the decrease of atmospheric temperature with height (δT/δz < 0.0) where T is the air temperature and z is height —see air temperature inversion, saturation-adiabatic lapse rate; kinds of lapse rate include the following:

—dry-adiabatic lapse rate the theoretical decrease of air temperature with altitude of a parcel of unsaturated air which is lifted adiabatically (no energy gained or lost), the temperature changing in response to decreasing pressure; the rate is δT/δz = —9.77°C/1,000 m (—5.4°F/1,000 ft) —note the term adiabatic gradient denotes the difference in temperature between two elevations and is used to calculate evapotranspiration or heat flux; the term lapse is generally used to describe the larger condition of the atmospheric surface layer

—environmental lapse rate the actual decrease of temperature with altitude —note if the environmental lapse rate is more negative than the (dry-) adiabatic lapse rate (air temperature decreases with altitude faster than the [dry-] adiabatic lapse rate), the air is unstable; if the environmental lapse rate is less negative than the (dry-) adiabatic lapse rate (air temperature decreases with altitude slower than the [dry-] adiabatic lapse rate), the air is stable; if the environmental lapse rate is nearly the same as the (dry-) adiabatic lapse rate, the air stability is neutral

—wet-adiabatic lapse rate the theoretical decrease of air temperature with altitude of a parcel of saturated air, i.e., in clouds or fog, which is lifted adiabatically (no energy gained or lost), the temperature changing in response to decreasing pressure; the rate is approximately 0.6 of the dry-adiabatic lapse rateThis definition last updated 07/21/2008