General description
PYVAR-CHIMERE is a regional atmospheric inversion system developed at LSCE. It is based on the regional Eulerian atmospheric chemistry-transport model CHIMERE (http://www.lmd.polytechnique.fr/chimere/), and on a variational data assimilation platform (Broquet et al. 2011).
Specific configuration for the EUROCOM project
The PYVAR-CHIMERE inversions in EUROCOM are set-up in a manner that is very close to that of Broquet et al. (2013).
A European configuration of CHIMERE is used. This configuration covers latitudes 31.5° - 74° and longitudes -15.5° - 35° with a 0.5°x0.5° horizontal resolution and 29 vertical layers up to 300 hPa. Meteorological forcing for CHIMERE is generated using the European Centre for Medium Range Weather Forecasting (ECMWF) operational forecasts. Initial, lateral and top boundary conditions for CO2 concentrations are generated from the CAMS LMDZ global inversions (Chevallier et al. [2010]).
The inversions control the 6-hourly mean land Net Ecosystem Exchange (NEE) and ocean fluxes at the 0.5°x0.5° horizontal resolution of CHIMERE. The prior estimate of the NEE, and its uncertainty, are specified using the the ORCHIDEE/VPRM NEE and respiration simulations, respectively. The temporal and spatial correlation scales for the prior uncertainty in the land NEE are set to ~1 month and 200 km, with no correlation between the four 6-hour windows of the same day. The configuration of the other parameters (in particular, the computation of the observation errors) follow that of Broquet et al. (2013).
The practical minimization of the cost function associated with the variational scheme uses the M1QN3 algorithm. Series of 1-year inversions are used to provide new (posterior) estimates of the NEE at 1-hour and 0.5°x0.5° resolution for the full period of analysis.
References
Broquet, G., Chevallier, F., Rayner, P., Aulagnier, C., Pison, I., Ramonet, M., Schmidt, M., Vermeulen, A., and Ciais, P.: A European summertime CO2 biogenic flux inversion at mesoscale from continuous in situ mixing ratio measurements. Journal of Geophysical Research-Atmospheres, 116., D23303, doi:10.1029/2011jd016202, 2011.
Broquet, G., Chevallier, F., Bréon, F.-M., Kadygrov, N., Alemanno, M., Apadula, F., Hammer, S., Haszpra, L., Meinhardt, F., Morguí, J. A., Necki, J., Piacentino, S., Ramonet, M., Schmidt, M., Thompson, R. L., Vermeulen, A. T., Yver, C., and Ciais, P.: Regional inversion of CO2 ecosystem fluxes from atmospheric measurements: reliability of the uncertainty estimates, Atmos. Chem. Phys., 13, 9039-9056, https://doi.org/10.5194/acp-13-9039-2013, 2013.