Stratosphere: Definition & Facts

Instructor: Rachel Tustin

Dr. Rachel Tustin has a PhD in Education focusing on Educational Technology, a Masters in English, and a BS in Marine Science. She has taught in K-12 for more than 15 years, and higher education for ten years.

This lesson will describe the defining characteristics of the stratosphere, which is the second layer of the atmosphere. These characteristics include temperature changes and the presence of the ozone layer.

An Invisible Cake in the Sky

If you look up at the sky, either on a clear day or a starry night, it probably wouldn't occur to you that you are looking through layers. Though the atmosphere may appear uniform to the naked eye, it is actually similar to a layer cake. We live in one layer, called the troposphere, where the clouds and most of the water vapor reside. However, just above that is an equally important layer called the stratosphere.

Mapping the Position of the Stratosphere

We live in the troposphere, which is the layer of the atmosphere closest to earth. Just above that is the stratosphere, the area of the atmosphere where passenger airplanes and weather balloons fly. There are a few other atmospheric layers as well -- you can take a look at a diagram of these below.

Layers of the Atmosphere

The stratosphere begins at around 10 kilometers above the surface of the earth. This is just an estimate, however, as the lower and upper boundaries actually vary with the latitude of the earth. Around the poles, it actually begins at around 7 kilometers, whereas around the equator it can be as high as 20 kilometers. The stratosphere ends where it transitions to the mesosphere, around 50 kilometers above the earth.

On a Clear Day in the Stratosphere

While the troposphere is filled with a vast assortment of clouds thanks to a gas we know as water vapor, the stratosphere is a vast, clear blue sky. There is very little water vapor in this layer of the atmosphere, so clouds are a rare occurrence. Clouds form when water vapor condenses into a liquid, and with very little water, vapor condensation is virtually impossible.

Convection is the process whereby warm air rises and cooler air descends. While common in the troposphere, very little convection takes place in the stratosphere. As a result, it tends to trap any and all gases that enter this region of the atmosphere. For years, CFCs - a chemical used in aerosols - were transported the stratosphere via convection and became trapped there. Gases and dust from volcanic eruptions often meet the same fate, remaining trapped in the stratosphere for months or even longer.

The Life Sustaining Properties of the Troposphere

The stratosphere is actually crucial to allowing us to live on earth, because within the stratosphere you will find the ozone layer. Ozone, which is actually a molecule made up of three oxygen atoms linked together by covalent bonds, absorbs harmful ultraviolet radiation that enters the Earth's atmosphere as part of sunlight.

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