A multi-nested approach has been employed for numerical simulations in the northern part of the Aegean Sea in the framework of the MFSTEP (Mediterranean Forecast System: Toward Environmental Predictions) project. The high resolution (∼1.6 km) hydrodynamic model of the North Aegean Sea (NAS) has been nested within a coarser model of the Eastern Mediterranean (resolution ∼3.6 km) which is also nested within a basin scale model for the Mediterranean Sea (resolution of ∼7 km). The high resolution

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... the NAS model allows the representation of topographic details that have never been reproduced in modelling studies of the region. Such details can enhance the simulation of coastal features, but can also influence basin-scale processes, such as the pathways of waters of Black Sea origin inflowing at the Dardanelles Straits and bifurcating through island passages. We employ comparisons of the North Aegean and Eastern Mediterranean models in terms of computed flow fields and distribution of hydrodynamic properties, to evaluate the nesting procedure, the initialization requirements and the ability of a nested model to perform reliable short term simulations that employ high resolution atmospheric forcing, when initialized from a coarser OGCM. We show that the topographic details of the high resolution, nested NAS model affect the distribution of the Dardanelles plume and the evolution of coastal currents, while the imposed high frequency, high resolution atmospheric forcing allows for the formation of an overall energetic flow field after a few days of spin-up period. Increased resolution and smaller coastal depth in the NAS simulations influence the flow through island passages and straits. A longer initialization procedure results in the establishment of stronger currents and better-developed buoyant plumes.