The radiant energy of the Sun is practically the only source of heat for the Earth's surface and its atmosphere. The radiation coming from the stars and the Moon is 30?106 times less than the solar radiation. The flow of heat from the depths of the Earth to the surface is 5000 times less than the heat received from the Sun.

Part of the solar radiation is visible light. Thus, the Sun is a source of not only heat for the Earth, but also light, which is important for life on our planet.

The radiant energy of the Sun is converted into heat partly in the atmosphere itself, but mainly on the earth's surface, where it is used to heat the upper layers of soil and water, and from them - the air. The heated earth's surface and the heated atmosphere, in turn, emit invisible infrared radiation. Giving radiation to the world space, the earth's surface and atmosphere are cooled.

Experience shows that the average annual temperatures of the earth's surface and atmosphere at any point on the earth vary little from year to year. If we consider the temperature conditions on the Earth over long multi-year periods of time, then we can accept the hypothesis that the Earth is in thermal equilibrium: the influx of heat from the Sun is balanced by its loss into outer space. But since the Earth (with the atmosphere) receives heat by absorbing solar radiation, and loses heat by its own radiation, the hypothesis of thermal equilibrium means at the same time that the Earth is in radiative equilibrium: the influx of short-wave radiation to it is balanced by the return of long-wave radiation to the world space .

direct solar radiation

Radiation coming to the earth's surface directly from the disk of the Sun is called direct solar radiation. Solar radiation propagates from the Sun in all directions. But the distance from the Earth to the Sun is so great that direct radiation falls on any surface on the Earth in the form of a beam of parallel rays emanating, as it were, from infinity. Even the entire globe as a whole is so small in comparison with the distance to the Sun that all solar radiation falling on it can be considered a beam of parallel rays without noticeable error.

It is easy to understand that the maximum possible amount of radiation under given conditions is received by a unit of area located perpendicular to the sun's rays. There will be less radiant energy per unit of horizontal area. The basic equation for calculating direct solar radiation is produced by the angle of incidence of the sun's rays, more precisely, by the height of the sun ( h): S" = S sin h; Where S"- solar radiation arriving on a horizontal surface, S- direct solar radiation with parallel rays.

The flow of direct solar radiation onto a horizontal surface is called insolation.

Changes in solar radiation in the atmosphere and on the earth's surface

About 30% of direct solar radiation incident on Earth is reflected back into outer space. The remaining 70% enters the atmosphere. Passing through the atmosphere, solar radiation is partially scattered by atmospheric gases and aerosols and passes into a special form of diffuse radiation. Partially direct solar radiation is absorbed by atmospheric gases and impurities and passes into heat, i.e. goes to warm the atmosphere.

Direct solar radiation that is not scattered and absorbed in the atmosphere reaches the earth's surface. A small fraction of it is reflected from it, and most of the radiation is absorbed by the earth's surface, as a result of which the earth's surface heats up. Part of the scattered radiation also reaches the earth's surface, partly reflected from it and partly absorbed by it. Another part of the scattered radiation goes up into interplanetary space.

As a result of the absorption and scattering of radiation in the atmosphere, direct radiation that has reached the earth's surface differs from that that has come to the boundary of the atmosphere. The flux of solar radiation decreases, and its spectral composition changes, since rays of different wavelengths are absorbed and scattered in the atmosphere in different ways.

At best, i.e. at the highest standing of the Sun and with sufficient air purity, one can observe a direct radiation flux of about 1.05 kW / m 2 on the Earth's surface. In the mountains at altitudes of 4–5 km, radiation fluxes up to 1.2 kW/m 2 or more were observed. As the sun approaches the horizon and the thickness of the air traversed by the sun's rays increases, the flux of direct radiation decreases more and more.

About 23% of direct solar radiation is absorbed in the atmosphere. Moreover, this absorption is selective: different gases absorb radiation in different parts of the spectrum and to different degrees.

Nitrogen absorbs radiation only at very short wavelengths in the ultraviolet part of the spectrum. The energy of solar radiation in this part of the spectrum is completely negligible, so the absorption by nitrogen has practically no effect on the flux of solar radiation. To a somewhat greater extent, but still very little, oxygen absorbs solar radiation - in two narrow sections of the visible part of the spectrum and in its ultraviolet part.

Ozone is a stronger absorber of solar radiation. It absorbs ultraviolet and visible solar radiation. Despite the fact that its content in the air is very small, it absorbs ultraviolet radiation in the upper atmosphere so strongly that waves shorter than 0.29 microns are not observed at all in the solar spectrum near the earth's surface. The total absorption of solar radiation by ozone reaches 3% of direct solar radiation.

Carbon dioxide (carbon dioxide) strongly absorbs radiation in the infrared region of the spectrum, but its content in the atmosphere is still small, so its absorption of direct solar radiation is generally small. Of the gases, the main absorber of radiation in the atmosphere is water vapor, concentrated in the troposphere and especially in its lower part. From the total flow of solar radiation, water vapor absorbs radiation in the wavelength intervals in the visible and near infrared regions of the spectrum. Clouds and atmospheric impurities also absorb solar radiation, i.e. aerosol particles suspended in the atmosphere. In general, absorption by water vapor and aerosol absorption accounts for about 15%, and 5% is absorbed by clouds.

In each individual place, absorption changes over time, depending both on the variable content of absorbing substances in the air, mainly water vapor, clouds and dust, and on the height of the Sun above the horizon, i.e. on the thickness of the air layer passed by the rays on their way to the Earth.

Direct solar radiation on its way through the atmosphere is attenuated not only by absorption, but also by scattering, and is attenuated more significantly. Scattering is a fundamental physical phenomenon of the interaction of light with matter. It can occur at all wavelengths of the electromagnetic spectrum, depending on the ratio of the size of the scattering particles to the wavelength of the incident radiation. When scattered, a particle that is in the path of propagation of an electromagnetic wave continuously “extracts” energy from the incident wave and re-radiates it in all directions. Thus, a particle can be considered as a point source of scattered energy. scattering called the transformation of part of the direct solar radiation, which before scattering propagates in the form of parallel rays in a certain direction, into radiation going in all directions. Scattering occurs in optically inhomogeneous atmospheric air containing the smallest particles of liquid and solid impurities - drops, crystals, smallest aerosols, i.e. in a medium where the refractive index varies from point to point. But an optically inhomogeneous medium is also pure air, free from impurities, since in it, due to the thermal movement of molecules, condensations and rarefactions, density fluctuations constantly occur. Meeting with molecules and impurities in the atmosphere, the sun's rays lose their rectilinear direction of propagation and scatter. Radiation propagates from scattering particles in such a way as if they themselves were emitters.

According to the laws of scattering, in particular, according to the Rayleigh law, the spectral composition of the scattered radiation differs from the spectral composition of the straight line. Rayleigh's law states that the scattering of rays is inversely proportional to the 4th power of the wavelength:

S ? = 32? 3 (m-1) / 3n? 4

Where S? – coeff. scattering; m is the refractive index in gas; n is the number of molecules per unit volume; ? is the wavelength.

About 26% of the energy of the total solar radiation flux is converted in the atmosphere into diffuse radiation. About 2/3 of the scattered radiation then comes to the earth's surface. But this will already be a special type of radiation, significantly different from direct radiation. First, scattered radiation comes to the earth's surface not from the solar disk, but from the entire firmament. Therefore, it is necessary to measure its flow to a horizontal surface. It is also measured in W/m2 (or kW/m2).

Secondly, scattered radiation differs from direct radiation in spectral composition, since rays of different wavelengths are scattered to different degrees. In the spectrum of scattered radiation, the ratio of the energy of different wavelengths in comparison with the spectrum of direct radiation is changed in favor of shorter-wavelength rays. The smaller the size of the scattering particles, the stronger the short-wavelength rays are scattered in comparison with the long-wavelength ones.

Radiation Scattering Phenomena

Phenomena such as the blue color of the sky, dusk and dawn, as well as visibility are associated with the scattering of radiation. The blue color of the sky is the color of the air itself, due to the scattering of solar rays in it. Air is transparent in a thin layer, as water is transparent in a thin layer. But in a powerful thickness of the atmosphere, the air has a blue color, just as water already in a relatively small thickness (several meters) has a greenish color. So how does molecular scattering of light happen inversely? 4, then in the spectrum of scattered light sent by the firmament, the energy maximum is shifted to blue. With height, as the air density decreases, i.e. the number of scattering particles, the color of the sky becomes darker and turns into deep blue, and in the stratosphere - into black-violet. The more impurities in the air of larger sizes than air molecules, the greater the proportion of long-wave rays in the spectrum of solar radiation and the more whitish the color of the firmament becomes. When the diameter of the particles of fog, clouds and aerosols becomes more than 1-2 microns, then the rays of all wavelengths are no longer scattered, but equally diffusely reflected; therefore, distant objects in fog and dusty haze are no longer clouded over by a blue, but by a white or gray curtain. Therefore, the clouds on which the solar (i.e. white) light falls appear white.

The scattering of solar radiation in the atmosphere is of great practical importance, since it creates scattered light in the daytime. In the absence of an atmosphere on Earth, it would be light only where direct sunlight or sunlight reflected by the earth's surface and objects on it would fall. As a result of scattered light, the entire atmosphere during the day serves as a source of illumination: during the day it is also light where the sun's rays do not directly fall, and even when the sun is hidden by clouds.

After sunset in the evening, darkness does not come immediately. The sky, especially in that part of the horizon where the Sun has set, remains bright and sends gradually decreasing scattered radiation to the earth's surface. Similarly, in the morning, even before sunrise, the sky brightens most of all in the direction of sunrise and sends diffused light to the earth. This phenomenon of incomplete darkness is called twilight - evening and morning. The reason for it is the illumination by the Sun, which is under the horizon, of the high layers of the atmosphere and the scattering of sunlight by them.

The so-called astronomical twilight continues in the evening until the Sun sets 18 degrees below the horizon; by this point it is so dark that the faintest stars are visible. Astronomical morning twilight begins when the sun has the same position below the horizon. The first part of the evening astronomical twilight or the last part of the morning, when the sun is below the horizon of at least 8 °, is called civil twilight. The duration of astronomical twilight varies with latitude and time of year. In the middle latitudes it is from 1.5 to 2 hours, in the tropics it is less, at the equator a little more than one hour.

At high latitudes in summer, the sun may not sink below the horizon at all or sink very shallowly. If the sun falls below the horizon by less than 18 o, then complete darkness does not occur at all and the evening twilight merges with the morning. This phenomenon is called white nights.

Twilight is accompanied by beautiful, sometimes very spectacular changes in the color of the firmament in the direction of the Sun. These changes begin before sunset and continue after sunrise. They have a fairly regular character and are called dawn. The characteristic colors of dawn are purple and yellow. But the intensity and variety of color shades of dawn vary widely depending on the content of aerosol impurities in the air. The tones of lighting clouds at dusk are also varied.

In the part of the sky opposite the sun, there is an anti-dawn, also with a change in color tones, with a predominance of purple and purple-violet. After sunset, the shadow of the Earth appears in this part of the sky: a grayish-blue segment that is growing in height and to the sides. Dawn phenomena are explained by the scattering of light by the smallest particles of atmospheric aerosols and by the diffraction of light by larger particles.

Distant objects are seen worse than close ones, and not only because their apparent size is reduced. Even very large objects at one or another distance from the observer become poorly distinguishable due to the turbidity of the atmosphere through which they are visible. This turbidity is due to the scattering of light in the atmosphere. It is clear that it increases with an increase in aerosol impurities in the air.

For many practical purposes, it is very important to know at what distance the outlines of objects behind the air curtain cease to be distinguished. The distance at which the outlines of objects cease to be distinguished in the atmosphere is called the visibility range, or simply visibility. The visibility range is most often determined by eye on certain, pre-selected objects (dark against the sky), the distance to which is known. There are also a number of photometric instruments for determining visibility.

In very clean air, for example, of Arctic origin, the visibility range can reach hundreds of kilometers, since the attenuation of light from objects in such air occurs due to scattering mainly on air molecules. In air containing a lot of dust or condensation products, the visibility range can be reduced to several kilometers or even meters. So, in light fog, the visibility range is 500–1000 m, and in heavy fog or strong sandy burs, it can be reduced to tens or even several meters.

Total radiation, reflected solar radiation, absorbed radiation, PAR, Earth's albedo

All solar radiation coming to the earth's surface - direct and scattered - is called total radiation. Thus, the total radiation

Q = S* sin h + D,

Where S– energy illumination by direct radiation,

D– energy illumination by scattered radiation,

h- the height of the sun.

With a cloudless sky, the total radiation has a daily variation with a maximum around noon and an annual variation with a maximum in summer. Partial cloudiness that does not cover the solar disk increases the total radiation compared to a cloudless sky; full cloudiness, on the contrary, reduces it. On average, cloudiness reduces the total radiation. Therefore, in summer, the arrival of total radiation in the pre-noon hours is on average greater than in the afternoon. For the same reason, it is larger in the first half of the year than in the second.

S.P. Khromov and A.M. Petrosyants give midday values ​​of total radiation in the summer months near Moscow with a cloudless sky: an average of 0.78 kW / m 2, with the Sun and clouds - 0.80, with continuous clouds - 0.26 kW / m 2.

Falling on the earth's surface, the total radiation is mostly absorbed in the upper thin layer of soil or in a thicker layer of water and turns into heat, and is partially reflected. The amount of reflection of solar radiation by the earth's surface depends on the nature of this surface. The ratio of the amount of reflected radiation to the total amount of radiation incident on a given surface is called the surface albedo. This ratio is expressed as a percentage.

So, from the total flux of total radiation ( S sin h + D) part of it is reflected from the earth's surface ( S sin h + D)And where A is the surface albedo. The rest of the total radiation ( S sin h + D) (1 – A) is absorbed by the earth's surface and goes to heat the upper layers of soil and water. This part is called absorbed radiation.

The albedo of the soil surface varies within 10–30%; in wet chernozem, it decreases to 5%, and in dry light sand it can rise to 40%. As soil moisture increases, the albedo decreases. The albedo of vegetation cover - forests, meadows, fields - is 10–25%. The albedo of the surface of freshly fallen snow is 80–90%, while that of long-standing snow is about 50% and lower. The albedo of a smooth water surface for direct radiation varies from a few percent (if the Sun is high) to 70% (if low); it also depends on excitement. For scattered radiation, the albedo of water surfaces is 5–10%. On average, the albedo of the surface of the World Ocean is 5–20%. The albedo of the upper surface of the clouds varies from a few percent to 70–80%, depending on the type and thickness of the cloud cover, on average 50–60% (S.P. Khromov, M.A. Petrosyants, 2004).

The above figures refer to the reflection of solar radiation, not only visible, but also in its entire spectrum. Photometric means measure the albedo only for visible radiation, which, of course, may differ somewhat from the albedo for the entire radiation flux.

The predominant part of the radiation reflected by the earth's surface and the upper surface of the clouds goes beyond the atmosphere into the world space. A part (about one-third) of the scattered radiation also goes into the world space.

The ratio of reflected and scattered solar radiation leaving space to the total amount of solar radiation entering the atmosphere is called the planetary albedo of the Earth, or simply Earth's albedo.

In general, the planetary albedo of the Earth is estimated at 31%. The main part of the planetary albedo of the Earth is the reflection of solar radiation by clouds.

Part of the direct and reflected radiation is involved in the process of plant photosynthesis, so it is called photosynthetically active radiation (FAR). FAR - the part of short-wave radiation (from 380 to 710 nm), which is the most active in relation to photosynthesis and the production process of plants, is represented by both direct and diffuse radiation.

Plants are able to consume direct solar radiation and reflected from celestial and terrestrial objects in the wavelength range from 380 to 710 nm. The flux of photosynthetically active radiation is approximately half of the solar flux, i.e. half of the total radiation, and practically regardless of weather conditions and location. Although, if for the conditions of Europe the value of 0.5 is typical, then for the conditions of Israel it is somewhat higher (about 0.52). However, it cannot be said that plants use PAR in the same way throughout their lives and under different conditions. The efficiency of PAR use is different, therefore, the indicators "PAR use coefficient" were proposed, which reflects the efficiency of PAR use and the "Efficiency of phytocenoses". The efficiency of phytocenoses characterizes the photosynthetic activity of the vegetation cover. This parameter has found the widest application among foresters for assessing forest phytocenoses.

It should be emphasized that plants themselves are able to form PAR in the vegetation cover. This is achieved due to the location of the leaves towards the sun's rays, the rotation of the leaves, the distribution of leaves of different sizes and angles at different levels of phytocenoses, i.e. through the so-called canopy architecture. In the vegetation cover, the sun's rays are repeatedly refracted, reflected from the leaf surface, thereby forming their own internal radiation regime.

The radiation scattered within the vegetation cover has the same photosynthetic value as the direct and diffuse radiation entering the surface of the vegetation cover.

Radiation of the earth's surface

The upper layers of soil and water, snow cover and vegetation themselves emit long-wave radiation; this terrestrial radiation is more commonly referred to as the intrinsic radiation of the earth's surface.

Self-radiation can be calculated by knowing the absolute temperature of the earth's surface. According to the Stefan-Boltzmann law, taking into account that the Earth is not a completely black body and therefore introducing the coefficient? (usually equal to 0.95), ground radiation E determined by the formula

E s = ?? T 4 ,

Where? is the Stefan-Boltzmann constant, T temperature, K.

At 288 K, E s \u003d 3.73 10 2 W / m 2. Such a large return of radiation from the earth's surface would lead to its rapid cooling, if this were not prevented by the reverse process - the absorption of solar and atmospheric radiation by the earth's surface. The absolute temperatures of the earth's surface are between 190 and 350 K. At such temperatures, the emitted radiation practically has wavelengths in the range of 4–120 µm, and its maximum energy is at 10–15 µm. Therefore, all this radiation is infrared, not perceived by the eye.

Counter-radiation or counter-radiation

The atmosphere heats up, absorbing both solar radiation (although in a relatively small fraction, about 15% of its total amount coming to the Earth), and the own radiation of the earth's surface. In addition, it receives heat from the earth's surface by conduction, as well as by condensation of water vapor evaporated from the earth's surface. The heated atmosphere radiates by itself. Just like the earth's surface, it emits invisible infrared radiation in about the same wavelength range.

Most (70%) of atmospheric radiation comes to the earth's surface, the rest goes into the world space. Atmospheric radiation reaching the earth's surface is called counterradiation. E a, since it is directed towards the own radiation of the earth's surface. The Earth's surface absorbs the counter radiation almost entirely (by 95–99%). Thus, the counter radiation is an important source of heat for the earth's surface in addition to the absorbed solar radiation. Counter radiation increases with increasing cloudiness, since the clouds themselves radiate strongly.

The main substance in the atmosphere that absorbs terrestrial radiation and sends back radiation is water vapor. It absorbs infrared radiation in a large region of the spectrum - from 4.5 to 80 microns, with the exception of the interval between 8.5 and 12 microns.

Carbon monoxide (carbon dioxide) strongly absorbs infrared radiation, but only in a narrow region of the spectrum; ozone is weaker and also in a narrow region of the spectrum. True, absorption by carbon dioxide and ozone falls on waves whose energy in the spectrum of terrestrial radiation is close to the maximum (7–15 μm).

The counter radiation is always somewhat less than the terrestrial one. Therefore, the earth's surface loses heat due to the positive difference between its own and counter radiation. The difference between the self-radiation of the earth's surface and the counter-radiation of the atmosphere is called the effective radiation E e:

E e = E s- E a.

Effective radiation is the net loss of radiant energy, and hence heat, from the earth's surface at night. Self-radiation can be determined according to the Stefan-Boltzmann law, knowing the temperature of the earth's surface, and counter-radiation can be calculated using the above formula.

The effective radiation on clear nights is about 0.07–0.10 kW/m 2 at lowland stations in temperate latitudes and up to 0.14 kW/m 2 at high altitude stations (where the counter radiation is less). With an increase in cloudiness, which increases the counterradiance, the effective radiation decreases. In cloudy weather it is much less than in clear weather; consequently, the nighttime cooling of the earth's surface is also less.

Effective radiation, of course, also exists during daylight hours. But during the day it is blocked or partially compensated by the absorbed solar radiation. Therefore, the earth's surface is warmer during the day than at night, but the effective radiation during the day is greater.

On average, the earth's surface in middle latitudes loses through effective radiation about half of the amount of heat that it receives from absorbed radiation.

By absorbing terrestrial radiation and sending counter radiation to the earth's surface, the atmosphere thereby reduces the cooling of the latter at night. During the day, it does little to prevent the heating of the earth's surface by solar radiation. This influence of the atmosphere on the thermal regime of the earth's surface is called the greenhouse effect, or greenhouse effect, due to the external analogy with the action of greenhouse glasses.

Radiation balance of the earth's surface

The difference between absorbed radiation and effective radiation is called the radiation balance of the earth's surface:

IN=(S sin h + D)(1 – A) – E e.

At night, when there is no total radiation, the negative radiation balance is equal to the effective radiation.

The radiation balance changes from nightly negative values ​​to daytime positive values ​​after sunrise at a height of 10–15°. From positive to negative values, it passes before sunset at the same height above the horizon. In the presence of snow cover, the radiation balance changes to positive values ​​only at a solar altitude of about 20–25 o, since with a large snow albedo, the absorption of total radiation by it is small. During the day, the radiation balance increases with increasing solar altitude and decreases with its decrease.

The average noon values ​​of the radiation balance in Moscow in the summer with a clear sky, cited by S.P. Khromov and M.A. Petrosyants (2004) are about 0.51 kW/m 2 , in winter only 0.03 kW/m 2 , under average cloudiness conditions in summer about 0.3 kW/m 2 , and in winter they are close to zero.

Figure 1 - Histogram of changes in the intensity of solar radiation (energy) on the way to the hot brine of the solar salt pond.

To assess the effectiveness of the active use of various types of solar radiation, we will determine which of the natural, technogenic and operational factors have a positive and which negative effect on the concentration (increase in the flow) of solar radiation into the pond and its accumulation with hot brine.

The Earth and the atmosphere receive from the Sun 1.3∙1024 cal of heat per year. It is measured by intensity, i.e. the amount of radiant energy (in calories) that comes from the Sun per unit of time to the surface area perpendicular to the sun's rays.

The radiant energy of the Sun reaches the Earth in the form of direct and scattered radiation, i.e. total. It is absorbed by the earth's surface and is not completely converted into heat, part of it is lost in the form of reflected radiation.

Direct and scattered (total), reflected and absorbed radiation belong to the short-wave part of the spectrum. Along with short-wave radiation, long-wave radiation from the atmosphere (counter radiation) enters the earth's surface, in turn, the earth's surface emits long-wave radiation (self-radiation).

Direct solar radiation refers to the main natural factor in the supply of energy to the water surface of a solar salt pond. Solar radiation arriving at the active surface in the form of a beam of parallel rays emanating directly from the solar disk is called direct solar radiation. Direct solar radiation belongs to the short-wave part of the spectrum (with wavelengths from 0.17 to 4 microns, in fact, rays with a wavelength of 0.29 microns reach the earth's surface)

The solar spectrum can be divided into three main areas:

Ultraviolet radiation (- visible radiation (0.4 µm) - infrared radiation (> 0.7 µm) - 46% intensity. , so that only a small fraction of this range of solar energy reaches the Earth's surface.

The far infrared (>12 µm) of solar radiation barely reaches Earth.

From the point of view of the use of solar energy on Earth, only radiation in the wavelength range of 0.29 - 2.5 μm should be taken into account / Most of the solar energy outside the atmosphere falls on the wavelength range of 0.2 - 4 μm, and on the Earth's surface - on range 0.29 - 2.5 µm.

Let's see how, in general terms, the energy flows that the Sun gives the Earth are redistributed. Let's take 100 arbitrary units of solar power (1.36 kW/m2) falling on the Earth and trace their paths in the atmosphere. One percent (13.6 W/m2), the short ultraviolet of the solar spectrum, is absorbed by molecules in the exosphere and thermosphere, heating them up. Another three percent (40.8 W/m2) of near ultraviolet is absorbed by stratospheric ozone. The infrared tail of the solar spectrum (4% or 54.4 W/m2) remains in the upper layers of the troposphere containing water vapor (there is practically no water vapor above).

The remaining 92 parts of solar energy (1.25 kW/m2) fall within the "transparency window" of the atmosphere of 0.29 µm. / m2), and the rest is distributed between the surface of the Earth and space. More goes into outer space than hits the surface, 30 shares (408 W/m2) up, 8 shares (108.8 W/m2) down.

This was the general, averaged, picture of the redistribution of solar energy in the Earth's atmosphere. However, it does not allow solving particular problems of using solar energy to meet the needs of a person in a specific area of ​​his residence and work, and here's why.

The Earth's atmosphere better reflects the oblique sun's rays, so the hourly insolation at the equator and at middle latitudes is much greater than at high latitudes.

The heights of the Sun (elevations above the horizon) of 90, 30, 20, and 12 ⁰ (the air (optical) mass (m) of the atmosphere corresponds to 1, 2, 3, and 5) with a cloudless atmosphere corresponds to an intensity of about 900, 750, 600 and 400 W / m2 (at 42 ⁰ - m = 1.5, and at 15 ⁰ - m = 4). In reality, the total energy of the incident radiation exceeds the indicated values, since it includes not only the direct component, but also the value of the scattered component of the radiation intensity on the horizontal surface scattered at air masses 1, 2, 3, and 5 under these conditions, respectively, is equal to 110, 90, 70, and 50 W/m2 (with a factor of 0.3 - 0.7 for the vertical plane, since only half of the sky is visible). In addition, in areas of the sky close to the Sun, there is a "circumsolar halo" in a radius of ≈ 5⁰.

The daily amount of solar radiation is maximum not at the equator, but near 40 ⁰. A similar fact is also a consequence of the inclination of the earth's axis to the plane of its orbit. During the summer solstice, the Sun in the tropics is almost all day overhead and the daylight hours are 13.5 hours, more than at the equator on the day of the equinox. With increasing latitude, the length of the day increases, and although the intensity of solar radiation decreases, the maximum value of daytime insolation occurs at a latitude of about 40 ⁰ and remains almost constant (for cloudless sky conditions) up to the Arctic Circle.

Taking into account cloudiness and atmospheric pollution by industrial waste, typical for many countries of the world, the values ​​given in the table should be at least halved. For example, for England in the 70s of the XX century, before the start of the struggle for environmental protection, the annual amount of solar radiation was only 900 kWh/m2 instead of 1700 kWh/m2.

The first data on the transparency of the atmosphere on Lake Baikal were obtained by V.V. Bufalom in 1964 He showed that the values ​​of direct solar radiation over Baikal are on average 13% higher than in Irkutsk. The average spectral transparency coefficient of the atmosphere in Northern Baikal in summer is 0.949, 0.906, 0.883 for red, green and blue filters, respectively. In summer the atmosphere is more optically unstable than in winter, and this instability varies considerably from the pre-noon hours to the afternoon. Depending on the annual course of attenuation by water vapor and aerosols, their contribution to the total attenuation of solar radiation also changes. Aerosols play the main role in the cold part of the year, and water vapor plays the main role in the warm part of the year. The Baikal Basin and Lake Baikal are distinguished by a relatively high integral transparency of the atmosphere. With an optical mass m = 2, the average values ​​of the transparency coefficient range from 0.73 (in summer) to 0.83 (in winter). Aerosols significantly reduce the flow of direct solar radiation into the pond water area, and they mainly absorb radiation of the visible spectrum, with the wavelength that freely passes through the fresh layer of the pond, and this is of great importance for the accumulation of solar energy by the pond. (A layer of water 1 cm thick is practically opaque to infrared radiation with a wavelength of more than 1 micron). Therefore, water several centimeters thick is used as a heat-shielding filter. For glass, the long-wavelength infrared transmission limit is 2.7 µm.

A large number of dust particles, freely transported across the steppe, also reduces the transparency of the atmosphere.

Electromagnetic radiation is emitted by all heated bodies, and the colder the body, the lower the intensity of the radiation and the further the maximum of its spectrum is shifted to the long-wave region. There is a very simple relation [ = 0.2898 cm∙deg. (Wien's law)], with the help of which it is easy to establish where the maximum radiation of a body with temperature (⁰K) is located. For example, a human body with a temperature of 37 + 273 = 310 ⁰K emits infrared rays with a maximum near the value = 9.3 µm. And the walls, for example, of a solar dryer, with a temperature of 90 ⁰С, will emit infrared rays with a maximum near the value = 8 microns. Visible solar radiation (0.4 microns) At one time, a great progress was the transition from an electric incandescent lamp with a carbon filament to a modern lamp with a tungsten filament. The thing is that a carbon filament can be brought to a temperature of 2100 ⁰K, and a tungsten filament - up to 2500 ⁰K "Why are these 400 ⁰K so important? The whole point is that the purpose of an incandescent lamp is not to heat, but to give light. Therefore, it is necessary to achieve such a position that the maximum of the curve falls on visible study. The ideal would be to have a thread that would withstand temperature of the surface of the Sun, but even the transition from 2100 to 2500 ⁰K increases the fraction of energy attributable to visible radiation, from 0.5 to 1.6%.

Everyone can feel the infrared rays emanating from a body heated to only 60 - 70 ⁰С by bringing the palm from below (to eliminate thermal convection). The arrival of direct solar radiation in the water area of ​​the pond corresponds to its arrival on the horizontal irradiation surface. At the same time, the above shows the uncertainty of the quantitative characteristics of the arrival at a particular point in time, both seasonal and daily. Only the height of the Sun (the optical mass of the atmosphere) is a constant characteristic.

The accumulation of solar radiation by the earth's surface and the pond differ significantly.

The natural surfaces of the Earth have different reflective (absorbing) abilities. Thus, dark surfaces (chernozem, peat bogs) have a low albedo value of about 10%. (The albedo of a surface is the ratio of the radiation flux reflected by this surface into the surrounding space to the flux that fell on it).

Light surfaces (white sand) have a large albedo, 35 - 40%. The albedo of grassy surfaces ranges from 15 to 25%. The crown albedo of a deciduous forest in summer is 14–17%, and that of a coniferous forest is 12–15%. The surface albedo decreases with increasing solar altitude.

The albedo of water surfaces is in the range of 3 - 45%, depending on the height of the Sun and the degree of excitement.

With a calm water surface, the albedo depends only on the height of the Sun (Figure 2).

Figure 2 - Dependence of the reflection coefficient of solar radiation for a calm water surface on the height of the Sun.

The entry of solar radiation and its passage through a layer of water has its own characteristics.

In general, the optical properties of water (its solutions) in the visible region of solar radiation are shown in Figure 3.

Figure 3 - Optical properties of water (its solutions) in the visible region of solar radiation

On the flat boundary of two media, air - water, the phenomena of reflection and refraction of light are observed.

When light is reflected, the incident beam, the reflected beam and the perpendicular to the reflecting surface, restored at the point of incidence of the beam, lie in the same plane, and the angle of reflection is equal to the angle of incidence. In the case of refraction, the incident beam, the perpendicular restored at the point of incidence of the beam to the interface between two media, and the refracted beam lie in the same plane. The angle of incidence and the angle of refraction (Figure 4) are related /, where is the absolute refractive index of the second medium, - the first. Since for air, the formula will take the form

Figure 4 - Refraction of rays during the transition from air to water

When the rays go from air into water, they approach the "perpendicular of incidence"; for example, a beam incident on water at an angle to the perpendicular to the surface of the water enters it already at an angle that is less than (Fig. 4a). But when an incident beam, sliding over the surface of the water, falls on the water surface at almost a right angle to the perpendicular, for example, at an angle of 89 ⁰ or less, then it enters the water at an angle less than a straight line, namely at an angle of only 48.5 ⁰. At a greater angle to the perpendicular than 48.5 ⁰, the beam cannot enter the water: this is the “limiting” angle for water (Figure 4, b).

Consequently, rays falling on water at various angles are compressed under water into a rather tight cone with an opening angle of 48.5 ⁰ + 48.5 ⁰ = 97 ⁰ (Fig. 4c). In addition, the refraction of water depends on its temperature, but these changes are not so significant that they cannot be of interest for engineering practice on the topic under consideration.

Let us now follow the course of the rays going back (from point P) - from water to air (Figure 5). According to the laws of optics, the paths will be the same, and all the rays contained in the mentioned 97-degree cone will go into the air at different angles, spreading over the entire 180-degree space above the water. Underwater rays that are outside the mentioned angle (97-degree) will not come out from under the water, but will be reflected entirely from its surface, as from a mirror.

Figure 5 - Refraction of rays during the transition from water to air

If only the reflected beam exists, there is no refracted beam (the phenomenon of total internal reflection).

Any underwater ray that meets the surface of the water at an angle greater than the “limiting” one (i.e., greater than 48.5 ⁰) is not refracted, but reflected: it undergoes “total internal reflection”. Reflection is called in this case total because all the incident rays are reflected here, while even the best polished silver mirror reflects only a part of the rays incident on it, while absorbing the rest. Water under these conditions is an ideal mirror. In this case, we are talking about visible light. Generally speaking, the refractive index of water, like other substances, depends on the wavelength (this phenomenon is called dispersion). As a consequence of this, the limiting angle at which total internal reflection occurs is not the same for different wavelengths, but for visible light when reflected at the water-air boundary, this angle changes by less than 1⁰.

Due to the fact that at a greater angle to the perpendicular than 48.5⁰, the sunbeam cannot enter the water: this is the “limiting” angle for water (Figure 4, b), then the water mass, in the entire range of values ​​​​of the Sun’s height, does not change so much insignificantly than air - it is always less.

However, since the density of water is 800 times greater than the density of air, the absorption of solar radiation by water will change significantly. In addition, if light radiation passes through a transparent medium, then the spectrum of such light has some features. Certain lines in it are strongly weakened, i.e., waves of the corresponding length are strongly absorbed by the medium under consideration. Such spectra are called absorption spectra. The form of the absorption spectrum depends on the substance under consideration.

Since the salt solution of a solar salt pond can contain different concentrations of sodium and magnesium chlorides and their ratios, it makes no sense to speak unambiguously about absorption spectra. Although research and data on this issue abound.

So, for example, studies carried out in the USSR (Yu. Usmanov) to identify the transmittance of radiation of various wavelengths for water and a solution of magnesium chloride of various concentrations obtained the following results (Figure 6). And B. J. Brinkworth shows a graphical dependence of the absorption of solar radiation and the monochromatic flux density of solar radiation (radiation) depending on the wavelength (Figure 7).

Consequently, the quantitative supply of direct solar radiation to the hot brine of the pond, after entering the water, will depend on: the monochromatic density of the solar radiation (radiation) flux; from the height of the sun. And also from the albedo of the pond surface, from the purity of the upper layer of the solar salt pond, consisting of fresh water, with a thickness of usually 0.1 - 0.3 m, where mixing cannot be suppressed, the composition, concentration and thickness of the solution in the gradient layer (insulating layer with brine concentration increasing downwards), on the purity of water and brine.

Figures 6 and 7 show that water has the highest transmission capacity in the visible region of the solar spectrum. This is a very favorable factor for the passage of solar radiation through the upper fresh layer of the solar salt pond.

Bibliography

1 Osadchiy G.B. Solar energy, its derivatives and technologies for their use (Introduction to RES energy) / G.B. Osadchy. Omsk: IPK Maksheeva E.A., 2010. 572 p.
2 Twydell J. Renewable energy sources / J. Twydell, A. Ware. M.: Energoatomizdat, 1990. 392 p.
3 Duffy J. A. Thermal processes using solar energy / J. A. Duffy, W. A. ​​Beckman. M.: Mir, 1977. 420 p.
4 Climatic resources of Baikal and its basin /N. P. Ladeyshchikov, Novosibirsk, Nauka, 1976, 318p.
5 Pikin S. A. Liquid crystals / S. A. Pikin, L. M. Blinov. M.: Nauka, 1982. 208 p.
6 Kitaygorodsky A. I. Physics for everyone: Photons and nuclei / A. I. Kitaygorodsky. M.: Nauka, 1984. 208 p.
7 Kuhling H. Handbook of Physics. / H. Kuhling. M.: Mir, 1982. 520 p.
8 Enokhovich A. S. Handbook of physics and technology / A. S. Enokhovich. Moscow: Education, 1989. 223 p.
9 Perelman Ya. I. Entertaining physics. Book 2 / Ya. I. Perelman. M.: Nauka, 1986. 272 ​​p.

Heat sources. Thermal energy plays a decisive role in the life of the atmosphere. The main source of this energy is the Sun. As for the thermal radiation of the Moon, planets and stars, it is so negligible for the Earth that in practice it cannot be taken into account. Much more thermal energy is provided by the internal heat of the Earth. According to the calculations of geophysicists, a constant influx of heat from the bowels of the Earth increases the temperature of the earth's surface by 0.1. But such an influx of heat is still so small that there is no need to take it into account either. Thus, only the Sun can be considered the only source of thermal energy on the Earth's surface.

Solar radiation. The sun, which has a temperature of the photosphere (radiating surface) of about 6000°, radiates energy into space in all directions. Part of this energy in the form of a huge beam of parallel solar rays hits the Earth. Solar energy that reaches the earth's surface in the form of direct rays from the sun is called direct solar radiation. But not all solar radiation directed to the Earth reaches the earth's surface, since the sun's rays, passing through a powerful layer of the atmosphere, are partially absorbed by it, partially scattered by molecules and suspended particles of air, some of it is reflected by clouds. The portion of solar energy that is dissipated in the atmosphere is called scattered radiation. Scattered solar radiation propagates in the atmosphere and reaches the Earth's surface. We perceive this type of radiation as uniform daylight, when the Sun is completely covered by clouds or has just disappeared below the horizon.

Direct and diffuse solar radiation, reaching the Earth's surface, is not completely absorbed by it. Part of the solar radiation is reflected from the earth's surface back into the atmosphere and is there in the form of a stream of rays, the so-called reflected solar radiation.

The composition of solar radiation is very complex, which is associated with a very high temperature of the radiating surface of the Sun. Conventionally, according to the wavelength, the spectrum of solar radiation is divided into three parts: ultraviolet (η<0,4<μ видимую глазом (η from 0.4μ to 0.76μ) and infrared (η >0.76μ). In addition to the temperature of the solar photosphere, the composition of solar radiation near the earth's surface is also influenced by the absorption and scattering of part of the sun's rays as they pass through the air envelope of the Earth. In this regard, the composition of solar radiation at the upper boundary of the atmosphere and near the Earth's surface will be different. Based on theoretical calculations and observations, it has been established that at the boundary of the atmosphere, ultraviolet radiation accounts for 5%, visible rays - 52% and infrared - 43%. At the earth's surface (at a Sun height of 40 °), ultraviolet rays make up only 1%, visible - 40%, and infrared - 59%.

Intensity of solar radiation. Under the intensity of direct solar radiation understand the amount of heat in calories received in 1 minute. from the radiant energy of the Sun by the surface in 1 cm 2, placed perpendicular to the sun.

To measure the intensity of direct solar radiation, special instruments are used - actinometers and pyrheliometers; the amount of scattered radiation is determined by a pyranometer. Automatic recording of the duration of solar radiation action is carried out by actinographs and heliographs. The spectral intensity of solar radiation is determined by a spectrobolograph.

At the boundary of the atmosphere, where the absorbing and scattering effects of the Earth's air envelope are excluded, the intensity of direct solar radiation is approximately 2 feces for 1 cm 2 surfaces in 1 min. This value is called solar constant. The intensity of solar radiation in 2 feces for 1 cm 2 in 1 min. gives such a large amount of heat during the year that it would be enough to melt a layer of ice 35 m thick, if such a layer covered the entire earth's surface.

Numerous measurements of the intensity of solar radiation give reason to believe that the amount of solar energy coming to the upper boundary of the Earth's atmosphere experiences fluctuations in the amount of several percent. Oscillations are periodic and non-periodic, apparently associated with the processes occurring on the Sun itself.

In addition, some change in the intensity of solar radiation occurs during the year due to the fact that the Earth in its annual rotation does not move in a circle, but in an ellipse, in one of the foci of which is the Sun. In this regard, the distance from the Earth to the Sun changes and, consequently, there is a fluctuation in the intensity of solar radiation. The greatest intensity is observed around January 3, when the Earth is closest to the Sun, and the smallest around July 5, when the Earth is at its maximum distance from the Sun.

For this reason, the fluctuation in the intensity of solar radiation is very small and can only be of theoretical interest. (The amount of energy at maximum distance is related to the amount of energy at minimum distance, as 100:107, i.e. the difference is completely negligible.)

Conditions for irradiation of the surface of the globe. Already the spherical shape of the Earth alone leads to the fact that the radiant energy of the Sun is distributed very unevenly on the earth's surface. So, on the days of the spring and autumn equinoxes (March 21 and September 23), only at the equator at noon, the angle of incidence of the rays will be 90 ° (Fig. 30), and as it approaches the poles, it will decrease from 90 to 0 °. Thus,

if at the equator the amount of radiation received is taken as 1, then at the 60th parallel it will be expressed as 0.5, and at the pole it will be equal to 0.

The globe, in addition, has a daily and annual movement, and the earth's axis is inclined to the plane of the orbit by 66 °.5. Due to this inclination, an angle of 23 ° 30 g is formed between the plane of the equator and the plane of the orbit. This circumstance leads to the fact that the angles of incidence of the sun's rays for the same latitudes will vary within 47 ° (23.5 + 23.5) .

Depending on the time of year, not only the angle of incidence of the rays changes, but also the duration of illumination. If in tropical countries at all times of the year the duration of day and night is approximately the same, then in polar countries, on the contrary, it is very different. For example, at 70° N. sh. in summer, the Sun does not set for 65 days, at 80 ° N. sh.- 134, and at the pole -186. Because of this, at the North Pole, radiation on the day of the summer solstice (June 22) is 36% more than at the equator. As for the entire summer half-year, the total amount of heat and light received by the pole is only 17% less than at the equator. Thus, in the summertime in polar countries, the duration of illumination largely compensates for the lack of radiation, which is a consequence of the small angle of incidence of the rays. In the winter half of the year, the picture is completely different: the amount of radiation at the same North Pole will be 0. As a result, the average amount of radiation at the pole is 2.4 times less than at the equator. From all that has been said, it follows that the amount of solar energy that the Earth receives by radiation is determined by the angle of incidence of the rays and the duration of exposure.

In the absence of an atmosphere at different latitudes, the earth's surface would receive the following amount of heat per day, expressed in calories per 1 cm 2(see table on page 92).

The distribution of radiation over the earth's surface given in the table is commonly called solar climate. We repeat that we have such a distribution of radiation only at the upper boundary of the atmosphere.

Attenuation of solar radiation in the atmosphere. So far, we have been talking about the conditions for the distribution of solar heat over the earth's surface, without taking into account the atmosphere. Meanwhile, the atmosphere in this case is of great importance. Solar radiation, passing through the atmosphere, experiences dispersion and, in addition, absorption. Both of these processes together attenuate solar radiation to a large extent.

The sun's rays, passing through the atmosphere, first of all experience scattering (diffusion). Scattering is created by the fact that the rays of light, refracting and reflecting from air molecules and particles of solid and liquid bodies in the air, deviate from the direct path To really "spread out".

Scattering greatly attenuates solar radiation. With an increase in the amount of water vapor and especially dust particles, the dispersion increases and the radiation is weakened. In large cities and desert areas, where the dust content of the air is greatest, dispersion weakens the strength of radiation by 30-45%. Thanks to scattering, the daylight is obtained, which illuminates objects, even if the sun's rays do not fall directly on them. Scattering determines the very color of the sky.

Let us now dwell on the ability of the atmosphere to absorb the radiant energy of the Sun. The main gases that make up the atmosphere absorb radiant energy relatively very little. Impurities (water vapor, ozone, carbon dioxide and dust), on the contrary, are distinguished by a high absorption capacity.

In the troposphere, the most significant admixture is water vapor. They absorb especially strongly infrared (long-wave), i.e., predominantly thermal rays. And the more water vapor in the atmosphere, the naturally more and. absorption. The amount of water vapor in the atmosphere is subject to large changes. Under natural conditions, it varies from 0.01 to 4% (by volume).

Ozone is very absorbent. A significant admixture of ozone, as already mentioned, is in the lower layers of the stratosphere (above the tropopause). Ozone absorbs ultraviolet (shortwave) rays almost completely.

Carbon dioxide is also very absorbent. It absorbs mainly long-wave, i.e., predominantly thermal rays.

Dust in the air also absorbs some of the sun's radiation. Heating up under the action of sunlight, it can significantly increase the temperature of the air.

Of the total amount of solar energy coming to Earth, the atmosphere absorbs only about 15%.

The attenuation of solar radiation by scattering and absorption by the atmosphere is very different for different latitudes of the Earth. This difference depends primarily on the angle of incidence of the rays. At the zenith position of the Sun, the rays, falling vertically, cross the atmosphere in the shortest way. As the angle of incidence decreases, the path of the rays lengthens and the attenuation of solar radiation becomes more significant. The latter is clearly seen from the drawing (Fig. 31) and the attached table (in the table, the path of the sun's beam at the zenith position of the Sun is taken as unity).

Depending on the angle of incidence of the rays, not only the number of rays changes, but also their quality. During the period when the Sun is at its zenith (overhead), ultraviolet rays account for 4%,

visible - 44% and infrared - 52%. At the position of the Sun, there are no ultraviolet rays at all at the horizon, visible 28% and infrared 72%.

The complexity of the influence of the atmosphere on solar radiation is aggravated by the fact that its transmission capacity varies greatly depending on the time of year and weather conditions. So, if the sky remained cloudless all the time, then the annual course of the influx of solar radiation at different latitudes could be graphically expressed as follows (Fig. 32) It is clearly seen from the drawing that with a cloudless sky in Moscow in May, June and July solar radiation would produce more than at the equator. Similarly, in the second half of May, in June and the first half of July, more heat would be generated at the North Pole than at the equator and in Moscow. We repeat that this would be the case with a cloudless sky. But in fact, this does not work, because cloud cover significantly weakens solar radiation. Let us give an example shown in the graph (Fig. 33). The graph shows how much solar radiation does not reach the Earth's surface: a significant part of it is retained by the atmosphere and clouds.

However, it must be said that the heat absorbed by the clouds partly goes to warm the atmosphere, and partly indirectly reaches the earth's surface.

The daily and annual course of the intensity of the solnight radiation. The intensity of direct solar radiation near the Earth's surface depends on the height of the Sun above the horizon and on the state of the atmosphere (on its dust content). If. the transparency of the atmosphere during the day was constant, then the maximum intensity of solar radiation would be observed at noon, and the minimum - at sunrise and sunset. In this case, the graph of the course of the daily intensity of solar radiation would be symmetrical with respect to half a day.

The content of dust, water vapor and other impurities in the atmosphere is constantly changing. In this regard, the transparency of the air changes and the symmetry of the graph of the course of the intensity of solar radiation is violated. Often, especially in summer, at midday, when the earth's surface is heated intensely, powerful ascending air currents occur, and the amount of water vapor and dust in the atmosphere increases. This leads to a significant decrease in solar radiation at noon; the maximum intensity of radiation in this case is observed in the pre-noon or afternoon hours. The annual course of the intensity of solar radiation is also associated with changes in the height of the Sun above the horizon during the year and with the state of transparency of the atmosphere in different seasons. In the countries of the northern hemisphere, the greatest height of the Sun above the horizon occurs in the month of June. But at the same time, the greatest dustiness of the atmosphere is also observed. Therefore, the maximum intensity usually occurs not in the middle of summer, but in the spring months, when the Sun rises quite high * above the horizon, and the atmosphere after winter remains relatively clean. To illustrate the annual course of the solar radiation intensity in the northern hemisphere, we present data on the average monthly midday values ​​of the radiation intensity in Pavlovsk.

The amount of heat from solar radiation. The surface of the Earth during the day continuously receives heat from direct and diffuse solar radiation or only from diffuse radiation (in cloudy weather). The daily value of heat is determined on the basis of actinometric observations: by taking into account the amount of direct and diffuse radiation that has entered the earth's surface. Having determined the amount of heat for each day, the amount of heat received by the earth's surface per month or per year is also calculated.

The daily amount of heat received by the earth's surface from solar radiation depends on the intensity of radiation and on the duration of its action during the day. In this regard, the minimum influx of heat occurs in the winter, and the maximum in the summer. In the geographic distribution of total radiation over the globe, its increase is observed with a decrease in the latitude of the area. This position is confirmed by the following table.

The role of direct and diffuse radiation in the annual amount of heat received by the earth's surface at different latitudes of the globe is not the same. At high latitudes, diffuse radiation predominates in the annual heat sum. With a decrease in latitude, the predominant value passes to direct solar radiation. So, for example, in the Tikhaya Bay, diffuse solar radiation provides 70% of the annual amount of heat, and direct radiation only 30%. In Tashkent, on the contrary, direct solar radiation gives 70%, diffused only 30%.

Reflectivity of the Earth. Albedo. As already mentioned, the Earth's surface absorbs only part of the solar energy coming to it in the form of direct and diffuse radiation. The other part is reflected into the atmosphere. The ratio of the amount of solar radiation reflected by a given surface to the amount of radiant energy flux incident on this surface is called albedo. Albedo is expressed as a percentage and characterizes the reflectivity of a given area of ​​the surface.

Albedo depends on the nature of the surface (properties of the soil, the presence of snow, vegetation, water, etc.) and on the angle of incidence of the Sun's rays on the Earth's surface. So, for example, if the rays fall on the earth's surface at an angle of 45 °, then:

From the above examples, it can be seen that the reflectivity of various objects is not the same. It is most near snow and least near water. However, the examples we have taken refer only to those cases where the height of the Sun above the horizon is 45°. As this angle decreases, the reflectivity increases. So, for example, at a height of the Sun at 90 °, water reflects only 2%, at 50 ° - 4%, at 20 ° -12%, at 5 ° - 35-70% (depending on the state of the water surface).

On average, with a cloudless sky, the surface of the globe reflects 8% of solar radiation. In addition, 9% reflects the atmosphere. Thus, the globe as a whole, with a cloudless sky, reflects 17% of the radiant energy of the Sun falling on it. If the sky is covered with clouds, then 78% of the radiation is reflected from them. If we take natural conditions, based on the ratio between a cloudless sky and a sky covered with clouds, which is observed in reality, then the reflectivity of the Earth as a whole is 43%.

Terrestrial and atmospheric radiation. The earth, receiving solar energy, heats up and itself becomes a source of heat radiation into the world space. However, the rays emitted by the earth's surface differ sharply from the sun's rays. The earth emits only long-wave (λ 8-14 μ) invisible infrared (thermal) rays. The energy emitted by the earth's surface is called earth radiation. Earth radiation occurs and. day and night. The intensity of the radiation is greater, the higher the temperature of the radiating body. Terrestrial radiation is determined in the same units as solar radiation, i.e., in calories from 1 cm 2 surfaces in 1 min. Observations have shown that the magnitude of terrestrial radiation is small. Usually it reaches 15-18 hundredths of a calorie. But, acting continuously, it can give a significant thermal effect.

The strongest terrestrial radiation is obtained with a cloudless sky and good transparency of the atmosphere. Cloudiness (especially low clouds) significantly reduces terrestrial radiation and often brings it to zero. Here we can say that the atmosphere, together with the clouds, is a good "blanket" that protects the Earth from excessive cooling. Parts of the atmosphere, like areas of the earth's surface, radiate energy according to their temperature. This energy is called atmospheric radiation. The intensity of atmospheric radiation depends on the temperature of the radiating part of the atmosphere, as well as on the amount of water vapor and carbon dioxide contained in the air. Atmospheric radiation belongs to the group of long-wave radiation. It spreads in the atmosphere in all directions; some of it reaches the earth's surface and is absorbed by it, the other part goes into interplanetary space.

ABOUT income and expenditure of solar energy on Earth. The earth's surface, on the one hand, receives solar energy in the form of direct and diffuse radiation, and on the other hand, loses part of this energy in the form of terrestrial radiation. As a result of the arrival and consumption of solar energy, some result is obtained. In some cases, this result can be positive, in others negative. Let's give examples of both.

January 8. The day is cloudless. For 1 cm 2 the earth's surface received per day 20 feces direct solar radiation and 12 feces scattered radiation; in total, thus received 32 cal. During the same time, due to radiation 1 cm? earth surface lost 202 cal. As a result, in the language of accounting, there is a loss of 170 feces(negative balance).

July 6th The sky is almost cloudless. 630 received from direct solar radiation cal, from scattered radiation 46 cal. In total, therefore, the earth's surface received 1 cm 2 676 cal. 173 lost by terrestrial radiation cal. In the balance sheet profit on 503 feces(balance positive).

From the above examples, among other things, it is quite clear why in temperate latitudes it is cold in winter and warm in summer.

The use of solar radiation for technical and domestic purposes. Solar radiation is an inexhaustible natural source of energy. The magnitude of solar energy on Earth can be judged by the following example: if, for example, we use the heat of solar radiation, which falls on only 1/10 of the area of ​​the USSR, then we can get energy equal to the work of 30 thousand Dneproges.

People have long sought to use the free energy of solar radiation for their needs. To date, many different solar installations have been created that operate on the use of solar radiation and are widely used in industry and to meet the household needs of the population. In the southern regions of the USSR, solar water heaters, boilers, salt water desalination plants, solar dryers (for drying fruits), kitchens, bathhouses, greenhouses, and apparatus for medical purposes operate on the basis of the widespread use of solar radiation in industry and public utilities. Solar radiation is widely used in resorts for the treatment and promotion of people's health.

- Source-

Polovinkin, A.A. Fundamentals of general geography / A.A. Polovinkin.- M.: State Educational and Pedagogical Publishing House of the Ministry of Education of the RSFSR, 1958.- 482 p.

Post Views: 312

) , let's turn to Figure 1 - which shows the parallel and sequential advancement of the heat of the Sun to hot brine solar salt pond. As well as the ongoing changes in the values ​​of various types of solar radiation and their total value along the way.

Figure 1 - Histogram of changes in the intensity of solar radiation (energy) on the way to the hot brine of the solar salt pond.

To assess the effectiveness of the active use of various types of solar radiation, we will determine which of the natural, technogenic and operational factors have a positive and which negative effect on the concentration (increase in the flow) of solar radiation into the pond and its accumulation with hot brine.

The Earth and the atmosphere receive from the Sun 1.3∙10 24 cal of heat per year. It is measured by intensity, i.e. the amount of radiant energy (in calories) that comes from the Sun per unit of time to the surface area perpendicular to the sun's rays.

The radiant energy of the Sun reaches the Earth in the form of direct and scattered radiation, i.e. total. It is absorbed by the earth's surface and is not completely converted into heat, part of it is lost in the form of reflected radiation.

Direct and scattered (total), reflected and absorbed radiation belong to the short-wave part of the spectrum. Along with short-wave radiation, long-wave radiation of the atmosphere (oncoming) enters the earth's surface, in turn, the earth's surface emits long-wave radiation (intrinsic).

Direct solar radiation refers to the main natural factor in the supply of energy to the water surface of a solar salt pond.

Solar radiation arriving at the active surface in the form of a beam of parallel rays emanating directly from the disk of the Sun is called direct solar radiation.

Direct solar radiation belongs to the short-wave part of the spectrum (with wavelengths from 0.17 to 4 microns, in fact, rays with a wavelength of 0.29 microns reach the earth's surface)

The solar spectrum can be divided into three main areas:

Ultraviolet radiation (λ< 0,4 мкм) - 9 % интенсивности.

Shortwave ultraviolet region (λ< 0,29 мкм) практически полностью отсутствует на уровне моря вследствие поглощения О 2 , О 3 , О, N 2 и их ионами.

Near ultraviolet range (0.29 µm<λ < 0,4 мкм) достигает Земли малой долей излучения, но вполне достаточной для загара;

Visible radiation (0.4 µm< λ < 0,7 мкм) - 45 % интенсивности.

The clear atmosphere transmits visible radiation almost completely, and it becomes a “window” open for this type of solar energy to pass to Earth. The presence of aerosols and atmospheric pollution can be the reasons for the significant absorption of radiation in this spectrum;

Infrared radiation (λ> 0.7 µm) - 46% intensity. Near infrared (0.7 µm< < 2,5 мкм). На этот диапазон спектра приходится почти половина интенсивности солнечного излучения. Более 20 % солнечной энергии поглощается в атмосфере, в основном парами воды и СО 2 (диоксидом углерода). Концентрация СО 2 в атмосфере относительно постоянна и составляет 0,03 %, а концентрация паров воды меняется очень сильно - почти до 4 %.

At wavelengths greater than 2.5 microns, weak extraterrestrial radiation is intensely absorbed by CO 2 and water, so that only a small part of this range of solar energy reaches the Earth's surface.

The far infrared range (λ> 12 microns) of solar radiation practically does not reach the Earth.

From the point of view of the use of solar energy on Earth, only radiation in the wavelength range of 0.29 - 2.5 μm should be taken into account

Most of the solar energy outside the atmosphere is in the 0.2 - 4 micron wavelength range, and on the Earth's surface - in the 0.29 - 2.5 micron wavelength range.

Let's see how they redistribute in general , flows of energy that the Sun gives the Earth. Let's take 100 arbitrary units of solar power (1.36 kW/m 2 ) falling on the Earth and follow their paths in the atmosphere. One percent (13.6 W/m2), the short ultraviolet of the solar spectrum, is absorbed by molecules in the exosphere and thermosphere, heating them up. Another three percent (40.8 W / m 2) of the near ultraviolet is absorbed by the ozone of the stratosphere. The infrared tail of the solar spectrum (4% or 54.4 W / m 2) remains in the upper layers of the troposphere containing water vapor (there is practically no water vapor above).

The remaining 92 shares of solar energy (1.25 kW / m 2) fall on the "transparency window" of the atmosphere of 0.29 microns< < 2,5 мкм. Они проникают в плотные приземные слои воздуха. Значительная часть их (45 единиц или 612 Вт/м 2), преимущественно в синей видимой части спектра, рассеиваются воздухом, придавая голубой цвет небу. Прямые солнечные лучи - оставшиеся 47 процентов (639,2 Вт/м 2) начального светового потока - достигают поверхности. Она отражает примерно 7 процентов (95,2 Вт/м 2) из этих 47 % (639,2 Вт/м 2) и этот свет по пути в космос отдает ещё 3 единицы (40,8 Вт/м 2) диффузному рассеянному свету неба. Forty shares of the energy of the sun's rays, and another 8 from the atmosphere (total 48 or 652.8 W / m 2) are absorbed by the Earth's surface, heating the land and ocean.

The light power scattered in the atmosphere (only 48 shares or 652.8 W / m 2) is partially absorbed by it (10 shares or 136 W / m 2), and the rest is distributed between the Earth's surface and space. More goes into outer space than hits the surface, 30 shares (408 W / m 2) up, 8 shares (108.8 W / m 2) down.

It has been described in common, averaged, a picture of the redistribution of solar energy in the Earth's atmosphere. However, it does not allow solving particular problems of using solar energy to meet the needs of a person in a specific area of ​​his residence and work, and here's why.

The Earth's atmosphere better reflects the oblique sun's rays, so the hourly insolation at the equator and at middle latitudes is much greater than at high latitudes.

The heights of the Sun (elevations above the horizon) of 90, 30, 20, and 12 ⁰ (the air (optical) mass (m) of the atmosphere corresponds to 1, 2, 3, and 5) with a cloudless atmosphere corresponds to an intensity of about 900, 750, 600 and 400 W / m 2 (at 42 ⁰ - m = 1.5, and at 15 ⁰ - m = 4). In reality, the total energy of the incident radiation exceeds the indicated values, since it includes not only the direct component, but also the value of the scattered component of the radiation intensity on the horizontal surface scattered at air masses 1, 2, 3, and 5 under these conditions, respectively, is equal to 110, 90, 70, and 50 W / m 2 (with a coefficient of 0.3 - 0.7 for the vertical plane, since only half of the sky is visible). In addition, in areas of the sky close to the Sun, there is a "circumsolar halo" in a radius of ≈ 5⁰.

Table 1 shows data on insolation for various regions of the Earth.

Table 1 - Insolation of the direct component by region for a clean atmosphere

Table 1 shows that the daily amount of solar radiation is maximum not at the equator, but near 40 ⁰. A similar fact is also a consequence of the inclination of the earth's axis to the plane of its orbit. During the summer solstice, the Sun in the tropics is almost all day overhead and the daylight hours are 13.5 hours, more than at the equator on the day of the equinox. With increasing latitude, the length of the day increases, and although the intensity of solar radiation decreases, the maximum value of daytime insolation occurs at a latitude of about 40 ⁰ and remains almost constant (for cloudless sky conditions) up to the Arctic Circle.

It should be emphasized that the data in Table 1 are valid only for a pure atmosphere. Taking into account cloudiness and atmospheric pollution by industrial waste, typical for many countries of the world, the values ​​given in the table should be at least halved. For example, for England in 70 of the XX century, before the start of the struggle for environmental protection, the annual amount of solar radiation was only 900 kWh/m 2 instead of 1700 kWh/m 2 .

The first data on the transparency of the atmosphere on Lake Baikal were obtained by V.V. Bufalom in 1964 He showed that the values ​​of direct solar radiation over Baikal are on average 13% higher than in Irkutsk. The average spectral transparency coefficient of the atmosphere in Northern Baikal in summer is 0.949, 0.906, 0.883 for red, green and blue filters, respectively. In summer the atmosphere is more optically unstable than in winter, and this instability varies considerably from the pre-noon hours to the afternoon. Depending on the annual course of attenuation by water vapor and aerosols, their contribution to the total attenuation of solar radiation also changes. Aerosols play the main role in the cold part of the year, and water vapor plays the main role in the warm part of the year. The Baikal Basin and Lake Baikal are distinguished by a relatively high integral transparency of the atmosphere. With an optical mass m = 2, the average values ​​of the transparency coefficient range from 0.73 (in summer) to 0.83 (in winter).

Aerosols significantly reduce the flow of direct solar radiation into the water area of ​​the pond, and they mainly absorb radiation of the visible spectrum, with the wavelength that freely passes through the fresh layer of the pond, and this for the accumulation of solar energy by the pond is of great importance.(A layer of water 1 cm thick is practically opaque to infrared radiation with a wavelength of more than 1 micron). Therefore, water several centimeters thick is used as a heat-shielding filter. For glass, the long-wavelength infrared transmission limit is 2.7 µm.

A large number of dust particles, freely transported across the steppe, also reduces the transparency of the atmosphere.

Electromagnetic radiation is emitted by all heated bodies, and the colder the body, the lower the intensity of the radiation and the further the maximum of its spectrum is shifted to the long-wave region. There is a very simple relation λmax×Τ=c¹[ c¹= 0.2898 cm∙deg. (Vina)], with the help of which it is easy to establish where the maximum radiation of a body with temperature Τ (⁰K) is located. For example, a human body with a temperature of 37 + 273 = 310 ⁰K emits infrared rays with a maximum near the value λmax = 9.3 µm. And the walls, for example, of a solar dryer, with a temperature of 90 ⁰С, will emit infrared rays with a maximum near the value λmax = 8 µm.

Visible solar radiation (0.4 µm< λ < 0,7 мкм) имеет 45 % интенсивности потому, что температура поверхности Солнца 5780 ⁰К.

In its great progress was the transition from an electric incandescent lamp with a carbon filament to a modern lamp with a tungsten filament. The thing is that a carbon filament can be brought to a temperature of 2100 ⁰K, and a tungsten filament - up to 2500 ⁰K. Why are these 400 ⁰K so important? The thing is that the purpose of an incandescent lamp is not to heat, but to give light. Therefore, it is necessary to achieve such a position that the maximum of the curve falls on the visible study. The ideal would be to have a filament that could withstand the temperature of the Sun's surface. But even the transition from 2100 to 2500 ⁰K increases the fraction of energy attributable to visible radiation, from 0.5 to 1.6%.

Everyone can feel the infrared rays emanating from a body heated to only 60 - 70 ⁰С by bringing the palm from below (to eliminate thermal convection).

The arrival of direct solar radiation in the water area of ​​the pond corresponds to its arrival on the horizontal irradiation surface. At the same time, the above shows the uncertainty of the quantitative characteristics of the arrival at a particular point in time, both seasonal and daily. Only the height of the Sun (the optical mass of the atmosphere) is a constant characteristic.

The accumulation of solar radiation by the earth's surface and the pond differ significantly.

The natural surfaces of the Earth have different reflective (absorbing) abilities. Thus, dark surfaces (chernozem, peat bogs) have a low albedo value of about 10%. ( Surface albedo is the ratio of the radiation flux reflected by this surface into the surrounding space to the flux that fell on it).

Light surfaces (white sand) have a large albedo, 35 - 40%. The albedo of grassy surfaces ranges from 15 to 25%. The crown albedo of a deciduous forest in summer is 14–17%, and that of a coniferous forest is 12–15%. The surface albedo decreases with increasing solar altitude.

The albedo of water surfaces is in the range of 3 - 45%, depending on the height of the Sun and the degree of excitement.

With a calm water surface, the albedo depends only on the height of the Sun (Figure 2).

Figure 2 - Dependence of the reflection coefficient of solar radiation for a calm water surface on the height of the Sun.

The entry of solar radiation and its passage through a layer of water has its own characteristics.

In general, the optical properties of water (its solutions) in the visible region of solar radiation are shown in Figure 3.

Ф0 - flux (power) of the incident radiation,

Photr - the flux of radiation reflected by the water surface,

Фabs is the flux of radiation absorbed by the water mass,

Фр - the flux of radiation that has passed through the water mass.

Body reflectance Fotr/Ф0

Absorption coefficient Фabl/Ф0

Transmittance Фpr/Ф0.

Figure 3 - Optical properties of water (its solutions) in the visible region of solar radiation

On the flat boundary of two media, air - water, the phenomena of reflection and refraction of light are observed.

When light is reflected, the incident beam, the reflected beam and the perpendicular to the reflecting surface, restored at the point of incidence of the beam, lie in the same plane, and the angle of reflection is equal to the angle of incidence. In the case of refraction, the incident beam, the perpendicular restored at the point of incidence of the beam to the interface between two media, and the refracted beam lie in the same plane. The angle of incidence α and the angle of refraction β (Figure 4) are related sin α /sin β=n2|n1, where n2 is the absolute refractive index of the second medium, n1 - of the first. Since for air n1≈1, the formula will take the form sin α /sin β=n2

Figure 4 - Refraction of rays during the transition from air to water

When the rays go from air into water, they approach the "perpendicular of incidence"; for example, a beam incident on water at an angle to the perpendicular to the surface of the water enters it already at an angle that is less than (Fig. 4a). But when an incident beam, sliding over the surface of the water, falls on the water surface at almost a right angle to the perpendicular, for example, at an angle of 89 ⁰ or less, then it enters the water at an angle less than a straight line, namely at an angle of only 48.5 ⁰. At a greater angle to the perpendicular than 48.5 ⁰, the beam cannot enter the water: this is the “limiting” angle for water (Figure 4, b).

Consequently, rays falling on water at various angles are compressed under water into a rather tight cone with an opening angle of 48.5 ⁰ + 48.5 ⁰ = 97 ⁰ (Fig. 4c).

In addition, the refraction of water depends on its temperature (Table 2), but these changes are not so significant that they cannot be of interest for engineering practice on the topic under consideration.

Table 2 - Refractive indexwater at different temperatures t

Let us now follow the course of the rays going back (from point P) - from water to air (Figure 5). According to the laws of optics, the paths will be the same, and all the rays contained in the mentioned 97-degree cone will go into the air at different angles, spreading over the entire 180-degree space above the water. Underwater rays that are outside the mentioned angle (97-degree) will not come out from under the water, but will be reflected entirely from its surface, as from a mirror.

Figure 5 - Refraction of rays during the transition from water to air

If n2< n1(вторая среда оптически менее плотная), то α < β. Наибольшему значению β = 90 ⁰ соответствует угол падения α0 , определяемый равенством sinα0=n2/n1. При угле падения α >α0, only the reflected beam exists, there is no refracted beam ( total internal reflection phenomenon).

Any underwater ray that meets the surface of the water at an angle greater than the "limiting" (i.e. greater than 48.5 ⁰) is not refracted, but reflected: it undergoes " total internal reflection". Reflection is called in this case total because all the incident rays are reflected here, while even the best polished silver mirror reflects only a part of the rays incident on it, while absorbing the rest. Water under these conditions is an ideal mirror. In this case, we are talking about visible light. Generally speaking, the refractive index of water, like other substances, depends on the wavelength (this phenomenon is called dispersion). As a consequence of this, the limiting angle at which total internal reflection occurs is not the same for different wavelengths, but for visible light when reflected at the water-air boundary, this angle changes by less than 1⁰.

Due to the fact that at a greater angle to the perpendicular than 48.5⁰, the sunbeam cannot enter the water: this is the “limiting” angle for water (Figure 4, b), then the water mass, in the entire range of values ​​​​of the Sun’s height, does not change so much insignificantly than air - it is always less .

However, since the density of water is 800 times greater than the density of air, the absorption of solar radiation by water will change significantly.

In addition, if light radiation passes through a transparent medium, then the spectrum of such light has some features. Certain lines in it are greatly weakened, i.e. waves of the corresponding wavelength are strongly absorbed by the medium under consideration. Such spectra are called absorption spectra. The form of the absorption spectrum depends on the substance under consideration.

Since the salt solution solar salt pond may contain different concentrations of sodium and magnesium chlorides and their ratios, then it makes no sense to speak unambiguously about absorption spectra. Although research and data on this issue abound.

So, for example, studies carried out in the USSR (Yu. Usmanov) to identify the transmittance of radiation of various wavelengths for water and a solution of magnesium chloride of various concentrations obtained the following results (Figure 6). And B. J. Brinkworth shows a graphical dependence of the absorption of solar radiation and the monochromatic flux density of solar radiation (radiation) depending on the wavelength (Figure 7).

Figure 7 - Absorption of solar radiation in water

Figure 6 - The dependence of the throughput of a solution of magnesium chloride on the concentration

Consequently, the quantitative supply of direct solar radiation to the hot brine of the pond, after entering the water, will depend on: the monochromatic density of the solar radiation (radiation) flux; from the height of the sun. And also from the albedo of the pond surface, from the purity of the upper layer of the solar salt pond, consisting of fresh water, with a thickness of usually 0.1 - 0.3 m, where mixing cannot be suppressed, the composition, concentration and thickness of the solution in the gradient layer (insulating layer with brine concentration increasing downwards), on the purity of water and brine.

Figures 6 and 7 show that water has the highest transmission capacity in the visible region of the solar spectrum. This is a very favorable factor for the passage of solar radiation through the upper fresh layer of the solar salt pond.

Bibliography

1 Osadchiy G.B. Solar energy, its derivatives and technologies for their use (Introduction to RES energy) / G.B. Osadchy. Omsk: IPK Maksheeva E.A., 2010. 572 p.

2 Twydell J. Renewable energy sources / J. Twydell, A . Weir. M.: Energoatomizdat, 1990. 392 p.

3 Duffy J. A. Thermal processes using solar energy / J. A. Duffy, W. A. ​​Beckman. M.: Mir, 1977. 420 p.

4 Climatic resources of Baikal and its basin /N. P. Ladeyshchikov, Novosibirsk, Nauka, 1976, 318p.

5 Pikin S. A. Liquid crystals / S. A. Pikin, L. M. Blinov. M.: Nauka, 1982. 208 p.

6 Kitaygorodsky A. I. Physics for everyone: Photons and nuclei / A. I. Kitaygorodsky. M.: Nauka, 1984. 208 p.

Solar energy equal to 100% arrives at the upper boundary of the atmosphere.

Ultraviolet radiation, which makes up 3% of 100% of incoming sunlight, is mostly absorbed by the ozone layer in the upper atmosphere.

About 40% of the remaining 97% interacts with clouds - of which 24% is reflected back into space, 2% is absorbed by clouds and 14% is scattered, reaching the earth's surface as scattered radiation.

32% of incoming radiation interacts with water vapor, dust and haze in the atmosphere - 13% of this is absorbed, 7% is reflected back into space and 12% reaches the earth's surface as scattered sunlight (Fig. 6)

Rice. 6. Radiation balance of the Earth

Therefore, out of the initial 100% of solar radiation on the Earth's surface, 2% of direct sunlight and 26% of diffused light reach.

Of this total, 4% is reflected from the earth's surface back to space, and the total reflection to space is 35% of the incident sunlight.

Of the 65% of the light absorbed by the Earth, 3% comes from the upper atmosphere, 15% from the lower atmosphere, and 47% from the Earth's surface - the ocean and land.

In order for the Earth to maintain thermal equilibrium, 47% of all solar energy that passes through the atmosphere and is absorbed by land and sea must be given off by land and sea back into the atmosphere.

The visible part of the spectrum of radiation entering the surface of the ocean and creating illumination consists of solar rays that have passed through the atmosphere (direct radiation) and some of the rays scattered by the atmosphere in all directions, including to the surface of the ocean (scattered radiation).

The ratio of the energy of these two light fluxes falling on a horizontal landing depends on the height of the Sun - the higher it is above the horizon, the greater the proportion of direct radiation

The illumination of the sea surface under natural conditions also depends on the cloudiness. High and thin clouds cast down a lot of scattered light, due to which the illumination of the sea surface at average heights of the Sun can be even greater than with a cloudless sky. Dense, rain clouds dramatically reduce illumination.

The light rays that create the illumination of the sea surface undergo reflection and refraction at the water-air boundary (Fig. 7) according to the well-known physical law of Snell.

Rice. 7. Reflection and refraction of a beam of light on the surface of the ocean

Thus, all light rays falling on the surface of the sea are partially reflected, refracted and enter the sea.

The ratio between refracted and reflected light fluxes depends on the height of the Sun. At a height of the Sun 0 0, the entire light flux is reflected from the surface of the sea. With an increase in the height of the Sun, the proportion of the light flux penetrating into the water increases, and at a Sun height of 90 0, 98% of the total flux incident on the surface penetrates into the water.

The ratio of the light flux reflected from the surface of the sea to the incident light is called sea ​​surface albedo . Then the albedo of the sea surface at a Sun height of 90 0 will be 2%, and for 0 0 - 100%. The sea surface albedo is different for direct and diffuse light fluxes. The albedo of direct radiation essentially depends on the height of the Sun, the albedo of scattered radiation practically does not depend on the height of the Sun.