Urban areas change profoundly the transport and mixing properties of the airflow, which has important applications in forecasting air quality and in emergency response to fires or toxic releases. These applications require understanding of the dynamical and thermodynamic interactions between the boundary layer and urban areas. Key questions requiring study are: What is the role of local advection and heterogeneity of both rural and urban surfaces in determining the structure of the ABL; What are the impacts of urban and rural areas on large scale weather?

A key component of modelling dispersion and air quality within the urban areas is the mixing and ventilation processes that set the concentrations and their fluctuations. These processes occur on a range of scales from street, to neighbourhood, to city. On the neighbourhood scales we need to understand what descriptors of the surface characterise the flow, mixing, and dispersion. Also on the city scale investigations are needed into what are the different roles played by tightly packed tall buildings in the city centre regions when compared to the low lying suburban regions in controlling transport, mixing, and ventilation in the urban boundary layer. Clarification is needed on how much of the understanding of plant canopies can be carried over to the urban canopy.

The research into those questions outlined in this paper is an integral part of the NERC National Centre for Atmospheric Science (NCAS) Universities Weather Research Network (UWERN) research programme. The work builds around both existing and planned scanning Doppler lidar data sets obtained in both urban and rural areas. The lidar system provides measurements on the scales from neighbourhood to city above the urban canopy layer to the top of the boundary layer and is therefore the ideal instrument with which to carry out this work. New urban measurements are to be made over Salford from SUBERB (Salford University Urban and Built Environment Research Base) and compared to existing rural data collected during both the NERC funded 2005 CSIP (Convective Storm Initiation Project (Browning, et al., 2006)) field campaign in Central-Southern England, and the 2006 Shoeburyness field trial to the East of London.

The Salford scanning Doppler lidar system is a ground based, mobile instrument. The system operates at an eye safe wavelength of 10.6µm and has an (atmospheric dependent) range capable of 9km. The range and scanning capabilities of the Salford Doppler lidar system allows probing of the atmosphere throughout the boundary layer and over relatively large areas. Comparisons of the Doppler lidar radial velocities with those of a simple idealised mathematical model suggest how the surface influences the boundary layer structure. The paper will focus on the preliminary results of the rural field trials and give an overview of ongoing measurements at SUBERB project. The model and examples of its use will be described in detail.

Browning, et al., 2006. The Convective Storm Initiation Project. Submitted Bull. Am. Met. Soc.