Interpreting the variability of space-borne CO2 column-averaged volume mixing ratios over North America using a chemistry transport model

[摘要] We use the GEOS-Chem chemistry transport model to interpret thesources and sinks of CO₂ that determine variabilityofcolumn-averaged volume mixing ratios (CVMRs), as observed by theSCIAMACHY satellite instrument, during the 2003 NorthAmerican growingseason.GEOS-Chem generally reproduces the magnitude and seasonal cycle ofobservedCO₂ surface VMRs across North America and is quantitativelyconsistent withcolumn VMRs in later years. However, it cannotreproducethe magnitude or variability of FSI-WFM-DOAS SCIAMACHY CVMRs.We use model tagged tracers to show that local fluxes largelydetermine CVMR variability over North America, with the largestindividual CVMR contributions (1.1%) from the land biosphere. Fuelsources are relatively constant while biomass burning makes asignificant contribution only during midsummer. We also show thatnon-local sources contribute significantly to total CVMRs over NorthAmerica, with the boreal Asian land biosphere contributing close to1% in midsummer at high latitudes.We used the monthly-mean Jacobian matrix for North America toillustrate that:~1) North American CVMRs represent a superposition ofmany weak flux signatures, but differences in flux distributionsshould permit independent flux estimation; and 2) the atmospherice-folding lifetimes for many of these flux signatures are 3–4months, beyond which time they are too well-mixed to interpret. Theselong lifetimes will improve the efficacy of observed CVMRs as surfaceCO₂ flux constraints.

[学科分类] 大气科学