Adiabatic lapse rate

From Glossary of Meteorology

adiabatic lapse rate

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

  1. Dry-adiabatic lapse rate
    A 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/cpd, where g is the gravitational acceleration and cpd 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.

  2. Moist-unsaturated adiabatic lapse rate
    The adiabatic lapse rate of unsaturated air containing water vapor.
    This differs from definition 1 by the factor
    Moist-unsat adiabatic LR
    where rv is the mixing ratio of water vapor and cpv is the specific heat of water vapor.

  3. 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 Γm in the following:
    Moist-adiabatic LR
    where g is the gravitational  acceleration, cpd is the  specific heat at constant pressure of dry air, rv is the mixing ratio of water vapor, Lv is the  latent heat of vaporizationR 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 Lv replaced by the latent heat of sublimation.

Term edited 16 August 2021.

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