(Meteor) (1) The rate of temperature decrease with altitude. (2) The rate of cooling of a rising or warming of a falling parcel of air. Note: Unsaturated rising air has a dry adiabatic lapse -rate of 5. 5⁰F per 1000 feet. The process is reversed for a dry falling parcel. The measured rate of change in temperature with change in height is called the environmental lapse rate. If the environmental lapse rate exceeds the adiabatic rate, the air becomes unstable. If the parcel of air is saturated with moisture, temperature changes associated with vertical movement follow the moist adiabatic lapse rate, which is less than the dry rate (2 to 5⁰F per 1000 feet) due to the latent heat of vaporization released by condensation. For dry air, the lapse rate equation is dT/dz = g/Cp, where dT is the change in temperature, dz is the change in height, g is the acceleration of gravity, and Cp is the heat capacity of the air at constant pressure