Greenhouse Gas Content of Frontal Structures: Results from the Atmospheric Carbon and Transport - America (ACT-A) Field Campaigns
The Pennsylvania State University
TCS Building 240
Incomplete knowledge of both greenhouse gas (GHG) sources and sinks, and atmospheric transport of these gases limits our ability to use atmospheric observations to infer surface fluxes. For instance, detailed understanding of the impact of frontal systems on the spatiotemporal variability of GHGs on regional scales is needed for the evaluation of transport models and for improving knowledge of GHG sources and sinks. The first Atmospheric Carbon and Transport (ACT) - America airborne field campaign (15 July - 31 Aug, 2016) was conducted across three regions (Mid-Atlantic, Upper Mid-West, and South) in the eastern United States to study the transport and fluxes of atmospheric carbon dioxide and methane. One primary goal is to measure how weather systems transport GHGs in the atmospheric boundary layer (ABL) and in the free troposphere (FT). High-resolution remote and in-situ airborne observations were collected with two aircraft (NASA's C-130 and B-200), including the first systematic study of frontal gradients in GHG mole fractions.
We hypothesize that typical synoptic weather events (e.g., cold front passage) perturb the spatial heterogeneity in the atmospheric GHG concentrations both horizontally and vertically across the frontal boundaries. We will report on the frontal gradient features in GHGs based on 12 selected research flights. Preliminary analyses suggest higher front-related CO2 gradients in the ABL compared to the upper and lower FT as well as larger case-to-case variability in front-related CO2 gradients in the ABL compared to the FT. We will discuss how CO2 and CH4 spatial variability can be modified by cold fronts, prefrontal troughs and wind shifts. We will relate these findings to available meteorological observations; WRF simulations of meteorological conditions and the CO2 fields; and GHG mole fractions from the global observing network. Using both observations and simulations we will build a conceptual framework of the CO2 and CH4 gradients at frontal boundaries and obtain insights into how ABL-regimes and synoptic-scale transport interact and influence the spatial variability in the vertical and horizontal CO2 and CH4 gradients. Highlights of preliminary observational findings for ACT-A winter field campaign (01 Feb - 10 Mar 2017) will also be presented.