Extended Abstract (40K)14.5
Doppler lidar and wind tunnel observations of flow over an urban canopy
Fay Davies, University of Salford, Salford, United Kingdom; and C. G. Collier and H. Cheng
The Salford lidar research group is a collaborator in the Joint Research Councils Urban Regeneration and the Environment (URGENT) program. The meteorological participants in this program include the Universities of Reading , Salford and Surrey in the UK. These universities, being members of UWERN (UK Universities Weather Research Network), form the UWERN Urban Meteorology Research Group. The aim of the UWERN urban meteorology program was to develop a numerical canopy model, verified using atmospheric boundary layer data and wind tunnel experiments.
As part of this project the Salford Lidar Research Group made a set of lidar measurements over the urban atmospheric boundary layer in the city of Salford, in the Greater Manchester area of the UK. The Salford lidar is a infrared, pulsed Doppler lidar that operates at an eye-safe wavelength of 10.6 µ m. The lidar system is based in a mobile laboratory and measures the velocity of naturally occuring aerosols that are advected with the wind field. Radial wind measurements taken with the lidar are used to calculate horizontal and vertical velocities and velocity variances.
Lidar data was collected on the 3rd April 2001 at approximately 13:00 UTC in near neutral atmospheric conditions. The prevailing wind was from a southerly direction (190 degrees). The measurement site, at the University of Salford, contained a convenient roughness step change position. Upstream of the site, to the south, was predominantly mixed height buildings in an 'urban' type canopy region. To the north was a low level housing estate of predominantly 2-story dwellings in a more 'suburban' type canopy. Data was collected to examine the growth of the internal boundary layer over the 'suburban' canopy region. A distinction is made here between the 'urban' canopy which has more mixed height buildings with multi-story and low level offices in a more sparsely packed canopy, and the 'suburban' region where the housing estate was predominantly low level and more tightly packed.
The lidar data is compared to wind tunnel data taken at EnFlo at the University of Surrey in the UK. The wind tunnel experiment was set to examine the initial flow field downstream of a step change in surface roughness. The roughness elements were designed to simulate a suburban canopy region. Experiments were conducted in a low speed open-circuit zero-pressure gradient tunnel with a test section of 600 mm high, 900 mm wide and 4.5 m long. The roughness covered the entire floor of the wind tunnel.
Data from these two experiments are compared in similar terms to examine the development of the internal boundary layer above the 'suburban' canopy region. The wake region and boundary layer adjustment downwind of the roughness change has been clearly observed using the lidar data.
Session 14, Urban boundary layer: observations
Friday, 24 May 2002, 8:00 AM-10:45 AM
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