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The Layers of the Atmosphere

Atmospheric Structure and Composition

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Contributed in part by Sharon Tomlinson

Understanding how weather works on our planet means we must first understand the atmosphere of our planet. Without our atmosphere there would be no weather; indeed, there would be no life on earth. The phenomenon of weather is simply an atmospheric effect.

Atmosphere is the gaseous envelope surrounding the earth, held in place by gravity. It is a collection of four distinct layers, and several intermediate layers. These layers start at ground level, measured at sea level, and rise into what we call outer space.

The Troposphere

Troposphere means, ‘where the air turns over’. A very appropriate name, since the air closest to the earth is in a constant up and down flow. Also in this layer, the air is hotter closer to the earth’s surface and colder the higher up you travel. The troposphere is immediately important in our daily activities.

Starting at sea level, the troposphere goes up seven miles. The bottom one third, that which is closest to us, contains 50% of all atmospheric gases. This is the only part of the whole makeup of the atmosphere that is breathable. This is the only area where all weather takes place. It also has the property of having a north –south oriented aspect. The air from the northern hemisphere and the air from the southern hemisphere meet and mingle at the equator, but never go farther. Next, is a thin layer called the tropopause, which is just a buffer between the troposphere and the stratosphere.

The Stratosphere

The stratosphere is the next layer of the atmosphere. Here the air doesn’t flow up and down, but flows parallel to the earth in very fast moving air streams. This is the layer where most jet planes fly. The stratosphere starts at approximately 10 kilometers (8-14.5 miles) and goes to approximately fifty kilometers high (about 30 miles). The top edge of the stratosphere is abundant with ozone. Ozone is the byproduct of sun radiation and oxygen; by capturing the ultraviolet rays of the sun and deploying it, ozone takes out the harmful effects. This is very important to all living things on earth, since unfiltered radiation from the sun can destroy all animal tissue. After the stratosphere, there is again a buffer layer, this time called the stratopause.

Detailed information on the ozone layer is available in several articles.

The Mesosphere

Above this from thirty miles up to fifty miles is the mesosphere. This area reaches the coldest temperatures of all the atmosphere, going to -130 degrees and lower. Here, meteors coming too close to earth burn up.

The Thermosphere

The last layer of the atmosphere called the thermosphere, and measured at fifty to ninety miles above earth, contains less than 0.01% of all air within the atmospheric envelope. Temperatures here reach upward to 2000 degrees, but the gas molecules making up the air are so far apart the temperature is not felt.

The Ionosphere

The very outer edge of the thermosphere is an area called the ionosphere and is not a separate layer. Gas atoms drift into space from here. It is called ionosphere because in this part of the atmosphere the sun’s radiation is ionized, or pulled apart as it travels earth’s magnetic fields to the north and south poles. This pulling apart is seen from earth as auroras.

The colorful displays of auroras are called the northern lights or aurora borealis in the Northern Hemisphere, the Southern Lights or Aurora Australis in the Southern Hemisphere. Also available is a detailed space weather tutorial on Auroras. The lesson includes images and even shows you where and when to view the Northern and Southern Lights from your location.

Without the ninety plus miles of atmosphere above us, the closest two plus miles where all our weather takes place would not be possible. Our atmosphere swirls around the earth and the weather closest to the surface has its overall effective place within it.

Now that you know the details of our atmosphere, select another lesson to learn about your favorite weather event. Soon you will be on your way to being a Storm Chaser!

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