Fact Sheet 2

The Troposphere (Lower Atmosphere)

Virtually all the atmospheric effects that we call "weather" occurs in the troposphere. The primary feature that characterizes the troposphere is its linear decrease in temperature with increasing altitude.

The graph to the left shows the average temperature of what scientists call the "ICAO. Standard Atmosphere" as a function of altitude.

The slope of the line on the linear portion (straight part) of the graph is called the thermal lapse rate or simply the "lapse rate."

The stratosphere begins at the height at which the lapse rate becomes non-linear. The temperature within the stratosphere increases with increasing altitude.

The atmospheric pressure drops as one increases altitude. The greatest rate of pressure change occurs at sea level.

As one moves upwards through the atmosphere the rate of pressure change per kilometre of altitude decreases. This is a non-linear (curved line) effect.

Unlike most liquids, gases are highly compressible. The compressibility of air causes its density (kg/m3) to be greatest at sea level.

As with pressure, the density of the atmosphere decreases (in a non-linear way) as one moves upwards through the atmosphere.

To reach atmospheric densities which approach zero one must move upwards to altitudes of at least several hundred kilometres.

There is no distinct boundary between the Earth's atmosphere and outer space. The Earth's atmosphere just keeps getting less and less dense, until its effects are considered negligible.