Synoptic weather systems are a major driver of spatial gradients in atmospheric CO2 mole fractions. During frontal passages, air masses from different regions meet at the frontal boundary creating significant gradients in CO2 mole fractions. We quantitatively describe the atmospheric transport of CO2 mole fractions during a mid-latitude cold front passage and explore the impact of various sources of CO2. We focus here on a cold front passage over Lincoln, Nebraska on August 4th, 2016 observed by aircraft during the Atmospheric Carbon and Transport (ACT)-America campaign. A band of air with elevated CO2was located along the frontal boundary. Observed and simulated differences in CO2 across the front were as high as 25 ppm. Numerical simulations using WRF-Chem at cloud resolving resolutions (3km), coupled with CO2 surface fluxes and boundary conditions from CarbonTracker (CT-NRTv2017x), were performed to explore atmospheric transport at the front. Model results demonstrate that the frontal CO2 difference in the upper troposphere can be explained largely by inflow from outside of North America. This difference is modified in the atmospheric boundary layer and lower troposphere by continental surface fluxes, dominated in this case by biogenic and fossil fuel fluxes. Horizontal and vertical advection are found to be responsible for the transport of CO2 mole fractions along the frontal boundary. We show that cold front passages lead to large CO2 transport events including a significant contribution from vertical advection, and that mid-continent frontal boundaries are formed from a complex mixture of CO2 sources.

Turbulence parameterizations (TP) in numerical weather prediction models remains one of the challenging tasks as we lack a comprehensive understanding on the turbulence processes under myriad weather conditions. One way to make improvements to these TPs is through obtaining empirical evidence of turbulence structures via exploring multi-parameter turbulence analyses. To the best of our knowledge, we reported here the first multi-parameter vertical profiles of turbulence characteristics based on the analyses of higher-order moments of five key thermodynamic variables in the lower part of the atmospheric boundary layer (ABL) over an arid region. Observational studies reporting turbulence features in the ABL over arid regions remain underexplored although drylands are home to more than 38% of the world’s population. Due to lack of adequate soil moisture, two of the key features of land-atmosphere feedback over an arid region are strong sensible-heat fluxes and intense turbulent-mixing. We used high-resolution (50-Hz) measurements of 3-d wind components, moisture, and temperature obtained at 10 vertical levels on a 200-m Tall Tower at Reese Technology Center in Lubbock located in Texas Panhandle in the US to explore turbulence characteristics under synoptically benign weather conditions. To demonstrate the method, we choose a case study (18 July 2020) where we used daytime measurements obtained on the tower from 17:00-00:00 UTC (12:00-19:00 LT). We found evidence that there is an altitude dependence on the location of the peak values of the variance and skewness of the vertical, zonal, and meridional velocity, potential temperature, and specific humidity.

The ability of current global models to simulate the transport of CO2 by mid-latitude, synoptic-scale weather systems (i.e. CO2 weather) is important for inverse estimates of regional and global carbon budgets but remains unclear without comparisons to targeted measurements. Here, we evaluate ten models that participated in the Orbiting Carbon Observatory-2 model intercomparison project (OCO-2 MIP version 9) with intensive aircraft measurements collected from the Atmospheric Carbon Transport (ACT)-America mission. We quantify model-data differences in the spatial variability of CO2 mole fractions, mean winds, and boundary layer depths in 27 mid-latitude cyclones spanning four seasons over the central and eastern United States. We find that the OCO-2 MIP models are able to simulate observed CO2 frontal differences with varying degrees of success in summer and spring, and most underestimate frontal differences in winter and autumn. The models may underestimate the observed boundary layer-to-free troposphere CO2 differences in spring and autumn due to model errors in boundary layer height. Attribution of the causes of model biases in other seasons remains elusive. Transport errors, prior fluxes, and/or inversion algorithms appear to be the primary cause of these biases since model performance is not highly sensitive to the CO2 data used in the inversion. The metrics presented here provide new benchmarks regarding the ability of atmospheric inversion systems to reproduce the CO2 structure of mid-latitude weather systems. Controlled experiments are needed to link these metrics more directly to the accuracy of regional or global flux estimates.

Past studies have demonstrated that synoptic weather events play an important role in the spatial and temporal variations of atmospheric carbon dioxide ( within and above the boundary layer. In this study, we investigate the spatial variability of column average CO2 dry air mole fraction (XCO2) due to the impact of synoptic-scale transport using retrievals from the Orbiting Carbon Observatory-2 for 66 summer cold frontal cases over the conterminous U.S. and Mexico above 20°N from 2015 to 2019. The results show that cold fronts in summer are in general agreement with data from the Atmospheric Chemistry and Transport (ACT-America) field campaign observations, which are significantly different compared to non-frontal spatial distributions in summer, though with reduced magnitude due to their nature as a column average as opposed to an in situ measurements in the boundary layer and free troposphere.

We use 148 airborne vertical profiles of CO2 for frontal cases from the summer 2016 Atmospheric Carbon and Transport-America (ACT-America) campaign to evaluate the skill of ten global CO2 in situ inversion models from the version 7 Orbiting Carbon Observatory-2 (OCO-2) Model Intercomparison Project (MIP). Model errors (model posterior-observed CO2 dry air mole fractions) were categorized by region (Mid-Atlantic, Midwest, and South), frontal sector (warm or cold), and transport model (predominantly Tracer Model 5 (TM5) and Goddard Earth Observing System-Chemistry (GEOS-Chem)). All inversions assimilated the same CO2 observations. Overall, the median inversion profiles reproduce the general structures of the observations (enhanced / depleted low-level CO2 in warm / cold sectors), but 1) they underestimate the magnitude of the warm / cold sector mole fraction difference, and 2) the spread among individual inversions can be quite large (> 5 ppm). Uniquely in the Mid-Atlantic, inversion biases segregated according to atmospheric transport model, where TM5 inversions biases were-3 to-4 ppm in warm sectors, while those of GEOS-Chem were +2 to +3 ppm in cold sectors. The large spread among the mean posterior CO2 profiles is not explained by the different atmospheric transport models. These results show that the inversion systems themselves are the dominant cause of this spread, and that the aircraft campaign data are clearly able to identify these large biases. Future controlled experiments should identify which inversions best reproduce midlatitude CO2 mole fractions, and how inversion system components are linked to system performance.

The Atmospheric Carbon and Transport (ACT) – America NASA Earth Venture Suborbital Mission set out to improve regional atmospheric greenhouse gas (GHG) inversions by exploring the intersection of the strong GHG fluxes and vigorous atmospheric transport that occurs within the midlatitudes. Two research aircraft instrumented with remote and in situ sensors to measure GHG mole fractions, associated trace gases, and atmospheric state variables collected 1140.7 flight hours of research data, distributed across 305 individual aircraft sorties, coordinated within 121 research flight days, and spanning five, six-week seasonal flight campaigns in the central and eastern United States. Flights sampled 31 synoptic sequences, including fair weather and frontal conditions, at altitudes ranging from the atmospheric boundary layer to the upper free troposphere. The observations were complemented with global and regional GHG flux and transport model ensembles. We found that midlatitude weather systems contain large spatial gradients in GHG mole fractions, in patterns that were consistent as a function of season and altitude. We attribute these patterns to a combination of regional terrestrial fluxes and inflow from the continental boundaries. These observations, when segregated according to altitude and air mass, provide a variety of quantitative insights into the realism of regional CO2 and CH4 fluxes and atmospheric GHG transport realizations. The ACT-America data set and ensemble modeling methods provide benchmarks for the development of atmospheric inversion systems. As global and regional atmospheric inversions incorporate ACT-America’s findings and methods, we anticipate these systems will produce increasingly accurate and precise sub-continental GHG flux estimates.

We present observations of local enhancements in carbon dioxide (CO2) from local emissions sources over three eastern US regions during four deployments of the Atmospheric Carbon Transport-America (ACT-America) campaign between summer 2016 and spring 2018. Local CO2 emissions were characterized by carbon monoxide (CO) to CO2 enhancement ratios (i.e. ΔCO/ΔCO2) in airmass mixing observed during aircraft transects within the atmospheric boundary layer. By analyzing regional-scale variability of CO2 enhancements as a function of ΔCO/ΔCO2 enhancement ratios, observed relative contributions to CO2 emissions were contrasted between different combustion regimes across regions and seasons. Ninety percent of observed summer combustion in all regions was attributed to high efficiency fossil fuel (FF) combustion (ΔCO/ΔCO2 < 0.5%). In other seasons, regional contributions increased from less efficient forms of FF combustion (ΔCO/ΔCO2 0.5-2%) to as much as 60% of observed combustion. CO2 emission contributions attributed to biomass burning (BB) (ΔCO/ΔCO2 > 4%) were negligible during summer and fall in all regions, but climbed to 10-12% of observed combustion in the South during winter and spring. Vulcan v3 CO2 2015 emission analysis showed increases in residential and commercial sectors seasonally matching increases in less efficient FF combustion, but could not explain regional trends. WRF-Chem modeling, driven by CarbonTracker CO2 fire emissions, matched observed winter and spring BB contributions, but conflictingly predicted similar levels of BB during fall. Satellite fire data from MODIS and VIIRS suggested higher spatial resolution fire data might improve modeled BB emissions.

The ACT-America project is a NASA Earth Venture Suborbital-2 mission designed to study the transport and fluxes of greenhouse gases. The open and freely available ACT-America datasets provide airborne in-situ measurements of atmospheric carbon dioxide, methane, trace gases, aerosols, clouds, and meteorological properties, airborne remote sensing measurements of aerosol backscatter, atmospheric boundary layer height and columnar content of atmospheric carbon dioxide, tower-based measurements, and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over the Central and Eastern United States. We conducted 121 research flights during five campaigns in four seasons during 2016-2019 over three regions of the US (Mid-Atlantic, Midwest and South) using two NASA research aircraft (B-200 and C-130). We performed three flight patterns (fair weather, frontal crossings, and OCO-2 underflights) and collected more than 1,140 hours of airborne measurements via level-leg flights in the atmospheric boundary layer, lower, and upper free troposphere and vertical profiles spanning these altitudes. We also merged various airborne in-situ measurements onto a common standard sampling interval, which brings coherence to the data, creates geolocated data products, and makes it much easier for the users to perform holistic analysis of the ACT-America data products. Here, we report on detailed information of datasets collected, and the workflow for datasets including storage and processing of the quality controlled and quality assured harmonized observations, and their archival and formatting for users. Finally, we provide some important information on the dissemination of data products including metadata and highlights of applications of datasets for future investigations.