不同平均时间对LOPEX10资料涡动相关湍流通量计算结果影响的探讨  

Influence of the Different Averaging Period on Computing the Turbulent Fluxes Using LOPEX10 Data

作　　者：吕少宁[1] 文军[1] 张宇[1] 王少影[1] 张堂堂 田辉[1] 刘蓉[1] 

机构地区：[1]中国科学院寒区旱区环境与工程研究所寒旱区陆面过程与气候变化重点实验室,甘肃兰州730000

出　　处：《高原气象》2012年第6期1530-1538,共9页Plateau Meteorology

基　　金：国家重点基础研究发展计划(973计划)项目(2009CB421402);国家自然科学基金项目(40905006)共同资助

摘　　要：通过处理涡动相关系统观测的近地层湍流脉动量可以获取地—气间感热和潜热通量,然而选择不同平均时间对通量计算的结果有较大影响。采用黄土高原陆面过程野外观测试验(LOPEX10)期间获得的涡动相关系统观测资料,分析了不同平均时间对湍流通量计算的影响,并采用雷诺平均和分解方法推导了平均时间引起的通量差值的数学表达式(Flux Compensation,FC)。结果表明:(1)FC公式可以说明采用不同平均时间数据之间的关系,也可以直接计算低频涡旋对湍流通量的贡献。FC公式计算的结果与直接计算的不同平均时间通量计算之差的相关系数在0.95以上,并可以确定计算湍流通量的最佳平均时间。(2)通过采用Ogive函数确定了计算LOPEX10期间通量的最佳平均时间长度为30min,印证了利用雷诺平均和分解方法计算湍流通量补偿的准确性。(3)通过进一步的数学变换,证明了平均时间对湍流通量计算的影响直接与湍流低频变化相关,FC公式可以用来确定涡动相关观测数据的最佳平均时间,并且在获得较高时间分辨率的湍流通量数据的同时,补偿因平均时间过短而遗漏的低频信息。The latent heat and sensible heat exchange between land surface and atmosphere can be obtained by processing the eddy covariance system observation data.However,the averaging period has essential influence on computing turbulent flux.The datasets collected from the LOess Plateau mesa region land surface process field EXperiment series（LOPEXs）have been analyzed to assess this influence.A formula named Flux Compensation（FC）has been derived for calculating the flux difference among the specified averaging periods.It shows that this formula could be applied to compensate flux loss due to shorter averaging periods and analyze the contribution from low-frequency eddies with a correlation coefficient around 0.95compared to that directly calculated from the eddy covariance system observation data.After carefully calculations and analyses,it is concluded that the optimum averaging period for LOPEXs proved to be 30min,and FC could also be applied to any other in-site data.It is the low-frequency eddies that cause the difference in flux with the different averaging periods.FC could be a technique in identifying optimum averaging periods and compensates the flux consumed by low-frequency eddies while keeping its high temporal resolution.

关 键 词：涡动相关 平均时间 黄土高原 湍流通量 

分 类 号：P425.2[天文地球—大气科学及气象学]