The lapse rate is the rate at which an atmospheric variable (usually temperature) decreases with altitude. It is expressed as the negative ratio of the temperature change and the altitude change, thus:

<math>\gamma = -\frac{T_2 - T_1}{z_2 - z_1}<math>

where γ = lapse rate in °C/km, T = temperature in degrees C, and z = altitude in kilometres, where the level 2 is at a higher altitude than level 1

Also see Dry adiabatic lapse rate.

External link

• National Science Digital Library - Lapse Rate (http://www.nsdl.arm.gov/Library/glossary.shtml#lapse_rate)