Report on Coordinated network design over Europe with mesoscale models

A coordinated network design study for Europe was performed using three different regional inversion systems for the estimation of biosphere-atmosphere exchange fluxes. Uncertainties for prior fluxes and model-data mismatch were harmonized to assure the inter-comparability of the inversion results. The prior error structure was based on a comparison of the different prior fluxes used in the inversions with eddy covariance observations. Uncertainty reductions in biosphere-atmosphere exchange fluxes were computed by the different inversion systems for the current and planned ICOS network of atmospheric stations, as well as for a hypothetic network with a gap in the area of Germany. Inversion results show a strong spatial inhomogeneity in the uncertainty reductions with typical values for seasonal fluxes around 30-50% near observing sites for the pixel scale (50 km), and around 50% for national scales. While the general level of uncertainty reduction differs between the inversion systems, the increase of uncertainty reduction with increasing number of stations per area or country is similar.