Retrieving high resolution CO2 fluxes in the South West of France by direct and inverse methods

The CarboEurope Regional Experiment (CERES) is designed to test the coherence of top-down and bottom-up estimates of carbon flux in a limited domain in southwestern France. Here we compare estimates from a biosphere model (ISBA-A-GS), an atmospheric inversion using the same model as a prior estimate and a network of flux towers. We focus on a four-day intensive period in which continuous measurements at two towers were augmented by aircraft measurements. ISBA-A-gs was used to estimate hourly CO2 fluxes at 8km resolution. Based on the model prior, we inverted CO2 fluxes on a limited domain of 700 by 700 km using the mesoscale atmospheric model MesoNH coupled with the Lagrangian particle model LPDM, using boundary conditions from the global transport model LMDz. Both tower and aircraft data were used for the flux inversion, and the model performance was evaluated by an ensemble of simulations. The prior flux uncertainty was estimated by comparing flux tower observation with the biosphere model results at hourly time step. The consistency of the top-down and bottom-up estimates is studied by comparing the structure of the correction in the atmospheric inversion with the differences between ISBA-A-GS and the flux observations.