How does artificial rainfall and hail suppression work?

Modern scientific research on weather modification began under the leadership of American scientist Langmuir. On November 13th, 1946, Schaefer conducted the first successful experiment of artificial snowfall and cloud removal. Since then, experiments of weather modification have been carried out all over the world, and dry ice and silver iodide have become the main catalysts. So far, nearly 1 countries or regions in the world have carried out this work. The scope of weather modification has quickly expanded from artificial rainfall and hail suppression to artificial fog removal, cloud removal, rain removal, lightning removal, typhoon weakening and other fields.

Weather modification is a complex system engineering, and it needs to strengthen scientific research and experiments and improve the technical level of operation continuously, so as to make this work develop continuously and healthily. According to statistics, the economic benefits of weather modification are great. It is generally estimated that the input-output ratio is about 1: 5 to 1: 3, and the economic benefits in some specific areas will be even greater. At the same time, this work also has potential social benefits that cannot be ignored.

Weather modification includes many contents. At present, artificial rainfall, hail suppression and fog elimination are widely carried out in China, and their technical methods are briefly described as follows:

Artificial rainfall is divided into artificial influence on Leng Yun to increase precipitation and artificial influence on warm clouds to increase precipitation. The main technical methods used to increase precipitation in Leng Yun are to use aircraft to carry Leng Yun catalyst (silver iodide, dry ice, liquid nitrogen, etc.) or to launch artificial rainfall anti-aircraft artillery shells. Catalyze in the area with supercooled water below -3℃ in the cloud to increase precipitation. Scientists engaged in weather modification in China have studied the cold cloud precipitation artificially catalyzed by stratiform clouds in northern China for more than 1 years, and the average precipitation enhancement efficiency is about 2%. Artificially influencing warm clouds to increase precipitation often uses warm cloud catalysts (salt powder, urea, etc.) carried by aircraft to catalyze in the cloud layer above ℃. Because the size requirement of warm cloud catalyst particles is much higher than that of Leng Yun catalyst, the dosage of warm cloud catalyst is 14 ~ 16 times higher than that of Leng Yun catalyst. Generally, a plane needs to carry thousands of kilograms of warm cloud catalyst in one flight.

Artificial hail suppression refers to preventing hail clouds from falling or weakening the intensity of hail. At present, the hail suppression operation widely carried out in China is to use anti-aircraft guns with a caliber of 37 mm to directly send shells filled with silver iodide into the hail growth area of the hail cloud to explode, so as to artificially increase the number of hail embryos. Because these numerous hail embryos compete for the limited water in the hail formation area, most of them cannot grow to the size of hail, thus limiting the hail growth and achieving the purpose of artificial hail suppression.

To artificially eliminate local supercooled fog, catalysts such as propane, dry ice, silver iodide or liquid nitrogen are usually used, which are sown in the fog to produce ice crystals, so that a large number of supercooled fog droplets gather on the ice crystals, and the ice crystals grow up by consuming the fog droplets and fall to the ground, thus improving visibility. Artificial elimination of local warm fog mainly adopts spreading hygroscopic particles, such as salt powder, calcium chloride solution, urea, etc., to absorb water vapor in the fog, thus improving visibility. There are also many successful examples of using dynamic method and heating method to eliminate warm fog.