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 (diffuse radiation).

The ratio of the energy of these two light fluxes falling on a horizontal platform 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 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.

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 turns 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 for long multi-year periods of time, then we can accept the hypothesis that the Earth is in thermal equilibrium: the arrival 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 conversion of part of 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 rarefaction, 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 into diffuse radiation in the atmosphere. 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 its 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 sky 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 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 more and more 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 BUT is the surface albedo. The rest of the total radiation ( S sin h + D) (1 – BUT) 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 was 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:

AT=(S sin h + D)(1 – BUT) – 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.

The sun radiates a huge amount of energy - approximately 1.1x1020 kWh per second. A kilowatt hour is the amount of energy required to run a 100 watt incandescent light bulb for 10 hours. The Earth's outer atmosphere intercepts approximately one millionth of the energy emitted by the Sun, or approximately 1500 quadrillion (1.5 x 1018) kWh annually. However, due to reflection, scattering and absorption by atmospheric gases and aerosols, only 47% of all energy, or approximately 700 quadrillion (7 x 1017) kWh, reaches the Earth's surface.

Solar radiation in the Earth's atmosphere is divided into the so-called direct radiation and scattered by particles of air, dust, water, etc. contained in the atmosphere. Their sum forms the total solar radiation. The amount of energy falling per unit area per unit time depends on a number of factors:

• latitude
• local climate season of the year
• the angle of inclination of the surface with respect to the sun.

Time and geographic location

The amount of solar energy falling on the Earth's surface changes due to the movement of the Sun. These changes depend on the time of day and season. Usually more solar radiation hits the Earth at noon than early in the morning or late in the evening. At noon, the Sun is high above the horizon, and the length of the path of the Sun's rays through the Earth's atmosphere is reduced. Consequently, less solar radiation is scattered and absorbed, which means more reaches the surface.

The amount of solar energy reaching the Earth's surface differs from the average annual value: in winter - less than 0.8 kWh / m2 per day in Northern Europe and more than 4 kWh / m2 per day in summer in this same region. The difference decreases as you get closer to the equator.

The amount of solar energy also depends on the geographical location of the site: the closer to the equator, the greater it is. For example, the average annual total solar radiation incident on a horizontal surface is: in Central Europe, Central Asia and Canada - approximately 1000 kWh/m2; in the Mediterranean - approximately 1700 kWh / m2; in most desert regions of Africa, the Middle East and Australia, approximately 2200 kWh/m2.

Thus, the amount of solar radiation varies significantly depending on the time of year and geographical location (see table). This factor must be taken into account when using solar energy.

	Southern Europe	Central Europe	Northern Europe	Caribbean region
January	2,6	1,7	0,8	5,1
February	3,9	3,2	1,5	5,6
March	4,6	3,6	2,6	6,0
April	5,9	4,7	3,4	6,2
May	6,3	5,3	4,2	6,1
June	6,9	5,9	5,0	5,9
July	7,5	6,0	4,4	6,0
August	6,6	5,3	4,0	6,1
September	5,5	4,4	3,3	5,7
October	4,5	3,3	2,1	5,3
November	3,0	2,1	1,2	5,1
December	2,7	1,7	0,8	4,8
YEAR	5,0	3,9	2,8	5,7

The influence of clouds on solar energy

The amount of solar radiation reaching the Earth's surface depends on various atmospheric phenomena and on the position of the Sun both during the day and throughout the year. Clouds are the main atmospheric phenomenon that determines the amount of solar radiation reaching the Earth's surface. At any point on the Earth, solar radiation reaching the Earth's surface decreases with increasing cloud cover. Consequently, countries with predominantly cloudy weather receive less solar radiation than deserts, where the weather is mostly cloudless.

The formation of clouds is influenced by the presence of local features such as mountains, seas and oceans, as well as large lakes. Therefore, the amount of solar radiation received in these areas and the regions adjacent to them may differ. For example, mountains may receive less solar radiation than adjacent foothills and plains. Winds blowing towards the mountains cause part of the air to rise and, cooling the moisture in the air, form clouds. The amount of solar radiation in coastal areas may also differ from those recorded in areas located inland.

The amount of solar energy received during the day is largely dependent on local atmospheric phenomena. At noon with a clear sky, the total solar

radiation falling on a horizontal surface can reach (for example, in Central Europe) a value of 1000 W/m2 (in very favorable weather conditions this figure can be higher), while in very cloudy weather it is below 100 W/m2 even at noon.

Effects of Atmospheric Pollution on Solar Energy

Anthropogenic and natural phenomena can also limit the amount of solar radiation reaching the Earth's surface. Urban smog, smoke from wildfires and airborne volcanic ash reduce the use of solar energy by increasing the dispersion and absorption of solar radiation. That is, these factors have a greater influence on direct solar radiation than on the total. With severe air pollution, for example, with smog, direct radiation is reduced by 40%, and the total - only by 15-25%. A strong volcanic eruption can reduce, and over a large area of ​​the Earth's surface, direct solar radiation by 20%, and total - by 10% for a period of 6 months to 2 years. With a decrease in the amount of volcanic ash in the atmosphere, the effect weakens, but the process of complete recovery may take several years.

The potential of solar energy

The sun provides us with 10,000 times more free energy than is actually used worldwide. The global commercial market alone buys and sells just under 85 trillion (8.5 x 1013) kWh of energy per year. Since it is impossible to follow the whole process, it is not possible to say with certainty how much non-commercial energy people consume (for example, how much wood and fertilizer is collected and burned, how much water is used to produce mechanical or electrical energy). Some experts estimate that such non-commercial energy accounts for one-fifth of all energy used. But even if this is true, then the total energy consumed by mankind during the year is only approximately one seven thousandth of the solar energy that hits the surface of the Earth in the same period.

In developed countries, such as the USA, energy consumption is approximately 25 trillion (2.5 x 1013) kWh per year, which corresponds to more than 260 kWh per person per day. This is the equivalent of running more than 100 100W incandescent bulbs daily for a full day. The average US citizen consumes 33 times more energy than an Indian, 13 times more than a Chinese, two and a half times more than a Japanese and twice as much as a Swede.

The amount of solar energy reaching the Earth's surface is many times greater than its consumption, even in countries such as the United States, where energy consumption is huge. If only 1% of the country's territory was used to install solar equipment (photovoltaic panels or solar hot water systems) operating at a 10% efficiency, then the US would be fully supplied with energy. The same can be said about all other developed countries. However, in a certain sense, this is unrealistic - firstly, due to the high cost of photovoltaic systems, and secondly, it is impossible to cover such large areas with solar equipment without harming the ecosystem. But the principle itself is correct.

It is possible to cover the same area by dispersing installations on the roofs of buildings, on houses, along roadsides, on predetermined areas of land, etc. In addition, in many countries already more than 1% of the land is allocated for the extraction, conversion, production and transportation of energy. And, since most of this energy is non-renewable at the scale of human existence, this kind of energy production is much more harmful to the environment than solar systems.

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 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%. Due 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. In the same way, 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 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 intensity of solar radiation in the northern hemisphere, we present data on the average monthly values ​​of the midday 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 (soil properties, 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 Sun height of 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.

O 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 fruit), 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

LECTURE 2.

SOLAR RADIATION.

Plan:

1. The value of solar radiation for life on Earth.

2. Types of solar radiation.

3. Spectral composition of solar radiation.

4. Absorption and dispersion of radiation.

5.PAR (photosynthetically active radiation).

6. Radiation balance.

1. The main source of energy on Earth for all living things (plants, animals and humans) is the energy of the sun.

The sun is a gas ball with a radius of 695300 km. The radius of the Sun is 109 times greater than the radius of the Earth (equatorial 6378.2 km, polar 6356.8 km). The sun is composed mainly of hydrogen (64%) and helium (32%). The rest account for only 4% of its mass.

Solar energy is the main condition for the existence of the biosphere and one of the main climate-forming factors. Due to the energy of the Sun, air masses in the atmosphere are constantly moving, which ensures the constancy of the gas composition of the atmosphere. Under the action of solar radiation, a huge amount of water evaporates from the surface of reservoirs, soil, plants. Water vapor carried by the wind from the oceans and seas to the continents is the main source of precipitation for land.

Solar energy is an indispensable condition for the existence of green plants, which convert solar energy into high-energy organic substances during photosynthesis.

The growth and development of plants is a process of assimilation and processing of solar energy, therefore, agricultural production is possible only if solar energy reaches the Earth's surface. A Russian scientist wrote: “Give the best cook as much fresh air, sunlight, a whole river of clean water as you like, ask him to prepare sugar, starch, fats and grains from all this, and he will think that you are laughing at him. But what seems absolutely fantastic to a person is performed without hindrance in the green leaves of plants under the influence of the energy of the Sun. It is estimated that 1 sq. a meter of leaves per hour produces a gram of sugar. Due to the fact that the Earth is surrounded by a continuous shell of the atmosphere, the sun's rays, before reaching the surface of the earth, pass through the entire thickness of the atmosphere, which partially reflects them, partially scatters, i.e. changes the amount and quality of sunlight entering the earth's surface. Living organisms are sensitive to changes in the intensity of illumination created by solar radiation. Due to the different response to the intensity of illumination, all forms of vegetation are divided into light-loving and shade-tolerant. Insufficient illumination in crops causes, for example, a weak differentiation of straw tissues of grain crops. As a result, the strength and elasticity of tissues decrease, which often leads to lodging of crops. In thickened corn crops, due to low solar radiation, the formation of cobs on plants is weakened.

Solar radiation affects the chemical composition of agricultural products. For example, the sugar content of beets and fruits, the protein content in wheat grain directly depend on the number of sunny days. The amount of oil in the seeds of sunflower, flax also increases with the increase in the arrival of solar radiation.

Illumination of the aerial parts of plants significantly affects the absorption of nutrients by the roots. Under low illumination, the transfer of assimilates to the roots slows down, and as a result, biosynthetic processes occurring in plant cells are inhibited.

Illumination also affects the emergence, spread and development of plant diseases. The period of infection consists of two phases, differing from each other in response to the light factor. The first of them - the actual germination of spores and the penetration of the infectious principle into the tissues of the affected culture - in most cases does not depend on the presence and intensity of light. The second - after the germination of spores - is most active in high light conditions.

The positive effect of light also affects the rate of development of the pathogen in the host plant. This is especially evident in rust fungi. The more light, the shorter the incubation period for wheat line rust, barley yellow rust, flax and bean rust, etc. And this increases the number of generations of the fungus and increases the intensity of the infection. Fertility increases in this pathogen under intense light conditions.

Some diseases develop most actively in low light, which causes weakening of plants and a decrease in their resistance to diseases (causative agents of various kinds of rot, especially vegetable crops).

Duration of lighting and plants. The rhythm of solar radiation (the alternation of the light and dark parts of the day) is the most stable and recurring environmental factor from year to year. As a result of many years of research, physiologists have established the dependence of the transition of plants to generative development on a certain ratio of the length of day and night. In this regard, cultures according to the photoperiodic reaction can be classified into groups: short day the development of which is delayed at a day length of more than 10 hours. A short day encourages flower formation, while a long day prevents it. Such crops include soybeans, rice, millet, sorghum, corn, etc.;

long day until 12-13 o'clock, requiring long-term illumination for their development. Their development accelerates when the day length is about 20 hours. These crops include rye, oats, wheat, flax, peas, spinach, clover, etc.;

neutral with respect to day length, the development of which does not depend on the length of the day, for example, tomato, buckwheat, legumes, rhubarb.

It has been established that the predominance of a certain spectral composition in the radiant flux is necessary for the beginning of flowering of plants. Short-day plants develop faster when the maximum radiation falls on blue-violet rays, and long-day plants - on red ones. The duration of the light part of the day (astronomical length of the day) depends on the time of year and geographic latitude. At the equator, the duration of the day throughout the year is 12 hours ± 30 minutes. When moving from the equator to the poles after the vernal equinox (21.03), the length of the day increases to the north and decreases to the south. After the autumn equinox (23.09) the distribution of day length is reversed. In the Northern Hemisphere, June 22 is the longest day, the duration of which is 24 hours north of the Arctic Circle. The shortest day in the Northern Hemisphere is December 22, and beyond the Arctic Circle in the winter months, the Sun does not rise above the horizon at all. In middle latitudes, for example, in Moscow, the length of the day during the year varies from 7 to 17.5 hours.

2. Types of solar radiation.

Solar radiation consists of three components: direct solar radiation, scattered and total.

DIRECT SOLAR RADIATIONS- radiation coming from the sun into the atmosphere and then to the earth's surface in the form of a beam of parallel rays. Its intensity is measured in calories per cm2 per minute. It depends on the height of the sun and the state of the atmosphere (cloudiness, dust, water vapor). The annual amount of direct solar radiation on the horizontal surface of the territory of the Stavropol Territory is 65-76 kcal/cm2/min. At sea level, with a high position of the Sun (summer, noon) and good transparency, direct solar radiation is 1.5 kcal/cm2/min. This is the short wavelength part of the spectrum. When the flow of direct solar radiation passes through the atmosphere, it weakens due to absorption (about 15%) and scattering (about 25%) of energy by gases, aerosols, clouds.

The flow of direct solar radiation falling on a horizontal surface is called insolation. S= S sin hois the vertical component of direct solar radiation.

S – amount of heat received by a surface perpendicular to the beam ,

ho – the height of the Sun, i.e. the angle formed by a sunbeam with a horizontal surface .

At the boundary of the atmosphere, the intensity of solar radiation isSo= 1,98 kcal/cm2/min. - according to the international agreement of 1958. It's called the solar constant. This would be at the surface if the atmosphere were absolutely transparent.

Rice. 2.1. The path of the sun's ray in the atmosphere at different heights of the sun

SCATTERED RADIATIOND – part of the solar radiation as a result of scattering by the atmosphere goes back into space, but a significant part of it enters the Earth in the form of scattered radiation. Maximum scattered radiation + 1 kcal/cm2/min. It is noted in a clear sky, if there are high clouds on it. Under a cloudy sky, the spectrum of scattered radiation is similar to that of the sun. This is the short wavelength part of the spectrum. Wavelength 0.17-4 microns.

TOTAL RADIATIONQ- consists of diffuse and direct radiation to a horizontal surface. Q= S+ D.

The ratio between direct and diffuse radiation in the composition of total radiation depends on the height of the Sun, cloudiness and pollution of the atmosphere, and the height of the surface above sea level. With an increase in the height of the Sun, the fraction of scattered radiation in a cloudless sky decreases. The more transparent the atmosphere and the higher the Sun, the smaller the proportion of scattered radiation. With continuous dense clouds, the total radiation consists entirely of scattered radiation. In winter, due to the reflection of radiation from the snow cover and its secondary scattering in the atmosphere, the proportion of scattered radiation in the composition of the total increases noticeably.

The light and heat received by plants from the Sun is the result of the action of total solar radiation. Therefore, data on the amounts of radiation received by the surface per day, month, growing season, and year are of great importance for agriculture.

reflected solar radiation. Albedo. The total radiation that has reached the earth's surface, partially reflected from it, creates reflected solar radiation (RK), directed from the earth's surface into the atmosphere. The value of reflected radiation largely depends on the properties and condition of the reflecting surface: color, roughness, humidity, etc. The reflectivity of any surface can be characterized by its albedo (Ak), which is understood as the ratio of reflected solar radiation to total. Albedo is usually expressed as a percentage:

Observations show that the albedo of various surfaces varies within relatively narrow limits (10...30%), with the exception of snow and water.

Albedo depends on soil moisture, with the increase of which it decreases, which is important in the process of changing the thermal regime of irrigated fields. Due to the decrease in albedo, when the soil is moistened, the absorbed radiation increases. The albedo of various surfaces has a well-pronounced daily and annual variation, due to the dependence of the albedo on the height of the Sun. The lowest albedo value is observed at around noon hours, and during the year - in summer.

The Earth's own radiation and the counter radiation of the atmosphere. Efficient radiation. The earth's surface as a physical body with a temperature above absolute zero (-273 ° C) is a source of radiation, which is called the Earth's own radiation (E3). It is directed into the atmosphere and is almost completely absorbed by water vapor, water droplets and carbon dioxide contained in the air. The radiation of the Earth depends on the temperature of its surface.

The atmosphere, absorbing a small amount of solar radiation and almost all the energy emitted by the earth's surface, heats up and, in turn, also radiates energy. About 30% of atmospheric radiation goes into outer space, and about 70% comes to the Earth's surface and is called the counter atmospheric radiation (Ea).

The amount of energy emitted by the atmosphere is directly proportional to its temperature, carbon dioxide content, ozone and cloud cover.

The surface of the Earth absorbs this counter radiation almost entirely (by 90...99%). Thus, it is an important source of heat for the earth's surface in addition to absorbed solar radiation. This influence of the atmosphere on the thermal regime of the Earth is called the greenhouse or greenhouse effect due to the external analogy with the action of glasses in greenhouses and greenhouses. Glass well transmits the sun's rays, which heat the soil and plants, but delays the thermal radiation of the heated soil and plants.

The difference between the own radiation of the Earth's surface and the counter radiation of the atmosphere is called the effective radiation: Eef.

Eef= E3-Ea

On clear and slightly cloudy nights, the effective radiation is much greater than on cloudy nights; therefore, the nightly cooling of the earth's surface is also greater. During the day, it is blocked by absorbed total radiation, as a result of which the surface temperature rises. At the same time, the effective radiation also increases. The earth's surface in middle latitudes loses 70...140 W/m2 due to effective radiation, which is about half of the amount of heat that it receives from the absorption of solar radiation.

3. Spectral composition of radiation.

The sun, as a source of radiation, has a variety of emitted waves. The fluxes of radiant energy along the wavelength are conditionally divided into shortwave (X < 4 мкм) и длинноволновую (А. >4 µm) radiation. The spectrum of solar radiation at the boundary of the earth's atmosphere is practically between the wavelengths of 0.17 and 4 microns, and the terrestrial and atmospheric radiation - from 4 to 120 microns. Consequently, the fluxes of solar radiation (S, D, RK) refer to short-wave radiation, and the radiation of the Earth (£3) and the atmosphere (Ea) - to long-wave radiation.

The spectrum of solar radiation can be divided into three qualitatively different parts: ultraviolet (Y< 0,40 мкм), ви­димую (0,40 мкм < Y < 0.75 µm) and infrared (0.76 µm < Y < 4 µm). Before the ultraviolet part of the spectrum of solar radiation lies X-ray radiation, and beyond the infrared - the radio emission of the Sun. At the upper boundary of the atmosphere, the ultraviolet part of the spectrum accounts for about 7% of the energy of solar radiation, 46% for the visible and 47% for the infrared.

The radiation emitted by the earth and atmosphere is called far infrared radiation.

The biological effect of different types of radiation on plants is different. ultraviolet radiation slows down growth processes, but accelerates the passage of the stages of formation of reproductive organs in plants.

The value of infrared radiation, which is actively absorbed by water in the leaves and stems of plants, is its thermal effect, which significantly affects the growth and development of plants.

far infrared radiation produces only a thermal effect on plants. Its influence on the growth and development of plants is insignificant.

Visible part of the solar spectrum, firstly, creates illumination. Secondly, the so-called physiological radiation (A, = 0.35 ... 0.75 μm), which is absorbed by leaf pigments, almost coincides with the region of visible radiation (partially capturing the region of ultraviolet radiation). Its energy has an important regulatory and energy significance in the life of plants. Within this region of the spectrum, a region of photosynthetically active radiation is distinguished.

4. Absorption and scattering of radiation in the atmosphere.

Passing through the earth's atmosphere, solar radiation is attenuated due to absorption and scattering by atmospheric gases and aerosols. At the same time, its spectral composition also changes. At different heights of the sun and different heights of the observation point above the earth's surface, the length of the path traveled by the sun's ray in the atmosphere is not the same. With a decrease in altitude, the ultraviolet part of the radiation decreases especially strongly, the visible part decreases somewhat less, and only slightly the infrared part.

The scattering of radiation in the atmosphere occurs mainly as a result of continuous fluctuations (fluctuations) in the density of air at every point in the atmosphere, caused by the formation and destruction of some "clusters" (clumps) of atmospheric gas molecules. Aerosol particles also scatter solar radiation. The scattering intensity is characterized by the scattering coefficient.

K = add formula.

The intensity of scattering depends on the number of scattering particles per unit volume, on their size and nature, and also on the wavelengths of the scattered radiation itself.

Rays scatter the stronger, the shorter the wavelength. For example, violet rays scatter 14 times more than red ones, which explains the blue color of the sky. As noted above (see Section 2.2), direct solar radiation passing through the atmosphere is partially dissipated. In clean and dry air, the intensity of the molecular scattering coefficient obeys the Rayleigh law:

k= s/Y4 ,

where C is a coefficient depending on the number of gas molecules per unit volume; X is the length of the scattered wave.

Since the far wavelengths of red light are almost twice the wavelengths of violet light, the former are scattered by air molecules 14 times less than the latter. Since the initial energy (before scattering) of violet rays is less than blue and blue, the maximum energy in scattered light (scattered solar radiation) is shifted to blue-blue rays, which determines the blue color of the sky. Thus, diffuse radiation is richer in photosynthetically active rays than direct radiation.

In air containing impurities (small water droplets, ice crystals, dust particles, etc.), scattering is the same for all areas of visible radiation. Therefore, the sky acquires a whitish tint (haze appears). Cloud elements (large droplets and crystals) do not scatter the sun's rays at all, but reflect them diffusely. As a result, clouds illuminated by the Sun are white.

5. PAR (photosynthetically active radiation)

Photosynthetically active radiation. In the process of photosynthesis, not the entire spectrum of solar radiation is used, but only its

part in the wavelength range of 0.38 ... 0.71 microns, - photosynthetically active radiation (PAR).

It is known that visible radiation, perceived by the human eye as white, consists of colored rays: red, orange, yellow, green, blue, indigo and violet.

The assimilation of the energy of solar radiation by plant leaves is selective (selective). The most intense leaves absorb blue-violet (X = 0.48 ... 0.40 microns) and orange-red (X = 0.68 microns) rays, less yellow-green (A. = 0.58 ... 0.50 microns) and far red (A.\u003e 0.69 microns) rays.

At the earth's surface, the maximum energy in the spectrum of direct solar radiation, when the Sun is high, falls on the region of yellow-green rays (the disk of the Sun is yellow). When the Sun is near the horizon, the far red rays have the maximum energy (the solar disk is red). Therefore, the energy of direct sunlight is little involved in the process of photosynthesis.

Since PAR is one of the most important factors in the productivity of agricultural plants, information on the amount of incoming PAR, taking into account its distribution over the territory and in time are of great practical importance.

The PAR intensity can be measured, but this requires special light filters that transmit only waves in the range of 0.38 ... 0.71 microns. There are such devices, but they are not used on the network of actinometric stations, but they measure the intensity of the integral spectrum of solar radiation. The PAR value can be calculated from data on the arrival of direct, diffuse or total radiation using the coefficients proposed by H. G. Tooming and:

Qfar = 0.43 S"+0.57 D);

distribution maps of monthly and annual amounts of Far on the territory of Russia were drawn up.

To characterize the degree of use of PAR by crops, the PAR efficiency is used:

KPIfar = (sumQ/ headlights/sumQ/ headlights) 100%,

where sumQ/ headlights- the amount of PAR spent on photosynthesis during the growing season of plants; sumQ/ headlights- the amount of PAR received for crops during this period;

Crops according to their average values ​​of CPIF are divided into groups (according to): usually observed - 0.5 ... 1.5%; good-1.5...3.0; record - 3.5...5.0; theoretically possible - 6.0 ... 8.0%.

6. RADIATION BALANCE OF THE EARTH'S SURFACE

The difference between the incoming and outgoing fluxes of radiant energy is called the radiation balance of the earth's surface (B).

The incoming part of the radiation balance of the earth's surface during the day consists of direct solar and diffuse radiation, as well as atmospheric radiation. The expenditure part of the balance is the radiation of the earth's surface and reflected solar radiation:

B= S / + D+ Ea-E3-Rk

The equation can also be written in another form: B = Q- RK - Eef.

For night time, the radiation balance equation has the following form:

B \u003d Ea - E3, or B \u003d -Eef.

If the input of radiation is greater than the output, then the radiation balance is positive and the active surface* heats up. With a negative balance, it cools. In summer, the radiation balance is positive during the day and negative at night. The zero crossing occurs in the morning approximately 1 hour after sunrise, and in the evening 1-2 hours before sunset.

The annual radiation balance in areas where a stable snow cover is established has negative values ​​in the cold season, and positive values ​​in the warm season.

The radiation balance of the earth's surface significantly affects the distribution of temperature in the soil and the surface layer of the atmosphere, as well as the processes of evaporation and snowmelt, the formation of fog and frost, changes in the properties of air masses (their transformation).

Knowledge of the radiation regime of agricultural land makes it possible to calculate the amount of radiation absorbed by crops and soil depending on the height of the Sun, the structure of crops, and the phase of plant development. Data on the regime are also necessary for evaluating various methods of regulating soil temperature and moisture, evaporation, on which plant growth and development, crop formation, its quantity and quality depend.

Effective agronomic methods of influencing the radiation and, consequently, the thermal regime of the active surface are mulching (covering the soil with a thin layer of peat chips, rotted manure, sawdust, etc.), covering the soil with plastic wrap, and irrigation. All this changes the reflective and absorptive capacity of the active surface.

* Active surface - the surface of soil, water or vegetation, which directly absorbs solar and atmospheric radiation and emits radiation into the atmosphere, thereby regulating the thermal regime of the adjacent layers of air and the underlying layers of soil, water, vegetation.