The Stratosphere lies above the Troposphere and extends upwards to about 50 km from the Earth’s surface.
‘Strato’ means ‘layered’ and the gases in the Stratosphere are actually layered. Air, in this layer, is very thin with little moisture in it, and is extremely cold in the lower Stratosphere. However, due to the presence of ozone layer in the upper part of the Stratosphere, heat increases with the increase of altitude. The ozone layer protects us from skin cancer and other health damage. While absorbing the damaging ultraviolet (UV) radiation from the Sun, the ozone molecules convert the UV energy into heat and warms up the atmosphere.
Thus, though the lower part of the stratosphere is cold, the temperature does not decrease with the increase of altitude. Moreover, as there is no vertical movement of the air like the troposphere, heat in the stratosphere increases with the increase of altitude. Temperatures in this layer are highest over the summer pole, and lowest over the winter pole. Here the air is very dry, and is about a thousand times thinner than the air at the surface. That is why, the jet aircrafts fly through this layer and while flying they leave white trails, the trail of moisture from the engines, which remain undisturbed due to the absence of any air movement.