Roughness Length
Encyclopedia
Roughness length is a parameter
of some vertical wind profile equations that model the horizontal mean wind speed near the ground; in the log wind profile
, it is equivalent to the height at which the wind speed is zero. It is so named because it is typically related to the height of terrain roughness elements. Whilst it is not a physical length, it can be considered as a length-scale a representation of the roughness of the surface.
As an approximation, the roughness length is approximately one-tenth of the height of the surface roughness elements. For example, short grass of height 0.01m has a roughness length of approximately 0.001m. Surfaces are rougher if they have more protrusions. Forests have much larger rougher lengths than tundra, for example. Roughness length is an important concept in urban meteorology as the building of tall structures, such as skyscrapers, has an effect on roughness length and wind patterns.
Parameter
Parameter from Ancient Greek παρά also “para” meaning “beside, subsidiary” and μέτρον also “metron” meaning “measure”, can be interpreted in mathematics, logic, linguistics, environmental science and other disciplines....
of some vertical wind profile equations that model the horizontal mean wind speed near the ground; in the log wind profile
Log wind profile
The Log wind profile is a semi-empirical relationship used to describe the vertical distribution of horizontal wind speeds above the ground within the atmospheric surface layer...
, it is equivalent to the height at which the wind speed is zero. It is so named because it is typically related to the height of terrain roughness elements. Whilst it is not a physical length, it can be considered as a length-scale a representation of the roughness of the surface.
As an approximation, the roughness length is approximately one-tenth of the height of the surface roughness elements. For example, short grass of height 0.01m has a roughness length of approximately 0.001m. Surfaces are rougher if they have more protrusions. Forests have much larger rougher lengths than tundra, for example. Roughness length is an important concept in urban meteorology as the building of tall structures, such as skyscrapers, has an effect on roughness length and wind patterns.
See also
- Von Kármán constantVon Kármán constantIn fluid dynamics, the Von Kármán constant , named for Theodore von Kármán, is a dimensionless constant describing the logarithmic velocity profile of a turbulent fluid flow near a boundary with a no-slip condition...
- Monin-Obukhov lengthMonin-Obukhov LengthThe is used to describe the effects of buoyancy on turbulent flows, particularly in the lower tenth of the atmospheric boundary layer. It was first defined by Alexander Obukhov in 1946,...
- Wind profile power lawWind profile power lawThe wind profile power law is a relationship between the wind speeds at one height, and those at another.The power law is often used in wind power assessments where wind speeds at the height of a turbine must be estimated from near surface wind observations , or where wind speed data at various...
- Log wind profileLog wind profileThe Log wind profile is a semi-empirical relationship used to describe the vertical distribution of horizontal wind speeds above the ground within the atmospheric surface layer...
- Displacement height