Profiling tropospheric CO<sub>2</sub> using the Aura TES and TCCON instruments
Abstract. Monitoring the global distribution and long-term variations of CO2 sources and sinks is required for characterizing the global carbon budget. Although total column measurements will be useful for estimating large regional fluxes, model transport error remains a significant error source, particularly for local sources and sinks. To improve the capability of estimating regional fluxes, we estimate near-surface CO2 values from ground-based near infrared (NIR) measurements with space-based thermal infrared (TIR) measurements. The NIR measurements are obtained from the Total Carbon Column Observing Network (TCCON) of solar measurements which provide an estimate of the total CO2 atmospheric column amount. Estimates of tropospheric CO2 that are co-located with TCCON are obtained by assimilating Tropospheric Emission Spectrometer (TES) free-tropospheric CO2 estimates into the GEOS-Chem model. Estimates of the boundary layer CO2 are obtained through simple subtraction, as the CO2 estimation problem is linear. We find that the calculated random uncertainties in total column and boundary layer estimates are consistent with actual uncertainties as compared to aircraft data. For the total column estimates the random uncertainty is about 0.55 ppm with a bias of −5.66 ppm, consistent with previously published results. After accounting for the total column bias, the bias in the boundary layer CO2 estimates is 0.26 ppm with a precision of 1.02 ppm This precision is sufficient for capturing the winter to summer variability of approximately 12 ppm in the lower troposphere; double the variability of the total column. This work shows that a combination of NIR and IR measurements can profile CO2 with the precisions and accuracy needed to quantify near-surface CO2 variability.