Abstract
We infer CO2 surface fluxes using satellite observations
of mid-tropospheric CO2 from the Tropospheric
Emission Spectrometer (TES) and measurements of CO2
from surface flasks in a time-independent inversion analysis
based on the GEOS-Chem model. Using TES CO2 observations
over oceans, spanning 40 S–40 N, we find that the
horizontal and vertical coverage of the TES and flask data are
complementary. This complementarity is demonstrated by
combining the datasets in a joint inversion, which provides
better constraints than from either dataset alone, when a posteriori
CO2 distributions are evaluated against independent
ship and aircraft CO2 data. In particular, the joint inversion
offers improved constraints in the tropics where surface measurements
are sparse, such as the tropical forests of South
America. Aggregating the annual surface-to-atmosphere
fluxes from the joint inversion for the year 2006 yields
−1.13±0.21 PgC for the global ocean, −2.77±0.20 PgC for
the global land biosphere and −3.90±0.29 PgC for the total
global natural flux (defined as the sum of all biospheric,
oceanic, and biomass burning contributions but excluding
CO2 emissions from fossil fuel combustion). These global
ocean and global land fluxes are shown to be near the median
of the broad range of values from other inversion results for 2006. To achieve these results, a bias in TES CO2 in
the Southern Hemisphere was assessed and corrected using
aircraft flask data, and we demonstrate that our results have
low sensitivity to variations in the bias correction approach.
Overall, this analysis suggests that future carbon data assimilation
systems can benefit by integrating in situ and satellite
observations of CO2 and that the vertical information
provided by satellite observations of mid-tropospheric CO2
combined with measurements of surface CO2, provides an
important additional constraint for flux inversions.