Interpreting the variability of space-borne CO2 column-averaged volume mixing ratios over North America using a chemistry transport model P. I. Palmer1, M. P. Barkley1, and P. S. Monks2 1School of GeoSciences, University of Edinburgh, UK 2Department of Chemistry, University of Leicester, UK
Abstract. We use the GEOS-Chem chemistry transport model to interpret the
sources and sinks of CO2 that determine variability of
column-averaged volume mixing ratios (CVMRs), as observed by the
SCIAMACHY satellite instrument, during the 2003 North
American growing season.
GEOS-Chem generally reproduces the magnitude and seasonal cycle of
observed CO2 surface VMRs across North America and is quantitatively
consistent with column VMRs in later years. However, it cannot
reproduce the magnitude or variability of FSI-WFM-DOAS SCIAMACHY CVMRs.
We use model tagged tracers to show that local fluxes largely
determine CVMR variability over North America, with the largest
individual CVMR contributions (1.1%) from the land biosphere. Fuel
sources are relatively constant while biomass burning makes a
significant contribution only during midsummer. We also show that
non-local sources contribute significantly to total CVMRs over North
America, with the boreal Asian land biosphere contributing close to
1% in midsummer at high latitudes.
We used the monthly-mean Jacobian matrix for North America to
illustrate that:~1) North American CVMRs represent a superposition of
many weak flux signatures, but differences in flux distributions
should permit independent flux estimation; and 2) the atmospheric
e-folding lifetimes for many of these flux signatures are 3–4
months, beyond which time they are too well-mixed to interpret. These
long lifetimes will improve the efficacy of observed CVMRs as surface
CO2 flux constraints.
Citation: Palmer, P. I., Barkley, M. P., and Monks, P. S.: Interpreting the variability of space-borne CO2 column-averaged volume mixing ratios over North America using a chemistry transport model, Atmos. Chem. Phys., 8, 5855-5868, doi:10.5194/acp-8-5855-2008, 2008.