城市建筑物对城市边界层三维结构影响的数值模拟

Effects of Urban Buildings on 3-Dimensional PBL Structures:WRF Simulation Study

设计了一个考虑城市建筑物动力作用和人为热量影响的城市边界层参数化方案(UBP),并将之耦合到新一代中尺度模式WRF中。利用WRF/UBP模式对北京地区夏季晴空下边界层结构进行了数值模拟分析,并与不考虑建筑物及人为热源影响的MYJ方案的模拟结果进行对比。结果表明,UBP方案模拟的边界层结构反映了城市下垫面作用下的边界层结构特征,近地面层风场和温度场的模拟与自动气象站的观测结果更为接近。人为热源使得城市热岛效应增强,诊断分析显示由于夜间为稳定边界层,而白天边界层发展,湍流输送加强,热岛效应的日变化与人为热源的日变化有明显的反相关。另外,对湍流动能和边界层高度也进行了对比分析,发现城市建筑物使得湍流动能增加,夜间边界层高度有明显升高。研究表明,考虑了建筑物影响的UBP方案大大改善了模式对于城市近地面要素的模拟能力,对城市边界层的描述更为合理。

The Urban Boundary Layer Parameterization（UBP） is developed to describe the dynamic and thermal effects of urban buildings on boundary-layer meteorological fields. The UBP is incorporated into the Weather Research and Forecasting（WRF） model, and is used to simulate the summer meteorological fields and Plantary Boundary Layer（PBL） structures in the Beijing area. Results show that the UBP scheme produces winds and temperatures at the surface layer that is more consistent with the observations than that simulated using the Mellor-Yamada-Janjic（MYJ） scheme. The UBP scheme gives weaker winds and a stronger hot-island effect than that by the MYJ scheme. Anthropogenic heating has little effects on the 2-meter temperature during daytime because turbulent diffusion is strong enough to transport heat to higher levels. It is concluded that the UBP scheme improves the simulation of the surface-layer meteorological fields in urban area, and that the description of the urban canopy-layer structures is more rational.