Sometimes the atmosphere surrounding our planet in a thick layer is called the fifth ocean. It is not for nothing that the second name of an aircraft is an aircraft. The atmosphere is a mixture of various gases, among which nitrogen and oxygen predominate. It is thanks to the latter that life is possible on the planet in the form to which we are all accustomed. Besides them, there are 1% of other components. These are inert (not entering into chemical interactions) gases, sulfur oxide. The fifth ocean also contains mechanical impurities: dust, ash, etc. All layers of the atmosphere in total extend almost 480 km from the surface (the data are different, we will dwell on this point in more detail Further). Such an impressive thickness forms a kind of impenetrable shield that protects the planet from harmful cosmic radiation and large objects.
The following layers of the atmosphere are distinguished: the troposphere, followed by the stratosphere, then the mesosphere and, finally, the thermosphere. The given order begins at the surface of the planet. The dense layers of the atmosphere are represented by the first two. They are the ones who filter out a significant part of the harmful
The lowest layer of the atmosphere, the troposphere, extends only 12 km above sea level (18 km in the tropics). Up to 90% of water vapor is concentrated here, which is why clouds form there. Most of the air is also concentrated here. All subsequent layers of the atmosphere are colder, since the proximity to the surface allows reflected solar rays to heat the air.
The stratosphere extends to almost 50 km from the surface. Most weather balloons "float" in this layer. Some types of aircraft can also fly here. One of the surprising features is the temperature regime: in the range from 25 to 40 km, the air temperature begins to increase. From -60 it rises to almost 1. Then there is a slight decrease to zero, which persists up to an altitude of 55 km. The upper limit is the infamous
Further, the mesosphere extends to almost 90 km. The air temperature here drops sharply. For every 100 meters of rise, there is a decrease of 0.3 degrees. It is sometimes called the coldest part of the atmosphere. The air density is low, but it is quite enough to create resistance to falling meteors.
The layers of the atmosphere in the usual sense end at an altitude of about 118 km. The famous auroras are formed here. The thermosphere region begins above. Due to X-rays, the ionization of those few air molecules contained in this area occurs. These processes create the so-called ionosphere (it is often included in the thermosphere and is therefore not considered separately).
Everything above 700 km is called the exosphere. air is extremely small, so they move freely without experiencing resistance due to collisions. This allows some of them to accumulate energy corresponding to 160 degrees Celsius, despite the fact that the surrounding temperature is low. Gas molecules are distributed throughout the volume of the exosphere in accordance with their mass, so the heaviest of them can be detected only in the lower part of the layer. The planet's gravity, which decreases with altitude, is no longer able to hold molecules, so high-energy cosmic particles and radiation impart an impulse to gas molecules sufficient to leave the atmosphere. This region is one of the longest: it is believed that the atmosphere completely transforms into the vacuum of space at altitudes greater than 2000 km (sometimes even the number 10,000 appears). Artificial ones rotate in orbits while still in the thermosphere.
All numbers indicated are indicative, since the boundaries of atmospheric layers depend on a number of factors, for example, on the activity of the Sun.
The atmosphere is a mixture of various gases. It extends from the Earth's surface to a height of 900 km, protecting the planet from the harmful spectrum of solar radiation, and contains gases necessary for all life on the planet. The atmosphere traps heat from the sun, warming the earth's surface and creating a favorable climate.
Atmospheric composition
The Earth's atmosphere consists mainly of two gases - nitrogen (78%) and oxygen (21%). In addition, it contains impurities of carbon dioxide and other gases. in the atmosphere it exists in the form of vapor, moisture droplets in clouds and ice crystals.
Layers of the atmosphere
The atmosphere consists of many layers, between which there are no clear boundaries. The temperatures of different layers differ markedly from each other.
- Airless magnetosphere. This is where most of the Earth's satellites fly outside the Earth's atmosphere.
- Exosphere (450-500 km from the surface). Almost no gases. Some weather satellites fly in the exosphere. The thermosphere (80-450 km) is characterized by high temperatures, reaching 1700°C in the upper layer.
- Mesosphere (50-80 km). In this area, the temperature drops as altitude increases. This is where most meteorites (fragments of space rocks) that enter the atmosphere burn up.
- Stratosphere (15-50 km). Contains ozone layer, i.e. a layer of ozone that absorbs ultraviolet radiation from the Sun. This causes temperatures near the Earth's surface to rise. Jet planes usually fly here because Visibility in this layer is very good and there is almost no interference caused by weather conditions.
- Troposphere. The height varies from 8 to 15 km from the earth's surface. It is here that the planet's weather is formed, since in This layer contains the most water vapor, dust and winds. The temperature decreases with distance from the earth's surface.
Atmosphere pressure
Although we don't feel it, layers of the atmosphere exert pressure on the Earth's surface. It is highest near the surface, and as you move away from it it gradually decreases. It depends on the temperature difference between land and ocean, and therefore in areas located at the same altitude above sea level there are often different pressures. Low pressure brings wet weather, while high pressure usually brings clear weather.
Movement of air masses in the atmosphere
And the pressures force the lower layers of the atmosphere to mix. This is how winds arise, blowing from areas of high pressure to areas of low pressure. In many regions, local winds also arise due to differences in temperature between land and sea. Mountains also have a significant influence on the direction of winds.
Greenhouse effect
Carbon dioxide and other gases that make up the earth's atmosphere trap heat from the sun. This process is commonly called the greenhouse effect, since it is in many ways reminiscent of the circulation of heat in greenhouses. The greenhouse effect causes global warming on the planet. In areas of high pressure - anticyclones - clear sunny weather sets in. Areas of low pressure - cyclones - usually experience unstable weather. Heat and light entering the atmosphere. Gases trap heat reflected from the earth's surface, thereby causing an increase in temperature on Earth.
There is a special ozone layer in the stratosphere. Ozone blocks most of the sun's ultraviolet radiation, protecting the Earth and all life on it from it. Scientists have found that the cause of the destruction of the ozone layer is special chlorofluorocarbon dioxide gases contained in some aerosols and refrigeration equipment. Over the Arctic and Antarctica, huge holes have been discovered in the ozone layer, contributing to an increase in the amount of ultraviolet radiation affecting the Earth's surface.
Ozone is formed in the lower atmosphere as a result between solar radiation and various exhaust fumes and gases. Usually it is dispersed throughout the atmosphere, but if a closed layer of cold air forms under a layer of warm air, ozone concentrates and smog occurs. Unfortunately, this cannot replace the ozone lost in ozone holes.
A hole in the ozone layer over Antarctica is clearly visible in this satellite photograph. The size of the hole varies, but scientists believe that it is constantly growing. Efforts are being made to reduce the level of exhaust gases in the atmosphere. Air pollution should be reduced and smokeless fuels used in cities. Smog causes eye irritation and suffocation for many people.
The emergence and evolution of the Earth's atmosphere
The modern atmosphere of the Earth is the result of long evolutionary development. It arose as a result of the combined actions of geological factors and the vital activity of organisms. Throughout geological history, the earth's atmosphere has undergone several profound changes. Based on geological data and theoretical premises, the primordial atmosphere of the young Earth, which existed about 4 billion years ago, could consist of a mixture of inert and noble gases with a small addition of passive nitrogen (N. A. Yasamanov, 1985; A. S. Monin, 1987; O. G. Sorokhtin, S. A. Ushakov, 1991, 1993). Currently, the view on the composition and structure of the early atmosphere has changed somewhat. The primary atmosphere (proto-atmosphere) at the earliest protoplanetary stage., i.e. older than 4.2 billion years, could consist of a mixture of methane, ammonia and carbon dioxide. As a result of degassing of the mantle and active weathering processes occurring on the earth's surface, water vapor, carbon compounds in the form of CO 2 and CO, sulfur and its compounds began to enter the atmosphere , as well as strong halogen acids - HCI, HF, HI and boric acid, which were supplemented by methane, ammonia, hydrogen, argon and some other noble gases in the atmosphere. This primary atmosphere was extremely thin. Therefore, the temperature at the earth's surface was close to the temperature of radiative equilibrium (A. S. Monin, 1977).
Over time, the gas composition of the primary atmosphere began to transform under the influence of weathering processes of rocks protruding on the earth's surface, the activity of cyanobacteria and blue-green algae, volcanic processes and the action of sunlight. This led to the decomposition of methane into carbon dioxide, ammonia into nitrogen and hydrogen; Carbon dioxide, which slowly sank to the earth's surface, and nitrogen began to accumulate in the secondary atmosphere. Thanks to the vital activity of blue-green algae, oxygen began to be produced in the process of photosynthesis, which, however, in the beginning was mainly spent on the “oxidation of atmospheric gases, and then rocks. At the same time, ammonia, oxidized to molecular nitrogen, began to accumulate intensively in the atmosphere. It is assumed that a significant amount of nitrogen in the modern atmosphere is relict. Methane and carbon monoxide were oxidized to carbon dioxide. Sulfur and hydrogen sulfide were oxidized to SO 2 and SO 3, which, due to their high mobility and lightness, were quickly removed from the atmosphere. Thus, the atmosphere from a reducing atmosphere, as it was in the Archean and Early Proterozoic, gradually turned into an oxidizing one.
Carbon dioxide entered the atmosphere both as a result of methane oxidation and as a result of degassing of the mantle and weathering of rocks. In the event that all the carbon dioxide released over the entire history of the Earth was preserved in the atmosphere, its partial pressure at present could become the same as on Venus (O. Sorokhtin, S. A. Ushakov, 1991). But on Earth the reverse process was at work. A significant part of carbon dioxide from the atmosphere was dissolved in the hydrosphere, in which it was used by hydrobionts to build their shells and biogenically converted into carbonates. Subsequently, thick strata of chemogenic and organogenic carbonates were formed from them.
Oxygen entered the atmosphere from three sources. For a long time, starting from the moment the Earth appeared, it was released during the degassing of the mantle and was mainly spent on oxidative processes. Another source of oxygen was the photodissociation of water vapor by hard ultraviolet solar radiation. Appearances; free oxygen in the atmosphere led to the death of most prokaryotes that lived in reducing conditions. Prokaryotic organisms changed their habitats. They left the surface of the Earth into its depths and areas where recovery conditions still remained. They were replaced by eukaryotes, which began to energetically convert carbon dioxide into oxygen.
During the Archean and a significant part of the Proterozoic, almost all the oxygen arising in both abiogenic and biogenic ways was mainly spent on the oxidation of iron and sulfur. By the end of the Proterozoic, all metallic divalent iron located on the earth's surface either oxidized or moved into the earth's core. This caused the partial pressure of oxygen in the early Proterozoic atmosphere to change.
In the middle of the Proterozoic, the oxygen concentration in the atmosphere reached the Jury point and amounted to 0.01% of modern levels. Starting from this time, oxygen began to accumulate in the atmosphere and, probably, already at the end of the Riphean its content reached the Pasteur point (0.1% of the modern level). It is possible that the ozone layer appeared in the Vendian period and that it never disappeared.
The appearance of free oxygen in the earth's atmosphere stimulated the evolution of life and led to the emergence of new forms with more advanced metabolism. If earlier eukaryotic unicellular algae and cyanea, which appeared at the beginning of the Proterozoic, required an oxygen content in water of only 10 -3 of its modern concentration, then with the emergence of non-skeletal Metazoa at the end of the Early Vendian, i.e. about 650 million years ago, the oxygen concentration in the atmosphere should be significantly higher. After all, Metazoa used oxygen respiration and this required that the partial pressure of oxygen reach a critical level - the Pasteur point. In this case, the anaerobic fermentation process was replaced by an energetically more promising and progressive oxygen metabolism.
After this, further accumulation of oxygen in the earth's atmosphere occurred quite quickly. The progressive increase in the volume of blue-green algae contributed to the achievement in the atmosphere of the oxygen level necessary for the life support of the animal world. A certain stabilization of the oxygen content in the atmosphere occurred from the moment when plants reached land - approximately 450 million years ago. The emergence of plants onto land, which occurred in the Silurian period, led to the final stabilization of oxygen levels in the atmosphere. From that time on, its concentration began to fluctuate within rather narrow limits, never exceeding the limits of the existence of life. The oxygen concentration in the atmosphere has completely stabilized since the appearance of flowering plants. This event occurred in the middle of the Cretaceous period, i.e. about 100 million years ago.
The bulk of nitrogen was formed in the early stages of the Earth's development, mainly due to the decomposition of ammonia. With the appearance of organisms, the process of binding atmospheric nitrogen into organic matter and burying it in marine sediments began. After organisms reached land, nitrogen began to be buried in continental sediments. The processes of processing free nitrogen especially intensified with the advent of land plants.
At the turn of the Cryptozoic and Phanerozoic, i.e. about 650 million years ago, the content of carbon dioxide in the atmosphere decreased to tenths of a percent, and it reached a content close to the modern level only recently, approximately 10-20 million years ago.
Thus, the gas composition of the atmosphere not only provided living space for organisms, but also determined the characteristics of their life activity and contributed to settlement and evolution. Emerging disruptions in the distribution of the gas composition of the atmosphere favorable for organisms, both due to cosmic and planetary reasons, led to mass extinctions of the organic world, which repeatedly occurred during the Cryptozoic and at certain boundaries of Phanerozoic history.
Ethnospheric functions of the atmosphere
The Earth's atmosphere provides the necessary substances, energy and determines the direction and speed of metabolic processes. The gas composition of the modern atmosphere is optimal for the existence and development of life. Being the area where weather and climate are formed, the atmosphere must create comfortable conditions for the life of people, animals and vegetation. Deviations in one direction or another in the quality of atmospheric air and weather conditions create extreme conditions for the life of flora and fauna, including humans.
The Earth's atmosphere not only provides the conditions for the existence of humanity, but is the main factor in the evolution of the ethnosphere. At the same time, it turns out to be an energy and raw material resource for production. In general, the atmosphere is a factor that preserves human health, and some areas, due to physical-geographical conditions and atmospheric air quality, serve as recreational areas and are areas intended for sanatorium-resort treatment and recreation of people. Thus, the atmosphere is a factor of aesthetic and emotional impact.
The ethnosphere and technosphere functions of the atmosphere, defined quite recently (E. D. Nikitin, N. A. Yasamanov, 2001), require independent and in-depth study. Thus, the study of atmospheric energy functions is very relevant, both from the point of view of the occurrence and operation of processes that damage the environment, and from the point of view of the impact on the health and well-being of people. In this case, we are talking about the energy of cyclones and anticyclones, atmospheric vortices, atmospheric pressure and other extreme atmospheric phenomena, the effective use of which will contribute to the successful solution of the problem of obtaining alternative energy sources that do not pollute the environment. After all, the air environment, especially that part of it that is located above the World Ocean, is an area where a colossal amount of free energy is released.
For example, it has been established that tropical cyclones of average strength release energy equivalent to the energy of 500 thousand atomic bombs dropped on Hiroshima and Nagasaki in just one day. In 10 days of the existence of such a cyclone, enough energy is released to satisfy all the energy needs of a country like the United States for 600 years.
In recent years, a large number of works by natural scientists have been published, in one way or another dealing with various aspects of activity and the influence of the atmosphere on earthly processes, which indicates the intensification of interdisciplinary interactions in modern natural science. At the same time, the integrating role of certain of its directions is manifested, among which we should note the functional-ecological direction in geoecology.
This direction stimulates analysis and theoretical generalization on the ecological functions and planetary role of various geospheres, and this, in turn, is an important prerequisite for the development of methodology and scientific foundations for the holistic study of our planet, the rational use and protection of its natural resources.
The Earth's atmosphere consists of several layers: the troposphere, stratosphere, mesosphere, thermosphere, ionosphere and exosphere. At the top of the troposphere and the bottom of the stratosphere there is a layer enriched with ozone, called the ozone shield. Certain (daily, seasonal, annual, etc.) patterns in the distribution of ozone have been established. Since its origin, the atmosphere has influenced the course of planetary processes. The primary composition of the atmosphere was completely different than at the present time, but over time the share and role of molecular nitrogen steadily increased, about 650 million years ago free oxygen appeared, the amount of which continuously increased, but the concentration of carbon dioxide decreased accordingly. The high mobility of the atmosphere, its gas composition and the presence of aerosols determine its outstanding role and active participation in a variety of geological and biosphere processes. The atmosphere plays a great role in the redistribution of solar energy and the development of catastrophic natural phenomena and disasters. Atmospheric vortices - tornadoes (tornadoes), hurricanes, typhoons, cyclones and other phenomena have a negative impact on the organic world and natural systems. The main sources of pollution, along with natural factors, are various forms of human economic activity. Anthropogenic impacts on the atmosphere are expressed not only in the appearance of various aerosols and greenhouse gases, but also in an increase in the amount of water vapor, and manifest themselves in the form of smog and acid rain. Greenhouse gases change the temperature regime of the earth's surface; emissions of some gases reduce the volume of the ozone layer and contribute to the formation of ozone holes. The ethnospheric role of the Earth's atmosphere is great.
The role of the atmosphere in natural processes
The surface atmosphere, in its intermediate state between the lithosphere and outer space and its gas composition, creates conditions for the life of organisms. At the same time, the weathering and intensity of destruction of rocks, the transfer and accumulation of clastic material depend on the amount, nature and frequency of precipitation, on the frequency and strength of winds and especially on air temperature. The atmosphere is a central component of the climate system. Air temperature and humidity, cloudiness and precipitation, wind - all this characterizes the weather, i.e. the continuously changing state of the atmosphere. At the same time, these same components characterize the climate, i.e., the average long-term weather regime.
The composition of gases, the presence of clouds and various impurities, which are called aerosol particles (ash, dust, particles of water vapor), determine the characteristics of the passage of solar radiation through the atmosphere and prevent the escape of the Earth's thermal radiation into outer space.
The Earth's atmosphere is very mobile. The processes that arise in it and changes in its gas composition, thickness, cloudiness, transparency and the presence of certain aerosol particles in it affect both the weather and the climate.
The action and direction of natural processes, as well as life and activity on Earth, are determined by solar radiation. It provides 99.98% of the heat supplied to the earth's surface. Every year this amounts to 134 * 10 19 kcal. This amount of heat can be obtained by burning 200 billion tons of coal. The reserves of hydrogen that create this flow of thermonuclear energy in the mass of the Sun will last for at least another 10 billion years, i.e., for a period twice as long as the existence of our planet and itself.
About 1/3 of the total amount of solar energy arriving at the upper boundary of the atmosphere is reflected back into space, 13% is absorbed by the ozone layer (including almost all ultraviolet radiation). 7% - the rest of the atmosphere and only 44% reaches the earth's surface. The total solar radiation reaching the Earth per day is equal to the energy that humanity received as a result of burning all types of fuel over the last millennium.
The amount and nature of the distribution of solar radiation on the earth's surface are closely dependent on cloudiness and transparency of the atmosphere. The amount of scattered radiation is affected by the height of the Sun above the horizon, the transparency of the atmosphere, the content of water vapor, dust, the total amount of carbon dioxide, etc.
The maximum amount of scattered radiation reaches the polar regions. The lower the Sun is above the horizon, the less heat enters a given area of the terrain.
Atmospheric transparency and cloudiness are of great importance. On a cloudy summer day it is usually colder than on a clear one, since daytime cloudiness prevents the heating of the earth's surface.
The dustiness of the atmosphere plays a major role in the distribution of heat. The finely dispersed solid particles of dust and ash found in it, which affect its transparency, negatively affect the distribution of solar radiation, most of which is reflected. Fine particles enter the atmosphere in two ways: either ash emitted during volcanic eruptions, or desert dust carried by winds from arid tropical and subtropical regions. Especially a lot of such dust is formed during droughts, when currents of warm air carry it into the upper layers of the atmosphere and can remain there for a long time. After the eruption of the Krakatoa volcano in 1883, dust thrown tens of kilometers into the atmosphere remained in the stratosphere for about 3 years. As a result of the 1985 eruption of the El Chichon volcano (Mexico), dust reached Europe, and therefore there was a slight decrease in surface temperatures.
The Earth's atmosphere contains variable amounts of water vapor. In absolute terms by weight or volume, its amount ranges from 2 to 5%.
Water vapor, like carbon dioxide, enhances the greenhouse effect. In the clouds and fogs that arise in the atmosphere, peculiar physical and chemical processes occur.
The primary source of water vapor into the atmosphere is the surface of the World Ocean. A layer of water with a thickness of 95 to 110 cm evaporates from it annually. Part of the moisture returns to the ocean after condensation, and the other is directed by air currents towards the continents. In areas of variable humid climate, precipitation moistens the soil, and in humid climates it creates groundwater reserves. Thus, the atmosphere is an accumulator of humidity and a reservoir of precipitation. and fogs that form in the atmosphere provide moisture to the soil cover and thereby play a decisive role in the development of flora and fauna.
Atmospheric moisture is distributed over the earth's surface due to the mobility of the atmosphere. It is characterized by a very complex system of winds and pressure distribution. Due to the fact that the atmosphere is in continuous motion, the nature and scale of the distribution of wind flows and pressure are constantly changing. The scale of circulation varies from micrometeorological, with a size of only a few hundred meters, to a global scale of several tens of thousands of kilometers. Huge atmospheric vortices participate in the creation of systems of large-scale air currents and determine the general circulation of the atmosphere. In addition, they are sources of catastrophic atmospheric phenomena.
The distribution of weather and climatic conditions and the functioning of living matter depend on atmospheric pressure. If atmospheric pressure fluctuates within small limits, it does not play a decisive role in the well-being of people and the behavior of animals and does not affect the physiological functions of plants. Changes in pressure are usually associated with frontal phenomena and weather changes.
Atmospheric pressure is of fundamental importance for the formation of wind, which, being a relief-forming factor, has a strong impact on the animal and plant world.
Wind can suppress plant growth and at the same time promote seed transfer. The role of wind in shaping weather and climate conditions is great. It also acts as a regulator of sea currents. Wind, as one of the exogenous factors, contributes to the erosion and deflation of weathered material over long distances.
Ecological and geological role of atmospheric processes
A decrease in the transparency of the atmosphere due to the appearance of aerosol particles and solid dust in it affects the distribution of solar radiation, increasing the albedo or reflectivity. Various chemical reactions that cause the decomposition of ozone and the generation of “pearl” clouds consisting of water vapor lead to the same result. Global changes in reflectivity, as well as changes in atmospheric gases, mainly greenhouse gases, are responsible for climate change.
Uneven heating, which causes differences in atmospheric pressure over different parts of the earth's surface, leads to atmospheric circulation, which is the hallmark of the troposphere. When a difference in pressure occurs, air rushes from areas of high pressure to areas of low pressure. These movements of air masses, together with humidity and temperature, determine the main ecological and geological features of atmospheric processes.
Depending on the speed, the wind performs various geological work on the earth's surface. At a speed of 10 m/s, it shakes thick tree branches, lifting and transporting dust and fine sand; breaks tree branches at a speed of 20 m/s, carries sand and gravel; at a speed of 30 m/s (storm) tears off the roofs of houses, uproots trees, breaks poles, moves pebbles and carries small rubble, and a hurricane wind at a speed of 40 m/s destroys houses, breaks and demolishes power line poles, uproots large trees.
Squalls and tornadoes (tornadoes) - atmospheric vortices that arise in the warm season on powerful atmospheric fronts, with speeds of up to 100 m/s, have a great negative environmental impact with catastrophic consequences. Squalls are horizontal whirlwinds with hurricane wind speeds (up to 60-80 m/s). They are often accompanied by heavy downpours and thunderstorms lasting from several minutes to half an hour. Squalls cover areas up to 50 km wide and travel a distance of 200-250 km. A squall storm in Moscow and the Moscow region in 1998 damaged the roofs of many houses and toppled trees.
Tornadoes, called tornadoes in North America, are powerful funnel-shaped atmospheric vortices, often associated with thunderclouds. These are columns of air tapering in the middle with a diameter of several tens to hundreds of meters. A tornado has the appearance of a funnel, very similar to the trunk of an elephant, descending from the clouds or rising from the surface of the earth. Possessing strong rarefaction and a high rotation speed, a tornado travels up to several hundred kilometers, drawing in dust, water from reservoirs and various objects. Powerful tornadoes are accompanied by thunderstorms, rain and have great destructive power.
Tornadoes rarely occur in subpolar or equatorial regions, where it is constantly cold or hot. There are few tornadoes in the open ocean. Tornadoes occur in Europe, Japan, Australia, the USA, and in Russia they are especially frequent in the Central Black Earth region, in the Moscow, Yaroslavl, Nizhny Novgorod and Ivanovo regions.
Tornadoes lift and move cars, houses, carriages, and bridges. Particularly destructive tornadoes are observed in the United States. Every year there are from 450 to 1500 tornadoes with an average death toll of about 100 people. Tornadoes are fast-acting catastrophic atmospheric processes. They are formed in just 20-30 minutes, and their lifetime is 30 minutes. Therefore, it is almost impossible to predict the time and place of tornadoes.
Other destructive but long-lasting atmospheric vortices are cyclones. They are formed due to a pressure difference, which under certain conditions contributes to the emergence of a circular movement of air flows. Atmospheric vortices originate around powerful upward flows of moist warm air and rotate at high speed clockwise in the southern hemisphere and counterclockwise in the northern. Cyclones, unlike tornadoes, originate over oceans and produce their destructive effects over continents. The main destructive factors are strong winds, intense precipitation in the form of snowfall, downpours, hail and surge floods. Winds with speeds of 19 - 30 m/s form a storm, 30 - 35 m/s - a storm, and more than 35 m/s - a hurricane.
Tropical cyclones - hurricanes and typhoons - have an average width of several hundred kilometers. The wind speed inside the cyclone reaches hurricane force. Tropical cyclones last from several days to several weeks, moving at speeds from 50 to 200 km/h. Mid-latitude cyclones have a larger diameter. Their transverse dimensions range from a thousand to several thousand kilometers, and the wind speed is stormy. They move in the northern hemisphere from the west and are accompanied by hail and snowfall, which are catastrophic in nature. In terms of the number of victims and damage caused, cyclones and associated hurricanes and typhoons are the largest natural atmospheric phenomena after floods. In densely populated areas of Asia, the death toll from hurricanes is in the thousands. In 1991, during a hurricane in Bangladesh, which caused the formation of sea waves 6 m high, 125 thousand people died. Typhoons cause great damage to the United States. At the same time, tens and hundreds of people die. In Western Europe, hurricanes cause less damage.
Thunderstorms are considered a catastrophic atmospheric phenomenon. They occur when warm, moist air rises very quickly. On the border of the tropical and subtropical zones, thunderstorms occur 90-100 days a year, in the temperate zone 10-30 days. In our country, the largest number of thunderstorms occur in the North Caucasus.
Thunderstorms usually last less than an hour. Particularly dangerous are intense downpours, hail, lightning strikes, gusts of wind, and vertical air currents. The hail hazard is determined by the size of the hailstones. In the North Caucasus, the mass of hailstones once reached 0.5 kg, and in India, hailstones weighing 7 kg were recorded. The most urban-dangerous areas in our country are located in the North Caucasus. In July 1992, hail damaged 18 aircraft at the Mineralnye Vody airport.
Dangerous atmospheric phenomena include lightning. They kill people, livestock, cause fires, and damage the power grid. About 10,000 people die from thunderstorms and their consequences every year around the world. Moreover, in some areas of Africa, France and the USA, the number of victims from lightning is greater than from other natural phenomena. The annual economic damage from thunderstorms in the United States is at least $700 million.
Droughts are typical for desert, steppe and forest-steppe regions. A lack of precipitation causes drying out of the soil, a decrease in the level of groundwater and in reservoirs until they dry out completely. Moisture deficiency leads to the death of vegetation and crops. Droughts are especially severe in Africa, the Near and Middle East, Central Asia and southern North America.
Droughts change human living conditions and have an adverse effect on the natural environment through processes such as soil salinization, dry winds, dust storms, soil erosion and forest fires. Fires are especially severe during drought in taiga regions, tropical and subtropical forests and savannas.
Droughts are short-term processes that last for one season. When droughts last more than two seasons, there is a threat of famine and mass mortality. Typically, drought affects the territory of one or more countries. Prolonged droughts with tragic consequences occur especially often in the Sahel region of Africa.
Atmospheric phenomena such as snowfalls, short-term heavy rains and prolonged lingering rains cause great damage. Snowfalls cause massive avalanches in the mountains, and rapid melting of fallen snow and prolonged rainfall lead to floods. The huge mass of water falling on the earth's surface, especially in treeless areas, causes severe soil erosion. There is an intensive growth of gully-beam systems. Floods occur as a result of large floods during periods of heavy precipitation or high water after sudden warming or spring melting of snow and, therefore, are atmospheric phenomena in origin (they are discussed in the chapter on the ecological role of the hydrosphere).
Anthropogenic atmospheric changes
Currently, there are many different anthropogenic sources that cause air pollution and lead to serious disturbances in the ecological balance. In terms of scale, two sources have the greatest impact on the atmosphere: transport and industry. On average, transport accounts for about 60% of the total amount of atmospheric pollution, industry - 15, thermal energy - 15, technologies for the destruction of household and industrial waste - 10%.
Transport, depending on the fuel used and the types of oxidizers, emits into the atmosphere nitrogen oxides, sulfur, carbon oxides and dioxides, lead and its compounds, soot, benzopyrene (a substance from the group of polycyclic aromatic hydrocarbons, which is a strong carcinogen that causes skin cancer).
Industry emits sulfur dioxide, carbon oxides and dioxides, hydrocarbons, ammonia, hydrogen sulfide, sulfuric acid, phenol, chlorine, fluorine and other chemical compounds into the atmosphere. But the dominant position among emissions (up to 85%) is occupied by dust.
As a result of pollution, the transparency of the atmosphere changes, causing aerosols, smog and acid rain.
Aerosols are dispersed systems consisting of solid particles or liquid droplets suspended in a gaseous environment. The particle size of the dispersed phase is usually 10 -3 -10 -7 cm. Depending on the composition of the dispersed phase, aerosols are divided into two groups. One includes aerosols consisting of solid particles dispersed in a gaseous medium, the second includes aerosols that are a mixture of gaseous and liquid phases. The former are called smokes, and the latter - fogs. In the process of their formation, condensation centers play an important role. Volcanic ash, cosmic dust, industrial emissions products, various bacteria, etc. act as condensation nuclei. The number of possible sources of concentration nuclei is constantly growing. So, for example, when dry grass is destroyed by fire on an area of 4000 m 2, an average of 11 * 10 22 aerosol nuclei are formed.
Aerosols began to form from the moment our planet appeared and influenced natural conditions. However, their quantity and actions, balanced with the general cycle of substances in nature, did not cause profound environmental changes. Anthropogenic factors of their formation have shifted this balance towards significant biosphere overloads. This feature has been especially evident since humanity began to use specially created aerosols both in the form of toxic substances and for plant protection.
The most dangerous to vegetation are aerosols of sulfur dioxide, hydrogen fluoride and nitrogen. When they come into contact with a damp leaf surface, they form acids that have a detrimental effect on living things. Acid mists enter the respiratory organs of animals and humans along with inhaled air and have an aggressive effect on the mucous membranes. Some of them decompose living tissue, and radioactive aerosols cause cancer. Among radioactive isotopes, Sg 90 is particularly dangerous not only for its carcinogenicity, but also as an analogue of calcium, replacing it in the bones of organisms, causing their decomposition.
During nuclear explosions, radioactive aerosol clouds are formed in the atmosphere. Small particles with a radius of 1 - 10 microns fall not only into the upper layers of the troposphere, but also into the stratosphere, where they can remain for a long time. Aerosol clouds are also formed during the operation of reactors in industrial installations that produce nuclear fuel, as well as as a result of accidents at nuclear power plants.
Smog is a mixture of aerosols with liquid and solid dispersed phases, which form a foggy curtain over industrial areas and large cities.
There are three types of smog: icy, wet and dry. Ice smog is called Alaskan smog. This is a combination of gaseous pollutants with the addition of dust particles and ice crystals that occur when droplets of fog and steam from heating systems freeze.
Wet smog, or London-type smog, is sometimes called winter smog. It is a mixture of gaseous pollutants (mainly sulfur dioxide), dust particles and fog droplets. The meteorological prerequisite for the appearance of winter smog is windless weather, in which a layer of warm air is located above the ground layer of cold air (below 700 m). In this case, there is not only horizontal, but also vertical exchange. Pollutants, usually dispersed in high layers, in this case accumulate in the surface layer.
Dry smog occurs during the summer and is often called Los Angeles-type smog. It is a mixture of ozone, carbon monoxide, nitrogen oxides and acid vapors. Such smog is formed as a result of the decomposition of pollutants by solar radiation, especially its ultraviolet part. The meteorological prerequisite is atmospheric inversion, expressed in the appearance of a layer of cold air above warm air. Typically, gases and solid particles lifted by warm air currents are then dispersed into the upper cold layers, but in this case they accumulate in the inversion layer. In the process of photolysis, nitrogen dioxides formed during the combustion of fuel in car engines decompose:
NO 2 → NO + O
Then ozone synthesis occurs:
O + O 2 + M → O 3 + M
NO + O → NO 2
Photodissociation processes are accompanied by a yellow-green glow.
In addition, reactions of the type occur: SO 3 + H 2 0 -> H 2 SO 4, i.e. strong sulfuric acid is formed.
With a change in meteorological conditions (the appearance of wind or a change in humidity), the cold air dissipates and the smog disappears.
The presence of carcinogenic substances in smog leads to breathing problems, irritation of mucous membranes, circulatory disorders, asthmatic suffocation and often death. Smog is especially dangerous for young children.
Acid rain is atmospheric precipitation acidified by industrial emissions of sulfur oxides, nitrogen and vapors of perchloric acid and chlorine dissolved in them. In the process of burning coal and gas, most of the sulfur contained in it, both in the form of oxide and in compounds with iron, in particular in pyrite, pyrrhotite, chalcopyrite, etc., is converted into sulfur oxide, which, together with carbon dioxide, is emitted into atmosphere. When atmospheric nitrogen and technical emissions combine with oxygen, various nitrogen oxides are formed, and the volume of nitrogen oxides formed depends on the combustion temperature. The bulk of nitrogen oxides occurs during the operation of vehicles and diesel locomotives, and a smaller portion occurs in the energy sector and industrial enterprises. Sulfur and nitrogen oxides are the main acid formers. When reacting with atmospheric oxygen and water vapor contained in it, sulfuric and nitric acids are formed.
It is known that the alkaline-acid balance of the environment is determined by the pH value. A neutral environment has a pH value of 7, an acidic environment has a pH value of 0, and an alkaline environment has a pH value of 14. In the modern era, the pH value of rainwater is 5.6, although in the recent past it was neutral. A decrease in pH value by one corresponds to a tenfold increase in acidity and, therefore, at present, rain with increased acidity falls almost everywhere. The maximum acidity of rain recorded in Western Europe was 4-3.5 pH. It should be taken into account that a pH value of 4-4.5 is lethal for most fish.
Acid rain has an aggressive effect on the Earth's vegetation, on industrial and residential buildings and contributes to a significant acceleration of the weathering of exposed rocks. Increased acidity prevents the self-regulation of neutralization of soils in which nutrients dissolve. In turn, this leads to a sharp decrease in yield and causes degradation of the vegetation cover. Soil acidity promotes the release of bound heavy soils, which are gradually absorbed by plants, causing serious tissue damage and penetrating the human food chain.
A change in the alkaline-acid potential of sea waters, especially in shallow waters, leads to the cessation of reproduction of many invertebrates, causes the death of fish and disrupts the ecological balance in the oceans.
As a result of acid rain, forests in Western Europe, the Baltic States, Karelia, the Urals, Siberia and Canada are at risk of destruction.
The Earth's atmosphere is heterogeneous: at different altitudes there are different air densities and pressures, temperature and gas composition changes. Based on the behavior of the ambient air temperature (i.e., the temperature increases or decreases with height), the following layers are distinguished in it: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The boundaries between layers are called pauses: there are 4 of them, because the upper boundary of the exosphere is very blurred and often refers to near space. The general structure of the atmosphere can be found in the attached diagram.
Fig.1 The structure of the Earth's atmosphere. Credit: website
The lowest atmospheric layer is the troposphere, the upper boundary of which, called the tropopause, varies depending on the geographic latitude and ranges from 8 km. in the polar up to 20 km. in tropical latitudes. In middle or temperate latitudes, its upper limit lies at altitudes of 10-12 km. During the year, the upper limit of the troposphere experiences fluctuations depending on the influx of solar radiation. Thus, as a result of sounding at the South Pole of the Earth by the US meteorological service, it was revealed that from March to August or September there is a steady cooling of the troposphere, as a result of which for a short period in August or September its boundary rises to 11.5 km. Then, in the period from September to December, it quickly decreases and reaches its lowest position - 7.5 km, after which its height remains virtually unchanged until March. Those. The troposphere reaches its greatest thickness in summer and its thinnest in winter.
It is worth noting that, in addition to seasonal ones, there are also daily fluctuations in the height of the tropopause. Also, its position is influenced by cyclones and anticyclones: in the first, it falls, because The pressure in them is lower than in the surrounding air, and secondly, it rises accordingly.
The troposphere contains up to 90% of the total mass of earth's air and 9/10 of all water vapor. Turbulence is highly developed here, especially in the near-surface and highest layers, clouds of all levels develop, cyclones and anticyclones form. And due to the accumulation of greenhouse gases (carbon dioxide, methane, water vapor) of sunlight reflected from the Earth's surface, the greenhouse effect develops.
The greenhouse effect is associated with a decrease in air temperature in the troposphere with height (since the heated Earth gives off more heat to the surface layers). The average vertical gradient is 0.65°/100 m (i.e., the air temperature decreases by 0.65° C for every 100 meters of rise). So, if the average annual air temperature at the surface of the Earth near the equator is +26°, then at the upper boundary it is -70°. The temperature in the tropopause region above the North Pole varies throughout the year from -45° in summer to -65° in winter.
With increasing altitude, air pressure also decreases, amounting to only 12-20% of the near-surface level at the upper boundary of the troposphere.
At the boundary of the troposphere and the overlying layer of the stratosphere lies a layer of the tropopause, 1-2 km thick. The lower boundaries of the tropopause are usually taken to be a layer of air in which the vertical gradient decreases to 0.2°/100 m versus 0.65°/100 m in the underlying regions of the troposphere.
Within the tropopause, air flows of a strictly defined direction are observed, called high-altitude jet streams or “jet streams”, formed under the influence of the rotation of the Earth around its axis and heating of the atmosphere with the participation of solar radiation. Currents are observed at the boundaries of zones with significant temperature differences. There are several centers of localization of these currents, for example, arctic, subtropical, subpolar and others. Knowledge of the localization of jet streams is very important for meteorology and aviation: the first uses streams for more accurate weather forecasting, the second for constructing aircraft flight routes, because At the boundaries of the flows, there are strong turbulent vortices, similar to small whirlpools, called “clear-sky turbulence” due to the absence of clouds at these altitudes.
Under the influence of high-altitude jet currents, breaks often form in the tropopause, and at times it disappears altogether, although it then forms anew. This is especially often observed in subtropical latitudes, which are dominated by a powerful subtropical high-altitude current. In addition, the difference in tropopause layers in ambient air temperature leads to the formation of gaps. For example, a large gap exists between the warm and low polar tropopause and the high and cold tropopause of tropical latitudes. Recently, a layer of the tropopause of temperate latitudes has also emerged, which has discontinuities with the previous two layers: polar and tropical.
The second layer of the earth's atmosphere is the stratosphere. The stratosphere can be roughly divided into two regions. The first of them, lying up to altitudes of 25 km, is characterized by almost constant temperatures, which are equal to the temperatures of the upper layers of the troposphere over a particular area. The second region, or inversion region, is characterized by an increase in air temperature to altitudes of approximately 40 km. This occurs due to the absorption of solar ultraviolet radiation by oxygen and ozone. In the upper part of the stratosphere, thanks to this heating, the temperature is often positive or even comparable to the temperature of the surface air.
Above the inversion region there is a layer of constant temperatures, which is called the stratopause and is the boundary between the stratosphere and mesosphere. Its thickness reaches 15 km.
Unlike the troposphere, turbulent disturbances are rare in the stratosphere, but there are strong horizontal winds or jet streams blowing in narrow zones along the boundaries of temperate latitudes facing the poles. The position of these zones is not constant: they can shift, expand, or even disappear altogether. Often jet streams penetrate into the upper layers of the troposphere, or, conversely, air masses from the troposphere penetrate into the lower layers of the stratosphere. Such mixing of air masses is especially typical in areas of atmospheric fronts.
There is little water vapor in the stratosphere. The air here is very dry, and therefore few clouds form. Only at altitudes of 20-25 km and in high latitudes can you notice very thin pearlescent clouds consisting of supercooled water droplets. During the day, these clouds are not visible, but with the onset of darkness they seem to glow due to the illumination of them by the Sun, which has already set below the horizon.
At the same altitudes (20-25 km) in the lower stratosphere there is the so-called ozone layer - the area with the highest content of ozone, which is formed under the influence of ultraviolet solar radiation (you can find out more about this process on the page). The ozone layer or ozonosphere is of extreme importance for maintaining the life of all organisms living on land, absorbing deadly ultraviolet rays with a wavelength of up to 290 nm. It is for this reason that living organisms do not live above the ozone layer; it is the upper limit of the distribution of life on Earth.
Under the influence of ozone, magnetic fields also change, atoms and molecules disintegrate, ionization occurs, and new formation of gases and other chemical compounds occurs.
The layer of the atmosphere lying above the stratosphere is called the mesosphere. It is characterized by a decrease in air temperature with height with an average vertical gradient of 0.25-0.3°/100 m, which leads to severe turbulence. At the upper boundaries of the mesosphere, in the region called the mesopause, temperatures down to -138°C were recorded, which is the absolute minimum for the entire Earth's atmosphere as a whole.
Here, within the mesopause, lies the lower boundary of the region of active absorption of X-ray and short-wave ultraviolet radiation from the Sun. This energy process is called radiant heat transfer. As a result, the gas is heated and ionized, which causes the atmosphere to glow.
At altitudes of 75-90 km at the upper boundaries of the mesosphere, special clouds were noted, occupying vast areas in the polar regions of the planet. These clouds are called noctilucent because of their glow at dusk, which is caused by the reflection of sunlight from the ice crystals of which these clouds are composed.
Air pressure within the mesopause is 200 times less than at the earth's surface. This suggests that almost all the air in the atmosphere is concentrated in its 3 lower layers: the troposphere, stratosphere and mesosphere. The overlying layers, the thermosphere and exosphere, account for only 0.05% of the mass of the entire atmosphere.
The thermosphere lies at altitudes from 90 to 800 km above the Earth's surface.
The thermosphere is characterized by a continuous increase in air temperature to altitudes of 200-300 km, where it can reach 2500°C. The temperature rises due to the absorption of X-rays and short-wavelength ultraviolet radiation from the Sun by gas molecules. Above 300 km above sea level, the temperature increase stops.
Simultaneously with the increase in temperature, the pressure and, consequently, the density of the surrounding air decreases. So if at the lower boundaries of the thermosphere the density is 1.8 × 10 -8 g/cm 3, then at the upper boundaries it is already 1.8 × 10 -15 g/cm 3, which approximately corresponds to 10 million - 1 billion particles per 1 cm 3.
All characteristics of the thermosphere, such as the composition of air, its temperature, density, are subject to strong fluctuations: depending on the geographical location, season of the year and time of day. Even the location of the upper boundary of the thermosphere changes.
The uppermost layer of the atmosphere is called the exosphere or scattering layer. Its lower limit is constantly changing within very wide limits; The average height is taken to be 690-800 km. It is installed where the probability of intermolecular or interatomic collisions can be neglected, i.e. the average distance that a chaotically moving molecule will cover before colliding with another similar molecule (the so-called free path) will be so great that in fact the molecules will not collide with a probability close to zero. The layer where the described phenomenon occurs is called thermal pause.
The upper boundary of the exosphere lies at altitudes of 2-3 thousand km. It is greatly blurred and gradually turns into a near-space vacuum. Sometimes, for this reason, the exosphere is considered part of outer space, and its upper limit is taken to be a height of 190 thousand km, at which the influence of solar radiation pressure on the speed of hydrogen atoms exceeds the gravitational attraction of the Earth. This is the so-called the earth's crown, consisting of hydrogen atoms. The density of the earth's corona is very small: only 1000 particles per cubic centimeter, but this number is more than 10 times higher than the concentration of particles in interplanetary space.
Due to the extreme rarefaction of the air in the exosphere, particles move around the Earth in elliptical orbits without colliding with each other. Some of them, moving along open or hyperbolic trajectories at cosmic speeds (hydrogen and helium atoms), leave the atmosphere and go into outer space, which is why the exosphere is called the scattering sphere.
The atmosphere is the gaseous shell of the Earth; it is thanks to the atmosphere that the origin and further development of life on our planet became possible. The importance of the atmosphere for the Earth is colossal - the atmosphere will disappear, the planet will disappear. But lately, from television screens and radio speakers, we have been hearing more and more often about the problem of air pollution, the problem of destruction of the ozone layer, and the harmful effects of solar radiation on living organisms, including humans. Here and there, environmental disasters occur that have varying degrees of negative impact on the earth’s atmosphere, directly affecting its gas composition. Unfortunately, we have to admit that with every year of human industrial activity the atmosphere becomes less and less suitable for the normal functioning of living organisms.
The appearance of the atmosphere
The age of the atmosphere is usually equated to the age of planet Earth itself - approximately 5000 million years. At the initial stage of its formation, the Earth warmed up to impressive temperatures. “If, as most scientists believe, the newly formed Earth was extremely hot (had a temperature of about 9000 ° C), then most of the gases that made up the atmosphere would have left it. As the Earth gradually cooled and solidified, gases dissolved in the liquid crust would escape from it.” From these gases the primary earth's atmosphere was formed, thanks to which the origin of life became possible.
As soon as the Earth cooled, an atmosphere formed around it from the released gases. Unfortunately, it is not possible to determine the exact percentage of elements in the chemical composition of the primary atmosphere, but it can be accurately assumed that the gases included in its composition were similar to those that are now emitted by volcanoes - carbon dioxide, water vapor and nitrogen. “Volcanic gases in the form of superheated water vapor, carbon dioxide, nitrogen, hydrogen, ammonia, acid fumes, noble gases and oxygen formed the proto-atmosphere. At this time, the accumulation of oxygen in the atmosphere did not occur, since it was spent on the oxidation of acidic fumes (HCl, SiO 2, H 2 S)” (1).
There are two theories about the origin of the most important chemical element for life - oxygen. As the Earth cooled, the temperature dropped to about 100° C, most of the water vapor condensed and fell to the earth's surface as the first rain, resulting in the formation of rivers, seas and oceans - the hydrosphere. “The water shell on Earth provided the possibility of accumulating endogenous oxygen, becoming its accumulator and (when saturated) supplier to the atmosphere, which by this time had already been cleared of water, carbon dioxide, acidic fumes, and other gases as a result of past rainstorms” (1).
Another theory states that oxygen was formed during photosynthesis as a result of the life activity of primitive cellular organisms, when plant organisms settled throughout the Earth, the amount of oxygen in the atmosphere began to increase rapidly. However, many scientists tend to consider both versions without mutual exclusion.
Changes in the composition of the Earth's atmosphere
|
Stages of development of life on Earth |
Change in atmospheric composition |
|
|
Education of the planet |
4.5 – 5 billion years ago |
No atmosphere |
|
The appearance of signs of life on Earth |
2.5 – 3 billion years ago |
The primary atmosphere contains no oxygen |
|
Active conquest of the Earth by living organisms |
The atmosphere began to form along with the formation of the Earth. During the evolution of the planet and as its parameters approached modern values, fundamentally qualitative changes occurred in its chemical composition and physical properties. According to the evolutionary model, at an early stage the Earth was in a molten state and about 4.5 billion years ago formed as a solid body. This milestone is taken as the beginning of the geological chronology. From that time on, the slow evolution of the atmosphere began. Some geological processes (for example, lava outpourings during volcanic eruptions) were accompanied by the release of gases from the bowels of the Earth. They included nitrogen, ammonia, methane, water vapor, CO oxide and carbon dioxide CO 2. Under the influence of solar ultraviolet radiation, water vapor decomposed into hydrogen and oxygen, but the released oxygen reacted with carbon monoxide to form carbon dioxide. Ammonia decomposed into nitrogen and hydrogen. During the process of diffusion, hydrogen rose upward and left the atmosphere, and heavier nitrogen could not evaporate and gradually accumulated, becoming the main component, although some of it was bound into molecules as a result of chemical reactions ( cm. CHEMISTRY OF THE ATMOSPHERE). Under the influence of ultraviolet rays and electrical discharges, a mixture of gases present in the original atmosphere of the Earth entered into chemical reactions, which resulted in the formation of organic substances, in particular amino acids. With the advent of primitive plants, the process of photosynthesis began, accompanied by the release of oxygen. This gas, especially after diffusion into the upper layers of the atmosphere, began to protect its lower layers and the surface of the Earth from life-threatening ultraviolet and X-ray radiation. According to theoretical estimates, the oxygen content, 25,000 times less than now, could already lead to the formation of an ozone layer with only half the concentration than now. However, this is already enough to provide very significant protection of organisms from the destructive effects of ultraviolet rays.
It is likely that the primary atmosphere contained a lot of carbon dioxide. It was used up during photosynthesis, and its concentration must have decreased as the plant world evolved and also due to absorption during certain geological processes. Because the Greenhouse effect associated with the presence of carbon dioxide in the atmosphere, fluctuations in its concentration are one of the important reasons for such large-scale climate changes in the history of the Earth as ice ages.
The helium present in the modern atmosphere is mostly a product of the radioactive decay of uranium, thorium and radium. These radioactive elements emit a particles, which are the nuclei of helium atoms. Since during radioactive decay an electric charge is neither formed nor destroyed, with the formation of each a-particle two electrons appear, which, recombining with the a-particles, form neutral helium atoms. Radioactive elements are contained in minerals dispersed in rocks, so a significant part of the helium formed as a result of radioactive decay is retained in them, escaping very slowly into the atmosphere. A certain amount of helium rises upward into the exosphere due to diffusion, but due to the constant influx from the earth's surface, the volume of this gas in the atmosphere remains almost unchanged. Based on spectral analysis of starlight and the study of meteorites, it is possible to estimate the relative abundance of various chemical elements in the Universe. The concentration of neon in space is approximately ten billion times higher than on Earth, krypton - ten million times, and xenon - a million times. It follows that the concentration of these inert gases, apparently initially present in the Earth’s atmosphere and not replenished during chemical reactions, decreased greatly, probably even at the stage of the Earth’s loss of its primary atmosphere. An exception is the inert gas argon, since in the form of the 40 Ar isotope it is still formed during the radioactive decay of the potassium isotope.
Barometric pressure distribution.
The total weight of atmospheric gases is approximately 4.5 10 15 tons. Thus, the “weight” of the atmosphere per unit area, or atmospheric pressure, at sea level is approximately 11 t/m 2 = 1.1 kg/cm 2. Pressure equal to P 0 = 1033.23 g/cm 2 = 1013.250 mbar = 760 mm Hg. Art. = 1 atm, taken as the standard average atmospheric pressure. For the atmosphere in a state of hydrostatic equilibrium we have: d P= –rgd h, this means that in the height interval from h before h+d h occurs equality between the change in atmospheric pressure d P and the weight of the corresponding element of the atmosphere with unit area, density r and thickness d h. As a relationship between pressure R and temperature T The equation of state of an ideal gas with density r, which is quite applicable to the earth’s atmosphere, is used: P= r R T/m, where m is the molecular weight, and R = 8.3 J/(K mol) is the universal gas constant. Then d log P= – (m g/RT)d h= – bd h= – d h/H, where the pressure gradient is on a logarithmic scale. Its inverse value H is called the atmospheric altitude scale.
When integrating this equation for an isothermal atmosphere ( T= const) or for its part where such an approximation is permissible, the barometric law of pressure distribution with height is obtained: P = P 0 exp(– h/H 0), where the height reference h produced from ocean level, where the standard mean pressure is P 0 . Expression H 0 = R T/ mg, is called the altitude scale, which characterizes the extent of the atmosphere, provided that the temperature in it is the same everywhere (isothermal atmosphere). If the atmosphere is not isothermal, then integration must take into account the change in temperature with height, and the parameter N– some local characteristic of atmospheric layers, depending on their temperature and the properties of the environment.
Standard atmosphere.
Model (table of values of the main parameters) corresponding to standard pressure at the base of the atmosphere R 0 and chemical composition is called a standard atmosphere. More precisely, this is a conditional model of the atmosphere, for which the average values of temperature, pressure, density, viscosity and other characteristics of air at altitudes from 2 km below sea level to the outer boundary of the earth’s atmosphere are specified for latitude 45° 32ў 33І. The parameters of the middle atmosphere at all altitudes were calculated using the equation of state of an ideal gas and the barometric law assuming that at sea level the pressure is 1013.25 hPa (760 mm Hg) and the temperature is 288.15 K (15.0 ° C). According to the nature of the vertical temperature distribution, the average atmosphere consists of several layers, in each of which the temperature is approximated by a linear function of height. In the lowest layer - the troposphere (h Ј 11 km) the temperature drops by 6.5 ° C with each kilometer of rise. At high altitudes, the value and sign of the vertical temperature gradient changes from layer to layer. Above 790 km the temperature is about 1000 K and practically does not change with altitude.
The standard atmosphere is a periodically updated, legalized standard, issued in the form of tables.
| Table 1. STANDARD MODEL OF THE EARTH'S ATMOSPHERE. The table shows: h– height from sea level, R- pressure, T– temperature, r – density, N– number of molecules or atoms per unit volume, H– height scale, l– free path length. Pressure and temperature at an altitude of 80–250 km, obtained from rocket data, have lower values. Values for altitudes greater than 250 km obtained by extrapolation are not very accurate. | ||||||
| h(km) | P(mbar) | T(°C) | r (g/cm 3) | N(cm –3) | H(km) | l(cm) |
| 0 | 1013 | 288 | 1.22 10 –3 | 2.55 10 19 | 8,4 | 7.4·10 –6 |
| 1 | 899 | 281 | 1.11·10 –3 | 2.31 10 19 | 8.1·10 –6 | |
| 2 | 795 | 275 | 1.01·10 –3 | 2.10 10 19 | 8.9·10 –6 | |
| 3 | 701 | 268 | 9.1·10 –4 | 1.89 10 19 | 9.9·10 –6 | |
| 4 | 616 | 262 | 8.2·10 –4 | 1.70 10 19 | 1.1·10 –5 | |
| 5 | 540 | 255 | 7.4·10 –4 | 1.53 10 19 | 7,7 | 1.2·10 –5 |
| 6 | 472 | 249 | 6.6·10 –4 | 1.37 10 19 | 1.4·10 –5 | |
| 8 | 356 | 236 | 5.2·10 -4 | 1.09 10 19 | 1.7·10 –5 | |
| 10 | 264 | 223 | 4.1·10 –4 | 8.6 10 18 | 6,6 | 2.2·10 –5 |
| 15 | 121 | 214 | 1.93·10 –4 | 4.0 10 18 | 4.6·10 –5 | |
| 20 | 56 | 214 | 8.9·10 –5 | 1.85 10 18 | 6,3 | 1.0·10 –4 |
| 30 | 12 | 225 | 1.9·10 –5 | 3.9 10 17 | 6,7 | 4.8·10 –4 |
| 40 | 2,9 | 268 | 3.9·10 –6 | 7.6 10 16 | 7,9 | 2.4·10 –3 |
| 50 | 0,97 | 276 | 1.15·10 –6 | 2.4 10 16 | 8,1 | 8.5·10 –3 |
| 60 | 0,28 | 260 | 3.9·10 –7 | 7.7 10 15 | 7,6 | 0,025 |
| 70 | 0,08 | 219 | 1.1·10 –7 | 2.5 10 15 | 6,5 | 0,09 |
| 80 | 0,014 | 205 | 2.7·10 –8 | 5.0 10 14 | 6,1 | 0,41 |
| 90 | 2.8·10 –3 | 210 | 5.0·10 –9 | 9·10 13 | 6,5 | 2,1 |
| 100 | 5.8·10 –4 | 230 | 8.8·10 –10 | 1.8 10 13 | 7,4 | 9 |
| 110 | 1.7·10 –4 | 260 | 2.1·10 –10 | 5.4 10 12 | 8,5 | 40 |
| 120 | 6·10 –5 | 300 | 5.6·10 –11 | 1.8 10 12 | 10,0 | 130 |
| 150 | 5·10 –6 | 450 | 3.2·10 –12 | 9 10 10 | 15 | 1.8 10 3 |
| 200 | 5·10 –7 | 700 | 1.6·10 –13 | 5 10 9 | 25 | 3 10 4 |
| 250 | 9·10 –8 | 800 | 3·10 –14 | 8 10 8 | 40 | 3·10 5 |
| 300 | 4·10 –8 | 900 | 8·10 –15 | 3 10 8 | 50 | |
| 400 | 8·10 –9 | 1000 | 1·10 –15 | 5 10 7 | 60 | |
| 500 | 2·10 –9 | 1000 | 2·10 –16 | 1·10 7 | 70 | |
| 700 | 2·10 –10 | 1000 | 2·10 –17 | 1 10 6 | 80 | |
| 1000 | 1·10 –11 | 1000 | 1·10 –18 | 1·10 5 | 80 | |
Troposphere.
The lowest and most dense layer of the atmosphere, in which the temperature decreases rapidly with height, is called the troposphere. It contains up to 80% of the total mass of the atmosphere and extends in the polar and middle latitudes to altitudes of 8–10 km, and in the tropics up to 16–18 km. Almost all weather-forming processes develop here, heat and moisture exchange occurs between the Earth and its atmosphere, clouds form, various meteorological phenomena occur, fog and precipitation occur. These layers of the earth's atmosphere are in convective equilibrium and, thanks to active mixing, have a homogeneous chemical composition, mainly consisting of molecular nitrogen (78%) and oxygen (21%). The vast majority of natural and man-made aerosol and gas air pollutants are concentrated in the troposphere. The dynamics of the lower part of the troposphere, up to 2 km thick, strongly depends on the properties of the underlying surface of the Earth, which determines the horizontal and vertical movements of air (winds) caused by the transfer of heat from warmer land through the infrared radiation of the earth's surface, which is absorbed in the troposphere, mainly by vapors water and carbon dioxide (greenhouse effect). The temperature distribution with height is established as a result of turbulent and convective mixing. On average, it corresponds to a temperature drop with height of approximately 6.5 K/km.
The wind speed in the surface boundary layer initially increases rapidly with height, and above it continues to increase by 2–3 km/s per kilometer. Sometimes narrow planetary flows (with a speed of more than 30 km/s) appear in the troposphere, western in the middle latitudes, and eastern near the equator. They are called jet streams.
Tropopause.
At the upper boundary of the troposphere (tropopause), the temperature reaches its minimum value for the lower atmosphere. This is the transition layer between the troposphere and the stratosphere located above it. The thickness of the tropopause ranges from hundreds of meters to 1.5–2 km, and the temperature and altitude, respectively, range from 190 to 220 K and from 8 to 18 km, depending on the latitude and season. In temperate and high latitudes in winter it is 1–2 km lower than in summer and 8–15 K warmer. In the tropics, seasonal changes are much less (altitude 16–18 km, temperature 180–200 K). Above jet streams tropopause breaks are possible.
Water in the Earth's atmosphere.
The most important feature of the Earth's atmosphere is the presence of significant amounts of water vapor and water in droplet form, which is most easily observed in the form of clouds and cloud structures. The degree of cloud coverage of the sky (at a certain moment or on average over a certain period of time), expressed on a scale of 10 or as a percentage, is called cloudiness. The shape of clouds is determined according to the international classification. On average, clouds cover about half of the globe. Cloudiness is an important factor characterizing weather and climate. In winter and at night, cloudiness prevents a decrease in the temperature of the earth's surface and the ground layer of air; in summer and during the day, it weakens the heating of the earth's surface by the sun's rays, softening the climate inside the continents.
Clouds.
Clouds are accumulations of water droplets suspended in the atmosphere (water clouds), ice crystals (ice clouds), or both together (mixed clouds). As droplets and crystals become larger, they fall out of the clouds in the form of precipitation. Clouds form mainly in the troposphere. They arise as a result of condensation of water vapor contained in the air. The diameter of cloud drops is on the order of several microns. The content of liquid water in clouds ranges from fractions to several grams per m3. Clouds are classified by height: According to the international classification, there are 10 types of clouds: cirrus, cirrocumulus, cirrostratus, altocumulus, altostratus, nimbostratus, stratus, stratocumulus, cumulonimbus, cumulus.
Pearlescent clouds are also observed in the stratosphere, and noctilucent clouds are observed in the mesosphere.
Cirrus clouds are transparent clouds in the form of thin white threads or veils with a silky sheen that do not provide shadows. Cirrus clouds are composed of ice crystals and form in the upper troposphere at very low temperatures. Some types of cirrus clouds serve as harbingers of weather changes.
Cirrocumulus clouds are ridges or layers of thin white clouds in the upper troposphere. Cirrocumulus clouds are built from small elements that look like flakes, ripples, small balls without shadows and consist mainly of ice crystals.
Cirrostratus clouds are a whitish translucent veil in the upper troposphere, usually fibrous, sometimes blurred, consisting of small needle-shaped or columnar ice crystals.
Altocumulus clouds are white, gray or white-gray clouds in the lower and middle layers of the troposphere. Altocumulus clouds have the appearance of layers and ridges, as if built from plates, rounded masses, shafts, flakes lying on top of each other. Altocumulus clouds form during intense convective activity and usually consist of supercooled water droplets.
Altostratus clouds are grayish or bluish clouds with a fibrous or uniform structure. Altostratus clouds are observed in the middle troposphere, extending several kilometers in height and sometimes thousands of kilometers in the horizontal direction. Typically, altostratus clouds are part of frontal cloud systems associated with upward movements of air masses.
Nimbostratus clouds are a low (from 2 km and above) amorphous layer of clouds of a uniform gray color, giving rise to continuous rain or snow. Nimbostratus clouds are highly developed vertically (up to several km) and horizontally (several thousand km), consist of supercooled water droplets mixed with snowflakes, usually associated with atmospheric fronts.
Stratus clouds are clouds of the lower tier in the form of a homogeneous layer without definite outlines, gray in color. The height of stratus clouds above the earth's surface is 0.5–2 km. Occasionally, drizzle falls from stratus clouds.
Cumulus clouds are dense, bright white clouds during the day with significant vertical development (up to 5 km or more). The upper parts of cumulus clouds look like domes or towers with rounded outlines. Typically, cumulus clouds arise as convection clouds in cold air masses.
Stratocumulus clouds are low (below 2 km) clouds in the form of gray or white non-fibrous layers or ridges of round large blocks. The vertical thickness of stratocumulus clouds is small. Occasionally, stratocumulus clouds produce light precipitation.
Cumulonimbus clouds are powerful and dense clouds with strong vertical development (up to a height of 14 km), producing heavy rainfall with thunderstorms, hail, and squalls. Cumulonimbus clouds develop from powerful cumulus clouds, differing from them in the upper part consisting of ice crystals.
Stratosphere.
Through the tropopause, on average at altitudes from 12 to 50 km, the troposphere passes into the stratosphere. In the lower part, for about 10 km, i.e. up to altitudes of about 20 km, it is isothermal (temperature about 220 K). It then increases with altitude, reaching a maximum of about 270 K at an altitude of 50–55 km. Here is the boundary between the stratosphere and the overlying mesosphere, called the stratopause. .
There is significantly less water vapor in the stratosphere. Still, thin translucent pearlescent clouds are sometimes observed, occasionally appearing in the stratosphere at an altitude of 20–30 km. Pearlescent clouds are visible in the dark sky after sunset and before sunrise. In shape, nacreous clouds resemble cirrus and cirrocumulus clouds.
Middle atmosphere (mesosphere).
At an altitude of about 50 km, the mesosphere begins from the peak of the broad temperature maximum . The reason for the increase in temperature in the region of this maximum is an exothermic (i.e. accompanied by the release of heat) photochemical reaction of ozone decomposition: O 3 + hv® O 2 + O. Ozone arises as a result of the photochemical decomposition of molecular oxygen O 2
O 2 + hv® O + O and the subsequent reaction of a triple collision of an oxygen atom and molecule with some third molecule M.
O + O 2 + M ® O 3 + M
Ozone voraciously absorbs ultraviolet radiation in the region from 2000 to 3000 Å, and this radiation heats the atmosphere. Ozone, located in the upper atmosphere, serves as a kind of shield that protects us from the effects of ultraviolet radiation from the Sun. Without this shield, the development of life on Earth in its modern forms would hardly have been possible.
In general, throughout the mesosphere, the atmospheric temperature decreases to its minimum value of about 180 K at the upper boundary of the mesosphere (called mesopause, altitude about 80 km). In the vicinity of the mesopause, at altitudes of 70–90 km, a very thin layer of ice crystals and particles of volcanic and meteorite dust may appear, observed in the form of a beautiful spectacle of noctilucent clouds shortly after sunset.
In the mesosphere, small solid meteorite particles that fall on the Earth, causing the phenomenon of meteors, mostly burn up.
Meteors, meteorites and fireballs.
Flares and other phenomena in the upper atmosphere of the Earth caused by the intrusion of solid cosmic particles or bodies into it at a speed of 11 km/s or higher are called meteoroids. An observable bright meteor trail appears; the most powerful phenomena, often accompanied by the fall of meteorites, are called fireballs; the appearance of meteors is associated with meteor showers.
Meteor shower:
1) the phenomenon of multiple falls of meteors over several hours or days from one radiant.
2) a swarm of meteoroids moving in the same orbit around the Sun.
The systematic appearance of meteors in a certain area of the sky and on certain days of the year, caused by the intersection of the Earth's orbit with the common orbit of many meteorite bodies moving at approximately the same and identically directed speeds, due to which their paths in the sky appear to emerge from a common point (radiant) . They are named after the constellation where the radiant is located.
Meteor showers make a deep impression with their light effects, but individual meteors are rarely visible. Much more numerous are invisible meteors, too small to be visible when they are absorbed into the atmosphere. Some of the smallest meteors probably do not heat up at all, but are only captured by the atmosphere. These small particles with sizes ranging from a few millimeters to ten thousandths of a millimeter are called micrometeorites. The amount of meteoric matter entering the atmosphere every day ranges from 100 to 10,000 tons, with the majority of this material coming from micrometeorites.
Since meteoric matter partially burns in the atmosphere, its gas composition is replenished with traces of various chemical elements. For example, rocky meteors introduce lithium into the atmosphere. The combustion of metal meteors leads to the formation of tiny spherical iron, iron-nickel and other droplets that pass through the atmosphere and settle on the earth's surface. They can be found in Greenland and Antarctica, where ice sheets remain almost unchanged for years. Oceanologists find them in bottom ocean sediments.
Most meteor particles entering the atmosphere settle within approximately 30 days. Some scientists believe that this cosmic dust plays an important role in the formation of atmospheric phenomena such as rain because it serves as condensation nuclei for water vapor. Therefore, it is assumed that precipitation is statistically related to large meteor showers. However, some experts believe that since the total supply of meteoric material is many tens of times greater than that of even the largest meteor shower, the change in the total amount of this material resulting from one such rain can be neglected.
However, there is no doubt that the largest micrometeorites and visible meteorites leave long traces of ionization in the high layers of the atmosphere, mainly in the ionosphere. Such traces can be used for long-distance radio communications, as they reflect high-frequency radio waves.
The energy of meteors entering the atmosphere is spent mainly, and perhaps completely, on heating it. This is one of the minor components of the thermal balance of the atmosphere.
A meteorite is a naturally occurring solid body that fell to the surface of the Earth from space. Usually a distinction is made between stony, stony-iron and iron meteorites. The latter mainly consist of iron and nickel. Among the meteorites found, most weigh from a few grams to several kilograms. The largest of those found, the Goba iron meteorite weighs about 60 tons and still lies in the same place where it was discovered, in South Africa. Most meteorites are fragments of asteroids, but some meteorites may have come to Earth from the Moon and even Mars.
A bolide is a very bright meteor, sometimes visible even during the day, often leaving behind a smoky trail and accompanied by sound phenomena; often ends with the fall of meteorites.
Thermosphere.
Above the temperature minimum of the mesopause, the thermosphere begins, in which the temperature, first slowly and then quickly begins to rise again. The reason is the absorption of ultraviolet radiation from the Sun at altitudes of 150–300 km, due to the ionization of atomic oxygen: O + hv® O + + e.
In the thermosphere, the temperature continuously increases to an altitude of about 400 km, where it reaches 1800 K during the day during the epoch of maximum solar activity. During the epoch of minimum solar activity, this limiting temperature can be less than 1000 K. Above 400 km, the atmosphere turns into an isothermal exosphere. The critical level (the base of the exosphere) is at an altitude of about 500 km.
Polar lights and many orbits of artificial satellites, as well as noctilucent clouds - all these phenomena occur in the mesosphere and thermosphere.
Polar lights.
At high latitudes, auroras are observed during magnetic field disturbances. They may last a few minutes, but are often visible for several hours. Auroras vary greatly in shape, color and intensity, all of which sometimes change very quickly over time. The spectrum of auroras consists of emission lines and bands. Some of the night sky emissions are enhanced in the aurora spectrum, primarily the green and red lines l 5577 Å and l 6300 Å oxygen. It happens that one of these lines is many times more intense than the other, and this determines the visible color of the aurora: green or red. Magnetic field disturbances are also accompanied by disruptions in radio communications in the polar regions. The cause of the disruption is changes in the ionosphere, which mean that during magnetic storms there is a powerful source of ionization. It has been established that strong magnetic storms occur when there are large groups of sunspots near the center of the solar disk. Observations have shown that storms are not associated with the sunspots themselves, but with solar flares that appear during the development of a group of sunspots.
Auroras are a range of light of varying intensity with rapid movements observed in high latitude regions of the Earth. The visual aurora contains green (5577Å) and red (6300/6364Å) atomic oxygen emission lines and molecular N2 bands, which are excited by energetic particles of solar and magnetospheric origin. These emissions usually appear at altitudes of about 100 km and above. The term optical aurora is used to refer to visual auroras and their emission spectrum from the infrared to the ultraviolet region. The radiation energy in the infrared part of the spectrum significantly exceeds the energy in the visible region. When auroras appeared, emissions were observed in the ULF range (
The actual forms of auroras are difficult to classify; The most commonly used terms are:
1. Calm, uniform arcs or stripes. The arc typically extends ~1000 km in the direction of the geomagnetic parallel (toward the Sun in polar regions) and has a width of one to several tens of kilometers. A stripe is a generalization of the concept of an arc; it usually does not have a regular arc-shaped shape, but bends in the form of the letter S or in the form of spirals. Arcs and stripes are located at altitudes of 100–150 km.
2. Rays of the aurora . This term refers to an auroral structure elongated along magnetic field lines, with a vertical extent of several tens to several hundred kilometers. The horizontal extent of the rays is small, from several tens of meters to several kilometers. The rays are usually observed in arcs or as separate structures.
3. Stains or surfaces . These are isolated areas of glow that do not have a specific shape. Individual spots may be connected to each other.
4. Veil. An unusual form of aurora, which is a uniform glow that covers large areas of the sky.
According to their structure, auroras are divided into homogeneous, hollow and radiant. Various terms are used; pulsating arc, pulsating surface, diffuse surface, radiant stripe, drapery, etc. There is a classification of auroras according to their color. According to this classification, auroras of the type A. The upper part or the entire part is red (6300–6364 Å). They usually appear at altitudes of 300–400 km with high geomagnetic activity.
Aurora type IN colored red in the lower part and associated with the glow of the bands of the first positive system N 2 and the first negative system O 2. Such forms of auroras appear during the most active phases of auroras.
Zones polar lights – These are the zones of maximum frequency of auroras at night, according to observers at a fixed point on the Earth's surface. The zones are located at 67° north and south latitude, and their width is about 6°. The maximum occurrence of auroras, corresponding to a given moment of geomagnetic local time, occurs in oval-like belts (oval auroras), which are located asymmetrically around the north and south geomagnetic poles. The aurora oval is fixed in latitude – time coordinates, and the aurora zone is the geometric locus of the points of the oval’s midnight region in latitude – longitude coordinates. The oval belt is located approximately 23° from the geomagnetic pole in the night sector and 15° in the daytime sector.
Aurora oval and aurora zones. The location of the aurora oval depends on geomagnetic activity. The oval becomes wider with high geomagnetic activity. Auroral zones or auroral oval boundaries are better represented by L 6.4 than by dipole coordinates. Geomagnetic field lines at the boundary of the daytime sector of the aurora oval coincide with magnetopause. A change in the position of the aurora oval is observed depending on the angle between the geomagnetic axis and the Earth-Sun direction. The auroral oval is also determined on the basis of data on precipitation of particles (electrons and protons) of certain energies. Its position can be independently determined from data on Kaspakh on the dayside and in the tail of the magnetosphere.
The daily variation in the frequency of occurrence of auroras in the aurora zone has a maximum at geomagnetic midnight and a minimum at geomagnetic noon. On the near-equatorial side of the oval, the frequency of occurrence of auroras sharply decreases, but the shape of the daily variations is preserved. On the polar side of the oval, the frequency of auroras decreases gradually and is characterized by complex diurnal changes.
Intensity of auroras.
Aurora intensity determined by measuring the apparent surface brightness. Luminosity surface I aurora in a certain direction is determined by the total emission of 4p I photon/(cm 2 s). Since this value is not the true surface brightness, but represents the emission from the column, the unit photon/(cm 2 column s) is usually used when studying auroras. The usual unit for measuring total emission is Rayleigh (Rl) equal to 10 6 photons/(cm 2 column s). More practical units of auroral intensity are determined by the emissions of an individual line or band. For example, the intensity of auroras is determined by the international brightness coefficients (IBRs) according to the intensity of the green line (5577 Å); 1 kRl = I MKY, 10 kRl = II MKY, 100 kRl = III MKY, 1000 kRl = IV MKY (maximum intensity of the aurora). This classification cannot be used for red auroras. One of the discoveries of the era (1957–1958) was the establishment of the spatiotemporal distribution of auroras in the form of an oval, shifted relative to the magnetic pole. From simple ideas about the circular shape of the distribution of auroras relative to the magnetic pole there was The transition to modern physics of the magnetosphere has been completed. The honor of the discovery belongs to O. Khorosheva, and the intensive development of ideas for the auroral oval was carried out by G. Starkov, Y. Feldstein, S. I. Akasofu and a number of other researchers. The auroral oval is the region of the most intense influence of the solar wind on the Earth's upper atmosphere. The intensity of the aurora is greatest in the oval, and its dynamics are continuously monitored using satellites.
Stable auroral red arcs.
Steady auroral red arc, otherwise called mid-latitude red arc or M-arc, is a subvisual (below the limit of sensitivity of the eye) wide arc, stretching from east to west for thousands of kilometers and possibly encircling the entire Earth. The latitudinal length of the arc is 600 km. The emission of the stable auroral red arc is almost monochromatic in the red lines l 6300 Å and l 6364 Å. Recently, weak emission lines l 5577 Å (OI) and l 4278 Å (N+2) were also reported. Sustained red arcs are classified as auroras, but they appear at much higher altitudes. The lower limit is located at an altitude of 300 km, the upper limit is about 700 km. The intensity of the quiet auroral red arc in the l 6300 Å emission ranges from 1 to 10 kRl (typical value 6 kRl). The sensitivity threshold of the eye at this wavelength is about 10 kRl, so arcs are rarely observed visually. However, observations have shown that their brightness is >50 kRL on 10% of nights. The usual lifespan of arcs is about one day, and they rarely appear in subsequent days. Radio waves from satellites or radio sources crossing persistent auroral red arcs are subject to scintillation, indicating the existence of electron density inhomogeneities. The theoretical explanation for red arcs is that the heated electrons of the region F The ionosphere causes an increase in oxygen atoms. Satellite observations show an increase in electron temperature along geomagnetic field lines that intersect persistent auroral red arcs. The intensity of these arcs is positively correlated with geomagnetic activity (storms), and the frequency of occurrence of arcs is positively correlated with sunspot activity.
Changing aurora.
Some forms of auroras experience quasiperiodic and coherent temporal variations in intensity. These auroras with approximately stationary geometry and rapid periodic variations occurring in phase are called changing auroras. They are classified as auroras forms R according to the International Atlas of Auroras A more detailed subdivision of the changing auroras:
R 1 (pulsating aurora) is a glow with uniform phase variations in brightness throughout the aurora shape. By definition, in an ideal pulsating aurora, the spatial and temporal parts of the pulsation can be separated, i.e. brightness I(r,t)= I s(r)· I T(t). In a typical aurora R 1 pulsations occur with a frequency from 0.01 to 10 Hz of low intensity (1–2 kRl). Most auroras R 1 – these are spots or arcs that pulsate with a period of several seconds.
R 2 (fiery aurora). The term is usually used to refer to movements like flames filling the sky, rather than to describe a distinct shape. The auroras have the shape of arcs and usually move upward from a height of 100 km. These auroras are relatively rare and occur more often outside the aurora.
R 3 (shimmering aurora). These are auroras with rapid, irregular or regular variations in brightness, giving the impression of flickering flames in the sky. They appear shortly before the aurora disintegrates. Typically observed frequency of variation R 3 is equal to 10 ± 3 Hz.
The term streaming aurora, used for another class of pulsating auroras, refers to irregular variations in brightness moving quickly horizontally in auroral arcs and streaks.
The changing aurora is one of the solar-terrestrial phenomena that accompany pulsations of the geomagnetic field and auroral X-ray radiation caused by the precipitation of particles of solar and magnetospheric origin.
The glow of the polar cap is characterized by high intensity of the band of the first negative system N + 2 (l 3914 Å). Typically, these N + 2 bands are five times more intense than the green line OI l 5577 Å; the absolute intensity of the polar cap glow ranges from 0.1 to 10 kRl (usually 1–3 kRl). During these auroras, which appear during periods of PCA, a uniform glow covers the entire polar cap up to a geomagnetic latitude of 60° at altitudes of 30 to 80 km. It is generated predominantly by solar protons and d-particles with energies of 10–100 MeV, creating a maximum ionization at these altitudes. There is another type of glow in aurora zones, called mantle aurora. For this type of auroral glow, the daily maximum intensity, occurring in the morning hours, is 1–10 kRL, and the minimum intensity is five times weaker. Observations of mantle auroras are few and far between; their intensity depends on geomagnetic and solar activity.
Atmospheric glow is defined as radiation produced and emitted by a planet's atmosphere. This is non-thermal radiation of the atmosphere, with the exception of the emission of auroras, lightning discharges and the emission of meteor trails. This term is used in relation to the earth's atmosphere (nightglow, twilight glow and dayglow). Atmospheric glow constitutes only a portion of the light available in the atmosphere. Other sources include starlight, zodiacal light, and daytime diffuse light from the Sun. At times, atmospheric glow can account for up to 40% of the total amount of light. Atmospheric glow occurs in atmospheric layers of varying height and thickness. The atmospheric glow spectrum covers wavelengths from 1000 Å to 22.5 microns. The main emission line in the atmospheric glow is l 5577 Å, appearing at an altitude of 90–100 km in a layer 30–40 km thick. The appearance of luminescence is due to the Chapman mechanism, based on the recombination of oxygen atoms. Other emission lines are l 6300 Å, appearing in the case of dissociative recombination of O + 2 and emission NI l 5198/5201 Å and NI l 5890/5896 Å.
The intensity of airglow is measured in Rayleigh. Brightness (in Rayleigh) is equal to 4 rv, where b is the angular surface brightness of the emitting layer in units of 10 6 photons/(cm 2 ster·s). The intensity of the glow depends on latitude (different for different emissions), and also varies throughout the day with a maximum near midnight. A positive correlation was noted for airglow in the l 5577 Å emission with the number of sunspots and solar radiation flux at a wavelength of 10.7 cm. Airglow is observed during satellite experiments. From outer space, it appears as a ring of light around the Earth and has a greenish color.
Ozonosphere.
At altitudes of 20–25 km, the maximum concentration of an insignificant amount of ozone O 3 is reached (up to 2×10 –7 of the oxygen content!), which arises under the influence of solar ultraviolet radiation at altitudes of approximately 10 to 50 km, protecting the planet from ionizing solar radiation. Despite the extremely small number of ozone molecules, they protect all life on Earth from the harmful effects of short-wave (ultraviolet and x-ray) radiation from the Sun. If you deposit all the molecules to the base of the atmosphere, you will get a layer no more than 3–4 mm thick! At altitudes above 100 km, the proportion of light gases increases, and at very high altitudes helium and hydrogen predominate; many molecules dissociate into individual atoms, which, ionized under the influence of hard radiation from the Sun, form the ionosphere. The pressure and density of air in the Earth's atmosphere decrease with altitude. Depending on the temperature distribution, the Earth's atmosphere is divided into the troposphere, stratosphere, mesosphere, thermosphere and exosphere. .
At an altitude of 20–25 km there is ozone layer. Ozone is formed due to the breakdown of oxygen molecules when absorbing ultraviolet radiation from the Sun with wavelengths shorter than 0.1–0.2 microns. Free oxygen combines with O 2 molecules and forms ozone O 3, which greedily absorbs all ultraviolet radiation shorter than 0.29 microns. O3 ozone molecules are easily destroyed by short-wave radiation. Therefore, despite its rarefaction, the ozone layer effectively absorbs ultraviolet radiation from the Sun that has passed through higher and more transparent atmospheric layers. Thanks to this, living organisms on Earth are protected from the harmful effects of ultraviolet light from the Sun.
Ionosphere.
Radiation from the sun ionizes the atoms and molecules of the atmosphere. The degree of ionization becomes significant already at an altitude of 60 kilometers and steadily increases with distance from the Earth. At different altitudes in the atmosphere, sequential processes of dissociation of various molecules and subsequent ionization of various atoms and ions occur. These are mainly molecules of oxygen O 2, nitrogen N 2 and their atoms. Depending on the intensity of these processes, the various layers of the atmosphere lying above 60 kilometers are called ionospheric layers , and their totality is the ionosphere . The lower layer, the ionization of which is insignificant, is called the neutrosphere.
The maximum concentration of charged particles in the ionosphere is achieved at altitudes of 300–400 km.
History of the study of the ionosphere.
The hypothesis about the existence of a conducting layer in the upper atmosphere was put forward in 1878 by the English scientist Stuart to explain the features of the geomagnetic field. Then in 1902, independently of each other, Kennedy in the USA and Heaviside in England pointed out that to explain the propagation of radio waves over long distances it was necessary to assume the existence of regions of high conductivity in the high layers of the atmosphere. In 1923, academician M.V. Shuleikin, considering the features of the propagation of radio waves of various frequencies, came to the conclusion that there are at least two reflective layers in the ionosphere. Then in 1925, English researchers Appleton and Barnett, as well as Breit and Tuve, first experimentally proved the existence of regions that reflect radio waves, and laid the foundation for their systematic study. Since that time, a systematic study has been carried out of the properties of these layers, generally called the ionosphere, which play a significant role in a number of geophysical phenomena that determine the reflection and absorption of radio waves, which is very important for practical purposes, in particular for ensuring reliable radio communications.
In the 1930s, systematic observations of the state of the ionosphere began. In our country, on the initiative of M.A. Bonch-Bruevich, installations for its pulse probing were created. Many general properties of the ionosphere, heights and electron concentration of its main layers were studied.
At altitudes of 60–70 km layer D is observed, at altitudes of 100–120 km layer E, at altitudes, at altitudes of 180–300 km double layer F 1 and F 2. The main parameters of these layers are given in Table 4.
| Table 4. | ||||||
| Ionospheric region | Maximum height, km | T i , K | Day | Night n e , cm –3 | a΄, ρm 3 s – 1 | |
| min n e , cm –3 | Max n e , cm –3 | |||||
| D | 70 | 20 | 100 | 200 | 10 | 10 –6 |
| E | 110 | 270 | 1.5 10 5 | 3·10 5 | 3000 | 10 –7 |
| F 1 | 180 | 800–1500 | 3·10 5 | 5 10 5 | – | 3·10 –8 |
| F 2 (winter) | 220–280 | 1000–2000 | 6 10 5 | 25 10 5 | ~10 5 | 2·10 –10 |
| F 2 (summer) | 250–320 | 1000–2000 | 2·10 5 | 8 10 5 | ~3·10 5 | 10 –10 |
| n e– electron concentration, e – electron charge, T i– ion temperature, a΄ – recombination coefficient (which determines the value n e and its change over time) | ||||||
Average values are given because they vary at different latitudes, depending on the time of day and seasons. Such data is necessary to ensure long-distance radio communications. They are used in selecting operating frequencies for various shortwave radio links. Knowledge of their changes depending on the state of the ionosphere at different times of the day and in different seasons is extremely important to ensure the reliability of radio communications. The ionosphere is a collection of ionized layers of the earth's atmosphere, starting from altitudes of about 60 km and extending to altitudes of tens of thousands of km. The main source of ionization of the Earth's atmosphere is ultraviolet and X-ray radiation from the Sun, which occurs mainly in the solar chromosphere and corona. In addition, the degree of ionization of the upper atmosphere is influenced by solar corpuscular streams that occur during solar flares, as well as cosmic rays and meteor particles.
Ionospheric layers
- these are areas in the atmosphere in which maximum concentrations of free electrons are reached (i.e., their number per unit volume). Electrically charged free electrons and (to a lesser extent, less mobile ions) resulting from the ionization of atoms of atmospheric gases, interacting with radio waves (i.e., electromagnetic oscillations), can change their direction, reflecting or refracting them, and absorb their energy. As a result of this, when receiving distant radio stations, various effects may occur, for example, fading of radio communications, increased audibility of remote stations, blackouts and so on. phenomena.
Research methods.
Classical methods of studying the ionosphere from Earth come down to pulse sounding - sending radio pulses and observing their reflections from various layers of the ionosphere, measuring the delay time and studying the intensity and shape of the reflected signals. By measuring the heights of reflection of radio pulses at various frequencies, determining the critical frequencies of various areas (the critical frequency is the carrier frequency of a radio pulse, for which a given region of the ionosphere becomes transparent), it is possible to determine the value of the electron concentration in the layers and the effective heights for given frequencies, and select the optimal frequencies for given radio paths. With the development of rocket technology and the advent of the space age of artificial Earth satellites (AES) and other spacecraft, it became possible to directly measure the parameters of near-Earth space plasma, the lower part of which is the ionosphere.
Measurements of electron concentration, carried out on board specially launched rockets and along satellite flight paths, confirmed and clarified data previously obtained by ground-based methods on the structure of the ionosphere, the distribution of electron concentration with height above various regions of the Earth and made it possible to obtain electron concentration values above the main maximum - the layer F. Previously, this was impossible to do using sounding methods based on observations of reflected short-wave radio pulses. It has been discovered that in some areas of the globe there are quite stable areas with a reduced electron concentration, regular “ionospheric winds”, peculiar wave processes arise in the ionosphere that carry local ionospheric disturbances thousands of kilometers from the place of their excitation, and much more. The creation of particularly highly sensitive receiving devices made it possible to receive pulse signals partially reflected from the lowest regions of the ionosphere (partial reflection stations) at ionospheric pulse sounding stations. The use of powerful pulsed installations in the meter and decimeter wavelength ranges with the use of antennas that allow for a high concentration of emitted energy made it possible to observe signals scattered by the ionosphere at various altitudes. The study of the features of the spectra of these signals, incoherently scattered by electrons and ions of the ionospheric plasma (for this, stations of incoherent scattering of radio waves were used) made it possible to determine the concentration of electrons and ions, their equivalent temperature at various altitudes up to altitudes of several thousand kilometers. It turned out that the ionosphere is quite transparent for the frequencies used.
The concentration of electric charges (the electron concentration is equal to the ion concentration) in the earth's ionosphere at an altitude of 300 km is about 10 6 cm –3 during the day. Plasma of such density reflects radio waves with a length of more than 20 m, and transmits shorter ones.
Typical vertical distribution of electron concentration in the ionosphere for day and night conditions.
Propagation of radio waves in the ionosphere.
Stable reception of long-distance broadcasting stations depends on the frequencies used, as well as on the time of day, season and, in addition, on solar activity. Solar activity significantly affects the state of the ionosphere. Radio waves emitted by a ground station travel in a straight line, like all types of electromagnetic waves. However, it should be taken into account that both the surface of the Earth and the ionized layers of its atmosphere serve as the plates of a huge capacitor, acting on them like the effect of mirrors on light. Reflecting from them, radio waves can travel many thousands of kilometers, circling the globe in huge leaps of hundreds and thousands of kilometers, reflecting alternately from a layer of ionized gas and from the surface of the Earth or water.
In the 20s of the last century, it was believed that radio waves shorter than 200 m were generally not suitable for long-distance communications due to strong absorption. The first experiments on long-distance reception of short waves across the Atlantic between Europe and America were carried out by English physicist Oliver Heaviside and American electrical engineer Arthur Kennelly. Independently of each other, they suggested that somewhere around the Earth there is an ionized layer of the atmosphere capable of reflecting radio waves. It was called the Heaviside-Kennelly layer, and then the ionosphere.
According to modern concepts, the ionosphere consists of negatively charged free electrons and positively charged ions, mainly molecular oxygen O + and nitric oxide NO +. Ions and electrons are formed as a result of the dissociation of molecules and ionization of neutral gas atoms by solar X-rays and ultraviolet radiation. In order to ionize an atom, it is necessary to impart ionization energy to it, the main source of which for the ionosphere is ultraviolet, x-ray and corpuscular radiation from the Sun.
While the gaseous shell of the Earth is illuminated by the Sun, more and more electrons are continuously formed in it, but at the same time some of the electrons, colliding with ions, recombine, again forming neutral particles. After sunset, the formation of new electrons almost stops, and the number of free electrons begins to decrease. The more free electrons there are in the ionosphere, the better high-frequency waves are reflected from it. With a decrease in electron concentration, the passage of radio waves is possible only in low frequency ranges. That is why at night, as a rule, it is possible to receive distant stations only in the ranges of 75, 49, 41 and 31 m. Electrons are distributed unevenly in the ionosphere. At altitudes from 50 to 400 km there are several layers or regions of increased electron concentration. These areas smoothly transition into one another and have different effects on the propagation of HF radio waves. The upper layer of the ionosphere is designated by the letter F. Here the highest degree of ionization (the fraction of charged particles is about 10 –4). It is located at an altitude of more than 150 km above the Earth's surface and plays the main reflective role in the long-distance propagation of high-frequency HF radio waves. In the summer months, region F splits into two layers - F 1 and F 2. Layer F1 can occupy heights from 200 to 250 km, and layer F 2 seems to “float” in the altitude range of 300–400 km. Usually layer F 2 is ionized much stronger than the layer F 1 . Night layer F 1 disappears and the layer F 2 remains, slowly losing up to 60% of its degree of ionization. Below layer F at altitudes from 90 to 150 km there is a layer E ionization of which occurs under the influence of soft X-ray radiation from the Sun. The degree of ionization of the E layer is lower than that of the F, during the day, reception of stations in the low-frequency HF ranges of 31 and 25 m occurs when signals are reflected from the layer E. Typically these are stations located at a distance of 1000–1500 km. At night in the layer E Ionization decreases sharply, but even at this time it continues to play a significant role in the reception of signals from stations on the 41, 49 and 75 m ranges.
Of great interest for receiving signals of high-frequency HF ranges of 16, 13 and 11 m are those arising in the area E layers (clouds) of highly increased ionization. The area of these clouds can vary from a few to hundreds of square kilometers. This layer of increased ionization is called the sporadic layer E and is designated Es. Es clouds can move in the ionosphere under the influence of wind and reach speeds of up to 250 km/h. In summer in mid-latitudes during the daytime, the origin of radio waves due to Es clouds occurs for 15–20 days per month. Near the equator it is almost always present, and in high latitudes it usually appears at night. Sometimes, during years of low solar activity, when there is no transmission on the high-frequency HF bands, distant stations suddenly appear on the 16, 13 and 11 m bands with good volume, the signals of which are reflected many times from Es.
The lowest region of the ionosphere is the region D located at altitudes between 50 and 90 km. There are relatively few free electrons here. From the area D Long and medium waves are well reflected, and signals from low-frequency HF stations are strongly absorbed. After sunset, ionization disappears very quickly and it becomes possible to receive distant stations in the ranges of 41, 49 and 75 m, the signals of which are reflected from the layers F 2 and E. Individual layers of the ionosphere play an important role in the propagation of HF radio signals. The effect on radio waves occurs mainly due to the presence of free electrons in the ionosphere, although the mechanism of radio wave propagation is associated with the presence of large ions. The latter are also of interest when studying the chemical properties of the atmosphere, since they are more active than neutral atoms and molecules. Chemical reactions occurring in the ionosphere play an important role in its energy and electrical balance.
Normal ionosphere. Observations made using geophysical rockets and satellites have provided a wealth of new information indicating that ionization of the atmosphere occurs under the influence of a wide range of solar radiation. Its main part (more than 90%) is concentrated in the visible part of the spectrum. Ultraviolet radiation, which has a shorter wavelength and higher energy than violet light rays, is emitted by hydrogen in the Sun's inner atmosphere (the chromosphere), and X-rays, which have even higher energy, are emitted by gases in the Sun's outer shell (the corona).
The normal (average) state of the ionosphere is due to constant powerful radiation. Regular changes occur in the normal ionosphere due to the daily rotation of the Earth and seasonal differences in the angle of incidence of the sun's rays at noon, but unpredictable and abrupt changes in the state of the ionosphere also occur.
Disturbances in the ionosphere.
As is known, powerful cyclically repeating manifestations of activity occur on the Sun, which reach a maximum every 11 years. Observations under the International Geophysical Year (IGY) program coincided with the period of the highest solar activity for the entire period of systematic meteorological observations, i.e. from the beginning of the 18th century. During periods of high activity, the brightness of some areas on the Sun increases several times, and the power of ultraviolet and X-ray radiation increases sharply. Such phenomena are called solar flares. They last from several minutes to one to two hours. During the flare, solar plasma (mostly protons and electrons) is erupted, and elementary particles rush into outer space. Electromagnetic and corpuscular radiation from the Sun during such flares has a strong impact on the Earth's atmosphere.
The initial reaction is observed 8 minutes after the flare, when intense ultraviolet and X-ray radiation reaches the Earth. As a result, ionization increases sharply; X-rays penetrate the atmosphere to the lower boundary of the ionosphere; the number of electrons in these layers increases so much that the radio signals are almost completely absorbed (“extinguished”). The additional absorption of radiation causes the gas to heat up, which contributes to the development of winds. Ionized gas is an electrical conductor, and when it moves in the Earth's magnetic field, a dynamo effect occurs and an electric current is created. Such currents can, in turn, cause noticeable disturbances in the magnetic field and manifest themselves in the form of magnetic storms.
The structure and dynamics of the upper atmosphere are significantly determined by non-equilibrium processes in the thermodynamic sense associated with ionization and dissociation by solar radiation, chemical processes, excitation of molecules and atoms, their deactivation, collisions and other elementary processes. In this case, the degree of nonequilibrium increases with height as the density decreases. Up to altitudes of 500–1000 km, and often higher, the degree of nonequilibrium for many characteristics of the upper atmosphere is quite small, which makes it possible to use classical and hydromagnetic hydrodynamics, taking into account chemical reactions, to describe it.
The exosphere is the outer layer of the Earth's atmosphere, starting at altitudes of several hundred kilometers, from which light, fast-moving hydrogen atoms can escape into outer space.
Edward Kononovich
Literature:
Pudovkin M.I. Fundamentals of Solar Physics. St. Petersburg, 2001
Eris Chaisson, Steve McMillan Astronomy today. Prentice-Hall, Inc. Upper Saddle River, 2002
Materials on the Internet: http://ciencia.nasa.gov/