Stratosphere

The stratosphere /ˈstrætɵsfɪər/ is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler higher up and warmer farther down. The border of the troposphere and stratosphere, the tropopause, is marked by where this inversion begins, which in terms of atmospheric thermodynamics is the equilibrium level. At moderate latitudes the stratosphere is situated between about 10–13 km (33,000–43,000 ft; 6.2–8.1 mi) and 50 km (160,000 ft; 31 mi) altitude above the surface, while at the poles it starts at about 8 km (26,000 ft; 5.0 mi) altitude, and near the equator it may start at altitudes as high as 18 km (59,000 ft; 11 mi).