Level 4 wind speed is 5.5-7.9m/s, which belongs to breeze, and the ground is characterized by blowing dust. Generally speaking, according to various phenomena caused by wind blowing on objects on the ground or water surface, the wind force is divided into 13, with a minimum of 0 and a maximum of 12.
In windy weather, it is recommended to take the train if you want to travel. Highway traffic is usually most affected by typhoons. As far away from the construction site as possible, it is best to keep a little distance when passing through the construction site, because some construction site walls may become loose after rainwater infiltration; There are also some fences that may collapse; Some materials scattered on high buildings that are not collected in time, such as steel pipes and hammers, may be blown down by the wind.
The cause of wind formation
Wind is a kind of air flow phenomenon on the earth, which is generally caused by solar radiation heat. Sunlight shines on the earth's surface, causing the surface temperature to rise, and the surface air to expand and become lighter and lighter. After the hot air rises, the cold air with low temperature flows in horizontally, and the rising air falls down because it gradually cools and becomes heavier. Because the surface temperature is high, it will heat the air and make it rise. This airflow is the wind.
When the gathered water vapor (cloud) forms water, its volume shrinks, and the surrounding water vapor comes to replenish it, forming wind. The wind on the earth is related to the water source, and the wind is produced by the expansion and contraction of water and steam. The wind blows from the ocean to the land, or the land blows to the ocean. In summer, when the ground temperature is high, air and water vapor expand and rise, so the air space on the ground should be supplemented by air and water vapor heavier than the sea surface, and air contracts when the sea surface temperature is low.
It is necessary to supplement the air space on the sea surface with air and water vapor rising from air with high ground temperature. In winter, when the sea surface temperature is high, the sea surface air rises, and when the ground temperature is low, the proportion of air is heavy, which supplements the sea surface space along the ground.