Traditional Culture Encyclopedia - Weather forecast - Why is it raining today?

Why is it raining today?

Rain is a natural phenomenon. When the cloud reaches a certain thickness, the water droplets that make up the cloud naturally fall to form rain.

Rain is the water on the earth after being irradiated by sunlight, which forms water vapor, evaporates and rises into the air, and condenses into water droplets when it meets cold air in the air. Condensation releases heat and raises the temperature, so the warm air will continue to rise, and when it is cold again, the water vapor will continue to condense, and so on. The updraft can extend from low altitude to 10,000 meters.

At higher altitudes, when the temperature is below 0℃, ice crystals will appear, and small water droplets and ice crystals will form cumulonimbus clouds. When the cumulonimbus cloud reaches the tropopause, the upward movement stops.

When the ice crystals in the cloud collide and fuse with each other, part of the water vapor directly condenses and adheres to the surface of the ice crystals, and small ice crystals will grow up. When the updraft can't hold up, it will fall under the action of gravity, forming various forms of precipitation (rain, snow, hail, etc. ) During the descent, the low-altitude temperature rises and the ice crystals melt, which becomes rainfall. When some small ice crystals become larger ice crystals, they will fall directly to form hail.

Extended data:

Several precursor clouds before rain

First, hook cirrus clouds.

People call it a "hook cloud". It floats horizontally in the sky like a wisp of silk, with the cloud upward and a small hook at one end. The color of the cloud is milky white and bright. Generally, it appears before the influence of cold air in the north or low pressure at high altitude. This cloud has appeared, and it will rain soon. Therefore, there is a saying that "clouds hook raindrops".

Second, cirrocumulus.

People call it "Fish Scale Day". It usually appears in the blue sky. Small white clouds, arranged neatly and closely, ripple like fish scales. The duration after formation is short, usually only a few minutes, and more than an hour. Its appearance shows that there is a trough of low pressure approaching over the local area, which is a sign that sunny days turn cloudy and rainy days. Therefore, there is a saying that "it's a fish scale day, it's windy and it doesn't rain".

Third, flocculent cumulus clouds

The masses call it "cotton cloud". It also often appears in the clear sky in summer, like clusters of scattered and broken cotton wool, and also like a burst of cotton. Clouds vary in size and height. It is formed under the condition of extremely unstable humid air, so the cloud is fragmented and a symbol of rain. Therefore, the agricultural proverb says, "There are cotton clouds in the sky, and there will be a thunderstorm soon."

Baidu encyclopedia-rain

China Weather Network-Several Precursor Clouds before Summer Rain