Dr. Xiaolan Li - Aug 23

Name:     Dr. Xiaolan Li

Title:    Characteristics of terrestrial CO2 fluxes, concentrations, and budget in Northeast China during 2016

Location: NWC 5600

Date:     2019/08/23

Time:     2:00 PM

Series:   Boundary Layer, Urban Meteorology, and Land-Surface Processes

Abstract: Co-authours: Dr.Xiao-Ming Hu (CAPS, OU),  Changjie Cai (DOEH, OU), Qinyu Jia (IAE, CMA), and Yao Zhang (DMPB, OU)

CO2 fluxes and concentrations are not well understood in Northeast China, where typical land surface types are mixed forest and cropland.  In this study, we analyzed the CO2 fluxes and concentrations using Eddy Covariance (EC) measurements and satellite observations.  We also applied the Weather Research and Forecasting model coupled with the Vegetation Photosynthesis and Respiration Model (WRF-VPRM) to simulate the CO2 fluxes and subsequent transport/dispersion, and quantify the biogenic and anthropogenic contributions to the atmospheric CO2 concentrations.  Finally, we investigated the uncertainties of simulated CO2 fluxes in relation to four VPRM parameters (including two empirical respiration parameters, maximum light use efficiency, and photosynthetically active radiation half-saturation value) using offline ensemble simulations with randomly disturbed parameter values.  The results indicated that, during the growing season (May through September), the EC-measured daily mean net
ecosystem exchange (NEE) reached a minimum of -10 μmol m-2 s-1 at rice paddy, and -6.5 μmol m-2 s-1 at mixed forest, respectively.  On average, mixed forest acted as a stronger CO2 source/sink due to longer growth period and stronger ecosystem respiration.  The monthly fluctuation of land-surface column averaged CO2 concentrations (XCO2) exceeded 10 ppm in Northeast China during 2016.  The negative biogenic contribution offset about 70% of anthropogenic contribution of XCO2 in this region.  The WRF-VPRM modeling successfully captured seasonal, diurnal, and episodic variations of NEE and CO2 concentrations, however, the NEE in mixed forest was underestimated during nighttime and overestimated during daytime, mainly due to the uncertainties of VPRM parameters, especially maximum light use efficiency.