Stratosphere

The stratosphere is the second major layer of Earth’s atmosphere, lying above the troposphere and below the mesosphere. It generally extends from about 10 to 15 kilometers (roughly 6 to 9 miles) at the tropics to around 50 kilometers (about 31 miles) above the surface, with exact boundaries varying by latitude and season. The layer is characterized by a relatively stable temperature profile, in which temperature increases with altitude due to the absorption of ultraviolet radiation by the ozone layer.

A key feature of the stratosphere is the ozone layer, located mainly in the lower to middle stratosphere. Ozone absorbs most of the Sun’s ultraviolet radiation, providing a protective shield for life on Earth. This absorption also heats the surrounding air, contributing to the thermal inversion that stabilizes the layer and reduces vertical mixing. Temperatures in the lower stratosphere are cold, while the upper stratosphere is warmer, with temperatures rising from about -60°C near the tropopause to around -2 to 0°C near the stratopause.

The composition of the stratosphere is similar to the troposphere in major gases such as nitrogen and oxygen, but it contains much less water vapor. Photochemical reactions driven by UV light dominate its chemistry, particularly in the ozone cycle. Atmospheric circulation in the stratosphere includes the Brewer-Dobson circulation, which transports ozone from equatorial regions toward higher latitudes.

Human activities have affected the ozone layer through emissions of halogenated compounds, leading to ozone depletion and the formation of polar ozone holes. International actions, notably the Montreal Protocol, have contributed to gradual ozone recovery. The stratosphere’s relative dryness and stability also make it favorable for certain high-altitude research, long-distance flights, and atmospheric observations.