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 action of 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 belts 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.
Formation of the atmosphere. Today, the Earth's atmosphere is a mixture of gases - 78% nitrogen, 21% oxygen and small amounts of other gases, such as carbon dioxide. But when the planet first appeared, there was no oxygen in the atmosphere - it consisted of gases that originally existed in the solar system.
Earth arose when small rocky bodies made of dust and gas from the solar nebula, known as planetoids, collided with each other and gradually took the shape of a planet. As it grew, the gases contained in the planetoids burst out and enveloped the globe. After some time, the first plants began to release oxygen, and the primordial atmosphere developed into the current dense air envelope.
Origin of the atmosphere
- A rain of small planetoids fell on the nascent Earth 4.6 billion years ago. Gases from the solar nebula trapped inside the planet burst out during the collision and formed the Earth's primitive atmosphere, consisting of nitrogen, carbon dioxide and water vapor.
- The heat released during the formation of the planet is retained by a layer of dense clouds in the primordial atmosphere. "Greenhouse gases" such as carbon dioxide and water vapor stop the radiation of heat into space. The surface of the Earth is flooded with a seething sea of molten magma.
- When planetoid collisions became less frequent, the Earth began to cool and oceans appeared. Water vapor condenses from thick clouds, and rain, lasting for several eons, gradually floods the lowlands. Thus the first seas appear.
- The air is purified as water vapor condenses to form oceans. Over time, carbon dioxide dissolves in them, and the atmosphere is now dominated by nitrogen. Due to the lack of oxygen, the protective ozone layer does not form, and ultraviolet rays from the sun reach the earth's surface without hindrance.
- Life appears in ancient oceans within the first billion years. The simplest blue-green algae are protected from ultraviolet radiation by seawater. They use sunlight and carbon dioxide to produce energy, releasing oxygen as a byproduct, which gradually begins to accumulate in the atmosphere.
- Billions of years later, an oxygen-rich atmosphere forms. Photochemical reactions in the upper atmosphere create a thin layer of ozone that scatters harmful ultraviolet light. Life can now emerge from the oceans onto land, where evolution produces many complex organisms.
Billions of years ago, a thick layer of primitive algae began releasing oxygen into the atmosphere. They survive to this day in the form of fossils called stromatolites.
Volcanic origin
1. Ancient, airless Earth. 2. Eruption of gases.
According to this theory, volcanoes were actively erupting on the surface of the young planet Earth. The early atmosphere likely formed when gases trapped in the planet's silicon shell escaped through volcanoes.
- the air shell of the globe, rotating together with the Earth. The upper boundary of the atmosphere is conventionally drawn at altitudes of 150-200 km. The lower boundary is the Earth's surface.
Atmospheric air is a mixture of gases. Most of its volume in the surface layer of air accounts for nitrogen (78%) and oxygen (21%). In addition, the air contains inert gases (argon, helium, neon, etc.), carbon dioxide (0.03), water vapor and various solid particles (dust, soot, salt crystals).
The air is colorless, and the color of the sky is explained by the characteristics of the scattering of light waves.
The atmosphere consists of several layers: the troposphere, stratosphere, mesosphere and thermosphere.
The lower ground layer of air is called troposphere. At different latitudes its power is not the same. The troposphere follows the shape of the planet and participates together with the Earth in axial rotation. At the equator, the thickness of the atmosphere varies from 10 to 20 km. At the equator it is greater, and at the poles it is less. The troposphere is characterized by maximum air density; 4/5 of the mass of the entire atmosphere is concentrated in it. The troposphere determines weather conditions: various air masses form here, clouds and precipitation form, and intense horizontal and vertical air movement occurs.
Above the troposphere, up to an altitude of 50 km, is located stratosphere. It is characterized by lower air density and lacks water vapor. In the lower part of the stratosphere at altitudes of about 25 km. there is an “ozone screen” - a layer of the atmosphere with a high concentration of ozone, which absorbs ultraviolet radiation, which is fatal to organisms.
At an altitude of 50 to 80-90 km it extends mesosphere. With increasing altitude, the temperature decreases with an average vertical gradient of (0.25-0.3)°/100 m, and the air density decreases. The main energy process is radiant heat transfer. The atmospheric glow is caused by complex photochemical processes involving radicals and vibrationally excited molecules.
Thermosphere located at an altitude of 80-90 to 800 km. The air density here is minimal, and the degree of air ionization is very high. Temperature changes depending on the activity of the Sun. Due to the large number of charged particles, auroras and magnetic storms are observed here.
The atmosphere is of great importance for the nature of the Earth. Without oxygen, living organisms cannot breathe. Its ozone layer protects all living things from harmful ultraviolet rays. The atmosphere smoothes out temperature fluctuations: the Earth's surface does not get supercooled at night and does not overheat during the day. In dense layers of atmospheric air, before reaching the surface of the planet, meteorites burn from thorns.
The atmosphere interacts with all layers of the earth. With its help, heat and moisture are exchanged between the ocean and land. Without the atmosphere there would be no clouds, precipitation, or winds.
Human economic activities have a significant adverse impact on the atmosphere. Atmospheric air pollution occurs, which leads to an increase in the concentration of carbon monoxide (CO 2). And this contributes to global warming and increases the “greenhouse effect”. The Earth's ozone layer is destroyed due to industrial waste and transport.
The atmosphere needs protection. In developed countries, a set of measures is being implemented to protect atmospheric air from pollution.
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Composition of the atmosphere. The air envelope of our planet - atmosphere protects the earth's surface from the harmful effects of ultraviolet radiation from the Sun on living organisms. It also protects the Earth from cosmic particles - dust and meteorites.
The atmosphere consists of a mechanical mixture of gases: 78% of its volume is nitrogen, 21% is oxygen and less than 1% is helium, argon, krypton and other inert gases. The amount of oxygen and nitrogen in the air is practically unchanged, because nitrogen almost does not combine with other substances, and oxygen, which, although very active and spent on respiration, oxidation and combustion, is constantly replenished by plants.
Up to an altitude of approximately 100 km, the percentage of these gases remains virtually unchanged. This is due to the fact that the air is constantly mixed.
In addition to the mentioned gases, the atmosphere contains about 0.03% carbon dioxide, which is usually concentrated near the earth's surface and is distributed unevenly: in cities, industrial centers and areas of volcanic activity, its amount increases.
There is always a certain amount of impurities in the atmosphere - water vapor and dust. The content of water vapor depends on the air temperature: the higher the temperature, the more vapor the air can hold. Due to the presence of vaporous water in the air, atmospheric phenomena such as rainbows, refraction of sunlight, etc. are possible.
Dust enters the atmosphere during volcanic eruptions, sand and dust storms, during incomplete combustion of fuel at thermal power plants, etc.
The structure of the atmosphere. The density of the atmosphere changes with altitude: it is highest at the Earth's surface and decreases as it goes up. Thus, at an altitude of 5.5 km, the density of the atmosphere is 2 times, and at an altitude of 11 km, it is 4 times less than in the surface layer.
Depending on the density, composition and properties of gases, the atmosphere is divided into five concentric layers (Fig. 34).
Rice. 34. Vertical section of the atmosphere (stratification of the atmosphere)
1. The bottom layer is called troposphere. Its upper boundary passes at an altitude of 8-10 km at the poles and 16-18 km at the equator. The troposphere contains up to 80% of the total mass of the atmosphere and almost all water vapor.
The air temperature in the troposphere decreases with height by 0.6 °C every 100 m and at its upper boundary is -45-55 °C.
The air in the troposphere is constantly mixed and moves in different directions. Only here are fogs, rains, snowfalls, thunderstorms, storms and other weather phenomena observed.
2. Above is located stratosphere, which extends to an altitude of 50-55 km. Air density and pressure in the stratosphere are negligible. Thin air consists of the same gases as in the troposphere, but it contains more ozone. The highest concentration of ozone is observed at an altitude of 15-30 km. The temperature in the stratosphere increases with altitude and at its upper boundary reaches 0 °C and above. This is because ozone absorbs short-wave energy from the sun, causing the air to warm up.
3. Lies above the stratosphere mesosphere, extending to an altitude of 80 km. There the temperature drops again and reaches -90 °C. The air density there is 200 times less than at the surface of the Earth.
4. Above the mesosphere is located thermosphere(from 80 to 800 km). The temperature in this layer increases: at an altitude of 150 km to 220 °C; at an altitude of 600 km up to 1500 °C. Atmospheric gases (nitrogen and oxygen) are in an ionized state. Under the influence of short-wave solar radiation, individual electrons are separated from the shells of atoms. As a result, in this layer - ionosphere layers of charged particles appear. Their densest layer is located at an altitude of 300-400 km. Due to the low density, the sun's rays are not scattered there, so the sky is black, stars and planets shine brightly on it.
In the ionosphere there are polar lights, Powerful electric currents are formed that cause disturbances in the Earth's magnetic field.
5. Above 800 km is the outer shell - exosphere. The speed of movement of individual particles in the exosphere is approaching critical - 11.2 mm/s, so individual particles can overcome gravity and escape into outer space.
The meaning of atmosphere. The role of the atmosphere in the life of our planet is exceptionally great. Without her, the Earth would be dead. The atmosphere protects the Earth's surface from extreme heating and cooling. Its effect can be likened to the role of glass in greenhouses: allowing the sun's rays to pass through and preventing heat loss.
The atmosphere protects living organisms from short-wave and corpuscular radiation from the Sun. The atmosphere is the environment where weather phenomena occur, with which all human activity is associated. The study of this shell is carried out at meteorological stations. Day and night, in any weather, meteorologists monitor the state of the lower layer of the atmosphere. Four times a day, and at many stations hourly they measure temperature, pressure, air humidity, note cloudiness, wind direction and speed, amount of precipitation, electrical and sound phenomena in the atmosphere. Meteorological stations are located everywhere: in Antarctica and in tropical rainforests, on high mountains and in vast expanses of tundra. Observations are also carried out on the oceans from specially built ships.
Since the 30s. XX century observations began in the free atmosphere. They began to launch radiosondes that rise to a height of 25-35 km and, using radio equipment, transmit information about temperature, pressure, air humidity and wind speed to Earth. Nowadays, meteorological rockets and satellites are also widely used. The latter have television installations that transmit images of the earth's surface and clouds.
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5. The air shell of the earth§ 31. Heating of the atmosphere
The Earth's atmosphere is heterogeneous: at different altitudes there are different air densities and pressures, temperature and gas composition changes. Based on the behavior of the ambient air temperature (i.e., the temperature increases or decreases with height), the following layers are distinguished in it: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The boundaries between layers are called pauses: there are 4 of them, because the upper boundary of the exosphere is very blurred and often refers to near space. The general structure of the atmosphere can be found in the attached diagram.
Fig.1 The structure of the Earth's atmosphere. Credit: website
The lowest atmospheric layer is the troposphere, the upper boundary of which, called the tropopause, varies depending on the geographic latitude and ranges from 8 km. in the polar up to 20 km. in tropical latitudes. In middle or temperate latitudes, its upper limit lies at altitudes of 10-12 km. During the year, the upper limit of the troposphere experiences fluctuations depending on the influx of solar radiation. Thus, as a result of sounding at the South Pole of the Earth by the US meteorological service, it was revealed that from March to August or September there is a steady cooling of the troposphere, as a result of which for a short period in August or September its boundary rises to 11.5 km. Then, in the period from September to December, it quickly decreases and reaches its lowest position - 7.5 km, after which its height remains virtually unchanged until March. Those. The troposphere reaches its greatest thickness in summer and its thinnest in winter.
It is worth noting that, in addition to seasonal ones, there are also daily fluctuations in the height of the tropopause. Also, its position is influenced by cyclones and anticyclones: in the first, it falls, because The pressure in them is lower than in the surrounding air, and secondly, it rises accordingly.
The troposphere contains up to 90% of the total mass of earth's air and 9/10 of all water vapor. Turbulence is highly developed here, especially in the near-surface and highest layers, clouds of all levels develop, cyclones and anticyclones form. And due to the accumulation of greenhouse gases (carbon dioxide, methane, water vapor) of sunlight reflected from the Earth's surface, the greenhouse effect develops.
The greenhouse effect is associated with a decrease in air temperature in the troposphere with height (since the heated Earth gives off more heat to the surface layers). The average vertical gradient is 0.65°/100 m (i.e., the air temperature decreases by 0.65° C for every 100 meters of rise). So, if the average annual air temperature at the surface of the Earth near the equator is +26°, then at the upper boundary it is -70°. The temperature in the tropopause region above the North Pole varies throughout the year from -45° in summer to -65° in winter.
With increasing altitude, air pressure also decreases, amounting to only 12-20% of the near-surface level at the upper boundary of the troposphere.
At the boundary of the troposphere and the overlying layer of the stratosphere lies a layer of the tropopause, 1-2 km thick. The lower boundaries of the tropopause are usually taken to be a layer of air in which the vertical gradient decreases to 0.2°/100 m versus 0.65°/100 m in the underlying regions of the troposphere.
Within the tropopause, air flows of a strictly defined direction are observed, called high-altitude jet streams or “jet streams”, formed under the influence of the rotation of the Earth around its axis and heating of the atmosphere with the participation of solar radiation. Currents are observed at the boundaries of zones with significant temperature differences. There are several centers of localization of these currents, for example, arctic, subtropical, subpolar and others. Knowledge of the localization of jet streams is very important for meteorology and aviation: the first uses streams for more accurate weather forecasting, the second for constructing aircraft flight routes, because At the boundaries of the flows, there are strong turbulent vortices, similar to small whirlpools, called “clear-sky turbulence” due to the absence of clouds at these altitudes.
Under the influence of high-altitude jet currents, breaks often form in the tropopause, and at times it disappears altogether, although it then forms anew. This is especially often observed in subtropical latitudes, which are dominated by a powerful subtropical high-altitude current. In addition, the difference in tropopause layers in ambient temperature leads to the formation of gaps. For example, a large gap exists between the warm and low polar tropopause and the high and cold tropopause of tropical latitudes. Recently, a layer of the tropopause of temperate latitudes has also emerged, which has discontinuities with the previous two layers: polar and tropical.
The second layer of the earth's atmosphere is the stratosphere. The stratosphere can be roughly divided into two regions. The first of them, lying up to altitudes of 25 km, is characterized by almost constant temperatures, which are equal to the temperatures of the upper layers of the troposphere over a particular area. The second region, or inversion region, is characterized by an increase in air temperature to altitudes of approximately 40 km. This occurs due to the absorption of solar ultraviolet radiation by oxygen and ozone. In the upper part of the stratosphere, thanks to this heating, the temperature is often positive or even comparable to the temperature of the surface air.
Above the inversion region there is a layer of constant temperatures, which is called the stratopause and is the boundary between the stratosphere and mesosphere. Its thickness reaches 15 km.
Unlike the troposphere, turbulent disturbances are rare in the stratosphere, but there are strong horizontal winds or jet streams blowing in narrow zones along the boundaries of temperate latitudes facing the poles. The position of these zones is not constant: they can shift, expand, or even disappear altogether. Often jet streams penetrate into the upper layers of the troposphere, or, conversely, air masses from the troposphere penetrate into the lower layers of the stratosphere. Such mixing of air masses is especially typical in areas of atmospheric fronts.
There is little water vapor in the stratosphere. The air here is very dry, and therefore few clouds form. Only at altitudes of 20-25 km and in high latitudes can you notice very thin pearlescent clouds consisting of supercooled water droplets. During the day, these clouds are not visible, but with the onset of darkness they seem to glow due to the illumination of them by the Sun, which has already set below the horizon.
At the same altitudes (20-25 km) in the lower stratosphere there is the so-called ozone layer - the area with the highest content of ozone, which is formed under the influence of ultraviolet solar radiation (you can find out more about this process on the page). The ozone layer or ozonosphere is of extreme importance for maintaining the life of all organisms living on land, absorbing deadly ultraviolet rays with a wavelength of up to 290 nm. It is for this reason that living organisms do not live above the ozone layer; it is the upper limit of the distribution of life on Earth.
Under the influence of ozone, magnetic fields also change, atoms and molecules disintegrate, ionization occurs, and new formation of gases and other chemical compounds occurs.
The layer of the atmosphere lying above the stratosphere is called the mesosphere. It is characterized by a decrease in air temperature with height with an average vertical gradient of 0.25-0.3°/100 m, which leads to severe turbulence. At the upper boundaries of the mesosphere, in the region called the mesopause, temperatures down to -138°C were recorded, which is the absolute minimum for the entire Earth's atmosphere as a whole.
Here, within the mesopause, lies the lower boundary of the region of active absorption of X-ray and short-wave ultraviolet radiation from the Sun. This energy process is called radiant heat transfer. As a result, the gas is heated and ionized, which causes the atmosphere to glow.
At altitudes of 75-90 km at the upper boundaries of the mesosphere, special clouds were noted, occupying vast areas in the polar regions of the planet. These clouds are called noctilucent because of their glow at dusk, which is caused by the reflection of sunlight from the ice crystals of which these clouds are composed.
Air pressure within the mesopause is 200 times less than at the earth's surface. This suggests that almost all the air in the atmosphere is concentrated in its 3 lower layers: the troposphere, stratosphere and mesosphere. The overlying layers, the thermosphere and exosphere, account for only 0.05% of the mass of the entire atmosphere.
The thermosphere lies at altitudes from 90 to 800 km above the Earth's surface.
The thermosphere is characterized by a continuous increase in air temperature to altitudes of 200-300 km, where it can reach 2500°C. The temperature rises due to the absorption of X-rays and short-wavelength ultraviolet radiation from the Sun by gas molecules. Above 300 km above sea level, the temperature increase stops.
Simultaneously with the increase in temperature, the pressure and, consequently, the density of the surrounding air decreases. So if at the lower boundaries of the thermosphere the density is 1.8 × 10 -8 g/cm 3, then at the upper boundaries it is already 1.8 × 10 -15 g/cm 3, which approximately corresponds to 10 million - 1 billion particles per 1 cm 3.
All characteristics of the thermosphere, such as the composition of air, its temperature, density, are subject to strong fluctuations: depending on the geographical location, season of the year and time of day. Even the location of the upper boundary of the thermosphere changes.
The uppermost layer of the atmosphere is called the exosphere or scattering layer. Its lower limit is constantly changing within very wide limits; The average height is taken to be 690-800 km. It is installed where the probability of intermolecular or interatomic collisions can be neglected, i.e. the average distance that a chaotically moving molecule will cover before colliding with another similar molecule (the so-called free path) will be so great that in fact the molecules will not collide with a probability close to zero. The layer where the described phenomenon occurs is called thermal pause.
The upper boundary of the exosphere lies at altitudes of 2-3 thousand km. It is greatly blurred and gradually turns into a near-space vacuum. Sometimes, for this reason, the exosphere is considered part of outer space, and its upper limit is taken to be a height of 190 thousand km, at which the influence of solar radiation pressure on the speed of hydrogen atoms exceeds the gravitational attraction of the Earth. This is the so-called the earth's crown, consisting of hydrogen atoms. The density of the earth's corona is very small: only 1000 particles per cubic centimeter, but this number is more than 10 times higher than the concentration of particles in interplanetary space.
Due to the extreme rarefaction of the air in the exosphere, particles move around the Earth in elliptical orbits without colliding with each other. Some of them, moving along open or hyperbolic trajectories at cosmic speeds (hydrogen and helium atoms), leave the atmosphere and go into outer space, which is why the exosphere is called the scattering sphere.
