Discover the phenomenon of tropospheric inversion in geography

This is the answer I knew in Baidu two years ago:

Generally speaking, the atmospheric temperature decreases with the elevation, and the temperature decreases by about 0℃ or 6℃ for every increase of 100m. That is to say, below a few kilometers, the lower atmosphere is always high temperature and low density, and the upper atmosphere is low temperature and high density, which is "top-heavy". This kind of atmospheric stratification is prone to rolling up and down, that is, "convection" movement, which can transport pollutants near the ground to high altitude or even far away, thus reducing the pollution level over the city. Therefore, under normal circumstances, the air over the city is slightly polluted and has little impact on human health. However, under some weather conditions, the atmospheric structure above the ground will have an abnormal phenomenon that the temperature increases with the increase of height, leading to a top-heavy atmospheric stratification, which meteorologists call "inversion" and the atmosphere with inversion is called "inversion layer". It is like a thick quilt covering our city and countryside. The air flow in the upper and lower layers is reduced, and the air pollutants in the near-surface layer "have no way to go", so they have to stay where they are, and air pollution is bound to increase.

There are many reasons for the phenomenon of "upside down". In winter in China, the temperature in the surface layer drops rapidly, mainly due to the radiation cooling of the ground. When the cold current strikes, the ground is controlled by the cold air mass, and the weather is clear, the wind is small and the temperature is low. Especially at night, ground heat radiates (radiates) to high altitude, which makes the temperature near the ground drop rapidly, while the temperature in the upper atmosphere drops slowly, resulting in the so-called "inversion" and "phenomenon" of "heating up and cooling down". Sometimes there is insufficient sunshine during the day, the ground temperature rises slowly, and it also maintains "inversion temperature" for a long time, and air pollution is becoming more and more serious.

There are many reasons for the inversion phenomenon, which are listed as follows:

1. Ground radiation cooling: On a clear night without wind or breeze, the ground is rapidly cooled by radiation, and the atmosphere near the ground is also cooled. Because the closer the air is to the ground, the greater the influence of the ground, so the closer it is to the ground, the lower the temperature; The farther away from the ground, the less the temperature drops, thus forming an inversion from the ground. With the intensification of ground radiation cooling, the inversion temperature gradually expands upward and reaches its strongest at dawn. Generally, after sunrise, the solar radiation gradually increases, the ground temperature rises rapidly, and the inversion gradually disappears from bottom to top. Summer nights are short, inversion layer is thin and disappears quickly, and winter nights are long, inversion layer is thick and disappears slowly.

2. Sinking in the air: mostly in mountainous areas. The cold air on the hillside sinks to the bottom of the valley, and the warm air at the bottom of the valley is pushed up by the cold air, causing inversion. This inversion is mainly formed under certain topographic conditions. So it is also called terrain inversion. For example, Los Angeles in the United States is surrounded by mountains on three sides, and there are more than 200 days of inversion every year.

Or as listed below:

1, the radiation inversion is formed by long-wave radiation cooling on the ground. On a clear and windless night, the ground radiation weakens, the ground atmosphere cools rapidly, and the upper atmosphere cools slowly, forming an inversion.

2. Front inversion means that warm air moves above cold air and forms a front at the intersection of cold and warm air. If the temperature difference between cold and warm air on the front is large, an inversion will be formed.

3. Terrain inversion is caused by local terrain conditions. In the valley basin, heavy cold air flows along the hillside at night and gathers at the valley bottom, forming a lower cold air layer and an upper warm air layer.

4. The temperature difference of reservoir water surface will also cause inversion. For example, after the completion of the Three Gorges Project on the Yangtze River, the Three Gorges Reservoir will cause inversion, which will reduce the temperature in the reservoir area in summer and increase the temperature in winter by about 2C, which will have a certain impact on the industrial sewage discharge in the reservoir area.