Inverse modeling of CO2 sources and sinks using satellite observations of CO2 from TES and surface flask measurements

摘要

We infer CO surface fluxes using satellite observations ofmid-tropospheric CO from the Tropospheric Emission Spectrometer (TES)and measurements of CO from surface flasks in a time-independentinversion analysis based on the GEOS-Chem model. Using TES COobservations over oceans, spanning 40° S–40° N, we find that thehorizontal and vertical coverage of the TES and flask data arecomplementary. This complementarity is demonstrated by combining thedatasets in a joint inversion, which provides better constraints than fromeither dataset alone, when a posteriori CO distributions are evaluatedagainst independent ship and aircraft CO data. In particular, thejoint inversion offers improved constraints in the tropics where surfacemeasurements are sparse, such as the tropical forests of South America.Aggregating the annual surface-to-atmosphere fluxes from the joint inversionfor the year 2006 yields −1.13±0.21 Pg C for the global ocean,−2.77±0.20 Pg C for the global land biosphere and −3.90±0.29 Pg Cfor the total global natural flux (defined as the sum of all biospheric,oceanic, and biomass burning contributions but excluding CO emissionsfrom fossil fuel combustion). These global ocean and global land fluxes areshown to be near the median of the broad range of values from otherinversion results for 2006. To achieve these results, a bias in TES COin the Southern Hemisphere was assessed and corrected using aircraft flaskdata, and we demonstrate that our results have low sensitivity to variationsin the bias correction approach. Overall, this analysis suggests that futurecarbon data assimilation systems can benefit by integrating in situ andsatellite observations of CO and that the vertical informationprovided by satellite observations of mid-tropospheric CO combinedwith measurements of surface CO, provides an important additionalconstraint for flux inversions.