Troposphere

The troposphere contains about 80% of the atmosphere and is the part of the atmosphere in which we live. In this layer, average temperatures decrease with height in a process known as adiabatic cooling (i.e. a change in temperature caused by a decrease in pressure). Even so, it is still more prone to vertical mixing by convective and turbulent transfer, than other parts of the atmosphere. These vertical motions and the abundance of water vapour make it the home of all important weather phenomena.

The troposphere's thermal profile is largely the result of the heating of the Earth's surface by incoming solar radiation. Heat is then transferred up through the troposphere by a combination of convective and turbulent transfer. This is in direct contrast with the stratosphere, where warming is the result of the direct absorption of solar radiation.

The troposphere is around 16 km high at the equator, with the temperature at the tropopause (the point where the troposphere meets the stratosphere) around -80°C. At the poles, the troposphere reaches a height of around 8 km, with the temperature of the tropopause around -40°C in summer and -60°C in winter.

We can see, therefore, despite the higher surface temperatures, the tropical tropopause is much cooler than at the poles due to the increase in altitude.