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坐标旋转是复杂地形条件下涡动协方差(EC)通量观测的必要步骤,系统评价不同坐标旋转方法的影响有助于提高EC通量观测的精度.以处于山谷坡面的帽儿山温带落叶阔叶林为例,采用标准主轴法探讨了复杂地形条件下不同倾斜校正方法对感热通量(H)、潜热通量(LE)、CO_2通量(F_c)、能量平衡、摩擦风速(u_*)和垂直速度(w)的影响.结果表明:与校正前的通量相比,二次旋转(DR)、平面拟合(PF)、垂直速度无偏平面拟合(NBPF)、月尺度平面拟合(MPF)、三次旋转(TR)和月尺度分风向区平面拟合(MSWPF)得到的H变幅依次为+1.5%、+3.8%、+3.1%、+3.3%、-1.3%和-7.1%.对LE来说,NBPF和DR分别升高1.0%和0.4%,PF增加0.671 W·m~(-2),MPF降低0.4%,但截距增加0.747 W·m~(-2),MSWPF和TR则分别降低4.5%和15.1%.坐标旋转后F_c降幅为6.0%(DR)~12.1%(TR).不同倾斜校正方法中,PF使能量平衡闭合平均提高约2%,TR却降低约6%.从校正后的u_*和w看,TR和NBPF不宜用于风速仪倾斜校正.考虑到EC观测精度和应用,帽儿山站坐标系统应优先选择PF,其次为DR.此结果为复杂地形条件下EC通量观测的风速仪倾斜校正提供参考.
Coordinate rotation is a necessary step for observing eddy covariance (EC) flux under complex terrain conditions, and systematically evaluating the effects of different coordinate rotation methods can improve the accuracy of EC flux observations. The deciduous broad-leaved forest was used as an example to study the effect of different slope correction methods on the sensible heat flux (H), latent heat flux (LE), CO_2 flux (F_c), energy balance and frictional wind speed under complex terrains u_ *) and vertical velocity (w). The results show that compared with the uncorrected flux, the quadratic rotation (DR), plane fitting (PF) The H amplitudes obtained from MPF, TR and MSWPF were +1.5%, + 3.8%, + 3.1%, + 3.3%, -1.3 % And -7.1%. For LE, NBPF and DR increased by 1.0% and 0.4%, PF increased by 0.671 W · m -2, MPF decreased by 0.4%, but intercept increased by 0.747 W · m ~ -2) and MSWPF and TR decreased by 4.5% and 15.1%, respectively, and the F_c decrease was 6.0% (DR) ~ 12.1% (TR) after coordinate rotation.The energy balance closure of PF increased by about 2% , TR decreased about 6% from the corrected u_ * And w, TR and NBPF should not be used for anemometer tilt correction. Considering EC observation accuracy and application, Maoershan station coordinate system should give priority to PF, followed by DR. The results for the complex terrain conditions EC flux observed Anemometer tilt correction for reference.