Where meteorites burn up. Why do most meteorites burn up before reaching the earth's surface? Aurora intensity

When a meteoroid body enters the earth's atmosphere, many interesting phenomena occur, which we will only mention. Speed ​​of any cosmic body always exceeds 11.2 km/s and can reach 40 km/s in the terrestrial environs with its arbitrary direction. Linear speed The Earth's motion when moving around the Sun is on average 30 km/s, so the maximum speed of a meteoroid's collision with the Earth's atmosphere can reach approximately 70 km/s (on opposite trajectories).

Initially, the body interacts with a very rarefied upper atmosphere, where the distances between gas molecules are greater than its diameter. Obviously, interactions with molecules of the upper atmosphere have practically no effect on the speed and state of the massive body. But if the mass of the body is small (comparable to the mass of the molecule or 2-3 orders of magnitude greater than it), then it can completely slow down already in the upper layers of the atmosphere and will slowly settle to 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 Earth. It has already been calculated that from 100 to 1000 tons of extraterrestrial matter arrive on Earth every day, but only 1% of this amount is represented by large debris that can reach its surface.

A moving sufficiently large body is acted upon by three main forces: braking, gravity and pushing (Archimedean force), which determine its trajectory of movement. Effective braking 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 environment, with high speed, is characterized by the Mach number - the ratio of the speed of the body to the speed of sound. This number varies at different flight altitudes of the meteoroid, 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 which 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 meteorites fell to Earth at such speeds. With a large mass, the meteoroid does not have time to either burn up or slow down much and collides with the surface at cosmic speed. In this case, an explosion occurs, caused by the transition of large kinetic energy of the body into thermal, mechanical and other types of energy, and an explosion crater is formed on the earth's surface. As a result, a significant part of the meteorite and the impacted earth's surface melts and evaporates.

Meteoroid(meteor body) - a celestial body intermediate in size between interplanetary dust and an asteroid.

Here we need to understand a little terminology. Flying into the Earth's atmosphere at great speed, due to friction it becomes very hot and burns, turning into a luminous meteor, or fireball, which can be seen as shooting star. The visible trail of a meteoroid entering the Earth's atmosphere is called meteor, and a meteoroid falling on the surface of the Earth is meteorite.
IN solar system full of these small space debris, which are called meteoroids. These could be specks of dust from comets, large blocks of stone, 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, significantly larger in size smaller than an asteroid, but significantly more 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.

- this is not an object, but phenomenon, i.e. glowing meteoroid trail. Regardless of whether it flies away from the atmosphere back into outer space, 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 and chemical composition(affects combustion color).
Meteors are often grouped into meteor showers- constant masses of meteors appearing at a certain time of the year, in a certain direction of the sky. The Leonids, Quadrantids and Perseids meteor showers are known. All meteor showers are generated by comets as a result of destruction during the melting process while passing through the inner solar system.

The meteor trail usually disappears in a matter of seconds, but can sometimes remain for minutes and be moved by the wind at the altitude of the meteor. Sometimes the Earth crosses the orbits of meteoroids. Then, passing through the earth's atmosphere and heating up, they flash with bright stripes of light, which are called meteors, or shooting stars.
On a clear night, several meteors can be seen in an hour. And when the Earth passes through a stream of dust grains left behind by a passing comet, dozens of meteors can be seen every hour.
Pieces of meteoroids that survive their passage through the atmosphere as meteors and fall to the ground as charred rocks are sometimes found. They are usually dark in color and very heavy. Sometimes they seem 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 Alabama. The meteorite, weighing about 4 kg, crashed 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 study of the movement of meteor trails allows us to obtain important information about the state and dynamics of the atmosphere at altitudes of about 100 km. It is possible to create meteor radio communication channels.

A body of cosmic origin that fell onto the surface of a large celestial object.
Most meteorites found weigh between a few grams and several kilograms. The largest meteorite ever found is Goba(weight about 60 tons). It is believed that 5-6 tons of meteorites fall to the Earth per day, or 2 thousand tons per year.
The Russian Academy of Sciences now has a special committee that supervises the collection, study and storage of meteorites. The committee has a large meteorite collection.
At the crash site large meteorite may form crater(astrobleme). One of the most famous craters in the world - Arizonan. It is assumed that the largest meteorite crater on Earth - Wilkes Land Crater in Antarctica(diameter about 500 km).

How it happens

The meteor body enters the Earth's atmosphere at speeds from 11 to 72 km/s. At this speed, it begins to warm up and glow. Due to ablation(burning and blowing away by the oncoming flow of particles of the meteoric body’s substance), the mass of the body that reaches 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 up almost completely. At such a speed 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 along almost the entire trajectory of its fall.
If the meteor body does not burn up in the atmosphere, then as it slows down it loses the horizontal component of its speed. This leads to a change in the trajectory of the fall. As it slows down, the glow of the meteorite decreases and it cools down (they often indicate that the meteorite was warm and not hot when it fell).
In addition, the meteorite body may break into fragments, which leads to meteor showers.

Large meteorites discovered in Russia

Tunguska meteorite(at the moment it is unclear exactly the meteorite origin of the Tunguska phenomenon). Fell on June 30, 1908 in the Podkamennaya Tunguska River basin in Siberia. The total energy is estimated at 40-50 megatons of TNT equivalent.
Tsarevsky meteorite(meteor shower). Fell on December 6, 1922 near the village of Tsarev, Volgograd region. This is a rock 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(total mass of fragments is 30 tons, energy is estimated at 20 kilotons). It was an iron meteorite. Fell in the Ussuri taiga on February 12, 1947.
Vitimsky car. Fell in the area of ​​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 equivalent, 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 the 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 over 250 years.”

In this article we will talk about those meteors and meteorites that, flying into the earth’s atmosphere, either burn up very quickly at high altitudes, forming a short-term trace in the night sky called a starfall, or, colliding with the ground, explode, like, for example, Tunguska. At the same time, neither one nor the other, as is known and generally accepted, leaves solid products combustion.

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 body to a temperature sufficient for its combustion. After all, an unheated body cannot ignite. Why does ignition still occur at high altitudes and such 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 should be the presence of a sufficiently high temperature of its body before entering the atmosphere. To do this, it must be well heated throughout its entire volume by the sun in advance. Then, in order for the entire volume of the meteor to warm up in space conditions due to the difference in temperatures of light and shadow, and upon contact with the atmosphere to quickly distribute 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 leaving an even fiery trail must be the preservation of the strength of the body during combustion. Since, having flown into the atmosphere, although rarefied, the meteor still experiences loads from the oncoming flow and if its body softens from the temperature, then it will simply be blown apart by the flow into separate parts and we would observe a scattering sheaf of flashes like fireworks.

Next. Since many substances, both metals and non-metals, burn, we will start discussing the composition of the meteor’s substance with the very first element of the periodic table, 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 begins in space. If we nevertheless assume that a body containing hydrogen ignites and burns in the atmosphere, then it will certainly leave behind a white trace of water vapor, as a result of the combustion of hydrogen in oxygen. Then we could see the white trail of a “falling star” during the day, under certain sunlight. Thus, these meteors cannot consist of or contain hydrogen in large quantities. And ice cannot exist in outer space at all, since according to the thermodynamic properties of water at cosmic pressure P = 0.001 m of water. Art. boiling point is close to absolute zero this is -273° C, there is no such temperature in the solar system. If 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 consist of metals or their alloys. Metals have good thermal conductivity, which meets the above requirements. But when heated, metals lose their strength and burn with the formation of oxides, oxides, i.e. solid slags are quite heavy, which, if they fell, would definitely be recorded by people on the ground, like hail, for example. But nowhere has such an active phenomenon been observed that even after a powerful “starfall” a slag hail would fall somewhere, and yet more than 3 thousand tons of substance flies to us every day. Although individual fragments of metallic and non-metallic meteorites are still found, this is a great rarity and with the daily phenomenon of “starfall” these finds are insignificant. Thus, our meteors also do not contain metals.

What substance can meet all these requirements? Namely:
1. Have high thermal conductivity;
2. Maintain strength when high temperatures;
3. Actively react with the rarefied atmosphere at high altitudes;
4. When burning, it does not form solid slags;

There is such a substance - it is carbon. Moreover, it is located in the hardest crystalline phase called diamond. It is diamond that meets all these requirements. If carbon is in any other phase, 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 for a body weighing 1 g. you need to fly about 13,000 km, but it flies about 40 km. Most likely, the luminous trail from a meteor is not the result of its combustion in the oxygen of the atmosphere, but the result of the reduction reaction of carbon with hydrogen, which also produces gases. At these altitudes there are small quantities CH 4, C 2 H 2, C 6 H 6, CO, CO 2 are also present at these altitudes, this indicates that carbon at these altitudes burns and is reduced, these gases themselves do not rise from the Earth’s surface to these altitudes they can.

Regarding Tunguska meteorite and a meteorite that fell in the fall of 2002 in the Irkutsk region of Russia in the valley of the Vitim River, then these meteorites are also most likely diamonds of only huge sizes. Due to their large mass, these meteorites did not have time to burn completely in the atmosphere. Having reached 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 respond well to impact. Since diamond has high thermal conductivity, the entire body of the meteorite was heated to combustion temperature before impact. Having crumbled into small pieces and bounced off the Earth, each fragment came into contact with the oxygen of the air and immediately burned, simultaneously releasing a certain amount of energy. There was simply a powerful 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 in the atmosphere. That is why meteoric remains are not found in these places. It is quite possible that in the area of ​​the explosion of these meteorites the remains of animals that died not only from shock wave, but also from carbon monoxide suffocation. And it’s not safe for people to visit these places immediately after the explosion. may remain in the lowlands carbon monoxide. This hypothesis of the Tunguska meteorite provides an explanation for almost all the anomalies observed after the explosion. If this meteorite falls into a body of water, then the water will not allow all the fragments to burn completely, and we may have another diamond deposit. All diamond deposits, by the way, are located in a thin surface layer of the Earth, almost 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 from suffocation, located far enough from the fires.

Falling on planets or satellites of planets that do not have an atmosphere or active gases, the unburned fragments of these meteorites 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 diamond also has a high refractive index. And beam systems lunar craters, for example, Tycho, Copernicus, clearly consist of scatterings of transparent material and certainly not ice, since the temperature on the illuminated surface of the Moon is +120 ° C.

Diamonds also exhibit the property of fluorescence when irradiated with short-wave electromagnetic radiation. Maybe this property will provide an explanation of the origin of the tails of comets when approaching the Sun, a powerful source of short-wave radiation?

The atmosphere began to form along with the formation of the Earth. During the evolution of the planet and as its parameters approach modern meanings 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 solid. 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 ultraviolet rays and electrical discharges, the mixture of gases present in the original atmosphere of the Earth entered into chemical reactions, as a result of which the formation occurred organic matter, 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 greenhouse effect associated with the presence of carbon dioxide in the atmosphere, fluctuations in its concentration are one of important reasons such large-scale climate changes in Earth's history as ice ages.

Present in modern atmosphere helium is mostly a product radioactive decay 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 contained in minerals scattered throughout the mass rocks, therefore, 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 Starlight and the study of meteorites can 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. The exception is 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 to h+d h takes place 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 dlog 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 by a linear function of height. In the lowest layer - the troposphere (h Ј 11 km) the temperature drops by 6.5 ° C with each kilometer of rise. At high altitudes, the value and sign of the vertical temperature gradient changes 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.

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, various meteorological phenomena occur, 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 consisting of 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 geographical 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 much less (altitude 16–18 km, temperature 180–200 K). Over jet streams tropopause breaks are possible.

Water in the Earth's atmosphere.

The most important feature of the Earth's atmosphere is the presence of significant amounts 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 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 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 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. Content liquid water in clouds - from fractions to several grams per m 3. 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 of fibrous or homogeneous 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 of a uniform gray color, 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 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 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, found 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 be possible.

In general, throughout the mesosphere, the atmospheric temperature decreases to its minimum value of about 180 K per upper limit mesosphere (called mesopause, altitude about 80 km). In the vicinity of the mesopause, at altitudes of 70–90 km, very thin layer ice crystals and particles of volcanic and meteorite dust, observed as a beautiful spectacle of noctilucent clouds shortly after sunset.

In the mesosphere, small solid meteorite particles that fall on the Earth mostly burn up, causing the phenomenon meteors.

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 common orbit many meteorite bodies moving at approximately the same and identically directed speeds, which is why their paths in the sky appear to emerge from one 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 fine 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 up in the atmosphere, it gas composition 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 important role in the formation of atmospheric phenomena such as rain, since they serve 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 of the thermal balance of the 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. Critical level(the base of the exosphere) is located at an altitude of about 500 km.

Polar lights and many orbits artificial satellites, as well as noctilucent clouds - all these phenomena occur in the mesosphere and thermosphere.

Polar lights.

At high latitudes during disturbances magnetic field auroras are observed. They may last several minutes, but are often visible for several hours. Auroras vary greatly in shape, color and intensity, all of which sometimes change very quickly over time. The 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 the visible color of the 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 (

Real forms 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 fields. power lines, with a vertical length from 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 certain 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. Used various terms; 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 radiance appear during the most active phases polar lights.

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°. Maximum occurrence of auroras corresponding to at this moment 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 geo magnetic pole in the night sector and by 15° in the day sector.

Aurora oval and aurora zones. The location of the aurora oval depends on geomagnetic activity. The oval becomes wider with 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 occurrence 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 aurora oval was carried out by G. Starkov, Y. Feldstein, S. I. Akasofu and a number of other researchers. The aurora oval represents the area of ​​most intense influence solar wind to 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 lifetime 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. Theoretical explanation 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 field lines geomagnetic field, which 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). This term is usually used to refer to movements similar languages flames filling the sky, and not to describe a separate 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 scattered light from the Sun. At times, atmospheric glow can account for up to 40% of the total amount of light. 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 the atmospheric glow in the l 5577 Å emission with the number sunspots and the flux of solar radiation at a wavelength of 10.7 cm. Atmospheric glow 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 harmful effects ultraviolet light 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. On various heights in the atmosphere, processes of dissociation of various molecules and subsequent ionization occur sequentially different atoms and ions. 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 they started systematic observations state of the ionosphere. In our country, on the initiative of M.A. Bonch-Bruevich, installations for its pulse probing were created. Many have been studied general properties ionosphere, heights and electron concentration of its main layers.

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.

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 is extremely important to ensure the reliability of radio communications. The ionosphere is a collection of ionized layers of the earth's atmosphere, starting from altitudes of about 60 km and extending to altitudes of tens of thousands of km. The main source of ionization of the earth's atmosphere is ultraviolet and x-ray radiation The sun, arising mainly in the solar chromosphere and corona. In addition, the degree of ionization of the upper atmosphere is influenced by solar corpuscular streams that occur during solar flares, as well as cosmic rays and meteor particles.

Ionospheric layers

- these are the areas in the atmosphere in which maximum values concentration of free electrons (i.e. their number per unit volume). Electrically charged free electrons and (to a lesser extent, less mobile ions) resulting from the ionization of 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 etc. 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 development rocket technology and with the onset space age 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.

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”, and peculiar wave processes, transferring local ionospheric disturbances thousands of kilometers from the place of their initiation, 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.

Concentration electric charges(electron concentration is equal to 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 radio waves. electromagnetic vibrations. 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 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 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.

While the gaseous 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 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 waves are reflected from it high frequency. 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, the 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 during the daytime, the origin of radio waves due to Es clouds occurs for 15–20 days per month. Near the equator it is almost always present, and in high latitudes it usually appears at night. Sometimes, in 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 flowing in the ionosphere play an important role in its energy and electrical balance.

Normal ionosphere. Observations made using geophysical rockets and satellites have provided a wealth of new information indicating that ionization of the atmosphere occurs under the influence of a wide range of 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 under the influence of the Earth's daily rotation and seasonal differences in the angle of incidence sun rays at noon, but unpredictable and sudden 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 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 electrical conductor, and when it moves in the Earth's magnetic field, a dynamo effect occurs and an electric current is generated. 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 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 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/