Profiling tropospheric CO2 using Aura TES and TCCON instruments

[摘要] Monitoring the global distribution and long-term variations of CO₂sources and sinks is required for characterizing the global carbon budget.Total column measurements are useful for estimating regional-scale fluxes;however, model transport remains a significant error source, particularlyfor quantifying local sources and sinks. To improve the capability ofestimating regional fluxes, we estimate lower tropospheric CO₂concentrations from ground-based near-infrared (NIR) measurements withspace-based thermal infrared (TIR) measurements. The NIR measurements areobtained from the Total Carbon Column Observing Network (TCCON) of solarmeasurements, which provide an estimate of the total CO₂ column amount.Estimates of tropospheric CO₂ that are co-located with TCCON areobtained by assimilating Tropospheric Emission Spectrometer (TES) freetropospheric CO₂ estimates into the GEOS-Chem model. We find thatquantifying lower tropospheric CO₂ by subtracting free troposphericCO₂ estimates from total column estimates is a linear problem, becausethe calculated random uncertainties in total column and lower troposphericestimates are consistent with actual uncertainties as compared to aircraftdata. For the total column estimates, the random uncertainty is about 0.55 ppmwith a bias of −5.66 ppm, consistent with previously published results.After accounting for the total column bias, the bias in the lowertropospheric CO₂ estimates is 0.26 ppm with a precision (one standarddeviation) of 1.02 ppm. This precision is sufficient for capturing thewinter to summer variability of approximately 12 ppm in the lowertroposphere; double the variability of the total column. This work showsthat a combination of NIR and TIR measurements can profile CO₂ with theprecision and accuracy needed to quantify lower tropospheric CO₂variability.

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