Can artificial rainfall achieve "calling for rain"? What conditions are needed to realize artificial rainfall?

Why artificial rainfall is needed and how to do it?

I hope the following answers are helpful to you. Thanks to the support of the post-80s generation:

1). Why artificial rainfall:

In the past, artificial precipitation enhancement was called artificial precipitation enhancement, which means that people choose the right time according to the physical characteristics of different clouds after deeply understanding the causes of precipitation, and use planes and rockets to spread dry ice, silver iodide, salt powder and other catalysts to the clouds to promote precipitation or increase precipitation. Artificial precipitation enhancement can be divided into warm cloud precipitation enhancement and Leng Yun precipitation enhancement. In order to make warm clouds (clouds with temperature higher than 0℃) precipitation or increase precipitation, hygroscopic particles such as salt powder and urea should be sown in the clouds to promote the formation of large cloud droplets, which will lead to the formation or increase of precipitation. If precipitation occurs in Leng Yun (cloud with temperature lower than 0℃), it is necessary to spread dry ice, silver iodide and other catalysts by plane to produce a large number of ice crystals, which will increase the density of ice crystals in the upper part of Leng Yun and promote or increase precipitation.

Artificial precipitation enhancement is carried out under specific weather conditions. As long as the cumulonimbus, cumulonimbus and nimbostratus are catalyzed in time, the precipitation can be increased and the expected effect can be achieved. Artificial precipitation enhancement is a scientific measure to take water from the sky and make good use of air water resources.

2). How does artificial rainfall work?

The basic principle of artificial rainfall is mainly based on people's understanding of the formation process of natural precipitation. Artificial rainfall mainly changes the physical process of microscopic formation and growth of clouds and precipitation particles through the influence of artificial rainfall operation, so as to achieve the purpose of rainfall. Artificial rainfall is conditional, there can be no cloudless rainfall, and the implementation of cloudy artificial rainfall may not be successful.

Artificial rainfall accelerates the growth of small raindrops with the help of catalysts, making them form precipitation according to natural processes. In the troposphere, the atmospheric temperature decreases with the increase of height, so the higher the height of cloud formation, the lower the temperature. When the temperature of the cloud is higher than 0 degrees Celsius, it is called warm cloud, while if the temperature of the cloud is lower than 0 degrees Celsius, it is called Leng Yun. In warm clouds, small water droplets merge into large water droplets by collision. Finally, the ice crystals in the cold cloud fall off from the bottom of the cloud after overcoming the internal buoyancy of the cloud and become rainfall. Similarly, when the ice crystals in the cold cloud grow enough to overcome the internal buoyancy of the cloud, they will fall off from the bottom of the cloud and become water droplets during the landing, forming rainfall.

When the water droplets in the cloud are too small or lack ice crystals, it cannot rain. At this time, artificial methods can be used to produce ice crystals or make small water droplets grow up, and artificial rainfall can be formed.

Artificial rainfall is actually artificial catalytic rainfall. If there are no clouds in the sky at all, it won't rain even if it is artificially rained. Clouds in the sky can't rain if there is less water, so artificial rainfall can only catalyze clouds with more water, that is, common cumulonimbus clouds, so as to make clouds that don't need to rain produce rain, or make clouds that have already dropped two drops drop drop more rain.

When rain or snowfall occurs in nature through the Leng Yun, there must be enough ice crystals in the cloud besides small water droplets. The ice crystals are formed by condensation or freezing of saturated water vapor or supercooled water droplets under the action of ice nuclei. Water molecules of water droplets in supercooled clouds will evaporate and condense on ice crystals, which will grow and fall into the snow. If the temperature under the clouds is higher than 0 degrees Celsius, they will melt into rain. If there are not enough ice crystals in this cloud in nature, because the water droplets in the cloud are very small and can be suspended in the air for a long time without falling, only the cloud has no rain. At this time, if silver iodide particles are sown in this cloud, a large number of artificial ice crystals can be produced, and the water on the water droplets in the cloud will be evaporated and quickly converted into these artificial ice crystals, so that the ice crystals will grow rapidly. If dry ice is sown at the same time, the growth rate of ice crystals will be greatly accelerated, which will lead to snowfall. If the ground temperature is relatively high, snow will form. In addition to artificial rainfall, silver iodide can also be used to artificially eliminate clouds, lightning and typhoons.

The role of silver iodide in artificial rainfall is called Leng Yun catalysis in meteorology.