A Case Study of the Upwind Urbanization Influence on the Urban Heat Island Effects along the Suzhou–Wuxi Corridor

The urban heat island (UHI) effect is one of the most significant phenomena caused by urbanization. This study investigated the UHI effect in the SuzhouWuxi area, China, on 1920 August 2010. Using a combination of meteorological station observations and Moderate Resolution Imaging Spectroradiometer (MODIS) surface skin temperature observations, this study demonstrated that an upwind UHI had an exacerbating influence on the downwind UHI during the study period. Numerical simulations using the Weather Research and Forecasting model also proved the importance of an upwind UHI influence on the leeward UHI in this area. For the near-surface UHI, the windward UHI effect is stronger at night than during the daytime because the background atmospheric stratification is more stable and the local lake breeze is weaker at night. However, in the daytime, a greater stability formed over the downwind city because of the warmer air heated by the windward urban area in the upper part of the planetary boundary layer and the cooler air transported from Tai Lake and the rural area in the lower part of the boundary layer. In comparison with the heating effect of a single city, the upwind UHI led to a decrease in the vertical wind speed of approximately 30% (from 0.15 to 0.10 m s super(-1)) in the upper boundary layer over the downwind city and also reduced the near-surface turbulent movement by 25% (from 0.73 to 0.55 m super(2) s super(-2)). These results improve the understanding of the overall influence of urban clusters on local synoptic/climate processes.