lapse rate


lapse rate
Meteorol.
the rate of decrease of atmospheric temperature with increase of elevation vertically above a given location.
[1915-20]

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      rate of change in temperature observed while moving upward through the Earth's atmosphere. The lapse rate is considered positive when the temperature decreases with elevation, zero when the temperature is constant with elevation, and negative when the temperature increases with elevation ( temperature inversion). The lapse rate of nonrising air—commonly referred to as the normal, or environmental, lapse rate—is highly variable, being affected by radiation, convection, and condensation; it averages about 6.5 °C per kilometre (18.8 °F per mile) in the lower atmosphere ( troposphere). It differs from the adiabatic lapse rate, which involves temperature changes due to the rising or sinking of an air parcel. Adiabatic lapse rates are usually differentiated as dry or moist.

      The dry adiabatic lapse rate for air depends only on the specific heat capacity of air at constant pressure and the acceleration due to gravity. The dry adiabatic lapse rate for the Earth's atmosphere equals 9.8 °C per kilometre (28.3 °F per mile); thus, the temperature of an air parcel that ascends or descends 5 km (3 miles) would fall or rise 49 °C (85 °F), respectively.

      When an air parcel that is saturated with water vapour rises, some of the vapour will condense and release latent heat. This process causes the parcel to cool more slowly than it would if it were not saturated. The moist adiabatic lapse rate varies considerably because the amount of water vapour in the air is highly variable. The greater the amount of vapour, the smaller the adiabatic lapse rate. As an air parcel rises and cools, it may eventually lose its moisture through condensation; its lapse rate then increases and approaches the dry adiabatic value.

      The difference between the normal lapse rate in the atmosphere and the dry and moist adiabatic lapse rates determines the vertical stability of the atmosphere—that is, the tendency of an air particle to return to its original position or to accelerate away from its original position after being given a slight vertical displacement. For this reason, the lapse rate is of prime importance to meteorologists in forecasting certain types of cloud formations, the incidence of thunderstorms (thunderstorm), and the intensity of atmospheric turbulence.

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Universalium. 2010.

Look at other dictionaries:

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  • lapse rate — n. the rate of decrease of an atmospheric variable, usually temperate, with increase of altitude …   English World dictionary

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  • lapse rate — The rate of decrease of an atmospheric variable with height. However, the term normally refers to the fall of temperature with height. The three types of lapse rates referred to in meteorology are dry adiabatic lapse rate, saturated adiabatic… …   Aviation dictionary

  • lapse rate — noun : the rate of change of any meteorological element with increase of height; specifically : the rate of decrease of temperature with increase of height called also vertical gradient * * * Meteorol. the rate of decrease of atmospheric… …   Useful english dictionary

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  • lapse rate — noun Date: 1918 the adiabatic rate of decrease of atmospheric temperature with increasing altitude …   New Collegiate Dictionary

  • lapse rate — noun The rate of change in atmospheric temperature with increase of height. The variable normally is temperature unless specified otherwise. This is a vertical direction of travel (up or down), and the temperature may rise or fall suddenly …   Wiktionary

  • lapse rate — noun the rate at which air temperature falls with increasing altitude …   English new terms dictionary

  • lapse rate — /ˈlæps reɪt/ (say laps rayt) noun the rate of decrease in an atmospheric variable, usually temperature, occurring with height …   Australian English dictionary


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