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Atmosphere: Composition of the Atmosphere

by Flight Learnings

in Weather Theory

In any given volume of air, nitrogen accounts for 78 percent of the gases that comprise the atmosphere, while oxygen makes up 21 percent. Argon, carbon dioxide, and traces of other gases make up the remaining one percent. This cubic foot also contains some water vapor, varying from zero to about five percent by volume. This small amount of water vapor is responsible for major changes in the weather. [Figure 11-1]

Figure 11-1. Composition of the atmosphere.

Figure 11-1. Composition of the atmosphere.

The envelope of gases surrounding the Earth changes from the ground up. Four distinct layers or spheres of the atmosphere have been identified using thermal characteristics (temperature changes), chemical composition, movement, and density. [Figure 11-2]

Figure 11-2. Layers of the atmosphere.

Figure 11-2. Layers of the atmosphere. Click to Enlarge

The first layer, known as the troposphere, extends from sea level up to 20,000 feet (8 kilometers (km)) over the northern and southern poles and up to 48,000 feet (14.5 km) over the equatorial regions. The vast majority of weather, clouds, storms, and temperature variances occur within this first layer of the atmosphere. Inside the troposphere, the temperature decreases at a rate of about 2 °Celsius (C) every 1,000 feet of altitude gain, and the pressure decreases at a rate of about one inch per 1,000 feet of altitude gain.

At the top of the troposphere is a boundary known as the tropopause, which traps moisture and the associated weather in the troposphere. The altitude of the tropopause varies with latitude and with the season of the year; therefore, it takes on an elliptical shape, as opposed to round. Location of the tropopause is important because it is commonly associated with the location of the jet stream and possible clear air turbulence.

Above the tropopause are three more atmospheric levels. The first is the stratosphere, which extends from the tropopause to a height of about 160,000 feet (50 km). Little weather exists in this layer and the air remains stable although certain types of clouds occasionally extend in it. Above the stratosphere are the mesosphere and thermosphere which have little influence over weather.

515G+mn0RuL._SX331_BO1,204,203,200_Learn more about aviation weather with Weather Flying by Robert Buck. Regarded as the bible of weather flying, this aviation classic not only continues to make complex weather concepts understandable for even the least experienced of flyers, but has now been updated to cover new advances in technology.


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