Preliminary Analysis of urban wind profiles for an urban flow index

Four sets of wind profiles were collected within and above a Central Business District (CBD) for further analysis. These data sets were collected during four different synoptic forcing conditions for full diurnal cycles to sort on similarities and differences of profile behavior. Profiles of wind speed and direction were measured at 5 m vertical spacing about every 5 minutes within the building layer. Profile behavior within the building layer, in the building's surface roughness layer, and through the ambient boundary layer to approximately 340 m agl is analyzed. In the ambient layer, both speed and direction profiles are essentially unchanging from about two times the building heights to 340 m for each case. Within the surface roughness layer, speed and direction decreased notably downward to the top of the building layer. Within the building layer, speed and direction values decreased with depth even more dramatically. A least squares analysis of the speed profiles is performed to further establish urban flow index values to be used to define a speed versus height relationship within the urban canopy layer. Current thinking is that urban canopies can be approximated by the same exponential relationship as that of vegetative canopies. The least squares analysis defines the slope of the profile curve and therefore the index. Index values are derived from this analysis. Conditional sampling with respect to wind direction, wind speed, and atmospheric stability is also performed to further sort out differences in profile structure and the resultant flow index.