133 1.4- o x* 1.2- 4 4 o 10 1.0 0 o 0.8- - 0 0.6- 0.4 e 0.2 I 10-4 1t3 12 10t Z* zo Figure 5-38. The horizontal dispersion coefficient a versus the Y dimensionless roughness length for two values of the downwind distance.