# roughness length

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## roughness length

[′rəf·nəs ‚leŋkth]
(oceanography)
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For the roughness length values belonging to two different surfaces, the following equation may be written for the increase of the limit layer height values:
Regarding the aerodynamic study of the turbine, the vertical wind velocity profile was determined from the potential model and the logarithmic model (Lysen profile), under a roughness length [Z.sub.0] = 0.8 and a roughness coefficient [alpha] = 0.2312.
Height of turbine shaft at ground 23 m level (Z) Displacement height (d = 12 m 0,8 hm) Average height of the buildings 15 m ([h.sub.m]) Surface roughness length ([Z.sub.0] = 1.8 m 0.12 hm) Table 2 Frequencies distribution of wind speed.
To derive daily ET, surface roughness length ([Z.sub.0]), the MODIS land cover map, and a digital elevation model (DEM) were used.
where K is the Karman constant (=0.41), Z is height of the anemometer (=10 m), U is wind velocity at height Z (m/s), [Z.sub.0] is surface roughness length for momentum transfer (m), d is the zero-plane displacement height (m), and [Z.sub.0]h is surface roughness length for the transfer of heat and vapor (m).
The aerodynamic roughness length ([z.sub.0]), which gives a measure of the capacity of the surface elements in absorbing momentum, is one of the fundamental parameters in atmospheric models to link up the turbulent exchange process with surface morphology.
Another key model parameter that has impact on the dispersion of pollutants is the surface roughness length. Surface roughness length characterises the roughness of the terrain, providing an indicator of how much drag the wind experiences from the ground.
The surface roughness length ([z.sub.0]) was determined on the logarithmic altitude scale by extending the wind velocity curves to zero.
The advantage of these relationships is to avoid three problems: 1) the estimation of the roughness length (involving in the sensible heat flux), 2) the lack of continuous measurement of surface temperature and 3) the estimation of the soil heat flux which is negligible on daily timescales.
[q.sup.2]l=0, by inclusion of surface roughness length l = [KAPPA][Z.sup.s] (11)
with the parameters [[beta].sub.1] and [[beta].sub.1] being dependent on the Pasquill stability classes of A-F and where [z.sub.o] is the surface aerodynamic roughness length.
The drag effect of roughness elements is very important for urban mesoscale numerical models and it is usually parameterized using an aerodynamic roughness length. Aerodynamic roughness length is usually defined as the height where the wind velocity is equal to zero.

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