Eddy Covariance Tilt Corrections over a Coastal Mountain Area in South-east China: Significance for Near-Surface Turbulence Characteristics

Turbulence characteristics of an atmospheric surface layer over a coastalmountain 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 interms of correction of eddy covariance flux. Using the commonly used DR andTR methods, unreasonable rotation angles are encountered at low wind speedsand 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 variableterrain slopes. In this paper, we propose another coordinate rotationscheme. The observational data were separated into two groups according towind direction. The PF method was adapted to find an ensemble-averagedstreamline plane for each group of hourly runs with wind speed exceeding 1.0m s^-1. Then, the coordinate systems were rotated to their respectivebest-fit planes for all available hourly observations. We call this the PF10method. The implications of tilt corrections for the turbulencecharacteristics are discussed with a focus on integral turbulencecharacteristics, the spectra of wind-velocity components, and sensible heatand momentum fluxes under various atmospheric stabilities. Our results showthat the adapted application of PF provides greatly improved estimates ofintegral turbulence characteristics in complex terrain and maintains dataquality. The comparisons of the sensible heat fluxes for four coordinaterotation methods to fluxes before correction indicate that the PF10 schemeis the best to preserve consistency between fluxes.