# Adiabatic lapse rate

From Glossary of Meteorology

## adiabatic lapse rate

The rate of decrease in temperature with height via an adiabatic process.

- Dry-adiabatic lapse rateA process lapse rate of temperature, the rate of decrease of temperature with height of a parcel of dry air lifted by a reversible adiabatic process through an atmosphere in hydrostatic equilibrium.This lapse rate is
*g*/*c*_{pd}, where*g*is the gravitational acceleration and*c*_{pd}is the specific heat of dry air at constant pressure, approximately 9.8°C km^{−1}. Potential temperature is constant with height in an atmospheric layer with this lapse rate. - Moist-unsaturated adiabatic lapse rateThe adiabatic lapse rate of unsaturated air containing water vapor.This differs from definition 1 by the factorwhere
*r*_{υ}is the mixing ratio of water vapor and*c*_{pυ}is the specific heat of water vapor. - Moist-adiabatic lapse rate (or saturation-adiabatic lapse rate or moist-saturated adiabatic lapse rate)The rate of decrease of temperature with height along a moist adiabat.It is given approximately by Γ
_{m}in the following:where*g*is the gravitational acceleration,*c*_{pd}is the specific heat at constant pressure of dry air,*r*_{υ}is the mixing ratio of water vapor,*L*_{υ}is the latent heat of vaporization,*R*is the gas constant for dry air,*ϵ*is the ratio of the gas constants for dry air and water vapor, and*T*is temperature. This expression is an approximation for both the reversible moist-adiabatic lapse rate and the pseudoadiabatic lapse rate, with more accurate expressions given under those definitions. When most of the condensed water is frozen, this may be replaced by a similar expression but with*L*_{υ}replaced by the latent heat of sublimation.

*Term edited 10 August 2021.*