4. Air Temperature

Earth's atmosphere. Photo courtesy of NASA Goddard Video and Photo/Flickr. 

As you've learned, temperature varies throughout the layers of Earth's atmosphere. Warm air rises, but why? Gas molecules are able to move more freely, and if they are uncontained, as they are in the atmosphere, they can take up more or less space. 

  • When gas molecules are cool, they are sluggish and do not take up as much space. With the same number of molecules in less space, both air density and air pressure are higher.
  • When gas molecules are warm, they move vigorously and take up more space. Air density and air pressure are lower.

Warmer, lighter air is more buoyant than the cooler air above it, so it rises. The cooler air then sinks down, because it is denser than the air beneath it. This is convection.  The property that changes most strikingly with altitude is air temperature. Unlike the change in pressure and density, which decrease with altitude, changes in air temperature are not regular. A change in temperature with distance is called a temperature gradient.

Source: Temperature of the Atmosphere. Retrieved from http://www.ck12.org/book/CK-12-Earth-Science-Concepts-For-High-School/r16/section/9.4/ on August 26, 2013. 

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