Extended data:
Cloud is a visible polymer floating in the air, which is condensed by water droplets or small ice crystals liquefied by water vapor in the atmosphere when it is cold.
Clouds are the tangible result of the huge water cycle on the earth. The sun shines on the surface of the earth, and water evaporates to form water vapor. Once the water vapor is supersaturated, water molecules will gather around the dust (condensation nucleus) in the air, and the generated water droplets or ice crystals will scatter sunlight in all directions, thus creating the appearance of clouds. Moreover, clouds can form various shapes, and they are divided into many kinds because of their different heights and shapes in the sky.
Definition:
Cloud refers to a large number of tiny water droplets or ice crystals suspended in the atmosphere near the ground or a visible aggregate of both (sometimes including some larger raindrops and ice particles). Its bottom does not touch the ground.
Strength grade:
The intensity of clouds is measured by the number of clouds (the percentage of clouds in the sky, divided into total clouds and low clouds), which are divided into three grades: the sky is clear without clouds or scattered clouds, but the amount of clouds is less than the sky area110; There are four? 70% of the low-middle clouds are still 6? 10% of the high clouds are cloudy; More than 80% of the medium and low clouds are cloudy.
Impact:
Clouds absorb heat from the ground and radiate it back, which helps to keep the earth warm. However, clouds also reflect sunlight directly back into space, which has a cooling effect. Which effect is dominant depends on the shape and location of the cloud. In the atmosphere more than ten kilometers from the ground, the closer to the ground, the higher the temperature and the richer the air; The higher the altitude, the lower the temperature and the thinner the air.
On the other hand, the water surface of rivers, lakes and seas, as well as the moisture of soil, animals and plants, evaporates into the air and becomes water vapor. After water vapor enters the atmosphere, it turns into clouds to cause rainfall, or condenses into frost dew, and then returns to the ground, permeates the soil or flows into rivers, lakes and seas. Later it will evaporate (vaporize) and then condense (condense) and drop. It goes on and on.
Water vapor enters the lower atmosphere from the evaporation surface, which has a high temperature and a lot of water vapor. If the hot and humid air is lifted, the temperature will gradually decrease, and when it reaches a certain height, the water vapor in the air will reach saturation. If the air continues to be lifted, there will be excess water vapor. If the temperature there is higher than 0℃, the excess water vapor will liquefy into small water droplets.
If the temperature is lower than 0℃, excess water vapor condenses into small ice crystals. When these small water droplets and small ice crystals gradually increase to a level that can be recognized by human eyes, what we call clouds are formed. Note: When the air pressure at high altitude decreases, the freezing point of water will increase and be higher than 0℃.