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. The relationship is well described in the planetary boundary layer literature [cite book|author=Oke, T.R.|title=Boundary Layer Climates|edition=|publisher=Methuen|year=1987|id=] .

The 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:

u_z = frac{u_*}{kappa} left [ln left(frac{z-d}{z_0} ight) + varphi(z,z_0,L) ight]
where u_* is the friction (or shear) velocity (m s-1), kappa is von Karman's constant (~0.41), d is the zero plane displacement, z_0 is the surface roughness (in meters), and varphi is a stability term where L is the Monin-Obukhov stability parameter. Under neutral stability conditions, z/L = 0 and varphi drops out.

Zero-plane 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 zero-plane 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 ≈ 0.1-0.25 m, and brush or forest ≈ 0.5-1.0 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.


Log wind profiles are generated and used in a good many atmospheric pollution dispersion models. [cite book|author=Beychok, Milton R.|title=Fundamentals Of Stack Gas Dispersion|edition=4th Edition|publisher=author-published|year=2005|id=ISBN 0-9644588-0-2]

ee also

* Compilation of atmospheric dispersion models


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Wind profile power law — The 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 [Elliott, D.L., C.G. Holladay, W.R. Barchet, H.P. Foote, and W.F. Sandusky, 1986,… …   Wikipedia

  • Wind gradient — In common usage, wind gradient, more specifically wind speed gradientcite book | last = Hadlock | first = Charles | title = Mathematical Modeling in the Environment | publisher = Mathematical Association of America | location = Washington | year …   Wikipedia

  • Log Law —   In reference to a wind energy conversion system, the wind speed profile in which wind speeds increase with the logarithmic of the height of the wind turbine above the ground …   Energy terms

  • Dive log — This is the cover of CMAS dive log book. A dive log is used by a scuba diver to record the details of their dives. The log may either be in a book, software, or web based. The log serves purposes both related to safety and personal records.… …   Wikipedia

  • Planetary boundary layer — Depiction of where the planetary boundary layer lies on a sunny day The planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL), is the lowest part of the atmosphere and its behavior is directly influenced by its… …   Wikipedia

  • Roughness Length — (z 0) is a parameter which is a measure of terrain roughness as seen by surface wind. It is formally the height (in meters) at which the wind speed becomes zero when the logarithmic wind profile above the roughness sub layer is extrapolated to… …   Wikipedia

  • Surface layer — The surface layer is the layer of a turbulent fluid most affected by interaction with a solid surface or the surface separating a gas and a liquid. In surface layers the characteristics of the turbulence depend on distance from the interface.… …   Wikipedia

  • Radiosonde — A GPS sonde, approx 220 × 80 ×75 mm (8.7 × 3.1 × 3 in) (with grounding station in background, used to perform a ground check and also recondition the humidity sensor) A radiosonde (Sonde is French for probe) is a unit for use in weather balloons… …   Wikipedia

  • Coal River (West Virginia) — For other uses, see Coal River (disambiguation). The Coal River at Upper Falls …   Wikipedia

  • Business and Industry Review — ▪ 1999 Introduction Overview        Annual Average Rates of Growth of Manufacturing Output, 1980 97, Table Pattern of Output, 1994 97, Table Index Numbers of Production, Employment, and Productivity in Manufacturing Industries, Table (For Annual… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.