It's finally snowing in the north! From Feb. 13 to Feb. 14, the largest and strongest snowfall occurred in North China since winter. The snow was very strong. It brought beautiful snow and fresh air and moistened the thirsty winter wheat in the north.
However, just when people's Wechat friends circle was brushed by snow scenery, there was a news circulating in many places that the snow was artificially increased. Artificial snow shells contain silver iodide, please pay attention not to let children eat snow; after playing with snow, wash hands in time to prevent damage to skin caused by silver iodide; after snow melting, silver iodide floats more in three or four days, remember to wear a mask...
There are also online posts that the implementation of artificial snow enhancement in upstream areas will "cut off water in the air", reduce precipitation in downstream areas, and affect the ecological environment.
It's hard to get out of the snow, but it's hard not to be "toxic" and harmful to health. What is the truth? Will artificial snow increase affect the ecology of downstream areas? Journalists in the "Evidence" column interviewed relevant experts.
How about artificial snow enhancement in this snowfall in North China?
Response: Nine provinces (regions and municipalities) have carried out artificial snow enhancement operations, increasing snowfall by about 7%-11%.
Reporters learned from the weather modification center of China Meteorological Administration that 9 provinces (districts and cities) such as Hebei, Shanxi and Inner Mongolia have carried out snow enhancement operations during the snowfall from 13 to 14 February. Among them, 720 ground snowing operations, 818 anti-aircraft artillery shells and 2306 rockets were fired, 17 aircraft snowing operations and 71 silver iodide flame bars were burned.
"The area affected by this operation is about 155,000 square kilometers, of which 55,000 square kilometers are affected by ground operation and 100,000 square kilometers are affected by aircraft operation." Li Jiming, an expert and researcher of China Meteorological Administration on weather modification, said, "Based on the reported data from various provinces and the preliminary assessment results of the National Weather Modification department, this artificial increase of snowfall is about 7%-11%. It has played an important role in alleviating drought, increasing soil moisture in winter wheat areas and reducing the fire risk level of forest and grassland."
Li Jiming introduced that the main catalyst for artificial snow enhancement was silver iodide. The principle is to sow the catalyst to the appropriate part of the cloud, increase the concentration of ice crystals in the cloud, and then trigger cloud snowfall or increase its snowfall intensity. If there are no ice crystals in natural clouds or the concentration of ice crystals is low, the natural snowfall process may be delayed or the snowfall amount is small. At this time, if the concentration of artificial ice crystals is increased by artificial sowing of silver iodide, the process of ice-water transformation can be promoted, so as to achieve the goal of early snowfall or increase the amount of snow.
"Artificial weather modification operations are local, the use of catalysts is minimal, and the operation time and impact range are limited. Relevant scientific research at home and abroad has shown that weather modification has no negative impact on the ecological environment and human health. Li Jiming said.
Does air moisture affect the downstream of artificial snow interception?
Response: Artificial snowfall in the upper reaches of the weather system will not affect the snowfall in the lower reaches.
Some people worry that artificial snow enhancement in the upper reaches of the weather system will affect the snowfall in the lower reaches, resulting in less snowfall in the lower reaches.
"Water vapor and clouds in the air are not water resources that can be directly utilized like rivers on the ground. In the process of large-scale precipitation, water vapor is constantly supplemented, updraft is constantly changing, and clouds are constantly forming and developing. Li Jiming said, "In a wide range of systematic snowfall weather process, artificial snowfall can only affect local clouds. It will not intercept upstream and reduce downstream water like river water, so it will not have an impact on the downstream cloud snowfall."
In the process of artificial snow enhancement, first of all, the cloud system suitable for snow enhancement should be determined in advance through weather forecast and cloud forecast, and the operational scheme should be designed, and the operational tools such as aircraft and rocket should be prepared. When the weather system is approaching, satellite and radar are used to track and monitor the cloud system. When it meets the snowing conditions, declare the operating airspace, launch aircraft, launch rockets, and carry out snowing operations. After the operation, the radar echo and ground snowfall data are comprehensively used to evaluate the operation effect.
"A large number of field scientific experiments of artificial snow and precipitation enhancement have been carried out at home and abroad. The long-term statistical results show that the precipitation can be increased by 6%-25% of natural precipitation if the artificial catalytic technology is used correctly. Li Jiming said.
With the continuous improvement of operational capacity, management level and service efficiency, weather modification plays an increasingly significant role in disaster prevention and mitigation, water resources security, drought and hail suppression, forest and grassland fire risk reduction and ecological restoration.
In the "China Water Tower" Sanjiangyuan area, since 2006, the state has supported the development of the ecological protection type artificial precipitation enhancement business of Sanjiangyuan. According to the Qinghai Provincial Weather Affection Department, after artificial precipitation enhancement in Sanjiang Source, the precipitation showed a significant increase trend. During the period of 2006-2017, under the combined action of natural precipitation and artificial precipitation and snow, the average annual precipitation reached 513 mm, an increase of 42.7 mm compared with that before the implementation of artificial precipitation and snow enhancement; the water inflow from the hydrological stations of Tangnaihai in the upper reaches of the Yellow River and Zhimen in the headwaters of the Yangtze River increased by 20.0% and 36.2%, respectively. The ecological environment of the source of the three rivers has shown a trend of improvement.