应用城市冠层模式研究建筑物形态对城市边界层的影响

Study on effects of buildings morphology on urban boundary layer using an urban canopy model

文中将城市冠层模式耦合到南京大学城市尺度边界层模式中,通过模拟对比发现,耦合模式对城市地区气温模拟结果更接近于观测值,尤其是对城市地区夜间气温模拟的改进。运用改进耦合模式通过多个敏感性试验的模拟,从城市面积扩张、建筑物高度增加、建筑物分布密度变化等角度研究城市建筑物三维几何形态变化对城市边界层及城市气象环境的影响,试验结果表明:(1)城市面积扩张使得城市下垫面的热通量增大,热力湍流活动增强,动量通量输送增强,城市湍能增大,湍流扩散系数变大,城市气温升高,且对不同时刻城市区域大气层结稳定度均有不同程度的影响。(2)建筑物高度增加增大了城市下垫面的粗糙度和零平面位移,同时也增大了城市街渠高宽比。城市建筑物越高,白天城市地区地表热通量越小,城市上空大气温度越低,平均风速减小,湍能减小;夜间由于高大建筑物释放储热比低矮建筑物要多,其热力湍流相对活跃,地表热通量增大,使得城市区域气温较高。(3)建筑物密度增大,会减小城市下垫面的粗糙度同时增强街渠对辐射的影响。建筑物密度增大在白天会减小地表热通量和动量通量,使城市气温降低,平均风速增大,城市湍流活动能力减弱;夜间城市释放较多储热使得气温较高。

An urban canopy model is incorporated into the Nanjing University Regional Boundary Layer Model. The simulation resuits of urban temperature with the urban canopy model are better than those with the traditional slab model, and are in more reasonable agreement with the observations, especially in the night time. The incorporated model is used to study the effect of buildings morphology on urban boundary layer and meteorological environment by changing urban area, building height and building density. By analyzing the results of sensitive experiments, the results are as followings： （1） When the urban area is expanded, the urban boundary layer heat flux increases, the thermal turbulence strengthens, the turbulent momentum flux and kinetic energy increases, and the surface air temperature also increases. The stability of urban atmospheric stratification is affected to different extents at different times in a day. （2） When the building height increases, the aerodynamic roughness height and zero plane displacement height of urban area increase, and the ratio of building height to street width also increases. Therefore, the increase in building height results in decreases in the surface heat flux, and decreases in urban surface temperature, mean wind speed and turbulent kinetic energy in the day time. While at night, as the more heat storage released by higher buildings, the thermal turbulence is more active and the surface heat flux increases, so urban temperature is higher. （3） As the increase in building density, the aerodynamic roughness height of urban area decreases, and the effect of urban canopy on radiation strengthens. The increase in buildings density results in decreases in urban surface heat Flux, momentum flux, and air temperature, the increase in mean wind speed, and the weakening of turbulences in the daytime. While at night, urban temperature increases due to the release of more heat storage.