2 structure of the atmosphere. Layers of the atmosphere in order from the surface of the earth

The atmosphere is the gaseous shell of our planet, which rotates along with the Earth. The gas in the atmosphere is called air. The atmosphere is in contact with the hydrosphere and partially covers the lithosphere. But the upper limits are difficult to determine. It is conventionally accepted that the atmosphere extends upward for approximately three thousand kilometers. There it smoothly flows into airless space.

Chemical composition of the Earth's atmosphere

The formation of the chemical composition of the atmosphere began about four billion years ago. Initially, the atmosphere consisted only of light gases - helium and hydrogen. According to scientists, the initial prerequisites for the creation of a gas shell around the Earth were volcanic eruptions, which, along with lava, emitted huge amounts of gases. Subsequently, gas exchange began with water spaces, with living organisms, and with the products of their activities. The composition of the air gradually changed and was fixed in its modern form several million years ago.

The main components of the atmosphere are nitrogen (about 79%) and oxygen (20%). The remaining percentage (1%) is made up of the following gases: argon, neon, helium, methane, carbon dioxide, hydrogen, krypton, xenon, ozone, ammonia, sulfur and nitrogen dioxides, nitrous oxide and carbon monoxide, which are included in this one percent.

In addition, the air contains water vapor and particulate matter (pollen, dust, salt crystals, aerosol impurities).

Recently, scientists have noted not a qualitative, but a quantitative change in some air ingredients. And the reason for this is man and his activities. In the last 100 years alone, carbon dioxide levels have increased significantly! This is fraught with many problems, the most global of which is climate change.

Formation of weather and climate

The atmosphere plays a critical role in shaping the climate and weather on Earth. A lot depends on the amount of sunlight, the nature of the underlying surface and atmospheric circulation.

Let's look at the factors in order.

1. The atmosphere transmits the heat of the sun's rays and absorbs harmful radiation. The ancient Greeks knew that the rays of the Sun fall on different parts of the Earth at different angles. The word “climate” itself translated from ancient Greek means “slope”. So, at the equator, the sun's rays fall almost vertically, which is why it is very hot here. The closer to the poles, the greater the angle of inclination. And the temperature drops.

2. Due to the uneven heating of the Earth, air currents are formed in the atmosphere. They are classified according to their sizes. The smallest (tens and hundreds of meters) are local winds. This is followed by monsoons and trade winds, cyclones and anticyclones, and planetary frontal zones.

All these air masses are constantly moving. Some of them are quite static. For example, trade winds that blow from the subtropics towards the equator. The movement of others depends largely on atmospheric pressure.

3. Atmospheric pressure is another factor influencing climate formation. This is the air pressure on the surface of the earth. As is known, air masses move from an area with high atmospheric pressure towards an area where this pressure is lower.

A total of 7 zones are allocated. The equator is a low pressure zone. Further, on both sides of the equator up to the thirties latitudes there is an area of ​​high pressure. From 30° to 60° - low pressure again. And from 60° to the poles is a high pressure zone. Air masses circulate between these zones. Those that come from the sea to land bring rain and bad weather, and those that blow from the continents bring clear and dry weather. In places where air currents collide, atmospheric front zones are formed, which are characterized by precipitation and inclement, windy weather.

Scientists have proven that even a person’s well-being depends on atmospheric pressure. According to international standards, normal atmospheric pressure is 760 mm Hg. column at a temperature of 0°C. This indicator is calculated for those areas of land that are almost level with sea level. With altitude the pressure decreases. Therefore, for example, for St. Petersburg 760 mm Hg. - this is the norm. But for Moscow, which is located higher, normal pressure is 748 mm Hg.

The pressure changes not only vertically, but also horizontally. This is especially felt during the passage of cyclones.

The structure of the atmosphere

The atmosphere is reminiscent of a layer cake. And each layer has its own characteristics.

. Troposphere- the layer closest to the Earth. The "thickness" of this layer changes with distance from the equator. Above the equator, the layer extends upward by 16-18 km, in temperate zones by 10-12 km, at the poles by 8-10 km.

It is here that 80% of the total air mass and 90% of water vapor are contained. Clouds form here, cyclones and anticyclones arise. The air temperature depends on the altitude of the area. On average, it decreases by 0.65° C for every 100 meters.

. Tropopause- transition layer of the atmosphere. Its height ranges from several hundred meters to 1-2 km. The air temperature in summer is higher than in winter. For example, above the poles in winter it is -65° C. And above the equator it is -70° C at any time of the year.

. Stratosphere- this is a layer whose upper boundary lies at an altitude of 50-55 kilometers. Turbulence here is low, the content of water vapor in the air is negligible. But there is a lot of ozone. Its maximum concentration is at an altitude of 20-25 km. In the stratosphere, the air temperature begins to rise and reaches +0.8° C. This is due to the fact that the ozone layer interacts with ultraviolet radiation.

. Stratopause- a low intermediate layer between the stratosphere and the mesosphere that follows it.

. Mesosphere- the upper boundary of this layer is 80-85 kilometers. Complex photochemical processes involving free radicals occur here. They are the ones who provide that gentle blue glow of our planet, which is seen from space.

Most comets and meteorites burn up in the mesosphere.

. Mesopause- the next intermediate layer, the air temperature in which is at least -90°.

. Thermosphere- the lower boundary begins at an altitude of 80 - 90 km, and the upper boundary of the layer runs approximately at 800 km. The air temperature is rising. It can vary from +500° C to +1000° C. During the day, temperature fluctuations amount to hundreds of degrees! But the air here is so rarefied that understanding the term “temperature” as we imagine it is not appropriate here.

. Ionosphere- combines the mesosphere, mesopause and thermosphere. The air here consists mainly of oxygen and nitrogen molecules, as well as quasi-neutral plasma. The sun's rays entering the ionosphere strongly ionize air molecules. In the lower layer (up to 90 km) the degree of ionization is low. The higher, the greater the ionization. So, at an altitude of 100-110 km, electrons are concentrated. This helps to reflect short and medium radio waves.

The most important layer of the ionosphere is the upper one, which is located at an altitude of 150-400 km. Its peculiarity is that it reflects radio waves, and this facilitates the transmission of radio signals over considerable distances.

It is in the ionosphere that such a phenomenon as the aurora occurs.

. Exosphere- consists of oxygen, helium and hydrogen atoms. The gas in this layer is very rarefied and hydrogen atoms often escape into outer space. Therefore, this layer is called the “dispersion zone”.

The first scientist to suggest that our atmosphere has weight was the Italian E. Torricelli. Ostap Bender, for example, in his novel “The Golden Calf” lamented that every person is pressed by a column of air weighing 14 kg! But the great schemer was a little mistaken. An adult experiences pressure of 13-15 tons! But we do not feel this heaviness, because atmospheric pressure is balanced by the internal pressure of a person. The weight of our atmosphere is 5,300,000,000,000,000 tons. The figure is colossal, although it is only a millionth of the weight of our planet.

At sea level 1013.25 hPa (about 760 mmHg). The global average air temperature at the Earth's surface is 15°C, with temperatures varying from approximately 57°C in subtropical deserts to -89°C in Antarctica. Air density and pressure decrease with height according to a law close to exponential.

The structure of the atmosphere. Vertically, the atmosphere has a layered structure, determined mainly by the features of the vertical temperature distribution (figure), which depends on the geographical location, season, time of day, and so on. The lower layer of the atmosphere - the troposphere - is characterized by a drop in temperature with height (by about 6°C per 1 km), its height from 8-10 km in polar latitudes to 16-18 km in the tropics. Due to the rapid decrease in air density with height, about 80% of the total mass of the atmosphere is located in the troposphere. Above the troposphere is the stratosphere, a layer generally characterized by an increase in temperature with height. The transition layer between the troposphere and stratosphere is called the tropopause. In the lower stratosphere, down to a level of about 20 km, the temperature changes little with height (the so-called isothermal region) and often even decreases slightly. Above that, the temperature increases due to the absorption of UV radiation from the Sun by ozone, slowly at first, and faster from a level of 34-36 km. The upper boundary of the stratosphere - the stratopause - is located at an altitude of 50-55 km, corresponding to the maximum temperature (260-270 K). The layer of the atmosphere located at an altitude of 55-85 km, where the temperature again drops with height, is called the mesosphere; at its upper boundary - the mesopause - the temperature reaches 150-160 K in summer, and 200-230 K in winter. Above the mesopause, the thermosphere begins - a layer characterized by a rapid increase in temperature, reaching 800-1200 K at an altitude of 250 km. In the thermosphere, corpuscular and X-ray radiation from the Sun is absorbed, meteors are slowed down and burned, so it acts as a protective layer of the Earth. Even higher is the exosphere, from where atmospheric gases are dispersed into outer space due to dissipation and where a gradual transition from the atmosphere to interplanetary space occurs.

Atmospheric composition. Up to an altitude of about 100 km, the atmosphere is almost homogeneous in chemical composition and the average molecular weight of the air (about 29) is constant. Near the Earth's surface, the atmosphere consists of nitrogen (about 78.1% by volume) and oxygen (about 20.9%), and also contains small amounts of argon, carbon dioxide (carbon dioxide), neon and other permanent and variable components (see Air ).

In addition, the atmosphere contains small amounts of ozone, nitrogen oxides, ammonia, radon, etc. The relative content of the main components of air is constant over time and uniform in different geographical areas. The content of water vapor and ozone is variable in space and time; Despite their low content, their role in atmospheric processes is very significant.

Above 100-110 km, dissociation of molecules of oxygen, carbon dioxide and water vapor occurs, so the molecular mass of air decreases. At an altitude of about 1000 km, light gases - helium and hydrogen - begin to predominate, and even higher the Earth's atmosphere gradually turns into interplanetary gas.

The most important variable component of the atmosphere is water vapor, which enters the atmosphere through evaporation from the surface of water and moist soil, as well as through transpiration by plants. The relative content of water vapor varies at the earth's surface from 2.6% in the tropics to 0.2% in polar latitudes. It falls quickly with height, decreasing by half already at an altitude of 1.5-2 km. The vertical column of the atmosphere at temperate latitudes contains about 1.7 cm of “precipitated water layer”. When water vapor condenses, clouds form, from which atmospheric precipitation falls in the form of rain, hail, and snow.

An important component of atmospheric air is ozone, concentrated 90% in the stratosphere (between 10 and 50 km), about 10% of it is in the troposphere. Ozone provides absorption of hard UV radiation (with a wavelength of less than 290 nm), and this is its protective role for the biosphere. The values ​​of the total ozone content vary depending on the latitude and season in the range from 0.22 to 0.45 cm (the thickness of the ozone layer at pressure p = 1 atm and temperature T = 0°C). In ozone holes observed in the spring in Antarctica since the early 1980s, ozone content can drop to 0.07 cm. It increases from the equator to the poles and has an annual cycle with a maximum in spring and a minimum in autumn, and the amplitude of the annual cycle is small in the tropics and grows towards high latitudes. A significant variable component of the atmosphere is carbon dioxide, the content of which in the atmosphere has increased by 35% over the past 200 years, which is mainly explained by the anthropogenic factor. Its latitudinal and seasonal variability is observed, associated with plant photosynthesis and solubility in sea water (according to Henry’s law, the solubility of a gas in water decreases with increasing temperature).

An important role in shaping the planet's climate is played by atmospheric aerosol - solid and liquid particles suspended in the air ranging in size from several nm to tens of microns. There are aerosols of natural and anthropogenic origin. Aerosol is formed in the process of gas-phase reactions from the products of plant life and human economic activity, volcanic eruptions, as a result of dust rising by the wind from the surface of the planet, especially from its desert regions, and is also formed from cosmic dust falling into the upper layers of the atmosphere. Most of the aerosol is concentrated in the troposphere; aerosol from volcanic eruptions forms the so-called Junge layer at an altitude of about 20 km. The largest amount of anthropogenic aerosol enters the atmosphere as a result of the operation of vehicles and thermal power plants, chemical production, fuel combustion, etc. Therefore, in some areas the composition of the atmosphere is noticeably different from ordinary air, which required the creation of a special service for observing and monitoring the level of atmospheric air pollution.

Evolution of the atmosphere. The modern atmosphere is apparently of secondary origin: it was formed from gases released by the solid shell of the Earth after the formation of the planet was completed about 4.5 billion years ago. During the geological history of the Earth, the atmosphere has undergone significant changes in its composition under the influence of a number of factors: dissipation (volatilization) of gases, mainly lighter ones, into outer space; release of gases from the lithosphere as a result of volcanic activity; chemical reactions between the components of the atmosphere and the rocks that make up the earth’s crust; photochemical reactions in the atmosphere itself under the influence of solar UV radiation; accretion (capture) of matter from the interplanetary medium (for example, meteoric matter). The development of the atmosphere is closely related to geological and geochemical processes, and over the last 3-4 billion years also to the activity of the biosphere. A significant part of the gases that make up the modern atmosphere (nitrogen, carbon dioxide, water vapor) arose during volcanic activity and intrusion, which carried them from the depths of the Earth. Oxygen appeared in appreciable quantities about 2 billion years ago as a result of photosynthetic organisms that originally arose in the surface waters of the ocean.

Based on data on the chemical composition of carbonate deposits, estimates of the amount of carbon dioxide and oxygen in the atmosphere of the geological past were obtained. Throughout the Phanerozoic (the last 570 million years of Earth's history), the amount of carbon dioxide in the atmosphere varied widely depending on the level of volcanic activity, ocean temperature and the rate of photosynthesis. For most of this time, the concentration of carbon dioxide in the atmosphere was significantly higher than today (up to 10 times). The amount of oxygen in the Phanerozoic atmosphere changed significantly, with a prevailing trend towards its increase. In the Precambrian atmosphere, the mass of carbon dioxide was, as a rule, greater, and the mass of oxygen was smaller compared to the Phanerozoic atmosphere. Fluctuations in the amount of carbon dioxide had a significant impact on the climate in the past, increasing the greenhouse effect with increasing concentrations of carbon dioxide, making the climate much warmer throughout the main part of the Phanerozoic compared to the modern era.

Atmosphere and life. Without an atmosphere, the Earth would be a dead planet. Organic life occurs in close interaction with the atmosphere and the associated climate and weather. Insignificant in mass compared to the planet as a whole (about a part in a million), the atmosphere is an indispensable condition for all forms of life. The most important of the atmospheric gases for the life of organisms are oxygen, nitrogen, water vapor, carbon dioxide, and ozone. When carbon dioxide is absorbed by photosynthetic plants, organic matter is created, which is used as a source of energy by the vast majority of living beings, including humans. Oxygen is necessary for the existence of aerobic organisms, for which the flow of energy is provided by oxidation reactions of organic matter. Nitrogen, assimilated by some microorganisms (nitrogen fixers), is necessary for the mineral nutrition of plants. Ozone, which absorbs hard UV radiation from the Sun, significantly weakens this part of solar radiation harmful to life. The condensation of water vapor in the atmosphere, the formation of clouds and subsequent precipitation supply water to land, without which no form of life is possible. The vital activity of organisms in the hydrosphere is largely determined by the amount and chemical composition of atmospheric gases dissolved in water. Since the chemical composition of the atmosphere significantly depends on the activities of organisms, the biosphere and atmosphere can be considered as part of a single system, the maintenance and evolution of which (see Biogeochemical cycles) was of great importance for changing the composition of the atmosphere throughout the history of the Earth as a planet.

Radiation, heat and water balances of the atmosphere. Solar radiation is practically the only source of energy for all physical processes in the atmosphere. The main feature of the radiation regime of the atmosphere is the so-called greenhouse effect: the atmosphere transmits solar radiation to the earth's surface quite well, but actively absorbs thermal long-wave radiation from the earth's surface, part of which returns to the surface in the form of counter radiation, compensating for radiative heat loss from the earth's surface (see Atmospheric radiation ). In the absence of an atmosphere, the average temperature of the earth's surface would be -18°C, but in reality it is 15°C. Incoming solar radiation is partially (about 20%) absorbed into the atmosphere (mainly by water vapor, water droplets, carbon dioxide, ozone and aerosols), and is also scattered (about 7%) by aerosol particles and density fluctuations (Rayleigh scattering). The total radiation reaching the earth's surface is partially (about 23%) reflected from it. The reflectance coefficient is determined by the reflectivity of the underlying surface, the so-called albedo. On average, the Earth's albedo for the integral flux of solar radiation is close to 30%. It varies from a few percent (dry soil and black soil) to 70-90% for freshly fallen snow. Radiative heat exchange between the earth's surface and the atmosphere significantly depends on albedo and is determined by the effective radiation of the earth's surface and the counter-radiation of the atmosphere absorbed by it. The algebraic sum of radiation fluxes entering the earth's atmosphere from outer space and leaving it back is called the radiation balance.

Transformations of solar radiation after its absorption by the atmosphere and the earth's surface determine the heat balance of the Earth as a planet. The main source of heat for the atmosphere is the earth's surface; heat from it is transferred not only in the form of long-wave radiation, but also by convection, and is also released during condensation of water vapor. The shares of these heat inflows are on average 20%, 7% and 23%, respectively. About 20% of heat is also added here due to the absorption of direct solar radiation. The flux of solar radiation per unit time through a single area perpendicular to the sun's rays and located outside the atmosphere at an average distance from the Earth to the Sun (the so-called solar constant) is equal to 1367 W/m2, changes are 1-2 W/m2 depending on cycle of solar activity. With a planetary albedo of about 30%, the time-average global influx of solar energy to the planet is 239 W/m2. Since the Earth as a planet emits on average the same amount of energy into space, then, according to the Stefan-Boltzmann law, the effective temperature of the outgoing thermal long-wave radiation is 255 K (-18 ° C). At the same time, the average temperature of the earth's surface is 15°C. The difference of 33°C is due to the greenhouse effect.

The water balance of the atmosphere generally corresponds to the equality of the amount of moisture evaporated from the Earth's surface and the amount of precipitation falling on the Earth's surface. The atmosphere over the oceans receives more moisture from evaporation processes than over land, and loses 90% in the form of precipitation. Excess water vapor over the oceans is transported to the continents by air currents. The amount of water vapor transferred into the atmosphere from the oceans to the continents is equal to the volume of the rivers flowing into the oceans.

Air movement. The Earth is spherical, so much less solar radiation reaches its high latitudes than the tropics. As a result, large temperature contrasts arise between latitudes. The temperature distribution is also significantly affected by the relative positions of the oceans and continents. Due to the large mass of ocean waters and the high heat capacity of water, seasonal fluctuations in ocean surface temperature are much less than on land. In this regard, in the middle and high latitudes, the air temperature over the oceans in summer is noticeably lower than over the continents, and higher in winter.

Uneven heating of the atmosphere in different regions of the globe causes a spatially inhomogeneous distribution of atmospheric pressure. At sea level, the pressure distribution is characterized by relatively low values ​​near the equator, increases in the subtropics (high pressure belts) and decreases in the middle and high latitudes. At the same time, over the continents of extratropical latitudes, the pressure is usually increased in winter and decreased in summer, which is associated with temperature distribution. Under the influence of a pressure gradient, air experiences acceleration directed from areas of high pressure to areas of low pressure, which leads to the movement of air masses. Moving air masses are also affected by the deflecting force of the Earth's rotation (Coriolis force), the friction force, which decreases with height, and, for curved trajectories, the centrifugal force. Turbulent mixing of air is of great importance (see Turbulence in the atmosphere).

A complex system of air currents (general atmospheric circulation) is associated with the planetary pressure distribution. In the meridional plane, on average, two or three meridional circulation cells can be traced. Near the equator, heated air rises and falls in the subtropics, forming a Hadley cell. The air of the reverse Ferrell cell also descends there. At high latitudes, a straight polar cell is often visible. Meridional circulation velocities are on the order of 1 m/s or less. Due to the Coriolis force, westerly winds are observed in most of the atmosphere with speeds in the middle troposphere of about 15 m/s. There are relatively stable wind systems. These include trade winds - winds blowing from high pressure zones in the subtropics to the equator with a noticeable eastern component (from east to west). Monsoons are fairly stable - air currents that have a clearly defined seasonal character: they blow from the ocean to the mainland in the summer and in the opposite direction in the winter. The Indian Ocean monsoons are especially regular. In mid-latitudes, the movement of air masses is mainly westerly (from west to east). This is a zone of atmospheric fronts on which large vortices arise - cyclones and anticyclones, covering many hundreds and even thousands of kilometers. Cyclones also occur in the tropics; here they are distinguished by their smaller sizes, but very high wind speeds, reaching hurricane force (33 m/s or more), the so-called tropical cyclones. In the Atlantic and eastern Pacific Oceans they are called hurricanes, and in the western Pacific Ocean they are called typhoons. In the upper troposphere and lower stratosphere, in the areas separating the direct Hadley meridional circulation cell and the reverse Ferrell cell, relatively narrow, hundreds of kilometers wide, jet streams with sharply defined boundaries are often observed, within which the wind reaches 100-150 and even 200 m/ With.

Climate and weather. The difference in the amount of solar radiation arriving at different latitudes to the earth's surface, which is varied in its physical properties, determines the diversity of the Earth's climates. From the equator to tropical latitudes, the air temperature at the earth's surface averages 25-30°C and varies little throughout the year. In the equatorial belt, there is usually a lot of precipitation, which creates conditions of excess moisture there. In tropical zones, precipitation decreases and in some areas becomes very low. Here are the vast deserts of the Earth.

In subtropical and middle latitudes, air temperature varies significantly throughout the year, and the difference between summer and winter temperatures is especially large in areas of the continents far from the oceans. Thus, in some areas of Eastern Siberia, the annual air temperature range reaches 65°C. Humidification conditions in these latitudes are very diverse, depend mainly on the regime of general atmospheric circulation and vary significantly from year to year.

In polar latitudes, the temperature remains low throughout the year, even if there is a noticeable seasonal variation. This contributes to the widespread distribution of ice cover on the oceans and land and permafrost, which occupy over 65% of its area in Russia, mainly in Siberia.

Over the past decades, changes in the global climate have become increasingly noticeable. Temperatures rise more at high latitudes than at low latitudes; more in winter than in summer; more at night than during the day. Over the 20th century, the average annual air temperature at the earth's surface in Russia increased by 1.5-2°C, and in some areas of Siberia an increase of several degrees was observed. This is associated with an increase in the greenhouse effect due to an increase in the concentration of trace gases.

The weather is determined by the conditions of atmospheric circulation and the geographical location of the area; it is most stable in the tropics and most variable in the middle and high latitudes. The weather changes most of all in zones of changing air masses caused by the passage of atmospheric fronts, cyclones and anticyclones carrying precipitation and increased wind. Data for weather forecasting are collected at ground-based weather stations, ships and aircraft, and from meteorological satellites. See also Meteorology.

Optical, acoustic and electrical phenomena in the atmosphere. When electromagnetic radiation propagates in the atmosphere, as a result of refraction, absorption and scattering of light by air and various particles (aerosol, ice crystals, water drops), various optical phenomena arise: rainbows, crowns, halo, mirage, etc. The scattering of light determines the apparent height of the vault of heaven and blue color of the sky. The visibility range of objects is determined by the conditions of light propagation in the atmosphere (see Atmospheric visibility). The transparency of the atmosphere at different wavelengths determines the communication range and the ability to detect objects with instruments, including the possibility of astronomical observations from the Earth’s surface. For studies of optical inhomogeneities of the stratosphere and mesosphere, the twilight phenomenon plays an important role. For example, photographing twilight from spacecraft makes it possible to detect aerosol layers. Features of the propagation of electromagnetic radiation in the atmosphere determine the accuracy of methods for remote sensing of its parameters. All these questions, as well as many others, are studied by atmospheric optics. Refraction and scattering of radio waves determine the possibilities of radio reception (see Propagation of radio waves).

The propagation of sound in the atmosphere depends on the spatial distribution of temperature and wind speed (see Atmospheric acoustics). It is of interest for atmospheric sensing by remote methods. Explosions of charges launched by rockets into the upper atmosphere provided rich information about wind systems and temperature variations in the stratosphere and mesosphere. In a stably stratified atmosphere, when the temperature decreases with height slower than the adiabatic gradient (9.8 K/km), so-called internal waves arise. These waves can propagate upward into the stratosphere and even into the mesosphere, where they attenuate, contributing to increased winds and turbulence.

The negative charge of the Earth and the resulting electric field, the atmosphere, together with the electrically charged ionosphere and magnetosphere, create a global electrical circuit. The formation of clouds and thunderstorm electricity plays an important role in this. The danger of lightning discharges has necessitated the development of lightning protection methods for buildings, structures, power lines and communications. This phenomenon poses a particular danger to aviation. Lightning discharges cause atmospheric radio interference, called atmospherics (see Whistling atmospherics). During a sharp increase in the electric field strength, luminous discharges are observed that appear on the tips and sharp corners of objects protruding above the earth's surface, on individual peaks in the mountains, etc. (Elma lights). The atmosphere always contains a greatly varying amount of light and heavy ions, depending on specific conditions, which determine the electrical conductivity of the atmosphere. The main ionizers of air near the earth's surface are radiation from radioactive substances contained in the earth's crust and atmosphere, as well as cosmic rays. See also Atmospheric electricity.

Human influence on the atmosphere. Over the past centuries, there has been an increase in the concentration of greenhouse gases in the atmosphere due to human economic activities. The percentage of carbon dioxide increased from 2.8-10 2 two hundred years ago to 3.8-10 2 in 2005, the methane content - from 0.7-10 1 approximately 300-400 years ago to 1.8-10 -4 at the beginning of the 21st century; about 20% of the increase in the greenhouse effect over the last century came from freons, which were practically absent in the atmosphere until the mid-20th century. These substances are recognized as stratospheric ozone depleters, and their production is prohibited by the 1987 Montreal Protocol. The increase in the concentration of carbon dioxide in the atmosphere is caused by the burning of ever-increasing amounts of coal, oil, gas and other types of carbon fuels, as well as the clearing of forests, as a result of which the absorption of carbon dioxide through photosynthesis decreases. The concentration of methane increases with an increase in oil and gas production (due to its losses), as well as with the expansion of rice crops and an increase in the number of cattle. All this contributes to climate warming.

To change the weather, methods have been developed to actively influence atmospheric processes. They are used to protect agricultural plants from hail by dispersing special reagents in thunderclouds. There are also methods for dispersing fog at airports, protecting plants from frost, influencing clouds to increase precipitation in desired areas, or for dispersing clouds during public events.

Study of the atmosphere. Information about physical processes in the atmosphere is obtained primarily from meteorological observations, which are carried out by a global network of permanently operating meteorological stations and posts located on all continents and on many islands. Daily observations provide information about air temperature and humidity, atmospheric pressure and precipitation, cloudiness, wind, etc. Observations of solar radiation and its transformations are carried out at actinometric stations. Of great importance for studying the atmosphere are networks of aerological stations, at which meteorological measurements are carried out up to an altitude of 30-35 km using radiosondes. At a number of stations, observations of atmospheric ozone, electrical phenomena in the atmosphere, and the chemical composition of the air are carried out.

Data from ground stations are supplemented by observations on the oceans, where “weather ships” operate, constantly located in certain areas of the World Ocean, as well as meteorological information received from research and other ships.

In recent decades, an increasing amount of information about the atmosphere has been obtained using meteorological satellites, which carry instruments for photographing clouds and measuring fluxes of ultraviolet, infrared and microwave radiation from the Sun. Satellites make it possible to obtain information about vertical profiles of temperature, cloudiness and its water supply, elements of the radiation balance of the atmosphere, ocean surface temperature, etc. Using measurements of the refraction of radio signals from a system of navigation satellites, it is possible to determine vertical profiles of density, pressure and temperature, as well as moisture content in the atmosphere . With the help of satellites, it has become possible to clarify the value of the solar constant and planetary albedo of the Earth, build maps of the radiation balance of the Earth-atmosphere system, measure the content and variability of small atmospheric pollutants, and solve many other problems of atmospheric physics and environmental monitoring.

Lit.: Budyko M.I. Climate in the past and future. L., 1980; Matveev L. T. Course of general meteorology. Atmospheric physics. 2nd ed. L., 1984; Budyko M.I., Ronov A.B., Yanshin A.L. History of the atmosphere. L., 1985; Khrgian A. Kh. Atmospheric Physics. M., 1986; Atmosphere: Directory. L., 1991; Khromov S.P., Petrosyants M.A. Meteorology and climatology. 5th ed. M., 2001.

G. S. Golitsyn, N. A. Zaitseva.

The atmosphere is what makes life possible on Earth. We receive the very first information and facts about the atmosphere in elementary school. In high school, we become more familiar with this concept in geography lessons.

Concept of earth's atmosphere

Not only the Earth, but also other celestial bodies have an atmosphere. This is the name given to the gaseous shell surrounding the planets. The composition of this gas layer varies significantly between planets. Let's look at the basic information and facts about otherwise called air.

Its most important component is oxygen. Some people mistakenly think that the earth's atmosphere consists entirely of oxygen, but in fact, air is a mixture of gases. It contains 78% nitrogen and 21% oxygen. The remaining one percent includes ozone, argon, carbon dioxide, and water vapor. Even though the percentage of these gases is small, they perform an important function - they absorb a significant part of the solar radiant energy, thereby preventing the luminary from turning all life on our planet into ashes. The properties of the atmosphere change depending on altitude. For example, at an altitude of 65 km, nitrogen is 86% and oxygen is 19%.

Composition of the Earth's atmosphere

• Carbon dioxide necessary for plant nutrition. It appears in the atmosphere as a result of the process of respiration of living organisms, rotting, and combustion. Its absence in the atmosphere would make the existence of any plants impossible.
• Oxygen- a vital component of the atmosphere for humans. Its presence is a condition for the existence of all living organisms. It makes up about 20% of the total volume of atmospheric gases.
• Ozone is a natural absorber of solar ultraviolet radiation, which has a detrimental effect on living organisms. Most of it forms a separate layer of the atmosphere - the ozone screen. Recently, human activity has led to the fact that it is gradually beginning to collapse, but since it is of great importance, active work is being carried out to preserve and restore it.
• water vapor determines air humidity. Its content may vary depending on various factors: air temperature, territorial location, season. At low temperatures there is very little water vapor in the air, maybe less than one percent, and at high temperatures its amount reaches 4%.
• In addition to all of the above, the composition of the earth’s atmosphere always contains a certain percentage solid and liquid impurities. These are soot, ash, sea salt, dust, water drops, microorganisms. They can get into the air both naturally and anthropogenically.

Layers of the atmosphere

The temperature, density, and quality composition of the air are not the same at different altitudes. Because of this, it is customary to distinguish different layers of the atmosphere. Each of them has its own characteristics. Let's find out what layers of the atmosphere are distinguished:

• Troposphere - this layer of the atmosphere is closest to the Earth's surface. Its height is 8-10 km above the poles and 16-18 km in the tropics. 90% of all water vapor in the atmosphere is located here, so active cloud formation occurs. Also in this layer processes such as air (wind) movement, turbulence, and convection are observed. Temperatures range from +45 degrees at midday in the warm season in the tropics to -65 degrees at the poles.
• The stratosphere is the second most distant layer of the atmosphere. Located at an altitude of 11 to 50 km. In the lower layer of the stratosphere the temperature is approximately -55; moving away from the Earth it rises to +1˚С. This region is called an inversion and is the boundary of the stratosphere and mesosphere.
• The mesosphere is located at an altitude of 50 to 90 km. The temperature at its lower boundary is about 0, at the upper it reaches -80...-90 ˚С. Meteorites entering the Earth's atmosphere completely burn up in the mesosphere, causing airglows to occur here.
• The thermosphere is approximately 700 km thick. The northern lights appear in this layer of the atmosphere. They appear due to the influence of cosmic radiation and radiation emanating from the Sun.
• The exosphere is the zone of air dispersion. Here the concentration of gases is small and they gradually escape into interplanetary space.

The boundary between the earth's atmosphere and outer space is considered to be 100 km. This line is called the Karman line.

Atmospheric pressure

When listening to the weather forecast, we often hear barometric pressure readings. But what does atmospheric pressure mean, and how can it affect us?

We figured out that air consists of gases and impurities. Each of these components has its own weight, which means that the atmosphere is not weightless, as was believed until the 17th century. Atmospheric pressure is the force with which all layers of the atmosphere press on the surface of the Earth and on all objects.

Scientists carried out complex calculations and proved that the atmosphere presses with a force of 10,333 kg per square meter of area. This means that the human body is subject to air pressure, the weight of which is 12-15 tons. Why don't we feel this? It is our internal pressure that saves us, which balances the external. You can feel the pressure of the atmosphere while on an airplane or high in the mountains, since the atmospheric pressure at altitude is much less. In this case, physical discomfort, blocked ears, and dizziness are possible.

A lot can be said about the surrounding atmosphere. We know many interesting facts about her, and some of them may seem surprising:

• The weight of the earth's atmosphere is 5,300,000,000,000,000 tons.
• It promotes sound transmission. At an altitude of more than 100 km, this property disappears due to changes in the composition of the atmosphere.
• The movement of the atmosphere is provoked by uneven heating of the Earth's surface.
• A thermometer is used to determine the air temperature, and a barometer is used to determine the pressure of the atmosphere.
• The presence of an atmosphere saves our planet from 100 tons of meteorites every day.
• The composition of the air was fixed for several hundred million years, but began to change with the onset of rapid industrial activity.
• The atmosphere is believed to extend upward to a height of 3000 km.

The importance of the atmosphere for humans

The physiological zone of the atmosphere is 5 km. At an altitude of 5000 m above sea level, a person begins to experience oxygen starvation, which is expressed in a decrease in his performance and deterioration in well-being. This shows that a person cannot survive in a space where there is no this amazing mixture of gases.

All information and facts about the atmosphere only confirm its importance for people. Thanks to its presence, it became possible to develop life on Earth. Already today, having assessed the scale of harm that humanity is capable of causing through its actions to the life-giving air, we should think about further measures to preserve and restore the atmosphere.

Atmosphere- this is the air shell that surrounds the Earth and is connected to it by gravity. The atmosphere is involved in the daily rotation and annual movement of our planet. Atmospheric air is a mixture of gases in which liquid (water droplets) and solid particles (smoke, dust) are suspended. The gas composition of the atmosphere is unchanged up to a height of 100-110 km, which is due to the balance in nature. The volume fractions of gases are: nitrogen - 78%, oxygen - 21%, inert gases (argon, xenon, krypton) - 0.9%, carbon - 0.03%. In addition, there is always water vapor in the atmosphere.

In addition to biological processes, oxygen, nitrogen and carbon are actively involved in the chemical weathering of rocks. The role of ozone 03 is very important; it absorbs most of the ultraviolet radiation from the Sun and, in large doses, is dangerous for living organisms. Solid particles, which are especially abundant over cities, serve as condensation nuclei (water droplets and snowflakes form around them).

Height, boundaries and structure of the atmosphere

The upper boundary of the atmosphere is conventionally drawn at an altitude of about 1000 km, although it can be traced much higher - up to 20,000 km, but there it is very rarefied.

Due to the different nature of changes in air temperature with height and other physical properties, several parts are distinguished in the atmosphere, which are separated from each other by transition layers.

The troposphere is the lowest and densest layer of the atmosphere. Its upper boundary is drawn at an altitude of 18 km above the equator and 8-12 km above the poles. The temperature in the troposphere decreases by an average of 0.6 ° C for every 100 m. It is characterized by significant horizontal differences in the distribution of temperature, pressure, wind speed, as well as the formation of clouds and precipitation. In the troposphere there is intense vertical air movement - convection. It is in this lower layer of the atmosphere that the weather is mainly formed. Almost all of the atmospheric water vapor is concentrated here.

The stratosphere extends mainly to an altitude of 50 km. The ozone concentration at an altitude of 20-25 km reaches its highest values, forming an ozone screen. The air temperature in the stratosphere, as a rule, increases with altitude by an average of 1-2 ° C per 1 km, reaching 0 ° C and higher at the upper limit. This occurs due to the absorption of solar energy by ozone. There is almost no water vapor or clouds in the stratosphere, and hurricane-force winds blow at speeds of up to 300-400 km/h.

In the mesosphere, the air temperature drops to -60...- 100 ° C, and intense vertical and horizontal air movements occur.

In the upper layers of the thermosphere, where the air is highly ionized, the temperature rises again to 2000 ° C. Auroras and magnetic storms are observed here.

The atmosphere plays a big role in the life of the Earth. It prevents excessive heating of the earth's surface during the day and its cooling at night, redistributes moisture on the Earth, and protects its surface from meteorite falls. The presence of an atmosphere is an indispensable condition for the existence of organic life on our planet.

Solar radiation. Atmospheric heating

The sun emits a huge amount of energy, only a small fraction of which the Earth receives.

The emission of light and heat from the Sun is called solar radiation. Solar radiation travels a long way through the atmosphere before reaching the earth's surface. Overcoming it, it is largely absorbed and dissipated by the air envelope. Radiation that directly reaches the earth's surface in the form of direct rays is called direct radiation. Some of the radiation that is scattered in the atmosphere also reaches the Earth's surface in the form of diffuse radiation.

The combination of direct and diffuse radiation arriving on a horizontal surface is called total solar radiation. The atmosphere absorbs about 20% of solar radiation arriving at its upper boundary. Another 34% of radiation is reflected from the Earth's surface and atmosphere (reflected radiation). 46% of solar radiation is absorbed by the earth's surface. Such radiation is called absorbed (absorbed).

The ratio of the intensity of reflected solar radiation to the intensity of all the radiant energy of the Sun arriving at the upper boundary of the atmosphere is called the Earth's albedo and is expressed as a percentage.

So, the albedo of our planet together with its atmosphere is on average 34%. The albedo value at different latitudes has significant differences associated with surface color, vegetation, cloudiness, and the like. A surface area covered with fresh snow reflects 80-85% of radiation, grass and sand - 26% and 30%, respectively, and water - only 5%.

The amount of solar energy received by individual areas of the Earth depends primarily on the angle of incidence of the sun's rays. The straighter they fall (i.e., the greater the height of the Sun above the horizon), the greater the amount of solar energy falling per unit area.

The dependence of the amount of total radiation on the angle of incidence of the rays is due to two reasons. Firstly, the smaller the angle of incidence of the sun's rays, the larger the area this light flux is distributed over and the less energy there is per unit surface. Secondly, the smaller the angle of incidence, the longer the path the beam travels in the atmosphere.

The amount of solar radiation that hits the earth's surface is also affected by the transparency of the atmosphere, especially cloudiness. The dependence of solar radiation on the angle of incidence of solar rays and the transparency of the atmosphere determines the zonal nature of its distribution. Differences in the amount of total solar radiation at one latitude are caused mainly by cloudiness.

The amount of heat entering the earth's surface is determined in calories per unit area (1 cm) per unit of time (1 year).

The absorbed radiation is spent on heating the thin surface layer of the Earth and evaporating water. The heated earth's surface transfers heat to the environment through radiation, conduction, convection and condensation of water vapor.

Changes in air temperature depending on the latitude of the place and the height above sea level

The total radiation decreases from equatorial-tropical latitudes to the poles. It is maximum - about 850 J/m2 per year (200 kcal/cm2 per year) - in tropical deserts, where direct solar radiation through the high altitude of the Sun and cloudless skies is intense. In the summer half of the year, differences in the flow of total solar radiation between low and high latitudes are smoothed out. This occurs due to the longer duration of the sun's illumination, especially in the polar regions, where the polar day lasts even six months.

Although the total solar radiation arriving at the earth's surface is partially reflected by it, most of it is absorbed by the earth's surface and turns into heat. The part of the total radiation that remains after it is spent on reflection and thermal radiation of the earth's surface is called the radiation balance (residual radiation). Overall for the year, it is positive everywhere on Earth, with the exception of the high ice deserts of Antarctica and Greenland. The radiation balance naturally decreases in the direction from the equator to the poles, where it is close to zero.

Accordingly, the air temperature is distributed zonally, that is, it decreases in the direction from the equator to the poles. .The air temperature also depends on the altitude of the area above sea level: the higher the area, the lower the temperature.

The distribution of land and water has a significant influence on air temperature. The land surface heats up quickly, but cools quickly, and the water surface heats up more slowly, but retains heat longer and releases it into the air more slowly.

As a result of different intensities of heating and cooling of the Earth's surface day and night, in the warm and cold seasons, the air temperature changes throughout the day and year.

Thermometers are used to determine air temperature. it is measured 8 times a day and the average per day is calculated. Using average daily temperatures, monthly averages are calculated. They are usually shown on climate maps as isotherms (lines that connect points with the same temperature over a certain period of time). To characterize temperatures, monthly averages in January and July are most often taken, less often annual ones. ,

The atmosphere began to form along with the formation of the Earth. During the evolution of the planet and as its parameters approached modern values, fundamentally qualitative changes occurred in its chemical composition and physical properties. According to the evolutionary model, at an early stage the Earth was in a molten state and about 4.5 billion years ago formed as a solid body. This milestone is taken as the beginning of the geological chronology. From that time on, the slow evolution of the atmosphere began. Some geological processes (for example, lava outpourings during volcanic eruptions) were accompanied by the release of gases from the bowels of the Earth. They included nitrogen, ammonia, methane, water vapor, CO oxide and carbon dioxide CO 2. Under the influence of solar ultraviolet radiation, water vapor decomposed into hydrogen and oxygen, but the released oxygen reacted with carbon monoxide to form carbon dioxide. Ammonia decomposed into nitrogen and hydrogen. During the process of diffusion, hydrogen rose upward and left the atmosphere, and heavier nitrogen could not evaporate and gradually accumulated, becoming the main component, although some of it was bound into molecules as a result of chemical reactions ( cm. CHEMISTRY OF THE ATMOSPHERE). Under the influence of ultraviolet rays and electrical discharges, a mixture of gases present in the original atmosphere of the Earth entered into chemical reactions, which resulted in the formation of organic substances, in particular amino acids. With the advent of primitive plants, the process of photosynthesis began, accompanied by the release of oxygen. This gas, especially after diffusion into the upper layers of the atmosphere, began to protect its lower layers and the surface of the Earth from life-threatening ultraviolet and X-ray radiation. According to theoretical estimates, the oxygen content, 25,000 times less than now, could already lead to the formation of an ozone layer with only half the concentration than now. However, this is already enough to provide very significant protection of organisms from the destructive effects of ultraviolet rays.

It is likely that the primary atmosphere contained a lot of carbon dioxide. It was used up during photosynthesis, and its concentration must have decreased as the plant world evolved and also due to absorption during certain geological processes. Because the Greenhouse effect associated with the presence of carbon dioxide in the atmosphere, fluctuations in its concentration are one of the important reasons for such large-scale climate changes in the history of the Earth as ice ages.

The helium present in the modern atmosphere is mostly a product of the radioactive decay of uranium, thorium and radium. These radioactive elements emit a particles, which are the nuclei of helium atoms. Since during radioactive decay an electric charge is neither formed nor destroyed, with the formation of each a-particle two electrons appear, which, recombining with the a-particles, form neutral helium atoms. Radioactive elements are contained in minerals dispersed in rocks, so a significant part of the helium formed as a result of radioactive decay is retained in them, escaping very slowly into the atmosphere. A certain amount of helium rises upward into the exosphere due to diffusion, but due to the constant influx from the earth's surface, the volume of this gas in the atmosphere remains almost unchanged. Based on spectral analysis of starlight and the study of meteorites, it is possible to estimate the relative abundance of various chemical elements in the Universe. The concentration of neon in space is approximately ten billion times higher than on Earth, krypton - ten million times, and xenon - a million times. It follows that the concentration of these inert gases, apparently initially present in the Earth’s atmosphere and not replenished during chemical reactions, decreased greatly, probably even at the stage of the Earth’s loss of its primary atmosphere. An exception is the inert gas argon, since in the form of the 40 Ar isotope it is still formed during the radioactive decay of the potassium isotope.

Barometric pressure distribution.

The total weight of atmospheric gases is approximately 4.5 10 15 tons. Thus, the “weight” of the atmosphere per unit area, or atmospheric pressure, at sea level is approximately 11 t/m 2 = 1.1 kg/cm 2. Pressure equal to P 0 = 1033.23 g/cm 2 = 1013.250 mbar = 760 mm Hg. Art. = 1 atm, taken as the standard average atmospheric pressure. For the atmosphere in a state of hydrostatic equilibrium we have: d P= –rgd h, this means that in the height interval from h before h+d h occurs equality between the change in atmospheric pressure d P and the weight of the corresponding element of the atmosphere with unit area, density r and thickness d h. As a relationship between pressure R and temperature T The equation of state of an ideal gas with density r, which is quite applicable to the earth’s atmosphere, is used: P= r R T/m, where m is the molecular weight, and R = 8.3 J/(K mol) is the universal gas constant. Then d log P= – (m g/RT)d h= – bd h= – d h/H, where the pressure gradient is on a logarithmic scale. Its inverse value H is called the atmospheric altitude scale.

When integrating this equation for an isothermal atmosphere ( T= const) or for its part where such an approximation is permissible, the barometric law of pressure distribution with height is obtained: P = P 0 exp(– h/H 0), where the height reference h produced from ocean level, where the standard mean pressure is P 0 . Expression H 0 = R T/ mg, is called the altitude scale, which characterizes the extent of the atmosphere, provided that the temperature in it is the same everywhere (isothermal atmosphere). If the atmosphere is not isothermal, then integration must take into account the change in temperature with height, and the parameter N– some local characteristic of atmospheric layers, depending on their temperature and the properties of the environment.

Standard atmosphere.

Model (table of values ​​of the main parameters) corresponding to standard pressure at the base of the atmosphere R 0 and chemical composition is called a standard atmosphere. More precisely, this is a conditional model of the atmosphere, for which the average values ​​of temperature, pressure, density, viscosity and other characteristics of air at altitudes from 2 km below sea level to the outer boundary of the earth’s atmosphere are specified for latitude 45° 32ў 33І. The parameters of the middle atmosphere at all altitudes were calculated using the equation of state of an ideal gas and the barometric law assuming that at sea level the pressure is 1013.25 hPa (760 mm Hg) and the temperature is 288.15 K (15.0 ° C). According to the nature of the vertical temperature distribution, the average atmosphere consists of several layers, in each of which the temperature is approximated 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 the latitude and season. In temperate and high latitudes in winter it is 1–2 km lower than in summer and 8–15 K warmer. In the tropics, seasonal changes are much less (altitude 16–18 km, temperature 180–200 K). Above jet streams tropopause breaks are possible.

Water in the Earth's atmosphere.

The most important feature of the Earth's atmosphere is the presence 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 ground layer of air; in summer and during the day, it weakens the heating of the earth's surface by the sun's rays, softening the climate inside the continents.

Clouds.

Clouds are accumulations of water droplets suspended in the atmosphere (water clouds), ice crystals (ice clouds), or both together (mixed clouds). As droplets and crystals become larger, they fall out of the clouds in the form of precipitation. Clouds form mainly in the troposphere. They arise as a result of condensation of water vapor contained in the air. The diameter of cloud drops is on the order of several microns. The content of liquid water in clouds ranges from fractions to several grams per m3. Clouds are distinguished 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 are composed 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 are a whitish translucent veil in the upper troposphere, usually fibrous, sometimes blurred, consisting of small needle-shaped or columnar ice crystals.

Altocumulus clouds are white, gray or white-gray clouds in the lower and middle layers of the troposphere. Altocumulus clouds have the appearance of layers and ridges, as if built from plates, rounded masses, shafts, flakes lying on top of each other. Altocumulus clouds form during intense convective activity and usually consist of supercooled water droplets.

Altostratus clouds are grayish or bluish clouds with a fibrous or uniform structure. Altostratus clouds are observed in the middle troposphere, extending several kilometers in height and sometimes thousands of kilometers in the horizontal direction. Typically, altostratus clouds are part of frontal cloud systems associated with upward movements of air masses.

Nimbostratus clouds are a low (from 2 km and above) amorphous layer of clouds 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, located in the upper atmosphere, serves as a kind of shield that protects us from the effects of ultraviolet radiation from the Sun. Without this shield, the development of life on Earth in its modern forms would hardly have been possible.

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

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

Meteors, meteorites and fireballs.

Flares and other phenomena in the upper atmosphere of the Earth caused by the intrusion of solid cosmic particles or bodies into it at a speed of 11 km/s or higher are called meteoroids. An observable bright meteor trail appears; the most powerful phenomena, often accompanied by the fall of meteorites, are called fireballs; the appearance of meteors is associated with meteor showers.

Meteor shower:

1) the phenomenon of multiple falls of meteors over several hours or days from one radiant.

2) a swarm of meteoroids moving in the same orbit around the Sun.

The systematic appearance of meteors in a certain area of ​​the sky and on certain days of the year, caused by the intersection of the Earth's orbit with the common orbit of many meteorite bodies moving at approximately the same and identically directed speeds, due to which their paths in the sky appear to emerge from a common point (radiant) . They are named after the constellation where the radiant is located.

Meteor showers make a deep impression with their light effects, but individual meteors are rarely visible. Much more numerous are invisible meteors, too small to be visible when they are absorbed into the atmosphere. Some of the smallest meteors probably do not heat up at all, but are only captured by the atmosphere. These small particles with sizes ranging from a few millimeters to ten thousandths of a millimeter are called micrometeorites. The amount of meteoric matter entering the atmosphere every day ranges from 100 to 10,000 tons, with the majority of this material coming from micrometeorites.

Since meteoric matter partially burns in the atmosphere, its gas composition is replenished with traces of various chemical elements. For example, rocky meteors introduce lithium into the atmosphere. The combustion of metal meteors leads to the formation of tiny spherical iron, iron-nickel and other droplets that pass through the atmosphere and settle on the earth's surface. They can be found in Greenland and Antarctica, where ice sheets remain almost unchanged for years. Oceanologists find them in bottom ocean sediments.

Most meteor particles entering the atmosphere settle within approximately 30 days. Some scientists believe that this cosmic dust plays an important role in the formation of atmospheric phenomena such as rain because it serves as condensation nuclei for water vapor. Therefore, it is assumed that precipitation is statistically related to large meteor showers. However, some experts believe that since the total supply of meteoric material is many tens of times greater than that of even the largest meteor shower, the change in the total amount of this material resulting from one such rain can be neglected.

However, there is no doubt that the largest micrometeorites and visible meteorites leave long traces of ionization in the high layers of the atmosphere, mainly in the ionosphere. Such traces can be used for long-distance radio communications, as they reflect high-frequency radio waves.

The energy of meteors entering the atmosphere is spent mainly, and perhaps completely, on heating it. This is one of the minor components 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. The critical level (the base of the exosphere) is at an altitude of about 500 km.

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

Polar lights.

At high latitudes, auroras are observed during magnetic field disturbances. They may last a few minutes, but are often visible for several hours. Auroras vary greatly in shape, color and intensity, all of which sometimes change very quickly over time. The spectrum of auroras consists of emission lines and bands. Some of the night sky emissions are enhanced in the aurora spectrum, primarily the green and red lines l 5577 Å and l 6300 Å oxygen. It happens that one of these lines is many times more intense than the other, and this determines 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 (

The actual forms of auroras are difficult to classify; The most commonly used terms are:

1. Calm, uniform arcs or stripes. The arc typically extends ~1000 km in the direction of the geomagnetic parallel (toward the Sun in polar regions) and has a width of one to several tens of kilometers. A stripe is a generalization of the concept of an arc; it usually does not have a regular arc-shaped shape, but bends in the form of the letter S or in the form of spirals. Arcs and stripes are located at altitudes of 100–150 km.

2. Rays of the aurora . This term refers to an auroral structure elongated along magnetic field lines, with a vertical extent of several tens to several hundred kilometers. The horizontal extent of the rays is small, from several tens of meters to several kilometers. The rays are usually observed in arcs or as separate structures.

3. Stains or surfaces . These are isolated areas of glow that do not have a specific shape. Individual spots may be connected to each other.

4. Veil. An unusual form of aurora, which is a uniform glow that covers large areas of the sky.

According to their structure, auroras are divided into homogeneous, hollow and radiant. Various terms are used; pulsating arc, pulsating surface, diffuse surface, radiant stripe, drapery, etc. There is a classification of auroras according to their color. According to this classification, auroras of the type A. The upper part or the entire part is red (6300–6364 Å). They usually appear at altitudes of 300–400 km with high geomagnetic activity.

Aurora type IN colored red in the lower part and associated with the glow of the bands of the first positive system N 2 and the first negative system O 2. Such forms of auroras appear during the most active phases of auroras.

Zones polar lights – These are the zones of maximum frequency of auroras at night, according to observers at a fixed point on the Earth's surface. The zones are located at 67° north and south latitude, and their width is about 6°. The maximum occurrence of auroras, corresponding to a given moment of geomagnetic local time, occurs in oval-like belts (oval auroras), which are located asymmetrically around the north and south geomagnetic poles. The aurora oval is fixed in latitude – time coordinates, and the aurora zone is the geometric locus of the points of the oval’s midnight region in latitude – longitude coordinates. The oval belt is located approximately 23° from the geomagnetic pole in the night sector and 15° in the daytime sector.

Aurora oval and aurora zones. The location of the aurora oval depends on geomagnetic activity. The oval becomes wider at high geomagnetic activity. Auroral zones or auroral oval boundaries are better represented by L 6.4 than by dipole coordinates. Geomagnetic field lines at the boundary of the daytime sector of the aurora oval coincide with magnetopause. A change in the position of the aurora oval is observed depending on the angle between the geomagnetic axis and the Earth-Sun direction. The auroral oval is also determined on the basis of data on precipitation of particles (electrons and protons) of certain energies. Its position can be independently determined from data on Kaspakh on the dayside and in the tail of the magnetosphere.

The daily variation in the frequency of occurrence of auroras in the aurora zone has a maximum at geomagnetic midnight and a minimum at geomagnetic noon. On the near-equatorial side of the oval, the frequency of occurrence of auroras sharply decreases, but the shape of the daily variations is preserved. On the polar side of the oval, the frequency of auroras decreases gradually and is characterized by complex diurnal changes.

Intensity of auroras.

Aurora intensity determined by measuring the apparent surface brightness. Luminosity surface I aurora in a certain direction is determined by the total emission of 4p I photon/(cm 2 s). Since this value is not the true surface brightness, but represents the emission from the column, the unit photon/(cm 2 column s) is usually used when studying auroras. The usual unit for measuring total emission is Rayleigh (Rl) equal to 10 6 photons/(cm 2 column s). More practical units of auroral intensity are determined by the emissions of an individual line or band. For example, the intensity of auroras is determined by the international brightness coefficients (IBRs) according to the intensity of the green line (5577 Å); 1 kRl = I MKY, 10 kRl = II MKY, 100 kRl = III MKY, 1000 kRl = IV MKY (maximum intensity of the aurora). This classification cannot be used for red auroras. One of the discoveries of the era (1957–1958) was the establishment of the spatiotemporal distribution of auroras in the form of an oval, shifted relative to the magnetic pole. From simple ideas about the circular shape of the distribution of auroras relative to the magnetic pole there was The transition to modern physics of the magnetosphere has been completed. The honor of the discovery belongs to O. Khorosheva, and the intensive development of ideas for the auroral oval was carried out by G. Starkov, Y. Feldstein, S. I. Akasofu and a number of other researchers. The auroral oval is the region of the most intense influence of the solar wind on the Earth's upper atmosphere. The intensity of the aurora is greatest in the oval, and its dynamics are continuously monitored using satellites.

Stable auroral red arcs.

Steady auroral red arc, otherwise called mid-latitude red arc or M-arc, is a subvisual (below the limit of sensitivity of the eye) wide arc, stretching from east to west for thousands of kilometers and possibly encircling the entire Earth. The latitudinal length of the arc is 600 km. The emission of the stable auroral red arc is almost monochromatic in the red lines l 6300 Å and l 6364 Å. Recently, weak emission lines l 5577 Å (OI) and l 4278 Å (N+2) were also reported. Sustained red arcs are classified as auroras, but they appear at much higher altitudes. The lower limit is located at an altitude of 300 km, the upper limit is about 700 km. The intensity of the quiet auroral red arc in the l 6300 Å emission ranges from 1 to 10 kRl (typical value 6 kRl). The sensitivity threshold of the eye at this wavelength is about 10 kRl, so arcs are rarely observed visually. However, observations have shown that their brightness is >50 kRL on 10% of nights. The usual lifespan of arcs is about one day, and they rarely appear in subsequent days. Radio waves from satellites or radio sources crossing persistent auroral red arcs are subject to scintillation, indicating the existence of electron density inhomogeneities. The theoretical explanation for red arcs is that the heated electrons of the region F The ionosphere causes an increase in oxygen atoms. Satellite observations show an increase in electron temperature along geomagnetic field lines that intersect persistent auroral red arcs. The intensity of these arcs is positively correlated with geomagnetic activity (storms), and the frequency of occurrence of arcs is positively correlated with sunspot activity.

Changing aurora.

Some forms of auroras experience quasiperiodic and coherent temporal variations in intensity. These auroras with approximately stationary geometry and rapid periodic variations occurring in phase are called changing auroras. They are classified as auroras forms R according to the International Atlas of Auroras A more detailed subdivision of the changing auroras:

R 1 (pulsating aurora) is a glow with uniform phase variations in brightness throughout the aurora shape. By definition, in an ideal pulsating aurora, the spatial and temporal parts of the pulsation can be separated, i.e. brightness I(r,t)= I s(r)· I T(t). In a typical aurora R 1 pulsations occur with a frequency from 0.01 to 10 Hz of low intensity (1–2 kRl). Most auroras R 1 – these are spots or arcs that pulsate with a period of several seconds.

R 2 (fiery aurora). The term is usually used to refer to movements like flames filling the sky, rather than to describe a distinct form. The auroras have the shape of arcs and usually move upward from a height of 100 km. These auroras are relatively rare and occur more often outside the aurora.

R 3 (shimmering aurora). These are auroras with rapid, irregular or regular variations in brightness, giving the impression of flickering flames in the sky. They appear shortly before the aurora disintegrates. Typically observed frequency of variation R 3 is equal to 10 ± 3 Hz.

The term streaming aurora, used for another class of pulsating auroras, refers to irregular variations in brightness moving quickly horizontally in auroral arcs and streaks.

The changing aurora is one of the solar-terrestrial phenomena that accompany pulsations of the geomagnetic field and auroral X-ray radiation caused by the precipitation of particles of solar and magnetospheric origin.

The glow of the polar cap is characterized by high intensity of the band of the first negative system N + 2 (l 3914 Å). Typically, these N + 2 bands are five times more intense than the green line OI l 5577 Å; the absolute intensity of the polar cap glow ranges from 0.1 to 10 kRl (usually 1–3 kRl). During these auroras, which appear during periods of PCA, a uniform glow covers the entire polar cap up to a geomagnetic latitude of 60° at altitudes of 30 to 80 km. It is generated predominantly by solar protons and d-particles with energies of 10–100 MeV, creating a maximum ionization at these altitudes. There is another type of glow in aurora zones, called mantle aurora. For this type of auroral glow, the daily maximum intensity, occurring in the morning hours, is 1–10 kRL, and the minimum intensity is five times weaker. Observations of mantle auroras are few and far between; their intensity depends on geomagnetic and solar activity.

Atmospheric glow is defined as radiation produced and emitted by a planet's atmosphere. This is non-thermal radiation of the atmosphere, with the exception of the emission of auroras, lightning discharges and the emission of meteor trails. This term is used in relation to the earth's atmosphere (nightglow, twilight glow and dayglow). Atmospheric glow constitutes only a portion of the light available in the atmosphere. Other sources include starlight, zodiacal light, and daytime diffuse light from the Sun. At times, 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 airglow in the l 5577 Å emission with the number of sunspots and solar radiation flux at a wavelength of 10.7 cm. Airglow is observed during satellite experiments. From outer space, it appears as a ring of light around the Earth and has a greenish color.

Ozonosphere.

At altitudes of 20–25 km, the maximum concentration of an insignificant amount of ozone O 3 is reached (up to 2×10 –7 of the oxygen content!), which arises under the influence of solar ultraviolet radiation at altitudes of approximately 10 to 50 km, protecting the planet from ionizing solar radiation. Despite the extremely small number of ozone molecules, they protect all life on Earth from the harmful effects of short-wave (ultraviolet and x-ray) radiation from the Sun. If you deposit all the molecules to the base of the atmosphere, you will get a layer no more than 3–4 mm thick! At altitudes above 100 km, the proportion of light gases increases, and at very high altitudes helium and hydrogen predominate; many molecules dissociate into individual atoms, which, ionized under the influence of hard radiation from the Sun, form the ionosphere. The pressure and density of air in the Earth's atmosphere decrease with altitude. Depending on the temperature distribution, the Earth's atmosphere is divided into the troposphere, stratosphere, mesosphere, thermosphere and exosphere. .

At an altitude of 20–25 km there is ozone layer. Ozone is formed due to the breakdown of oxygen molecules when absorbing ultraviolet radiation from the Sun with wavelengths shorter than 0.1–0.2 microns. Free oxygen combines with O 2 molecules and forms ozone O 3, which greedily absorbs all ultraviolet radiation shorter than 0.29 microns. O3 ozone molecules are easily destroyed by short-wave radiation. Therefore, despite its rarefaction, the ozone layer effectively absorbs ultraviolet radiation from the Sun that has passed through higher and more transparent atmospheric layers. Thanks to this, living organisms on Earth are protected from the harmful effects of ultraviolet light from the Sun.

Ionosphere.

Radiation from the sun ionizes the atoms and molecules of the atmosphere. The degree of ionization becomes significant already at an altitude of 60 kilometers and steadily increases with distance from the Earth. At different altitudes in the atmosphere, sequential processes of dissociation of various molecules and subsequent ionization of various atoms and ions occur. These are mainly molecules of oxygen O 2, nitrogen N 2 and their atoms. Depending on the intensity of these processes, the various layers of the atmosphere lying above 60 kilometers are called ionospheric layers , and their totality is the ionosphere . The lower layer, the ionization of which is insignificant, is called the neutrosphere.

The maximum concentration of charged particles in the ionosphere is achieved at altitudes of 300–400 km.

History of the study of the ionosphere.

The hypothesis about the existence of a conducting layer in the upper atmosphere was put forward in 1878 by the English scientist Stuart to explain the features of the geomagnetic field. Then in 1902, independently of each other, Kennedy in the USA and Heaviside in England pointed out that to explain the propagation of radio waves over long distances it was necessary to assume the existence of regions of high conductivity in the high layers of the atmosphere. In 1923, academician M.V. Shuleikin, considering the features of the propagation of radio waves of various frequencies, came to the conclusion that there are at least two reflective layers in the ionosphere. Then in 1925, English researchers Appleton and Barnett, as well as Breit and Tuve, first experimentally proved the existence of regions that reflect radio waves, and laid the foundation for their systematic study. Since that time, a systematic study has been carried out of the properties of these layers, generally called the ionosphere, which play a significant role in a number of geophysical phenomena that determine the reflection and absorption of radio waves, which is very important for practical purposes, in particular for ensuring reliable radio communications.

In the 1930s, systematic observations of the state of the ionosphere began. In our country, on the initiative of M.A. Bonch-Bruevich, installations for its pulse probing were created. Many general properties of the ionosphere, heights and electron concentration of its main layers were studied.

At altitudes of 60–70 km layer D is observed, at altitudes of 100–120 km layer E, at altitudes, at altitudes of 180–300 km double layer F 1 and F 2. The main parameters of these layers are given in Table 4.

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 from the Sun, which occurs mainly in the solar chromosphere and corona. In addition, the degree of ionization of the upper atmosphere is influenced by solar corpuscular streams that occur during solar flares, as well as cosmic rays and meteor particles.

Ionospheric layers

- these are areas in the atmosphere in which maximum concentrations of free electrons are reached (i.e., their number per unit volume). Electrically charged free electrons and (to a lesser extent, less mobile ions) resulting from the ionization of atoms of atmospheric gases, interacting with radio waves (i.e., electromagnetic oscillations), can change their direction, reflecting or refracting them, and absorb their energy. As a result of this, when receiving distant radio stations, various effects may occur, for example, fading of radio communications, increased audibility of remote stations, blackouts and so on. phenomena.

Research methods.

Classical methods of studying the ionosphere from Earth come down to pulse sounding - sending radio pulses and observing their reflections from various layers of the ionosphere, measuring the delay time and studying the intensity and shape of the reflected signals. By measuring the heights of reflection of radio pulses at various frequencies, determining the critical frequencies of various areas (the critical frequency is the carrier frequency of a radio pulse, for which a given region of the ionosphere becomes transparent), it is possible to determine the value of the electron concentration in the layers and the effective heights for given frequencies, and select the optimal frequencies for given radio paths. With the development of rocket technology and the advent of the space age of artificial Earth satellites (AES) and other spacecraft, it became possible to directly measure the parameters of near-Earth space plasma, the lower part of which is the ionosphere.

Measurements of electron concentration, carried out on board specially launched rockets and along satellite flight paths, confirmed and clarified data previously obtained by ground-based methods on the structure of the ionosphere, the distribution of electron concentration with height above various regions of the Earth and made it possible to obtain electron concentration values ​​above the main maximum - the layer F. Previously, this was impossible to do using sounding methods based on observations of reflected short-wave radio pulses. It has been discovered that in some areas of the globe there are quite stable areas with a reduced electron concentration, regular “ionospheric winds”, peculiar wave processes arise in the ionosphere that carry local ionospheric disturbances thousands of kilometers from the place of their excitation, and much more. The creation of particularly highly sensitive receiving devices made it possible to receive pulse signals partially reflected from the lowest regions of the ionosphere (partial reflection stations) at ionospheric pulse sounding stations. The use of powerful pulsed installations in the meter and decimeter wavelength ranges with the use of antennas that allow for a high concentration of emitted energy made it possible to observe signals scattered by the ionosphere at various altitudes. The study of the features of the spectra of these signals, incoherently scattered by electrons and ions of the ionospheric plasma (for this, stations of incoherent scattering of radio waves were used) made it possible to determine the concentration of electrons and ions, their equivalent temperature at various altitudes up to altitudes of several thousand kilometers. It turned out that the ionosphere is quite transparent for the frequencies used.

The concentration of electric charges (the electron concentration is equal to the ion concentration) in the earth's ionosphere at an altitude of 300 km is about 10 6 cm –3 during the day. Plasma of such density reflects radio waves with a length of more than 20 m, and transmits shorter ones.

Typical vertical distribution of electron concentration in the ionosphere for day and night conditions.

Propagation of radio waves in the ionosphere.

Stable reception of long-distance broadcasting stations depends on the frequencies used, as well as on the time of day, season and, in addition, on solar activity. Solar activity significantly affects the state of the ionosphere. Radio waves emitted by a ground station travel in a straight line, like all types of electromagnetic waves. However, it should be taken into account that both the surface of the Earth and the ionized layers of its atmosphere serve as the plates of a huge capacitor, acting on them like the effect of mirrors on light. Reflecting from them, radio waves can travel many thousands of kilometers, circling the globe in huge leaps of hundreds and thousands of kilometers, reflecting alternately from a layer of ionized gas and from the surface of the Earth or water.

In the 20s of the last century, it was believed that radio waves shorter than 200 m were generally not suitable for long-distance communications due to strong absorption. The first experiments on long-distance reception of short waves across the Atlantic between Europe and America were carried out by English physicist Oliver Heaviside and American electrical engineer Arthur Kennelly. Independently of each other, they suggested that somewhere around the Earth there is an ionized layer of the atmosphere capable of reflecting radio waves. It was called the Heaviside-Kennelly layer, and then the ionosphere.

According to modern 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 high-frequency waves are reflected from it. With a decrease in electron concentration, the passage of radio waves is possible only in low frequency ranges. That is why at night, as a rule, it is possible to receive distant stations only in the ranges of 75, 49, 41 and 31 m. Electrons are distributed unevenly in the ionosphere. At altitudes from 50 to 400 km there are several layers or regions of increased electron concentration. These areas smoothly transition into one another and have different effects on the propagation of HF radio waves. The upper layer of the ionosphere is designated by the letter F. Here the highest degree of ionization (the fraction of charged particles is about 10 –4). It is located at an altitude of more than 150 km above the Earth's surface and plays the main reflective role in the long-distance propagation of high-frequency HF radio waves. In the summer months, region F splits into two layers - F 1 and F 2. Layer F1 can occupy heights from 200 to 250 km, and layer F 2 seems to “float” in the altitude range of 300–400 km. Usually layer F 2 is ionized much stronger than the layer F 1 . Night layer F 1 disappears and the layer F 2 remains, slowly losing up to 60% of its degree of ionization. Below layer F at altitudes from 90 to 150 km there is a layer E ionization of which occurs under the influence of soft X-ray radiation from the Sun. The degree of ionization of the E layer is lower than that of the F, during the day, reception of stations in the low-frequency HF ranges of 31 and 25 m occurs when signals are reflected from the layer E. Typically these are stations located at a distance of 1000–1500 km. At night in the layer E Ionization decreases sharply, but even at this time it continues to play a significant role in the reception of signals from stations on the 41, 49 and 75 m ranges.

Of great interest for receiving signals of high-frequency HF ranges of 16, 13 and 11 m are those arising in the area E layers (clouds) of highly increased ionization. The area of ​​these clouds can vary from a few to hundreds of square kilometers. This layer of increased ionization is called the sporadic layer E and is designated Es. Es clouds can move in the ionosphere under the influence of wind and reach speeds of up to 250 km/h. In summer in mid-latitudes 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, during years of low solar activity, when there is no transmission on the high-frequency HF bands, distant stations suddenly appear on the 16, 13 and 11 m bands with good volume, the signals of which are reflected many times from Es.

The lowest region of the ionosphere is the region D located at altitudes between 50 and 90 km. There are relatively few free electrons here. From the area D Long and medium waves are well reflected, and signals from low-frequency HF stations are strongly absorbed. After sunset, ionization disappears very quickly and it becomes possible to receive distant stations in the ranges of 41, 49 and 75 m, the signals of which are reflected from the layers F 2 and E. Individual layers of the ionosphere play an important role in the propagation of HF radio signals. The effect on radio waves occurs mainly due to the presence of free electrons in the ionosphere, although the mechanism of radio wave propagation is associated with the presence of large ions. The latter are also of interest when studying the chemical properties of the atmosphere, since they are more active than neutral atoms and molecules. Chemical reactions occurring in the ionosphere play an important role in its energy and electrical balance.

Normal ionosphere. Observations 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 due to the daily rotation of the Earth and seasonal differences in the angle of incidence of the sun's rays at noon, but unpredictable and abrupt changes in the state of the ionosphere also occur.

Disturbances in the ionosphere.

As is known, powerful cyclically repeating manifestations of activity occur on the Sun, which reach a maximum every 11 years. Observations under the International Geophysical Year (IGY) program coincided with the period of the highest solar activity for the entire period of systematic meteorological observations, i.e. from the beginning of the 18th century. During periods of high activity, the brightness of some areas on the Sun increases several times, and the power of ultraviolet and X-ray radiation increases sharply. Such phenomena are called solar flares. They last from several minutes to one to two hours. During the flare, solar plasma (mostly protons and electrons) is erupted, and elementary particles rush into outer space. Electromagnetic and corpuscular radiation from the Sun during such flares has a strong impact on the Earth's atmosphere.

The initial reaction is observed 8 minutes after the flare, when intense ultraviolet and X-ray radiation reaches the Earth. As a result, ionization increases sharply; X-rays penetrate the atmosphere to the lower boundary of the ionosphere; the number of electrons in these layers increases so much that the radio signals are almost completely absorbed (“extinguished”). The additional absorption of radiation causes the gas to heat up, which contributes to the development of winds. Ionized gas is an electrical conductor, and when it moves in the Earth's magnetic field, a dynamo effect occurs and an electric current is created. Such currents can, in turn, cause noticeable disturbances in the magnetic field and manifest themselves in the form of magnetic storms.

The structure and dynamics of the upper atmosphere are significantly determined by non-equilibrium processes in the thermodynamic sense associated with ionization and dissociation by solar radiation, chemical processes, excitation of molecules and atoms, their deactivation, collisions and other elementary processes. In this case, the degree of nonequilibrium increases with height as the density decreases. Up to altitudes of 500–1000 km, and often higher, the degree of nonequilibrium for many characteristics of the upper atmosphere is quite small, which makes it possible to use classical and hydromagnetic hydrodynamics, taking into account chemical reactions, to describe it.

The exosphere is the outer layer of the Earth's atmosphere, starting at altitudes of several hundred kilometers, from which light, fast-moving hydrogen atoms can escape into outer space.

Edward Kononovich

Literature:

Pudovkin M.I. Fundamentals of Solar Physics. St. Petersburg, 2001
Eris Chaisson, Steve McMillan Astronomy today. Prentice-Hall, Inc. Upper Saddle River, 2002
Materials on the Internet: http://ciencia.nasa.gov/