南京夏季城郊湍流特征对比分析

利用2010年南京夏季城市热岛三维观测试验资料,对比分析了南京夏季城市和郊区下垫面的湍流特征。结果表明:①郊区大气层结呈现规律性的日变化特征,而城市大气几乎全天处于不稳定层结状态;②不稳定层结下,城市、郊区三个方向无量纲风速标准差与稳定度参数均呈1/3幂次关系;城市无量纲水平风速标准差小于郊区,而在垂直方向无明显差异,郊区略小于城市;③城、郊下垫面归一化风速谱曲线在高频段随无因次频率满足-2/3幂次律;低频段谱曲线集中在相对狭窄范围内;郊区风速谱曲线要比城市开阔且平缓;城市风速谱有明显拐点,水平风速谱和垂直风速谱拐点对应的无因次频率分别为0.007和0.01;④南京城、郊的垂直风速脉动含能涡区的特征尺度均小于水平风速脉动含能涡区,湍流动能在垂直方向上主要分布于小尺度湍涡。

Comparison of atmospheric turbulence characteristics between urban site and suburban site in Nanjing

To figure out the atmospheric turbulence characteristics over the urban and suburban surface, the turbulent data observed in the summer at the top of the DangXiao Building in the urban area of Nanjing city and at the meteorological tower in the Nanjing University Information Science and Technology which lies in the suburban area are analyzed and compared. The results showed that: (1) The atmospheric stability over the urban surface is mostly unstable but over the suburban surface the atmospheric stability has a regular diurnal variation. (2) When the atmosphere is unstable the horizontal turbulent Decimalized standard deviations over the urban surface are always less than those over the suburban area. The variances with the stability in the surface layer under unstable stratification satisfy the Monin-Obukhov similarity theory. (3) The spectral characteristics over DX and NUIST sites show that low frequency spectral curves are concentrated in a relatively narrow range. The velocity spectra over suburban area reveal a flatter peak than that over urban area. The spectral peak of the vertical velocity component occurs a higher frequency than horizontal velocity. The velocity spectra over urban area have obvious turning points. (4) The vertical fluctuation eddy scale is less than horizontal eddy scale in Nanjing urban or suburban site.