土地扩张对城市边界层风热环境影响的模拟研究——以沈阳市为例

A numerical simulation study on the effects of urban expansion on the wind and thermal environment in boundary layer:a case study of Shenyang

利用WRF模式中的UCM+AH城市冠层方案,以2005年8月两个晴天为天气背景,对比研究了1993年与2005年不同下垫面情况下,沈阳市城市扩张对近地层风热环境及边界层的影响。结果表明:UCM+AH方案能够较合理准确地模拟出城市范围的2 m气温与10 m风速的日变化特征,且对2 m气温的模拟效果要优于10 m风速;模拟2 m气温的日较差偏大,模拟10 m风速系统性偏高0.5—1.0 m·s-1;城市土地扩张后,城区普遍增温,且夜间增温幅度较大,扩建城区夜间最大增温能达到7℃,老城区在夜间增温幅度最大可达3℃,上风向增温幅度较大;城区日间增温不明显,在0—1℃;城市土地扩张后,老城区风速普遍减小,但减小值<1 m·s-1;扩建城区风速减小近1 m·s-1,城区内可能出现的高温辐合中心对周围近地层风速有加速作用;城市扩张对边界层最显著的影响体现在午后,城区的扩张增大了湍流动能的影响范围,湍流动能在数值上增加0.2—0.3 m2·s-2;扩建城区上空的边界层高度在14时抬升100—200 m,且下风向边界层内部的局地环流与垂直上升运动增强。

Based on the land use data in 1993 and 2005,the effects of urban expansion on the near-surface wind and thermal environment and boundary layer were investigated using the UCM+AH scheme in the WRF model under the conditions of two clear days in August 2005.The results show that UCM+AH scheme is able to properly and accurately simulate the diurnal variations of 2 m temperature and 10 m wind speed,and the accuracy of simulated 2 m temperature is better than that of 10 m wind speed.The scheme overestimates the diurnal range of the simulated 2m temperature and the wind speed systematically by 0.5-1.0 m·s^-1.Urban expansion can lead to a general warming in the urban area especially in nighttime.The maximal increasing amplitudes of 7℃and 3℃at nighttime are distributed in the expanded and old urban area,respectively.The increasing amplitude is larger in the upwind direction than in other directions.The warming with a range between 0-1℃at daytime is not obvious in the urban area.In addition,after urban expansion,the wind speed decreases generally with a magnitude smaller than 1.0 m·s^-1 in the old urban area and close to 1.0 m·s^-1 in the expanded urban area.At the same time,a high-temperature convergent zone in the urban area accelerating the near ground wind speed in the surrounding areas is probably caused by urban expansion.Besides,the urban expansion affects significantly the boundary layer in the afternoon and results in Turbulent Kinematic Energy with an increase of 0.2-0.3 m^2·s^-2 expanding its range of influence.Moreover,the boundary layer height is risen up by 100-200 m at 14:00 and the local thermal circulation and vertical upward motion are strengthened over the expanded area.