Profiling tropospheric CO<sub>2</sub> using Aura TES and TCCON instruments

Abstract

Abstract.Monitoring the global distribution and long-term variations of CO 2 sources 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, particularly for quantifying local sources and sinks. To improve the capability of estimating regional fluxes, we estimate lower tropospheric CO 2 concentrations from groundbased 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 CO 2 column amount. Estimates of tropospheric CO 2 that are co-located with TCCON are obtained by assimilating Tropospheric Emission Spectrometer (TES) free tropospheric CO 2 estimates into the GEOS-Chem model. We find that quantifying lower tropospheric CO 2 by subtracting free tropospheric CO 2 estimates from total column estimates is a linear problem, because the calculated random uncertainties in total column and lower tropospheric 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 lower tropospheric CO 2 estimates is 0.26 ppm with a precision (one standard deviation) 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 TIR measurements can profile CO 2 with the precision and accuracy needed to quantify lower tropospheric CO 2 variability.

Comparison of improved Aura Tropospheric Emission Spectrometer CO<sub>2</sub> with HIPPO and SGP aircraft profile measurements

“…2. Even though little information seems to be added by using the full profile, 3-D var assimilation of TES profiles (described in Kuai et al, 2013) compared better to validation data than a single level assimilation (unpublished work).…”

Quantifying lower tropospheric methane concentrations using GOSAT near-IR and TES thermal IR measurements

“…M. Worden et al, 2010;Kuai et al, 2013). In the case where the trace gas varies significantly in the free troposphere, it is necessary to estimate the trace gas profile from the radiances when the reflected sunlight and thermal IR measurement observe the same air parcel (e.g., H. M. Worden et al, 2010).…”

“…In the case where the trace gas varies significantly in the free troposphere, it is necessary to estimate the trace gas profile from the radiances when the reflected sunlight and thermal IR measurement observe the same air parcel (e.g., H. M. Worden et al, 2010). For long- lived trace gases such as CO 2 (e.g., Kuai et al, 2013) we can subtract the free-tropospheric/stratospheric posterior estimate (based on thermal IR radiances) from the total column (based on reflected sunlight radiances). In this case observations that are not exactly co-located in space and time can be used together to estimate lower-tropospheric concentrations because of the long mixing length scales of these trace gases in the free troposphere and stratosphere (Sect.…”

Evaluation and attribution of OCO-2 XCO<sub>2</sub> uncertainties

“…In this paper we evaluate the calculated uncertainties due to noise and interferences in the OCO-2 data product (version 7). Our approach follows the methodology described in Boxe et al (2010) and Kuai et al (2013) in which variations of the observed trace gas over a small "area" are compared to the calculated errors.…”