Presentation and validation of a new building downwash model

Abstract

Olesen et al. (Bound Layer Meteorol 131(1):73–83, 2009) have shown that current building downwash parameterizations, which are essential in the vicinity of build up areas, perform poorly at very short distances. Therefore, a new building downwash model has been developed based on the Thompson-wind tunnel dataset. The model consists of the Gaussian transport and diffusion equation, in which the variables xR (distance source-receptor) and Hs (stack height) have been replaced with functions that define a receptor dependent virtual origin. The virtual source functions account for the impact of building downwash (1) by changing the height of the plume to account for the vertical displacement of the plume and the extra turbulence around the building, (2) by using an upwind displacement of the plume origin to simulate the impact of the wind-upward displacement of the plume and (3) by accounting for the entrainment of clean air into the plume by increasing the distance between the virtual source and the receptor point. The model results are compared to the several measurement time series in Flanders, Belgium, at industrial locations where building downwash plays an important role. We have shown an increased modeling ability in all cases: For instance, biases ranging from −4 to −33 ng/m3 (−46 to −77 %) improve to values ranging from 1.3 to −7.5 ng/m3 (−29 to +14 %) and R2 values improve dramatically (up to 0.83 from 0.65 in cases with a strong building downwash effect).