Progress toward Improving Regional Atmospheric Inversions Using Airborne Measurements: Results from ACT-America

The Atmospheric Carbon and Transport (ACT) - America mission aims to improve our understanding of transport and fluxes of greenhouse gases (GHGs) via airborne campaigns spanning a range of mid-latitude weather conditions, and thus to improve the accuracy and precision of regional inverse flux estimates of GHGs. ACT-America has conducted three field campaigns with two aircraft across three regions of the eastern United States during summer 2016, winter 2017 and fall 2017. Simulations of atmospheric GHGs have been conducted for a subset of these field campaigns. We present progress from these campaigns.

Mid-summer aircraft observations suggest a net biological source of CO₂ to the atmosphere in the Gulf coast states. These observations are inconsistent with terrestrial biosphere models that show strong net uptake of CO₂ in this region in summer. Methane observations downwind of major sources in the MidAtlantic region suggest that these sources are represented fairly well by existing emissions inventories. Flux estimation in other regions and seasons is underway.

Spatially-coherent differences in GHGs that extend throughout the depth of the troposphere are observed at frontal boundaries in summer and winter. These spatial structures are captured in global and mesoscale model simulations, though the simulated GHG mole fractions are sometimes biased with respect to observations, suggesting potential biases in synoptic transport. Mesoscale simulations of atmospheric CO₂ overestimate spatial differences in ABL CO₂ mole fractions in fair weather conditions as compared to airborne observations and the CarbonTracker global inverse modeling system. ABL depths appear to be simulated fairly well by both mesoscale and global modeling systems, suggesting that either weather-scale flux amplitudes are overestimated by CarbonTracker, or the mesoscale model is lacking parameterized transport above the ABL.

Evaluation of the spatial variability in both OCO-2 and airborne lidar XCO₂ observations is defining the regional precision and accuracy of these observational methods.

These findings are moving us toward improved regional GHG inverse flux estimates via a synthesis of better understanding of prior fluxes, atmospheric transport, and satellite CO₂ observations.