tropopauze

The tropopauze, or tropopause, is the boundary between the troposphere and the stratosphere. It marks a transition in the vertical profile of temperature: in the troposphere, air generally cools with height, while above the tropopause the temperature trend changes in the lower stratosphere. Operationally, the tropopause is defined as the lowest altitude at which the lapse rate—the rate of temperature decrease with height—reaches 2 degrees Celsius per kilometer or less, averaged over about 2 kilometers. A related definition uses the concept of potential temperature to identify the limit between the two atmospheric layers.

The altitude of the tropopause varies with latitude and season. It is typically around 8–12 kilometers above sea level in mid-latitudes, higher in the tropics (roughly 15–18 kilometers), and lower in polar regions (about 7–9 kilometers). This variability is influenced by atmospheric dynamics, including jet streams and seasonal heating.

The tropopause acts as a loose barrier to vertical mixing between the troposphere and stratosphere, influencing weather, humidity, and chemical composition. It helps regulate the distribution of ozone and water vapor and is involved in stratosphere–troposphere exchange processes. Aviation commonly encounters the tropopause region, as many commercial flights cruise near these altitudes, where atmospheric conditions can still be stable and predictable, though weather systems and jet streams can elevate or lower the boundary locally.