Retrieval of Micro scale Flow Structures from Dual-Doppler Lidar Data Measured in the Urban Boundary Layer

Two coherent Doppler lidars from the US Army Research Laboratory (ARL) and Arizona State University (ASU) were deployed in the Joint Urban 2003 atmospheric dispersion field experiment held in Oklahoma City. This provided the opportunity to evaluate the accuracy of the four-dimensional variational data assimilation (4DVAR) method and gain new insights into the boundary layer transport processes of contaminants in and around cities. One objective of this work is to determine the fidelity of the data retrieved from the single Doppler lidar and assess model errors by use of the second lidar data. The other objective is to interpret the retrieved micro-scale flow structures by comparison with the satellite ground building data. Finally, we examined the difference between our results and those of Newsom et al. (2005) that employed a periodic lateral boundary condition with the specified profiles of eddy viscosity and thermal diffusivity in their 4DVAR. The correlation between ARL retrieved velocities and ASU observational data is 0.915. The correlation between dual-lidar retrieved velocities and ASU observational data is improved to 0.990. This indicates that single-lidar retrieval could yield accurate velocity fields, whereas dual-lidar retrieval produces better results. Due to lower quality data from the ASU lidar during this period, the results of ASU retrieval are not as good as those of ARL retrieval. By comparison with the satellite map of the city, a strong updraft above the airpark and a downdraft above the central business district (CBD) were observed in the retrieved velocity field.