Numerical analyses of urban thermal environment in a basin climate - application of a k- epsilon model to complex terrain

摘要

Meteorological field observations were conducted at an urban area in a basin in summer. On a calm clear day a mixing layer of about 1500 m height was generated by the thermally induced circulation over the basin. The maximum air temperature in the urban area was recorded at around 18:00 LST, even though the area is only a few kilometers in extent and consists of low buildings and low anthropogenic heat release. Numerical analysis was conducted, to evaluate the daytime heating process and urban effects, using a three-dimensional k- epsilon model. The 100 x 120 km computational domain was discretized horizontally using a nested grid system consisting of three overlapping grids. The results were in good agreement with the observed values of air temperature, mixing ratio, and wind profiles. The large circulations experienced in this region were predicted with the downward wind over the lake bringing a warm and dry air mass to the ground. The air temperature in the urban area rose and maintained its high value until late afternoon, mainly due to the local circulation adding to the urban effects.