Roughness length

Using a log-linear profile of the wind speed, and assuming a surface roughness length of about 0.3 m, u is estimated from the 10-meter wind speed, u,o, as ... 

Dorman, J. L. and Sellers, P. J. (1989). A global climatology of albedo, roughness length and stomatal resistance for atmospheric general circulation models as represented by the simple biosphere model (SiB), /. Appl. Meteorol. 28, 833-855. 

Table 5.2 Dynamic roughness lengths, zo, for typical atmospheric surfaces (Turner, 1979)...

A burning dump emits 5 g/s of nitrous oxide (NO), spread over 50 m x 50 m, with an initial cloud height of 3 m. Estimate the maximum downwind concentration of NO at 5 km from the dump when the wind speed is 8 m/s at 3 m height over farmland, with a roughness length of 0.2 m. The threshold limit for NO is 25 ppm(v). Is this exceeded at 5 km from the dump ... 

In (6.11), z0 is a constant of integration. When u(z) is plotted against In z, a straight line is obtained, and z0 is the intercept of this line on the axis. It is termed the roughness length. 

Thus B 1 also is a measure of the ratio of the roughness lengths for momentum and vapour. 

In assessing evapotranspiration, it was sometimes assumed that the temperature profile over a canopy, when extrapolated to z — d = 0, gave a measure of the surface temperature. More correctly the profile should be extrapolated to the roughness length for heat transfer, which is nearly the same as zv for water vapour. In typical mid-day conditions, this increases the estimated surface temperature by several degrees (Thom, 1972). 

Figure 6.11 shows the velocity of deposition of Lycopodium spores to bare soil in the wind tunnel (Chamberlain Chadwick, 1972). The roughness length was 3 mm. When the soil was wet, v, increased with u, but levelled off at high speeds (in the field, = 1 m s-1 would correspond to u = 20 m s-1 at z = 10 m). With dry soil, vg hardly... 

The theoretical concentration in air downwind of an area source as a function of the roughness length and atmospheric stability has been given by Wilson (1982). Shinn et al. found z0 = 0.02 m at the Nevada site. The dimensionless concentration u Xi/Q from (6.25) is 8.3, and this would agree with Wilson s calculations for average (neutral) stability if the fetch of wind over the source of resuspended dust was 10 km. 

In a hemiface trial in humans 5% vitamin E reduced rhytides, skin roughness, length of facial lines, and depth of wrinkles more than vehicle.68 Topical tocopherol acetate was also shown to significantly increase stratum corneum hydration in human volunteers with additionally enhancing the water-binding capacity as compared to vehicle. The optimum concentration for these effects was 5% tocopherol acetate.69... 

The flow field and dispersion over such a non-porous region is similar to that over a solid obstacle with low slope with roughness change (since the effective surface roughness length z0 over the central urban area is greater than that upwind). FAM methods are available for point, line and area sources (e.g. ADMS, AERMOD). 

Proceeding from the urban LUC, the calculation of the main aerodynamic characteristics of urban areas such as the roughness length and displacement height, can be performed based on the morphometric or morphologic methods. 

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