The Weather Research and Forecasting (WRF) model coupled with a single-layer Urban Canopy Model (UCM) is used to simulate the Urban Heat Island (UHI) features in Shanghai and Nanjing, two different cities in China. Results show that the horizontal distribution of UHI is determined by large-scale surface wind, which causes high air temperature of downstream rural area. Cross sections of the difference of air temperature between the urban and rural surfaces are analyzed, the model suggests that more heat is transported from the land to the air over urban area, which leads to the continuous transportation of heat to the downstream rural surface under the control of the steady large-scale wind. It is concluded that the effect of large-scale surface wind on UHI can increase the downstream rural air temperature, which shouldn't be ignored.%利用耦合模式WRF-UCM模拟了上海、南京两个地区4次城市热岛现象,发现城市热岛效应高温的水平分布与大尺度环境风场之间有着密切的联系:城市热岛的高温带在地面风的影响下,向下风方平移,导致城市下游郊区的气温明显上升.从气温垂直剖面图上可以看出,在地面风的作用下,低层大气都出现了一个水平方向上的高温带,从城区一直延伸到下游郊区.气温差异的垂直剖面图表明:城市化过程使城市以及城郊过渡带上空大气获得更多的热量,气温明显上升.在计算城郊过渡带的平流加热率后发现,大尺度环境风场下城市对下风方郊区大气的平流加热作用不可忽视.
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