Stratosphere is a layer of Earth’s atmosphere. It lies above the troposphere, the atmospheric layer nearest Earth. The stratosphere begins about 6 miles (10 kilometers) above Earth’s surface in the polar regions and about 12 miles (19 kilometers) near the equator. The upper boundary, called the stratopause, lies at an altitude of about 30 miles (48 kilometers).
The stratosphere generally has a lower layer of nearly steady temperature and an upper layer in which the temperature increases with altitude. The lower layer has a temperature of about –67 °F (–55 °C). Near the top, the stratosphere reaches a maximum temperature of about 28 °F (–2 °C). The increase in temperature with height is due mainly to the absorption of sunlight by ozone (a form of oxygen) in the stratosphere. Stratospheric ozone also shields human beings from ultraviolet radiation of the sun. About 80 to 90 percent of the total ozone in the atmosphere is found in the stratosphere. See Ozone .
Although the stratosphere has complex wind systems, violent storms do not occur there. The stratosphere is nearly cloudless and extremely dry, except for the polar regions. There, ice clouds form during winter.
