Challenges in Constraining Surface Trace Gas Exchanges from Observations

Progress in modeling the complexity of the hydrological and carbon cycles has outpaced advancements in observational tests of these models. The challenge arises in separating the contributions of surface and atmospheric processes to observed concentration gradients. This study uses idealized single-column models to show that existing diagnostic methods relate boundary layer water vapor and carbon dioxide concentrations directly to surface exchanges by neglecting radiative and turbulent fluxes that couple the surface to the boundary layer and troposphere. These methods therefore underestimate the uncertainty in both the carbon cycle and precipitation sensitivity to climate change. This presentation will propose a statistical approach to test climate models and inverse methods by comparing the decay rates of observed and modeled fluctuations in boundary layer concentrations. The method follows an analytical solution to the conservation equation, and diagnoses the boundary layer-free troposphere mass exchange in data from the U.S. Southern Great Plains Atmospheric Radiation Measurement Climate Research Facility.