Weather modification refers to the transformation of weather phenomena in a predetermined direction by artificial means under appropriate weather conditions. International weather modification began to rise in the 1950s, during which some famous scientific experiments were carried out, and the development of weather modification was promoted. Following the international pace, China has also carried out research on weather modification. After continuous off-site and indoor tests, a cloud-seeding and hail suppression system using aircraft, anti-aircraft guns and rockets as the main means has been preliminarily formed. At the beginning of the 21st century, due to the need of drought prevention, disaster reduction and improvement of the ecological environment, the scope of weather modification services has been expanded, has been extended to artificial rain reduction, fog reduction and forest fire prevention and other fields.

    During a forest fire in Yalong River town, Muli County, Liangshan Prefecture, Sichuan Province, in 2019, Samsung General Airlines, under the direction and coordination of the Sichuan Meteorological Bureau's Human Figure office, carried out aerial rain raising operations, which "created" 3.5 millimeters of rain in Liangshan area during the dry season, effectively reducing the spread of the fire. Taiwan Province is experiencing a drought this year, which is rare in decades. The effective water storage of major reservoirs in the southern part of the province was less than 20 percent in March. Can artificial rain be used to "create" precipitation to alleviate the drought? It should be noted that weather modification is not equal to artificial weather manufacturing, which needs to be carried out smoothly under specific conditions and achieve the desired effect. So what is the appropriate conditions for cloud-seeding?

    Precipitation is the phenomenon that the water in the cloud falls to the ground in the form of liquid or solid state. The formation of precipitation needs three basic conditions: sufficient water vapor; The gas block can be lifted and cooled to condense; More condensation nuclei. The natural precipitation process is generally divided into two stages: cloud formation and precipitation. The cloud formation process is caused by the air block in the atmosphere being lifted and cooled, so that the water vapor in the air reaches the saturated or supersaturated state. The precipitation process is the growth of large and small cloud droplets into precipitation particles through the collision process and the transformation of ice water.

  We cannot change the cloud formation stage of natural precipitation. We can only rely on nature to select objects that can produce precipitation for artificial influence. We can sow cold cloud catalyst (dry ice, artificial ice core) or warm cloud catalyst hypersonic core (such as salt particles) in the cloud body with potential to accelerate the condensation or consolidation of cloud droplets to form precipitation.

  Artificial precipitation methods include: ground layout AgI combustion furnace as the main means of ground precipitation (adapted to often have topographic cloud development, inconvenient transportation in mountainous areas), anti-aircraft artillery and rocket-based ground operations (adapted to work in the fixed target area, there are strong convective clouds under the case of catalytic operations), aircraft catalytic operations. Catalytic operation flexibility, can accurately grasp the plane position, and can use the plane in front of the catalytic homework imager loaded particle detector, such as precipitation, cloud combination detector, aerosol detector to detect in the air, such as the content of each particle concentration, get the cloud master appropriate catalytic place and time, to provide help for artificial precipitation enhancement operation, Reduce the blindness of cloud-seeding operation.

   The plane flew almost in a cold cloud, according to data from an aircraft survey conducted by Samsung General Aviation over the Sichuan Basin. The first cloud entry height is 4976m, and the lowest cloud entry height is 2363m. During the period, the layer cloud with 753m thickness passes through. The 0℃ altitude layer in the ascending stage is 3339m, and the 0℃ altitude layer in the descending stage is 2574m. In addition, most of the flight was in the seeding area, and a small part was in the strong seeding area. In the seeding area, there was a rich cloud water area. The average supercooled water content was about 0.2g/cm3, and the temperature was about -5℃. According to the CIP particle image, there was a seeding layer with rich ice crystal content in this flight, which provided certain help to judge the timing of artificial precipitation operation.

Cip particle image