Abstract. We describe a method of evaluating systematic errors in measurements of total column dry-air mole fractions of CO 2 (X CO 2 ) from space, and we illustrate the method by applying it to the v2.8 Atmospheric CO 2 Observations from Space retrievals of the Greenhouse Gases Observing Satellite (ACOS-GOSAT) measurements over land. The approach exploits the lack of large gradients in X CO 2 south of 25 • S to identify large-scale offsets and other biases in the ACOS-GOSAT data with several retrieval parameters and errors in instrument calibration. We demonstrate the effectiveness of the method by comparing the ACOS-GOSAT data in the Northern Hemisphere with ground truth provided by the Total Carbon Column Observing Network (TCCON). We use Correspondence to: D. Wunch (dwunch@gps.caltech.edu) the observed correlation between free-tropospheric potential temperature and X CO 2 in the Northern Hemisphere to define a dynamically informed coincidence criterion between the ground-based TCCON measurements and the ACOS-GOSAT measurements. We illustrate that this approach provides larger sample sizes, hence giving a more robust comparison than one that simply uses time, latitude and longitude criteria. Our results show that the agreement with the TC-CON data improves after accounting for the systematic errors, but that extrapolation to conditions found outside the region south of 25 • S may be problematic (e.g., high airmasses, large surface pressure biases, M-gain, measurements made over ocean). A preliminary evaluation of the improved v2.9 ACOS-GOSAT data is also discussed.
Methane (CH 4 ) is a potent greenhouse gas and ozone precursor. Quantifying methane emissions is critical for projecting and mitigating changes to climate and air quality. Here we present CH 4 observations made from space combined with Earth-based remote sensing column measurements. Results indicate the largest anomalous CH 4 levels viewable from space over the conterminous U.S. are located at the Four Corners region in the Southwest U.S. Emissions exceeding inventory estimates, totaling 0.59 Tg CH 4 /yr [0.50-0.67; 2σ], are necessary to bring high-resolution simulations and observations into agreement. This underestimated source approaches 10% of the EPA estimate of total U.S. CH 4 emissions from natural gas. The persistence of this CH 4 signal from 2003 onward indicates that the source is likely from established gas, coal, and coalbed methane mining and processing. This work demonstrates that space-based observations can identify anomalous CH 4 emission source regions and quantify their emissions with the use of a transport model.
We describe a method of evaluating systematic errors in measurements of total column dry-air mole fractions of CO2 (XCO2) from space, and we illustrate the method by applying the method to the Atmospheric CO2 Observations from Space retrievals of the Greenhouse Gases Observing Satellite (ACOS-GOSAT) v2.8 data. The approach exploits the lack of large gradients in XCO2 south of 25° S to identify large-scale offsets and other biases in the ACOS-GOSAT data with several retrieval parameters and errors in instrument calibration. We demonstrate the effectiveness of the method by comparing the ACOS-GOSAT data in the Northern Hemisphere with ground truth provided by the Total Carbon Column Observing Network (TCCON). We use the correlation between free-tropospheric temperature and XCO2 in the Northern Hemisphere to define a dynamically informed coincidence criterion between the ground-based TCCON measurements and the ACOS-GOSAT measurements. We illustrate that this approach provides larger sample sizes, hence giving a more robust comparison than one that simply uses time, latitude and longitude criteria. Our results show that the agreement with the TCCON data improves after accounting for the systematic errors
A new Bruker IFS 125HR Fourier transform spectrometer has been installed at the Polar Environment Atmospheric Research Laboratory at Eureka, Nunavut, Canada (80.05°N, 86.42°W). This instrument will become the Network for the Detection of Atmospheric Composition Change’s (NDACC’s) primary instrument at Eureka, replacing the existing Bomem DA8 Fourier transform spectrometer, and will operate throughout the sunlit parts of the year. This paper introduces the new instrument and describes the retrieval procedure, including a comprehensive error analysis. Total columns of O3, HCl, HF, HNO3, N2O, CH4, and CO are presented for the first full year of measurements (2007). Perturbations in the total column resulting from the presence of the Arctic polar vortex over Eureka and the chemical processes within it are visible, as are annual cycles driven by photochemistry and dynamics. Enhancements in the CO total column resulting from specific biomass burning smoke events can also be seen. An intercomparison between the existing Bomem DA8 and the new Bruker IFS 125HR was carried out in July 2007 and is presented here. The total columns derived from the two instruments are shown to be in excellent agreement, with mean differences for all gases of less than 2.3%.
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