On the Benefit of GOSAT Observations to the Estimation of Regional CO2 Fluxes

We assessed the utility of global CO2 distributions brought by the Greenhouse gases Observing SATellite (GOSAT) in the estimation of regional CO2 fluxes. We did so by estimating monthly fluxes and their uncertainty over a one-year period between June 2009 and May 2010 from 1) observational data collected in existing networks of surface CO2 measurement sites (GLOBALVIEW-CO2 2010; extrapolated to the year 2010) and 2) both the surface observations and column-averaged dry air mole fractions of CO2 (X-CO2) retrieved from GOSAT soundings. Monthly means of the surface observations and GOSAT X-CO2 retrievals gridded to 5 degrees x 5 degrees cells were used here. The estimation was performed for 64 subcontinental-scale regions. We compared these two sets of results in terms of change in uncertainty associated with the flux estimates. The rate of reduction in the flux uncertainty, which represents the degree to which the GOSAT X-CO2 retrievals contribute to constraining the fluxes, was evaluated. We found that the GOSAT X-CO2 retrievals could lower the flux uncertainty by as much as 48% (annual mean). Pronounced uncertainty reduction was found in the fluxes estimated for regions in Africa, South America, and Asia, where the sparsity of the surface monitoring sites is most evident.