A comparison of satellite observations with the XCO 2 surface obtained by fusing TCCON measurements and GEOS-Chem model outputs

Ground observations can capture CO 2 concentrations accurately but the number of available TCCON (Total Carbon Column Observing Network) sites is too small to support a comprehensive analysis (i.e. validation) of satellite observations. Atmospheric transport models can provide continuous atmospheric CO 2 concentrations in space and time, but some information is difficult to generate with model simulations. The HASM platform can model continuous column-averaged CO 2 dry air mole fraction (XCO 2 ) surface taking TCCON observations as its optimum control constraints and an atmospheric transport model as its driving field. This article presents a comparison of the satellite observations with a HASM XCO 2 surface obtained by fusing TCCON measurements with GEOS-Chem model results. We first verified the accuracy of the HASM XCO 2 surface using six years (2010–2015) of TCCON observations and the GEOS-Chem model XCO 2 results. The validation results show that the largest MAE of bias between the HASM results and observations was 0.85 ppm and the smallest MAE was only 0.39 ppm. Next, we modeled the HASM XCO 2 surface by fusing the TCCON measurements and GEOS-Chem XCO 2 model results for the period 9/1/14 to 8/31/15. Finally, we compared the GOSAT and OCO-2 observations with the HASM XCO 2 surface and found that the global OCO-2 XCO 2 estimates more closely resembled the HASM XCO 2 surface than the GOSAT XCO 2 estimates.