1Fundación CEAM. Parque Tecnológico, c/ Charles R. Darwin 14, 46980 Paterna (Valencia), Spain
2Laboratoire des Sciences du Climat et de l’Environnement, UMR Commissariat à l’Energie Atomique/CNRS 1572, Gif-sur-Yvette, France
3Escuela Técnica Superior de Ingenieros Industriales de Bilbao, Universidad del País Vasco/Euskal Herriko Unibertsitatea, Bilbao, Spain
4IBIMET-CNR, Instituto di Biometeorologia, Consiglio Nazionale delle Ricerche, Firenze, Italy
5Max-Planck-Institut für Biogeochemie, Hans-Knöll-Strasse 10, 07745 Jena, Germany
Abstract. Several consecutive vertical profiles of CO2 concentration and meteorological parameters were collected during an intensive summer campaign in a coastal complex terrain region within the frame of the European Project RECAB (Regional Assessment and Modelling of the Carbon Balance in Europe). The region presents a marked diurnal cycle in the wind flow (analyzed in detail in a companion paper) as a consequence of the development of mesoscale circulations. In terms of the different stages of the diurnal cycle in the meteorology, these circulations result in an important coupling between atmospheric transport and surface CO2 fluxes. To understand the effects of this interaction on the spatial variability of the observed CO2 concentrations, we conduct a high-resolution simulation with a coupled biosphere-atmosphere model in the area of interest during a representative case study. Our model approach consists of estimating the regional NEE distribution by using a set of eddy-covariance measurements that are transported by a mesoscale model coupled to a Lagrangian particle dispersion model. Our simulations were able to successfully reproduce crucial processes controlling the mesoscale transport of CO2. Availability of both simulations and observations for our analysis allowed us to characterize the influence of the coupling between mesoscale circulations and biological processes in the spatial gradients of the CO2 concentrations. Temporal averages in the simulated CO2 distribution show a 3-D rectification effect consisting of: 1) horizontally, a CO2 deficit over land, mirrored by a CO2 excess over the sea and 2) vertically, the prevalence of mean CO2 depletion between 500 and 2000 m, and the permanent build-up of CO2 in the lower levels.