The tropopause is the atmospheric boundary that separates the troposphere from the stratosphere.
The troposphere is the lowest major atmospheric layer and contains nearly all of Earth’s weather. Temperature generally decreases with altitude there. Above it, in the stratosphere, temperature begins to increase with height because ozone absorbs ultraviolet radiation from the Sun.
The tropopause is not a perfectly level global shell. It is generally higher over the tropics, where it can reach about 17 kilometres, and lower near the poles, where it may be roughly 8 kilometres high. Its altitude also changes with season and weather patterns.
The tropopause should not be confused with the stratopause, which separates the stratosphere from the mesosphere. Aircraft can sometimes cruise near or just below the tropopause, where the air is relatively stable, although strong jet-stream winds and turbulence may occur nearby.