Layers of the atmosphere

So, what is the atmosphere? It’s a very thin gaseous envelope around the Earth which is kept in place by gravitational attraction.

Photograph taken from space, showing part of the Earth at night with city lights visible. The blue glow of the thin atmosphere is also visible. View from near-space showing how thin our atmosphere is

It is comprised of four main layers: the troposphere (which is where most of our weather occurs), the stratosphere, mesosphere and the thermosphere. There is a fifth layer called the exosphere, where the atmosphere gradually thins and merges with interplanetary space, but we won’t consider this further as the molecules are so far apart, it no longer behaves like a gas.

Diagram showing the Earth and the layers of the atmosphere going out into space: the troposphere out to 10 kilometres, the stratosphere out to 50 kilometres represented, the mesosphere out to 80 kilometres, the thermosphere out to 500 kilometres The layers of the atmosphere; troposphere, stratosphere, mesosphere and thermosphere

These layers are partly characterised by the way temperature changes with height.

The troposphere is where we live, and so is the part of the atmosphere that we are most interested in. In the troposphere, temperature tends to decrease with height - that makes sense; we know that it gets colder when you climb a mountain for example. The depth of the troposphere varies, but on average it is around 8 km at the poles and 16 km at the equator. This is incredibly thin when you think about how far that is, most people probably drive further than that to get to work. The troposphere is well mixed and is rich in water.

For more information about the water in our atmosphere see the Met Office Factsheet on water in the atmosphere

But temperature doesn’t decrease with height in all of the spheres, in fact average temperature increases with height in both the stratosphere and the thermosphere. The boundary between the troposphere and the stratosphere is called the tropopause, and the rising temperature at this boundary acts like a lid, keeping our weather in the lowest section of the atmosphere.

How altitude affects temperature: A graph with altitude on the y axis and temperature on the x axis, showing how temperature varies in the layers of the atmosphere. Temperature decreases with height in the troposphere, the boundary between the troposphere and stratosphere is the tropopause at 20 kilometres. Temperature increases with height in the stratosphere, the boundary between the stratosphere and the mesosphere is the stratopause at 50 kilometres. Temperature decreases with height in the mesosphere, the boundary between the mesosphere and the exosphere is the mesopause at 85 kilometres. Temperature increases with height in the thermosphere, the boundary at the top of the thermosphere is the thermopause at 690 kilometres. Average temperature falls with altitude in the troposphere and mesosphere, but rises with altitude in the stratosphere and thermosphere

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