小兴安岭近地层湍流能谱特征

Characteristics of Surface-layer Turbulence Spectra in Xiaoxing’an Mountains

利用小兴安岭南麓五营地区涡动相关系统的观测资料,分析不同大气稳定度条件的湍流速度谱、温度谱、湿度谱、协谱及局地各向同性特征。结果表明:三维速度(u、v、w)谱和垂直速度(w)与水平纵向速度(u)、温度(θ)的协谱(uw、θw)的谱峰均随稳定度的增加而向高频端移动。湍流速度(u、v、w)谱、温度(θ)谱和湿度(q)谱在惯性副区均满足-2/3定律。uw协谱、θw协谱和垂直速度(w)与湿度(q)的协谱(qw)在惯性副区并不完全遵循-4/3定律,尤其是uw协谱的拟合斜率更接近-1。水平方向湍流谱峰波长范围为130~1820 m,垂直范围为49~113 m。温度谱谱峰波长范围为149~260 m,湿度谱谱峰波长范围为198~455 m。uw协谱谱峰波长范围为228~455 m,θw协谱谱峰波长范围为172~260 m,qw协谱谱峰波长范围为172~346 m。v谱在惯性副区基本满足局地各向同性,w谱在惯性副区不满足局地各向同性,可能与森林下垫面对垂直方向湍流大涡的破碎作用有关。

Based on the turbulence data obtained from eddy covariance system at the height of 50 m in Wuying over the Xiaoxing’an Mountains,the spectra and cospectra of turbulence under different atmospheric stability are analyzed. The results indicate that the peaks of the normalized spectra of velocity(u,v,w)moves to the high frequency with the increased of atmospheric stability. The characteristics of the normalized spectra of temperature(θ)and humidity(q)are similar to those of the velocity(u,v,w)spectra,but the spectral density curves are dispersed under different stability conditions. The normalized cospectra of the vertical wind component(w)and u-wind component(u)are similar to those of the spectra of velocity(u,v,w),which are same as the normalized cospectra of the vertical wind component(w)and temperature(θ). The normalized spectra of velocity(u,v,w)and temperature(θ)and humidity(q)follow the-2/3 law in the higher frequency. The normalized cospectra of uw and θw and qw do not completely follow the-4/3 law in the higher frequency,especially the slopes of fitting line for uw-cospectra is closer to -1. The peak wavelength of u-spectra is about 130~1820 m,and the spectra of w and θ and q are about 49~113 m,149~260 m and 198~455 m,respectively. The peak wavelength of the cospectra of uw and θw and qw are about 228~455 m,172~260 m and 172~346 m,respectively. The v-spectra conforms the local isotropy in the higher frequency,and the w-spectra does not satisfy the local isotropy,which may be attributed to the fragmentation of the vertical turbulent vortex in forest underlying surface.