Relating urban boundary layer structure to upwind terrain for the Salfex campaign

Barlow, JF; Rooney, GG; von Hünerbein, S; Bradley, SG

Abstract

Profiles of wind and turbulence over an urban area evolve with fetch in response to surface characteristics. Sodar measurements, taken on 22nd April 2002 during the Salfex campaign, are here related to upstream terrain. A logarithmic layer up to z=65m was observed in all half hour averaged profiles. Above this height the profile showed a different gradient, suggesting a change in surface cover upstream. The drag coefficient varied by a factor of two over a 20° direction change. Profiles of óu, óv and ów showed a decrease with
height, and their ratio suggested an underestimate of óu compared to previous results. Mean urban and suburban cover within the source area for each height decreased sharply between z=20 and 50m, increasing slightly above. This indicates varying urban canopy density on scales impacting profiles up to 100m. Finally, mean streamline angle decreased exponentially from 2.7° at the surface up to z=65m, giving a height scale of 159m. The derived length scale of surface heterogeneity was 997m, falling within the range of urban canopy variation estimated from surface data (between 144 and 1099m). Heterogeneity in urban canopy drag on neighbourhood scales clearly perturbs the flow throughout the surface layer. Hence measurements made within a log layer could still exhibit spatial dependence. Results shown here call for development of a suitable theoretical framework describing the impact of a heterogeneous urban canopy on surface layer flow.

Citation

Barlow, J., Rooney, G., von Hünerbein, S., & Bradley, S. (2008). Relating urban boundary layer structure to upwind terrain for the Salfex campaign. Boundary-Layer Meteorology, 127(2), 173-191. https://doi.org/10.1007/s10546-007-9261-y

• Journal Article Type: Article
• Publication Date: May 1, 2008
• Deposit Date: Sep 19, 2007
• Journal: Boundary-Layer Meteorology
• Print ISSN: 0006-8314
• Publisher: Springer Verlag
• Peer Reviewed: Peer Reviewed
• Volume: 127
• Issue: 2
• Pages: 173-191
• DOI: https://doi.org/10.1007/s10546-007-9261-y
• Publisher URL: http://dx.doi.org/10.1007/s10546-007-9261-y