10.7: Stratosphere

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Can we take a field trip to the stratosphere?

Sure we can! If you've ever flown on a jet airplane, you've been in the stratosphere. Airplanes fly in the stratosphere, because there is less friction. They get better gas mileage, and so costs are lower. There is also less turbulence, so passengers are happier. Can you identify the bottom of the stratosphere in the photo? It's where the clouds begin. Remember that all weather is in the troposphere.

Stratosphere

The stratosphere is the layer above the troposphere. The layer rises to about 50 kilometers (31 miles) above the surface.

Temperature in the Stratosphere

Air temperature in the stratosphere increases with altitude. Why? The stratosphere gets most of its heat from the Sun. Therefore, it’s warmer closer to the Sun. The air at the bottom of the stratosphere is cold. The cold air is dense, so it doesn’t rise. As a result, there is little mixing of air in this layer.

The Ozone Layer

The previous section said that the troposphere is the most important layer of the atmosphere. But it's not the only important layer. The stratosphere contains a layer of ozone gas. Ozone consists of three oxygen atoms (O₃). The ozone layer is in the stratosphere. Ozone in the layer absorbs high-energy ultraviolet (UV) radiation. UV radiation splits the ozone molecule (Figure below). The split creates an oxygen molecule (O₂) and an oxygen atom (O). This split releases heat that warms the stratosphere. By absorbing UV radiation, ozone also protects Earth’s surface. UV radiation would harm living things without the ozone layer.

Diagram of the ozone layer

How does the ozone layer protect Earth’s surface from UV light?

Stratopause

At the top of the stratosphere is a thin layer called the stratopause. It acts as a boundary between the stratosphere and the mesosphere.

Summary

There is little mixing between the troposphere and the stratosphere.
Ozone gas protects life on Earth from harmful UV light.
The ozone layer is in the stratosphere. It has a higher concentration of ozone than the rest of the atmosphere.