一次冰雹期间郊区下垫面大气湍流统计特征分析

Analysis of Statistical Characteristics of Atmospheric Turbulence Spectra over Urban Surface in a Hailstorm

利用2012年2月28日至3月1日在合肥市郊的35 m气象塔上测量得到的湍流观测数据,对不同稳定度条件下的湍流谱、局地各向同性和风速归一化标准差进行了分析。实验期间有短暂的冰雹过程。结果表明,惯性子区对应于无因次频率为0.02～2的范围,惯性子区的大小和局地各向同性均与稳定度有关;稳定度越高,惯性子区越小;稳定度越低,惯性子区越大;在稳定和不稳定条件下,σ_w/u_*随稳定度的变化基本上满足1/3次方定律,在近中性层结条件下,σ_(w/u_*)=1.12;冰雹发生前后,风速,动量通量和感热通量出现剧烈变化,表明在冰雹发生前后的短时间内,出现了强对流天气过程。

The turbulent data obtained at the Hefei 35 m meteorological tower from 28, February, 2012 to 1, March, 2012 have been analyzed. Turbulence spectra, local isotropy and normalized standard deviation of velocity are analyzed with the stability. A hail process happened during the experiment. Results show that inertial sub-range is corresponding to dimensionless frequency which ranges from 0.02 to 2; inertial sub- range and the turbulent spectral isotropy vary with stable condition; the inertial sub-range is smaller under stable condition than under unstable condition; the normalized standard deviation of vertical velocity obeys the well-known 1/3 law under stable and unstable condition, and the value of the dimensionless variance of vertical velocity is 1.12 near neutral condition; wind speed, momentum flux and heat flux changed dramatically occurred before and after the hail; and strong convection occurred during this process.