Earth's atmosphere is the gaseous envelope of our planet. Its lower boundary passes at the level of the earth's crust and hydrosphere, and the upper one passes into the near-Earth region of outer space. The atmosphere contains about 78% nitrogen, 20% oxygen, up to 1% argon, carbon dioxide, hydrogen, helium, neon and some other gases.
This earth shell is characterized by clearly defined layering. The layers of the atmosphere are determined by the vertical distribution of temperature and the different density of gases at its different levels. There are such layers of the Earth's atmosphere: troposphere, stratosphere, mesosphere, thermosphere, exosphere. The ionosphere is distinguished separately.
Up to 80% of the total mass of the atmosphere is the troposphere - the lower surface layer of the atmosphere. The troposphere in the polar zones is located at a level of up to 8-10 km above the earth's surface, in the tropical zone - up to a maximum of 16-18 km. Between the troposphere and the overlying stratosphere is the tropopause - the transition layer. In the troposphere, temperature decreases as altitude increases, and atmospheric pressure decreases with altitude. The average temperature gradient in the troposphere is 0.6°C per 100 m. The temperature at different levels of this shell is determined by the absorption features solar radiation and efficiency of convection. Almost all human activity takes place in the troposphere. The highest mountains do not go beyond the troposphere, only air transport can cross the upper boundary of this shell to a small height and be in the stratosphere. A large proportion of water vapor is contained in the troposphere, which determines the formation of almost all clouds. Also, almost all aerosols (dust, smoke, etc.) that form on the earth's surface are concentrated in the troposphere. In the boundary lower layer of the troposphere, daily fluctuations in temperature and air humidity are expressed, the wind speed is usually reduced (it increases with altitude). In the troposphere, there is a variable division of the air column into air masses in the horizontal direction, which differ in a number of characteristics depending on the belt and the area of their formation. At atmospheric fronts - the boundaries between air masses - cyclones and anticyclones are formed, which determine the weather in a certain area for a specific period of time.
The stratosphere is the layer of the atmosphere between the troposphere and the mesosphere. The limits of this layer range from 8-16 km to 50-55 km above the Earth's surface. In the stratosphere, the gas composition of air is approximately the same as in the troposphere. A distinctive feature is a decrease in the concentration of water vapor and an increase in the ozone content. Ozone layer atmosphere, protecting the biosphere from the aggressive effects of ultraviolet light, is at a level of 20 to 30 km. In the stratosphere, the temperature rises with height, and the temperature values are determined by solar radiation, and not by convection (movements of air masses), as in the troposphere. The heating of the air of the stratosphere is due to the absorption ultraviolet radiation ozone.
The mesosphere extends above the stratosphere up to a level of 80 km. This layer of the atmosphere is characterized by the fact that the temperature decreases from 0 ° C to - 90 ° C as the height increases. This is the coldest region of the atmosphere.
Above the mesosphere is the thermosphere up to a level of 500 km. From the border with the mesosphere to the exosphere, the temperature varies from approximately 200 K to 2000 K. Up to a level of 500 km, the air density decreases by several hundred thousand times. The relative composition of the atmospheric components of the thermosphere is similar to the surface layer of the troposphere, but with increasing altitude, more oxygen passes into the atomic state. A certain proportion of molecules and atoms of the thermosphere is in an ionized state and distributed in several layers, they are united by the concept of the ionosphere. The characteristics of the thermosphere vary over a wide range depending on geographical latitude, the magnitude of solar radiation, time of year and day.
The upper layer of the atmosphere is the exosphere. This is the thinnest layer of the atmosphere. In the exosphere, the mean free paths of particles are so huge that particles can freely escape into interplanetary space. The mass of the exosphere is one ten millionth of the total mass of the atmosphere. The lower boundary of the exosphere is the level of 450-800 km, and the upper boundary is the area where the concentration of particles is the same as in outer space - several thousand kilometers from the Earth's surface. The exosphere is made up of plasma, an ionized gas. Also in the exosphere are the radiation belts of our planet.
Video presentation - layers of the Earth's atmosphere:
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The structure of the Earth's atmosphere
The atmosphere is the gaseous shell of the Earth with aerosol particles contained in it, moving together with the Earth in world space as a whole and at the same time taking part in the rotation of the Earth. At the bottom of the atmosphere, most of our lives take place.
Almost all of our planets have their own atmospheres. solar system, but only the Earth's atmosphere is capable of supporting life.
When our planet formed 4.5 billion years ago, it was apparently devoid of an atmosphere. The atmosphere was formed as a result of volcanic emissions of water vapor with impurities of carbon dioxide, nitrogen and other chemical substances from the depths of a young planet. But the atmosphere can only contain a limited amount of moisture, so the excess moisture through condensation gave rise to the oceans. But then the atmosphere was devoid of oxygen. The first living organisms that originated and developed in the ocean, as a result of the photosynthesis reaction (H 2 O + CO 2 = CH 2 O + O 2), began to release small portions of oxygen, which began to enter the atmosphere.
The formation of oxygen in the Earth's atmosphere led to the formation of the ozone layer at altitudes of about 8 - 30 km. And, thus, our planet has acquired protection from the harmful effects of ultraviolet study. This circumstance served as an impetus for the further evolution of life forms on Earth, since. as a result of increased photosynthesis, the amount of oxygen in the atmosphere began to grow rapidly, which contributed to the formation and maintenance of life forms, including on land.
Today our atmosphere is 78.1% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon dioxide. Very small fractions compared to the main gases are neon, helium, methane, krypton.
The particles of gas contained in the atmosphere are affected by the force of gravity of the Earth. And, given that air is compressible, its density gradually decreases with height, passing into outer space without a clear boundary. Half of the entire mass of the earth's atmosphere is concentrated in the lower 5 km, three-quarters - in the lower 10 km, nine-tenths - in the lower 20 km. 99% of the mass of the Earth's atmosphere is concentrated below a height of 30 km, and this is only 0.5% of the equatorial radius of our planet.
At sea level, the number of atoms and molecules per cubic centimeter of air is about 2 * 10 19 , at an altitude of 600 km it is only 2 * 10 7 . At sea level, an atom or molecule travels about 7 * 10 -6 cm before colliding with another particle. At an altitude of 600 km, this distance is about 10 km. And at sea level, about 7 * 10 9 such collisions occur every second, at an altitude of 600 km - only about one per minute!
But not only pressure changes with altitude. The temperature also changes. For example, at the foot high mountain it can be quite hot, while the top of the mountain is covered with snow and the temperature there at the same time is below zero. And it is worth climbing by plane to a height of about 10-11 km, as you can hear a message that it is -50 degrees overboard, while at the surface of the earth it is 60-70 degrees warmer ...
Initially, scientists assumed that the temperature decreases with height until it reaches absolute zero (-273.16 ° C). But it's not.
The Earth's atmosphere consists of four layers: troposphere, stratosphere, mesosphere, ionosphere (thermosphere). Such a division into layers is taken on the basis of data on temperature changes with height. The lowest layer, where air temperature drops with height, is called the troposphere. The layer above the troposphere, where the temperature drop stops, is replaced by isotherm and, finally, the temperature begins to rise, is called the stratosphere. The layer above the stratosphere where the temperature drops rapidly again is the mesosphere. And, finally, the layer where the temperature rise again begins, called the ionosphere or thermosphere.
The troposphere extends on average in the lower 12 km. This is where our weather is formed. The highest clouds (cirrus) form at the highest upper layers troposphere. The temperature in the troposphere decreases adiabatically with height, i.e. The change in temperature is due to the decrease in pressure with height. The temperature profile of the troposphere is largely determined by the solar radiation reaching the Earth's surface. As a result of the heating of the Earth's surface by the Sun, upward convective and turbulent flows are formed, which form the weather. It is worth noting that the influence of the underlying surface on the lower layers of the troposphere extends to a height of about 1.5 km. Of course, excluding mountainous areas.
The upper boundary of the troposphere is the tropopause, the isothermal layer. Recall the characteristic appearance of thunderclouds, the top of which is an "ejection" of cirrus clouds, called "anvil." This "anvil" just "spreads" under the tropopause, because due to isotherm, the ascending air currents are significantly weakened, and the cloud ceases to develop vertically. But in special, rare cases, the tops of cumulonimbus clouds can invade the lower layers of the stratosphere, overcoming the tropopause.
The height of the tropopause depends on the geographic latitude. So, at the equator, it is at an altitude of about 16 km, and its temperature is about -80 ° C. At the poles, the tropopause is located lower - approximately at an altitude of 8 km. Its temperature here is -40°C in summer and -60°C in winter. Thus, despite higher temperatures near the Earth's surface, the tropical tropopause is much colder than at the poles.
The thickness of the atmosphere is about 120 km from the Earth's surface. The total mass of air in the atmosphere is (5.1-5.3) 10 18 kg. Of these, the mass of dry air is 5.1352 ± 0.0003 10 18 kg, the total mass of water vapor is on average 1.27 10 16 kg.
tropopause
The transitional layer from the troposphere to the stratosphere, the layer of the atmosphere in which the decrease in temperature with height stops.
Stratosphere
The layer of the atmosphere located at an altitude of 11 to 50 km. A slight change in temperature in the 11-25 km layer (lower layer of the stratosphere) and its increase in the 25-40 km layer from −56.5 to 0.8 ° (upper stratosphere or inversion region) are typical. 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 the mesosphere.
Stratopause
The boundary layer of the atmosphere between the stratosphere and the mesosphere. There is a maximum in the vertical temperature distribution (about 0 °C).
Mesosphere
Earth's atmosphere
Earth's atmosphere boundary
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 up to high altitudes. Under the influence of ultraviolet and x-ray solar radiation and cosmic radiation, air is ionized ("polar lights") - 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 - for example, in 2008-2009 - there is a noticeable decrease in the size of this layer.
Thermopause
The region of the atmosphere above the thermosphere. In this region, the absorption of solar radiation is insignificant and the temperature does not actually change with height.
Exosphere (scattering sphere)
Up to a height of 100 km, the atmosphere is a homogeneous, well-mixed mixture of gases. In higher layers, the distribution of gases in height depends on their molecular masses, 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 are observed in time and space.
At an altitude of about 2000-3500 km, the exosphere gradually passes into the so-called near space vacuum, which is filled with highly rarefied particles of interplanetary gas, mainly hydrogen atoms. But this gas is only part of the interplanetary matter. The other part is composed of dust-like particles of cometary and meteoric origin. In addition to extremely rarefied dust-like 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 accounts for 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 neutrosphere 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, they emit homosphere and heterosphere. heterosphere- this is an area where gravity affects the separation of gases, since their mixing at such a height is negligible. Hence follows the 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 turbopause, it lies at an altitude of about 120 km.
Physiological and other properties of the atmosphere
Already at an altitude of 5 km above sea level, an untrained person develops oxygen starvation and, without adaptation, a person's performance is significantly reduced. This is where the physiological zone of the atmosphere ends. Human breathing becomes impossible at an altitude of 9 km, although up to about 115 km the atmosphere contains oxygen.
The atmosphere provides us with the oxygen we need to breathe. However, due to the drop in the total pressure of the atmosphere as you rise to a height, the partial pressure of oxygen also decreases accordingly.
In rarefied layers of air, the propagation of sound is impossible. Up to altitudes of 60-90 km, it is still possible to use air resistance and lift for controlled aerodynamic flight. But starting from altitudes of 100-130 km, the concepts of the M number and the sound barrier familiar to every pilot lose their meaning: there passes the conditional Karman line, beyond which the area of \u200b\u200bpurely ballistic flight begins, which can only be controlled using reactive forces.
At altitudes above 100 km, the atmosphere is also devoid of another remarkable property - the ability to absorb, conduct and transmit thermal energy by convection (i.e., with the help of air mixing). This means that various elements of equipment, equipment of the orbital space station will not be able to be cooled from the outside in the way it is usually done on an airplane - with the help of air jets and air radiators. At such a height, as in space in general, the only way to transfer heat is thermal radiation.
History of the formation of the atmosphere
According to the most common theory, the Earth's atmosphere in time was in three different compositions. Initially, it consisted of light gases (hydrogen and helium) captured from interplanetary space. This so-called primary atmosphere(about four billion years ago). At the next stage, active volcanic activity led to the saturation of the atmosphere with gases other than hydrogen (carbon dioxide, ammonia, water vapor). This is how secondary atmosphere(about three billion years before our days). This atmosphere was restorative. Further, the process of formation of the atmosphere was determined by the following factors:
- leakage of light gases (hydrogen and helium) into interplanetary space;
- chemical reactions occurring in the atmosphere under the influence of ultraviolet radiation, lightning discharges and some other factors.
Gradually, these factors led to the formation tertiary atmosphere, characterized by a much lower content of hydrogen and a much higher content of nitrogen and carbon dioxide (formed as a result of chemical reactions from ammonia and hydrocarbons).
Nitrogen
The formation of a large amount of nitrogen N 2 is due to the oxidation of the ammonia-hydrogen atmosphere by molecular oxygen O 2, which began to come from the surface of the planet as a result of photosynthesis, starting from 3 billion years ago. Nitrogen N 2 is also released into the atmosphere as a result of the denitrification of nitrates and other nitrogen-containing compounds. Nitrogen is oxidized by ozone to NO in the upper atmosphere.
Nitrogen N 2 enters into reactions only under specific conditions (for example, during a lightning discharge). Oxidation of molecular nitrogen by ozone during electrical discharges is used in small quantities in the industrial production of nitrogen fertilizers. It can be oxidized with low energy consumption and converted into a biologically active form by cyanobacteria (blue-green algae) and nodule bacteria that form rhizobial symbiosis with legumes, the so-called. green manure.
Oxygen
The composition of the atmosphere began to change radically with the advent of living organisms on Earth, as a result of photosynthesis, accompanied by the release of oxygen and the absorption of carbon dioxide. Initially, oxygen was spent on the oxidation of reduced compounds - ammonia, hydrocarbons, the ferrous form of iron contained in the oceans, etc. At the end of this stage, the oxygen content in the atmosphere began to grow. Gradually, a modern atmosphere with oxidizing properties formed. Since this caused serious and abrupt changes in many processes occurring in the atmosphere, lithosphere and biosphere, this event was called the Oxygen catastrophe.
noble gases
Air pollution
Recently, man has begun to influence the evolution of the atmosphere. The result of his activities was a constant significant increase in the content of carbon dioxide in the atmosphere due to the combustion of hydrocarbon fuels accumulated in previous geological epochs. Huge amounts of CO 2 are consumed during photosynthesis and absorbed by the world's oceans. This gas enters the atmosphere due to the decomposition of carbonate rocks and organic substances of plant and animal origin, as well as due to volcanism and human production activities. Over the past 100 years, the content of CO 2 in the atmosphere has increased by 10%, with the main part (360 billion tons) coming from fuel combustion. If the growth rate of fuel combustion continues, then in the next 200-300 years the amount of CO 2 in the atmosphere will double and may lead to global climate change.
Fuel combustion is the main source of polluting gases (СО,, SO 2). Sulfur dioxide is oxidized by atmospheric oxygen to SO 3 in the upper atmosphere, which in turn interacts with water vapor and ammonia, and the resulting sulfuric acid (H 2 SO 4) and ammonium sulfate ((NH 4) 2 SO 4) return to the surface of the Earth in the form of a so-called. acid rain. The use of internal combustion engines leads to significant air pollution with nitrogen oxides, hydrocarbons and lead compounds (tetraethyl lead Pb (CH 3 CH 2) 4)).
Aerosol pollution of the atmosphere is caused by natural causes(volcanic eruption, dust storms, entrainment of drops of sea water and plant pollen, etc.), and human economic activity (mining of ores and building materials, fuel combustion, cement production, etc.). Intensive large-scale removal of particulate matter into the atmosphere is one of the possible causes planetary climate change.
see also
- Jacchia (atmosphere model)
Notes
Links
Literature
- V. V. Parin, F. P. Kosmolinsky, B. A. Dushkov"Space biology and medicine" (2nd edition, revised and supplemented), M .: "Prosveshchenie", 1975, 223 pages.
- N. V. Gusakova"Chemistry of the environment", Rostov-on-Don: Phoenix, 2004, 192 with ISBN 5-222-05386-5
- Sokolov V. A. Geochemistry of natural gases, M., 1971;
- McEwen M, Phillips L. Chemistry of the atmosphere, M., 1978;
- Wark K., Warner S. Air pollution. Sources and control, trans. from English, M.. 1980;
- Monitoring of background pollution of natural environments. v. 1, L., 1982.
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At sea level 1013.25 hPa (about 760 mmHg). The average global air temperature at the Earth's surface is 15°C, while the temperature varies from about 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 is 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 in the troposphere. Above the troposphere is the stratosphere - a layer that is characterized in general by an increase in temperature with height. The transition layer between the troposphere and stratosphere is called the tropopause. In the lower stratosphere, up to a level of about 20 km, the temperature changes little with height (the so-called isothermal region) and often even slightly decreases. Higher, the temperature rises due to the absorption of solar UV radiation 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 drops again 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. The thermosphere begins above the mesopause - a layer, characterized by a rapid increase in temperature, reaching values of 800-1200 K at an altitude of 250 km. The corpuscular and X-ray radiation of the Sun is absorbed in the thermosphere, meteors are slowed down and burned out, so it performs the function of the Earth's protective layer. Even higher is the exosphere, from where atmospheric gases are dissipated into world space due to dissipation and where a gradual transition from the atmosphere to interplanetary space takes place.
Composition of the atmosphere. Up to an altitude of about 100 km, the atmosphere is practically homogeneous in chemical composition and the average molecular mass air (about 29) in it 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 constant 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 the 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 the low content, their role in atmospheric processes is very significant.
Above 100-110 km, the dissociation of oxygen, carbon dioxide and water vapor molecules occurs, so the molecular weight 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 near the earth's surface from 2.6% in the tropics to 0.2% in the polar latitudes. With height, it quickly falls, decreasing by half already at a height of 1.5-2 km. The vertical column of the atmosphere at temperate latitudes contains about 1.7 cm of the “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 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, ranging from 0.22 to 0.45 cm (the thickness of the ozone layer at a pressure of p= 1 atm and a temperature of T = 0°C). In the ozone holes observed in spring in Antarctica since the early 1980s, the ozone content can drop to 0.07 cm. grows at 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 gas in water decreases with increasing temperature).
An important role in the formation of 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 waste products of plants and economic activity human, volcanic eruptions, as a result of the rise of dust by the wind from the surface of the planet, especially from its desert regions, and is also formed from cosmic dust that enters the upper 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 industries, fuel combustion, etc. Therefore, in some areas the composition of the atmosphere differs markedly from ordinary air, which required the creation of a special service for monitoring and controlling the level of atmospheric air pollution.
Atmospheric evolution. The modern atmosphere is apparently of secondary origin: it was formed from the 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 the matter of the interplanetary medium (for example, meteoric matter). The development of the atmosphere is closely connected with geological and geochemical processes, and for the last 3-4 billion years also with 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 out from the depths of the Earth. Oxygen appeared in appreciable quantities about 2 billion years ago as a result of the activity of photosynthetic organisms that originally originated in the surface waters of the ocean.
Based on the 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. During the Phanerozoic (the last 570 million years of the Earth's history), the amount of carbon dioxide in the atmosphere varied widely in accordance with the level of volcanic activity, ocean temperature and photosynthesis. Most of this time, the concentration of carbon dioxide in the atmosphere was significantly higher than the current one (up to 10 times). The amount of oxygen in the atmosphere of the Phanerozoic changed significantly, and the tendency to increase it prevailed. In the Precambrian atmosphere, the mass of carbon dioxide was, as a rule, greater, and the mass of oxygen, less than in the atmosphere of the Phanerozoic. Fluctuations in the amount of carbon dioxide have had a significant impact on the climate in the past, increasing the greenhouse effect with an increase in the concentration of carbon dioxide, due to which the climate during the main part of the Phanerozoic was much warmer than in the modern era.
atmosphere and life. Without an atmosphere, Earth would be a dead planet. Organic life proceeds in close interaction with the atmosphere and its associated climate and weather. Insignificant in mass compared to the planet as a whole (about a millionth part), the atmosphere is a sine qua non for all life forms. Oxygen, nitrogen, water vapor, carbon dioxide, and ozone are the most important atmospheric gases for the life of organisms. When carbon dioxide is absorbed by photosynthetic plants, organic matter is created, which is used as an energy source by the vast majority of living beings, including humans. Oxygen is necessary for the existence of aerobic organisms, for which the energy supply is provided by the oxidation reactions of organic matter. Nitrogen, assimilated by some microorganisms (nitrogen fixers), is necessary for the mineral nutrition of plants. Ozone, which absorbs the Sun's harsh UV radiation, significantly attenuates this life-threatening portion of the sun's radiation. Condensation of water vapor in the atmosphere, the formation of clouds and the subsequent precipitation of 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 number and chemical composition 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. main feature radiation regime of the atmosphere - the so-called greenhouse effect: the atmosphere transmits solar radiation to the earth's surface quite well, but actively absorbs the thermal long-wave radiation of the earth's surface, part of which returns to the surface in the form of counter radiation, compensating for the radiative heat loss of 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, 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). Total radiation, reaching the earth's surface, is partially (about 23%) reflected from it. The reflectance is determined by the reflectivity of the underlying surface, the so-called albedo. On average, the Earth's albedo for the integral solar radiation flux is close to 30%. It varies from a few percent (dry soil and black soil) to 70-90% for freshly fallen snow. The radiative heat exchange between the earth's surface and the atmosphere essentially depends on the 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 the radiation fluxes included in 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 the 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 of 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 1367 W / m 2, the changes are 1-2 W / m 2 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/m 2 . Since the Earth as a planet emits the same amount of energy into space on average, 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 33°C difference is due to the greenhouse effect.
The water balance of the atmosphere as a whole corresponds to the equality of the amount of moisture evaporated from the surface of the Earth, 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 carried to the continents by air currents. The amount of water vapor transported into the atmosphere from the oceans to the continents is equal to the volume of river flow that flows into the oceans.
air movement. The Earth has a spherical shape, so much less solar radiation comes to its high latitudes than to the tropics. As a result, large temperature contrasts arise between latitudes. The relative position of the oceans and continents also significantly affects the distribution of temperature. Due to the large mass ocean waters and the high heat capacity of water, seasonal fluctuations in ocean surface temperature are much less than those of land. In this regard, in the middle and high latitudes, the air temperature over the oceans is noticeably lower in summer than over the continents, and higher in winter.
Unequal heating of the atmosphere in different areas the globe causes a spatially non-uniform distribution of atmospheric pressure. At sea level, the pressure distribution is characterized by relatively low values near the equator, an increase in the subtropics (high-pressure zones) and a decrease in middle and high latitudes. At the same time, over the continents of extratropical latitudes, the pressure is usually increased in winter, and lowered in summer, which is associated with the temperature distribution. Under the action of a pressure gradient, the air experiences an acceleration directed from areas of high pressure to areas of low pressure, which leads to the movement of air masses. The moving air masses are also affected by the deflecting force of the Earth's rotation (the Coriolis force), the friction force, which decreases with height, and in the case of curvilinear trajectories, the centrifugal force. Of great importance is the turbulent mixing of air (see Turbulence in the atmosphere).
Associated with planetary pressure distribution a complex system air currents (general circulation of the atmosphere). In the meridional plane, on average, two or three meridional circulation cells are 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 direct polar cell is often traced. 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 quite stable - air currents that have a clearly pronounced seasonal character: they blow from the ocean to the mainland in summer and in the opposite direction in winter. The monsoons of the Indian Ocean are especially regular. In middle latitudes, the movement of air masses is mainly western (from west to east). This is a zone of atmospheric fronts, on which large eddies arise - cyclones and anticyclones, covering many hundreds and even thousands of kilometers. Cyclones also occur in the tropics; here they differ in smaller sizes, but very high wind speeds, reaching hurricane force (33 m/s or more), the so-called tropical cyclones. In the Atlantic and in the east Pacific Ocean they are called hurricanes, and in the western Pacific, typhoons. In the upper troposphere and lower stratosphere, in the areas separating the direct cell of the Hadley meridional circulation 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 coming at different latitudes to the earth's surface, which is diverse in physical properties, determines the diversity of the Earth's climates. From the equator to tropical latitudes, the air temperature near the earth's surface averages 25-30 ° C and changes little during the year. In the equatorial zone, a lot of precipitation usually falls, which creates conditions for excessive moisture there. In tropical zones, the amount of precipitation decreases and in some areas becomes very small. 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 remote from the oceans. Yes, in some areas Eastern Siberia the annual amplitude of air temperature reaches 65°C. Humidification conditions in these latitudes are very diverse, depend mainly on the regime of the general circulation of the atmosphere, and vary significantly from year to year.
In the 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, occupying over 65% of Russia's area, mainly in Siberia.
Over the past decades, changes in the global climate have become more and more noticeable. The temperature rises 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 near the earth's surface in Russia increased by 1.5-2 ° C, and in some regions of Siberia, an increase of several degrees is observed. This is associated with an increase in the greenhouse effect due to an increase in the concentration of small gaseous impurities.
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. Most of all, the weather changes in the zones of change of air masses, due to the passage of atmospheric fronts, cyclones and anticyclones, carrying precipitation and increasing wind. Data for weather forecasting is collected from ground-based weather stations, ships and aircraft, and meteorological satellites. See also meteorology.
Optical, acoustic and electrical phenomena in the atmosphere. When spread electromagnetic radiation 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: rainbow, crowns, halo, mirage, etc. Scattering of light determines the apparent height of the firmament and the 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 possibility of detecting objects with instruments, including the possibility of astronomical observations from the Earth's surface. For studies of optical inhomogeneities in the stratosphere and mesosphere, the phenomenon of twilight plays an important role. For example, photographing twilight with spacecraft allows detection of 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, like 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 remote sensing of the atmosphere. Explosions of charges launched by rockets into the upper atmosphere provided a wealth of information about wind systems and the course of temperature in the stratosphere and mesosphere. In a stably stratified atmosphere, when the temperature falls with height more slowly 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 wind 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. An important role is played by the formation of clouds and lightning electricity. The danger of lightning discharges necessitated the development of methods for lightning protection of buildings, structures, power lines and communications. This phenomenon is of particular danger to aviation. Lightning discharges cause atmospheric radio interference, called atmospherics (see Whistling atmospherics). During a sharp increase in the strength of the electric field, luminous discharges are observed that arise on the points 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 quantity of light and heavy ions, which varies greatly depending on the specific conditions, which determine electrical conductivity atmosphere. The main air ionizers near the earth's surface - radiation of radioactive substances contained in earth's crust and in the 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 activities. The percentage of carbon dioxide increased from 2.8-10 2 two hundred years ago to 3.8-10 2 in 2005, the content of methane - from 0.7-10 1 about 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 past century was given by freons, which practically did not exist in the atmosphere until the middle of the 20th century. These substances are recognized as stratospheric ozone depleters and their production is prohibited by the 1987 Montreal Protocol. The increase in carbon dioxide concentration in the atmosphere is caused by the burning of ever-increasing amounts of coal, oil, gas and other carbon fuels, as well as the deforestation, which reduces the absorption of carbon dioxide through photosynthesis. The concentration of methane increases with the growth of 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 of active influence on atmospheric processes have been developed. They are used to protect agricultural plants from hail damage by dispersing special reagents in thunderclouds. There are also methods for dispelling fog at airports, protecting plants from frost, influencing clouds to increase rainfall in the right places, or to disperse clouds at times of mass events.
Study of the atmosphere. Information about the physical processes in the atmosphere is obtained primarily from meteorological observations, which are carried out by a global network of permanent meteorological stations and posts located on all continents and on many islands. Daily observations provide information about the temperature and humidity of the air, atmospheric pressure and precipitation, cloudiness, wind, etc. Observations of solar radiation and its transformations are carried out at actinometric stations. Networks of aerological stations are of great importance for the study of the atmosphere, at which meteorological measurements are carried out with the help of radiosondes up to a height of 30-35 km. A number of stations monitor atmospheric ozone, electrical phenomena in the atmosphere, the chemical composition of the air.
Data from ground stations are supplemented by observations on the oceans, where "weather ships" operate, permanently 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 with the help of meteorological satellites, on which instruments are installed for photographing clouds and measuring the fluxes of ultraviolet, infrared, and microwave radiation from the Sun. Satellites make it possible to obtain information about vertical temperature profiles, cloudiness and its water content, elements of the atmospheric radiation balance, 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 became possible to clarify the value of the solar constant and the planetary albedo of the Earth, build maps of the radiation balance of the Earth-atmosphere system, measure the content and variability of small atmospheric impurities, 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. Physics of the atmosphere. 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: A Handbook. L., 1991; Khromov S. P., Petrosyants M. A. Meteorology and climatology. 5th ed. M., 2001.
G. S. Golitsyn, N. A. Zaitseva.
The gaseous envelope that surrounds 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 transitional 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 the weather happens
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 at its bottom - the surface of the planet. It envelops the surface of the Earth and extends upwards for several kilometers. The word troposphere means "change of the ball". A very fitting name, as this layer is where our day to day weather happens.
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. It is the only part of the entire composition of the 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 is a thin layer called the tropopause, which is just a buffer between the troposphere and stratosphere.
Stratosphere: home of ozone
Stratosphere - next layer 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 balloons travel.
Here, the air does not flow up and down, but moves parallel to the surface in very fast air currents. Temperatures increase as you ascend, thanks to an abundance of naturally occurring ozone (O3), a by-product of solar radiation, and oxygen, which has the ability to absorb the sun's harmful ultraviolet rays (any rise in temperature with altitude is known in meteorology as an "inversion") .
Because the stratosphere has warmer temperatures at the bottom and cooler temperatures at the top, convection (vertical movements 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, since the layer acts as a "cap" for convection, through which storm clouds do not penetrate.
The stratosphere is again followed by 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
The mesosphere and mesopause are followed by the thermosphere, located between 80 and 700 km above the surface of the planet, and containing less than 0.01% of the total air in the atmospheric shell. Temperatures here reach up to +2000° C, but due to the strong rarefaction of the air and the lack of gas molecules to transfer heat, these high temperatures are perceived as very cold.
Exosphere: the boundary of 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 meteorological satellites revolve around the Earth.
How about the ionosphere?
The ionosphere is not a separate layer, and in fact this term is used to refer to the atmosphere at an altitude of 60 to 1000 km. 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 Sun's radiation is ionized when it passes through magnetic fields Land on