抄録
It is well known that the generalized profile equation of the vertical wind distribution above crop canopies is written experimentally by the logarithmic profile
U=U*/κlnZ-d/Z0
where d is a zero-plane displacement.
The zero-plane displacement d was introduced quite empirically to fit the validity of the logarithmic profile in the space over the crop canopies, and it is considered that a change in d depend not only on the mechanical and geometrical properties of the crop canopy, but also on the wind velocity.
It was clarified from several experiments that the vertical wind distribution above the crop canopies could be divided into two layers (fig. 4); the first region is considered to be the approach velocity of the wind and the second is that of the boundary layer of air, newly arose by the surface of the crop canopy.
Results of an analysis made with the above assumption are as follows;
(1) The vertical distribution of mean wind velocity is well represented by the logarithmic law
U=U*/κlnZ-H/Z0
where H is the height of the crop canopy surface.
The value of the zero-plane displacement d is equal to H.
(2) The vertical distribution of mean wind velocity in the second region is given by the power law
U∝(Z-H)n
where the exponent n is approximately equal to 1/7
