Mesoscale simulations of atmospheric CO2 variations using a high-resolution model system with process-based CO2 fluxes

A new coupled high-resolution biosphere-atmosphere model (TerrSysMP-CO2) is applied to simulate mesoscale and diurnal variations of atmospheric CO2 mixing ratios. The model is characterized by process-based parametrization calculating atmospheric dynamics and biogenic processes considering the prognostically varying CO2 content at the surface. An advanced parametrization of soil respiration is used distinguishing between heterotrophic and autotrophic respiration and explicitly considering the effect of varying soil moisture. In addition to biogenic CO2 fluxes, high-resolution anthropogenic emissions are included in the simulations. The model performance is verified with eddy-covariance fluxes and meteorological and CO2 concentration measurements at various heights of a tower. It is found that a correct representation of turbulent mixing is most critical for a precise prediction of near-surface CO2 mixing ratios and respective vertical gradients. High-resolution simulations were performed for a region with complex terrain, heterogeneous land use and densely populated areas. The relative influence of diverse land use, orography as well as of synoptic and mesoscale transport on the spatio-temporal CO2 distribution is analyzed. The results indicate that, in regions with hilly terrain at night and in the morning, the CO2 patterns are strongly influenced by terrain-induced local circulations. Moreover, in densely populated regions, fossil fuel emissions are an important source of atmospheric CO2. Finally, the simulated canopy fluxes and atmospheric conditions, calculated using two different crop physiological parameter sets, are compared.