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 itself emits long-wave radiation into the surrounding atmosphere. The atmosphere, absorbing some of the solar radiation and most of the radiation of the earth's surface, itself also emits long-wave radiation. Most of this radiation of the atmosphere is directed towards the earth's surface. It is calledcounter-radiation of the atmosphere .
The difference between the fluxes of radiant energy coming to the active layer of the Earth and the fluxes of radiant energy leaving it is calledradiation balance active layer.
The radiation balance consists of from shortwave and longwave radiation. It includes the following elements, called components of the radiation balance:direct radiation, scattered radiation, reflected radiation (shortwave), radiation from the earth's surface, counter radiation from the atmosphere .
Consider the components of the radiation balance.
Straight solar radiation
The energetic illumination 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 hardly transmit direct radiation.
The wavelengths of solar radiation reaching the earth's surface are in the range of 0.29-4.0 microns. About half of her energy comes from phthosynthetically active radiation... In the area of PAR the weakening of radiation with decreasing solar altitude occurs faster than in the infrared radiation. The arrival of direct solar radiation, as already indicated, depends on the height of the Sun above the horizon, which changes both during the day and during the year. This determines the daily and annual variation of direct radiation.
The change in direct radiation during a cloudless day (diurnal variation) is expressed by a unimodal curve with a maximum at true solar noon. In summer, over land the maximum can come before noon, since the dustiness of the atmosphere increases by noon.
When moving from the poles to the equator, the arrival of direct radiation at any time of the year increases, since this increases the midday height of the Sun.
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 falls on a period close to the day of the winter solstice (December). At the equator, there are two peaks equal to about 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 solstices.
Scattered radiation
The maximum of scattered radiation is usually much less than the maximum of a straight line. The greater the height of the Sun and the greater the pollution of 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 amount of clouds, their vertical power and optical properties. Scattered radiation from a cloudy sky can fluctuate more than 10 times.
Snow cover, which reflects up to 70-90% of direct radiation, increases the scattered radiation, which is then scattered in the atmosphere. With an increase in the altitude of a place above sea level, scattered radiation decreases with a clear sky.
Diurnal and annual variation scattered radiation with a clear sky generally corresponds to the course of direct radiation. However, in the morning, scattered radiation appears even before the sun rises, and in the evening it still arrives during twilight, i.e. after sunset. In the annual course, the maximum of scattered radiation is observed in summer.
Total radiation
The sum of scattered and direct radiation falling on a horizontal surface is calledtotal radiation .
It is the main component of the radiation balance. Its spectral composition, in comparison with 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 scattered radiation in the total radiation depends on the height of the Sun, cloudiness and atmospheric pollution. With an increase in the height of the Sun, the fraction of scattered radiation in a cloudless sky decreases. The more transparent the atmosphere, the less the fraction of scattered radiation. With continuous dense clouds 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 arrival of total radiation in the presence of cloud cover varies within wide limits. Its greatest arrival is observed with a clear sky or with a slight cloudiness that does not cover the Sun.
In the diurnal and annual variations, changes in total radiation are almost directly proportional to changes in the height of the Sun. In the diurnal course, the maximum total radiation in a cloudless sky usually falls at noon. In the annual course, the maximum total radiation is observed in the northern hemisphere, usually in June, in the southern - 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 total incoming total radiation is calledreflectivity , oralbedo (A) of the underlying surface.
The albedo of a surface depends on its color, roughness, moisture content and other properties.
Albedo of various natural surfaces (according to V.L. Gaevsky and M.I.Budyko)
Surface | Albedo,% | Surface | Albedo,% |
Fresh dry snow | 80-95 | Fields of rye and wheat | 10-25 |
Contaminated snow | 40-50 | Potato fields | 15-25 |
Sea ice | 30-40 | Cotton fields | 20-25 |
Dark soils | 5-15 | Meadows | 15-25 |
Dry clay soils | 20-35 | Dry steppe | 20-30 |
The albedo of water surfaces at a height of the Sun over 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 steep incidence of the rays, A = 2-5%, with the Sun's height less than 10 ° A = 50-70%. The large albedo of ice and snow is responsible for the slower course of spring in the polar regions and the preservation of eternal ice there.
Observations of the albedo of land, sea and cloud cover are carried out from artificial satellites Earth. The albedo of the sea makes it possible to calculate the height of the waves, the albedo of clouds characterizes their thickness, and the albedo of different land areas makes it possible to judge the degree of snow cover of fields and the state of the vegetation cover.
The albedo of all surfaces, especially water, depends on the height of the Sun: the lowest albedo occurs at noon hours, and the highest in the morning and evening. This is due to the fact that at a low altitude of the Sun in the composition of the total radiation, the fraction of scattered radiation increases, which in to a greater extent than direct radiation is reflected from the rough underlying surface.
Long-wave radiation of the Earth and the atmosphere
Terrestrial radiationslightly less blackbody radiation at the same temperature.
Radiation from the earth's surface occurs continuously. The higher the temperature of the emitting surface, the more intense its radiation. Also, the atmosphere is constantly radiating, 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% higher. About 62-64% of this radiation is directed towards the earth's surface. Its arrival on the earth's surface is the counter radiation of 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, on air temperature and humidity, as well as on cloudiness. With an increase in the temperature of the earth's surface, Eef increases, and with an increase in temperature and humidity, it decreases. Clouds especially affect the effective radiation, since cloud droplets radiate in almost the same way as the active layer of the Earth. On average, Eef 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 rate effective radiation is characterized by a maximum at 12-14 hours and a minimum before sunrise.Annual move 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 maritime climate, the annual course of effective radiation is less pronounced than in areas located in the interior of the continent.
Radiation from the earth's surface is absorbed by water vapor and carbon dioxide contained in the air. But the short-wave radiation of the Sun is largely passed through by the atmosphere. This property of the atmosphere is called"Greenhouse effect" , since the atmosphere in this case acts like glass in greenhouses: glass passes the sun's rays well, heating the soil and plants in the greenhouse, but poorly passes the thermal radiation of the heated soil into the outer space. Calculations show that in the absence of an atmosphere, the average temperature of the active layer of the Earth would be 38 ° C lower than the actual temperature, and the Earth would be covered with eternal ice.
If the arrival of radiation is greater than the consumption, 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 with a clear sky is close to the course of direct radiation.
The study of 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 crop structure, and the phase of plant development. To assess various methods of regulating soil temperature and moisture, evaporation and other quantities, the radiation balance of agricultural fields is determined for various types of vegetation cover.
Methods for measuring solar radiation and components of the radiation balance
To measure solar radiation fluxes,absolute 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 meteorological stations, as well as in expeditions and in field observations. The most widely used of them are thermoelectric devices: actinometer, pyranometer and albedometer. Thermopiles composed of two metals (usually manganin and constantan) serve as a receiver for solar radiation in these devices. Depending on the radiation intensity, a temperature difference is created between the thermopile junctions and an electric current of varying strength arises, which is measured by a galvanometer. To convert the divisions of the galvanometer scale into absolute units, conversion factors are used, which are determined for this pair: actinometric device - galvanometer.
Thermoelectric actinometer (M-3) Savinov - Yanishevsky is used to measure direct radiation coming to the 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 the scattered radiation, the pyranometer is shaded from direct radiation by a shadow screen in the form of a round disk fixed on a rod at a distance of 60 cm from the receiving surface. When measuring the total radiation, the shadow screen is retracted to the side
Albedometer is a pyranometer fitted as well. For measuring reflected radiation. For this, a device is used that allows the receiving part of the device to be turned up (for measuring a straight line) and down (for measuring reflected radiation). Having determined the total and reflected radiation by the 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 devices considered, luxmeters are also used - photometric devices for measuring illumination, spectrophotometers, various devices for measuring the PAR, etc. Many actinometric devices are adapted for continuous recording of the components of the radiation balance.
An important characteristic of the solar radiation regime is the duration of the sunshine. To determine it isheliograph .
In the field, pyranometers, travel albedometers, balance meters and lux meters are most often used. For observations among plants, the most convenient walking albedometers and luxmeters, as well as special micropyranometers.
Solar radiation
Solar radiation
electromagnetic radiation emanating from the sun and entering the earth's atmosphere. The wavelengths of solar radiation are concentrated in the range from 0.17 to 4 microns with a max. at a wavelength of 0.475 microns. OK. 48% of the energy of solar radiation is in the visible part of the spectrum (wavelengths from 0.4 to 0.76 microns), 45% - on the infrared (more than 0.76, microns), and 7% - on the ultraviolet (less than 0.4 μm). Solar radiation - main. a source of energy for processes in the atmosphere, ocean, biosphere, etc. It is measured in units of energy per unit area per unit of time, for example. W / m². Solar radiation at the upper boundary of the atmosphere on Wed. distance of the Earth from the Sun is called solar constant and is approx. 1382 W / m². Passing through the earth's atmosphere, solar radiation changes in intensity and spectral composition due to absorption and scattering by air particles, gas impurities and aerosols. Near the Earth's surface, the spectrum of solar radiation is limited to 0.29–2.0 microns, and the intensity is significantly reduced depending on the content of impurities, altitude and cloudiness. Direct radiation reaches the earth's surface, weakened when passing through the atmosphere, as well as scattered radiation formed when a straight line is scattered in the atmosphere. Part of the direct solar radiation is reflected from the earth's surface and clouds and goes into space; scattered radiation also partially escapes into space. The rest of the solar radiation in the main. turns into heat, heating the earth's surface and partly the air. Solar radiation, t. Arr., Is one of the main. components of the radiation balance.
Geography. Modern illustrated encyclopedia. - M .: Rosman. Edited by prof. A.P. Gorkina. 2006 .
See what "solar radiation" is in other dictionaries:
Electromagnetic and corpuscular radiation of the Sun. Electromagnetic radiation covers the wavelength range from gamma radiation to radio waves, its energy maximum falls on the visible part of the spectrum. The corpuscular component of the solar ... ... Big encyclopedic Dictionary
solar radiation- The total flux of electromagnetic radiation emitted by the Sun and hitting the Earth ... Geography Dictionary
This term has other meanings, see Radiation (disambiguation). This article is missing links to sources of information. Information must be verifiable, otherwise it can be called into question ... Wikipedia
All processes on the surface of the globe, whatever they may be, have solar energy as their source. Are purely mechanical processes being studied, chemical processes in air, water, soil, physiological processes or whatever ... ... Encyclopedic Dictionary of F.A. Brockhaus and I.A. Efron
Electromagnetic and corpuscular radiation of the Sun. Electromagnetic radiation covers the wavelength range from gamma radiation to radio waves, its energy maximum falls on the visible part of the spectrum. The corpuscular component of the solar ... ... encyclopedic Dictionary
solar radiation- Saulės spinduliuotė statusas T sritis fizika atitikmenys: angl. solar radiation vok. Sonnenstrahlung, f rus. solar radiation, n; solar radiation, f; solar radiation, n pranc. rayonnement solaire, m ... Fizikos terminų žodynas
solar radiation- Saulės spinduliuotė statusas T sritis ekologija ir aplinkotyra apibrėžtis Saulės atmosferos elektromagnetinė (infraraudonoji 0.76 nm sudaro 45%, matomoji 0.38–0.76 nm - 48%, ultravioletinė 0.38 nm - 7%) gama kvantų ir ... ... Ekologijos terminų aiškinamasis žodynas
Radiation of the Sun of electromagnetic and corpuscular nature. S. p. the main source of energy for most of the processes occurring on Earth. Corpuscular S. p. consists mainly of protons with speeds of 300 1500 ... ... Great Soviet Encyclopedia
Email magn. and corpuscular radiation of the Sun. Email magn. radiation covers the range of wavelengths from gamma radiation to radio waves, its energetic. the maximum falls on the visible part of the spectrum. Corpuscular component S. of the river. consists of Ch. arr. from… … Natural science. encyclopedic Dictionary
direct solar radiation- Solar radiation coming directly from the solar disk ... Geography Dictionary
Books
- Solar radiation and the Earth's climate, Fedorov Valery Mikhailovich. The book presents the results of studies of variations in the Earth's insolation associated with celestial-mechanical processes. Low-frequency and high-frequency changes in the solar climate are analyzed ...
The energy illumination created by radiation coming to the Earth directly from the solar disk in the form of a beam of parallel solar rays is called direct solar radiation.
Direct solar radiation arriving at the upper boundary of the atmosphere varies over time within a small range, therefore it is called the solar constant (S0). With an average distance from the Earth to the Sun of 149.5 106 km, it is about 1400 W / m2.
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.
According to the Bouguer weakening law direct solar radiation arriving at the Earth's surface with a vertical (perpendicular) incidence of rays,
Formula
where? - coefficient of transparency of the atmosphere; m is the number of optical masses of the atmosphere.
The weakening of the solar flux in the atmosphere depends on the height of the Sun above the Earth's horizon and the transparency of the atmosphere. The lower its height above the horizon, the more the optical masses of the atmosphere passes the sunbeam. For one optical mass of the atmosphere take the mass that the rays pass at the position of the Sun at the zenith (Fig. 3.1).
Figure 3.1. Diagram of the path of the sunbeam in the atmosphere at different heights of the Sun(available by downloading the full version of the tutorial)
table(available by downloading the full version of the tutorial)
The farther the sun's rays travel through the atmosphere, the stronger their absorption and scattering, and the more their intensity changes.
Transparency coefficient depends on the content of water vapor and aerosols in the atmosphere: the more there are, the lower the transparency coefficient for the same number of passable optical masses. On average for the entire radiation flux in a perfectly clean atmosphere? at sea level it is about 0.9, in actual atmospheric conditions - 0.70-0.85, in winter it is slightly higher than in summer.
The arrival of direct radiation on the earth's surface depends on the angle of incidence of the sun's rays... The flux of direct solar radiation falling on a horizontal surface is called insolation:
Formula(available by downloading the full version of the tutorial)
where h0 is the height of the sun
The energetic illumination of direct radiation depends on the height of the Sun and the transparency of the atmosphere and increases with increasing altitude above sea level. In the main agricultural regions of Russia in the summer, the midday values of the irradiance of direct radiation are in the range of 700-900 W / m2. At an altitude of 1 km, the increase is 70-140 W / m2. At an altitude of 4-5 km, the illumination of direct radiation exceeds 1180 W / m2. Low-level clouds usually do not allow direct radiation to pass through almost completely.
The arrival of direct solar radiation depends on the height of the sun above the horizon, which changes both during the day and throughout the year. This determines the diurnal and annual variation of direct radiation.
The change in direct radiation during a cloudless day (diurnal variation) is expressed by a unimodal curve with a maximum at true solar noon. In summer, over land the maximum can come before noon, since the dustiness of the atmosphere increases by noon.
Annual variation of direct radiation it is most pronounced at the poles, since in winter there is no solar radiation at all, and in summer its arrival reaches 900 W / m2. In middle 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 falls on a period close to the day winter solstice(December). At the equator, there are two peaks equal to about 920 W / m2. on the days of the spring and autumn equinox, and two minimums (about 55 W / m2) on the days of the summer and winter solstices.
Download full version textbook (with pictures, formulas, maps, diagrams and tables) in one file in MS Office Word format
A bright luminary heats us up with hot rays and makes us think about the significance of radiation in our life, its benefits and harms. What is solar radiation? Lesson school physics invites us to get started with the concept of electromagnetic radiation in general. This term denotes another form of matter - different from matter. This includes both visible light and the spectrum that the eye cannot see. That is, X-rays, gamma rays, ultraviolet and infrared.
Electromagnetic waves
In the presence of a source-emitter of radiation, its electromagnetic waves propagate in all directions at the speed of light. These waves, like any others, have certain characteristics. These include vibration frequency and wavelength. Any body whose temperature differs from absolute zero has the property to emit radiation.
The sun is the main and most powerful source of radiation near our planet. In turn, the Earth (its atmosphere and surface) itself emits radiation, but in a different range. Observing temperature conditions on the planet for long periods of time gave rise to a hypothesis about the balance of the amount of heat received from the Sun and given to outer space.
Sun radiation: spectral composition
The vast majority (about 99%) of solar energy in the spectrum lies in the wavelength range from 0.1 to 4 microns. The remaining 1% is longer and shorter rays, including radio waves and X-rays. About half of the sun's radiant energy falls on the spectrum that we perceive with our eyes, about 44% - on infrared radiation, 9% - for ultraviolet. How do we know how solar radiation is divided? The calculation of its distribution is possible thanks to research from space satellites.
There are substances that can enter a special state and emit additional radiation in a different wavelength range. For example, there is a glow when low temperatures not typical for the emission of light by the given substance. This type of radiation, called luminescent radiation, does not lend itself to the usual principles of thermal radiation.
The phenomenon of luminescence occurs after a substance has absorbed a certain amount of energy and a transition to another state (the so-called excited state), which is energetically higher than at the substance's own temperature. Luminescence appears during the reverse transition - from an excited state to a familiar state. In nature, we can observe it in the form of night sky glow and aurora borealis.
Our luminary
The energy of the sun's rays is almost the only source of heat for our planet. The intrinsic radiation coming from its depths to the surface has an intensity that is about 5 thousand times less. In this case, visible light is one of critical factors life on the planet is only a fraction of solar radiation.
The energy of the sun's rays is converted into heat in a smaller part - in the atmosphere, and most of it - on the surface of the Earth. There it is spent on heating water and soil (upper layers), which then give off heat to the air. When heated, the atmosphere and the earth's surface, in turn, emit infrared rays into space, while cooling.
Solar radiation: definition
The radiation that goes to the surface of our planet directly from the solar disk is usually called direct solar radiation. The sun spreads it in all directions. Given the enormous distance from the Earth to the Sun, direct solar radiation at any point on the earth's surface can be represented as a bundle of parallel rays, the source of which is practically at infinity. Area perpendicular to the beams 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 of time per unit of area. This value is measured - irradiance - in W / m 2. Our Earth, as everyone knows, revolves around the Sun in an ellipsoidal orbit. The sun is at one of the focuses of this ellipse. Therefore, every year in certain time(at the beginning of January) the Earth occupies a position closest to the Sun and in another (at the beginning of July) - farthest from it. In this case, the magnitude of the irradiance changes in inverse proportion with respect to the square of the distance to the luminary.
Where is the solar radiation that has reached the Earth? Its types are determined by many factors. Depending on the latitude, humidity, cloudiness, part of it is scattered in the atmosphere, part is absorbed, but most still reach the surface of the planet. In this case, a small amount is reflected, and the main one is absorbed by the earth's surface, under the influence of which it is heated. Scattered solar radiation also partially falls on the earth's surface, partially absorbed by it and partially reflected. The rest of it goes into outer space.
How is the distribution
Is solar radiation uniform? Its types after all the "losses" in the atmosphere can differ in their spectral composition. After all, rays with different lengths are both scattered and absorbed in different ways. On average, the atmosphere absorbs about 23% of its original amount. Approximately 26% of the total flux turns into scattered radiation, 2/3 of which then falls on the Earth. In essence, this is a different kind of radiation, different from the original one. Scattered radiation is sent to the Earth not by the disk of the Sun, but by the firmament. It has a different spectral composition.
Absorbs radiation mainly ozone - the visible spectrum, and ultraviolet rays. Infrared radiation is absorbed by carbon dioxide (carbon dioxide), which, by the way, is very small in the atmosphere.
Scattering of radiation, which attenuates it, occurs for all wavelengths of the spectrum. In the process, its particles, falling under the electromagnetic influence, redistribute the energy of the incident wave in all directions. That is, the particles serve as point sources of energy.
Daylight
As a result of scattering, the light coming from the sun changes color as it passes through layers of atmospheres. The practical value of scattering is in creating daylight. If the Earth were deprived of the atmosphere, illumination would exist only in places where direct or surface-reflected rays of the sun hit. That is, the atmosphere is a source of illumination during the day. Thanks to her, it is light both in places inaccessible to direct rays, and when the sun is hiding behind clouds. It is scattering that gives color to the air - we see the sky in blue.
And what else does solar radiation depend on? The turbidity factor should not be overlooked either. After all, the weakening of radiation occurs in two ways - by the atmosphere itself and by water vapor, as well as by various impurities. Dust content increases in summer (as does the content of water vapor in the atmosphere).
Total radiation
It refers to the total amount of radiation falling on the earth's surface, both direct and scattered. The total solar radiation decreases with cloudy weather.
For this reason, in summer, the total radiation is on average higher before noon than after it. And in the first half of the year - more than in the second.
What happens to the total radiation on the earth's surface? Getting there, it is mostly absorbed by the top layer of soil or water and turns into heat, some of it is reflected. The degree of reflection depends on the nature of the earth's surface. Indicator expressing percentage the reflected solar radiation to its total amount falling on the surface is called the surface albedo.
The concept of self-radiation of the earth's surface is understood as long-wave radiation emitted by vegetation, snow cover, upper layers of water and soil. The radiation balance of a surface is the difference between its absorbed and radiated amount.
Effective radiation
It has been proven that the counter-radiation is almost always less than the terrestrial one. Because of this, the surface of the earth bears heat losses. The difference between the values of the intrinsic radiation of the surface and the atmospheric one is called effective radiation. This is actually a net loss of energy and, as a result, heat at night.
It also exists in the daytime. But during the day, it is partially compensated or even blocked by the absorbed radiation. Therefore, the surface of the earth is warmer during the day than at night.
About the geographical distribution of radiation
Solar radiation on Earth is unevenly distributed throughout the year. Its distribution is zonal, and the isolines (connecting the points the same values) of the radiation flux are not at all identical to the latitudinal circles. This discrepancy is caused by different levels of cloudiness and transparency of the atmosphere in different regions. Globe.
The total solar radiation during the year is of greatest importance in subtropical deserts with a low cloud atmosphere. It is much less in forest areas. equatorial belt... The reason for this is increased cloudiness. This indicator decreases towards both poles. But in the region of the poles it grows again - in the northern hemisphere it is less, in the region of snowy and low-cloud Antarctica - more. Above the surface of the oceans, on average, solar radiation is less than over the continents.
Almost everywhere on Earth, the surface has a positive radiation balance, that is, for the same time, the radiation inflow is greater than the effective radiation. The exceptions are the regions of Antarctica and Greenland with their ice plateaus.
Do we face global warming?
But the above does not mean annual warming of the earth's surface. The excess of absorbed radiation is compensated by the leakage of heat from the surface into the atmosphere, which occurs when the phase of the water changes (evaporation, condensation in the form of clouds).
Thus, there is no radiation equilibrium as such on the Earth's surface. But there is thermal equilibrium- the supply and loss of heat is balanced by different ways, including radiation.
Distribution of balance on the card
At the same latitudes of the Earth, the radiation balance is greater on the ocean surface than over land. This can be explained by the fact that the layer that absorbs radiation in the oceans is thicker, while the effective radiation there is less because of the cold sea surface compared to land.
Significant fluctuations in the amplitude of its distribution are observed in deserts. The balance is lower there due to the high effective radiation in dry air and low cloud conditions. To a lesser extent, it is lowered in regions of the monsoon climate. In the warm season, the cloudiness there is increased, and the absorbed solar radiation is less than in other regions of the same latitude.
Of course, the main factor on which the average annual solar radiation depends is the latitude of a particular region. Record "portions" of ultraviolet radiation go to countries located near the equator. This is Northeast Africa, its east coast, the Arabian Peninsula, north and west of Australia, part of the islands of Indonesia, Western part coast of South America.
In Europe, Turkey, southern Spain, Sicily, Sardinia, the islands of Greece, the coast of France (southern part), as well as part of the regions of Italy, Cyprus and Crete take on the largest dose of both light and radiation.
And how are we?
The total solar radiation in Russia is distributed, at first glance, unexpectedly. On the territory of our country, oddly enough, it is not the Black Sea resorts that hold the palm. The largest doses of solar radiation occur on the territories bordering China and the Northern Land. In general, solar radiation in Russia is not particularly intense, which is fully explained by our northern geographic location. Minimal amount sunshine goes to the north-western region - St. Petersburg, along with the adjacent areas.
Solar radiation in Russia is inferior to that of Ukraine. There most of the ultraviolet radiation goes to the Crimea and the territories beyond the Danube, in second place is the Carpathians with the southern regions of Ukraine.
The total (it includes both direct and scattered) solar radiation falling on a horizontal surface is given monthly in specially developed tables for different territories and is measured in MJ / m2. For example, solar radiation in Moscow ranges from 31-58 in the winter months to 568-615 in the summer.
About solar insolation
Insolation, or the amount of useful radiation incident on a sunlit surface, varies considerably from one geographic point to another. Annual insolation is calculated for 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 such factors as the time of the year (in winter, the illumination and the length of the day are lower), the nature of the terrain (mountains can obscure the sun), weather conditions characteristic of the area - fog, frequent rains and clouds. The light-receiving plane can be oriented vertically, horizontally or obliquely. The amount of insolation, as well as the distribution of solar radiation in Russia, is data grouped into a table by city and region, indicating the geographic latitude.
Necessary devices and accessories: thermoelectric actinometer M-3, universal pyranometer M-80M, traveling albedometer, thermoelectric balance meter M-10M, universal heliograph model GU-1, luxmeter Yu-16.
The main source of energy coming to the Earth is radiant energy coming from the Sun. The flow of electromagnetic waves emitted by the Sun is commonly called solar radiation. This radiation is practically the only source of energy for all processes occurring in the atmosphere and on the earth's surface, including for all processes occurring in living organisms.
Solar radiation provides plants with energy, which they use in the process of photosynthesis to create organic matter, affects the processes of growth and development, the arrangement and structure of leaves, the duration of the growing season, etc. Quantitatively, solar radiation can be characterized by a radiation flux .
Radiation flux - it is the amount of radiant energy that is delivered per unit of time per unit of surface.
In the SI system of units, the radiation flux is measured in watts per 1m 2 (W / m 2) or kilowatts per 1m 2 (kW / m 2). Previously, it was measured in calories per cm 2 per minute (cal / (cm 2 min)).
1 cal / (cm 2 min) = 698 W / m 2 or 0.698 kW / m 2
The flux density of solar radiation at the upper boundary of the atmosphere with an average distance from the Earth to the Sun is called solar constant S 0... According to the international agreement of 1981 S 0 = 1.37 kW / m 2 (1.96 1 cal / (cm 2 min)).
If the Sun is not at its zenith, then the amount of solar energy falling on a horizontal surface will be less than on a surface located perpendicular to the Sun's rays. This amount depends on the angle of incidence of the rays on the horizontal surface. To determine the amount of heat received by a horizontal surface per minute, the following formula is used:
S ′ = S sin h ©
where S ′ is the amount of heat received per minute by the horizontal surface; S is the amount of heat received by the surface perpendicular to the beam; h© - the angle formed by the sunbeam with a horizontal surface (the angle h is called the height of the sun).
Passing through the earth's atmosphere, solar radiation is attenuated due to absorption and scattering by atmospheric gases and aerosols. The attenuation of the solar radiation flux depends on the length of the path traversed by the beam in the atmosphere and on the transparency of the atmosphere along this path. The length of the beam path in the atmosphere depends on the height of the sun. When the sun is at its zenith, the sun's rays pass the most short way... In this case, the mass of the atmosphere traversed by the sun's rays, i.e. the mass of a vertical column of air with a base of 1 cm 2 is taken as one conventional unit (m = 1). As the sun descends to the horizon, the path of the rays in the atmosphere increases, and, consequently, the number of passable masses also increases (m> 1). When the sun is near the horizon, the rays travel the longest path in the atmosphere. Calculations show that m is 34.4 times greater than at the position of the Sun at its zenith. The attenuation of the direct solar radiation flux in the atmosphere is described by the Bouguer formula. Transparency coefficient p shows what fraction of solar radiation arriving at the upper boundary of the atmosphere reaches the earth's surface at m = 1.
S m = S 0 p m ,
where S m is the direct solar radiation flux reaching the Earth; S 0 - solar constant; p - transparency coefficient; m- the mass of the atmosphere.
The transparency coefficient depends on the content of water vapor and aerosols in the atmosphere: the more there are, the lower the transparency coefficient for the same number of passable masses. The transparency coefficient ranges from 0.60 up to 0.85.
Types of solar radiation
Direct solar radiation(S ′) - radiation arriving at the earth's surface directly from the Sun in the form of a beam of parallel rays.
Direct solar radiation depends on the sun's height above the horizon, the transparency of the air, cloud cover, the altitude of the place above sea level, and the distance between the Earth and the Sun.
Scattered solar radiation(D) – part of the radiation scattered by the earth's atmosphere and clouds and arriving at the earth's surface from the firmament. The intensity of scattered radiation depends on the height of the sun above the horizon, cloudiness, air transparency, altitude above sea level, and snow cover. 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 re-scattering in the atmosphere, can increase the scattered radiation flux several times.
Scattered radiation substantially complements direct solar radiation and significantly increases the flow of solar energy to the earth's surface.
Total radiation(Q) - the sum of the fluxes of direct and scattered radiation entering the horizontal surface:
Before sunrise, during the daytime and after sunset, in case of continuous clouds, the total radiation reaches the earth completely, and at low solar heights 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 the flux is many times greater than the flux of scattered radiation.
Most of the total radiation flux entering the earth's surface is absorbed by the top layer of soil, water and vegetation. In this case, the radiant energy is converted into heat, heating the absorbing layers. The rest of the total radiation flux is reflected by the earth's surface, forming reflected radiation(R). Almost the entire flux of reflected radiation passes through the atmosphere and goes into world space, but some of it is scattered in the atmosphere and partially returns to the earth's surface, increasing the scattered radiation, and, consequently, the total radiation.
Reflectivity different surfaces called albedo... It is the ratio of the reflected radiation flux to the total flux of total radiation incident on this surface:
The albedo is expressed in fractions of a unit or as a percentage. Thus, the earth's surface reflects a part of the total radiation flux, equal to QA, and is absorbed and converted into heat - Q (1-A). The last quantity is called absorbed radiation.
The albedo of various land surfaces depends mainly on the color and roughness of those surfaces. Dark and rough surfaces have lower albedos than light and smooth surfaces. The albedo of soils decreases with increasing moisture content, since their color becomes darker. The albedo values for some natural surfaces are given in Table 1.
Table 1 - Albedo of various natural surfaces
The reflectivity of the upper surface of the clouds is very high, especially at their high power. On average, the albedo of clouds is about 50-60%, in individual cases- more than 80-85%.
Photosynthetically active radiation(PAR) - part of the total radiation flux that can be used by green plants in photosynthesis. The PAR flow can be calculated using the formula:
PAR = 0.43S '+ 0.57D,
where S ′ - direct solar radiation entering the horizontal surface; D - diffused solar radiation.
The PAR flux falling on the sheet is mostly absorbed by it, much smaller portions of this flux are reflected by the surface and passed through by the sheet. The leaves of most tree species absorb about 80%, reflect and transmit up to 10-12% of the total PAR flow. Of the part of the PAR flux absorbed by the leaves, only a few percent of the radiant energy is used by plants directly for photosynthesis and is converted into chemical energy of organic substances synthesized by the leaves. The rest, more than 95% of radiant energy, is converted into heat and is spent mainly on transpiration, heating the leaves themselves and their heat exchange with the surrounding air.
Long-wave radiation of the Earth and the atmosphere.
Radiation balance of the earth's surface
Most of the solar energy entering the Earth is absorbed by its surface and atmosphere, some of it is emitted. Radiation from the earth's surface occurs around the clock.
Part of the rays emitted by the earth's surface is absorbed by the atmosphere and thus contributes to the heating of the atmosphere. The atmosphere, in turn, sends rays back to the surface of the earth, as well as into outer space. This property of the atmosphere to retain heat emitted by the earth's surface is called greenhouse effect... The difference between the arrival of heat in the form of counter radiation of the atmosphere and its consumption in the form of radiation from the active layer is called effective radiation active layer. The effective radiation is especially large at night, when the heat loss by the earth's surface significantly exceeds the heat flux emitted by the atmosphere. In the daytime, when the total solar radiation is added to the radiation of the atmosphere, an excess of heat is obtained, which goes to heating the soil and air, evaporating water, etc.
The difference between the absorbed total radiation and the effective radiation of the active layer is called radiation balance active layer.
The incoming part of the radiation balance is made up of direct and scattered solar radiation, as well as the counter radiation of the atmosphere. The expendable part is made up of reflected solar radiation and long-wave radiation of the earth's surface.
The radiation balance is the actual arrival of radiant energy on the surface of the Earth, on which it depends whether it will be heated or cooled.
If the arrival of radiant energy is greater than its consumption, then the radiation balance is positive and the surface heats up. If the income is less than the flow rate, then the balance is negative and the surface is cooled. The radiation balance of the earth's surface is one of the main climate-forming factors. It depends on the height of the Sun, the duration of the sunshine, the nature and condition of the earth's surface, the turbidity of the atmosphere, the content of water vapor in it, the presence of clouds, etc.
Instruments for measuring solar radiation
Thermoelectric actinometer М-3(Fig. 3) is designed to measure the intensity of direct solar radiation on a surface perpendicular to the sun's rays.
The actinometer receiver is a thermopile of alternating manganin and constantan plates, made in the form of an asterisk. The internal junctions of the thermopile are glued to the disk made of silver foil through an insulating gasket, the side of the disk facing the sun is blackened. External joints are glued to a massive copper ring through an insulating gasket. It is protected from heating by radiation with a chrome cap. The thermopile is located at the bottom of a metal tube, which is directed towards the sun during measurements. The inner surface of the tube is blackened, and 7 diaphragms (ring-shaped constrictions) are arranged in the tube to prevent scattered radiation from entering the actinometer receiver.
For observations, the arrow on the base of the device 11 (Fig. 2) is oriented to the north, and to facilitate tracking the sun, an actinometer is installed according to the latitude of the observation site (along the sector 9 and the risk at the top of the appliance rack 10 ). Aiming at the sun is done with a screw 3 and handles 6 located at the top of the appliance. The screw allows the tube to be rotated in a vertical plane; when the handle is rotated, the tube is guided behind the sun. A small hole is made in the outer diaphragm for precise aiming at the Sun. Opposite this hole at the bottom of the appliance there is White screen 5 ... At correct installation of the device, the sunbeam penetrating through this hole should give a bright spot (spot) in the center of the screen.
Rice. 3 Thermoelectric actinometer M-3: 1 - cover; 2, 3 - screws; 4 - axis; 5 - screen; 6 - handle; 7 - tube; 8 - axis; 9 - latitude sector; 10 - rack; 11 - base.
Universal pyranometer M-80M(Fig. 4) is designed to measure the total (Q) and scattered (D) radiation. Knowing them, it is possible to calculate the intensity of direct solar radiation on the horizontal surface S ′. The M-80M pyranometer has a device for overturning the instrument stand with the receiver downward, which allows you to measure the intensity of the reflected radiation and determine the albedo of the underlying surface.
Pyranometer receiver 1 is a thermoelectric battery, arranged in the shape of a square. Its receiving surface is painted black and white colors in the form of a chessboard. Half of the thermopile junctions are under the white cells, the other half under the black cells. The top of the receiver is covered with a hemispherical glass to protect it from wind and precipitation. To measure the intensity of scattered radiation, the receiver is shaded by a special screen 3 ... During measurements, the receiver of the device is installed strictly horizontally; for this, the pyranometer is equipped with a circular level 7 and set screws 4. At the bottom of the receiver there is a glass dryer filled with a water-absorbing substance, which prevents moisture condensation on the receiver and the glass. When inoperative, the pyranometer receiver is closed with a metal cap.
Rice. 4 Universal pyranometer M-80M: 1 - pyranometer head; 2 - locking spring; 3 - shade hinge; 4 - set screw; 5 - base; 6 - hinge of the folding tripod; 7 - level; 8 - screw; 9 - rack with a dehumidifier inside; 10 - thermopile receiving surface.
Traveling albedometer(Fig. 5) is designed to measure the intensities of the total, scattered and reflective radiation in the field. The receiver is the pyranometer head 1 mounted on a self-balancing gimbal 3 ... This suspension allows you to install the device in two positions - with the receiver up and down, and the horizontal position of the receivers is provided automatically. With the position of the receiving surface of the device upward, the total radiation Q is determined. Then, to measure the reflected radiation R, the handle of the albedometer is turned by 180 0. Knowing these values, you can determine the albedo.
Thermoelectric balance meter M-10M(Fig. 6) is designed to measure the total radiation balance of the underlying surface. The receiver of the balancer is a thermopile square shape consisting of many copper bars 5 wrapped in constantan tape 10 ... Half of each screw of the tape is electroplated silver plated, the beginning and end of the silver layer 9 are thermal junctions. Half of the junctions are glued to the upper, the other half to the lower receiving surfaces, which are used as copper plates 2 painted black. The balance meter receiver is housed in a round metal frame 1 ... When measuring, it is located strictly horizontally using a special overlay level. For this, the balance meter receiver is mounted on a ball joint. 15 ... To increase the measurement accuracy, the balance meter receiver can be shielded from direct solar radiation by a round shield 12 ... The intensity of direct solar radiation is measured in this case with an actinometer or pyranometer.
Rice. 5 Traveling albedometer: 1 - pyranometer head; 2 - tube; 3 - gimbal; 4 - handle
Rice. 6 Thermoelectric balance meter M-10M: a) - schematic cross-section: b) - separate thermopile; c) - appearance; 1 - receiver frame; 2 - receiving plate; 3, 4 - joints; 5 - copper bar; 6, 7 - insulation; 8 - thermopile; 9 - silver layer; 10 - constantan tape; 11 - handle; 12 - shadow screen; 13, 15 - hinges; 14 - bar; 16 - screw; 17 - cover
Instruments for measuring the duration of the solar
shine and illumination
The duration of sunshine is the time during which direct solar radiation is equal to or greater than 0.1 kW / m 2. Expressed in hours per day.
The method for determining the duration of sunshine is based on recording the time during which the intensity of direct solar radiation is sufficient to obtain a burn-through on a special tape, fixed in the optical focus of a ball glass lens, and is not less than 0.1 kW / m 2.
The duration of sunshine is measured by a heliograph instrument (Fig. 7).
Universal heliograph model GU-1(fig. 7). The base of the device is a flat metal plate with two posts 1 ... Between the posts on the horizontal axis 2 reinforced the movable part of the device, consisting of a column 3 with limb 4 and bottom stop 7 , staples 6 with a cup 5 and the upper stop 15 and a glass ball 8 which is a spherical lens. A sector is fixed at one end of the horizontal axis 9 with a scale of latitudes. When moving the horizontal axis 2 the instrument from west to east and turning the upper part of the instrument around it, the column axis 3 is installed parallel to the axis of rotation of the Earth (axis of the world). A screw is used to secure the set angle of inclination of the column axis 11 .
Top part the instrument can be rotated around the column axis 3 and fixed in four specific positions. For this, a special pin is used. 12 , which is inserted through the hole of the dial 4 into one of the four holes of the disc 13 fixed on the axis 2 ... The alignment of the holes in the limb 4 and disk 13 determined by the coincidence of marks A, B, C and D on the dial 4 with index 14 on disk.
Rice. 7 Heliograph universal model GU – 1.
1 - rack; 2 - horizontal axis; 3 - column; 4 - limb; 5 - cup; 6 - bracket; 7 - emphasis; 8 - glass ball; 9 - sector; 10 - latitude indicator; 11 - screw for fixing the angle of inclination of the axis; 12 - pin; 13 - disk; 14 - index on the disk; 15 - top stop.
At the meteorological site, the heliograph is installed on a concrete or wooden pillar 2 m high, on the upper part of which there is a platform made of boards with a thickness of at least 50 mm, so that at any position of the Sun relative to the sides of the horizon, separate buildings, trees and random objects do not obscure it. It is installed strictly horizontally and oriented along the geographic meridian and latitude of the meteorological station; the axis of the heliograph must be strictly parallel to the axis of the world.
The heliograph ball must be kept clean, since the presence of dust, traces of precipitation, dew, frost, frost and ice on the ball weakens and distorts the burn-through on the heliograph tape.
Depending on the possible duration of sunshine, the recording for one day should be made on one, two or three tapes. Depending on the season, straight or curved bands should be used and placed in the top, middle or bottom slots of the cup. Bookmark ribbons should be matched in the same color throughout the month.
For the convenience of working with the heliograph, a ladder with a platform is installed to the south of the support (pillar) with the device. The ladder should not touch the post and should be comfortable enough.
Light meter U-16(Fig. 8) is used to measure the illumination created by light or artificial light sources.
Rice. 8 Luxmeter U – 16. 1 - photocell; 2 - wire; 3 - meter; 4 - absorber; 5 - terminals; 6 - switch of measurement limits; 7 - proofreader.
The device consists of a selenium photocell 1 connected by a wire 2 with meter 3 , and absorber 4 ... The photocell is enclosed in a plastic case with a metal frame; to increase the measurement range by 100 times, an absorber made of milk glass is put on the case. The light meter is a magnetoelectric dial gauge mounted in a plastic case with a scale window. In the lower part of the body there is a corrector 7 for setting the arrow to zero, in the upper part - terminals 5 for connecting the wires from the photocell and the knob for switching the measurement limits 6 .
The scale of the meter is divided into 50 divisions and has 3 rows of numbers corresponding to the three measurement limits - up to 25, 100 and 500 lux (lx). When using an absorber, the limits are increased to 2500, 10000 and 50,000 lux.
When working with a light meter, it is necessary to carefully monitor the cleanliness of the photocell and absorber; if they get dirty, wipe them with a cotton swab dipped in alcohol.
The photocell is placed horizontally during measurements. The corrector set the meter arrow to zero division. Connect the photocell to the meter and take measurements after 4-5 s. To reduce overloads, they start with a larger measurement limit, then move to smaller limits until the arrow is in the working part of the scale. The reading is taken in scale divisions. In case of small deviations of the arrow, to improve the measurement accuracy, it is recommended to switch the meter to a lower limit. To prevent fatigue of the selenium photocell, shade the photocell for 3-5 minutes every 5-10 minutes of device operation.
Illumination is determined by multiplying the reading by the scale division value and by the correction factor (for natural light it is 0.8, for incandescent lamps -1). The scale division is equal to the measurement limit divided by 50. When using one or two absorbers, the resulting value is multiplied by 100 or 10000, respectively.
1 Get acquainted with the device of thermoelectric devices (actinometer, pyranometer, albedometer, balance meter).
2 To get acquainted with the device of the universal heliograph, with the methods of its installation at different times of the year.
3 Get acquainted with the device of the light meter, measure the natural and artificial illumination in the audience.
Place the entries in a notebook.
