黄土高原大孔径闪烁仪观测特征量T_＊的研究

Study of Characteristic Quantity T_* by Large Aperture Scintillometer over Chinese Loess Plateau

基于黄土高原定西站2009年9月大孔径闪烁仪(LAS)的观测数据,结合涡动相关系统(EC)和梯度塔的同步观测资料,分析了LAS和EC在测量感热通量过程中的温度特征尺度T*及其差异与近地层气象要素风向、位温梯度和稳定度等的关系。结果表明,黄土高原下垫面LAS测量的T*LAS和EC测量的T*EC有很好的相关性,相关系数达到0.955,拟合的线性趋势系数是1.482。对9月进行风向统计,主风向为NNE和SE,NNE风向上T*LAS和T*EC的相关系数是0.960,拟合的线性趋势系数是1.349,SE风向上T*LAS和T*EC的相关系数是0.968,拟合的线性趋势系数是1.619,风向对T*有显著影响。位温梯度与T*呈很好的线性相关关系,T*LAS相较于T*EC与位温梯度有更好的相关性。当稳定度z/L<1.5时,T*LAS/T*EC随着z/L的增大而减小;当z/L>1.5时,T*LAS/T*EC随着z/L的增大而增大。T*LAS/T*EC的变化范围随着z/L的增大逐渐变小,当z/L增大到4后,T*LAS/T*EC开始保持较小的变化范围。

Combined with the synchronous data observed by Eddy Covariance system（EC）and gradient tow- er, the relationship between the characteristic scale of temperature T＊ and its difference in the process of sensible heat flux measured by Large Aperture Scintillometer（LAS） and EC and the meteorological ele- ments of surface layer such as wind, potential temperature gradient and stability are analyzed based on the data measured, in the experimental field of Dingxi over the Loess Plateau during September 2009. The re- sults show that there is a very good correlation between T＊ LAS measured by LAS and T＊ EC measured by EC on the underlying surface over Loess Plateau with the correlation coefficient up to 0. 955 and the fitting lin- ear trend coefficient is 1. 482. The main wind direction is NNE and SE in September after making a wind statistics, the results show that the correlation coefficient is 0. 960 and the fitting linear trend coefficient is 1. 349 in NNE wind direction while in SE wind direction the correlation coefficient is 0. 968 and the fitting linear trend coefficient is 1. 619, which indicates that the wind direction has a significant influence on T＊. There is a good linear correlation between potential temperature gradient and T＊ , but the correlation be- tween T. 1.AS and potential temperature gradient is better than that between T＊ EC and potential temperature gradient. The ratio of T＊ measured by LAS and EC decreases when stability z/L is smaller than 1. 5, when stability z/L is greater than 1.5, the ratio of T＊ tends to increasing along with z/L increasing. The variation range of T.LAs/T＊EC gradually becomes smaller along with z/L increasing, and begins to keep the smaller range when z/L increases to 4.