Extended Abstract (76K)10.1
On the characterisation of urban boundary layer flow using morphology and Doppler lidar measurements
Chris G. Collier, University of Salford, Salford, United Kingdom; and K. E. Bozier
A ground based, pulsed infrared Doppler lidar system has been used to make observations of the atmospheric boundary layer within the urban conurbation of Greater Manchester, northwest England, UK. Comparisons are made with previously published measurements of roughness length, zero plane displacement, friction velocity and the surface drag coefficient for homogenous zones within cities.
The Salford scanning Doppler infrared lidar system operates with an eye safe wavelength (10.6 µm) providing radial (line of sight) velocity and backscattered intensity measurements. The lidar has a theoretical maximum range of 4.6 km, a pulse repetition frequency of 120 Hz , a velocity accuracy of 0.5 ms-1 with a range resolution of 112 m. The lidar system is equipped with a scanner enabling the lidar beam to be pointing in different directions generating data over a large area from a centrally located position.
Values of zero plane displacement and aerodynamic roughness length have been evaluated from observations of wind field statistics made on 27th August 1998 and 3rd April 2001. On both days the boundary layer was near neutral, although on 3rd April it became more unstable later in the observation period. At its closest point the edge of the urban area is approximately 18 km to the west of the measurement site. The terrain to the west is relatively flat consisting of low level, two storey, housing. To the east at a distance of 1.6 km, is Manchester city centre consisting of high rise buildings, twenty storeys, rising above closely packed, five / six storey buildings. The area to the north, which rises at a gentle slope towards the west Pennine Moors, consists mainly of residential, low level housing, with a sparse scattering of high rise tower blocks. To the south, airflow is generally over buildings having similar form with several groups of high rise buildings within a few kilometres to the southwest. In the immediate vicinity of the measurement site is an urban parkland area with approximate dimensions 350 m length and 250 m width.
The observations on 27th August 1998 indicate an airflow from the north / northeast over the urban parkland area and university campus. Roughness parameters have been derived for airflow over medium / tall buildings with low / medium density. The measurements made on 3rd April 2001 indicated airflow over closely packed low / medium height roughness elements, with similar form and height. The values of zero plane displacement and aerodynamic roughness length are compared in the context of the urban field studies and morphological estimates of roughness given by Grimmond and Oke (1999). Of particular interest is the verification of the morphological estimates provided by the lidar measurements in the region of low values of the packing density.
Session 10, Roughness lengths, surface resistances and CO2 Fluxes
Wednesday, 22 May 2002, 1:30 PM-3:15 PM
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