Stratosphere

In marked contrast to the troposphere, temperatures in the stratosphere actually rise with increasing altitude. Another distinctive feature of the stratosphere is the absorption of ultraviolet radiation by ozone (O3). This is greatest at around 50 km altitude, which is where the stratopause (the point where the stratosphere meets the mesosphere) occurs. Temperatures reach a maximum here, and according to latitude and season, they range from -30°C over the winter pole to +20°C over the summer pole.

As well as a noticeable change in temperature, the move from the troposphere into the stratosphere is also marked by an abrupt change in the concentrations of the variable trace constituents. Water vapour decreases sharply, whilst ozone concentrations increase. These strong contrasts in concentrations are a reflection of little mixing between the moist, ozone-poor troposphere and the dry, ozone-rich stratosphere.

Despite the dryness of the stratosphere, some clouds have developed in winter months over high latitudes at altitudes between 17 and 30 km, stretching into the stratosphere. They generally display iridescence and are known as nacreous clouds.

The stratosphere extends up to around 48 km above the surface, and together with the troposphere, they account for 99.9% of the Earth's atmosphere.