Four years of global carbon cycle observed from OCO-2 version 9 and in situ data, and comparison to OCO-2 v7

Abstract

Abstract. The Orbiting Carbon Observatory 2 (OCO-2) satellite has been provided information to estimate carbon dioxide (CO2) fluxes at global and regional scales since 2014 through the combination of CO2 retrievals with top-down atmospheric inversion methods. Column average CO2 dry air mole fraction retrievals has been constantly improved. A bias correction has been applied in the OCO-2 version 9 retrievals compared to the previous OCO-2 version 7r improving data accuracy and coverage. We study an ensemble of ten atmospheric inversions all characterized by different transport models, data assimilation algorithm and prior fluxes using first OCO-2 v7 in 2015-2016 and then OCO-2 version 9 land observations for the longer period 2015- 2018. Inversions assimilating in situ (IS) measurements have been also used to provide a baseline against which to compare the satellite-driven results. The times series at different scales (going from global to regional scales) of the models emissions are analyzed and compared to each experiments using either OCO-2 or IS data. We then evaluate the inversion ensemble based on dataset from TCCON, aircraft, and in-situ observations, all independent from assimilated data. While we find a similar constraint of global total carbon emissions between the ensemble spread using IS and both OCO-2 retrievals, differences between the two retrieval versions appear over regional scales and particularly in tropical Africa. A difference in the carbon budget between v7 and v9 is found over this region which seems to show the impact of corrections applied in retrievals. However, the lack of data in the tropics limits our conclusions and the estimation of carbon emissions over tropical Africa require further analysis.

OCO‐2 Satellite‐Imposed Constraints on Terrestrial Biospheric CO2 Fluxes Over South Asia

“…ObsPack presents calibrated CO 2 measurements from different observing platforms, such as surface flasks, tall towers, and aircrafts operated by numerous institutes in a common format. For this study, we applied ObsPack data derived for the OCO‐2 v9 MIP (Peiro et al., 2021). We assimilated ObsPack measurements which were flagged as “assimilable” by a prior run of NOAA’s CarbonTracker data assimilation system.…”

Interannual variability in the Australian carbon cycle over 2015–2019, based on assimilation of OCO-2 satellite data

“…4). These global inversions are part of the OCO-2 Model Intercomparison Project (MIP) (Crowell et al, 2019;Peiro et al, 2021). In this study, we used the OCO-2 MIP flux version found in Peiro et al (2021).…”

“…These global inversions are part of the OCO-2 Model Intercomparison Project (MIP) (Crowell et al, 2019;Peiro et al, 2021). In this study, we used the OCO-2 MIP flux version found in Peiro et al (2021). In Peiro et al (2021), the global inversions were performed using the assimilation OCO-2 (version…”

“…In this study, we used the OCO-2 MIP flux version found in Peiro et al (2021). In Peiro et al (2021), the global inversions were performed using the assimilation OCO-2 (version…”

“…In February 2018, for example, we found biases of about -1.83 (RMSE = 1.95), which are similar to the biases found in the same period of 2019. These negative biases may be related to the small number of OCO-2 soundings located around the site (see Appendix A, Figs A4 and A5) or local biases in the OCO-2 data (Peiro et al, 2021). The small number of OCO-2 observations around Darwin is due to the presence of cloud cover and aerosols.…”