Characterization of a Densely Placed Carbon Observation Network

Abstract:

We present a detailed analysis of the suitability of a network with four densely placed, continuous carbon measurement sites located on the Swiss Plateau for regional-scale (~100-500 km) carbon exchange studies. Two sites are located atop mountain ridges approximately 500 m above the valley floor, one site is a small tower in flat terrain, and one site is a 212 m tall tower atop a gentle hill. The analysis concentrates on the evaluation of a regional numerical weather prediction model’s ability to represent the local meteorology, and on source sensitivities (footprints) simulated with a Lagrangian particle dispersion model. Simulated and measured meteorology compares very well for the flatland sites whereas the mountaintop site comparisons illustrate discrepancies in simulated meteorological variables due to the inability of the model to resolve the complex topography. Furthermore, the meteorological comparison suggests an accurate representation of the convective boundary layer over the Swiss Plateau on average. We find large differences between the simulated footprint extents in winter and summer and between summer's nocturnal and daily footprint, illustrating the ability of simulations to represent seasonal and diurnal variability. We find that far-field influence increases with increasing measurement height as well as being dependent on local topography-induced flow patterns. This study illustrates the fruitfulness of simulated and measured meteorology comparison and detailed analysis of footprint simulations, and we argue that similar analysis is a necessary initial step for regional carbon exchange studies. The four measurement sites with the CarboCount CH project complement one another to represent typical land cover types for Switzerland and Europe, and provide information rich data sets for forthcoming regional carbon exchange studies, of which we also present first results.