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. Located above 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.
| |
5. The air shell of the earth§ 31. Heating of the atmosphere
Troposphere
Its upper limit is at an altitude of 8-10 km in polar, 10-12 km in temperate and 16-18 km in tropical latitudes; lower in winter than in summer. The lower, main layer of the atmosphere contains more than 80% of the total mass of atmospheric air and about 90% of the total water vapor present in the atmosphere. Turbulence and convection are highly developed in the troposphere, clouds arise, and cyclones and anticyclones develop. Temperature decreases with increasing altitude with an average vertical gradient of 0.65°/100 m
Tropopause
The transition layer from the troposphere to the stratosphere, a layer of the atmosphere in which the decrease in temperature with height stops.
Stratosphere
A layer of the atmosphere located at an altitude of 11 to 50 km. Characterized by a slight change in temperature in the 11-25 km layer (lower layer of the stratosphere) and an increase in temperature in the 25-40 km layer from −56.5 to 0.8 ° C (upper layer of the stratosphere or inversion region). Having reached a value of about 273 K (almost 0 °C) at an altitude of about 40 km, the temperature remains constant up to an altitude of about 55 km. This region of constant temperature is called the stratopause and is the boundary between the stratosphere and mesosphere.
Stratopause
The boundary layer of the atmosphere between the stratosphere and mesosphere. In the vertical temperature distribution there is a maximum (about 0 °C).
Mesosphere
The mesosphere begins at an altitude of 50 km and extends to 80-90 km. Temperature decreases with height with an average vertical gradient of (0.25-0.3)°/100 m. The main energy process is radiant heat transfer. Complex photochemical processes involving free radicals, vibrationally excited molecules, etc. cause atmospheric luminescence.
Mesopause
Transitional layer between the mesosphere and thermosphere. There is a minimum in the vertical temperature distribution (about -90 °C).
Karman Line
The height above sea level, which is conventionally accepted as the boundary between the Earth's atmosphere and space. The Karman line is located at an altitude of 100 km above sea level.
Boundary of the Earth's atmosphere
Thermosphere
The upper limit is about 800 km. The temperature rises to altitudes of 200-300 km, where it reaches values of the order of 1500 K, after which it remains almost constant to high altitudes. Under the influence of ultraviolet and x-ray solar radiation and cosmic radiation, ionization of the air (“auroras”) occurs - the main regions of the ionosphere lie inside the thermosphere. At altitudes above 300 km, atomic oxygen predominates. The upper limit of the thermosphere is largely determined by the current activity of the Sun. During periods of low activity, a noticeable decrease in the size of this layer occurs.
Thermopause
The region of the atmosphere adjacent to the thermosphere. In this region, the absorption of solar radiation is negligible and the temperature does not actually change with altitude.
Exosphere (scattering sphere)
Atmospheric layers up to an altitude of 120 km
The exosphere is the dispersion zone, the outer part of the thermosphere, located above 700 km. The gas in the exosphere is very rarefied, and from here its particles leak into interplanetary space (dissipation).
Up to an altitude of 100 km, the atmosphere is a homogeneous, well-mixed mixture of gases. In higher layers, the distribution of gases by height depends on their molecular weights; the concentration of heavier gases decreases faster with distance from the Earth's surface. Due to the decrease in gas density, the temperature drops from 0 °C in the stratosphere to −110 °C in the mesosphere. However, the kinetic energy of individual particles at altitudes of 200-250 km corresponds to a temperature of ~150 °C. Above 200 km, significant fluctuations in temperature and gas density in time and space are observed.
At an altitude of about 2000-3500 km, the exosphere gradually turns into the so-called near-space vacuum, which is filled with highly rarefied particles of interplanetary gas, mainly hydrogen atoms. But this gas represents only part of the interplanetary matter. The other part consists of dust particles of cometary and meteoric origin. In addition to extremely rarefied dust particles, electromagnetic and corpuscular radiation of solar and galactic origin penetrates into this space.
The troposphere accounts for about 80% of the mass of the atmosphere, the stratosphere - about 20%; the mass of the mesosphere is no more than 0.3%, the thermosphere is less than 0.05% of the total mass of the atmosphere. Based on the electrical properties in the atmosphere, the neutronosphere and ionosphere are distinguished. It is currently believed that the atmosphere extends to an altitude of 2000-3000 km.
Depending on the composition of the gas in the atmosphere, homosphere and heterosphere are distinguished. The heterosphere is an area where gravity affects the separation of gases, since their mixing at such a height is negligible. This implies a variable composition of the heterosphere. Below it lies a well-mixed, homogeneous part of the atmosphere called the homosphere. The boundary between these layers is called the turbopause; it lies at an altitude of about 120 km.
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 the 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 structure and composition of the Earth’s atmosphere, it must be said, were not always constant values in one or another period of the development of our planet. Today, the vertical structure of this element, which has a total “thickness” of 1.5-2.0 thousand km, is represented by several main layers, including:
- The troposphere.
- Tropopause.
- Stratosphere.
- Stratopause.
- Mesosphere and mesopause.
- Thermosphere.
- Exosphere.
Basic elements of atmosphere
The troposphere is a layer in which strong vertical and horizontal movements are observed; it is here that weather, sedimentary phenomena, and climatic conditions are formed. It extends 7-8 kilometers from the surface of the planet almost everywhere, with the exception of the polar regions (up to 15 km there). In the troposphere, there is a gradual decrease in temperature, approximately by 6.4 ° C with each kilometer of altitude. This indicator may differ for different latitudes and seasons.
The composition of the Earth's atmosphere in this part is represented by the following elements and their percentages:
Nitrogen - about 78 percent;
Oxygen - almost 21 percent;
Argon - about one percent;
Carbon dioxide - less than 0.05%.
Single composition up to an altitude of 90 kilometers
In addition, here you can find dust, water droplets, water vapor, combustion products, ice crystals, sea salts, many aerosol particles, etc. This composition of the Earth’s atmosphere is observed up to approximately ninety kilometers in altitude, so the air is approximately the same in chemical composition, not only in the troposphere, but also in the overlying layers. But there the atmosphere has fundamentally different physical properties. The layer that has a general chemical composition is called the homosphere.
What other elements make up the Earth's atmosphere? In percentage (by volume, in dry air) gases such as krypton (about 1.14 x 10 -4), xenon (8.7 x 10 -7), hydrogen (5.0 x 10 -5), methane (about 1.7 x 10 -5) are represented here. 4), nitrous oxide (5.0 x 10 -5), etc. As a percentage by mass, the most of the listed components are nitrous oxide and hydrogen, followed by helium, krypton, etc.
Physical properties of different atmospheric layers
The physical properties of the troposphere are closely related to its proximity to the surface of the planet. From here, reflected solar heat in the form of infrared rays is directed back upward, involving the processes of conduction and convection. That is why the temperature drops with distance from the earth's surface. This phenomenon is observed up to the height of the stratosphere (11-17 kilometers), then the temperature becomes almost unchanged up to 34-35 km, and then the temperature rises again to altitudes of 50 kilometers (the upper limit of the stratosphere). Between the stratosphere and the troposphere there is a thin intermediate layer of the tropopause (up to 1-2 km), where constant temperatures are observed above the equator - about minus 70 ° C and below. Above the poles, the tropopause “warms up” in summer to minus 45°C; in winter, temperatures here fluctuate around -65°C.
The gas composition of the Earth's atmosphere includes such an important element as ozone. There is relatively little of it at the surface (ten to the minus sixth power of one percent), since the gas is formed under the influence of sunlight from atomic oxygen in the upper parts of the atmosphere. In particular, the most ozone is at an altitude of about 25 km, and the entire “ozone screen” is located in areas from 7-8 km at the poles, from 18 km at the equator and up to fifty kilometers in total above the surface of the planet.
The atmosphere protects from solar radiation
The composition of the air in the Earth's atmosphere plays a very important role in the preservation of life, since individual chemical elements and compositions successfully limit the access of solar radiation to the earth's surface and the people, animals, and plants living on it. For example, water vapor molecules effectively absorb almost all ranges of infrared radiation, with the exception of lengths in the range from 8 to 13 microns. Ozone absorbs ultraviolet radiation up to a wavelength of 3100 A. Without its thin layer (only 3 mm on average if placed on the surface of the planet), only water at a depth of more than 10 meters and underground caves where solar radiation does not reach can be inhabited. .
Zero Celsius at the stratopause
Between the next two levels of the atmosphere, the stratosphere and mesosphere, there is a remarkable layer - the stratopause. It approximately corresponds to the height of ozone maxima and the temperature here is relatively comfortable for humans - about 0°C. Above the stratopause, in the mesosphere (starts somewhere at an altitude of 50 km and ends at an altitude of 80-90 km), a drop in temperature is again observed with increasing distance from the Earth's surface (to minus 70-80 ° C). Meteors usually burn up completely in the mesosphere.
In the thermosphere - plus 2000 K!
The chemical composition of the Earth's atmosphere in the thermosphere (begins after the mesopause from altitudes of about 85-90 to 800 km) determines the possibility of such a phenomenon as gradual heating of layers of very rarefied “air” under the influence of solar radiation. In this part of the “air blanket” of the planet, temperatures range from 200 to 2000 K, which are obtained due to the ionization of oxygen (atomic oxygen is located above 300 km), as well as the recombination of oxygen atoms into molecules, accompanied by the release of a large amount of heat. The thermosphere is where auroras occur.
Above the thermosphere is the exosphere - the outer layer of the atmosphere, from which light and rapidly moving hydrogen atoms can escape into outer space. The chemical composition of the Earth's atmosphere here is represented mostly by individual oxygen atoms in the lower layers, helium atoms in the middle layers, and almost exclusively hydrogen atoms in the upper layers. High temperatures prevail here - about 3000 K and there is no atmospheric pressure.
How was the earth's atmosphere formed?
But, as mentioned above, the planet did not always have such an atmospheric composition. In total, there are three concepts of the origin of this element. The first hypothesis suggests that the atmosphere was taken through the process of accretion from a protoplanetary cloud. However, today this theory is subject to significant criticism, since such a primary atmosphere should have been destroyed by the solar “wind” from a star in our planetary system. In addition, it is assumed that volatile elements could not be retained in the formation zone of terrestrial planets due to too high temperatures.
The composition of the Earth's primary atmosphere, as suggested by the second hypothesis, could have been formed due to the active bombardment of the surface by asteroids and comets that arrived from the vicinity of the Solar system in the early stages of development. It is quite difficult to confirm or refute this concept.
Experiment at Institute of Geography RAS
The most plausible seems to be the third hypothesis, which believes that the atmosphere appeared as a result of the release of gases from the mantle of the earth's crust approximately 4 billion years ago. This concept was tested at the Institute of Geography of the Russian Academy of Sciences during an experiment called “Tsarev 2”, when a sample of a substance of meteoric origin was heated in a vacuum. Then the release of gases such as H 2, CH 4, CO, H 2 O, N 2, etc. was recorded. Therefore, scientists rightly assumed that the chemical composition of the Earth’s primary atmosphere included water and carbon dioxide, hydrogen fluoride (HF), carbon monoxide gas (CO), hydrogen sulfide (H 2 S), nitrogen compounds, hydrogen, methane (CH 4), ammonia vapor (NH 3), argon, etc. Water vapor from the primary atmosphere participated in the formation of the hydrosphere, carbon dioxide was to a greater extent in a bound state in organic substances and rocks, nitrogen passed into the composition of modern air, and also again into sedimentary rocks and organic substances.
The composition of the Earth's primary atmosphere would not allow modern people to be in it without breathing apparatus, since there was no oxygen in the required quantities then. This element appeared in significant quantities one and a half billion years ago, believed to be in connection with the development of the process of photosynthesis in blue-green and other algae, which are the oldest inhabitants of our planet.
Minimum oxygen
The fact that the composition of the Earth's atmosphere was initially almost oxygen-free is indicated by the fact that easily oxidized, but not oxidized graphite (carbon) is found in the oldest (Catarchaean) rocks. Subsequently, so-called banded iron ores appeared, which included layers of enriched iron oxides, which means the appearance on the planet of a powerful source of oxygen in molecular form. But these elements were found only periodically (perhaps the same algae or other oxygen producers appeared in small islands in an oxygen-free desert), while the rest of the world was anaerobic. The latter is supported by the fact that easily oxidized pyrite was found in the form of pebbles processed by flow without traces of chemical reactions. Since flowing waters cannot be poorly aerated, the view has developed that the atmosphere before the Cambrian contained less than one percent of the oxygen composition of today.
Revolutionary change in air composition
Approximately in the middle of the Proterozoic (1.8 billion years ago), an “oxygen revolution” occurred when the world switched to aerobic respiration, during which 38 can be obtained from one molecule of a nutrient (glucose), and not two (as with anaerobic respiration) units of energy. The composition of the Earth's atmosphere, in terms of oxygen, began to exceed one percent of what it is today, and an ozone layer began to appear, protecting organisms from radiation. It was from her that, for example, such ancient animals as trilobites “hid” under thick shells. From then until our time, the content of the main “respiratory” element gradually and slowly increased, ensuring the diversity of development of life forms on the planet.
The gaseous envelope surrounding our planet Earth, known as the atmosphere, consists of five main layers. These layers originate on the surface of the planet, from sea level (sometimes below) and rise to outer space in the following sequence:
- Troposphere;
- Stratosphere;
- Mesosphere;
- Thermosphere;
- Exosphere.
Diagram of the main layers of the Earth's atmosphere
In between each of these main five layers are transition zones called "pauses" where changes in air temperature, composition and density occur. Together with pauses, the Earth's atmosphere includes a total of 9 layers.
Troposphere: where weather occurs
Of all the layers of the atmosphere, the troposphere is the one with which we are most familiar (whether you realize it or not), since we live on its bottom - the surface of the planet. It envelops the surface of the Earth and extends upward for several kilometers. The word troposphere means "change of the globe." A very appropriate name, since this layer is where our everyday weather occurs.
Starting from the surface of the planet, the troposphere rises to a height of 6 to 20 km. The lower third of the layer, closest to us, contains 50% of all atmospheric gases. This is the only part of the entire atmosphere that breathes. Due to the fact that the air is heated from below by the earth's surface, which absorbs the thermal energy of the Sun, the temperature and pressure of the troposphere decrease with increasing altitude.
At the top there is a thin layer called the tropopause, which is just a buffer between the troposphere and the stratosphere.
Stratosphere: home of the ozone
The stratosphere is the next layer of the atmosphere. It extends from 6-20 km to 50 km above the Earth's surface. This is the layer in which most commercial airliners fly and hot air balloons travel.
Here the air does not flow up and down, but moves parallel to the surface in very fast air currents. As you rise, the temperature increases, thanks to the abundance of naturally occurring ozone (O3), a byproduct of solar radiation and oxygen, which has the ability to absorb the sun's harmful ultraviolet rays (any increase in temperature with altitude in meteorology is known as an "inversion") .
Because the stratosphere has warmer temperatures at the bottom and cooler temperatures at the top, convection (vertical movement of air masses) is rare in this part of the atmosphere. In fact, you can view a storm raging in the troposphere from the stratosphere because the layer acts as a convection cap that prevents storm clouds from penetrating.
After the stratosphere there is again a buffer layer, this time called the stratopause.
Mesosphere: middle atmosphere
The mesosphere is located approximately 50-80 km from the Earth's surface. The upper mesosphere is the coldest natural place on Earth, where temperatures can drop below -143°C.
Thermosphere: upper atmosphere
After the mesosphere and mesopause comes the thermosphere, located between 80 and 700 km above the surface of the planet, and contains less than 0.01% of the total air in the atmospheric envelope. Temperatures here reach up to +2000° C, but due to the extreme thinness of the air and the lack of gas molecules to transfer heat, these high temperatures are perceived as very cold.
Exosphere: the boundary between the atmosphere and space
At an altitude of about 700-10,000 km above the earth's surface is the exosphere - the outer edge of the atmosphere, bordering space. Here weather satellites orbit the Earth.
What about the ionosphere?
The ionosphere is not a separate layer, but in fact the term is used to refer to the atmosphere between 60 and 1000 km altitude. It includes the uppermost parts of the mesosphere, the entire thermosphere and part of the exosphere. The ionosphere gets its name because in this part of the atmosphere the radiation from the Sun is ionized when it passes through the Earth's magnetic fields at and. This phenomenon is observed from the ground as the northern lights.
