The diffusion properties are strongly affected by thermal stratification in atmosphere. Numerous field observations about the relationship between diffusion properties and thermal stratification in the boundary layer have been conducted. In addition, many researchers have developed diffusion models based on the result of above observations. However these field observation results may include some noise. Therefore, precise experiments in the laboratory are required. By contrast, wind tunnel

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... iments are considered effective, because they enable the systematic setting of multiple parameters. Accordingly, in this study, in order to comprehend the heat and momentum properties in the urban boundary layer, the authors have conducted wind tunnel experiments under various atmospheric stability conditions. Furthermore, numerical simulations based on the standard k-� model were conducted based on the same flow and temperature fields as the experiments. The results of the numerical simulations are compared with those of the experiments. The prediction accuracy of the k-� model is estimated, and the way for modification of the k-� model is considered. In the results, new viscous and diffusion models available to various thermal stratification in the atmosphere are suggested.