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:
| 150 m | 7.94 m/s |
| 140 m | 7.87 m/s |
| 130 m | 7.78 m/s |
| 120 m | 7.70 m/s |
| 110 m | 7.60 m/s |
| 100 m | 7.50 m/s |
| 90 m | 7.39 m/s |
| 80 m | 7.26 m/s |
| 70 m | 7.11 m/s |
| 60 m | 6.95 m/s |
| 50 m | 6.75 m/s |
| 40 m | 6.51 m/s |
| 30 m | 6.19 m/s |
| 20 m | 5.75 m/s |
| 10 m | 5.00 m/s |
| Roughness class |
Roughness length z0 |
Land cover types |
|---|---|---|
| 0 | 0.0002 m | Water surfaces: seas and Lakes |
| 0.5 | 0.0024 m | Open terrain with smooth surface, e.g. concrete, airport runways, mown grass etc. |
| 1 | 0.03 m | Open agricultural land without fences and hedges; maybe some far apart buildings and very gentle hills |
| 1.5 | 0.055 m | Agricultural land with a few buildings and 8 m high hedges seperated by more than 1 km |
| 2 | 0.1 m | Agricultural land with a few buildings and 8 m high hedges seperated by approx. 500 m |
| 2.5 | 0.2 m | Agricultural land with many trees, bushes and plants, or 8 m high hedges seperated by approx. 250 m |
| 3 | 0.4 m | Towns, villages, agricultural land with many or high hedges, forests and very rough and uneven terrain |
| 3.5 | 0.6 m | Large towns with high buildings |
| 4 | 1.6 m | Large cities with high buildings and skyscrapers |
On the ground, the wind is strongly braked by obstacles and surface roughness. High above the ground in the undisturbed air layers of the geostrophic wind (at approx. 5 km above ground) the wind is no longer influenced by the surface. Between these two extremes, wind speed changes with height. This phenomenon is called vertical wind shear.
In flat terrain and with a neutrally stratisfied atmosphere, the logarithmic wind profile is a good estimation for the vertical wind shear:
The reference wind speed v1 is measured at height h1. v2 is the wind speed at height h2. z0 is the roughness length (see table above).