A large eddy simulation study of carbon dioxide and water vapor isotopes in the atmospheric boundary layer

The goal of this study is to investigate the transport and dispersion of the stable isotopes of water vapor and carbon dioxide in the atmospheric boundary layer (ABL). The isotopic species of interest are 18O-CO2, 18O-H2O and 13C-CO2. These isotopes offer powerful insights into the carbon and water fluxes on land. To date, rich empirical data exist on how biological processes discriminate against the isotopic exchange between plants and the atmosphere. But little is known of the role the ABL flow plays in the exchange process. This study will explore the extent to which the local atmospheric budgets of these isotopes are linked to wind circulation on land. The primary method to be deployed is a large eddy simulation (LES) model that is dynamically coupled with the isotopic parameterization of land surface processes. LES simulations are conducted to quantify the relationships of the surface and the entrainment isotopic fluxes to the geostrophic wind above and turbulent motion in the ABL. The simulated turbulence time series are used to evaluate the accuracy of the Keeling mixing line method for inferring the source isotopic signature of the ABL water vapor and carbon dioxide.