Solar radiation

The closest star to the Earth, as is known, is the Sun. It emits electromagnetic waves of different lengths. So, some are presented in the form of light, others - in the form of infrared rays, bringing heat, the third is a whole group of rays invisible to human sight (radio waves, ultraviolet, x-ray).

Radio waves with a short range and visible light pass best through the atmosphere of the Earth. Gamma rays, ultraviolet and X -rays are absorbed by the air envelope. At the boundary of the Earth's atmosphere, the intensity of the solar radiation is constant and amounts to 1.35 kW / m2.

The sun is the only natural source of light and heat on the planet. Dissipated and direct radiation are the main types of solar radiation. The rays passing through the existing layers of the atmosphere slightly heat them up. The solar radiation reaching the Earth's surface, which is not scattered and not absorbed in the air envelope, is called a straight line. The intensity of this radiation in the territory depends on the geographical latitude of the terrain: to the poles from the terrestrial equator the flux decreases, the intensity decreases, especially with increasing cloudiness and reduced transparency in the atmosphere.

Due to the fact that the air contains small dust particles, droplets of water, particles of salt, crystals, individual rays coming from the light, encounter these obstacles, dissipate. Such solar radiation is called scattered. It converts about 25% of the total flux of absorbed rays. On a cloudless day, the scattered radiation is 0.07 kW / m2, cloudy, cloudy weather - 0.5 kW / m2. With a decrease in the height of the solstice, an increase in cloudiness, a decrease in the transparency of the atmosphere, the proportion of this radiation increases. As studies show, at low latitudes the fraction of scattered radiation is much lower than in temperate and high latitudes. The surrounding natural light on an overcast day is fully provided by these rays.

The total solar radiation is composed of all the scattered and direct radiation that reached the Earth. The amount of it depends on various factors, including the duration of the day, the transparency of the angle of incidence of rays and cloudiness in the atmosphere. Thus, in tropical latitudes the annual total radiation is about 200 kcal / cm2, while in the polar zone it is about 50 kcal / cm2.

In an insignificant amount, solar radiation is absorbed by impurities and molecules of atmospheric gases. At the same time, the radiation incident on the Earth is absorbed partly by the surface of the planet, partially reflected, leaving the atmosphere back.

There is a value characterizing the ratio of the reflected radiation to the albedo incident on the surface of the Earth. This percentage is expressed. It should be noted that the magnitude of the albedo covers a fairly wide range and depends on the territory. So, for the steppe and forest this indicator is about 13%, and on the fresh snow cover it grows to 90%. There is a significant dependence of the albedo of the water surface on the angle of incidence of the rays. With direct solar radiation and high altitude of the Sun, the value of this indicator is about 3-4%, with a low standing - almost 100%. For diffused radiation, the albedo is about 8-10%. 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 the Earth, having a direct effect on the human body, the thermal state, metabolic processes, the functional activity of systems and organs, and so on.

The intensity of the ultraviolet radiation reaching the surface 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.