An expanded planar-fit (PF) method over complex terrain is presented and applied to coordinate rotation of the eddy-covariance (EC) flux and vertical velocity estimation. Theoretical analysis indicates that PF coefficients depend on wind direction, and an expression of vertical velocity is deduced. We applied the theory using 1 year of observations from the KoFlux site in the Gwangneung Forest in Korea and investigated the influence of wind direction on the PF method. Then, we performed an expansion of the PF method to consider dependence of PF coefficients on wind direction and applied the PF method to every sector. The results show that the PF coefficients and tilt angles over complex terrain vary with wind direction. Two hundred 30-min data sets are sufficient to derive stable PF coefficients over hilly terrain for each sector. The relative difference in eddy-covariance flux between the general planar fit (GPF) and sector planar fit (SPF) is less than 10% for the scalar flux and about 18% for friction velocity. Vertical velocity and vertical advection (VA) terms were also calculated and compared using SPF and GPF methods, and a normal distribution and diurnal trend of real vertical velocity on clear days are presented.
Bibliographical noteFunding Information:
This research was supported in part by the Knowledge Innovation Project of the Chinese Academy of Sciences (No. KZCX2-YW-QN502), and a grant (Code: 1-8-2) from Sustainable Water Resources Research Center of 21st Century Frontier Research Program, the Eco-Technopia 21 Project from the Ministry of Environment, and the BK21 program from the Ministry of Education and Human Resource Management of Korea. Ministry. Thanks will be given to Dr. Yonghua Wu, Optical Remote Sensing Lab, The City College of New York, for his revision and comments on the manuscript. We also thank an anonymous reviewer for his constructive and helpful comments.
All Science Journal Classification (ASJC) codes
- Atmospheric Science