If you want to shoot a few shells before it rains heavily, it will stop raining.

Artificial weather modification refers to the rational use of climate resources to avoid or mitigate meteorological disasters and artificially influence the physical and chemical processes of the local atmosphere through scientific and technological means under appropriate conditions to achieve increased rain, snow, and prevention. Hail, rain, fog, frost and other purposes.

Basic Principles

Using the physical principles of clouds and precipitation, the main method is to spread catalysts into clouds to transform certain local weather processes in a direction that is beneficial to humans. A scientific and technological measure. Also known as artificial weather control. It is a general term for artificial precipitation, artificial hail prevention, artificial cloud elimination, artificial fog elimination, artificial frost prevention, artificial weakening of storms (typhoons) and artificial suppression of lightning.

The energy of natural weather processes is huge. The amount of water vapor condensed in a storm is about 10 million tons, and its latent heat of condensation is about 2.5×1016 Joules, which is equivalent to the heat of burning 4.8 million barrels of oil. The heat released every minute by condensed water vapor in a typhoon is equivalent to the energy released by exploding 20 megaton nuclear bombs. It is actually impossible to directly expend such a huge amount of energy to create or destroy a weather process, and it is also uneconomical. Therefore, we must look for the conditions that can be exploited in the natural weather process and use a small amount of expenditure to promote their transformation in the predetermined direction. This is the weather modification experiment.

Implementation form

Among various experimental studies on artificial weather modification, artificial precipitation is the most frequently carried out. The scale of artificial hail prevention is second only to artificial precipitation. China, the United States, the former Soviet Union, Switzerland and other countries have conducted a large number of artificial hail prevention experiments, which has reduced losses in orchards and other cash crops, but strict scientific tests have mixed results. Artificial fog elimination was carried out earlier. In the 1940s, heating methods were used to eliminate fog on airport runways. Although it was expensive, it was quite effective. Technology that uses dry ice or liquefied propane to eliminate cold fog has been put into operational use at some airports. Artificial cloud elimination is rarely carried out, but local supercooled stratus clouds can be eliminated under certain conditions. Warming fog elimination, artificial weakening of typhoons, artificial suppression of lightning, etc. are still in the exploratory stage.

The energy of natural weather processes is huge. The amount of water condensed in a storm is about 10 million tons, and its latent heat of condensation is 2.5 × 10 joules, which is equivalent to the heat of burning 4.8 million barrels of oil. The latent heat released by the water vapor in the typhoon every minute is equivalent to the energy released by the explosion of 20 megaton nuclear bombs. It is actually impossible and economically uneconomical to directly consume such a huge amount of energy to create or destroy a weather process. Therefore, it is necessary to find the conditions that can be exploited in the natural weather process and use a small amount of expenditure to promote their transformation in the predetermined direction. The way to artificially influence weather is mainly to use the microphysical process of clouds. For example, there are a large number of unfrozen water droplets in clouds with temperatures below 0°C. Using a seeding ice-forming catalyst (see cloud seeding catalyst) can convert the water droplets into ice crystals and release latent heat, thus changing the microphysical processes and thermal properties of the cloud. Power structure. Using this method to artificially modify the weather is relatively low-cost and may have great benefits.

Artificial weather modification is called "Cloud Seeding", a name that evokes various imaginations about agricultural seeding. For a Chinese farmer, reducing natural disasters and preserving a year's harvest is more practical than anything else. This need serves as the starting point, which directly leads to the fact that the scale of China’s “human shadow” (artificial weather modification) ranks first in the world.

“China has far more cloud seeding operations than the rest of the world combined.” Professor Daniel Rosfeld is a professor at the School of Earth Sciences at the Hebrew University of Jerusalem, Israel. In his opinion, drought and drip irrigation Israel, which is famous for its agriculture, has a much greater demand for precipitation than China, and China's frequency of artificial weather modification is "almost unimaginable."

Method Overview

The most important method of artificial weather modification is cloud seeding, which uses aircraft, rockets or ground generators to sow catalysts such as silver iodide into clouds to change the microstructure of the clouds. The structure changes weather phenomena such as clouds, fog, and precipitation.

Catalyst classification

According to the nature of the objects, the catalysts used in cloud seeding are also different. The catalytic process can be divided into two categories:

①Cold cloud catalysis . Supercooled water droplets often exist in clouds with a temperature of 0 to -30°C. If ice-forming catalysts such as silver iodide or solid carbon dioxide (also known as dry ice) are sown in such clouds, a large number of artificial ice crystals can be generated. The ice-forming efficiency of this type of catalyst is very high. One gram of catalyst can generate an order of magnitude of 1 trillion ice crystals, resulting in a concentration of 1 ice crystal per liter in 1 cubic kilometer of cloud body. In some clouds, artificial ice crystals can form precipitation through the Bergeron process (see Cloud and Precipitation Microphysics), thereby achieving the purpose of artificial precipitation. In strong convective clouds, artificial ice crystals can grow into hail embryos and compete with natural hail for water, so that individual hailstones cannot grow into large hailstones that cause serious damage. This can achieve the purpose of preventing hail. In supercooled clouds (fogs), artificial ice crystals cause cloud (fog) droplets to evaporate and grow and fall, thereby achieving the purpose of eliminating clouds (fog). The huge latent heat released during the catalysis process of cold clouds will change the thermal and dynamic processes of the clouds. Catalysis that focuses on this dynamic effect is called dynamic catalysis. Dynamic catalysis can cause the development of certain convective clouds and increase precipitation.

Dynamic catalysis in certain parts of the typhoon cloud system may change the circulation structure of the typhoon and weaken its maximum wind force, thereby reducing the disaster caused by the typhoon.

②Warm cloud catalysis. Water droplets with a diameter slightly larger than 0.04 mm are sown in the cloud, causing them to collide with the cloud droplets, grow into raindrops and fall to the ground. This method is very inefficient, only a few million raindrop embryos can be formed per gram of water. If you sow hygroscopic salt particles of appropriate size, it can also promote the formation of raindrops, and the efficiency is higher than sowing water droplets. Each gram of salt can form approximately tens of millions of raindrop embryos, and then form raindrops through the collision and merger process. This method can promote warm weather. Clouds increase precipitation. Spreading salt particles in warm fog or some warm clouds causes the fog droplets or cloud droplets to evaporate. The salt particles absorb moisture and grow up and fall, which can also achieve the purpose of eliminating fog or clouds.

Means of cloud seeding

① Sowing on the ground, brought into the cloud through air movement. Although this method is simple, it is difficult to control where the catalyst enters the cloud and how much it can enter the cloud.

② Load the catalyst into a rocket warhead or anti-aircraft shell and launch it to a predetermined location in the cloud. Although this method is rapid and direct, its capacity is limited.

③Use an airplane to sow the catalyst directly into the cloud. This method has high maneuverability and large carrying capacity, but is sometimes limited by flight safety.

In addition to the cloud seeding method, heating the air to eliminate fog or prevent frost also has certain effects. However, this method is very expensive and can only be used in a small area, such as fog elimination on airport runways and frost protection in orchards. In addition, the upward jet of high-temperature airflow is used to promote convective movement of local air in the sky or clouds, increasing local water vapor condensation and precipitation; changing the ground state or spreading carbon black particles in the air to absorb more solar radiation, changing Thermal structure of local air. These methods are still in the exploratory stage.

Relationship with other disciplines Artificial weather modification involves a variety of disciplines and technologies. Its theoretical basis is atmospheric science, specifically the physics of clouds and precipitation. It widely applies the results of mathematical statistics in experimental design and effect testing. In the research process of cloud seeding catalysts, knowledge from disciplines such as crystallography and surface chemistry is used. The diffusion of catalysts in the air and clouds involves atmospheric turbulence and small-scale motions. In terms of observation technology, it involves measurement technology of meteorological elements and cloud particles, weather radar (including Doppler radar, dual-wavelength radar) technology, microwave detection technology (see microwave atmospheric remote sensing), meteorological satellite measurement and tracer measurement, Ultra-trace chemical analysis, etc. In terms of cloud seeding technology, it involves the design and production of rockets, artillery shells and pyrotechnic agents. The progress of numerical simulation depends on the development of electronic computers. On the other hand, the development of artificial weather modification has also promoted the development of atmospheric science and related fields.