- 169 - Modelling the circulation off Iberian Peninsula Ramiro Neves 1 , Henrique Coelho 2 , Aires dos Santos 1 , Hélder Martins 1 and Paulo Leitão 1 1 – Instituto Superior Técnico 2 – Universidade do Algarve Introduction The major task of IST in OMEX is the implementation and validation of a 3-D ocean model for the study area, in order to determine relevant water fluxes. To achieve this objective IST uses the 3-D ocean model, MOHID3D (Santos, 1995), previously implemented during OMEX I and OMEX II-I. The model was upgraded to a finite volume spatial discretization method that uses a generic vertical coordinate (Martins et al., in press). Coupled to MOHID3D there is an eulerian transport module of able to compute advective and diffusive fluxes of any property. There is also a lagrangian transport module capable to simulate the dispersion of particles/water masses containing a large number of properties such as volume, phytoplankton concentration, nutrient concentration, etc. Circulation in the Atlantic Iberian continental margin is markedly seasonal being dominated by a southward surface current driven by the wind during the upwelling season and by a poleward density driven current during the winter. The poleward current extends from about the depth of Mediterranean Water to 200 m during the upwelling season and reaches the surface when the upwelling favorable wind relax. In this context the major task for physicists is to determine the volume transport across OMEX boundary boxes. This seasonal variability and other features related to a very complex bottom topography make the circulation around Galicia very difficult to understand and simulate. Thus it needs some previous understanding of some isolated processes. IST is conducting numerical experiments to investigate discrepancies between simulated and observed currents (see also Task II.3). Results from 3-D ocean circulation model IST is involved in several tasks both in WP I, WP II and WP IV. However all the work already done and to be done by IST in OMEX is based in the 3-D Ocean Circulation model, MOHID3D. For that reason it is appropriate to describe model results obtained during the second year of the project and then link them to each task. Model Domain MOHID3D was implemented in a domain covering the entire West Coast of Iberia. It is a box of 10 by 10 degrees located between 36ºN and 46ºN in the N/S direction and between 16ºW and 6ºW in the W/E direction (Figure 1). The horizontal spatial step is 8 km. In the vertical 22 layers were used. The vertical coordinate is a double sigma coordinate with the interface between the two domains located at 300 m. Bottom topography was derived from ETOPO5 database. Initial Conditions Initial conditions were derived from the World Ocean Atlas (WOA94) based on Levitus (1982). Spring climatological temperature and salinity were used to initialize the model. The original fields were interpolated to the model grid using an inverse square weighting method. After interpolation the obtained fields were spatially filtered. The ocean was assumed to be at rest with a horizontal sea surface.