Moisture in the atmosphere enters the atmosphere through the evaporation of various water bodies in the ocean and mainland, as well as soil and plants, and is transported and exchanged through airflow movement. Although the moisture content in the atmosphere is not much, its existence shows complex weather phenomena such as clouds, fog, rain, snow, frost, dew and hail.

Liquid water or solid water, such as rain, that falls from the clouds to the ground. Snow and hail are collectively called precipitation.

There are two reasons, one is water vapor saturation, and the other is that condensation nuclei (dust and impurities in the air) can form precipitation.

Cloud, rain, snow, hail, fog, dew and frost are all members of the water family. When the sun shines on rivers, lakes and seas, water evaporates, and water vapor rises to high altitude with low temperature, liquefying into small water droplets or condensing into small ice crystals to form white clouds. If you encounter cold air again, small water droplets will gradually grow into large water droplets, and white clouds will become dark clouds. When the big water droplets get heavier and heavier, they overcome the support of the updraft and fall to the ground. This is rain.

In winter, the air is colder, and the water vapor cools sharply, directly condensing into hexagonal small ice crystals-snowflakes. When snowflakes fall, they combine with each other and change from small to large into snowflakes or large snowflakes. At this time, it snowed heavily.

What's it like to hail in summer? It turned out that the raindrops in the clouds were taken to the upper air below 0℃ and liquefied into small ice beads; The airflow weakens and the small ice beads fall back; When the updraft containing water vapor increases again, the small ice beads rise again and increase; So jumping up and down, small ice beads may gradually turn into heavy hail and finally fall to the ground.

When there is more water vapor near the ground and cold air is encountered, the water vapor will liquefy into small water droplets with dust in the air as the core, which is fog.

In summer, the ground is very hot and there is a lot of water vapor. When the temperature is low before dawn, water vapor will condense into dew on leaves and flowers.

In the winter morning, the temperature on the ground is very low, and when the water vapor is cold, it condenses into frost on the ground.

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Rain: Water droplets melted by water vapor or ice crystals fall to the ground and become rain.

Snow: Ice crystals condensed by water vapor fall to the ground.

Cloud: Small water droplets liquefied by water vapor or small ice crystals condensed by condensation float in the air.

Fog: Water vapor liquefies on the ground and becomes small water droplets floating near the ground.

Dew: Water droplets liquefied by water vapor on plants on the ground.

Frost: Small ice crystals condensed by water vapor adhere to the ground or plants.

Hail: With the accumulation of water vapor in the cloud, rainfall can be formed, and hail will be formed if cold air is encountered during the rainfall.