On Roughness Length and Zero-Plane Displacement in the Wind Profile of the Lowest Air Layer

[摘要] To describe the turbulent character in plant canopies, a simple model is assumed, and from conditions of the turbulent flow consisting at the boundary of two spaces, i. e. over and under a plant canopy, a relation is deduced which connects d (zero-plane displacement), z0 (roughness length) and H (roughness height). It is made clear that when the wind rises, i. e. H decreases, there are several cases of variation of d against z0. The experimental results appearing very complicated at first sight is shown as expected from the theory. A diagram is given which illustrates the relation between d, z0, H and (u/ν∗)z=H and in which any rough surface is represented by a single point, being specified by not only the surface is smooth or rough, but also its roughness is dense or sparse. Also the so called skin-friction coefficient is discussed, and it is shown that the coefficient generally does not have a simple relation with d or z0, but it increases when the rough surface becomes more dense.

[学科分类] 大气科学