How are rain, snow, clouds, fog, dew, frost and hail formed?

People often see that the sky is sometimes blue and cloudless, sometimes white clouds are blooming, and sometimes dark clouds are gathering. Why sometimes there are clouds in the sky and sometimes there are no clouds? How are clouds formed? What is it made of?

Clouds floating in the sky are composed of many tiny water droplets or ice crystals, some of which are mixed together. Sometimes it also contains some big raindrops and ice particles. The bottom of the cloud does not touch the ground and has a certain thickness.

The formation of clouds is mainly caused by water vapor condensation.

As we all know, the closer to the ground, the higher the temperature in the atmosphere more than 10 kilometers from the ground, and the denser 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, evaporate into the air at any time and become 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 evaporation (sublimation) condensation (condensation) drops. It goes on and on.

After the water vapor enters the lower atmosphere from the evaporation surface, the temperature here is high and there is much 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 condense into small water droplets; If the temperature is lower than 0℃, excess water vapor will condense 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, it is a cloud.

People often see that the sky is sometimes blue and cloudless, sometimes white clouds are blooming, and sometimes dark clouds are gathering. Why sometimes there are clouds in the sky and sometimes there are no clouds? How are clouds formed? What is it made of?

Clouds floating in the sky are composed of many tiny water droplets or ice crystals, some of which are mixed together. Sometimes it also contains some big raindrops and ice particles. The bottom of the cloud does not touch the ground and has a certain thickness.

The formation of clouds is mainly caused by water vapor condensation.

As we all know, the closer to the ground, the higher the temperature in the atmosphere more than 10 kilometers from the ground, and the denser 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, evaporate into the air at any time and become 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 evaporation (sublimation) condensation (condensation) drops. It goes on and on.

After the water vapor enters the lower atmosphere from the evaporation surface, the temperature here is high and there is much 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 condense into small water droplets; If the temperature is lower than 0℃, excess water vapor will condense 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, it is a cloud.

Fog and clouds are water vapor condensates composed of small water droplets or ice crystals floating in the air, but fog is generated in the near layer of the atmosphere, while clouds are generated in the higher layer of the atmosphere. Since fog is water vapor condensation, we should look for its reason from the conditions that cause water vapor condensation. There are two reasons for water vapor saturation in the atmosphere: first, evaporation increases water vapor in the atmosphere; The other is the cooling of the air itself. Cooling is more important for fog. When there are condensation nuclei in the air, if water vapor continues to increase or melt, condensation will occur in saturated air. Fog is formed when condensed water drops reduce the horizontal visibility to less than 1 km.

In addition, excessive wind speed and strong disturbance are not conducive to the formation of fog.

Therefore, in the area that is conducive to the cooling of the lower air layer, if the water vapor is sufficient, the wind is mild, the atmospheric stratification is stable, and there are a large number of condensation nuclei, it is most likely to produce fog. Generally speaking, there are more opportunities to form fog in industrial areas and urban centers, because there are abundant condensation nuclei there.

In the early morning of cold season, grass leaves and clods are often covered with a layer of frost crystals. They shine in the rising sun and melt when the sun rises. People usually call this phenomenon "frosting". Looking through the calendar, every year from 10, there is always the solar term "first frost". We have seen snow and rain, but no one has seen frost. In fact, frost does not fall from the sky, but is formed in the air near the ground.

Frost is a kind of white ice crystal, which mostly forms at night. In a few cases, it can also begin to form before sunset when the sun is tilted. Usually, the frost will melt soon after sunrise. But when the weather is cold or in a cool place, the frost will last all day.

Frost itself is neither harmful nor harmful to plants. What people usually call "freezing injury" is actually the "freezing injury" when frost forms.

The formation of frost is not only related to the weather conditions at that time, but also related to the nature of attached objects. When the surface temperature of the object is very low, but the air temperature near the surface of the object is relatively high, there is a temperature difference between the air and the surface of the object. If the temperature difference between the surface of an object and the air is mainly caused by the radiation cooling of the surface of the object, when the warmer air contacts the surface of the object, the air will be cooled, and when the water vapor is supersaturated, the excess water vapor will be precipitated. If the temperature is lower than 0℃, the excess water vapor condenses into ice crystals on the surface of the object, which is frost. Therefore, frost is always formed under weather conditions that are conducive to radiation cooling on the surface of objects.

In addition, clouds hinder the radiation cooling of ground objects at night, and clouds in the sky are not conducive to the formation of frost. Therefore, frost often appears on clear nights, that is, when the ground radiation cools down strongly.

In addition, the wind also has an effect on the formation of frost. When there is a breeze, air flows slowly over the surface of supercooled objects, constantly supplying water vapor, which is beneficial to the formation of frost. But when the wind is strong, because the air flows quickly, the time to contact the surface of cold objects is too short. At the same time, when the wind is strong, the air in the upper and lower layers is easy to mix with each other, which is not conducive to cooling down and will also hinder the formation of frost. Generally speaking, when the wind speed reaches level 3 or above, it is not easy to frost.

Therefore, frost usually forms in sunny, breezy or calm nights in cold seasons.

The formation of frost is not only related to the above weather conditions, but also related to the properties of ground objects. Frost is formed on the surface of an object cooled by radiation, so the easier it is to radiate heat and the faster it cools, the easier it is to frost on it. Similar objects, under the same conditions, have the same mass and heat. If they radiate and dissipate heat at the same time at night, objects with large surface area will dissipate more heat, and at the same time, the temperature will drop faster, and it will be easier to frost on them. That is to say, if the surface area of an object is relatively large relative to its mass, it is easy to form frost on it. Grass leaves are very light, but they have a large surface area and are easy to frost on. In addition, the rough surface of an object is more conducive to heat dissipation than the smooth surface, so the rough surface is more prone to frost, such as clods.

Frost disappears in two ways: one is to sublimate into steam, and the other is to melt into water. The most common thing is that it melts and disappears after sunrise due to the rising temperature. Water melted by frost is good for crops.

We already know that clouds are made up of many small water droplets and small ice crystals, and raindrops and snowflakes are also made up of them. So, how do small water droplets and small ice crystals get bigger in the cloud?

In the water cloud, all water droplets are small water droplets. They are mainly increased by continuing to condense and collide with each other. Therefore, in water clouds, if cloud droplets are to increase to the size of raindrops, first of all, the clouds need to be thick, dense and rich in water, so that they can continue to condense and grow; Secondly, there needs to be strong vertical movement in the water cloud, so as to increase the chances of multiple collisions and mergers. In a thinner and more stable water cloud, there is not enough opportunity for cloud droplets to condense and grow together, which can only cause cloudy days and is unlikely to rain.

In different clouds, the distribution of cloud droplet size is different, and the reason of uneven cloud droplet size is the transportation of water vapor in the surrounding air and the evaporation of cloud droplets. The factors that make cloud droplets grow are condensation process and collision and merger process. In the case of condensation, the size of cloud droplets is uniform, but due to the supplement of water vapor, some cloud droplets grow, and the result of merger is that larger cloud droplets continue to grow and become raindrops. Raindrops fall under the action of gravity. When there is an updraft, raindrops will be subjected to an upward force, which will slow down their falling speed and some small raindrops may be picked up. Only when raindrops increase to a certain extent can they fall to the ground and form rainfall.