Differences of the inverted terrestrial ecosystem carbon flux between using GOSAT and OCO-2 XCO<sub>2</sub> retrievals

Abstract

<p><strong>Abstract.</strong> In this study, both the Greenhouse Gases Observing Satellite (GOSAT) and the Orbiting Carbon Observatory 2 (OCO-2) XCO<sub>2</sub> retrievals are assimilated within the GEOS-Chem 4D-Var assimilation framework to constrain the terrestrial ecosystem carbon flux during Jul 1, 2014 to Dec 31, 2015. The inverted global and regional carbon fluxes during Jan 1 to Dec 31, 2015 are shown and discussed. Surface CO<sub>2</sub> mixing ratios from 47 surface flask sites and XCO<sub>2</sub> measurements from 13 TCCON sites are used to evaluate the simulated concentrations with the posteriori carbon fluxes. The results show that globally, the terrestrial ecosystem carbon sink (excluding biomass burning emissions) estimated from GOSAT data is stronger than that inferred from OCO-2 data, and the annual atmospheric CO<sub>2</sub> growth rate estimated from GOSAT data is more consistent with the estimate of GCP 2017. Regionally, in most regions, the land sinks inferred from GOSAT data are also stronger than those from OCO-2 data. Compared with the prior fluxes, the carbon fluxes in northern temperate regions change most, followed by tropical and southern temperate regions, and the smallest changes occur in boreal regions. Basically, in temperate regions, the inferred land sinks are significantly increased, while those in tropical regions are decreased. The different changes in different regions are mainly related to the spatial coverage and the amount of XCO<sub>2</sub> data in these regions. Compared with CT2016, the inferred carbon sinks are comparable in most temperate regions, but much weaker in boreal and tropical regions. Evaluations using flask and TCCON observations suggest that GOSAT and OCO-2 data, can effectively improve the carbon flux estimates in the northern hemisphere, while in the southern hemisphere the optimized carbon sinks may be overestimated, especially for GOSAT data.</p>

Validation of GOSAT and OCO-2 against In Situ Aircraft Measurements and Comparison with CarbonTracker and GEOS-Chem over Qinhuangdao, China

“…Under clear atmospheric conditions, TCCON measures the CO 2 concentration with a precision of 0.25% [12]. However, TCCON sites are not sufficient for accurately measuring the amount of atmospheric CO 2 at regional and global scales due to their uneven distribution and limited spatial coverage [13][14][15].…”

Multi-Year Comparison of CO2 Concentration from NOAA Carbon Tracker Reanalysis Model with Data from GOSAT and OCO-2 over Asia

“…However, because of limited spatial coverage and uneven distribution of the TCCON sites, accurate CO 2 amounts cannot be measured on sub-continental and regional spatial scales [17]. Studies suggest that the satellite observations, with their lower precision than the ground-based measurements but higher spatial coverage, can help to improve the CO 2 measurements [18][19][20].…”