Uncertainties in Turbulent Statistics and Fluxes of CO<sub>2</sub> Associated With Density Effect Corrections
Zhongming Gao, Heping Liu, Evan Arntzen, D. Mcfarland, Xingyuan Chen, Maoyi Huang
Abstract
Abstract Density effect corrections (DECs) are applied to adjust raw CO 2 fluxes measured by eddy covariance (EC) systems with open‐path gas analyzers. DEC is also required for adjusting the measured CO 2 concentration fluctuations to obtain the adjusted CO 2 concentrations for analyzing turbulent statistics or quantifying fluxes. However, our data show that the power spectra of the DEC‐adjusted CO 2 concentrations are distorted in the high‐frequency range, as compared with the corresponding spectra of temperature and water vapor density. This contradicts the similarity behavior of scalars, as suggested by Monin‐Obukhov similarity theory. It is demonstrated that such a distortion is caused by the DEC‐induced spikes in the DEC‐adjusted CO 2 , altering turbulent statistics of CO 2 and scalar similarity between CO 2 and other scalars. Our results suggest that CO 2 fluxes are overestimated by applying DEC especially under high Bowen ratio conditions, potentially leading to substantial uncertainties in long‐term ecosystem carbon exchange in dry regions.