stratosphere

A layer of the earth’s atmosphere above the troposphere and just below the mesosphere. This layer is stratified, with the upper layers being much warmer than the lower levels. At the earth's surface, on the other hand, temperature decreases with altitude. One of the reasons that the upper reaches of the stratosphere are warmer than the lower reaches is because the stratosphere also includes the ozone layer, which is composed of a type of oxygen molecule by the same name. The ozone layer traps ultraviolet rays from the sun, causing a chemical reaction that releases small, yet incrementally cumulative, amounts of heat, thereby providing a protective thermal layer for the earth.