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/c_pd, where g is 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. 2. The adiabatic lapse rate of unsaturated air containing water vapor.

This differs from definition 1 by the factor