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The stratosphere is the second major layer of the atmosphere. It lies above the troposphere and is separated from it by the tropopause. It occupies the region of atmosphere from about 12 to 50 km, although its lower boundary tends to be higher nearer the equator and lower nearer the poles.

The stratosphere defines a layer in which temperatures rises with increasing altitude. At the top of the stratosphere the thin air may attain temperatures close to 0°C. This rise in temperature is caused by the absorption of ultraviolet (UV) radiation from the Sun by the ozone layer. Such a temperature profile creates very stable atmospheric conditions, and the stratosphere lacks the air turbulence that is so prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds or other forms of weather.

The stratosphere provides some advantages for long-distant flight because it is above stormy weather and has strong, steady, horizontal winds.

The stratosphere is separated from the mesosphere above by the stratopause.