Available in various lengths. So, some are presented in the form of light, others - in the form of bringing warmth, while others are a whole group of rays invisible to the human eye (radio waves, ultraviolet, X-rays).
Short-range radio waves and visible light travel best through the Earth's atmosphere. and X-rays are absorbed by the air envelope. At the border, the intensity of solar radiation is constant and amounts to 1.35 kW / m2.
The sun is the only one and the warmth on the planet. Scattered and direct radiation are the main types of solar radiation. Rays passing through the existing layers of the atmosphere heat them up to an insignificant extent. The solar radiation reaching the Earth's surface, which is not scattered or absorbed in the air envelope, is called direct. The intensity of this radiation on the territory depends on the terrain: to the poles from the earth's equator, the flow decreases, the intensity decreases, especially with an increase in cloudiness and a decrease in transparency in the atmosphere.
Due to the fact that the air contains small dusty particles, water droplets, salt particles, crystals, individual rays coming from the luminary, colliding with these obstacles, scatter. Such solar radiation is called diffuse. About 25% of the total flux of absorbed rays turns into it. On a cloudless day, the scattered radiation is 0.07 kW / m2, in cloudy, cloudy weather - 0.5 kW / m2. With a decrease in the solstice altitude, an increase in cloudiness, a decrease in the transparency of the atmosphere, the proportion of this radiation increases. Studies show that at low latitudes, the fraction of scattered radiation is significantly lower than at temperate and high latitudes. Ambient natural light on a cloudy day is fully provided by these rays.
The total solar radiation is made up of all scattered and direct radiation that reaches the Earth. Its amount depends on various factors, including the length of the day, the transparency of the angle of incidence of the rays and cloudiness in the atmosphere. So, in tropical latitudes annual indicators of total radiation are about 200 kcal / cm2, in the polar zone - about 50 kcal / cm2.
In an insignificant amount, solar radiation is absorbed by impurities and molecules of gases in the atmosphere. In this case, the radiation that hits the Earth is partially absorbed by the surface of the planet, partially reflected, leaving the atmosphere back.
There is a quantity that characterizes the ratio of the reflected radiation to the incident on the Earth's surface - albedo. This indicator is expressed as a percentage. It should be noted that the albedo value covers a fairly wide range and depends on the territory. So, for the steppe and forest, this figure is about 13%, and on fresh snow cover it increases to 90%. A significant dependence of the albedo of the water surface on the angle of incidence of the rays is noted. With direct solar radiation and high altitude the standing of the Sun, the value of this indicator is about 3-4%, with a low standing - almost 100%. For scattered radiation, the albedo is about 8-10%. At the same time, there is practically no dependence on the height of the solstice.
As you know, the light of the Sun is the source of life on Earth, exerting a direct effect on the human body, thermal state, metabolic processes, functional activity of systems and organs, etc.
The intensity of the ultraviolet radiation reaching the surface also depends on the height of the solstice. When the height of the Sun is less than 25%, UV radiation, the most biologically active, does not reach the Earth.
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 ball of gas with a radius of 695300 km. The radius of the Sun is 109 times 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 are constantly moving, 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 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 is supplied to the Earth's surface. The Russian scientist wrote: “Give the best chef as much fresh air, sunshine, a whole river pure water, ask him to make you sugar, starch, fats and grains out of all this, and he will decide that you are laughing at him. But what seems absolutely fantastic to a person is unimpeded 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 them, 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 different reactions to the intensity of illumination, all forms of vegetation are divided into light-loving and shade-tolerant. Insufficient illumination in crops causes, for example, weak differentiation of tissues of the straw of grain crops. As a result, tissue strength and elasticity decrease, which often leads to crop lodging. In thickened corn crops, due to the low illumination of solar radiation, the formation of cobs on the plants is weakened.
Solar radiation affects chemical composition agricultural products. For example, the sugar content of beets and fruits, the protein content in the grain of wheat directly depends on the number of sunny days. The amount of oil in sunflower and flax seeds also increases with an increase in the arrival of solar radiation.
The illumination of the aboveground part of plants significantly affects the absorption of nutrients by the roots. In low light, the transfer of assimilates to the roots slows down, and as a result, biosynthetic processes in plant cells are inhibited.
Illumination also affects the appearance, distribution 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 spore germination, is most active at 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. The 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 damage. Under conditions of intense illumination, this pathogen increases its fertility.
Some diseases develop most actively with insufficient lighting, causing 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 (alternation of 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 by physiologists, the dependence of the transition of plants to generative development on a certain ratio of the length of day and night has been established. In this regard, cultures by photoperiodic reaction can be classified into groups: have a short day, the development of which is delayed when the duration of the day is more than 10 hours. A short day encourages the setting of flowers, while a long day prevents it. Such crops include soybeans, rice, millet, sorghum, corn, etc .;
a long day up to 12-13 hours., requiring continuous illumination for their development. Their development is accelerated when the length of the day is about 20 hours. These crops include rye, oats, wheat, flax, peas, spinach, clover, etc .;
length-neutral, the development of which does not depend on the length of the day, for example, tomato, buckwheat, legumes, rhubarb.
It was found that for the beginning of flowering of plants, a predominance of a certain spectral composition in the radiant flux is necessary. Short-day plants develop faster when blue-violet rays are at their maximum, and long-day plants are red. The duration of the daylight hours (astronomical length of the day) depends on the time of the year and geographic latitude... At the equator, the length of the day throughout the year is 12 hours ± 30 minutes. 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 autumnal equinox (23.09), the distribution of the length of the day is reversed. In the Northern Hemisphere, 22.06 has the longest day, the duration of which is 24 hours north of the Arctic Circle. The shortest day in the Northern Hemisphere is 22.12, and beyond the Arctic Circle in the winter months the Sun does not rise above the horizon. In middle latitudes, for example in Moscow, the length of the day varies from 7 to 17.5 hours throughout the year.
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 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 at high position Sun (summer, noon) and good transparency, direct solar radiation is 1.5 kcal / cm2 / min. This is the shortwave part of the spectrum. When the flow of direct solar radiation passes through the atmosphere, its weakening occurs, caused by the absorption (about 15%) and scattering (about 25%) of energy by gases, aerosols, clouds.
The flux of direct solar radiation falling on a horizontal surface is called insolation S= S sin ho- the vertical component of direct solar radiation.
S – the amount of heat received by the surface perpendicular to the beam ,
ho – the height of the sun, i.e. the angle formed by the sunbeam with a horizontal surface .
At the border of the atmosphere, the intensity of solar radiation isSo= 1,98 kcal / cm2 / min. - according to the international agreement of 1958. And it is called the solar constant. It would be like that at the surface if the atmosphere were absolutely transparent.
Rice. 2.1. The path of the sunbeam 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. Scattered radiation maximum + 1 kcal / cm2 / min. It is noted with a clear sky, if there are high clouds on it. With a cloudy sky, the spectrum of scattered radiation is similar to that of the sun. This is the shortwave part of the spectrum. Wavelength 0.17-4μm.
TOTAL RADIATIONQ- consists of scattered and direct radiation on a horizontal surface. Q= S+ D.
The ratio between direct and scattered radiation in the 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 less the fraction 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 total composition noticeably increases.
The light and heat received by plants from the Sun is the result of the action of the total solar radiation. Therefore, data on the amount 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 reaching earth surface, partially reflecting 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 state 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 the 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 the decrease in albedo, the absorbed radiation increases when the soil is moistened. 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 oncoming radiation of the atmosphere. Effective radiation. The earth's surface as a physical body with a temperature higher 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 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 practically 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 the oncoming radiation of the atmosphere (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 oncoming 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 transmits well the sun's rays, heating the soil and plants, but retains the thermal radiation of the heated soil and plants.
The difference between the intrinsic radiation of the Earth's surface and the oncoming radiation of the atmosphere is called effective radiation: Eef.
Eef = E3-Ea
On clear and slightly cloudy nights, the effective radiation is much greater than on cloudy ones, therefore, the nighttime cooling of the earth's surface is greater. During the day, it is blocked 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 of the amount of heat that it receives from absorbing solar radiation.
3. Spectral composition of radiation.
The sun, as a source of radiation, has a variety of emitted waves. Radiant energy fluxes along the 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 is practically between the wavelengths of 0.17 and 4 microns, and the spectrum of terrestrial and atmospheric radiation - from 4 to 120 microns. Hence the flows solar radiation(S, D, RK) refer to shortwave radiation, and radiation from the Earth (£ 3) and the atmosphere (Ea) - to longwave.
The solar radiation spectrum 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 solar radiation spectrum lies X-ray radiation, and beyond the infrared - radio emission from the Sun. At the upper limit of the atmosphere, the ultraviolet part of the spectrum accounts for about 7% of the energy of solar radiation, 46 - visible and 47% - infrared.
The radiation emitted by the Earth and the atmosphere is called far infrared radiation.
Biological action different types radiation to plants is different. Ultraviolet radiation slows down the growth processes, but accelerates the passage of the stages of the formation of reproductive organs in plants.
The importance of infrared radiation, which is actively absorbed by the water of the leaves and stems of plants, consists in 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.
The visible part of the solar spectrum, firstly, it creates illumination. Secondly, the so-called physiological radiation (A, = 0.35 ... 0.75 microns), which is absorbed by the pigments of the leaf, almost coincides with the area of visible radiation (covering partly the area of ultraviolet radiation). Its energy has an important regulatory and energy value 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.
Going through earthly atmosphere, solar radiation is attenuated by 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 traversed by the sunbeam in the atmosphere is not the same. With a decrease in altitude, the ultraviolet part of the radiation decreases especially strongly, the visible part is slightly 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 air density at each point in the atmosphere, caused by the formation and destruction of certain "clusters" (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 scattering intensity 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 scattered the rays. For example, violet rays are scattered 14 times stronger 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 the Rayleigh law:
k = s /Y4 ,
where C is a coefficient depending on the number of gas molecules per unit volume; X is the scattered wavelength.
Because 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, scattered radiation is richer in photosynthetically active rays than direct radiation.
In air containing impurities (small water droplets, ice crystals, dust particles, etc.), the scattering is the same for all areas of visible radiation. Therefore, the sky becomes whitish (haze appears). Cloudy elements (large droplets and crystals) do not scatter the sun's rays at all, but reflect them diffusely. As a result, the 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
the part located in the wavelength interval 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, blue and violet.
The assimilation of solar radiation energy by plant leaves is selective (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 on the region of yellow-green rays (the Sun's disk is yellow). When the Sun is at the horizon, the distant red rays (the sun's disk is red) have the maximum energy. Therefore, the energy of direct sunlight is little involved in the process of photosynthesis.
Since the PAR is one of the critical factors the productivity of agricultural plants, information on the amount of incoming PAR, accounting for its distribution over the territory and in time are of great practical importance.
The intensity of the PAR 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 the data on the arrival of direct, scattered or total radiation using the coefficients proposed by H. G. Tooming and:
Qfar = 0.43 S"+0.57 D);
maps of distribution of monthly and annual amounts of Pharma on the territory of Russia were compiled.
To characterize the degree of use of PAR by crops, the efficiency factor of the PAR 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 values KPIFAR 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 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 consumable 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 - Eef.
For night time, the radiation balance equation has the following form:
B = Ea - E3, or B = -Eef.
If the arrival of radiation is greater than the consumption, then the radiation balance is positive and the active surface * heats up. With a negative balance, it cools down. 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 in the warm season.
The radiation balance of the earth's surface significantly affects the temperature distribution in the soil and the surface layer of the atmosphere, as well as the processes of evaporation and snow melting, the formation of fogs and frosts, and changes in properties. 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 the assessment of various methods of regulating soil temperature and moisture, evaporation, on which the growth and development of plants, the formation of the crop, its quantity and quality depend.
Mulching (covering the soil with a thin layer of peat chips, rotted manure, sawdust, etc.), covering the soil with plastic wrap, and irrigation are effective agronomic methods of influencing the radiation, and, consequently, the thermal regime of the active surface. 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 gives off radiation into the atmosphere, thereby regulating the thermal regime of the adjacent layers of air and underlying layers of soil, water, vegetation.
SOLAR RADIATION
SOLAR RADIATION- electromagnetic and corpuscular radiation of the Sun. Electromagnetic radiation travels in the form of electromagnetic waves at the speed of light and penetrates the earth's atmosphere. Solar radiation reaches the earth's surface in the form of direct and scattered radiation.
Solar radiation is the main source of energy for all physical and geographical processes occurring on the earth's surface and in the atmosphere (see Insolation). Solar radiation is usually measured by its thermal effect and is expressed in calories per unit surface per unit of time. In total, the Earth receives from the Sun less than one two billionth of its radiation.
The spectral range of the Sun's electromagnetic radiation is very wide - from radio waves to X-rays - but its maximum intensity falls on the visible (yellow-green) part of the spectrum.
There is also a corpuscular part of solar radiation, consisting mainly of protons moving from the Sun at speeds of 300-1500 km / s (solar wind). During solar flares, high-energy particles are also formed (mainly protons and electrons), which form the solar component of cosmic rays.
The energy contribution of the corpuscular component of solar radiation to its total intensity is small in comparison with the electromagnetic one. Therefore, in a number of applications, the term "solar radiation" is used in a narrow sense, meaning only its electromagnetic part.
The amount of solar radiation depends on the height of the sun, the season, the transparency of the atmosphere. Actinometers and pyrheliometers are used to measure solar radiation. The intensity of solar radiation is usually measured by its thermal effect and is expressed in calories per unit surface per unit of time.
Solar radiation strongly affects the Earth only during the daytime, of course - when the Sun is above the horizon. Also, solar radiation is very strong near the poles, during the polar days, when the Sun is above the horizon even at midnight. However, in winter in the same places, the Sun does not rise above the horizon at all, and therefore does not affect the region. Solar radiation is not blocked by clouds, and therefore all the same goes to the Earth (when the Sun is directly above the horizon). Solar radiation is a combination of the bright yellow color of the Sun and heat; heat also passes through the clouds. Solar radiation is transmitted to the Earth through radiation, and not by thermal conduction.
The amount of radiation received by a celestial body depends on the distance between the planet and the star - when the distance is doubled, the amount of radiation coming from the star to the planet is fourfold (proportional to the square of the distance between the planet and the star). Thus, even small changes in the distance between the planet and the star (depending on the eccentricity of the orbit) lead to a significant change in the amount of radiation entering the planet. The eccentricity of the earth's orbit is also not constant - over the millennia, it changes, periodically forming an almost perfect circle, sometimes the eccentricity reaches 5% (currently it is 1.67%), that is, at perihelion, the Earth is currently receiving at 1,033 more solar radiation than in aphelion, and with the greatest eccentristitis - more than 1.1 times. However, much more strongly the amount of incoming solar radiation depends on the changes of the seasons - at present, the total amount of solar radiation entering the Earth remains practically unchanged, but at latitudes 65 N (latitude of the northern cities of Russia, Canada) in the summer the amount of incoming solar radiation more than 25% more than in winter. This is due to the fact that the Earth is tilted at an angle of 23.3 degrees in relation to the Sun. Winter and summer changes are mutually compensated, but nevertheless, as the latitude of the observation site increases, the gap between winter and summer becomes more and more, so, at the equator, there is no difference between winter and summer. On the other hand, beyond the Arctic Circle, solar radiation is very high in summer and very little in winter. This shapes the climate on Earth. In addition, periodic changes in the eccentricity of the Earth's orbit can lead to the emergence of various geological eras: for example,
The energy emitted by the sun is called solar radiation. When entering the Earth, most of the solar radiation turns into heat.
Solar radiation is practically the only source of energy for the Earth and the atmosphere. Compared to solar energy, the value of other energy sources for the Earth is negligible. For example, the temperature of the Earth, on average, increases with depth (approximately 1 ° C for every 35 m). Due to this, the surface of the Earth receives some heat from the interior. It is estimated that, on average, 1 cm 2 of the earth's surface receives about 220 J per year from the interior of the earth. This amount is 5,000 times less than the heat received from the Sun. The Earth receives a certain amount of heat from stars and planets, but it is also many times (approximately 30 million) less than the heat coming from the Sun.
The amount of energy sent by the Sun to Earth is enormous. Thus, the power of the solar radiation flux entering an area of 10 km 2 is 7-9 kW in summer, cloudless (taking into account the weakening of the atmosphere). This is more than the capacity of the Krasnoyarsk hydroelectric power station. The amount of radiant energy coming from the Sun in 1 second to an area of 15 × 15 km (this is less than the area of Leningrad) in the midday hours in summer exceeds the capacity of all power plants of the disintegrated USSR (166 million kW).
Figure 1 - The sun is a source of radiation
> Types of solar radiation
In the atmosphere, solar radiation on its way to the earth's surface is partially absorbed, and partially scattered and reflected from clouds and the earth's surface. Three types of solar radiation are observed in the atmosphere: direct, scattered and total.
Direct solar radiation- radiation coming to the earth's surface directly from the solar disk. Solar radiation spreads 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 Earth in the form of a beam of parallel rays emanating from infinity, as it were. Even the whole Earth on the whole, it is so small in comparison with the distance to the Sun that all the solar radiation falling on it, without a noticeable error, can be considered a beam of parallel rays.
Only direct radiation reaches the upper boundary of the atmosphere. About 30% of the radiation falling on the Earth is reflected into outer space. Oxygen, nitrogen, ozone, carbon dioxide, water vapor (clouds) and aerosol particles absorb 23% of direct solar radiation in the atmosphere. Ozone absorbs ultraviolet and visible radiation. Despite the fact that its content in the air is very small, it absorbs all the ultraviolet part of the radiation (this is about 3%). Thus, it is not observed at all near the earth's surface, which is very important for life on Earth.
Direct solar radiation is also scattered on its way through the atmosphere. A particle (drop, crystal or molecule) of air, located in the path of an electromagnetic wave, continuously "extracts" energy from the incident wave and re-radiates it in all directions, becoming an energy emitter.
About 25% of the energy of the total flow of solar radiation passing through the atmosphere is scattered by molecules of atmospheric gases and aerosol and turns into scattered solar radiation in the atmosphere. Thus diffuse solar radiation- solar radiation scattered in the atmosphere. Scattered radiation comes to the earth's surface not from the solar disk, but from the entire firmament. Scattered radiation differs from a straight line in spectral composition, since beams of different wavelengths are scattered to different degrees.
Since the primary source of scattered radiation is direct solar radiation, the scattered radiation flux depends on the same factors that affect the direct radiation flux. In particular, the flux of scattered radiation increases as the height of the Sun increases and vice versa. It also increases with an increase in the number of scattering particles in the atmosphere, i.e. with a decrease in the transparency of the atmosphere, and decreases with altitude above sea level due to a decrease in the amount of scattering particles in the overlying layers of the atmosphere. Cloudiness and snow cover have a very large effect on scattered radiation, which, due to the scattering and reflection of direct and scattered radiation falling on them and their repeated scattering in the atmosphere, can increase the scattered solar radiation several times.
Scattered radiation substantially complements direct solar radiation and significantly increases the flow of solar energy to the earth's surface. Its role is especially great in winter at high latitudes and in other regions with increased cloudiness, where the fraction of scattered radiation can exceed the fraction of a straight line. For example, in the annual amount of solar energy, scattered radiation accounts for 56% in Arkhangelsk, and 51% in St. Petersburg.
Total solar radiation is the sum of the fluxes of direct and scattered radiation entering the horizontal surface. Before sunrise and after sunset, as well as in the daytime with continuous clouds, the total radiation is completely, and at low altitudes of the Sun it mainly consists of scattered radiation. In a cloudless or slightly cloudy sky, with an increase in the height of the Sun, the proportion of direct radiation in the total composition rapidly increases and in the daytime its flux is many times greater than the flux of scattered radiation. Cloudiness, on average, weakens the total radiation (by 20-30%), however, with partial clouds that do not cover the solar disk, its flux can be greater than with a cloudless sky. Snow cover significantly increases the total radiation flux by increasing the scattered radiation flux.
The total radiation falling on the earth's surface is mostly absorbed by the top layer of the soil or by a thicker layer of water (absorbed radiation) and turns into heat, and is partially reflected (reflected radiation).
All types of sunlight reach the earth's surface in three ways - in the form of direct, reflected and scattered solar radiation.
Direct solar radiation- these are rays coming directly from the sun. Its intensity (efficiency) depends on the height of the sun above the horizon: the maximum is observed at noon, and the minimum is observed in the morning and evening; from the season: maximum - in summer, minimum - in winter; from the height of the terrain above sea level (higher in the mountains than on the plain); on the state of the atmosphere (air pollution reduces it). The solar radiation spectrum also depends on the height of the sun above the horizon (the lower the sun is above the horizon, the less ultraviolet rays).
Reflected solar radiation- these are the rays of the sun, reflected by the earth or water surface. It is expressed as a percentage of the reflected rays to their total flux and is called albedo. The albedo value depends on the nature of the reflective surfaces. When organizing and carrying out sunbathing, it is necessary to know and take into account the albedo of the surfaces on which sunbathing is carried out. Some of them are characterized by selective reflectivity. Snow fully reflects infrared rays, and ultraviolet rays to a lesser extent.
Scattered solar radiation formed by the scattering of sunlight in the atmosphere. Air molecules and particles suspended in it (the smallest droplets of water, ice crystals, etc.), called aerosols, reflect part of the rays. As a result of multiple reflections, some of them still reach the earth's surface; these are the scattered rays of the sun. Mainly ultraviolet, violet and blue rays are scattered, which determines the blue color of the sky in clear weather. The specific gravity of scattered rays is high in high latitudes (in the northern regions). There the sun stands low above the horizon, and therefore the path of the rays to the earth's surface is longer. On a long path, the rays meet more obstacles and are more scattered.
(http://new-med-blog.livejournal.com/204
Total solar radiation- all direct and scattered solar radiation entering the earth's surface. Total solar radiation is characterized by intensity. With a cloudless sky, the total solar radiation has a maximum value around noon, and during the year - in summer.
Radiation balance
The radiation balance of the earth's surface is the difference between the total solar radiation absorbed by the earth's surface and its effective radiation. For the earth's surface
- the incoming part is the absorbed direct and scattered solar radiation, as well as the absorbed counter radiation of the atmosphere;
- the consumable part consists of heat loss due to the own radiation of the earth's surface.
The radiation balance can be positive(daytime, summertime) and negative(at night, in winter); measured in kW / m2 / min.
The radiation balance of the earth's surface is the most important component of the heat balance of the earth's surface; one of the main climate-forming factors.
Thermal balance of the earth's surface- the algebraic sum of all types of heat input and expenditure on the surface of land and ocean. The nature of the heat balance and its energy level determine the characteristics and intensity of most exogenous processes. The main components of the heat balance of the ocean are:
- radiation balance;
- heat consumption for evaporation;
- turbulent heat exchange between the ocean surface and the atmosphere;
- vertical turbulent heat exchange of the ocean surface with the underlying layers; and
- horizontal oceanic advection.
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Measurement of solar radiation.
Actinometers and pyrheliometers are used to measure solar radiation. The intensity of solar radiation is usually measured by its thermal effect and is expressed in calories per unit surface per unit of time.
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The measurement of the intensity of solar radiation is carried out with a Yanishevsky pyranometer complete with a galvanometer or potentiometer.
When measuring the total solar radiation, the pyranometer is installed without a shadow screen, while measuring scattered radiation with a shadow screen. Direct solar radiation is calculated as the difference between total and scattered radiation.
When determining the intensity of incident solar radiation on the fence, the pyranometer is installed on it so that the perceived surface of the device is strictly parallel to the surface of the fence. In the absence of automatic recording of radiation, measurements should be made 30 minutes later between sunrise and sunset.
Radiation falling on the surface of the fence is not completely absorbed. Depending on the texture and color of the fence, some of the rays are reflected. The ratio of reflected radiation to incident radiation, expressed as a percentage, is called surface albedo and is measured by P.K. Kalitina complete with galvanometer or potentiometer.
For greater accuracy, observation should be carried out with a clear sky and with intense solar irradiation of the fence.
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