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Wind profiles

Sven-Erik Gryning

Learning objectives

After this lecture you will be able to:

• Summarize the physics and theory for the

wind profile

• Explain why the wind profile differs between

night and day

Troen & Petersen, 1989: European Wind Atlas

z 0 =0.4 m (urban, forest and farm land with many wind breaks)

z 0 =0.03 m (open areas with few bushes and trees)

z 0 =0.1 m (farm land with bushes and trees)

z o=0.0002 m (sea, fjords and lakes)

Roughness length

Z 0 [m] Terrain surface characteristics (land use) 1.50 Sparse forest 1.00 City 0.80 Dense forest 0.50 Suburbs 0.40 Shelter belts 0.20 Many trees and/or bushes 0.10 Farmland with closed appearance 0.05 Farmland with open appearance 0.03 Farmland with very few buildings/trees 0.02 Airport areas with some buildings and trees 0.01 Airport runway areas 0.008 Mown grass 0.005 Bare soil (smooth) 0.001 Snow surfaces (smooth) 0.0003 Sand surfaces (smooth) 0.0002 Water areas (lakes, fjords, open sea)

Roughness length

WAsP Course notes

Atmospheric stability - day

Atmospheric stability - night

D

Wind speed and direction varies with height

night Windy night With low-level jet

Summary

In this lecture you have learnt that:

• The wind profile is logarithmic at

high wind speeds

• The wind speed depends on the

surface roughness

• Winds are different during day and

night

However, the wind profile also depends on the height of the boundary layer and the

horizontal temperature gradient (baroclinicity).