Relating Urban Surface-layer Structure to Upwind Terrain for the Salford Experiment (Salfex)

• Published in: Boundary-layer meteorology Vol. 127; no. 2; pp. 173 - 191
• Main Authors: Barlow, J. F, Rooney, G. G, von Hünerbein, S, Bradley, S. G
• Format: Journal Article
• Language: English
• Published: Dordrecht Dordrecht : Springer Netherlands 01.05.2008; Springer Netherlands; Springer; Springer Nature B.V
• Subjects: Atmospheric boundary layer; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Heterogeneity; Meteorology; Original Paper; Sodar; Source area; Surface heterogeneity; Turbulence; Upstream; Urban areas; Urban boundary layer; Urban canopy; Wind; Wind profile; England; United Kingdom; Great Britain; Europe; Western Europe; British Isles; British Isles, England, Greater Manchester, Manchester, Salford; Urban boundary layer; Wind profile; Sodar; Surface heterogeneity; Urban canopy; Source area; Conurbation; Wind field; Urban structure; urban areas; Urban atmosphere; layer; heterogeneous media; Complex terrain; Urban boundary; Atmospheric boundary layer; Lidar; Observation data; Turbulence intensity; Doppler radar; Drag coefficient; Radio sounding; Turbulence structure; Boundary layer turbulence
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/s10546-007-9261-y

Profiles of wind and turbulence over an urban area evolve with fetch in response to surface characteristics. Sodar measurements, taken on 22 April 2002 during the Salford Experiment in the UK (Salfex), 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 vertical gradient, suggesting a change in surface cover upstream. The drag coefficient varied by a factor of two over only a 20° direction change. Turbulence intensity (σ x ) for each wind component (x) decreased with height, but the ratio suggested an underestimate of σ u compared to previous results. Mean urban and suburban cover fraction within the source area for each height decreased sharply between z = 20 and 50m, increasing slightly above. The near-convergence of cover fractions thus occured for source areas of minimum length [almost equal to] 2,200 m. In comparison, the mean length scale of heterogeneity L P was calculated from surface cover data to be 1,284 m, and the corresponding mean blending height h b was 175 m. Finally, the mean streamline angle, α, was negative and the magnitude decreased with height. An exponential fit to α for z <= 65m gave an e-folding height scale of 159 m. A simple relationship between this height scale and L P was assumed, giving L P [almost equal to] 1,080 m, which is in reasonable agreement with the estimate from surface cover type. The results suggest that more emphasis is required on modelling and measuring surface-layer flow over heterogeneous urban canopies.