On the Vertical Distribution of Wind Velocity and Eddy Diffusion Coefficient over the City

Abstract

The vertical distribution of mean wind velocity was observed, using several Robinson small cup anemometers, in the lower layer over three places in Tokyō.
From the results, the vertical distribution of wind velocity was fitted to the logarithmic law as follows :
U(Z)=(U_∗/k) log_e ((Z-d)/Z₀)………(1)
where U_∗, k, Z₀ and d denote the friction velocity, Kármán’s const. 0.45, roughness parameter and zero plane displacement (d was chosen to give the best fit in wind profile). The values of d and Z₀ are observed.
Then, the vertical diffusion coefficient (K_z) is given by (2), from Prandtl’s theory on the turbulence mixing.
K_z=kU_∗ (Z-d)………(2)
The calculated values of K_z was the order of 10⁴cm²/sec, for U_av varying form 3.6m/s to 6.4m/s at height from the ground 10m.