What does rain mean?

It refers to the weather phenomenon that condensed water vapor in the atmosphere falls to the surface of the earth in different ways.

artificial rainfall

As the saying goes, "something unexpected happens in the sky." However, with the development of science and technology, this view has become a thing of the past. For thousands of years, the human desire to "sow clouds and rain" has now become a reality. The first scientist to realize artificial rainfall was irving langmuir, an outstanding American physical chemist. 188111October 3 1 was born in Brooklyn, new york, USA. Langmuir was very interested in natural science and applied technology since he was a child. When he was young, he had a great ideal: to realize artificial rainfall and get rid of the fate of relying on the weather for food. Langmuir understood farmers' thirst for rain in dry season. Facing the farmers' eyes for rain, Langmuir faced them. As a scientist, he made a rational and scientific exploration. After in-depth research, he finally figured out the mystery. It turns out that the water vapor on the ground is a "cloud" when it rises and condenses when it meets cold. The tiny freezing point in the cloud is only about 0.0 1 mm in diameter and can be suspended in the air for a long time. Small ice crystals can be formed when they meet some impurity particles (called ice cores). Once the ice crystals appear, water vapor will quickly condense on the surface of the ice crystals, making small ice crystals grow into snowflakes. Many snowflakes stick together and become snowflakes. When the snowflake is big enough and heavy enough, it will roll down from the sky. This is snowfall. If a snowflake collides with a cloud drop during falling, the cloud drop condenses on the snowflake and then forms an opaque ice hockey, which is called hail. If the snowflake falls to a warm area with a temperature higher than 0℃, it will melt into water droplets and start to rain. However, clouds do not necessarily rain. This is because there are not enough ice cores in the cloud and the number of ice crystals is too small. At that time, there was a popular view among the people that raindrops regarded dust particles as "ice crystals" If it rains, there must be dust particles in the air besides water vapor. This popular view seriously restricts people's experiments and research on artificial rainfall. Because it is not easy to raise dust on cloudy days. Langmuir is a rigorous scholar. A practical scientist. He was then the deputy director of the research laboratory of General Electric Company in Schenectady, new york. In his laboratory, there are artificial clouds, which are water vapor filled in the refrigerator. Langmuir tried his best to make the water vapor in the refrigerator the same as that in the atmosphere before it rained. He kept adjusting the temperature and adding all kinds of dust to carry out experiments. 1946 One day in July, it was sunny. The weather is very hot. Langmuir is conducting an experiment nervously. Suddenly the refrigerator stopped cooling because of some equipment failures, and the temperature in the refrigerator could not drop. He decided to use dry ice to cool down. The gasification heat of solid carbon dioxide is very high, which is 87.2 calories/g at -60℃. Under normal pressure, it can be quickly converted into gas, and the ambient temperature can be reduced to about -78℃ by absorbing environmental heat. A wonderful picture appeared: small ice particles were flying and hovering in the ice room, and snowflakes were falling from the floor. The whole igloo was chilly, and artificial clouds turned into ice and snow. Langmuir analyzed this phenomenon and realized that dust is not an absolutely necessary condition for rainfall. Dry ice has a unique function of condensing water vapor, that is, ice crystals or ice cores in the cloud are used as "seeds". Temperature drop is also one of the important factors that water vapor turns into rain. He constantly adjusted the amount of dry ice and changed the temperature, and found that artificial rainfall was successful as long as the temperature dropped below MINUS 40℃. The dry ice cloud distribution method developed by Langmuir is a breakthrough in the study of artificial rainfall, which has got rid of the shackles of old ideas. Interestingly, this breakthrough invention was obtained in the refrigerator in hot summer. Langmuir is determined to apply dry ice cloud distribution method to artificial rainfall practice. Although he is a 66-year-old man in 20438+0946, he is still burning with enthusiasm for exploring the mysteries of nature like a young man. One day in 20438+0946, under the command of Langmuir, a plane took off and flew over the sea of clouds. The experimenter scattered 207 kilograms of dry ice into the sea of clouds. Just like a farmer sowing seeds in a wheat field, 30 minutes later, a strong wind suddenly blew and it rained heavily in the basin. The first artificial rainfall experiment was successful. Langmuir initiated a new era of artificial rainfall. According to the theory of ice crystal nucleation in supercooled clouds, scientists found that silver iodide (AgI) can be used as the "seed" of artificial rainfall. And from the effect point of view, silver iodide is better than dry ice. Silver iodide can be sprinkled on the ground. It is easier to float in the clouds than dry ice rain. "Artificial rainfall" is a new "meteorological weapon" in the war. During the US-Vietnam War, the "Ho Chi Minh Trail" from Cambodia to Vietnam was busy, and foreign war materials supporting the Vietnamese people in their resistance to the US imperialist aggressors were continuously sent to the front through this unique channel. However, there are often heavy rains and disastrous floods there. Bridges were destroyed, dams were destroyed, and a large number of transport vehicles struggled along muddy mountain roads. Traffic is greatly affected, and its damage is no less than bombing. At first, Vietnam knew nothing about this sudden rainstorm. Later, after many investigations, I learned that this was a secret weather operation approved and implemented by President Johnson of the United States for six years. That is, the United States carried out "artificial rainfall" in the air on that road. The meaning of "there is a measurable storm in the sky" is not only "artificial rainfall", but also inspires people to control the weather reasonably. Langmuir also studied it, hoping to use the method of manual control to nip it in the bud before storm warning. This idea is not only reasonable but also feasible, and it has been widely used now.