Regional sunshine hours

Solar radiation is the main source of all energy on the earth, and its changes have great influence on atmospheric thermal conditions, plant growth and human activities. In the absence of any ground objects, clouds and fog, the time required for the sun to shine from the eastern horizon to the western horizon to the ground in a certain place is called "illumination hours". The number of hours that the sun actually shines on the ground in a place is called "sunshine hours". Sunshine hours are measured in hours and can be measured by heliometer. The ratio of sunshine hours to sunshine hours, that is, sunshine percentage, can measure the lighting conditions in an area.

There is a close relationship between solar radiation and illumination. Geographically, we generally use "sunshine hours" to study climate. The length of sunshine is closely related to agricultural production, so sunshine hours are the items that all meteorological stations must observe. The distribution of annual average sunshine hours in China is less in the southeast and more in the northwest, increasing from southeast to northwest.

Illumination refers to the situation where there is direct sunlight, also called sunshine. It is related to day and night changes, weather, air pollution and other factors. Last year, the total solar radiation in the world was the highest in the middle of the Sahara Desert in North Africa. The highest annual total solar radiation in China-Qinghai-Tibet Plateau. The annual total solar radiation in China is less —— Sichuan Basin and Guizhou Plateau. "Qinghai-Tibet Plateau: high altitude, thin air, less water vapor, less dust, good transparency, low latitude, high solar altitude, strong solar radiation and long sunshine time. Sichuan Basin and Yunnan-Guizhou Plateau: There are many rainy days, heavy clouds and weakened solar radiation. Sichuan Basin is a subtropical sugarcane producing area outside the tropical sugarcane producing areas in China (Guangdong, Guangxi, Fujian, Taiwan Province Province) because of its abundant heat, while the climate in Qinghai-Tibet Plateau is extremely cold, with tropical and subtropical sun overhead and temperature in the temperate zone next to it. These two contradictions have been well unified on the low latitude plateau. The so-called "the sun warms the chest and the wind blows the cold behind it" is a true portrayal of this kind of climate with cold sun and no sun.

1. Latitude position: low latitude makes the high angle of the sun at noon large, and the distance of solar radiation passing through the atmosphere is short, so it is less weakened by the atmosphere, so the solar radiation reaching the ground is strong; On the contrary, it is weak. This is also one of the reasons why solar radiation decreases from low latitude to two poles.

2. Weather conditions: On sunny days, due to the few and thin clouds, 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 low pressure in the equatorial region controls rainy weather and the subtropical high pressure controls sunny weather, so the solar radiation in the equatorial region is weaker than that in the subtropical region.

3. Altitude: the altitude is high, the air is thin, and the atmosphere has a weak weakening effect on solar radiation, so the solar radiation reaching the ground is strong; On the contrary, it is weak. This is the main reason why the Qinghai-Tibet Plateau has become the region with the strongest solar radiation in China.

4. Sunshine length: long sunshine time, strong solar radiation, short sunshine time and weak solar radiation. The days in high latitudes in summer and autumn are long, which makes up for the energy lost in low solar altitude angle.