단일 높이에서 관측된 저장 플럭스를 사용할 때 발생하는 논의 이산화탄소, 수증기, 현열의 순생태계교환량 오차

Abstract

Using eddy covariance method, net ecosystem exchange (NEE) of CO2 (FCO2 ), H2O (LE), and sensible heat (H) can be approximated as the sum of eddy flux (FC) and storage flux term (FS). Depending on strength and distribution of sink/source of scalars and magnitude of vertical turbulence mixing, the rates of changes in scalars are different with height. In order to calculate FS accurately, the differences should be considered using scalar profile measurement. However, most of flux sites for agricultural lands in Asia do not operate profile system and estimate FS using single-level scalars from eddy covariance system under the assumption that the rates of changes in scalars are constant regardless of the height. In this study, we measured FC and FS of CO2, H2O, and air temperature (Ta) using eddy covariance and profile system (i.e., the multi-level measurement system in scalars from eddy covariance measurement height to the land surface) at the Chengmicheon farmland site in Korea (CFK) in order to quantify the differences between FS calculated by single-level measurements (FS_single i.e., FS from scalars measured by profile system only at eddy covariance system measurement height) and FS calculated by profile measurements and verify the errors of NEE caused by FS_single. The rate of change in CO2, H2O, and Ta were varied with height depending on the magnitudes and distribution of sink and source and the stability in the atmospheric boundary layer. Thus, FS_single underestimated or overestimated FS (especially 21% underestimation in FS of CO2 around sunrise and sunset (0430-0800 h and 1630-2000 h)). For FCO2 , the errors in FS_single generated 3% and 2% underestimation of FCO2 during nighttime (2030-0400 h) and around sunrise and sunset, respectively. In the process of nighttime correction and partitioning of FCO2 , these differences would cause an underestimation in carbon balance at the rice paddy. In contrast, there were little differences at the errors in LE and H caused by the error in FS_single, irrespective of time.