A new coupled high-resolution biosphere-atmosphere model (TerrSysMP-CO 2 ) is applied to simulate mesoscale and diurnal variations of atmospheric CO 2 mixing ratios. The model is characterized by process-based parametrization calculating atmospheric dynamics and biogenic processes considering the prognostically varying CO 2 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 CO 2 fluxes, high-resolution anthropogenic emissions are included in the simulations.The model performance is verified with eddy-covariance fluxes and meteorological and CO 2 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 nearsurface CO 2 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 CO 2 distribution is analyzed. The results indicate that, in regions with hilly terrain at night and in the morning, the CO 2 patterns are strongly influenced by terrain-induced local circulations. Moreover, in densely populated regions, fossil fuel emissions are an important source of atmospheric CO 2 . Finally, the simulated canopy fluxes and atmospheric conditions, calculated using two different crop physiological parameter sets, are compared.

This study examines a fast-propagating squall line over Western and Central Europe. A high-resolution regional weather prediction model is used to analyze the threedimensional wind field and the corresponding air mass transport induced by the mesoscale convective system. The squall line can be divided into a bow-shaped strong part with a continuous line of heavy convective precipitation, and a weaker part exhibiting several isolated multi-cell storms. In the strong part, a deep and intense rear inflow jet occurs with relative wind speeds of 12-18 m s −1 . This part is also characterized by moderate to strong wind shear, in contrast to the weaker part of the squall line where a shallow cold pool surges under the potentially unstable presquall air.To investigate the air mass transport along the squall line, in the model simulations passive fluid tracers are initialized in several vertical layers with different thermodynamic conditions. At the strong part of the squall line a very efficient vertical tracer transport occurs. Potentially warm low-level air is lifted from the lowermost 2 km to the upper troposphere where an organized horizontal outflow is observed. The potentially coldest presquall air descends just in front of the updraught region and partly penetrates the convective precipitation area. In the weaker part of the squall line, the potential instability is not significantly reduced because the vertical air mass transport is less effective there. Additionally, passive tracers are used to analyze the composition of the cold pool which turns out to be a very heterogeneous mixture of descending post-frontal cold air and presquall air originating at different heights.

The accuracy of regional or mesoscale carbon budgeting by means of inverse modelling depends strongly on the ability of the atmospheric model to capture relevant atmospheric transport processes. In order to analyze the influence of terrain-induced flow dynamics and intense local anthropogenic emissions, we present high-resolution (forward) simulations of spatio-temporal CO 2 variations using a recent biosphere-atmosphere model. The selected region is characterized by complex terrain and both rural and densely populated areas. The results indicate that, in situations with weak synoptic forcing, the nocturnal near-surface CO 2 distribution is strongly affected by terrain-induced turbulent kinetic energy (TKE) above mountain ridges and by local convergent downslope winds. By increasing the grid spacing from ≈ 1 to ≈ 3 km, we show that, due to the smoothed model topography, the atmospheric flow causing the CO 2 heterogeneity cannot be resolved any more. Finally, we quantify the influence of intense anthropogenic CO 2 sources on atmospheric CO 2 concentrations. A significant anthropogenic signal can be identified around and downstream of industrial and urban areas, especially in the morning but also within a well-mixed planetary boundary layer in the daytime. The results provide valuable information for including non-background CO 2 observations in mesoscale inverse modelling studies using coarser resolutions than in this study.