Aeronautical Terms beginning with L

Land breeze

A coastal breeze blowing from land to sea, caused by temperature difference when the sea surface is warmer than the adjacent land. Therefore, it usually blows at night and alternates with a sea breeze, which blows in the opposite direction by day.


Lapse rate

The rate of decrease of an atmospheric variable with height; commonly refers to decrease of temperature with height.


Latent heat

The amount of heat absorbed (converted to kinetic energy) during the processes of change of liquid water to water vapor, ice to water vapor, or ice to liquid water; or the amount released during the reverse processes. Four basic classifications are: latent heat of condensation, latent heat of fusion, latent heat of sublimation, and latent heat of vaporization.


Latent heat of condensation

Heat released during change of water vapor to water.


Latent heat of fusion

Heat released during change of water to ice or the amount absorbed in change of ice to water.


Latent heat of sublimation

Heat released during change of water vapor to ice or the amount absorbed in the change of ice to water vapor.


Latent heat of vaporization

Heat absorbed in the change of water to water vapor; the negative of latent heat of condensation.


Layer

In reference to sky cover, clouds or other obscuring phenomena whose bases are approximately at the same level. The layer may be continuous or composed of detached elements. The term “layer” does not imply that a clear space exists between the layers or that the clouds or obscuring phenomena composing them are of the same type.


Lee wave

Any stationary wave disturbance caused by a barrier in a fluid flow. In the atmosphere when sufficient moisture is present, this wave will be evidenced by lenticular clouds to the lee of mountain barriers; also called mountain wave or standing wave.


Lenticular cloud (or lenticularis)

A species of cloud whose elements have the form of more or less isolated, generally smooth lenses or almonds. These clouds appear most often in formations of orographic origin, the result of lee waves, in which case they remain nearly stationary with respect to the terrain (standing cloud), but they also occur in regions without marked orography.


Level of free convection (abbreviated LFC)

The level at which a parcel of air lifted dry-adiabatically until saturated and moist-adiabatically thereafter would become warmer than its surroundings in a conditionally unstable atmosphere.


Lifting condensation level (abbreviated LCL)

The level at which a parcel of unsaturated air lifted dry-adiabatically would become saturated. Compare level of free convection and convective condensation level.


Lightning

Generally, any and all forms of visible electrical discharge produced by a thunderstorm.


Lithometeor

The general term for dry particles suspended in the atmosphere such as dust, haze, smoke, and sand.


Low

An area of low barometric pressure, with its attendant system of winds. Also called a barometric depression or cyclone.


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