近地面层湍流通量输送相似性及相干结构特征

Characteristics of turbulent transport similarity and coherent structures in the atmospheric surface layer

利用2018年广东省环珠江口气候环境与空气质量变化野外科学观测研究站70 m气象塔上涡动协方差系统连续观测资料,对不同大气稳定度条件下近地面层相干结构的统计特征及其对湍流通量相似性的影响进行了初步研究.结果表明:(1)无量纲风速标准差(稳定、不稳定)和气温标准差(不稳定)遵循莫宁-奥布霍夫相似理论;(2)湍流速度(u、v、w)谱、温度(T)谱、CO_(2)和H_(2)O浓度谱在惯性副区均满足-2/3定律.w-T协谱、垂直速度(w)与标量(CO_(2)、H_(2)O)浓度的协谱(w-CO_(2)、w-H_(2)O)在惯性副区遵循-4/3定律;(3)不稳定条件下,热力湍流对H_(2)O和CO_(2)标量具有很好的输送作用,而以动量通量输送为代表的机械作用在弱不稳定条件下对H_(2)O和CO_(2)的输送效果最好;(4)上冲和下扫运动对湍流通量输送起主导作用,且随湍涡尺度的变化略有差异,湍流通量输送对大气层结的依赖性较弱.

Using the eddy covariance data observed on a 70-meter meteorological tower located in the Guangdong Province Ring Pearl River Estuary Climate,Environment and Air Quality Change Field Scientific Observation and Research Station in 2018,we analyzed the characteristics of nearsurface coherent structures and its influence on turbulent transport similarities under different atmospheric stability conditions.The results show that:(1)the Monin-Obukhov similarity theory well describes the dimensionless standard deviations of turbulent velocities under both stable and unstable conditions,while its validity is challenged for the dimensionless standard deviation of temperature in stable conditions;(2)the turbulent velocity(u,v and w)and scalar(T,CO_(2)and H_(2)O)spectra follow the-2/3 law in the inertial subregion,while the cospectra(w-T,w-CO_(2),and w-H_(2)O)depict a-4/3 law in the inertial subregion;(3)under weakly stable conditions,scalars are mainly transported by shear-generated turbulence,while buoyancygenerated turbulence dominates the vertical transport of scalars in the convective boundary layer;(4)the vertical flux transport is mainly associated with ejections and sweeps which are related to the vortex scales but relatively independent to thermal stratification.