all these phenomena occur in the mesosphere and thermosphere.
Polar Lights.
At high latitudes, auroras are observed during magnetic field disturbances. They may last for several minutes, but are often visible for several hours. Auroras vary greatly in shape, color and intensity, all of which sometimes change very rapidly over time. The aurora spectrum consists of emission lines and bands. Some of the emissions from the night sky are enhanced in the aurora spectrum, primarily the green and red lines of l 5577 Å and l 6300 Å of oxygen. It happens that one of these lines is many times more intense than the other, and this determines the visible color of the radiance: green or red. Disturbances in the magnetic field are also accompanied by disruptions in radio communications in the polar regions. The disruption is caused by changes in the ionosphere, which means that during magnetic storms a powerful source of ionization operates. It has been established that strong magnetic storms occur when there are large groups of spots near the center of the solar disk. Observations have shown that storms are associated not with the spots themselves, but with solar flares that appear during the development of a group of spots.
The auroras are a range of light of varying intensity with rapid movements observed in the high latitude regions of the Earth. The visual aurora contains green (5577Å) and red (6300/6364Å) emission lines of atomic oxygen and N 2 molecular bands, which are excited by energetic particles of solar and magnetospheric origin. These emissions are usually displayed at an altitude of about 100 km and above. The term optical aurora is used to refer to the visual auroras and their infrared to ultraviolet emission spectrum. The radiation energy in the infrared part of the spectrum significantly exceeds the energy of the visible region. When auroras appeared, emissions were observed in the ULF range (
The actual forms of auroras are difficult to classify; The following terms are most commonly used:
1. Calm uniform arcs or stripes. The arc usually extends for ~1000 km in the direction of the geomagnetic parallel (toward the Sun in the polar regions) and has a width from one to several tens of kilometers. A strip is a generalization of the concept of an arc, it usually does not have a regular arcuate shape, but bends in the form of an S or in the form of spirals. Arcs and bands are located at altitudes of 100–150 km.
2. Rays of aurora . This term refers to an auroral structure stretched along magnetic field lines with a vertical extension from several tens to several hundreds of kilometers. The length of the rays along the horizontal is small, from several tens of meters to several kilometers. Rays are usually observed in arcs or as separate structures.
3. Stains or surfaces . These are isolated areas of glow that do not have a specific shape. Individual spots may be related.
4. Veil. An unusual form of aurora, which is a uniform glow that covers large areas of the sky.
According to the structure, the auroras are divided into homogeneous, polish and radiant. Various terms are used; pulsating arc, pulsating surface, diffuse surface, radiant stripe, drapery, etc. There is a classification of auroras according to their color. According to this classification, auroras of the type BUT. The upper part or completely are red (6300–6364 Å). They usually appear at altitudes of 300–400 km during high geomagnetic activity.
Aurora type AT are colored red in the lower part and are associated with the luminescence of the bands of the first positive N 2 system and the first negative O 2 system. Such forms of aurora appear during the most active phases of auroras.
Zones auroras – these are zones of maximum frequency of occurrence of auroras at night, according to observers at a fixed point on the Earth's surface. The zones are located at 67° north and south latitude, and their width is about 6°. The maximum occurrence of auroras, corresponding to a given moment of local geomagnetic time, occurs in oval-like belts (aurora oval), which are located asymmetrically around the north and south geomagnetic poles. The aurora oval is fixed in latitude-time coordinates, and the aurora zone is the locus of points in the midnight region of the oval in latitude-longitude coordinates. The oval belt is located approximately 23° from the geomagnetic pole in the night sector and 15° in the day sector.
Auroral oval and aurora zones. The location of the aurora oval depends on geomagnetic activity. The oval becomes wider at high geomagnetic activity. Aurora zones or aurora oval boundaries are better represented by L 6.4 than by dipole coordinates. The geomagnetic field lines at the boundary of the daytime sector of the aurora oval coincide with magnetopause. There is a change in the position of the aurora oval depending on the angle between the geomagnetic axis and the Earth-Sun direction. The auroral oval is also determined on the basis of data on the precipitation of particles (electrons and protons) of certain energies. Its position can be independently determined from data on caspakh on the dayside and in the magnetotail.
The daily variation in the frequency of occurrence of auroras in the aurora zone has a maximum at geomagnetic midnight and a minimum at geomagnetic noon. On the near-equatorial side of the oval, the frequency of occurrence of auroras sharply decreases, but the shape of diurnal variations is retained. On the polar side of the oval, the frequency of occurrence of auroras decreases gradually and is characterized by complex diurnal changes.
Intensity of auroras.
Aurora Intensity determined by measuring the apparent luminance surface. Brightness surface I auroras in a certain direction is determined by the total emission 4p I photon/(cm 2 s). Since this value is not the true surface brightness, but represents the emission from the column, the unit photon/(cm 2 column s) is usually used in the study of auroras. The usual unit for measuring total emission is Rayleigh (Rl) equal to 10 6 photon / (cm 2 column s). A more practical unit of aurora intensity is determined from the emissions of a single line or band. For example, the intensity of the auroras is determined by the international brightness coefficients (ICF) according to the green line intensity data (5577 Å); 1 kRl = I MKH, 10 kRl = II MKH, 100 kRl = III MKH, 1000 kRl = IV MKH (maximum aurora intensity). This classification cannot be used for red auroras. One of the discoveries of the epoch (1957–1958) was the establishment of the spatial and temporal distribution of auroras in the form of an oval displaced relative to the magnetic pole. From simple ideas about the circular shape of the distribution of auroras relative to the magnetic pole, the transition to modern physics of the magnetosphere was completed. The honor of the discovery belongs to O. Khorosheva, and G. Starkov, J. Feldshtein, S-I. The aurora oval is the region of the most intense impact of the solar wind on the Earth's upper atmosphere. The intensity of auroras is greatest in the oval, and its dynamics are continuously monitored by satellites.
Stable auroral red arcs.
Steady auroral red arc, otherwise called the mid-latitude red arc or M-arc, is a subvisual (below the sensitivity limit of the eye) wide arc, stretched from east to west for thousands of kilometers and encircling, possibly, the entire Earth. The latitudinal extent of the arc is 600 km. The emission from the stable auroral red arc is almost monochromatic in the red lines l 6300 Å and l 6364 Å. Recently, weak emission lines l 5577 Å (OI) and l 4278 Å (N + 2) have also been reported. Persistent red arcs are classified as auroras, but they appear at much higher altitudes. The lower limit is located at an altitude of 300 km, the upper limit is about 700 km. The intensity of the quiet auroral red arc in the l 6300 Å emission ranges from 1 to 10 kRl (a typical value is 6 kRl). The sensitivity threshold of the eye at this wavelength is about 10 kR, so arcs are rarely observed visually. However, observations have shown that their brightness is >50 kR on 10% of nights. The usual lifetime of the arcs is about one day, and they rarely appear in the following days. Radio waves from satellites or radio sources crossing stable auroral red arcs are subject to scintillations, indicating the existence of electron density inhomogeneities. The theoretical explanation of the red arcs is that the heated electrons of the region F ionospheres cause an increase in oxygen atoms. Satellite observations show an increase in electron temperature along geomagnetic field lines that cross stable auroral red arcs. The intensity of these arcs correlates positively with geomagnetic activity (storms), and the frequency of occurrence of arcs correlates positively with solar sunspot activity.
Changing aurora.
Some forms of auroras experience quasi-periodic and coherent temporal intensity variations. These auroras, with a roughly stationary geometry and rapid periodic variations occurring in phase, are called changing auroras. They are classified as auroras forms R according to the International Atlas of Auroras A more detailed subdivision of the changing auroras:
R 1 (pulsating aurora) is a glow with uniform phase variations in brightness throughout the form of the aurora. By definition, in an ideal pulsating aurora, the spatial and temporal parts of the pulsation can be separated, i.e. brightness I(r,t)= I s(r)· I T(t). In a typical aurora R 1, pulsations occur with a frequency of 0.01 to 10 Hz of low intensity (1–2 kR). Most auroras R 1 are spots or arcs that pulsate with a period of several seconds.
R 2 (fiery aurora). This term is usually used to refer to movements like flames filling the sky, and not to describe a single form. The auroras are arc-shaped and usually move upward from a height of 100 km. These auroras are relatively rare and occur more often outside of the auroras.
R 3 (flickering aurora). These are auroras with rapid, irregular or regular variations in brightness, giving the impression of a flickering flame in the sky. They appear shortly before the collapse of the aurora. Commonly observed variation frequency R 3 is equal to 10 ± 3 Hz.
The term streaming aurora, used for another class of pulsating auroras, refers to irregular variations in brightness moving rapidly horizontally in arcs and bands of auroras.
The changing aurora is one of the solar-terrestrial phenomena accompanying the pulsations of the geomagnetic field and auroral X-ray radiation caused by 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 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 affected by solar corpuscular streams that occur during solar flares, as well as cosmic rays and meteor particles.
Ionospheric layers
are areas in the atmosphere in which the maximum values of the concentration of free electrons are reached (i.e. their number per unit volume). Electrically charged free electrons and (to a lesser extent, less mobile ions) resulting from the ionization of atmospheric gas atoms, interacting with radio waves (i.e. electromagnetic oscillations), can change their direction, reflecting or refracting them, and absorb their energy. As a result, when receiving distant radio stations, various effects may occur, for example, radio fading, increased audibility of distant stations, blackouts etc. phenomena.
Research methods.
The classical methods of studying the ionosphere from the Earth are reduced to pulse sounding - sending radio pulses and observing their reflections from various layers of the ionosphere with measuring the delay time and studying the intensity and shape of the reflected signals. By measuring the heights of reflection of radio pulses at different frequencies, determining the critical frequencies of various regions (the carrier frequency of the radio pulse for which this region of the ionosphere becomes transparent is called the critical frequency), it is possible to determine the value of the electron density in the layers and the effective heights for given frequencies, and choose the optimal frequencies for given radio paths. With the development of rocket technology and the advent of the space age of artificial Earth satellites (AES) and other spacecraft, it became possible to directly measure the parameters of the near-Earth space plasma, the lower part of which is the ionosphere.
Electron density measurements carried out from specially launched rockets and along satellite flight paths confirmed and refined data previously obtained by ground-based methods on the structure of the ionosphere, the distribution of electron density with height over different regions of the Earth, and made it possible to obtain electron density values above the main maximum - the layer F. Previously, it was impossible to do this by sounding methods based on observations of reflected short-wavelength radio pulses. It has been found that in some regions of the globe there are fairly stable regions with low electron density, regular “ionospheric winds”, peculiar wave processes arise in the ionosphere that carry local ionospheric disturbances thousands of kilometers from the place of their excitation, and much more. The creation of especially highly sensitive receiving devices made it possible to carry out at the stations of pulsed sounding of the ionosphere the reception of pulsed signals partially reflected from the lowest regions of the ionosphere (station of partial reflections). The use of powerful pulse installations in the meter and decimeter wavelength ranges with the use of antennas that 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 if the 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 jumps of hundreds and thousands of kilometers, reflecting alternately from a layer of ionized gas and from the surface of the Earth or water.
In the 1920s, it was believed that radio waves shorter than 200 m were generally not suitable for long-distance communications due to strong absorption. The first experiments on long-range reception of short waves across the Atlantic between Europe and America were carried out by the English physicist Oliver Heaviside and the American electrical engineer Arthur Kennelly. Independently of each other, they suggested that somewhere around the Earth there is an ionized layer of the atmosphere that can reflect radio waves. It was called the Heaviside layer - Kennelly, and then - the ionosphere.
According to modern concepts, the ionosphere consists of negatively charged free electrons and positively charged ions, mainly molecular oxygen O + and nitric oxide NO + . Ions and electrons are formed as a result of the dissociation of molecules and the ionization of neutral gas atoms by solar X-ray and ultraviolet radiation. In order to ionize an atom, it is necessary to inform it of ionization energy, the main source of which for the ionosphere is the ultraviolet, X-ray and corpuscular radiation of the Sun.
As long as the gas shell of the Earth is illuminated by the Sun, more and more electrons are continuously formed in it, but at the same time, some of the electrons, colliding with ions, recombine, again forming neutral particles. After sunset, the production of new electrons almost stops, and the number of free electrons begins to decrease. The more free electrons in the ionosphere, the better high-frequency waves are reflected from it. With a decrease in the electron concentration, the passage of radio waves is possible only in low-frequency ranges. That is why at night, as a rule, it is possible to receive distant stations only in the ranges of 75, 49, 41 and 31 m. Electrons are distributed unevenly in the ionosphere. At an altitude of 50 to 400 km, there are several layers or regions of increased electron density. These areas smoothly transition into one another and affect the propagation of HF radio waves in different ways. The upper layer of the ionosphere is denoted by the letter F. Here is the highest degree of ionization (the fraction of charged particles is about 10–4). It is located at an altitude of more than 150 km above the Earth's surface and plays the main reflective role in the long-range propagation of radio waves of high-frequency HF bands. In the summer months, the F region breaks up into two layers - F 1 and F 2. The F1 layer can occupy heights from 200 to 250 km, and the layer F 2 seems to “float” in the altitude range of 300–400 km. Usually layer F 2 is ionized much stronger than the layer F one . night layer F 1 disappears and layer F 2 remains, slowly losing up to 60% of its degree of ionization. Below the F layer, at altitudes from 90 to 150 km, there is a layer E, whose ionization occurs under the influence of soft X-ray radiation from the Sun. The degree of ionization of the E layer is lower than that of the F, during the day, reception of stations of low-frequency HF bands of 31 and 25 m occurs when signals are reflected from the layer E. Usually these are stations located at a distance of 1000–1500 km. At night in a layer E ionization sharply decreases, but even at this time it continues to play a significant role in the reception of signals from stations in the bands 41, 49 and 75 m.
Of great interest for receiving signals of high-frequency HF bands of 16, 13 and 11 m are those arising in the area E interlayers (clouds) of strongly increased ionization. The area of these clouds can vary from a few to hundreds of square kilometers. This layer of increased ionization is called the sporadic layer. E and denoted Es. Es clouds can move in the ionosphere under the influence of wind and reach speeds of up to 250 km/h. In summer, in the middle latitudes during the daytime, the origin of radio waves due to Es clouds occurs 15–20 days per month. Near the equator, it is almost always present, and at high latitudes it usually appears at night. Sometimes, in years of low solar activity, when there is no passage to the high-frequency HF bands, distant stations suddenly appear with good loudness on the bands of 16, 13 and 11 m, the signals of which were repeatedly reflected from Es.
The lowest region of the ionosphere is the region D located at altitudes between 50 and 90 km. There are relatively few free electrons here. From area D long and medium waves are well reflected, and the signals of low-frequency HF stations are strongly absorbed. After sunset, ionization disappears very quickly and it becomes possible to receive distant stations in the ranges of 41, 49 and 75 m, the signals of which are reflected from the layers F 2 and E. Separate layers of the ionosphere play an important role in the propagation of HF radio signals. The impact on radio waves is mainly due to the presence of free electrons in the ionosphere, although the propagation mechanism of radio waves is associated with the presence of large ions. The latter are also of interest in the study of the chemical properties of the atmosphere, since they are more active than neutral atoms and molecules. Chemical reactions occurring in the ionosphere play an important role in its energy and electrical balance.
normal ionosphere. Observations carried out with the help of geophysical rockets and satellites have given a lot of new information, indicating that the ionization of the atmosphere occurs under the influence of broad-spectrum solar radiation. Its main part (more than 90%) is concentrated in the visible part of the spectrum. Ultraviolet radiation with a shorter wavelength and more energy than violet light rays is emitted by hydrogen in the inner part of the Sun's atmosphere (the chromosphere), and X-rays, which have even higher energy, are emitted by the gases of the Sun's outer shell (corona).
The normal (average) state of the ionosphere is due to constant powerful radiation. Regular changes occur in the normal ionosphere under the influence of the daily rotation of the Earth and seasonal differences in the angle of incidence of the sun's rays at noon, but unpredictable and abrupt changes in the state of the ionosphere also occur.
Disturbances in the ionosphere.
As is known, powerful cyclically repeating manifestations of activity occur on the Sun, which reach a maximum every 11 years. Observations under the program of the International Geophysical Year (IGY) coincided with the period of the highest solar activity for the entire period of systematic meteorological observations, i.e. from the beginning of the 18th century. During periods of high activity, the brightness of some areas on the Sun increases several times, and the power of ultraviolet and X-ray radiation increases sharply. Such phenomena are called solar flares. They last from several minutes to one or two hours. During a flare, solar plasma erupts (mainly protons and electrons), and elementary particles rush into outer space. The electromagnetic and corpuscular radiation of the Sun at the moments of such flares has a strong effect on the Earth's atmosphere.
The initial reaction is noted 8 minutes after the flash, when intense ultraviolet and X-ray radiation reaches the Earth. As a result, ionization sharply increases; x-rays penetrate the atmosphere to the lower boundary of the ionosphere; the number of electrons in these layers increases so much that the radio signals are almost completely absorbed ("extinguished"). Additional absorption of radiation causes heating of the gas, which contributes to the development of winds. Ionized gas is an electrical conductor, and when it moves in the Earth's magnetic field, a dynamo effect appears and an electric current occurs. Such currents can, in turn, cause noticeable perturbations of the magnetic field and manifest themselves in the form of magnetic storms.
The structure and dynamics of the upper atmosphere is essentially determined by thermodynamically nonequilibrium processes associated with ionization and dissociation by solar radiation, chemical processes, excitation of molecules and atoms, their deactivation, collision, and other elementary processes. In this case, the degree of nonequilibrium increases with height as the density decreases. Up to altitudes of 500–1000 km, and often even higher, the degree of nonequilibrium for many characteristics of the upper atmosphere is sufficiently small, which allows one to use classical and hydromagnetic hydrodynamics with allowance for chemical reactions to describe it.
The exosphere is the outer layer of the Earth's atmosphere, starting at altitudes of several hundred kilometers, from which light, fast-moving hydrogen atoms can escape into outer space.
Edward Kononovich
Literature:
Pudovkin M.I. Fundamentals of solar physics. St. Petersburg, 2001
Eris Chaisson, Steve McMillan Astronomy today. Prentice Hall Inc. Upper Saddle River, 2002
Online materials: http://ciencia.nasa.gov/
When a meteoroid body enters the earth's atmosphere, many interesting phenomena occur, which we will only mention. The speed of any cosmic body always exceeds 11.2 km/s and can reach 40 km/s in the earth's vicinity with its arbitrary direction. The linear speed of the Earth when moving around the Sun is on average 30 km/s, so the maximum speed of meteoroid collision with the Earth's atmosphere can reach approximately 70 km/s (on opposite trajectories).
First, the body interacts with a very rarefied upper atmosphere, where the distances between gas molecules are greater than its diameter. Obviously, interactions with the molecules of the upper atmosphere practically do not affect the speed and state of a fairly massive body. But if the mass of the body is small (comparable to the mass of a molecule or exceeds it by 2-3 orders of magnitude), then it can completely slow down already in the upper layers of the atmosphere and will slowly settle to the earth's surface under the influence of gravity. It turns out that in this way, that is, in the form of dust, the lion's share of solid cosmic matter falls to the Earth. It has already been calculated that from 100 to 1000 tons of extraterrestrial matter enters the Earth daily, but only 1% of this amount is represented by large fragments that can reach its surface.
Three main forces act on a moving sufficiently large body: deceleration, gravity and expulsion (Archimedean force), which determine its trajectory. Effective deceleration of the largest objects begins only in dense layers of the atmosphere, at altitudes less than 100 km.
The movement of a meteoroid, like any solid body in a gaseous medium at high speed, is characterized by the Mach number - the ratio of the body's speed to the speed of sound. This number varies at different meteoroid flight altitudes, but often exceeds 50. A shock wave is formed in front of the meteoroid in the form of highly compressed and heated atmospheric gases. The surface of the body itself as a result of interaction with them
If the mass of the body is not too small and not very large, and its speed is in the range from 11 km / s to 22 km / s (this is possible on trajectories "catching up" with the Earth), then it has time to slow down in the atmosphere without burning up. After that, the meteoroid moves at such a speed at which ablation is no longer effective, and can reach the earth's surface unchanged. If the mass of the body is not very large, then a further decrease in its speed continues until the force of air resistance equals the force of gravity, and its almost vertical fall begins at a speed of 50-150 m / s. Most of the meteorites fell to Earth with such speeds. With a large mass, the meteoroid does not have time to either burn out or slow down strongly and collides with the surface at cosmic speed. In this case, an explosion occurs, caused by the transition of a large kinetic energy of the body into thermal, mechanical and other types of energy, and an explosive crater is formed on the earth's surface. As a result, a significant part of the meteorite and the earth's surface subject to impact melts and evaporates.
This article will focus on those meteors and meteorites that, flying into the earth's atmosphere, either burn out very quickly at high altitudes, forming a short-term trail in the night sky called starfall, or, colliding with the earth, explode like, for example, Tunguska. At the same time, neither one nor the other, as is known and commonly believed, do not leave solid combustion products.
Meteors burn up at the slightest contact with the atmosphere. Their combustion already ends at an altitude of 80 km. The oxygen concentration at this altitude is low and amounts to 0.004 g/m 3 , and the rarefied atmosphere has a pressure P = 0.000012 kg/m 2 and cannot provide sufficient friction to instantly heat the entire volume of the meteor's body to a temperature sufficient for its combustion. After all, an unheated body cannot ignite. Why, then, does ignition occur at high altitudes and such a rapid and even combustion of meteors? What conditions are necessary for this?
One of the conditions for the ignition and rapid combustion of a meteor must be the presence of a sufficiently high temperature of its body before entering the atmosphere. To do this, it must be well warmed up in advance throughout the volume by the sun. Then, in order for the entire volume of the meteor to be able to warm up under space conditions due to the difference in temperatures of light and shadow, and when it comes into contact with the atmosphere, it would also have time to quickly spread additional heat from friction throughout the body, the substance of the meteor must have high thermal conductivity.
The next condition for the combustion of a meteor, which leaves an even trail of fire, must be the preservation of the strength of the body during combustion. Since, having flown into the atmosphere, albeit rarefied, the meteor still experiences loads from the oncoming flow, and if its body softens from temperature, it will simply be blown apart by the flow into separate parts and we would observe a flying sheaf of fireworks.
Further. Since many substances, both metals and non-metals, burn, we will begin our discussion of the composition of the meteor substance with the very first element of the periodic system, hydrogen. Let us assume that this body consists of solid hydrogen or its solid compounds, for example, water ice. Having warmed up to high temperatures, this body will simply evaporate before ignition even in space. If, nevertheless, we assume that a body containing hydrogen ignited and burned out in the atmosphere, then it will certainly leave behind a white trace of water vapor, as a result of the process of combustion of hydrogen in oxygen. Then we could see a white trail of "starfall" during the day, under certain illumination by the sun. Thus, these meteors cannot contain or contain hydrogen in large quantities. And ice in outer space cannot exist at all, since according to the thermodynamic properties of water at a cosmic pressure of P = 0.001 m of water. Art. the boiling point is close to absolute zero, it is -273 ° C, there is no such temperature in the solar system. If the ice gets into outer space in the solar system, it will immediately evaporate from the heat of a powerful torch - the Sun. We further assume that our meteors are composed of metals or their alloys. Metals have good thermal conductivity, which meets the above requirements. But when heated, metals lose their strength, and they burn with the formation of oxides, oxides, i.e. solid slags are quite heavy, which, when falling, would certainly be fixed by people on the ground, like hail, for example. But nowhere else has such an active phenomenon been noted, so that even after a powerful "starfall" a slag hail fell somewhere, and after all, more than 3 thousand tons of matter flies into us every day. Although individual fragments of metallic and non-metallic meteorites are still found, but this is a rarity and with the daily phenomenon of "starfall" these finds are negligible. Thus, our meteors also do not contain metals.
What substance can meet all these requirements? Namely:
1. Have high thermal conductivity;
2. Maintain strength at high temperatures;
3. Actively react with a rarefied atmosphere at high altitudes;
4. Do not form solid slags when burning;
There is such a substance - it is carbon. Moreover, located in the hardest crystalline phase called diamond. It is the diamond that meets all these requirements. If carbon is in any of its other phases, then it will not meet our second requirement, namely, to maintain strength at high temperatures. It is diamond that astronomers confuse with ice when observing "starfall".
Further, in order to burn in an oxygen concentration of less than 0.004 g / m 3 a body weighing 1 g. you need to fly about 13,000 km., flies about 40 km. Most likely, the luminous trail from the meteor is not the result of its combustion in the oxygen of the atmosphere, but the result of the reaction of carbon reduction with hydrogen, in which gases are also formed. At these heights, CH 4, C 2 H 2, C 6 H 6 are present in small amounts, CO, CO 2 are also present at these heights, this indicates that carbon at these heights burns and is reduced, these gases themselves rise from the surface of the Earth to these heights cannot.
As for the Tunguska meteorite and the meteorite that fell in the autumn of 2002 in the Irkutsk region of Russia in the valley of the Vitim River, these meteorites are also, most likely, only huge diamonds. Due to their large mass, these meteorites did not have time to burn out completely in the atmosphere. Having flown to the ground and not being destroyed by the air flow, hitting a hard surface with very great force, this block of diamond crumbled into small pieces. It is known that diamond is a hard but brittle material that does not work well on impact. Since diamond has a high thermal conductivity, the entire body of the meteorite was heated to the combustion temperature before impact. Having crumbled into small pieces and bounced off the Earth, each fragment, having come into contact with the oxygen of the air, immediately burned out, releasing a certain amount of energy at the same time. And there was just a huge explosion. After all, an explosion is not the result of a strong mechanical shock, as for some reason it is commonly believed in astronomy, but the result of an active chemical reaction, and it does not matter where it occurred on Earth, on Jupiter, as long as there is something to react with. All the burned carbon formed carbon dioxide, which dissolved into the atmosphere. Therefore, they do not find meteor remnants in these places. It is quite possible that in the region of the explosion of these meteorites, the remains of animals that died not only from the shock wave, but also from suffocation with carbon monoxide can be found. And it’s not safe for people to visit these places immediately after the explosion. carbon monoxide may remain in the lowlands. This hypothesis of the Tunguska meteorite provides an explanation for almost all anomalies observed after the explosion. If this meteorite falls into a reservoir, then the water will not allow all the fragments to completely burn out, and we can have another diamond deposit. All diamond deposits, by the way, are located in a thin surface layer of the Earth, practically only on its surface. The presence of carbon in meteorites is also confirmed by the meteor shower that occurred on October 8, 1871 in Chicago, when, for some unknown reason, houses ignited and even a metal slipway melted. When thousands of people died of suffocation, located far enough from the fires.
Falling on planets or satellites of planets that do not have an atmosphere and active gases, fragments of these meteorites that have not "burned out" will partially cover the surface of these planets or satellites. Maybe that's why our natural satellite, the Moon, reflects light from the Sun so well, because a diamond also has a high refractive index. And the ray systems of lunar craters, for example, Tycho, Copernicus, obviously consist of placers of transparent material and certainly not of ice, since the temperature on the illuminated surface of the Moon is + 120 ° C.
Diamonds also exhibit the property of fluorescence when exposed to short-wavelength electromagnetic radiation. Maybe this property will give an explanation of the origin of the tails of comets when approaching the Sun, a powerful source of short-wave radiation?
