stratosphere
stratosphere The atmospheric layer above the troposphere, which extends on average from about 10 to 50 km above the Earth's surface. The stratosphere is a major stable layer whose base is marked by the tropopause, and where temperatures overall average approximately −60 °C. Temperature in the lower stratosphere is isothermal but increases markedly in the upper part, to reach a maximum of about 0 °C at the stratopause. High stratospheric temperatures result from absorption of ultraviolet radiation (0.20–0.32 μm wavelengths) by ozone concentrated at 15–30 km. Due to the very low air density, even the small amount of ozone concentrated in the upper stratosphere is extremely effective in absorbing radiation, thus giving high temperatures at 50 km. The isothermal condition at the base of the stratospheric inversion layer creates stability, which generally limits vertical extensions of cloud and leads to the lateral spreading of high cumulonimbus cloud with characteristic anvil heads. See also ATMOSPHERIC STRUCTURE.
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stratosphere