The stratosphere is the layer of Earth's atmosphere which, at the equator, is situated between about 17 km and 50 km altitude above the surface, while at the poles it starts at about 8 km altitude due to the lower tropopause height caused by the lower tropospheric temperature there.
The stratosphere sits directly above the troposphere and directly below the mesosphere. Within this layer, temperature increases as altitude increases; the top of the stratosphere has a temperature of about 270 K. This top is called the stratopause, above which temperature again decreases with height.
The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which horizontal mixing of gaseous components proceeds much more rapidly than vertical mixing. The stratosphere is warmer than the upper troposphere, primarily because of a stratospheric ozone layer that absorbs solar ultraviolet radiation.
An interesting feature of stratospheric circulation is the quasi-Biennial Oscillation (QBO) in the tropical latitudes, which is driven by gravity waves that are convectively generated in the troposphere. The QBO induces a secondary circulation that is important for the global stratospheric transport of tracers such as ozone or water vapor.
In northern hemispheric winter, sudden stratospheric warmings can often be observed which are caused by the absorption of Rossby waves in the stratosphere.
See also