Tropospheric formation

Located at the bottom of the atmosphere, it concentrates about 75% of air quality and more than 90% of water vapor quality. Its lower boundary is connected with the ground, and its upper boundary height varies with geographical latitude and season. The average height is low latitude 17 ~ 18km, middle latitude 10 ~ 12km, and the polar regions are 8 ~ 9km. Summer is higher than winter.

In the troposphere, the temperature decreases with the elevation, with an average increase of 100 m, and the temperature decreases by about 0.65℃. Due to the great influence of the surface, the horizontal distribution of meteorological elements (temperature, humidity, etc.). ) uneven. The regular vertical movement of air and the irregular turbulence are quite intense. The water vapor, dust and heat in the upper and lower layers are exchanged and mixed. Because more than 90% of water vapor is concentrated in the troposphere, many weather phenomena such as clouds, fog, rain and snow occur in the troposphere.

In the troposphere, according to the distribution characteristics of airflow and weather phenomena, it can be divided into low layer, middle layer and high layer. ?

(1) Lower layer: The lower layer is also called disturbance layer or friction layer. It generally ranges from the ground to a height of 2 kilometers. With the difference of seasons and days and nights, there are some changes in the scope of the lower layer, which is generally higher in summer than in winter and higher in day than at night. In this layer, the airflow is greatly influenced by ground friction, and the turbulent exchange is particularly strong. Usually with the increase of height, the wind speed increases and the wind direction deflects. This layer is affected by the ground thermal effect, and the temperature also has obvious diurnal variation. Due to the high content of water vapor and dust particles in this layer, low clouds, fog and floating dust often appear. ?

(2) Intermediate layer: the bottom boundary of the intermediate layer and the top boundary of the friction layer, and the height of the upper layer is about 6 kilometers. The influence of the ground is much less than that of the friction layer, and the airflow can basically represent the air movement trend of the whole troposphere. Most of the clouds and precipitation in the atmosphere are generated in this layer. ?

(3) Upper layer: The upper layer extends from a height of 6 kilometers to the tropopause. This layer is less affected by the ground, the temperature is below 0℃ all the year round, the water vapor content is less, and all kinds of clouds are composed of ice crystals and supercooled water droplets. In mid-latitude and tropical areas, strong wind belts with wind speed equal to or greater than 30m/s often appear in this layer, which is called jet stream.

In addition, between the troposphere and the stratosphere, there is a transitional layer with a thickness of several hundred meters to 1 ~ 2 kilometers, which is called the tropopause. The main feature of this layer is that the temperature drops suddenly with height. The changes are as follows: the temperature decreases slowly with the increase of height, or is almost isothermal. According to the initial height of this change, the position of the tropopause is determined. The temperature of the tropopause is about -83℃ at low latitudes and -53℃ at high latitudes. The tropopause has a great blocking effect on the vertical airflow, and the rising water vapor and dust particles gather under it, which makes the visibility there often poor.