Shulou(Shulou.com)11/24 Report--

The largest sandstorm so far this year has hit Hefei. How did the dust blow to Hefei? What kind of impact will it have?

Since March 20, the north has experienced the largest sandstorm this year. For comrades in the northern region, it is no longer particularly obvious whether the dust is "maximum" this time, because the north has already experienced three sandstorms in March, and the Beijing-Tianjin-Hebei region has also experienced two. However, this time the dust still uses some special scenes to show its "maximum" status. The same Martian "Blue Sun" appeared in Beijing; in Changchun, Rain Water absorbed sand and dust, resulting in an immediate sense of mud rain, and the owner of the car wash was so busy that he fainted.

Although there are many windy and dusty weather in March, the causes of sandy dust are basically unchanged, that is, windy weather and sandy dust. Winter and spring is the season of frequent cold air and strong winds, but the surface freezes and even snows in winter, while the warmer temperatures in spring and the sun make the surface loose, and when the strong wind passes through these sand sources, it will sweep the dust into the air. As the strong wind blew to the southeast, the dust weather swept in.

Whenever the sand and dust weather strikes, some people will question the role of the three-north shelterbelt, but this is difficult for the three-north shelterbelt. The sand sources of sand and dust weather are Mongolia, western Inner Mongolia and Gansu. For the sand and dust weather in Beijing-Tianjin-Hebei region, Mongolia is the main source of sand and dust, which is beyond the capacity of the three-north shelterbelt. In addition, the height of sand and dust is often only a few hundred meters, while the height of dozens of meters of shelterbelt is obviously only partially protected. Although the protective capacity is limited, the role of shelterbelt in sand prevention and sand fixation is still obvious. The research of the Institute of Atmospheric Physics of the Chinese Academy of Sciences shows that the activity of sandstorms in East Asia has weakened in the past 20 years. From the perspective of the reasons for the change, the weakening of surface wind speed, the increase of vegetation cover and soil moisture all played an important role, contributing 46%, 30% and 24%, respectively.

Fig. 1 comparison between the simulated surface sand flux (magenta line) and the number of sandstorm days (black line) observed at the station in the main dust source areas of northern China and Mongolia (linear trend, R is the correlation coefficient between the two), but for comrades in the south, sand and dust is mostly a scene living in the news, and this is the case of "less"-the south will also face dust weather. This is also the reason why this sand dust is called the largest sand dust weather: not only large, but also wide. According to the forecast of the Central Meteorological Observatory, sand and dust will affect Hefei from 23 to 24. Henan roommates who heard the news said: I feel at home. Zhejiang roommate said: how can there be dust in Hefei?

Hefei is still cloudy and rainy, how can there be sand and dust? In terms of the specific reasons, the dust weather is one of the results caused by the cold air moving south. The precipitation in Hefei in recent days is also the result of the confluence of cold air and warm air masses moving south. With the invasion of cold air to the south, the main rain belt has been suppressed to the area of Jiangxi and Fujian, which means that Hefei has been controlled by cold air masses-which is creating conditions for sand and dust weather. Therefore, this round of cold air has brought both precipitation and dust to the south.

Fig. 2 Radar reflectivity map considering the recent overcast and rainy weather in Hefei, some people will be worried: will it rain like Changchun? The answer is no. On the one hand, the precipitation process in Hefei is basically over; on the other hand, after long-distance transportation, the larger particles in the dust have taken the lead in settling, while the particles arriving in Hefei are relatively small and relatively difficult to settle. At the same time, the sand and dust weather has gradually weakened from blowing sand to blowing dust, which can be said to be weak. At the time of writing this article, Hefei was still in a state of rain and fog, which also played an inhibitory role in sand and dust.

Figure 3 12:00 PM10 map on the 23rd, you can see from the map that the sand and dust front has crossed Hefei and headed further south. However, due to weather, vegetation, topography and other factors, the impact of sand and dust farther south will be less and less. It will be more difficult for comrades in Jiangxi, Fujian and other regions to feel the attack of sand and dust.

I hope that friends from all over the country will be able to have this kind of difficulty in the future.

reference

Wu C, Lin Z, Shao Y, et al. Drivers of recent decline in dust activity over East Asia [J]. Nature Communications, 2022, 13 (1): 7105.

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), author: Xing Si

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