A bright luminary heats us up with hot rays and makes us think about the significance of radiation in our life, its benefits and harms. What is solar radiation? The lesson of school physics invites us to get acquainted with the concept of electromagnetic radiation in general for a start. This term denotes another form of matter - different from matter. This includes both visible light and the spectrum that the eye cannot see. That is, X-rays, gamma rays, ultraviolet and infrared.
Electromagnetic waves
In the presence of a source-emitter of radiation, its electromagnetic waves propagate in all directions at the speed of light. These waves, like any others, have certain characteristics. These include vibration frequency and wavelength. Any body whose temperature differs from absolute zero has the property to emit radiation.
The sun is the main and most powerful source of radiation near our planet. In turn, the Earth (its atmosphere and surface) itself emits radiation, but in a different range. Observing the temperature conditions on the planet for long periods of time gave rise to a hypothesis about the equilibrium of the amount of heat received from the Sun and given into space.
Sun radiation: spectral composition
The vast majority (about 99%) of solar energy in the spectrum lies in the wavelength range from 0.1 to 4 microns. The remaining 1% is longer and shorter rays, including radio waves and X-rays. About half of the sun's radiant energy falls on the spectrum that we perceive with our eyes, about 44% on infrared radiation, 9% on ultraviolet radiation. How do we know how solar radiation is divided? The calculation of its distribution is possible thanks to research from space satellites.
There are substances that can enter a special state and emit additional radiation in a different wavelength range. For example, there is a glow at low temperatures, not typical for the emission of light by this substance. This type of radiation, called luminescent radiation, does not lend itself to the usual principles of thermal radiation.
The phenomenon of luminescence occurs after a substance has absorbed a certain amount of energy and a transition to another state (the so-called excited state), which is energetically higher than at the substance's own temperature. Luminescence appears during the reverse transition - from an excited state to a familiar state. In nature, we can observe it in the form of night sky glow and aurora borealis.
Our luminary
The energy of the sun's rays is almost the only source of heat for our planet. The intrinsic radiation coming from its depths to the surface has an intensity that is about 5 thousand times less. At the same time, visible light - one of the most important factors of life on the planet - is only a part of solar radiation.
The energy of the sun's rays is converted into heat in a smaller part - in the atmosphere, and most of it - on the surface of the Earth. There it is spent on heating water and soil (upper layers), which then give off heat to the air. When heated, the atmosphere and the earth's surface, in turn, emit infrared rays into space, while cooling.
Solar radiation: definition
The radiation that goes to the surface of our planet directly from the solar disk is usually called direct solar radiation. The sun spreads it in all directions. Given the enormous distance from the Earth to the Sun, direct solar radiation at any point on the earth's surface can be represented as a bundle of parallel rays, the source of which is practically at infinity. The area perpendicular to the rays of sunlight thus receives the largest amount.
Radiation flux density (or irradiance) is a measure of the amount of radiation falling on a specific surface. This is the amount of radiant energy falling per unit of time per unit of area. This value is measured - irradiance - in W / m 2. Our Earth, as everyone knows, revolves around the Sun in an ellipsoidal orbit. The sun is at one of the focuses of this ellipse. Therefore, every year at a certain time (at the beginning of January) the Earth takes the position closest to the Sun and at another (at the beginning of July) - the farthest from it. In this case, the magnitude of the irradiance changes in inverse proportion with respect to the square of the distance to the luminary.
Where is the solar radiation that has reached the Earth? Its types are determined by many factors. Depending on the latitude, humidity, cloudiness, part of it is scattered in the atmosphere, part is absorbed, but most still reach the surface of the planet. In this case, a small amount is reflected, and the main one is absorbed by the earth's surface, under the influence of which it is heated. Scattered solar radiation also partially falls on the earth's surface, partially absorbed by it and partially reflected. The rest of it goes into outer space.
How is the distribution
Is solar radiation uniform? Its types after all the "losses" in the atmosphere can differ in their spectral composition. After all, rays with different lengths are both scattered and absorbed in different ways. On average, the atmosphere absorbs about 23% of its original amount. Approximately 26% of the total flux turns into scattered radiation, 2/3 of which then falls on the Earth. In essence, this is a different kind of radiation, different from the original one. Scattered radiation is sent to the Earth not by the disk of the Sun, but by the firmament. It has a different spectral composition.
Absorbs radiation mainly ozone - the visible spectrum, and ultraviolet rays. Infrared radiation is absorbed by carbon dioxide (carbon dioxide), which, by the way, is very small in the atmosphere.
Scattering of radiation, which attenuates it, occurs for all wavelengths of the spectrum. In the process, its particles, falling under the electromagnetic influence, redistribute the energy of the incident wave in all directions. That is, the particles serve as point sources of energy.
Daylight
As a result of scattering, the light coming from the sun changes color as it passes through layers of atmospheres. The practical value of scattering is in creating daylight. If the Earth were deprived of the atmosphere, illumination would exist only in places where direct or surface-reflected rays of the sun hit. That is, the atmosphere is a source of illumination during the day. Thanks to her, it is light both in places inaccessible to direct rays, and when the sun is hiding behind clouds. It is scattering that gives color to the air - we see the sky in blue.
And what else does solar radiation depend on? The turbidity factor should not be overlooked either. After all, the weakening of radiation occurs in two ways - by the atmosphere itself and by water vapor, as well as by various impurities. Dust content increases in summer (as does the content of water vapor in the atmosphere).
Total radiation
It refers to the total amount of radiation falling on the earth's surface, both direct and scattered. The total solar radiation decreases with cloudy weather.
For this reason, in summer, the total radiation is on average higher before noon than after it. And in the first half of the year - more than in the second.
What happens to the total radiation on the earth's surface? Getting there, it is mostly absorbed by the top layer of soil or water and turns into heat, some of it is reflected. The degree of reflection depends on the nature of the earth's surface. The indicator expressing the percentage of reflected solar radiation to its total amount falling on the surface is called the surface albedo.
The concept of self-radiation of the earth's surface is understood as long-wave radiation emitted by vegetation, snow cover, upper layers of water and soil. The radiation balance of a surface is the difference between its absorbed and radiated amount.
Effective radiation
It has been proven that the counter-radiation is almost always less than the terrestrial one. Because of this, the surface of the earth bears heat losses. The difference between the values of the intrinsic radiation of the surface and the atmospheric one is called effective radiation. This is actually a net loss of energy and, as a result, heat at night.
It also exists in the daytime. But during the day, it is partially compensated or even blocked by the absorbed radiation. Therefore, the surface of the earth is warmer during the day than at night.
About the geographical distribution of radiation
Solar radiation on Earth is unevenly distributed throughout the year. Its distribution is zonal, and the isolines (connecting points of the same values) of the radiation flux are not at all identical to the latitudinal circles. This discrepancy is caused by different levels of cloudiness and transparency of the atmosphere in different regions of the globe.
The total solar radiation during the year is of greatest importance in subtropical deserts with a low cloud atmosphere. It is much less in the forest areas of the equatorial belt. The reason for this is increased cloudiness. This indicator decreases towards both poles. But in the region of the poles it grows again - in the northern hemisphere it is less, in the region of snowy and low-cloud Antarctica - more. Above the surface of the oceans, on average, solar radiation is less than over the continents.
Almost everywhere on Earth, the surface has a positive radiation balance, that is, for the same time, the radiation inflow is greater than the effective radiation. The exceptions are the regions of Antarctica and Greenland with their ice plateaus.
Do we face global warming?
But the above does not mean annual warming of the earth's surface. The excess of absorbed radiation is compensated by the leakage of heat from the surface into the atmosphere, which occurs when the phase of the water changes (evaporation, condensation in the form of clouds).
Thus, there is no radiation equilibrium as such on the Earth's surface. On the other hand, there is thermal equilibrium - the supply and loss of heat is balanced by different ways, including radiation.
Distribution of balance on the card
At the same latitudes of the Earth, the radiation balance is greater on the ocean surface than over land. This can be explained by the fact that the layer that absorbs radiation in the oceans is thicker, while the effective radiation there is less because of the cold sea surface compared to land.
Significant fluctuations in the amplitude of its distribution are observed in deserts. The balance is lower there due to the high effective radiation in dry air and low cloud conditions. To a lesser extent, it is lowered in regions of the monsoon climate. In the warm season, the cloudiness there is increased, and the absorbed solar radiation is less than in other regions of the same latitude.
Of course, the main factor on which the average annual solar radiation depends is the latitude of a particular region. Record "portions" of ultraviolet radiation go to countries located near the equator. These are Northeast Africa, its east coast, the Arabian Peninsula, north and west of Australia, part of the islands of Indonesia, and the western part of the coast of South America.
In Europe, Turkey, southern Spain, Sicily, Sardinia, the islands of Greece, the coast of France (southern part), as well as part of the regions of Italy, Cyprus and Crete take on the largest dose of both light and radiation.
And how are we?
The total solar radiation in Russia is distributed, at first glance, unexpectedly. On the territory of our country, oddly enough, it is not the Black Sea resorts that hold the palm. The largest doses of solar radiation occur on the territories bordering China and the Northern Land. In general, solar radiation in Russia is not particularly intense, which is fully explained by our northern geographic location. The minimum amount of sunshine goes to the northwestern region - St. Petersburg, along with the surrounding areas.
Solar radiation in Russia is inferior to that of Ukraine. There most of the ultraviolet radiation goes to the Crimea and the territories beyond the Danube, in second place is the Carpathians with the southern regions of Ukraine.
The total (it includes both direct and scattered) solar radiation falling on a horizontal surface is given monthly in specially developed tables for different territories and is measured in MJ / m2. For example, solar radiation in Moscow ranges from 31-58 in the winter months to 568-615 in the summer.
About solar insolation
Insolation, or the amount of useful radiation incident on a sunlit surface, varies considerably from one geographic point to another. Annual insolation is calculated per square meter in megawatts. For example, in Moscow this value is 1.01, in Arkhangelsk - 0.85, in Astrakhan - 1.38 MW.
When determining it, it is necessary to take into account such factors as the time of the year (in winter, the illumination and the length of the day are lower), the nature of the terrain (mountains can obscure the sun), weather conditions characteristic of the area - fog, frequent rains and clouds. The light-receiving plane can be oriented vertically, horizontally or obliquely. The amount of insolation, as well as the distribution of solar radiation in Russia, is data grouped into a table by city and region, indicating the geographic latitude.
All types of sunlight reach the earth's surface in three ways - in the form of direct, reflected and scattered solar radiation.
Direct solar radiation- these are rays coming directly from the sun. Its intensity (efficiency) depends on the height of the sun above the horizon: the maximum is observed at noon, and the minimum is observed in the morning and evening; from the season: maximum - in summer, minimum - in winter; from the height of the terrain above sea level (higher in the mountains than on the plain); on the state of the atmosphere (air pollution reduces it). The solar radiation spectrum also depends on the height of the sun above the horizon (the lower the sun is above the horizon, the less ultraviolet rays).
Reflected solar radiation- these are the rays of the sun, reflected by the earth or water surface. It is expressed as a percentage of the reflected rays to their total flux and is called albedo. The albedo value depends on the nature of the reflective surfaces. When organizing and carrying out sunbathing, it is necessary to know and take into account the albedo of the surfaces on which sunbathing is carried out. Some of them are characterized by selective reflectivity. Snow fully reflects infrared rays, and ultraviolet rays to a lesser extent.
Scattered solar radiation formed by the scattering of sunlight in the atmosphere. Air molecules and particles suspended in it (the smallest droplets of water, ice crystals, etc.), called aerosols, reflect part of the rays. As a result of multiple reflections, some of them still reach the earth's surface; these are the scattered rays of the sun. Mainly ultraviolet, violet and blue rays are scattered, which determines the blue color of the sky in clear weather. The specific gravity of scattered rays is high in high latitudes (in the northern regions). There the sun stands low above the horizon, and therefore the path of the rays to the earth's surface is longer. On a long path, the rays meet more obstacles and are more scattered.
(http://new-med-blog.livejournal.com/204
Total solar radiation- all direct and scattered solar radiation entering the earth's surface. Total solar radiation is characterized by intensity. With a cloudless sky, the total solar radiation has a maximum value around noon, and during the year - in summer.
Radiation balance
The radiation balance of the earth's surface is the difference between the total solar radiation absorbed by the earth's surface and its effective radiation. For the earth's surface
- the incoming part is the absorbed direct and scattered solar radiation, as well as the absorbed counter radiation of the atmosphere;
- the consumable part consists of heat loss due to the own radiation of the earth's surface.
The radiation balance can be positive(daytime, summertime) and negative(at night, in winter); measured in kW / m2 / min.
The radiation balance of the earth's surface is the most important component of the heat balance of the earth's surface; one of the main climate-forming factors.
Thermal balance of the earth's surface- the algebraic sum of all types of heat input and expenditure on the surface of land and ocean. The nature of the heat balance and its energy level determine the characteristics and intensity of most exogenous processes. The main components of the heat balance of the ocean are:
- radiation balance;
- heat consumption for evaporation;
- turbulent heat exchange between the ocean surface and the atmosphere;
- vertical turbulent heat exchange of the ocean surface with the underlying layers; and
- horizontal oceanic advection.
(http://www.glossary.ru/cgi-bin/gl_sch2.c gi? RQgkog.outt: p! hgrgtx! nlstup! vuilw) tux yo)
Measurement of solar radiation.
Actinometers and pyrheliometers are used to measure solar radiation. The intensity of solar radiation is usually measured by its thermal effect and is expressed in calories per unit surface per unit of time.
(http://www.ecosystema.ru/07referats/slo vgeo / 967.htm)
The measurement of the intensity of solar radiation is carried out with a Yanishevsky pyranometer complete with a galvanometer or potentiometer.
When measuring the total solar radiation, the pyranometer is installed without a shadow screen, while measuring scattered radiation with a shadow screen. Direct solar radiation is calculated as the difference between total and scattered radiation.
When determining the intensity of incident solar radiation on the fence, the pyranometer is installed on it so that the perceived surface of the device is strictly parallel to the surface of the fence. In the absence of automatic recording of radiation, measurements should be made 30 minutes later between sunrise and sunset.
Radiation falling on the surface of the fence is not completely absorbed. Depending on the texture and color of the fence, some of the rays are reflected. The ratio of reflected radiation to incident radiation, expressed as a percentage, is called surface albedo and is measured by P.K. Kalitina complete with galvanometer or potentiometer.
For greater accuracy, observation should be carried out with a clear sky and with intense solar irradiation of the fence.
(http://www.constructioncheck.ru/default.a spx? textpage = 5)
The amount of direct solar radiation (S) arriving at the earth's surface in a cloudless sky depends on the height of the sun and transparency. The table for three latitudinal zones shows the distribution of monthly sums of direct radiation in a cloudless sky (possible sums) in the form of averaged values for the central months of the seasons and the year.
The increased arrival of direct radiation in the Asian part is due to the higher transparency of the atmosphere in this region. High values of direct radiation in summer in the northern regions of Russia are explained by a combination of high transparency of the atmosphere and long day length
Reduces the arrival of direct radiation and can significantly change its daily and annual course. However, under average cloud conditions, the astronomical factor is predominant and, therefore, the maximum direct radiation is observed at the highest sun altitude.
In most of the continental regions of Russia in the spring-summer months, direct radiation in the pre-noon hours is greater than in the afternoon. This is associated with the development of convective cloudiness in the afternoon hours and with a decrease in the transparency of the atmosphere at this time of the day as compared to the morning hours. In winter, the ratio of pre- and afternoon values of radiation is the opposite - the pre-noon values of direct radiation are lower due to the morning maximum cloud cover and its decrease in the second half of the day. The difference between the pre- and afternoon values of direct radiation can reach 25–35%.
In the annual course, the maximum of direct radiation falls on June-July, with the exception of the regions of the Far East, where it shifts to May, and in the south of Primorye in September, a secondary maximum is noted.
The maximum monthly amount of direct radiation on the territory of Russia is 45–65% of that possible with a cloudless sky, and even in the south of the European part it reaches only 70%. The minimum values are observed in December and January.
The contribution of direct radiation to the total arrival under actual cloudiness conditions reaches its maximum in the summer months and averages 50–60%. An exception is the Primorsky Territory, where the largest contribution of direct radiation falls on the autumn and winter months.
The distribution of direct radiation under average (actual) cloudiness conditions over the territory of Russia largely depends on. This leads to a noticeable violation of the zonal distribution of radiation in certain months. This is especially evident in the spring. So, in April, there are two maximums - one in the southern regions and the Amur region, the second - in the northeast of Yakutia and on, which is also the result of a combination of high atmospheric transparency, high frequency of clear skies and the length of the day.
The data shown on the maps are based on valid cloud conditions.
If the atmosphere let all the sun's rays pass to the surface of the earth, then the climate of any point on the Earth would depend only on the geographical latitude. So it was believed in antiquity. However, when the sun's rays pass through the earth's atmosphere, as we have already seen, their weakening occurs due to the simultaneous processes of absorption and scattering. Water droplets and ice crystals, which make up clouds, absorb and scatter a lot.
That part of solar radiation that enters the earth's surface after scattering it by the atmosphere and clouds is called scattered radiation. That part of solar radiation that passes through the atmosphere without scattering is calleddirect radiation.
Radiation is scattered not only by clouds, but also in a clear sky - by molecules, gases and dust particles. The ratio between direct and scattered radiation varies widely. If, with a clear sky and vertical incidence of sunlight, the fraction of scattered radiation is 0.1% direct, then
in a cloudy sky, scattered radiation may be more direct.
In those parts of the earth where clear weather prevails, for example in Central Asia, direct solar radiation is the main source of heating of the earth's surface. Where cloudy weather predominates, as, for example, in the north and northwest of the European territory of the USSR, diffuse solar radiation becomes essential. Tikhaya Bay, located in the north, receives scattered radiation almost one and a half times more than the straight one (Table 5). In Tashkent, on the contrary, scattered radiation is less than 1/3 of direct radiation. Direct solar radiation in Yakutsk is greater than in Leningrad. This is explained by the fact that in Leningrad there are more cloudy days and less transparency of the air.
Albedo of the earth's surface. The earth's surface has the ability to reflect rays falling on it. The amount of absorbed and reflected radiation depends on the properties of the earth's surface. The ratio of the amount of radiant energy reflected from the surface of the body to the amount of incident radiant energy is called albedo. Albedo characterizes the reflectivity of a body surface. When, for example, they say that the albedo of freshly fallen snow is 80-85%, this means that 80-85% of all radiation falling on the snow surface is reflected from it.
The albedo of snow and ice depends on their purity. In industrial cities, due to the deposition of various impurities on the snow, mainly soot, the albedo is lower. On the contrary, in the arctic regions the snow albedo sometimes reaches 94%. Since the albedo of snow is the highest in comparison with the albedo of other types of the earth's surface, then with a snow cover, the heating of the earth's surface occurs weakly. The albedo of grass and sand is much less. The albedo of grass vegetation is 26%, and that of sand is 30%. This means that the grass absorbs 74% of the sun's energy and the sand 70%. The absorbed radiation is used for evaporation, plant growth and heating.
The most important source from which the Earth's surface and atmosphere receive thermal energy is the Sun. It sends into space a colossal amount of radiant energy: heat, light, ultraviolet. Electromagnetic waves emitted by the Sun propagate at a speed of 300,000 km / s.
The heating of the earth's surface depends on the magnitude of the angle of incidence of the sun's rays. All the sun's rays come to the surface of the Earth parallel to each other, but since the Earth has a spherical shape, the sun's rays fall on different parts of its surface at different angles. When the Sun is at its zenith, its rays fall vertically and the Earth heats up more.
The entire set of radiant energy sent by the Sun is called solar radiation, it is usually expressed in calories per surface area per year.
Solar radiation determines the temperature regime of the Earth's air troposphere.
It should be noted that the total amount of solar radiation is more than two billion times the amount of energy received by the Earth.
Radiation reaching the earth's surface consists of direct and diffuse.
The radiation that comes to the Earth directly from the Sun in the form of direct sunlight in a cloudless sky is called straight. It carries the greatest amount of heat and light. If our planet did not have an atmosphere, the earth's surface would receive only direct radiation.
However, passing through the atmosphere, about a quarter of the solar radiation is scattered by gas molecules and impurities, deviates from the direct path. Some of them reach the surface of the Earth, forming scattered solar radiation. Due to the scattered radiation, light also penetrates into places where direct sunlight (direct radiation) does not penetrate. This radiation creates daylight and gives color to the sky.
Total solar radiation
All the rays of the sun entering the Earth are total solar radiation, that is, the totality of direct and scattered radiation (Fig. 1).
Rice. 1. Total solar radiation for the year
Distribution of solar radiation over the earth's surface
Solar radiation is unevenly distributed over the earth. It depends:
1.from the density and humidity of the air - the higher they are, the less radiation the earth's surface receives;
2. from the geographical latitude of the area - the amount of radiation increases from the poles to the equator. The amount of direct solar radiation depends on the length of the path that the sun's rays travel through the atmosphere. When the Sun is at its zenith (the angle of incidence of the rays is 90 °), its rays hit the Earth by the shortest route and intensively give up their energy in a small area. On Earth, this occurs in a strip between 23 ° N. NS. and 23 ° S. sh., that is, between the tropics. As you move away from this zone to the south or north, the length of the path of the sun's rays increases, that is, the angle of their incidence on the earth's surface decreases. The rays begin to fall on the Earth at a smaller angle, as if sliding, approaching in the region of the poles to the tangent line. As a result, the same energy flow is spread over a large area, therefore the amount of reflected energy increases. Thus, in the equatorial region, where the sun's rays fall on the earth's surface at an angle of 90 °, the amount of direct solar radiation received by the earth's surface is higher, and as it moves to the poles, this amount sharply decreases. In addition, the length of the day at different times of the year also depends on the latitude of the area, which also determines the amount of solar radiation entering the earth's surface;
3. from the annual and daily motion of the Earth - in middle and high latitudes, the intake of solar radiation varies greatly with the seasons, which is associated with a change in the midday height of the Sun and the length of the day;
4. on the nature of the earth's surface - the lighter the surface, the more sunlight it reflects. The ability of a surface to reflect radiation is called albedo(from lat. whiteness). Snow (90%) reflects radiation especially strongly, sand is weaker (35%), chernozem is even weaker (4%).
Earth's surface absorbing solar radiation (absorbed radiation), heats up and radiates heat into the atmosphere itself (reflected radiation). The lower layers of the atmosphere to a large extent inhibit terrestrial radiation. The radiation absorbed by the earth's surface is spent on heating the soil, air, and water.
That part of the total radiation that remains after reflection and thermal radiation of the earth's surface is called radiation balance. The radiation balance of the earth's surface changes during the day and according to the seasons of the year, but on average for the year it has a positive value everywhere, with the exception of the icy deserts of Greenland and Antarctica. The radiation balance reaches its maximum values at low latitudes (between 20 ° N and 20 ° S) - over 42 * 10 2 J / m2, at a latitude of about 60 ° of both hemispheres it decreases to 8 * 10 2 - 13 * 10 2 J / m 2.
The sun's rays give up to 20% of their energy to the atmosphere, which is distributed throughout the entire thickness of the air, and therefore the heating of the air caused by them is relatively small. The sun heats the surface of the Earth, which transfers heat to the atmospheric air due to convection(from lat. convectio- delivery), that is, the vertical movement of air heated at the earth's surface, in place of which colder air descends. This is how the atmosphere receives most of the heat - on average, three times more than directly from the Sun.
The presence of carbon dioxide and water vapor does not allow the heat reflected from the earth's surface to freely escape into outer space. They create Greenhouse effect, due to which the temperature drop on Earth during the day does not exceed 15 ° C. In the absence of carbon dioxide in the atmosphere, the earth's surface would cool by 40-50 ° C overnight.
As a result of an increase in the scale of human economic activity - the burning of coal and oil at thermal power plants, emissions from industrial enterprises, an increase in automobile emissions - the content of carbon dioxide in the atmosphere is increasing, which leads to an increase in the greenhouse effect and threatens global climate change.
The sun's rays, passing through the atmosphere, fall on the surface of the Earth and heat it, and that, in turn, gives off heat to the atmosphere. This explains the characteristic feature of the troposphere: a decrease in air temperature with height. But there are times when the upper layers of the atmosphere are warmer than the lower ones. This phenomenon is called temperature inversion(from Latin inversio - overturning).
