Stratosphere and stratopause

The atmosphere of Earth can be divided into semi-horizontal layers or spheres, based on properties such as temperature variation, gas components, or electrical properties. While air pressure and air density always decrease with altitude in the atmosphere, it is not the case for temperature. Four temperature-varying layers of Earth's atmosphere can be distinguished: the troposphere , the stratosphere, the mesosphere , and the thermosphere . In the troposphere and the mesosphere, the temperature decreases with altitude, but in the stratosphere and thermosphere, the temperature increases with altitude (called temperature inversion). Between these layers, the temperature remains the same in the tropopause (between the troposphere and the stratosphere), the stratopause (separating the stratosphere and the mesosphere), and the mesopause (between the mesosphere and the thermosphere).

The stratosphere is the second lowest layer of Earth's atmosphere, located between the troposphere and mesosphere. The stratosphere and the mesosphere together are called the middle atmosphere. The stratosphere, which literally means the layered sphere, is located from about 12 miles (20 km) to 30 miles (50 km) altitude. About 99% of the total air mass of the atmosphere can be found in the bottom two layers, the troposphere and stratosphere. The stratosphere is not only less dense than the troposphere, but it also contains very dry air. The stratospheric temperature is warmer than the upper tropospheric temperature; the average temperature at the bottom of the stratosphere is around −76°F (−60°C), and at the upper bound around −26°F (−3°C). The temperature increases with height in the stratosphere because of the thin, but highly concentrated, stratospheric ozone layer. It is located between 13 to 19 miles (20 to 30 km), and reaches its peak density at an altitude of about 16 miles (25 km).

Ozone is a special molecular form of oxygen , consisting of three oxygen atoms bonded together. It is created by incoming solar radiation, which breaks up ordinary molecular oxygen (O₂) into individual oxygen atoms, which can later combine with another ordinary oxygen molecule to form ozone (O₃). Because the ozone layer absorbs and scatters solar radiation, a form of energy, the stratosphere consequently warms up. Without the ozone layer life could not exist on Earth; ozone is the only atmospheric gas that protects the biosphere from the damaging effects of the sun's ultraviolet radiation. This is why the depletion of the ozone layer (ozone hole) caused by anthropogenic chlorofluorocarbons (CFCs) is a cause for scientific concern and study.

See also Atmospheric composition and structure; Ozone layer depletion; Troposphere and tropopause