Why do landmark buildings in Beijing collectively "disappear"?

201July 4th, Beijing Meteorological Observatory issued the blue warning signal of sandstorm at 05: 30 on May 4th, 201July. Affected by the upstream sandstorm and sand blowing weather, it is expected that there will be sand blowing or floating dust weather in Beijing from the morning of the 4th to the day, and the visibility will drop obviously. Please take preventive measures.

At present, many landmark buildings in Beijing collectively "disappear" under the influence of dusty weather.

The picture shows the Forbidden City and Beihai in Beijing on May 4th, 20 17.

The picture shows that on May 4th, 20 17, Beijing boarded Wanchun Pavilion in Jingshan Park and looked around. The whole capital is like a "foggy city".

The picture shows the Olympic Park and the Bird's Nest behind it.

The picture shows the Monument to the People's Heroes.

Small knowledge of sandstorm:

Many sandstorms have no sand.

"Sandstorm" is not an accurate scientific term. Most of the major disastrous weather events related to sandstorms in the world are "sandstorms", not "sandstorms".

A large number of dust particles, under the repeated action of the wind, will be blown to the downwind in the distance sooner or later and deposited, eventually forming loess. Therefore, under the action of wind, the debris formed by rock weathering is sorted into three places, gravel is left in the local area to form Gobi desert, sand forms sand dunes not far from the parent rock, and moves slowly with the wind, while dust is carried far away by the wind to form loess accumulation.

Grades and standards of sandstorms

Classification of floating dust: a weather phenomenon in which dust and fine sand float evenly in the air, making the horizontal visibility less than 10 km; Sand blowing: a weather phenomenon in which the wind blows up dust on the ground, making the air quite turbid and the horizontal visibility is within the range of 1 km to1km; Sandstorm: a weather phenomenon in which strong winds blow up a lot of dust on the ground, making the air very turbid and the horizontal visibility is less than 1 km; Strong sandstorm: a weather phenomenon in which strong winds blow up dust on the ground, making the air fuzzy and turbid, and the horizontal visibility is less than 500 meters; Super sandstorm: a weather phenomenon in which strong winds blow up dust on the ground, making the air particularly turbid and the horizontal visibility is less than 50 meters.

According to the standard, the yellow warning standard of sandstorm: 12 hours, sandstorm weather may occur (visibility is less than 1000 meters). Orange warning standard for sandstorm: Strong sandstorm weather may occur within 6 hours (visibility is less than 500m). Red warning standard of sandstorm: Strong sandstorm weather may occur within 6 hours (visibility is less than 50 meters).