What is direct radiation? Direct and diffuse solar radiation. Distribution of solar radiation over the earth's surface

LECTURE 2.

SOLAR RADIATION.

Plan:

1. The importance 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 695,300 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 primarily 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 continuously move, which ensures the constancy of the gas composition of the atmosphere. Under the influence of solar radiation, a huge amount of water evaporates from the surface of reservoirs, soil, and 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 through the process of 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 surface of the Earth. The Russian scientist wrote: “Give the best cook as much fresh air as he wants, sunlight, a whole river of clean water, ask him to prepare sugar, starch, fats and grains from all this, and he will decide that you are laughing at him. But what seems absolutely fantastic to a person occurs unhindered 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 produces a gram of sugar per hour. Due to the fact that the Earth is surrounded by a continuous shell of the atmosphere, Sun rays Before reaching the surface of the earth, they pass through the entire thickness of the atmosphere, which partially reflects them and partially scatters them, i.e., changes the quantity and quality of sunlight arriving at the surface of the earth. Living organisms react sensitively to changes in the intensity of illumination created by solar radiation. Due to different reactions to light intensity, all forms of vegetation are divided into light-loving and shade-tolerant. Insufficient illumination in crops causes, for example, poor 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 dense corn crops, due to low solar radiation, the formation of cobs on plants is weakened.

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

Illumination of the above-ground parts of plants significantly affects the absorption of nutrients by roots. In low light conditions, the transfer of assimilates to the roots slows down, and as a result, the biosynthetic processes occurring in plant cells are inhibited.

Illumination also affects the appearance, spread and development of plant diseases. The infection period consists of two phases that differ in their reaction 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 germination of the spores - is most active under increased illumination.

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. How more light, the shorter the incubation period for linear rust of wheat, yellow rust of barley, rust of flax and beans, etc. And this increases the number of generations of the fungus and increases the intensity of the damage. Fertility increases in this pathogen under intense lighting conditions

Some diseases develop most actively in insufficient lighting, which causes weakening of plants and a decrease in their resistance to diseases (pathogens of various types of rot, especially vegetable crops).

Light duration and plants. The rhythm of solar radiation (alternation of light and dark parts of the day) is the most stable and repeating factor from year to year. external environment. 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, crops can be classified into groups according to their photoperiodic reaction: short day the development of which is delayed when the day length is more than 10 hours. A short day promotes flower initiation, while a long day prevents this. Such crops include soybeans, rice, millet, sorghum, corn, etc.;

long day until 12-13 o'clock, requiring prolonged lighting 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.;

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

It has been established that for plants to begin flowering, a predominance of a certain spectral composition in the radiant flux is necessary. 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 daylight hours (astronomical day length) depends on the time of year and latitude. At the equator, the length of the day throughout the year is 12 hours ± 30 minutes. As you move from the equator to the poles after the spring equinox (21.03), the length of the day increases to the north and decreases to the south. After the autumnal equinox (September 23), 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 varies throughout the year from 7 to 17.5 hours.

2. Types of solar radiation.

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

DIRECT SOLAR RADIATIONS – radiation coming from the Sun into the atmosphere and then onto 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 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 the absorption (about 15%) and dissipation (about 25%) of energy by gases, aerosols, and clouds.

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

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

ho – the height of the Sun, i.e. the angle formed by a solar ray 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 And it's called the solar constant. This is how it would look at the surface if the atmosphere were absolutely transparent.

Rice. 2.1. Path of a solar ray in the atmosphere at different heights of the Sun

SCATTERED RADIATIOND – As a result of scattering by the atmosphere, part of the solar radiation goes back into space, but a significant part of it arrives on Earth in the form of scattered radiation. Maximum scattered radiation + 1 kcal/cm2/min. It is observed when the sky is clear and there are high clouds. Under cloudy skies, 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 onto 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 atmospheric pollution, and the height of the surface above sea level. As the height of the Sun increases, the proportion of scattered radiation in a cloudless sky decreases. The more transparent the atmosphere and the higher the Sun, the lower 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 share of scattered radiation in the total radiation increases noticeably.

The light and heat received by plants from the Sun are the result of the total solar radiation. That's why great importance for agriculture they have data on the amount of radiation received by the surface per day, month, growing season, year.

Reflected solar radiation. Albedo. The total radiation that reaches 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 the value of 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 an increase in which it decreases, which is important in the process of changing the thermal regime of irrigated fields. Due to a decrease in albedo when the soil is moistened, the absorbed radiation increases. The albedo of various surfaces has a well-defined daily and annual variation, due to the dependence of the albedo on the height of the Sun. Lowest value albedo is observed around midday and throughout the year in the summer.

Earth's own radiation and counter radiation from the atmosphere. Effective radiation. The Earth's surface as a physical body having 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 Earth's radiation depends on its surface temperature.

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 emits energy. About 30% of atmospheric radiation goes into outer space, and about 70% comes to the surface of the Earth and is called counter atmospheric radiation (Ea).

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

The Earth's surface absorbs this counter radiation almost entirely (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 effect of glass in greenhouses and greenhouses. Glass transmits the sun's rays well, heating the soil and plants, but blocks the thermal radiation of the heated soil and plants.

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

Eef= E3-EA

On clear and partly cloudy nights, the effective radiation is much greater than on cloudy nights, and therefore the night cooling of the earth's surface is greater. During the day, it is covered by the absorbed total radiation, as a result of which the surface temperature rises. At the same time, effective radiation also increases. The earth's surface in mid-latitudes loses 70...140 W/m2 due to effective radiation, which is approximately half the amount of heat 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. Radiant energy fluxes according to wavelength are conventionally 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 practically lies between wavelengths of 0.17 and 4 microns, and that of terrestrial and atmospheric radiation - from 4 to 120 microns. Consequently, the fluxes of solar radiation (S, D, RK) belong to short-wave radiation, and the radiation of the Earth (£3) and the atmosphere (Ea) belongs 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). Up to the ultraviolet part of the spectrum of solar radiation lies x-ray radiation, and behind the infrared is 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 solar radiation energy, 46% for the visible and 47% for the infrared.

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

Biological effect different types radiation on plants varies. Ultraviolet radiation slows down growth processes, but accelerates the passage of stages of formation of reproductive organs in plants.

Meaning of infrared radiation, which is actively absorbed by water from 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 energetic significance in plant life. Within this part of the spectrum, a region of photosynthetically active radiation is distinguished.

4. Absorption and dispersion of radiation in the atmosphere.

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

The dispersion of radiation in the atmosphere occurs mainly as a result of continuous fluctuations (fluctuations) in air density at each point in the atmosphere, caused by the formation and destruction of certain “clumps” (clumps) of atmospheric gas molecules. Solar radiation is also scattered by aerosol particles. 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, as well as on the wavelengths of the scattered radiation itself.

The shorter the wavelength, the more strongly the rays are scattered. For example, violet rays are scattered 14 times more strongly 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 scattered. In clean and dry air, the intensity of the molecular scattering coefficient obeys Rayleigh's law:

k= c/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 wavelength of red light is almost double longer waves 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 that of blue and cyan ones, the maximum energy in scattered light (scattered solar radiation) shifts to blue-blue rays, which determines the blue color of the sky. Thus, scattered 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 takes on a whitish tint (haze appears). Cloud elements (large droplets and crystals) do not scatter the sun's rays at all, but diffusely reflect them. As a result, clouds illuminated by the Sun have White color.

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 located in the wavelength range 0.38...0.71 µm - 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 absorption of solar radiation energy by plant leaves is selective. The leaves most intensively absorb blue-violet (X = 0.48...0.40 µm) and orange-red (X = 0.68 µm) rays, less - yellow-green (A. = 0.58... 0.50 µm) and far red (A. > 0.69 µm) rays.

At the earth's surface, the maximum energy in the spectrum of direct solar radiation, when the Sun is high, falls in the region of yellow-green rays (the solar disk is yellow). When the Sun is located near the horizon, the far red rays have maximum energy (the solar disk is red). Therefore, the energy of direct sunlight contributes little to 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 intensity of the phased array can be measured, but this requires special filters that transmit only waves in the range of 0.38...0.71 microns. Such devices exist, but they are not used in the network of actinometric stations; 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 X. G. Tooming and:

Qfar = 0.43 S" +0.57 D);

maps of the distribution of monthly and annual Fara amounts on the territory of Russia were compiled.

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

KPIfar= (amountQ/ headlights/amountQ/ 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 KPIFAr values ​​are divided into groups (by): 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 scattered 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 be written in another form: B = Q- RK - Eph.

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

B = Ea - E3, or B = -Eeff.

If the radiation inflow is greater than the outflow, then the radiation balance is positive and the active surface* heats up. When the balance is negative, 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 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 fogs and frosts, 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 the crop, and the phase of plant development. Data on the regime are also necessary for assessing various methods of regulating temperature, soil moisture, evaporation, on which the growth and development of plants, crop formation, its quantity and quality depend.

Effective agronomic techniques for 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 film, and irrigation. All this changes the reflectivity and absorption capacity of the active surface.

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

The bright star burns us with hot rays and makes us think about the meaning of radiation in our lives, its benefits and harms. What is solar radiation? Lesson school physics invites us to begin by familiarizing ourselves with the concept of electromagnetic radiation in general. This term denotes another form of matter - different from substance. This includes both visible light and the spectrum that is not perceived by the eye. That is, X-rays, gamma rays, ultraviolet and infrared.

Electromagnetic waves

In the presence of a source-emitter of radiation, its electromagnetic waves propagate in all directions at the speed of light. These waves, like any other, have certain characteristics. These include vibration frequency and wavelength. Any body whose temperature differs from absolute zero has the property of emitting radiation.

The sun is the main and most powerful source of radiation near our planet. In turn, the Earth (its atmosphere and surface) itself emits radiation, but in a different range. Observation of temperature conditions on the planet over long periods of time gave rise to the hypothesis of a balance in the amount of heat received from the Sun and released into outer space.

Solar radiation: spectral composition

The absolute majority (about 99%) of solar energy in the spectrum lies in the wavelength range from 0.1 to 4 microns. The remaining 1% are rays of longer and shorter lengths, including radio waves and x-rays. About half of the sun's radiant energy comes from the spectrum that we perceive with our eyes, approximately 44% from infrared radiation, and 9% from ultraviolet radiation. How do we know how solar radiation is divided? Calculation of its distribution is possible thanks to studies from space satellites.

There are substances that can enter a special state and emit additional radiation of a different wavelength range. For example, there is a glow when low temperatures, not characteristic of the emission of light by this substance. This type of radiation, called luminescent, does not respond to the usual principles of thermal radiation.

The phenomenon of luminescence occurs after a substance absorbs a certain amount of energy and transitions to another state (the so-called excited state), which is higher in energy than at the substance’s own temperature. Luminescence appears during the reverse transition - from an excited state to a familiar state. In nature, we can observe it in the form of night sky glows and aurora borealis.

Our luminary

The energy of the sun's rays is almost the only source of heat for our planet. Its own radiation coming from its depths to the surface has an intensity that is approximately 5 thousand times less. At the same time, visible light - one of the most important factors of life on the planet - is only a part of solar radiation.

The energy of the sun's rays is converted into heat, a smaller part - in the atmosphere, and a larger part - on the surface of the Earth. There it is spent on heating water and soil (upper layers), which then give off heat to the air. Being heated, the atmosphere and the earth's surface, in turn, emit infrared rays into space, while cooling.

Solar radiation: definition

The radiation that comes to the surface of our planet directly from the solar disk is usually called direct solar radiation. The sun spreads it in all directions. Taking into account the enormous distance from the Earth to the Sun, direct solar radiation at any point on the earth's surface can be represented as a beam of parallel rays, the source of which is almost infinity. The area located perpendicular to the rays of sunlight thus receives its greatest amount.

Radiation flux density (or irradiance) is a measure of the amount of radiation falling on a specific surface. This is the amount of radiant energy falling per unit time per unit area. This quantity is measured - irradiance - in W/m2. Our Earth, as everyone knows, revolves around the Sun in an ellipsoidal orbit. The sun is located at one of the foci of this ellipse. Therefore, every year at a certain time (in early January) the Earth occupies a position closest to the Sun and at another (in early July) - farthest from it. In this case, the amount of energy illumination changes in inverse proportion to the square of the distance to the luminary.

Where does the solar radiation that reaches the Earth go? Its types are determined by many factors. Depending on the geographic latitude, humidity, cloudiness, some of it is scattered in the atmosphere, some is absorbed, but the majority still reaches the surface of the planet. In this case, a small amount is reflected, and the main amount is absorbed by the earth's surface, under the influence of which it is heated. Scattered solar radiation also partially falls on the earth's surface, is partially absorbed by it and partially reflected. The rest of it goes into outer space.

How does the distribution take place?

Is solar radiation uniform? Its types after all the “losses” in the atmosphere may differ in their spectral composition. After all, rays with different lengths are both scattered and absorbed in different ways. On average, the atmosphere absorbs about 23% of its original amount. Approximately 26% of the total flux turns into scattered radiation, 2/3 of which then hits the Earth. In essence, this is a different type of radiation, different from the original one. Scattered radiation is sent to Earth not by the disk of the Sun, but by the vault of heaven. It has a different spectral composition.

Absorbs radiation mainly from ozone - the visible spectrum, and ultraviolet rays. Infrared radiation is absorbed carbon dioxide(carbon dioxide), which, by the way, is very little in the atmosphere.

Radiation scattering, which weakens it, occurs for any wavelength in the spectrum. In the process, its particles, falling under electromagnetic influence, redistribute the energy of the incident wave in all directions. That is, particles serve as point sources of energy.

Daylight

Due to scattering, light coming from the sun changes color when passing through layers of atmospheres. The practical significance of scattering is to create daylight. If the Earth were deprived of an atmosphere, lighting would exist only in places where direct or reflected rays of the sun hit the surface. That is, the atmosphere is the source of illumination during the day. Thanks to it, it is light both in places inaccessible to direct rays and when the sun is hidden behind the clouds. It is scattering that gives the air color - we see the sky blue.

What else does solar radiation depend on? The turbidity factor should not be discounted. After all, radiation is weakened in two ways - by the atmosphere itself and water vapor, as well as various impurities. The dust level increases in the summer (as does the water vapor content in the atmosphere).

Total radiation

It refers to the total amount of radiation falling on the earth's surface, both direct and diffuse. Total solar radiation decreases during cloudy weather.

For this reason, in summer the total radiation is on average higher before noon than after it. And in the first half of the year - more than in the second.

What happens to the total radiation on the earth's surface? When it gets there, it is mostly absorbed by the top layer of soil or water and turns into heat, while part of it is reflected. The degree of reflection depends on the nature of the earth's surface. An indicator expressing the percentage of reflected solar radiation to the total amount falling on the surface is called surface albedo.

The concept of intrinsic radiation of the earth's surface refers to long-wave radiation emitted by vegetation, snow cover, upper layers of water and soil. The radiation balance of a surface is the difference between the amount absorbed and the amount emitted.

Effective radiation

It has been proven that counter radiation is almost always less than terrestrial radiation. Because of this, the surface of the earth suffers heat losses. The difference between the values ​​of the surface's own radiation and the atmospheric radiation is called effective radiation. This is actually a net loss of energy and, as a result, heat at night.

It also exists during the daytime. But during the day it is partially compensated or even covered by absorbed radiation. Therefore, the earth's surface is warmer during the day than at night.

On the geographical distribution of radiation

Solar radiation on Earth is distributed unevenly throughout the year. Its distribution is zonal in nature, with isolines (connecting points identical values) radiation flux are not at all identical to latitudinal circles. This discrepancy is caused by different levels of cloudiness and atmospheric transparency in different areas Globe.

The total solar radiation throughout the year is greatest in subtropical deserts with a partly cloudy atmosphere. It is much less in the forest areas of the equatorial belt. The reason for this is increased cloudiness. Towards both poles this indicator decreases. But in the region of the poles it increases again - in the northern hemisphere it is less, in the area of ​​​​snowy and partly cloudy Antarctica - more. Over the surface of the oceans, on average, solar radiation is less than over the continents.

Almost everywhere on Earth the surface has a positive radiation balance, that is, over the same time, the influx of radiation is greater than the effective radiation. The exceptions are the regions of Antarctica and Greenland with their ice plateaus.

Is global warming at risk?

But the above does not mean annual warming of the earth's surface. The excess absorbed radiation is compensated by heat leakage from the surface into the atmosphere, which occurs when the phase of water changes (evaporation, condensation in the form of clouds).

Thus, radiation equilibrium as such does not exist on the Earth's surface. But there is thermal equilibrium - the supply and loss of heat is balanced in different ways, including radiation.

Card balance distribution

At the same latitudes of the globe, the radiation balance is greater on the surface of the ocean than above the land. This can be explained by the fact that the layer that absorbs radiation in the oceans is thicker, while at the same time the effective radiation there is less due to the coldness of the sea surface compared to land.

Significant fluctuations in the amplitude of its distribution are observed in deserts. The balance there is lower due to high effective radiation in dry air and low cloud conditions. It is reduced to a lesser extent in areas of monsoon climate. In the warm season, cloudiness there is increased, and absorbed solar radiation is less than in other areas of the same latitude.

Of course, the main factor on which average annual solar radiation depends is the latitude of a particular area. Record “portions” of ultraviolet radiation go to countries located near the equator. This is Northeast Africa, its eastern coast, the Arabian Peninsula, the north and west of Australia, part of the islands of Indonesia, and the western coast of South America.

In Europe, the largest dose of both light and radiation is received by Turkey, southern Spain, Sicily, Sardinia, the islands of Greece, the coast of France (southern part), as well as parts of Italy, Cyprus and Crete.

What about us?

The total solar radiation in Russia is distributed, at first glance, unexpectedly. On the territory of our country, oddly enough, it is not the Black Sea resorts that hold the palm. The highest doses of solar radiation occur in the territories bordering China and Severnaya Zemlya. In general, solar radiation in Russia is not particularly intense, which is fully explained by our northern geographical location. Minimal amount sunlight goes to the northwestern region - St. Petersburg, along with the surrounding areas.

Solar radiation in Russia is inferior to that of Ukraine. There, the most ultraviolet radiation goes to Crimea and the territories beyond the Danube, with the Carpathians and the southern regions of Ukraine in second place.

The total (this includes both direct and diffuse) solar radiation falling on a horizontal surface is given by month in specially developed tables for different territories and is measured in MJ/m2. For example, solar radiation in Moscow ranges from 31-58 in the winter months to 568-615 in the summer.

About solar insolation

Insolation, or the amount of beneficial radiation falling on a sunlit surface, varies significantly in different geographic locations. Annual insolation is calculated per one square meter in megawatts. For example, in Moscow this value is 1.01, in Arkhangelsk - 0.85, in Astrakhan - 1.38 MW.

When determining it, it is necessary to take into account factors such as the time of year (in winter there is lower illumination and day length), the nature of the terrain (mountains can block the sun), weather conditions characteristic of the area - fog, frequent rains and cloudiness. The light-receiving plane can be oriented vertically, horizontally or obliquely. The amount of insolation, as well as the distribution of solar radiation in Russia, is presented as data grouped in a table by city and region, indicating geographic latitude.

All types of solar rays reach the earth's surface in three ways - in the form of direct, reflected and diffuse solar radiation.
Direct solar radiation- These are rays coming directly from the sun. Its intensity (effectiveness) depends on the height of the sun above the horizon: the maximum is observed at noon, and the minimum in the morning and evening; depending on the time of year: maximum - in summer, minimum - in winter; on the altitude of the area above sea level (higher in the mountains than on the plain); on the state of the atmosphere (air pollution reduces it). The spectrum of solar radiation depends on the height of the sun above the horizon (the lower the sun is above the horizon, the less ultraviolet rays).
Reflected solar radiation- These are the rays of the sun reflected by the earth or water surface. It is expressed as a percentage of reflected rays to their total flux and is called albedo. The magnitude of albedo depends on the nature of the reflecting surfaces. When organizing and conducting sunbathing, it is necessary to know and take into account the albedo of the surfaces on which sunbathing is carried out. Some of them are characterized by selective reflectivity. Snow completely reflects infrared rays, and ultraviolet rays to a lesser extent.

Scattered solar radiation formed as a result of the scattering of sunlight in the atmosphere. Air molecules and particles suspended in it (tiny droplets of water, ice crystals, etc.), called aerosols, reflect part of the rays. As a result of multiple reflections, some of them still reach the earth's surface; These are scattered rays of the sun. Mostly ultraviolet, violet and blue rays are scattered, which determines the blue color of the sky in clear weather. The proportion of scattered rays is high at high latitudes (in the northern regions). There the sun is low above the horizon, and therefore the path of the rays to the earth's surface is longer. On long way the rays encounter more obstacles and are scattered to a greater extent.

(http://new-med-blog.livejournal.com/204

Total solar radiation- all direct and diffuse solar radiation reaching the earth's surface. Total solar radiation is characterized by intensity. With a cloudless sky, the total solar radiation has a maximum value around noon, and throughout the year - in the summer.

Radiation balance
The radiation balance of the earth's surface is the difference between the total solar radiation absorbed by the earth's surface and its effective radiation. For the earth's surface
- the incoming part is absorbed direct and diffuse solar radiation, as well as absorbed counter radiation from the atmosphere;
- the consumable part consists of heat loss due to the earth’s own radiation.

The radiation balance may be positive(daytime, summer) and negative(at night, in winter); measured in kW/sq.m/min.
The radiation balance of the earth's surface is the most important component of the heat balance of the earth's surface; one of the main climate-forming factors.

Heat balance of the earth's surface- the algebraic sum of all types of heat inflow and outflow to the surface of land and ocean. The nature of the heat balance and its energy level determine the characteristics and intensity of most exogenous processes. The main components of the ocean heat balance are:
- radiation balance;
- heat consumption for evaporation;
- turbulent heat exchange between the ocean surface and the atmosphere;
- vertical turbulent heat exchange of the ocean surface with the underlying layers; And
- horizontal oceanic advection.

(http://www.glossary.ru/cgi-bin/gl_sch2.c gi?RQgkog.outt:p!hgrgtx!nlstup!vuilw)tux yo)

Solar radiation measurement.

Actinometers and pyrheliometers are used to measure solar radiation. The intensity of solar radiation is usually measured by its thermal effect and is expressed in calories per unit surface area per unit time.

(http://www.ecosystema.ru/07referats/slo vgeo/967.htm)

The intensity of solar radiation is measured using a Janiszewski pyranometer complete with a galvanometer or potentiometer.

When measuring total solar radiation, the pyranometer is installed without a shadow screen, while when measuring scattered radiation, it is installed with a shadow screen. Direct solar radiation is calculated as the difference between total and diffuse radiation.

When determining the intensity of incident solar radiation on a fence, the pyranometer is installed on it so that the perceived surface of the device is strictly parallel to the surface of the fence. If there is no automatic recording of radiation, measurements should be taken every 30 minutes between sunrise and sunset.

Radiation falling on the surface of the fence is not completely absorbed. Depending on the texture and color of the fence, some of the rays are reflected. The ratio of reflected radiation to incident radiation, expressed as a percentage, is called surface albedo and is measured by an albedometer P.K. Kalitina complete with galvanometer or potentiometer.

For greater accuracy, observations should be made under clear skies and with intense sunlight irradiating the fence.

(http://www.constructioncheck.ru/default.a spx?textpage=5)

The amount of direct solar radiation (S) reaching the earth's surface under cloudless sky conditions depends on the height of the sun and transparency. The table for three latitude zones shows the distribution of monthly amounts of direct radiation under cloudless skies (possible amounts) in the form of averaged values ​​for the central months of the seasons and the year.

The increased arrival of direct radiation in the Asian part is due to the higher transparency of the atmosphere in this region. High values ​​of direct radiation in summer in the northern regions of Russia are explained by a combination of high atmospheric transparency and long day length

Reduces the arrival of direct radiation and can significantly change its daily and annual cycle. However, under average cloudy conditions, the astronomical factor is predominant and, therefore, the maximum direct radiation is observed at the highest solar altitude.

In most of the continental regions of Russia in the spring and summer months, direct radiation in the afternoon hours is greater than in the afternoon. This is due to the development of convective clouds in the afternoon and a decrease in atmospheric transparency at this time of day compared to the morning hours. In winter, the ratio of pre- and afternoon radiation values ​​is the opposite - the pre-noon values ​​of direct radiation are lower due to the morning maximum of cloudiness and its decrease in the second half of the day. The difference between the before and afternoon direct radiation values ​​can reach 25–35%.

In the annual course, the maximum direct radiation occurs in June-July, with the exception of the regions Far East, where it shifts to May, and in the south of Primorye a secondary maximum is noted in September.
The maximum monthly amount of direct radiation on the territory of Russia is 45–65% of what is possible under cloudless skies, and even in the south of the European part it reaches only 70%. Minimum values ​​are observed in December and January.

The contribution of direct radiation to the total arrival under actual cloudy conditions reaches its maximum in the summer months and averages 50–60%. The exception is Primorsky Krai, where the largest contribution of direct radiation occurs in the autumn and winter months.

The distribution of direct radiation under average (actual) cloud conditions over the territory of Russia largely depends on. This leads to a noticeable disruption of the zonal distribution of radiation in individual months. This is especially evident in the spring. Thus, in April there are two maximums - one in the southern regions and the Amur region, the second in the north-east of Yakutia and on, which is also the result of a combination of high atmospheric transparency, high frequency of clear skies and day length.

The data shown on the maps refers to actual cloud conditions.

LECTURE 3

RADIATION BALANCE AND ITS COMPONENTS

Solar radiation that reaches the earth's surface is partially reflected from it and partially absorbed by the Earth. However, the Earth not only absorbs radiation, but also emits long-wave radiation into the surrounding atmosphere. The atmosphere, absorbing some of the solar radiation and most of the radiation from the earth's surface, itself also emits long-wave radiation. Most of this atmospheric radiation is directed towards the earth's surface. It is calledcounter radiation from the atmosphere .

The difference between the flows of radiant energy arriving at the active layer of the Earth and leaving it is calledradiation balance active layer.

The radiation balance consists from short-wave and long-wave radiation. It includes the following elements, called components of the radiation balance:direct radiation, diffuse radiation, reflected radiation (shortwave), radiation from the earth's surface, counter radiation from the atmosphere .

Let us consider the components of the radiation balance.

Direct solar radiation

The energy irradiance of direct radiation depends on the height of the Sun and the transparency of the atmosphere and increases with increasing altitude above sea level. Low-level clouds usually completely or almost do not transmit direct radiation.

The wavelengths of solar radiation reaching the earth's surface lie in the range of 0.29-4.0 microns. About half of its energy comes from phtosynthetically active radiation. In area PAR The weakening of radiation with decreasing altitude of the Sun occurs faster than in the region of infrared radiation. The arrival of direct solar radiation, as already indicated, depends on the height of the Sun above the horizon, varying both during the day and throughout the year. This determines the daily and annual cycle of direct radiation.

The change in direct radiation during a cloudless day (diurnal cycle) is expressed by a single-peak curve with a maximum at true solar noon. In summer, over land, the maximum may occur before noon, as the dustiness of the atmosphere increases towards noon.

As you move from the poles to the equator, the arrival of direct radiation at any time of the year increases, since the midday altitude of the Sun increases.

The annual course of direct radiation is most pronounced at the poles, since in winter there is no solar radiation here at all, and in summer its arrival reaches 900 W/m². In mid-latitudes, the maximum of direct radiation is sometimes observed not in summer, but in spring, since in the summer months, due to an increase in the content of water vapor and dust, the transparency of the atmosphere decreases. The minimum occurs in the period close to the winter solstice (December). At the equator, two maximums are observed, equal to approximately 920 W/m² on the days of the spring and autumn equinox, and two minimums (about 550 W/m²) on the days of the summer and winter solstice.

Scattered radiation

The maximum of scattered radiation is usually much less than the maximum of direct radiation. The higher the height of the Sun and the more polluted the atmosphere, the greater the flux of scattered radiation. Clouds that do not cover the Sun increase the arrival of scattered radiation compared to a clear sky. The dependence of the arrival of scattered radiation on cloudiness is complex. It is determined by the type and number of clouds, their vertical power and optical properties. The diffuse radiation of a cloudy sky can fluctuate by a factor of more than 10.

Snow cover, which reflects up to 70-90% of direct radiation, increases diffuse radiation, which then dissipates into the atmosphere. As the altitude of a location increases above sea level, scattered radiation under clear skies decreases.

Daily and annual cycle scattered radiation under clear skies generally corresponds to the course of direct radiation. However, in the morning, scattered radiation appears before sunrise, and in the evening it still arrives during the twilight period, that is, after sunset. In the annual course, the maximum of scattered radiation is observed in summer.

Total radiation

The sum of diffuse and direct radiation incident on a horizontal surface is calledtotal radiation .

It is the main component of the radiation balance. Its spectral composition, compared to direct and scattered radiation, is more stable and almost does not depend on the height of the Sun when it is more than 15°.

The ratio between direct and diffuse radiation in the composition of total radiation depends on the height of the Sun, cloudiness and atmospheric pollution. As the height of the Sun increases, the proportion of scattered radiation in a cloudless sky decreases. The more transparent the atmosphere, the lower 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 share of scattered radiation in the total radiation increases noticeably.

The arrival of total radiation in the presence of clouds varies within wide limits. Its greatest arrival is observed in clear skies or in light clouds that do not obscure the Sun.

On a daily and annual basis, changes in total radiation are almost directly proportional to changes in the altitude of the Sun. In a daily cycle, the maximum total radiation under a cloudless sky usually occurs at midday. In the annual course, the maximum of total radiation is usually observed in the northern hemisphere in June, and in the southern hemisphere in December.

Reflected radiation. Albedo

Part of the total radiation coming to the active layer of the Earth is reflected from it. The ratio of the reflected part of the radiation to the entire incoming total radiation is calledreflectivity , oralbedo (A) of a given underlying surface.

The albedo of a surface depends on its color, roughness, humidity and other properties.

Albedo of various natural surfaces (according to V. L. Gaevsky and M. I. Budyko)

The albedo of water surfaces at a solar altitude above 60° is less than the albedo of land, since the sun's rays, penetrating into the water, are largely absorbed and scattered in it. With a vertical incidence of rays A = 2-5%, with a solar height of less than 10° A = 50-70%. The large albedo of ice and snow causes a slower pace of spring in the polar regions and the preservation of eternal ice there.

Observations of albedo of land, sea and cloud cover are carried out from artificial satellites Earth. The albedo of the sea allows us to calculate the height of waves, the albedo of clouds characterizes their power, and the albedo of different land areas allows us to judge the degree of snow coverage of fields and the state of vegetation cover.

The albedo of all surfaces, especially water surfaces, depends on the height of the Sun: the lowest albedo occurs at midday, the highest in the morning and evening. This is due to the fact that at a low solar altitude, the proportion of scattered radiation in the total radiation increases, which, to a greater extent than direct radiation, is reflected from the rough underlying surface.

Long-wave radiation from the Earth and atmosphere

Terrestrial radiationsome less radiation absolute black body at the same temperature.

Radiation from the earth's surface occurs continuously. The higher the temperature of the radiating surface, the more intense its radiation. There is also continuous radiation from the atmosphere, which, absorbing part of the solar radiation and radiation from the earth's surface, itself emits long-wave radiation.

In temperate latitudes with a cloudless sky, atmospheric radiation is 280-350 W/m², and in the case of a cloudy sky it is 20-30% more. About 62-64% of this radiation is directed towards the earth's surface. Its arrival on the earth's surface constitutes counter radiation from the atmosphere. The difference between these two flows characterizes the loss of radiant energy by the active layer. This difference is calledeffective radiation Eef .

The effective radiation of the active layer depends on its temperature, air temperature and humidity, and cloud cover. With increasing temperature of the earth's surface, Eeff increases, and with increasing temperature and air humidity it decreases. Clouds especially influence the effective radiation, since cloud droplets emit almost the same as the active layer of the Earth. On average, Eeff at night and during the day with a clear sky at different points on the earth’s surface varies within 70-140 W/m².

Daily cycle effective radiation is characterized by a maximum at 12-14 hours and a minimum before sunrise.Annual course effective radiation in areas with a continental climate is characterized by a maximum in the summer months and a minimum in the winter. In areas with a marine climate, the annual variation of effective radiation is less pronounced than in areas located inland

Radiation from the earth's surface is absorbed by water vapor and carbon dioxide contained in the air. But the atmosphere largely transmits short-wave radiation from the Sun. This property of the atmosphere is called"greenhouse effect" , since the atmosphere acts like glass in greenhouses: glass allows the sun's rays to pass through well, heating the soil and plants in the greenhouse, but does not allow the thermal radiation of the heated soil to pass through well into the outside space. Calculations show that in the absence of an atmosphere, the average temperature of the Earth’s active layer would be 38°C lower than actually observed, and the Earth would be covered with eternal ice.

If the radiation inflow is greater than the outflow, then the radiation balance is positive and the active layer of the Earth heats up. With a negative radiation balance, this layer cools. The radiation balance is usually positive during the day and negative at night. Approximately 1-2 hours before sunset it becomes negative, and in the morning, on average 1 hour after sunrise, it becomes positive again. The course of the radiation balance during the day under clear skies is close to the course of direct radiation.

Studying the radiation balance 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 the crop, and the phase of plant development. To evaluate different methods for regulating temperature and soil moisture, evaporation and other quantities, the radiation balance of agricultural fields is determined for different types of vegetation cover.

Methods for measuring solar radiation and components of the radiation balance

To measure solar radiation fluxes, they are usedabsolute Andrelative methods and accordingly developed absolute and relative actinometric instruments. Absolute instruments are usually used only for calibration and verification of relative instruments.

Relative instruments are used for regular observations at a network of weather stations, as well as on expeditions and during field observations. Of these, the most widely used thermoelectric instruments are the actinometer, pyranometer and albedometer. The receiver of solar radiation in these devices are thermopiles composed of two metals (usually manganin and constantan). Depending on the intensity of radiation between the junctions of the thermopile, a temperature difference is created and an electric current of varying strength appears, which is measured by a galvanometer. To convert the galvanometer scale divisions into absolute units, conversion factors are used, which are determined for a given pair: actinometric device - galvanometer.

Thermoelectric actinometer (M-3) Savinov-Yanishevsky is used to measure direct radiation arriving at a surface perpendicular to the sun's rays.

Pyranometer (M-80M) Yanishevsky is used to measure the total and scattered radiation arriving on a horizontal surface.

During observations, the receiving part of the pyranometer is installed horizontally. To determine scattered radiation, the pyranometer is shaded from direct radiation by a shadow screen in the form of a round disk mounted on a rod at a distance of 60 cm from the receiving surface. When measuring total radiation, the shadow screen is moved to the side

Albedometer is a pyranometer, also adapted. For measuring reflected radiation. For this purpose, a device is used that allows you to rotate the receiving part of the device up (to measure direct radiation) and down (to measure reflected radiation). Having determined the total and reflected radiation with an albedometer, the albedo of the underlying surface is calculated. For field measurements, a traveling albedometer M-69 is used.

Thermoelectric balance meter M-10M. This device is used to measure the radiation balance of the underlying surface.

In addition to the instruments discussed, luxmeters are also used - photometric instruments for measuring illumination, spectrophotometers, various instruments for measuring PAR, etc. Many actinometric instruments are adapted for continuous recording of the components of the radiation balance.

An important characteristic of the solar radiation regime is the duration of sunshine. To determine it, useheliograph .

In field conditions, the most commonly used are pyranometers, walking albedometers, balance meters and lux meters. For observations among plants, hiking albedometers and lux meters, as well as special micropyranometers, are most convenient.