Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 2 2006 10.5194/acpd-6-2853-2006 http://www.atmos-chem-phys-discuss.net/6/2853/2006/ http://www.atmos-chem-phys-discuss.net/6/2853/2006/acpd-6-2853-2006.html http://www.atmos-chem-phys-discuss.net/6/2853/2006/acpd-6-2853-2006.pdf 2853 2895 2006-04-11 Mesoscale circulations over complex terrain in the Valencia coastal region, Spain, Part 2: linking CO₂ surface fluxes with observed concentrations G. Pérez-Landa P. Ciais G. Gangoiti J. L. Palau A. Carrara B. Gioli F. Miglietta M. Schumacher M. M. Millán M. J. Sanz Fundación CEAM. Parque Tecnológico, c/ Charles R. Darwin 14, 46980 Paterna (Valencia), Spain Laboratoire des Sciences du Climat et de l’Environnement, UMR Commissariat à l’Energie Atomique/CNRS 1572, Gif-sur-Yvette, France Escuela Técnica Superior de Ingenieros Industriales de Bilbao, Universidad del País Vasco/Euskal Herriko Unibertsitatea, Bilbao, Spain IBIMET-CNR, Instituto di Biometeorologia, Consiglio Nazionale delle Ricerche, Firenze, Italy Max-Planck-Institut für Biogeochemie, Hans-Knöll-Strasse 10, 07745 Jena, Germany 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.