Stratosphere

The stratosphere is the second layer of Earth's atmosphere, sitting above the troposphere and below the mesosphere, and its name comes from the Greek word for a layer or stratum. It begins at different heights depending on latitude, around 20 kilometers over the equator, about 10 kilometers over the mid latitudes, and only about 7 kilometers over the poles. Unlike the troposphere, where temperature falls with height, the stratosphere warms with altitude, from an average of about minus 51 degrees Celsius near its base to about minus 15 degrees Celsius near its top, because ozone there absorbs the Sun's ultraviolet radiation and releases heat as it is broken down and reformed; this inversion keeps the layer stable and largely free of the turbulence found lower down. Even so, the stratosphere carries strong winds, including the Southern Hemisphere's polar vortex, where speeds can approach 60 meters per second.