rain

[yǔ]

natural phenomena

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Rain, a natural precipitation phenomenon, is produced by the disturbance of the atmospheric cycle, is an indispensable part of the earth's water cycle, and is the only way for almost all terrestrial plants far away from rivers to supply fresh water. Raindrops fall from the sky, big and small, fast and slow. The evaporation of water on the earth's surface is rising, and it is cooled to form rain. Rain is the most important fresh water resource in human life.

Rain is a drop of water falling from the clouds, and the water on the land and sea surface evaporates into steam When the water vapor rises to a certain height, it becomes small water droplets when cooled cloud They collide with each other in the cloud and merge into large water droplets. When it is too big for the air to hold, it falls from the cloud and forms rain. Rain is the most important in human life freshwater Resources and plants also need to thrive on the moisture of rain and dew. But the flood caused by rainstorm will also bring huge disasters to mankind.

Chinese name: rain
Foreign name: rain

Resources: The most important freshwater resource in human life
natural phenomena: The water of the earth forms. The water vapor cools and forms rain
Measurement method: mm

catalog

seven Related proverbs
eight Impact on war

Generation mechanism

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Rain refers to liquid water drops falling from the atmosphere to the ground.^[3] The causes of rain are diverse, and its manifestations are also unique, including drizzle, continuous rain, and downpour showers. When the water on the earth is irradiated by the sunlight, it becomes water vapor and evaporates into the air. When water vapor encounters cold air at high altitude, it condenses into small water droplets. These small water droplets are very small, with a diameter of only 0.01~0.02 mm and a maximum of only 0.2 mm. They are small and light, held in the air by the updraft in the air. It is these small drops of water that form clouds in the air. These small water drops will become raindrops and fall to the ground, and their volume will increase by more than one million times.

How do these small water droplets increase their volume to more than one million times? It mainly depends on two means, one is condensation and sublimation. The second is to rely on the collision and enlargement of cloud drops. At the initial stage of raindrop formation, cloud droplets mainly rely on continuous absorption of moisture around the cloud body to condense and sublimate themselves. If the water and gas energy source in the cloud body is continuously supplied and supplemented, so that the cloud drop surface is often in an oversaturated state, then this condensation process will continue, making the cloud drop continuously increase and become a raindrop. But sometimes the moisture content in the cloud is limited. In the same cloud, the supply of moisture often exceeds the demand, so it is impossible to make every cloud drop grow into a larger raindrop, and some smaller cloud drops have to be merged into larger cloud drops. If water droplets and ice crystals coexist in the cloud, the process of condensation and accretion will be greatly accelerated. When the cloud drops in the cloud increase to a certain extent, because the volume and weight of large cloud drops continue to increase, they can not only catch up with those small cloud drops with slower speed, but also "swallow" more small cloud drops to grow up. When a big cloud drop grows bigger and bigger, and finally becomes too big for the air to hold it, it falls directly from the cloud to the ground, becoming our common rainwater.

Main forms

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Rain usually occurs in four forms:

1、 Frontal rain (Mei Yu): From ocean The warm and humid air flow of is forced to rise due to the heavy cold air and light warm air. When it is cold, the warm and humid air flow condenses, forming a long and wide rain belt, which is frontal rain.

2、 Convective rain In summer, under the strong sunlight, the warm and humid air in some areas rises sharply and condenses when it is cold, forming rainfall, which is called convective rain. Meteorology is called "thunderstorm", and we usually call it "exploding sky". In addition, typhoon rain is also a kind of convective rain.

3、 Orographic rain : The warm and humid air flow from the ocean is forced to rise when encountering mountains, and condenses when encountering cold, forming rainfall.

4、 Typhoon storm The humid and hot air on the tropical ocean surface rotates and rises strongly on a large scale. During the rising process, the temperature drops rapidly, and a large amount of water vapor condenses into clouds and rain, which is called typhoon rain.

origin

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The causes of rain are diverse, and its manifestations are also unique, including drizzle, continuous rain, and downpour showers. When the water on the earth is irradiated by the sunlight, it becomes water vapor and evaporates into the air. When water vapor encounters cold air at high altitude, it condenses into small water droplets. These small water droplets are very small, with a diameter of only 0.01~0.02 mm and a maximum of only 0.2 mm. They are small and light, held in the air by the updraft in the air. It is these small drops of water that form clouds in the air. These small water drops will become raindrops and fall to the ground, and their volume will increase by more than one million times. How do these small water droplets increase their volume to more than one million times? It mainly depends on two means, one of which is coagulation and Sublimation enlarge. The second is to rely on the collision and enlargement of cloud drops. At the initial stage of raindrop formation, cloud droplets mainly rely on continuous absorption of moisture around the cloud body to condense and sublimate themselves. If the water and gas energy source in the cloud body is continuously supplied and supplemented, so that the cloud drop surface is often in an oversaturated state, then this condensation process will continue, making the cloud drop continuously increase and become a raindrop. But sometimes the moisture content in the cloud is limited. In the same cloud, the supply of moisture often exceeds the demand, so it is impossible to make every cloud drop grow into a larger raindrop, and some smaller cloud drops have to be merged into larger cloud drops. If water droplets and ice crystals coexist in the cloud, the process of condensation and accretion will be greatly accelerated. When the cloud drops in the cloud increase to a certain extent, because the volume and weight of large cloud drops continue to increase, they can not only catch up with those small cloud drops with slower speed, but also "swallow" more small cloud drops to grow up. When a big cloud drop grows bigger and bigger, and finally becomes too big for the air to hold it, it falls directly from the cloud to the ground, becoming our common rainwater. except acid rain In addition to colorful rain, there are many interesting rain, such as frog rain, iron rain, Golden Rain , even money rain. They are tornado A masterpiece of.

Main components

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The main component of rainwater is water (chemical formula H2O ）, a small amount sulfur dioxide (chemical formula SO2 ）、 Nitrogen dioxide (chemical formula NO2 ）, usually rainwater PH value About 5.6, PH value Rainwater less than 5.6 is acid rain In case of thunderstorm, rainwater will contain a small amount of Ozone molecule (due to lightning ), as well as various impurities and floating dust in the air.

Rainfall class

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Meteorologically, the rainfall within 24 hours is less than 10.0 mm, or the rainfall within an hour is less than 2.5 mm, which is called light rain 。 The rainfall within 24 hours is less than 10.0~24.9 mm, or the hourly rainfall is less than 2.6~8.0 mm, which is called moderate rain 。 The rainfall within 24 hours is less than 25.0~49.9 mm, or the rainfall within an hour is less than 8.1~15.9 mm, which is called heavy rain 。 The rainfall within 24 hours is less than 50.0~99.9 mm, or the rainfall within an hour is more than 16.0 mm, which is called rainstorm 。 The rainfall within 24 hours is less than 100.0~199.9 mm and reaches or exceeds 200.0 mm, which is called Heavy rain 。 When the precipitation is less than 0.05 mm or there is precipitation before observation, but it is not observed because of rapid evaporation, the precipitation should be recorded as 0.0 mm, which cannot be omitted, because it is a rainfall process.^[1] Flood and rain: flood and flood caused by dumping super rainstorm are rare natural phenomena. According to the way of rainfall, it can be divided into: thunderstorm, topographic rain and typhoon rain, cyclone rain^[2]

effect

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1． rain , is an indispensable part of the earth, is almost all away from the river Terrestrial plant The only way to supply fresh water.

2. Rain can irrigate crops and facilitate afforestation.

3. Rain can reduce the dust , can reduce the temperature.

4. Raining is beneficial to reservoir water storage, can supplement groundwater, can supplement river water, and is beneficial to power generation and navigation.

5. When it rains, you can isolate the noisy world and create a peaceful environment. You can hypnotize and wash the streets.

6. Rain can wash away garbage on the ground, dilute toxic substances and purify the environment.

seven Rain can purify the air, and you will feel cheerful after rain.

On the other hand, more rain will affect the growth of plants, which can inhibit Botany And even death.

2. Every time in the middle and lower reaches of the Yangtze River in China Plum Rain In the season, there will be a long period of gloomy and rainy weather. At this time, Baiwu is vulnerable to damp and mildew.

3. When a thunderstorm comes, there will be strong wind and thunderstorm Weather phenomenon 。 When the strong wind comes, sand and stones fly, overturn the roof and blow down the wall. In the wind and rain, things on the street dance with the wind, flying everywhere, even uprooting trees.

4. Continuous rainy days will affect people's mood and make people feel bored Repression 。

5. Too much rain will cause traffic jam , throw Mountain landslide 、 Debris flow And other natural disasters.

6. Acid rain will erode many buildings. (See the term "acid rain" for details)

7. It may cause road skidding, which may lead to an accident.

8. Rain will bring toxic substances in soil into groundwater, thus polluting groundwater.

9. Excessive rainfall will cause the water level of reservoirs, rivers and lakes to rise sharply, causing floods.

10. Excessive rainfall will cause serious water and soil loss.

Related proverbs

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Dragonflies and swallows fly low, ants move, fish breathe on the water, and heavy rain will come soon.

It rains in the morning and sunny that day. It rains until dawn at night.

If you have a rainy mountain, you should wear a hat. If you have no rainy mountain, you should have no waist. The moonlight is hazy, either windy or rainy.

Swallows fly low in the snake passage. The heavy rain will come soon.