stratosphere - Ozone Depletion

The layer of the Earth's atmosphere at a height of c.15–50 km/10–30 mi, separated from the troposphere below by the tropopause, and from the mesosphere above by the stratopause. A stable layer, unaffected by the weather, it has a gradually increasing temperature with height from about ?50°C to around 0°C. It contains the ozone layer.

The stratosphere is a layer of Earth's atmosphere that is stratified in temperature, with warmer layers higher up and cooler layers farther down. The stratosphere is situated between about 10 km and 50 km altitude above the surface at moderate latitudes, while at the poles it starts at about 8 km altitude. The stratosphere sits directly above the troposphere and directly below the mesosphere.

The stratosphere is layered in temperature because it is heated from above by absorption of ultraviolet radiation from the Sun. the top of the stratosphere has a temperature of about 270 K, about the same as the ground level temperature. The vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. The heating is caused by an ozone layer that absorbs solar ultraviolet radiation, heating the upper layers of the stratosphere. The base of the stratosphere occurs where heating by conduction from above and heating by convection from below (through the troposphere) balance out; hence, the stratosphere begins at lower altitudes near the poles due to the lower ground temperature there.

Commercial airliners typically cruise at an altitude near 10 km in temperate latitudes, in the lower reaches of the stratosphere. these plumes end at the base of the stratosphere, setting a limit to how high gliders can fly in most parts of the world. (Some gliders do fly higher, using wave lift from mountain ranges to lift them into the stratosphere.)

The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which horizontal mixing of gaseous components proceeds much more rapidly than vertical mixing.

In northern hemispheric winter, sudden stratospheric warmings can often be observed which are caused by the absorption of Rossby waves in the stratosphere.

Ozone Depletion

The reported main cause of ozone depletion is the presence of chlorofluorocarbons (aka CFCs - CF2Cl2, CFCl3) in the Earth's stratosphere. These molecules eventually find their way to the stratosphere, where they undergo a series of chain reactions which ultimately lead to the destruction of the ozone layer. The amounts of CFCs in the stratosphere rose until early 2000, and are expected to reach acceptable levels by mid-century.