巴丹吉林沙漠北缘拐子湖流沙下垫面近地层湍流强度和陆面过程特征

The Turbulence Intensity of Surface Layer and Land Surface Processes over Guaizi Lake Shifting Sandy Land on the Northern Margin of Badain Jaran Desert

利用巴丹吉林沙漠北缘拐子湖流沙下垫面2013年7、10月和2014年1、4月的湍流通量资料,计算并分析了研究区近地层湍流强度,同时针对风速分量、温度、水汽和CO2归一化标准差随稳定度的变化关系和总体输送系数等陆面过程特征进行分析。结果表明:(1)风速各分量的湍流强度均随风速的增加逐渐减小,风速处于2 m·s^-1以下时湍流发展最为旺盛。湍流强度主要由水平方向风速分量决定,垂直方向风速的作用较小,且近中性和不稳定层结利于湍流的发展。与其他地区相比,平坦且没有建筑物的沙漠地区,机械湍流较弱,湍流强度相应较小。(2)风速各分量的归一化标准差与稳定度(z/L)均满足1/3次方函数规律,其中垂直方向风速分量的拟合曲线方程较好。(3)动量输送系数Cd具有明显的夏季高、冬季低的变化状态且各月的日变化形态均呈夜间低、日间高的循环形态。热量输送系数Ch的不同月份日变化间并没有明显的排列次序,且日出日落前后具有明显的波动。不稳定层结时,Cd和Ch均随风速的增加逐渐减小;稳定层结时,Cd和Ch均随着风速的增加逐渐上升。

In this paper,we analyzed the turbulent intensity,the relationship between normalized standard deviations of wind velocity components,temperature,water vapor,CO2 and stability parameters z/L and bulk transfer coefficients in the atmospheric surface layer over Guaizi Lake shifting sandy land based on land-atmosphere turbulent flux data in July,October 2013 and January and April 2014.The results indicated that the turbulent intensity of wind velocity components decreased with the increase of wind velocity.The development of turbulence was much vigorous,when the average wind velocity was below 2 m·s^-1.The near-neutral and unstable atmospheric stratification condition were favorable to the development of turbulence.Also,the horizontal components of wind velocity were main factor that could impact turbulent intensity,and the influence of vertical wind velocity was relatively weak.Compared with other underlying surface,because of the desert was relatively flat,the mechanical turbulence of desert was weak.So the turbulent intensity of desert also was small.Further,we also found the normalized standard deviations of wind velocity components(i.e.,σu/u*,σv/u*andσw/u*)and stability parameter(z/L)generally met 1/3 power law,andσu/u*,σv/u*andσw/u*increased as the upward of|z/L|.Meanwhile,the regression curve equation of normalized standard deviation of vertical wind speed component and z/L were better than that of horizontal wind speed components.On the other hand,under the near-neutral condition,normalized standard deviations of wind velocity components were approximately constant,which presented more similar to those in hinterland of Taklimakan Desert and Heihe Gobi,and significantly smaller those in alpine meadow and sparse vegetation regions of the Qinghai-Tibet Plateau.In addition,the monthly average daily variation of momentum transfer coefficient(Cd)illustrated the standard unimodal type daily cycle pattern.Meanwhile,the daily variation curve of Cd showed the apparent seasonal variations owing to the difference of season,namely,with the highest Cd in summer,the second in spring and autumn,and the lowest in winter.The monthly mean daily variation of heat transfer coefficient(Ch)presented the less regularity and the obvious fluctuation was found at sunrise and sunset during diurnal variation.Bulk transfer coefficients decrease with increasing wind speeds under unstable atmospheric condition,and increase with increasing wind speeds under stable atmospheric condition.