Numerical study on development of a multil ayer urban canopy model

Based on the assumption of 3dimension building geometry, a multiplayer urban c anopy model were developed to research the relationship between atm ospheric movement and the urban developing. The canopy model, which consists of a set of dynamic equations with a drag force, and there are three major paramete rs: building width, distance between buildings, and vertical floor density distr ibution, which is the distribution of a ratio of the number of the buildings tha t are taller than some level to all the buildings in the urban area under consid eration. In addition, an irradiative process in the canopy is introduced, in whi ch the model geometry is assumed to be an infinitely extended regular array of u niform buildings in the horizontal, each of which is composed of six faces (roof , floor, and four vertical walls). Both of the drag force of the buildings and t he irradiative process, including the radiation shadowing and trapping effect, d epend on the floor density distribution in the vertical. The off line validation of the canopy model shows that the simulation is agr eed with wind tunnel test data and the observation data in subdomain very well . As a new urban landsurface scheme, the canopy model was then coupled with Re gional Boundary Layer Model of Nanjing University（NJURBLM）, and online cas es were performed for 4 August 2004 in Beijing city. The simulation result comp ared with observations from a dense operational observational network. The compa rison result shows that the coupled scheme (MUCM case) correctly reproduces t he temperature (within 1-2 K difference from the observations) and wind spee d(about 1 m/s difference from the observations), and is better than the soil veg etation modified scheme (SLAB case), especially for temperature simulation in ni ght time. Besides, the comparison of ground surface temperature between simulated and observed results by Landsat satellite shows that the new urban landsurfa ce process scheme improved the simulation performance at urban underplaying rema rkably for taking care of the more reasonable radiation process in threedimen sion buildings structure.