Artificial rainfall will come down as soon as it is said？ What is the biggest impact on the landing site when the typhoon hits？ Meteorological Day tells you the truth.

　　Typhoon must bring heavy precipitation, artificial precipitation can be increased if it wants, lightning will not hit the same place twice, and fault clouds can predict earthquakes … … 365 days a year, typhoons, thunder and rain, these weather phenomena are closely related to our "looking up but not looking down", and are closely related to human production and life. So, are these statements circulating on the Internet true?

　　March 23rd is World Meteorological Day, also known as "International Meteorological Day", which is the anniversary of the establishment of the World Meteorological Organization in 1960. The theme of this year’s Meteorological Day is: climate and water. The reporter of Science and Technology Daily visited many experts in Nanjing University of Information Science & Technology and listened to what they said.

　　Typhoon landing point is the strongest and most affected?

　　Truth: The storm is most concentrated about 30 kilometers away from the typhoon eye.

　　In 2019, the super tropical storm "Lichima" was frightening. But surprisingly, when it moves to the east of Taihu Lake at a speed of 15 kilometers per hour, the typhoon eye is almost calm and calm, while the storm outside is about 100 kilometers.

　　It is not news that the weather in the eye of typhoon is mild, but if you ask where the typhoon is most affected, many people may say it is the landing place, because the more you think, the weaker the power of moving the typhoon inland. Actually, typhoon is a complicated weather system, which is not as simple as everyone thinks.

　　A mature typhoon cyclone usually has a radius of 500 to 1000 kilometers and a height of 20 kilometers. The typhoon consists of three parts: the peripheral area, the maximum wind speed area and the typhoon eye. The landing place of the typhoon is the place where the typhoon center initially moved to land.

　　When it comes to the place with the strongest wind and rain, the "eye wall" does its part. "The place about 30 kilometers away from the typhoon eye is the area with the strongest wind and rain, which we call the eye wall. There is a strong updraft on the eye wall, and there are frequent storms and the weather is the worst. " Ge Xuyang, a professor at Nanjing University of Information Science & Technology Institute of Atmospheric Sciences, said.

　　No matter how big or small a typhoon is, it will not only affect the typhoon center or landing place. There was a strange phenomenon in 2004. At that time, Typhoon No.18 landed in the eastern part of Fujian Province on August 22, with heavy rain in the central area and weakened into a tropical storm around August 28. Unexpectedly, there were also heavy rains in Shandong, Henan and other places far away from the typhoon, which brought different degrees of influence to the local area.

　　Ge Xuyang explained: "Typhoon precipitation is divided into two types, typhoon main precipitation and remote precipitation." The main precipitation is the precipitation within the scope of typhoon, which is the most common and the focus of prevention at present. Long-distance precipitation occurs hundreds of kilometers away from the typhoon. When warm air from above the ocean meets cold air from the north, and the interaction of inland mid-latitude systems, long-distance precipitation will occur.

　　In Ge Xuyang’s view, typhoon precipitation has a certain relationship with typhoon intensity. Some typhoons have low intensity, so the wind and rain are not great. Although some typhoons have high intensity, their intensity will gradually decrease due to ground friction after landing. There is no doubt that typhoon arrival brings precipitation, but it may not always be heavy precipitation.

　　Can artificial precipitation increase if you want?

　　Truth: It is a prerequisite that natural clouds have already fallen or are close to falling.

　　After burning for 210 days, the fire in Australia finally went out on February 13th this year. The fire caused heavy losses in Australia, killing hundreds of millions of animals and destroying 11.7 million hectares of land.

　　Someone will ask, why not directly use artificial rainfall to put out the fire? Don’t be naive, artificial rainfall can’t fall if you want.

　　Industrial rainfall does not make rain out of thin air, but requires certain natural conditions.

　　Dr. Jing Xiaoqin from Nanjing University of Information Science & Technology Institute of Atmospheric Physics introduced that there are two main methods of artificial rainfall — — Warm cloud catalysis and Leng Yun catalysis. Warm cloud refers to the cloud whose temperature is higher than 0℃, which mainly relies on the collision mechanism of cloud droplets to trigger precipitation. Leng Yun below 0℃ needs an appropriate amount of ice cores to rain. Without such physical conditions, even if the weather situation is good and the water vapor conditions are good, it is difficult to achieve rainfall.

　　The process of artificial rainfall is not complicated, and the common way is to shoot the shells loaded with catalysts into the clouds. Jing Xiaoqin concluded that there are "three appropriateness" in artificial rainfall, that is, appropriate position, appropriate dose and appropriate time.

　　Artificial snowfall containing silver iodide is harmful to human body?

　　Truth: The content per unit area is far below the WHO standard.

　　In recent years, there are rumors on the Internet that the rain and snow brought by the use of silver iodide catalyst contain heavy metals, so some people call on children not to eat snow and wash their hands in time after playing. So, is silver iodide really so poisonous?

　　Generally speaking, a shell has only 10g of catalyst, and silver iodide is scattered in a large area, and the content of heavy metals per unit area is very small. Researchers have investigated a region in the midwest of the United States for many years. This region is relatively short of water, and artificial rainfall has been used for a long time. The monitoring results show that the iodine concentration in the local air is far below the standards of the World Health Organization. People need not be nervous.

　　In addition, the catalysts used in warm clouds are different from those used in Leng Yun. In warm clouds, hygroscopic particles such as salt powder and urea are used to generate large cloud droplets, while in Leng Yun, catalysts such as dry ice and silver iodide are used to increase the density of ice nuclei or ice crystals in the air. "Among these catalysts, the nucleation efficiency of silver iodide is very high, and only 1 gram is needed to form 1015 ice nuclei." Jing Xiaoqin said.

　　In recent years, scientists continue to develop efficient and safe catalysts, such as lasers, but at present, they are limited to the laboratory stage and have not been put into large-scale application.

　　Can fault clouds predict earthquakes?

　　Truth: The obvious dividing line in the sky is influenced by the weather system.

　　We often hear that there are "earthquake clouds" in our lives. Many people think that those strange-looking clouds can predict earthquakes. In fact, the "earthquake cloud" does not exist at all, and experts have rumored it for many years.

　　"I saw some pictures of fault clouds posted by netizens on the Internet. In fact, most of them are altocumulus clouds, which are ordinary clouds. The reason why the clouds in the sky are uniformly cut off by half and the clouds and the blue sky are distinct is actually caused by the influence of different weather systems. " Wang Weiwei, a senior experimenter at Nanjing University of Information Science & Technology Atmospheric and Environmental Experimental Teaching Center, explained, "If there is strong dry and cold air, the cold air will push the original clouds in the sky to move in a certain direction, and the blue sky will become larger and larger. There will be a clear dividing line between the clouds. "

　　For ordinary people, it is very beneficial to identify some rain clouds or clouds representing fine weather in the sky for daily travel.

　　It is often said in the weather forecast that "there will be formation precipitation in some areas in the afternoon". This kind of convective precipitation is local and difficult to predict accurately. Wang Weiwei gave us a trick. If it is found that there are only a few light cumulus clouds and a few clouds (thick cumulus clouds) like cauliflower in the sky, and the cauliflower clouds do not develop vertically to the high altitude, it will not rain. And if the cauliflower becomes huge and heavy, and the cloud top keeps developing to the high altitude, be careful at this time, it may rain.

　　Lightning doesn’t strike the same place twice?

　　Truth: The taller you are, the greater the probability of being struck by lightning.

　　The clouds are erratic. By contrast, Lei is much more "quiet" because he will visit one place more than once.

　　If you still believe that lightning can’t strike the same place twice, then the lightning rod will tell you that this is not true.

　　"Although lightning is highly random, in the same area, the higher the building, the greater the probability of lightning strike. &lsquo in Guangzhou; Small waist ’ It is a very typical example. It attracts more than 100 lightning strikes a year, and almost all the lightning within one kilometer of Fiona Fang is absorbed by it. " Tan Yongbo, a professor at Nanjing University of Information Science & Technology Institute of Atmospheric Physics, said.

　　Tan Yongbo told reporters that Guangdong and Guangxi are high-incidence areas of lightning in China, which is related to the fact that the two provinces are located in the tropics and subtropics. Coupled with the influence of the monsoon, there are more strong convective weather. In addition, the southeast coastal areas are also lightning-prone areas, and with the decreasing precipitation, the lightning in the central and western regions is gradually decreasing.

　　"But there is one exception. There are relatively many mountain thunderstorms on the Qinghai-Tibet Plateau. This is because the altitude there is higher, the ground temperature is lower, and the clouds in the sky can easily reach 0 C, producing a large number of ice cores, which is conducive to the formation of convective weather. " Tan yongbo said.