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.
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.
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.
When the ozone absorbs ultraviolet radiation, it actually causes another phenomenon that is used to identify different layers in the atmosphere. As you rise through the troposphere, the temperature decreases to around -60 degrees Fahrenheit. However, as you enter the stratosphere, the ozone gas absorbs the ultraviolet light entering the atmosphere from the sun. As it absorbs the UV light, it absorbs energy. This results in an increase in temperature from about -76 degrees Fahrenheit to around 5 degrees Fahrenheit. Once you leave the stratosphere, and enter the mesosphere, the temperature dramatically decreases until plummeting to around -184 degrees Fahrenheit.
The stratosphere is the second layer of the atmosphere, in between the troposphere and the mesosphere. Unlike the troposphere, it contains little water vapor so there are no clouds in this layer of the atmosphere. The stratosphere also contains the ozone layer, which absorbs harmful ultraviolet radiation as it enters our atmosphere from the sun. As the ozone layer absorbs UV radiation, it causes the temperature in this layer to increase.
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