Aerodynamic roughness of urban areas derived from wind observations

This study contributes to the sparse literature on anemometrically determin ed roughness parameters in cities. Data were collected using both slow and fast response anemometry in suburban areas of Chicago, Los Angeles, Miami a nd Vancouver. In all cases the instruments were mounted on tall towers, dat a were sorted by stability condition, and zero-plane displacement (z(d)) wa s taken into account. Results indicate the most reliable slow response esti mates of surface roughness are based on the standard deviation of the wind speed obtained from observations at one level. For residential areas, winte r roughness values (leaf-off) are 80-90% of summer (leaf-on) values. Direct comparison of fast and slow response methods at one site give very similar results. However, when compared to estimates using morphometric methods at a wider range of sites, the fast response methods tend to give larger roug hness length values. A temperature variance method to determine z(d) from f ast response sensors is found to be useful at only one of the four sites. T here is no clear best choice of anemometric method to determine roughness p arameters. There is a need for more high quality field observations, especi ally using fast response sensors in urban settings.