Causes of strong solar radiation

The reasons for strong solar radiation are weather conditions, sunshine time and latitude position.

1, weather conditions

Long sunshine time and strong solar radiation; Short sunshine time and weak solar radiation. For example, in summer in China, the temperature difference between north and south is not big, because the higher the latitude, the longer the day, which makes up for the energy lost due to the low height of the sun.

2. Sunshine length

On sunny days, because the clouds are few and thin, the atmosphere has a weak weakening effect on solar radiation, and the solar radiation reaching the ground is strong; In rainy weather, due to the thick and many clouds, the atmosphere has a strong weakening effect on solar radiation, and the solar radiation reaching the ground is weak.

For example, the equatorial region is controlled by the equatorial low pressure belt, with more convective rain, while the subtropical region is controlled by the subtropical high pressure, with more sunny days, so the solar radiation in the equatorial region is weaker than that in the subtropical region.

3. Latitude position

The intensity of solar radiation is mainly affected by the height of the sun at noon. At low latitudes, the solar altitude angle is large at noon, and the distance of solar radiation passing through the atmosphere is short, so it is less weakened by the atmosphere, so more solar radiation reaches the ground; On the contrary, it is even less.

Wavelength distribution and radiation intensity of solar radiation;

1, wavelength distribution

The wavelength distribution of solar energy can be simulated by a blackbody radiation with a temperature of 5800K K, and the wavelength distribution of solar energy is in ultraviolet light, visible light and infrared light. These bands are affected by atmospheric attenuation to varying degrees. Most visible radiation can reach the ground, but ozone in the upper atmosphere absorbs most ultraviolet radiation.

Due to the thinning of the ozone layer, especially in the Antarctic and Arctic regions, more and more ultraviolet radiation reaches the ground. Part of the incident infrared radiation is absorbed by gases such as carbon dioxide and water vapor, while most of the infrared radiation with longer wavelength from the earth's surface is transmitted to outer space at night.

2. Radiation intensity

The physical quantity representing solar radiation intensity is called solar radiation intensity. The unit is Joule/cm2, that is, the solar radiation energy vertically projected on a unit area in a unit time. The intensity of solar radiation in the upper atmosphere depends on the altitude angle of the sun, the distance between the sun and the earth and the sunshine time. The greater the solar altitude angle, the greater the solar radiation intensity.