Atmospheric State Variables

State variables include:




State variables are related to one another by the Ideal Gas Law (IDL)

IDL often referred to as the “Equation of State”


Air is mostly made up of free molecules in constant motion (gases).State Variables

Air molecules have mass.

You can feel the mass of the air when the wind is blowing hard.

Surface Pressure

  • The pressure at the surface is caused by the weight of all the air molecules in the column above the surface.
  • Add more air molecules to the column and the pressure goes up. (High Pressure areas)
  • Take away air molecules from the column and the pressure goes down. (Low Pressure areas)


Air density is the mass of the air divided by the volume of measurement.

As one goes higher in the atmosphere the number of molecules in a given volume decreases, so like pressure, density also decreases monotonically with height.

Since don’t have as many molecules on top of you, the air pressure also decreases with height.