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The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, falls with altitude. Lapse rate arises from the word lapse, in the sense of a gradual fall. In dry air, the adiabatic lapse rate is 9.8 °C/km (5.4 °F per 1,000 ft). At Saturated Air Lapse Rate (SALR), where value is 1.1 °C/1000ft - 2.8 °C/1000ft as obtained from ICAO. It corresponds to the vertical component of the spatial gradient of temperature. Although this concept is most often applied to the Earth's troposphere, it can be extended to any gravitationally supported parcel of gas. Definition A formal definition from the Glossary of Meteorology is: :The decrease of an atmospheric variable with height, the variable being temperature unless otherwise specified. Typically, the lapse rate is the negative of the rate of temperature change with altitude change: :\Gamma = -\frac{\mathrm{d}T}{\mathrm{d}z} where \Gamma (sometimes L)

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