Eddy Covariance Tilt Corrections over a Coastal
Mountain Area in South-east China: Significance
for Near-Surface Turbulence Characteristics |
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| Authors: | LIU Li WANG Tijian SUN Zhenhai WANG Qingeng ZHUANG Bingliang HAN Yong and LI Shu |
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| Institution: | School of Atmospheric Sciences, Nanjing University, Nanjing 210093,
Guizhou Key Laboratory of Mountainous Climate and Resources, Guiyang 550002;School of Atmospheric Sciences, Nanjing University, Nanjing 210093;Institute of Microorganism Epidemic, Academy of Military Medical Sciences, Beijing 100071;School of Environment, Nanjing University, Nanjing 210093;School of Atmospheric Sciences, Nanjing University, Nanjing 210093;School of Atmospheric Sciences, Nanjing University, Nanjing 210093;School of Atmospheric Sciences, Nanjing University, Nanjing 210093 |
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| Abstract: | Turbulence characteristics of an atmospheric surface layer over a coastal
mountain area were investigated under different coordinate frames.
Performances of three methods of coordinate rotation: double rotation (DR),
triple rotation (TR), and classic planar-fit rotation (PF) were examined in
terms of correction of eddy covariance flux. Using the commonly used DR and
TR methods, unreasonable rotation angles are encountered at low wind speeds
and cause significant run-to-run errors of some turbulence characteristics.
The PF method rotates the coordinate system to an ensemble-averaged plane,
and shows large tilt error due to an inaccurate fit plane over variable
terrain slopes. In this paper, we propose another coordinate rotation
scheme. The observational data were separated into two groups according to
wind direction. The PF method was adapted to find an ensemble-averaged
streamline plane for each group of hourly runs with wind speed exceeding 1.0
m s-1. Then, the coordinate systems were rotated to their respective
best-fit planes for all available hourly observations. We call this the PF10
method. The implications of tilt corrections for the turbulence
characteristics are discussed with a focus on integral turbulence
characteristics, the spectra of wind-velocity components, and sensible heat
and momentum fluxes under various atmospheric stabilities. Our results show
that the adapted application of PF provides greatly improved estimates of
integral turbulence characteristics in complex terrain and maintains data
quality. The comparisons of the sensible heat fluxes for four coordinate
rotation methods to fluxes before correction indicate that the PF10 scheme
is the best to preserve consistency between fluxes. |
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| Keywords: | complex terrain atmospheric surface layer eddy
covariance method tilt correction turbulence characteristics flux-variance similarity |
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