It is extremely important and urgent for urban management and public services, as well as for individuals and families to take precautions against high winds

□Author: Kong Feng (Associate Professor, Department of Public Administration and Development, College of Humanities and Development, China Agricultural University)

4月10日，北京市氣象局發佈大風橙色預警，這是北京近十年發佈的首個全市大風橙色預警。預計，11日17時北京市延慶、昌平、門頭溝、房山開始出現大風天氣，20時前後影響城區，夜間陣風逐漸增大至8、9級，12日6時至22時為風力最強時段，全市平均風可達6級，平原地區陣風9-11級，延慶、昌平、門頭溝、房山、懷柔、平谷、密雲等區的部分地區陣風11-13級，山區局地陣風可達13級以上，並伴有沙塵和強降溫天氣。罕見極端大風如何形成？我們又該怎麼防範？

"Several factors" in the formation of extreme gales

From the point of view of the cause, this time極端大風It is affected by a combination of cold vortex system, seasonal factors and topographic factors.

根據公開報導，4月10日白天冷渦在蒙古國生成，沿西北-東南方向於4月11日夜間移至北京，隨後加強並緩慢東移。冷渦後不斷有強冷空氣持續影響北京，從而帶來極端大風天氣，這是此次大風的主要成因。

In terms of seasons, spring is a period of frequent alternation of cold and warm air, with cold air masses dominating in winter and warm air masses in summer, while cold and warm air alternate frequently in spring, and strong winds are brought every time strong cold air moves south at high latitudes. At the same time, after the vernal equinox, the solar radiation increases, and the surface and near-surface air heat up rapidly, but the upper-air atmosphere still retains the characteristics of low temperature and strong wind in the winter half of the year. When the temperature difference between the ground and the upper altitude is large, the movement of warm air rising and cold air falling is more frequent and intense, and the wind energy at the upper level is easy to be transmitted to the ground, making the ground wind greater.

Due to the complex topography of Beijing, with mountains and plains, when the airflow enters the narrow terrain from the open area, such as valleys and canyons, the channel becomes smaller, the air circulation speed accelerates, and the wind force will increase suddenly, resulting in a narrow tube effect. Strong winds are generated between high-rise buildings in cities with small spacing, and when strong cold air is encountered, the wind can suddenly increase and become disastrous windy weather.

Why is the wind "extraordinary"? Ma Xueyuan, chief forecaster of the Central Meteorological Observatory, believes that this is related to the violent confrontation between cold and warm air, the "downward transmission of energy" of high-altitude strong winds, and the "magnifying glass" effect of topography and cities.

Before the arrival of cold air, North China experienced a significant "frontal warming", and the convergence of cold and warm air formed a strong temperature gradient (40°C/0 km) and a pressure gradient (0 hPa/0 km), which was the maximum value in the same period in the past ten years, which directly drove the generation of surface winds. In the middle troposphere, there is a westerly jet with winds of up to 0 m/s (0 km/h), which is affected by solar radiation during the day, the atmospheric thermal conditions are sufficient, and the strong winds at high altitude conduct energy to the ground through turbulence, increasing the surface wind speed by an additional 0% to 0%. The "V" forms a type of "natural wind channel" in the valley land at the eastern foot of Taihang Mountain and the southern foot of Yanshan Mountain, and the compressed air flow causes a sudden increase in wind speed. The high-rise buildings in megacities such as Beijing and Tianjin form a "wind corridor", and the local wind speed is 0% stronger than that of the surrounding areas, and the wind direction disorder is easy to cause local extreme strong winds.

Apart from“Do not travel unless necessary”What else can be done?

According to relevant common sense, gusts of wind above level 30 will have a greater negative impact on production and life; When the gust of wind reaches level 0, it is very difficult to walk outdoors; Category 0 gusts can blow off trees up to about 0 cm in diameter. Therefore, it is extremely important and urgent for urban management and public services as well as individual families to take precautions against high winds.

City managementIn terms of public services, it is necessary to strengthen the inspection and maintenance of facilities, do a good job in traffic management and guidance, and prepare for emergency rescue. For example, strengthen the inspection of outdoor billboards, plaques, street lights, bus stops, telephone poles and other public facilities, and repair or replace damaged parts in a timely manner; The traffic management department should timely release road condition information and traffic control measures through radio, television, Internet and other media to remind drivers to pay attention to safety; Strengthen the management of airports, railway stations, long-distance bus stations and other transportation hubs, adjust flights and train numbers in a timely manner, and do a good job in the evacuation and resettlement of passengers. In addition, firefighting, medical, electricity, water supply and other departments should make emergency rescue preparations, arrange on-duty personnel and rescue equipment in advance, and ensure that they can respond quickly when disasters caused by strong winds.

Individuals and families need to enhance their safety awareness, do a good job of home protection, and "do not travel unless necessary". Pay close attention to the gale warning information, understand the specific situation of the gale, such as the start time, end time, wind level, impact range, etc., plan and prepare in advance, and avoid unnecessary outing activities in windy weather; Carefully check whether the doors and windows are firm, clean up the flower pots, sundries, drying racks and other items on the balcony, window sill, and roof to prevent pedestrians from being blown off by strong winds and injuring pedestrians or damaging items; If you must go out, wear windproof clothing to avoid being blown down by strong winds or injured; Stay away from billboards, neon signs, street light poles, power poles, large trees, and other objects that may be blown down, and try to choose an open road without obstacles.

Educational institutions and other public places should strengthen safety education and safety precautions in public places. Carry out safety education for students in windy weather, and inform students of the precautions in windy weather, such as not chasing and fighting outdoors, not approaching dangerous objects, etc. Shopping malls, theaters, stations and other public places should do a good job of safety management, strengthen the guidance of personnel, avoid gathering at entrances and exits, passages and other places, and prevent accidents such as crowding and falling due to strong winds.

Communities and property management should also do a good job in property protection while strengthening community publicity and organization. For example, timely publicize the hazards and defense knowledge of windy weather to residents, improve residents' awareness of self-protection, and strengthen security patrols in the community to detect and deal with potential safety hazards in a timely manner.

Editor: Wang Yintao

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