A simple data assimilation technique for a fast response urban wind model

The QUIC (Quick Urban & Industrial Complex) dispersion modeling system has been developed to provide high-resolution wind and concentration fields in cities. The fast response 3D diagnostic urban wind model QUIC-URB initializes the flow field with a horizontally uniform velocities based on wind speed and wind direction information obtained from a single sensor upwind of the urban area. This wind field is then modified by empirical building flow parameterizations. The final flow field is then solved for by ensuring mass conservation. Previous urban studies have shown that often cities are subject to large scale spatially varying inflows. As a result of this spatial heterogeneity, the winds individual buildings are exposed to at different locations within the city can vary widely. Failure to include these effects in an urban wind model can lead to poor predictions of the final wind field and ultimately in dispersion calculations. To account for such variation, a Quasi-3D Barnes Objective Map Analysis Scheme (a Gaussian weighted-averaging technique) has been implemented to compute the initial flow field in QUIC-URB using multiple wind sensors located around the perimeter of a city. Wind sensor data are used to derive vertical profiles at different measurement locations around the urban core. The 2D weighted analysis scheme is then successively applied at vertical planes to compute the initial wind field. This 3D wind field is then used apply the standard empirical building flow features based on the new local approach wind direction for each building. As a preliminary evaluation test, the model has been compared against the standard QUIC-URB model using a simulation from the Salt Lake City Urban 2000 database.