城市下垫面扩张对局地热力环流影响的模拟

采用WRF模式及其城市冠层参数化方案,选取2010年8月1日至3日晴天天气为模拟背景,两个算例分别为南京1993年土地利用类型及2010年土地利用类型分布。模式的模拟结果表明城市扩张使城区内2 m高度处气温有了一定幅度的增温,夜间24:00最大增温幅度达3 K。同时城市扩张使得城区风速明显减小,产生减速效应。对比两个算例风速的模拟结果,郊区风速均大于城区,风速低对物质的水平输送、扩散带来不利影响。由于城市热岛的影响,城区范围内产生有辐合上升的运动;随着城区面积的扩大,湍流动能强度及其影响范围也在扩大。2010年算例,正午湍流强度最大值与1993年算例相比较,由2.1 m~2·s2增至2.7 m~2·s2。城区内湍流运动较为强烈的区域,在一定程度上促进物质垂直方向上的输送与扩散。城市扩张后物质在城区上方垂直方向上湍流扩散得到加强,而在水平向下的输送受到抑制,更多地被阻隔在城市局地。

Simulation of the Land-use Change Effect on Urban Local Thermodynamic Circulation

With the acceleration of urbanization, urbanization process will inevitably lead to changes in land use types, changes in land cover occur will have a huge impact on the surface energy of the region, the air flow field characteristics, atmospheric turbulence characteristics of meteorological elements, etc. impact the material transport within the region of atmospheric diffusion process impact, furthermore. In this paper, with the urban canopy schemes coupled to WRF model, some numerical experiments are employed to investigate the impact of land-use change on local thermodynamic circulation. The land cover of Nanjing city in 1993 and 2010 are taken as examples. The simulation results show that 2m temperature in urban region increases from 1993 to 2010, and the addition of temperature can reach 3K at 24:00. Results show that urbanization weakens the wind and enhances the pollutant trapping and therefore contributes to the overall poor air quality in the region. Urban heat island leads to the convergence of airflow in the lower layer of atmosphere, With more urbanized region, stronger turbulent kinetic energy(TKE), for example the maximum of TKE at noon increased from 2.1 m2.s2 to 2.7 m2.s2. Urban sprawl enhances vertical mixing and hinders horizontal downward dispersion which caused pollutants to accumulate in urban areas.