Abstract
In the aerodynamic method, if the constant flux layer is under the conditions of neutral stability, then the wind profile in the layer can be written as u= (u*/k) ·ln {(z-d)/z0} over a tall canopy, in which u is the wind velocity at elevation z, u* is the friction velocity, k is von Kármán's constant, d is the zero-plane displacement height and z0 is the roughness length.
The above d is usually chosen as a fraction of canopy height or by the selection of a value which forces the above canopy neutral wind profile to be semi-logarithmic. In this paper, these methods of determining the value of d were examined by using wind profiles measured under the conditions of neutral stability and the friction velocity measured by the eddy correlation method.The results obtained are summarized as follows:
1) The value of d ought be determined with the value of k.
2) If the value of d was determined by the former method, then the friction velocity, u*, which was obtained from the above equation, could not always be estimated with high accuracy.This result is mainly because the value of d depends on the wind velocity.
3) If wind velocities were measured with high accuracy, then the appropriate value of d could be determined by the latter method.If they were measured with cup anemometers over a field, however, then u* could not always be estimated with high accuracy by the use of d determined with the latter method.
