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Log wind profileThe Log wind profile is a semiempirical relationship used to describe the vertical distribution of horizontal wind speeds above the ground within the atmospheric surface layer. The relationship is well described in the planetary boundary layer literature ^{[1]}. Additional recommended knowledgeThe logarithmic profile of wind speeds is generally limited to the lowest 100 meters (325') of the atmosphere (i.e., the surface layer of the atmospheric boundary layer). In the free atmosphere, geostrophic wind relationships should be used. The equation to estimate the wind speed (u) at height z (meters) above the ground is:
where u_{ * } is the friction (or shear) velocity (m s^{1}), κ is von Karman's constant (~0.41), d is the zero plane displacement, z_{0} is the surface roughness (in meters), and is a stability term where L is the MoninObukhov stability parameter. Under neutral stability conditions, z / L = 0 and drops out. Zeroplane displacement (d) is the height in meters above the ground at which zero wind speed is achieved as a result of flow obstacles such as trees or buildings. It is generally approximated as ^{2}/_{3} of the average height of the obstacles. For example, if estimating winds over a forest canopy of height h = 30 m, the zeroplane displacement would be d = 20 m. Roughness length (z_{0}) is a corrective measure to account for the effect of the roughness of a surface on wind flow, and is between ^{1}/_{10} and ^{1}/_{30} of the average height of the roughness elements on the ground. Over smooth, open water, expect a value around 0.0002 m, while over flat, open grassland z_{0} ≈ 0.03 m, cropland ≈ 0.10.25 m, and brush or forest ≈ 0.51.0 m (values above 1 m are rare and indicate excessively rough terrain). The log wind profile is generally considered to be a more reliable estimator than the Wind profile power law, which is commonly used when neutral conditions are assumed and roughness information is not available. ApplicationsLog wind profiles are generated and used in a good many atmospheric pollution dispersion models.^{[2]} See also
References

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Log_wind_profile". A list of authors is available in Wikipedia. 