Total solar radiation. Solar Radiation: Views

17 Сен

Total solar radiation. Solar Radiation: Views

The bright luminaire blends us with hot rays and makes think about the meaning of radiation in our life, its benefits and harm. What is solar radiation? School physics lesson invites us to get acquainted with the concept of electromagnetic radiation as a whole. This term denote another form of matter — different from the substance. This also includes visible lights, and a spectrum that is not perceived by the eye. That is, X-rays, gamma rays, ultraviolet and infrared.

In the presence of a source of radiation emitter, its electromagnetic waves propagate in all directions at the speed of light. These waves, like any other, have certain characteristics. These include frequency of oscillations and wavelength. The property to emit radiation has any bodies whose temperature differs from absolute zero.

The sun is the main and most powerful source of radiation near our planet. In turn, the Earth (its atmosphere and the surface) and itself radiates radiation, but in another range. Monitoring the temperature conditions on the planet for long periods of time gave rise to a hypothesis about equilibrium of the amount of heat obtained from the Sun and given to outer space.

The absolute majority (about 99%) of solar energy in the spectrum lies in the wavelength range from 0.1 to 4 microns. The remaining 1% rays of greater and smaller length, including radio waves and X-rays. About half of the radiant energy of the Sun accounts for the spectrum, which we perceive the look, about 44% — on infrared radiation, 9% — on ultraviolet. How do we know how to share solar radiation? The calculation of its distribution is possible due to research with space satellites.

There are substances that can come into a special state and emit an additional radiation of another wave range. For example, a glow is found at low temperatures that are not characteristic of the emission of light by this substance. This type of radiation called fluorescent is not amenable to conventional thermal radiation principles.

The luminescence phenomenon occurs after absorbing a substance of a certain amount of energy and the transition to another state (T. n. Excited), more energetically high than at its own temperature of the substance. Luminescence appears when transition — from excited to the usual state. In nature, we can observe it in the form of night glows of the sky and polar radiance.

The energy of sun rays is almost the only source of heat for our planet. Own radiation, which comes from its depths to the surface, has an intensity less than about 5 thousand times. At the same time, visible light is one of the most important factors of life on the planet — only part of solar radiation.

The energy of the sun’s rays goes into heat less part — in the atmosphere, greater — on the surface of the Earth. There it is spent on the heating of water and soil (upper layers), which then give heat air. Being a heated, the atmosphere and earthly surface, in turn, emit infrared rays into space, while cooling.

TU RADIATION, which goes to the surface of our planet directly from the solar disk, is customary to refer to direct solar radiation. The sun spreads it in all directions. Taking into account the huge distance from the ground to the Sun, direct solar radiation at any point of the earth’s surface can be represented as a bundle of parallel rays, the source of which is almost in infinity. The area located perpendicular to the rays of sunlight is thus obtained by its greatest amount.

The density of the radiation stream (or energy illumination) serves as a measure of its amount falling on a certain surface. This is the volume of radiant energy falling per unit time per unit area. This magnitude is measured — energy illumination — in W / m 2. Our land, as everyone knows, draws around the Sun on the ellipsoid orbit. The sun is in one of the focus of this ellipse. Therefore, annually at a certain time (in early January), the land occupies a position closest to the Sun and another (in early July) — Further from him. At the same time, the magnitude of the energy illumination changes in the reverse proportion relative to the square of the distance to the shine.

Where does solar radiation come out to the ground? Its species are determined by many factors. Depending on geographical latitude, humidity, clouds, part of it dissipates in the atmosphere, part is absorbed, but most still reaches the surface of the planet. In this case, a minor amount is reflected, and the main one is absorbed by the earth’s surface, under the action of which it is exposed to heating. The scattered solar radiation partially also falls onto the earth’s surface, partly it is absorbed and partially reflected. The residue goes into outer space.

Is solar radiation homogeneous? Types of it after all «losses» in the atmosphere may differ in their spectral composition. After all, rays with different lengths and dissipate, and are absorbed in different ways. In the middle atmosphere, about 23% of its initial number is absorbed. Approximately 26% of the entire flow turns into a scattered radiation, 2/3 of which then falls on the ground. In essence, this is another type of radiation, different from the initial one. The scattered radiation is sent to Earth not the disk of the Sun, and the heavenly arch. It has a different spectral composition.

Absorbs radiation mainly ozone — visible spectrum, and ultraviolet rays. The radiation of the infrared range is absorbed by carbon dioxide (carbon dioxide), which, by the way, is very few in the atmosphere.

Radiation scattering, weakening it, occurs for any spectrum wavelengths. In the process of its particle, falling under electromagnetic effects, the energy of the incident wave is redistributed in all directions. That is, particles serve as point sources.

Due to the scattering, the light coming from the Sun, when the layers are passed, the atmosphew changes the color. The practical value of scattering is in the creation of daylight. If the Earth was deprived of the atmosphere, the lighting would only exist in places of direct or reflected as the surface of the rays of the sun. That is, the atmosphere is a source of lighting during the day. Thanks to it, it is light and in places inaccessible to the straight rays, and when the sun hides behind the clouds. It is scattering that gives air color — we see the sky blue.

And what does solar radiation depend on? Do not be discounted and factor of turbidity. After all, the weakening of radiation occurs in two ways — actually an atmosphere and water vapor, as well as various impurities. The dust level increases in the summer (as well as the content in the atmosphere of water vapor).

Under it implies the total amount of radiation falling onto the earth’s surface — both direct, and scattered. Total solar radiation decreases with cloud weather.

For this reason, in summer, the total radiation is on average above until 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? Finding there, it is mostly absorbed by the upper layer of soil or water and turns into heat, part of it is reflected. The degree of reflection depends on the nature of the earth’s surface. An indicator expressing the percentage of reflected solar radiation to a total number of it falling on the surface is called the albedo surface.

Under the concept of its own radiation of the earth’s surface, long-wave radiation, emitted by vegetation, snow cover, upper layers of water and soil. The radiation balance of the surface refer to the difference between its absorbed number and radiated.

It has been proven that the counter-radiation is almost always less than the earthly. Because of this, the surface of the earth carries thermal losses. The difference between the values of its own radiation of the surface and the atmospheric received the name of effective radiation. This is actually a clean energy loss and as a result — warm at night.

There is it in daytime. But during the day is partially compensated or even overlaps with absorbed radiation. Therefore, the surface of the earth is warmer in the afternoon than at night.

Solar radiation on Earth is unevenly distributed during the year. Its distribution carries a zonal character, and the insulance (connecting points of the same values) of the radiation flow is not at all identical to the latitudinal circles. Such a discrepancy is caused by various levels of cloudiness and transparency of the atmosphere in different parts of the globe.

The greatest value of the total solar radiation during the year has in subtropical deserts with a cloudless atmosphere. It is much smaller in the forest areas of the equatorial belt. The reason for this is increased clouds. In the direction of both poles, this indicator decreases. But in the area of the poles, it increases again — in the northern hemisphere less, in the area of the snowy and stingy Antarctica — more. Above the surface of the oceans on average solar radiation is less than above the mainland.

Almost everywhere on Earth, the surface has a positive radiation balance, that is, in the same time, the inflow of radiation is more effective radiation. The exceptions are the areas of Antarctica and Greenland with their ice plateau.

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

Thus, radiation equilibrium as such on the surface of the Earth does not exist. But there is a thermal equilibrium — the flow and decrease of heat is balanced by different paths, including radiation.

In the same latitudes of the globe, the radiation balance is larger on the surface of the ocean than above the land. This can be explained by the fact that the layer absorbing radiation in the oceans has a greater thickness, while at the same time effective radiation there is less due to the cold of the sea surface compared to land.

Significant fluctuations in the amplitude of the distribution of it are observed in the deserts. Balance there is lower due to high efficient radiation in dry air and low clouds. To a lesser extent, it is reduced in the regions of the monsoon climate. In the warm season, cloudiness is raised there, and the absorbed solar radiation is less than in other areas of the same latitude.

Of course, the main factor on which the average annual solar radiation depends is the latitude of one or another area. Record «portions» of ultraviolet goes near the equator. This is Northeast Africa, her east coast, the Arabian Peninsula, North and West of Australia, part of Indonesia Islands, the western part of South America’s coast.

In Europe, the greatest dose of both light and radiation takes on Turkey, South Spain, Sicily, Sardinia, Islands of Greece, the coast of France (southern part), as well as part of the regions of Italy, Cyprus and Crete.

Solar summary radiation in Russia is distributed, at first glance, unexpectedly. On the territory of our country, oddly enough, not Black Sea resorts hold the palm of championship. The greatest doses of solar radiation fall on the territory, border with China, and the Northern Earth. In general, solar radiation in Russia does not differ in particular intensity, which is fully explained by our northern geographical position. The minimum number of sunlight gets to the North-West region — St. Petersburg together with the surrounding areas.

Solar radiation in Russia is inferior to the indicators of Ukraine. There, the most ultraviolet gets the Crimea and territories for the Danube, in second place — the Carpathians with the southern regions of Ukraine.

The total (it also includes direct, and scattered) solar radiation falling on the horizontal surface is given by months in specially developed tables for different territories and is measured in MJ / m 2. For example, solar radiation in Moscow has indicators from 31-58 in the winter months to 568-615 in the summer.

Insolation, or the amount of useful radiation falling on the surface illuminated by the Sun, varies significantly in different geographic points. Annual insolation is calculated on 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 needs to be taken into account such factors as the time of year (in winter below the illumination and longitude of the day), the nature of the area (the mountains can be blown up the sun), characteristic of this locality weather conditions — fog, frequent rains and clouds. The light-crossing plane can be oriented vertically, horizontally or tilt. The amount of insolation, as well as the distribution of solar radiation in Russia, is the data grouped into a table by cities and areas indicating geographic latitude.

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