Reversible moist-adiabatic process

From Glossary of Meteorology

reversible moist-adiabatic process

A moist-adiabatic process in which the air is maintained at saturation by the evaporation or condensation of water substance, the enthalpy of water vapor formed or removed being supplied by or to the air, respectively.

In contrast to a pseudoadiabatic expansion, the liquid water that condenses in an air parcel expanding through a reversible moist-adiabatic process is carried with the parcel, so that subsequent compression occurs with moist-adiabatic warming, leading to the original state. This can only happen if the condensed water drops are small enough to have negligible fallout velocities. The moist-adiabatic lapse rate for the reversible process is given by
where Γrm is the reversible moist-adiabatic lapse rate; g is gravity; rv, rl, and rt are the mixing of water vapor, liquid water, and total water; cpd, cpv, and c are the specific heats at constant pressure of dry air, water vapor, and liquid water; Lv is the heat of vaporization; R is the dry air gas constant; ε is the ratio of the gas constants of dry air and water vapor (≈ 0.622); and T is temperature.