A New Parameterization of the Scale Length in Urban Canopy Using the LES Database

The diffusivity to calculate momentum and heat flux in urban canopy used a scale length and λp (lot ratio) in the Multi-layer Urban Canopy Model (MUCM) (Kondo et al. 2005). The scale length was employed with a similar idea to that in forest canopy (Watanabe and Kondo 1990). Recently, Kanda et al. (2013) performed Large-Eddy Simulation (LES) for approximately 100 areas, including precise morphology in Tokyo, and proposed new aerodynamic parameterization for urban areas. We are now constructing a new scale length parameterization inside an urban canopy using the same database. The database includes horizontally averaged mean wind profile, vertical momentum flux in neutral stability, and morphological parameters. From these data we can calculate average scale length. The vertical profile of the scale length shows that the effective Karman constant in urban canopy is smaller than 0.4. Some formulae of the scale length for the MUCM as a function of the vertical distribution of normalized lot ratio are considered and compared with the results of the LES.