Popular science articles on the causes of rain, snow, clouds, fog, dew, frost and hail and their relationship with human life.

1) the formation of rain

Clouds are made up of many small water droplets and small ice crystals.

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.

(B) the formation of snow

As we all know, clouds are composed of many small water droplets and small ice crystals, and raindrops and snowflakes are composed of these small water droplets and small ice crystals. So, how is snow formed?

In the water cloud, all water droplets are small water droplets. They grow into raindrops mainly through continuous condensation and collision.

Ice cloud is made up of tiny ice crystals. When these small ice crystals collide with each other, the surface of the ice crystals will heat up and melt, and they will stick together and freeze again. Repeat this for many times, and ice crystals will increase. In addition, there is water vapor in the cloud, so ice crystals can continue to grow through condensation. However, where the ice cloud is generally high but not thick, and there is not much water vapor, the condensation growth is slow, and there are not many opportunities to collide with each other, so it cannot grow to a great extent to form precipitation. Even if it causes precipitation, it often evaporates on the way down and rarely falls to the ground.

Similarly, the size of snow is also classified according to precipitation. Snow can be divided into three categories: light snow, medium snow and heavy snow.

(C) the formation of clouds

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.

(4) Formation of fog

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.

(5) the formation of dew

In the early morning of warm season, the dew that people often see on the grass, leaves and crops on the roadside does not fall from the sky. The reason and process of dewing are the same as frost, but the temperature is above 0℃.

Above 0℃, the temperature at which air is saturated with water vapor due to cooling is called "dew point temperature". In warm seasons, when the ground objects are cooled by intense radiation at night, the temperature of the air in contact with the surface of the objects drops, and after it drops to the "dew point", excess water vapor is precipitated. Because the temperature is above 0℃ at this time, these excess water vapor condenses into water droplets and adheres to ground objects, which is dew.

(vi) Frost formation

At night, grass, wood, stones and other objects on the ground will cool down because of heat radiation. When the temperature drops to the dew point, the water vapor in the air near the ground object will reach saturation. If the dew point is higher than 0 degrees Celsius, water vapor can condense into small water droplets on the surface of ground objects, which is dew.

If the dew point is below 0 degrees Celsius, water vapor will directly condense into water ice particles on the surface of ground objects, which is frost.

If at night, not only the temperature of objects on the ground drops below the dew point, but also the air temperature slightly higher on the ground drops below the dew point, then the water vapor in the air will condense into tiny water droplets with dust as the core, which is fog.

When the air temperature in the sky drops below the dew point, if the dew point is higher than 0 degrees, the water vapor in the air condenses into fine water droplets on the dust, which is the cloud, and the condensation into larger water droplets is the rain. If the dew point is below 0 degrees, the water vapor in the air will directly condense into snow on the dust.

Therefore, dew, frost and fog do not fall from the sky, but are directly condensed when the water vapor in the air near the ground reaches saturation. Only snow and rain fall from the sky, that is, the water vapor in the sky condenses when it reaches saturation.

(7) Formation of hail

Hail falls from the clouds like rain and snow. But the clouds that hail are very strong cumulonimbus clouds, and only very strong cumulonimbus clouds can hail.

Cumulonimbus clouds, like all kinds of clouds, are formed by the rising and condensation of air near the ground. When air rises from the ground, the air pressure decreases and the volume expands. If there is no heat exchange between the rising air and its surroundings, the air temperature will decrease, because expansion consumes energy. This temperature change is called adiabatic cooling. According to the calculation, every time the air in the atmosphere rises 100 m, the temperature will decrease by about 1 degree due to the adiabatic change. We know that at a given temperature, there is a limit to the amount of water vapor contained in the air, and reaching this limit is called "saturation". When the temperature is lowered, the amount of water vapor that may be contained in the air will decrease. Therefore, the originally unsaturated air may reach saturation due to adiabatic cooling in the upward movement. After the air reaches saturation, excess water vapor will attach to the floating condensation nuclei in the air and form water droplets. When the temperature is below zero degrees Celsius, excess water vapor will condense into fine ice crystals. These water droplets and ice crystals gather together and float in the air to become clouds.

The relationship between rain, snow, fog, dew, frost and hail and human life

It is difficult to tell the relationship between these natural phenomena and human life ... for example, drought has a great impact on human life: drought and water shortage are a worldwide problem. In the early 1990s, southern Africa suffered from drought and lack of rain for four consecutive years, with farmland cracked and reservoirs dried up. Drought has made the already fragile economic security of some countries here lose its vitality. Agricultural drought and water shortage in China are also very serious. In the 1970s, 654.38+0.7 billion mu of farmland suffered from drought every year, which increased to 400 million mu in the 1990s. China's irrigation areas lack about 30 billion cubic meters of water every year. Drought and water shortage have affected the stable development of agriculture and the safe supply of food. Drought affects not only cities but also rural areas. 1995, Xi' an is short of water, so the university has to stop the final exam and take the summer vacation early. This shows the significance of rain to human life. However, if there is too much rain, floods will also cause floods, threatening the safety of human life and property.

Another example is snow. In the vast areas of northern North China, if there is more snow in winter, the early spring snow melting can water the crops once, which is beneficial to the growth of crops. However, like the winter snowstorm in Inner Mongolia, the temperature will drop to MINUS 30-40 degrees, which will cause a large number of sheep to freeze to death and bring great losses to local herders.

Another example is fog. For tea-producing mountainous areas, the famous "Yunwu tea" can be baked because of fog. However, heavy fog will cause highway traffic accidents and bring losses to people's lives and property.

As for hail, it is absolutely not good for mankind, but will only bring disaster to mankind:

Hail is a common disastrous weather in China, and our province is a hail-prone area. Heavy hail often destroys crops, hurts people and animals, and causes disasters. Hail also has different degrees of harm to transportation, housing construction, industry and so on. Therefore, how to reduce hail disaster is an important issue in national economic development, especially in agricultural production.

Hail is very harmful to crops and will cause mechanical damage to crops. The harm of hail depends on its size, duration, crop species and its development stage. If the heavy hail is fierce or lasts for a long time, the crops will be seriously damaged. Dicotyledonous crops such as beans and cotton suffer more than Gramineae crops. Crops in flowering or maturity are more seriously damaged than those in seedling stage, and even can cause devastating damage. Fruit trees and trees are attacked by hail, which will affect their growth in the current year and later, and diseases and insect pests are also prone to occur after trauma. Different crops have different hail disaster resistance, and the same crop has different hail disaster resistance at different growth stages. Gramineae crops have strong anti-injury ability in the early growth stage and weak anti-injury ability in the late growth stage. If the ear of wheat is broken by hail before heading, as long as the stubble remains, it can still resume growth and obtain a certain yield. However, if wheat breaks its ear at the late heading stage, the yield will be low and late, which will affect the sowing of the next crop.

Therefore, the relationship between rain, snow, fog, frost and hail and human life is both beneficial and harmful. ....