Comparing atmospheric transport models for future regional inversions over Europe – Part 1: mapping the atmospheric CO<sub>2</sub> signals

Abstract

Abstract. The CO 2 source and sink distribution across Europe can be estimated in principle through inverse methods by combining CO 2 observations and atmospheric transport models. Uncertainties of such estimates are mainly due to insufficient spatiotemporal coverage of CO 2 observations and biases of the models. In order to assess the biases related to the use of different models the CO 2 concentration field over Europe has been simulated with five different Eulerian atmospheric transport models as part of the EU-funded AE-ROCARB project, which has the main goal to estimate the carbon balance of Europe. In contrast to previous comparisons, here both global coarse-resolution and regional higherresolution models are included. Continuous CO 2 observations from continental, coastal and mountain sites as well as flasks sampled on aircrafts are used to evaluate the models' ability to capture the spatiotemporal variability and distribution of lower troposphere CO 2 across Europe. 14 CO 2 is used in addition to evaluate separately fossil fuel signal predictions. The simulated concentrations show a large range of variation, with up to ∼10 ppm higher surface concentrations over Western and Central Europe in the regional models with highest (mesoscale) spatial resolution.The simulation -data comparison reveals that generally high-resolution models are more successful than coarse models in capturing the amplitude and phasing of the observed Correspondence to: C. Geels (cag@dmu.dk) short-term variability. At high-altitude stations the magnitude of the differences between observations and models and in between models is less pronounced, but the timing of the diurnal cycle is not well captured by the models.The data comparisons show also that the timing of the observed variability on hourly to daily time scales at lowaltitude stations is generally well captured by all models. However, the amplitude of the variability tends to be underestimated. While daytime values are quite well predicted, nighttime values are generally underpredicted. This is a reflection of the different mixing regimes during day and night combined with different vertical resolution between models. In line with this finding, the agreement among models is increased when sampling in the afternoon hours only and when sampling the mixed portion of the PBL, which amounts to sampling at a few hundred meters above ground. The main recommendations resulting from the study for constraining land carbon sources and sinks using high-resolution concentration data and state-of-the art transport models through inverse methods are given in the following: 1) Low altitude stations are presently preferable in inverse studies. If high altitude stations are used then the model level that represents the specific sites should be applied, 2) at low altitude sites only the afternoon values of concentrations can be represented sufficiently well by current models and therefore afternoon values are more appropriate for constraining large-scale sources and sinks in combination with tr...

Sensitivity of the recent methane budget to LMDz sub-grid-scale physical parameterizations

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Variability and budget of CO<sub>2</sub> in Europe: analysis of the CAATER airborne campaigns – Part 2: Comparison of CO<sub>2</sub> vertical variability and fluxes between observations and a modeling framework

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“…Geels et al, 2007). However, the value of CO 2 fluxes is still uncertain, especially at the regional scale of 100-1000 km (e.g.…”

Variation of CO<sub>2</sub> mole fraction in the lower free troposphere, in the boundary layer and at the surface

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