1CNRM-GAME, Météo France, 42 avenue Coriolis, 31057 Toulouse, France
2CESBIO, 8 av. E. Belin, 31401 Toulouse, France
3LSCE, CEA/Saclay, 91191 Gif-sur-Yvette, France
4Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
5ALTERRA, Droevendaalsesteeg 3, 6708 PB Wageningen, The Netherlands
6Max Planck Institute for Biogeochemistry, Hans-Knoell-Str. 10, 07745 Jena, Germany
7INRA, B. P. 81, 33883 Villenave d'Ornon, France
*now at: CESBIO, 8 av. E. Belin, 31401 Toulouse, France
Received: 22 May 2008 – Published in Biogeosciences Discuss.: 23 Jul 2008 – Published: 22 Jan 2009
Abstract. An atmospheric Lagrangian experiment for regional CO2 budgeting with aircraft measurements took place during the CarboEurope Regional Experiment Strategy campaign (CERES) in south-west France, in June 2005. The atmospheric CO2 aircraft measurements taken upstream and downstream of an active and homogeneous pine forest revealed a CO2 depletion in the same air mass, using a Lagrangian strategy. This field experiment was analyzed with a meteorological meso-scale model interactively coupled with a surface scheme, with plant assimilation, ecosystem respiration, anthropogenic CO2 emissions and sea fluxes. First, the model was carefully validated against observations made close to the surface and in the atmospheric boundary layer. Then, the carbon budget was evaluated using the numerous CERES observations, by upscaling the surface fluxes observations, and using the modeling results, in order to estimate the relative contribution of each physical process.
A good agreement is found between the two methods which use the same vegetation map: the estimation of the regional CO2 surface flux by the Eulerian meso-scale model budget is close to the budget deduced from the upscaling of the observed surface fluxes, and found a budget between −9.4 and −12.1 μmol.m−2.s−1, depending on the size of the considered area. Nevertheless, the associated uncertainties are rather large for the upscaling method and reach 50%. A third method, using Lagrangian observations of CO2 estimates a regional CO2 budget a few different and more scattered, (−16.8 μmol.m−2.s−1 for the small sub-domain and −8.6 μmol.m−2.s−1 for the larger one). For this budgeting method, we estimate a mean of 31% error, mainly arising from the time of integration between the two measurements of the Lagrangian experiment. The paper describes in details the three methods to assess the regional CO2 budget and the associated errors.
Sarrat, C., Noilhan, J., Lacarrère, P., Masson, V., Ceschia, E., Ciais, P., Dolman, A., Elbers, J., Gerbig, C., and Jarosz, N.: CO2 budgeting at the regional scale using a Lagrangian experimental strategy and meso-scale modeling, Biogeosciences, 6, 113-127, doi:10.5194/bg-6-113-2009, 2009.