Adiabatic Lapse Rate
The rate at which the temperature of a rising or descending air parcel changes as it expands or compresses adiabatically without heat exchange with surroundings.
Governing formula
Dry: Γ_d = g / c_p ≈ 9.8 °C/km; Moist: Γ_m ≈ 4–7 °C/km
SI unit
°C/km or K/km
In depth
As an air parcel rises, decreasing ambient atmospheric pressure causes it to expand and cool adiabatically. Un-saturated dry air cools at ~9.8 °C/km (DALR). Saturated air cools slower at ~5 °C/km (MALR) due to latent heat release from condensing water vapor.
Examples in the real world
Rising moist air cooling at the moist adiabatic lapse rate to reach condensation level and form clouds.