What is the basis of atmospheric stratification?

There are different ways to divide the structure of the earth's atmosphere. But it is generally divided into five layers.

The layer closest to the ground is the troposphere. The average thickness of the troposphere is about 12km, which is the densest layer in the atmosphere, and it concentrates about 75% of the atmospheric mass and more than 90% of the water vapor mass. The most prominent feature of the troposphere is strong convective movement, and all kinds of weather phenomena occur in the troposphere.

Above the troposphere is the stratosphere. The stratosphere is the atmosphere from the tropopause to a height of about 50 kilometers, also known as the stratosphere. Stratospheric airflow mainly shows horizontal motion, and convection phenomenon is weakened. There is basically no water vapor here, it is clear and cloudless, and the weather has not changed much, which is suitable for aircraft navigation. At an altitude of 20~30 kilometers, oxygen molecules form the ozone layer under the action of ultraviolet rays, which acts as a barrier to protect life on earth from ultraviolet rays and high-energy particles from the sun.

Above the stratosphere is the middle layer, also known as the "middle layer". It is the atmosphere between the top of the stratosphere and 85 kilometers. The temperature near the top of the interlayer is about190k; The air is mainly nitrogen and oxygen, with little ozone. Air molecules can be ionized after absorbing solar ultraviolet radiation, which is customarily called the D layer of the ionosphere. At this altitude, sometimes noctilucent clouds will appear at dusk in summer in high latitudes.

Above is the ionosphere. It is the upper atmospheric airspace of the earth (overlapping with the middle layer), extending from about 50 kilometers above the ground to about 1000 kilometers. Among them, atmospheric molecules are ionized under the ultraviolet radiation of the sun, and there are quite a lot of free electrons and ions, which can change the propagation speed of radio waves, refract, reflect and scatter, produce the rotation of polarization plane, and be absorbed to varying degrees.

Above the mesosphere, 500 kilometers away from the earth's surface, it is called the "thermosphere". From the mesosphere to the ionosphere, there are often many interesting astronomical phenomena, such as aurora and meteors.

Further outward, it is the outer layer of the atmosphere, also called escape layer or escape layer, which is the outer atmosphere above the thermosphere and extends to 1000 km from the earth's surface. The atmosphere here is extremely thin, and the density is one billionth of the sea level. The outer atmosphere is the outermost layer of the atmosphere and the transition zone from the atmosphere to interstellar space. There is no clear boundary between the outer atmosphere and space.

Usually, the height of the atmosphere is within 1000 km, that is, within the ionosphere, that is, the thickness of the atmosphere is about 1000 km.