Before the heavy rain, a few shells won't come down.

Weather modification refers to the activities that artificially affect the physical and chemical processes of the local atmosphere through scientific and technological means under appropriate conditions, so as to avoid or mitigate meteorological disasters and achieve the purposes of increasing rain and snow, hail suppression, rain elimination, fog elimination and frost prevention.

fundamental principle

According to the physics principle of cloud and precipitation, it is a scientific and technical measure to transform some local weather processes into a direction beneficial to human beings mainly by sowing catalysts in the cloud. Also known as weather control. Artificial precipitation enhancement, hail suppression, cloud elimination, fog elimination, frost prevention, storm (typhoon) mitigation and lightning suppression.

The energy of natural weather process is enormous. The amount of water vapor condensed by a storm is about 6.5438+million tons, and its latent heat of condensation is about 2.5× 10 16 joules, which is equivalent to the heat of burning 4.8 million barrels of oil. The heat released by the condensed water vapor per minute of a typhoon is equivalent to the energy released by the explosion of a 20 million-ton nuclear bomb. It is actually impossible and uneconomical to directly consume so much energy to create or eliminate a weather process. Therefore, it is necessary to find the available conditions in the natural weather process and promote it to the predetermined direction at a small cost. This is an experiment of weather modification.

Form of implementation

In the experimental study of weather modification, artificial precipitation enhancement is the most widely carried out. The scale of artificial hail suppression is second only to artificial precipitation enhancement. China, the United States, the former Soviet Union, Switzerland and other countries have carried out a large number of artificial hail suppression experiments, reducing the loss of cash crops such as orchards, but after strict scientific inspection, the results are different. Manual defogging was carried out earlier. In the 1940s, an attempt was made to eliminate the fog on the airport runway by heating, which cost a lot, but achieved considerable results. The technology of eliminating cold fog with dry ice or liquefied propane has been put into operation in some airports. Artificial cloud elimination is less carried out, and local supercooled stratus can be eliminated under certain conditions. Eliminating warm fog, artificially reducing typhoon and artificially suppressing lightning are still in the exploration stage.

The energy of natural weather process is enormous. The amount of water condensed by a storm is about 6.5438+million tons, and its latent heat of condensation is 2.5× 10 joule, which is equivalent to the heat of burning 4.8 million barrels of oil. The latent heat of water vapor released by a typhoon per minute is equivalent to the energy released by the explosion of a 20-million-ton nuclear bomb. It is actually impossible and uneconomical to directly consume so much energy to create or eliminate a weather process. Therefore, it is necessary to find the available conditions in the natural weather process and promote it to the predetermined direction at a small cost. The way to artificially influence the weather is mainly to use the microphysical process of clouds. For example, there are a large number of unfrozen water droplets in the cloud with the temperature below 0℃. Using seeding catalyst (see seeding catalyst), water droplets can be transformed into ice crystals and release latent heat, thus changing the microphysical process, thermal and dynamic structure of the cloud. Using this method to artificially influence the weather, the cost is relatively small, and the benefits may be great.

Weather modification is called "cloud seeding", which can not help but arouse people's imagination of agricultural seeding. For a farmer in China, it is more practical than anything to reduce natural disasters and keep a year's harvest. This demand, as a starting point, directly led to China's "shadow" (weather modification) ranking first in the world.

"The number of cloud seeding operations in China far exceeds the sum of other countries in the world." Professor daniel ross Field is a professor at the Institute of Earth Sciences of Hebrew University in Jerusalem. According to him, the demand for precipitation in Israel, which is famous for its drought and drip irrigation agriculture, should be much greater than that in China, while the frequency of weather modification in China is "almost unimaginable".

Overview of methods

The main method of weather modification is cloud seeding, that is, using airplanes, rockets or ground generators to sow catalysts such as silver iodide into the clouds, thus changing the microstructure of the clouds and changing weather phenomena such as clouds, fog and precipitation.

Catalyst classification

According to the nature of the object, the catalysts used for seeding clouds are also different, and the catalytic process can be divided into two categories:

① Leng Yun catalysis. There are often supercooled water droplets in clouds with the temperature of 0 ~-30℃. If ice-forming catalysts such as silver iodide or solid carbon dioxide (also known as dry ice) are sown in this cloud, a large number of artificial ice crystals can be generated. This catalyst has high icing efficiency. 1 g catalyst can generate 1 trillion ice crystals, which makes the concentration of 1 ice crystals per liter/kloc-0 in the cloud of cubic kilometers. In some clouds, artificial ice crystals can form precipitation through the Bergeron process (see microphysics of clouds and precipitation), thus achieving the purpose of artificial precipitation enhancement. In strong convective clouds, artificial ice crystals can grow into hail embryos and compete with natural hail for water, so that each hail can not grow into a large hail block with serious harm, thus achieving the purpose of hail suppression. In Leng Yun (fog), artificial ice crystals make cloud (fog) droplets evaporate, grow and land on their own, and can also achieve the purpose of eliminating clouds (fog). The huge latent heat released in the process of Leng Yun catalysis will change the thermodynamic and kinetic process of clouds, and the catalysis focusing on this dynamic effect is called kinetic catalysis. Kinetic catalysis can make some convective clouds develop and increase precipitation. The dynamic catalysis of some parts of the typhoon cloud system may change the circulation structure of the typhoon, weaken its maximum wind force, and thus alleviate the disasters caused by the typhoon.

② Warm cloud catalysis. Scatter water droplets slightly larger than 0.04 mm in diameter in the cloud, so that they collide with the cloud droplets, grow into raindrops and fall to the ground. This method is inefficient, and only a few million raindrop embryos can be formed per gram of water. If the hygroscopic salt particles with appropriate size are sown, raindrops can also be produced, which is more efficient than sowing raindrops. Each gram of salt can form tens of millions of raindrop embryos, and then raindrops are formed through the collision process. This method can promote warm clouds and increase precipitation. Sprinkling salt particles in warm fog or some warm clouds makes the fog or cloud droplets evaporate, and the salt particles absorb moisture and grow up and fall, which can also achieve the purpose of eliminating fog or cloud.

Cloud seeding means

(1) Sow seeds on the ground and enter the clouds through air movement. Although this method is simple, it is difficult to grasp the location and quantity of catalyst that can enter the cloud.

(2) Load the catalyst into the rocket warhead or anti-aircraft gun shell and launch it to a predetermined position in the cloud. Although this method is fast and direct, its load is limited.

(3) The catalyst is directly spread to the cloud by airplane. This method has strong maneuverability and heavy load, but it is sometimes limited by flight safety.

In addition to sowing clouds, heating air to eliminate fog or prevent frost also has certain effects. However, this method is expensive and can only be used in a small range, such as defogging of airport runways and frost prevention of orchards. In addition, the upward high-temperature airflow is used to promote the local air in the air or in the cloud to produce convective motion, which increases the local water vapor condensation and precipitation; Changing the ground state or dispersing carbon black particles in the air can absorb more solar radiation and change the thermal structure of the local air. These methods are still in the exploratory stage.

Relationship with other disciplines Weather modification involves many disciplines and technologies. Its theoretical basis is atmospheric science, especially the physics of clouds and precipitation. It widely uses the results of mathematical statistics in experimental design and effect test. The knowledge of crystallography and surface chemistry is applied to the study of catalytic clouds. The diffusion of catalyst in air and clouds involves atmospheric turbulence and small-scale movement. In terms of observation technology, it involves the measurement technology of meteorological elements and particles in the cloud, meteorological radar (including Doppler radar and dual-wavelength radar), microwave detection technology (see microwave atmospheric remote sensing), meteorological satellite measurement, tracer measurement and ultra-micro chemical analysis. In the aspect of cloud seeding technology, it involves the design and manufacture of rockets, shells and initiating explosive devices. The progress of numerical simulation depends on the development of electronic computers. On the other hand, weather modification has also promoted the development of atmospheric science and related fields.