Scale analysis of the wind field variability in time and space over the Washington DC metropolitan area

A question that is relevant to understanding and predicting atmospheric transport and diffusion in urban areas is related to the amount of variability that exists in the wind field above the rooftops. That is, is there important variability on the "neighborhood" scale that must be known, in order to provide necessary input to CFD models that define street-canyon conditions? A unique opportunity to answer this question for the Washington, D.C. area is provided by the operational Doppler lidar that is a component of the Pentagon Shield building-protection system. These lidar data, when processed through a data-assimilation system, provide a three-dimensional volume of gridded winds that covers the entire metropolitan area, where the refresh rate is about 5 min and the horizontal grid increment is 100 m. In addition, the operational Doppler radar data from the Sterling, Virginia NEXRAD, when similarly processed, provide wind data over the same metropolitan area on a 1-km grid-increment grid. Lastly, a mesoscale data assimilation and forecasting system that is running as part of the Pentagon Shield system provides wind analyses on even coarser grids. A comparison of the wind fields from all of these observation and data-assimilation systems provides, for the first time, an accurate characterization of the multiple scales in the wind flow over an urban area.