ATMOSPHERIC TRAJECTORY MODELS FOR SIMULATION OF LONG-RANGE TRANSPORT AND DIFFUSION OVER THE WESTERN MEDITERRANEAN

Studies carried out in the Centre d'Estudis Avancats de Blanes about t he importance of the atmospheric fluxes of nutrients near the coast in dicate that the quantities of nitrate deposited are of the same order of magnitude as the vertical diffusive fluxes from deep waters. Theref ore, the atmosphere would be an important source of nutrients for the marine productivity, particularly, in oligotrophic waters constituting the greatest part of the Mediterranean Sea. Implementation of long-ra nge trajectory models has been made in order to simulate transport of pollutants over the Western Mediterranean. Three lagrangian models of increasing complexity have been developed assuming different simplific ations to the conservation equations. The first one, a purely kinemati c 2-D method uses averaged wind in a layer. It is appropriate for dete rmining the dominant fluxes at a region of interest, considering a lar ge number of trajectories. The second, an isentropic model, computes t rajectories following the surfaces of constant potential temperature: Finally, a 3-D model for complex regions, incorporates physical proces ses such as those induced by orography, flux energy, atmospheric stabi lity and horizontal thermal gradients.