What is the city wind? How is the urban wind formed? Is there a difference between urban wind and rural wind?

In the north of Liaodong Peninsula, there is a beautiful small town-Phoenix, which stretches for hundreds of kilometers by the sea. About 400 meters east of Phoenix, there is a mountain with an altitude of 900 meters, called Phoenix Mountain.

As a famous mountain in Liaoning and a gathering place for tourists, Phoenix Mountain was once known as "the first risk in the world".

When I was a child, I grew up at the foot of Phoenix Mountain and had a special complex for Phoenix Mountain. The winding Yanghe River and the beautiful Phoenix Mountain have brought me fantastic childhood and colorful fantasies. The environment near the mountain and the water has created the children's spiritual hearts and simple feelings of Shan Ye.

In the memory of childhood, Phoenix Mountain is as mysterious and distant as a natural screen. Let me listen to the legend left by my ancestors in the legend of Phoenix Mountain. ...

It is said that in the early years of the Tang Dynasty, Li Shimin, the king of the Tang Dynasty, led an army across the sea to conquer the East. Starting from Xi 'an, the capital, I boarded the boat from tanggu port, Tianjin, disembarked at Bayuquan, Yingkou, and stayed in the house at the foot of the Phoenix Mountain at the junction of the two countries at that time. At this time, he saw a pair of phoenixes dancing in front of the mountain, hovering over the head of the Tang king for three times and hiding in the mountain, but there was no trace of them.

The king of Tang was very happy when he saw this scene, and gladly led the officers and men to ride up the mountain.

When I walked to both sides of the mountain road, suddenly, it was full of sunshine and singing. The mountains seem to be covered with colorful clouds. Tang Wang had a good time, thinking it was a precursor to the crusade, and rode into the mountains quickly. Not far from the gate, a cave was found. The cave was empty, only a few phoenix feathers were scattered on the ground.

When Li Shimin was happy, he happily took up the pen and named the cave "Phoenix Cave", which has continued to this day.

The army led by Marshal Xue () of the Tang Dynasty fought decisively with North Korea in the east of Phoenix. Break through the camp of the three armies of Korea in one fell swoop and capture Marshal Gai Wenshu alive. Then come to the foot of Phoenix Mountain to negotiate.

At that time, Li Xue's archery was superb, so he proposed to use arrows to determine national boundaries. Where the arrow he shot landed, the national boundaries were divided. Gai Wenshu questioned that Li Xue's arrow shot too far, so he rode with Li Xue to a small town under Phoenix at that time, about 20 kilometers away from the location of Phoenix Mountain.

In order not to embarrass Han Feng too much, Betty left room for archery. The arrow passed through the main peak of Phoenix Mountain and landed at the gate of the Second Dam of Yalu River, so the Yalu River was the dividing line between Tang Dynasty and Korea.

Since then, Korea has to bow to the Tang Dynasty every year and pay tribute to it. It became a vassal state of Datang.

In order to commemorate the beginning and end of this crusade, people call the position where Li Xue stood, the place where he put the arrow, the hole where Li Xue shot through, the peak of the arrow eye and the place where the arrow landed "the crusade".

And this beautiful town was named Phoenix, and Phoenix Mountain was also named happily.

After several generations, until now, the beautiful legend of Phoenix Mountain has spread among the people and become the pride of people in rural fields and small towns.

Every leisure time, there will be some distant tourists coming to Phoenix Mountain one after another for sightseeing, and then set foot on the traces of Li Xue's voyage to the West to appreciate the ancient heroism.

On April 28th every year, tourists from all over the world flock to Phoenix Mountain to catch up with the temple fair, praying for the arrival of Phoenix and good omen for life.

As the seventh and eighth day of Liaodong Peninsula, Phoenix Mountain stands impressively at the top of the mountains and stands out from the crowd on the ocean line at an altitude of 1000 meters.

After years of wind and rain baptism, the face of Phoenix Mountain is still young and magnificent, and I have grown up under the hard feeding of Dayang River in Phoenix Mountain.

The majestic mountain gate, the mysterious Phoenix Cave, the straight back of an old cow, the eye of an arrow, a wide one-man mountain road, and numerous temples and pavilions, all these mysterious legends have brought the mystery and beauty of Phoenix Mountain into the eyes of the world, making people feel the mind of Phoenix Mountain in the aftertaste and watch its holiness and openness in the spiritual leap.

I love Phoenix Mountain. Although I left the small town, the warmth of my home and the complex of my hometown are still my dreams.

Wandering in her beautiful legend, looking for peace at the top of the mountain, the world can be seen at a glance from a distance. ...

Most industrial pollution sources are concentrated in cities, and the pollution concentration is inversely proportional to the square of wind speed, and the wind direction determines the transportation direction of pollutants. Knowing the wind direction and speed of your residence from the perspective of the whole city, combined with the weather forecast, will help you to take measures to prevent air pollution and avoid danger.

1, urban buildings gather with different heights, which increases the resistance of wind flow, so the wind speed in cities is generally smaller than that in suburbs; The city reduces the wind speed. Take Shanghai, the largest city in China, as an example. According to the average data for many years, the annual average wind speed in Shanghai is below 3m/s, while that in Yangpu District and Xuhui District with the lowest wind speed is only 2.3-2.4m/s, that in eight suburban counties is generally between 3m/s and that in Chongming and Nanhui outer suburbs is above 4m/s ... But specifically, the value of reducing wind speed in cities varies with the wind speed: there are fewer strong winds and fewer small winds. For example, high-rise buildings began to appear around the former site of Balizhuang in Beijing Meteorological Observatory in the late 1980s, which greatly reduced the number of windy days with high wind level, while the number of windy days with low wind level did not decrease much. When the air flows through the city, the wind direction will change and the wind speed will decrease. This is because when the wind speed in the urban area decreases, the geostrophic deflection force on the airflow also decreases, which will slightly deflect the airflow to the left. For example, in the balloon experiment at an altitude of 400 meters in Oklahoma City, USA, under the southerly wind condition of 1.3 m/s, the wind speed component on the left side of the low pressure side caused by the decrease of urban wind speed is 1 m/s. ..

2. Cities will also produce local strong winds, which will lead to disasters. Because the rough underlying surface of the city is like a mountainous area with complex terrain, the street and two buildings are like the tuyere of the mountainous area, with dense streamline and increased wind speed, which can create strong winds in the wild without strong winds. In addition, according to the wind tunnel experiment, strong wind areas can also appear around high-rise buildings, that is, eddy current areas in front of high-rise buildings and angular flow areas around two sides of buildings. The wind speed in these places is about 30% higher than that in the flat land. This is because the wind speed increases rapidly with the increase of height. When the high-altitude wind is blocked in the upper part of the high-rise building and forced to turn sharply, it also brings the momentum of the high-altitude wind to drop. If there is an air duct on the ground floor (behind the building) of a tall building, the wind speed near the air duct is about 2 times greater than that on the flat ground. That is to say, when the ambient wind speed is 6 m/s, it can reach 18 m/s near the air duct at this time, which is an 8-level gale. There have been many examples of billboards on the roof being blown down by strong winds in cities, many of which were caused by local strong winds in buildings. In foreign countries, because high-rise buildings were blown down by the wind and injured people, there have been too many cases of complaining to the court about huge compensation. It can also generate its own special wind system.

3. Cities also have their own unique wind system-urban heat island circulation. This is because the air flow in the urban heat island is rising, and the air flow in the surrounding countryside is constantly flowing to the city to supplement it. Because they come from the countryside, just like the wind from the north is called the north wind, the ground part of this urban heat island circulation is called "country wind" The wind speed of rural wind is generally only 1-2 m/s, and Shanghai is a megacity. As long as there is no strong wind, the urban heat island is obvious (sunny), and the heat island circulation is also obvious. For example, the heat island in Shanghai ranges from 1980 to 12.7. At this time, both Baosteel and Minhang in the north of the city are blowing northerly winds below 500 meters, and Longhua in the south of the city is blowing from the ground to the south to 600 meters, which is to gather in the city center. But at high altitude, Baosteel and Minhang began to turn to the south wind at 700 meters, and Longhua began to turn to the north wind at 900 meters, that is, a complete heat island circulation circle was formed, with the lower layer converging to the city center and the upper layer diverging to the city center. From the self-recording paper of the temperature self-recording instrument placed in the city center, it can often be found that the temperature change curve has a sudden drop in temperature like a cold front passing by at night. This is a witness of the cold country wind attacking the city. It can also be known that the circulation of urban heat island is not continuous and uniform, but has obvious array. There is a smaller wind system in the city, which can be called "car wind". This is caused by the continuous passing of high-speed vehicles in opposite directions on both sides of the road center line. For example, on1988 65438+1October 15, the wind speed in Guangzhou was very small, with an average daily wind speed of only 0.69 m/s. On Renmin Road in the north-south direction, due to the influence of traffic in different directions, at the measuring point of 3 meters high, the northerly wind prevailed on the west side of the street, and the sum of the frequencies of northwest wind and northwest west wind reached 79. Southerly winds prevail in the east, and the sum of the frequencies of southeast and easterly winds is as high as 86.9%. On this day, the car wind appeared for 20-22 hours. However, this kind of automobile wind not only has a small horizontal range, but also disappears rapidly with the increase of the height from the ground. The cause of rural wind is different from that of automobile wind. The former is caused by thermal action, and the wind speed is determined by the temperature difference between urban and rural areas, while the latter is caused by mechanical friction. When the traffic volume decreases or the speed slows down, the wind stops.