This study systematically examines the regional uncertainties and biases in carbon dioxide<br>(CO2) mole fractions from two of the state-of-the-art global CO2 analysis products, namely, the Copernicus<br>Atmosphere Monitoring Service (CAMS) real-time atmospheric analysis from the European Centre for<br>Medium-RangeWeather Forecasts (ECMWF) and the CarbonTracker Near-Real-Time (CT-NRT)<br>reanalysis from the National Oceanic and Atmospheric Administration (NOAA), by evaluation against<br>hundreds of hours of airborne in situ measurements from the summer 2016 and winter 2017 Atmospheric<br>Carbon and Transport (ACT)-America field campaigns. Both the CAMS and CT-NRT analyses agree<br>reasonably well with the independent ACT-America airborne CO2 measurements in the free troposphere,<br>with root-mean-square deviations (RMSDs) between analyses and observations generally between 1 and<br>2 ppm but show considerably larger uncertainties in the atmospheric boundary layer where the RMSDs<br>exceed 8 ppm in the lowermost 1 km of the troposphere in summer. There are strong variations in accuracy<br>and bias between seasons, and across three different subregions in the United States (Mid-Atlantic,<br>Midwest, and South), with the largest uncertainties in the Mid-Atlantic region in summer. Overall, the<br>RMSDs of the CAMS and CT-NRT analyses against airborne data are comparable to each other and largely<br>consistent with the differences between the two analyses. The current study provides uncertainty estimates<br>for both analysis products over North America and suggests that these two independent estimates can be<br>used to approximate regional CO2 analysis uncertainties. Both statistics are important in future studies in<br>quantifying the uncertainties in regional CO2 mole fraction and flux estimates.
|Journal||Journal of Geophysical Research-Atmospheres|
|State||Published - Jun 15 2019|