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Model coupling system, architecture and results

In CLEOPATRA the main research theme on models is based on the idea that a significant part of the necessary improvement in pollutant drift modelling can be achieved by coupling, at a high level of resolution, the atmosphere, ocean and wave part of our model chains, with the aim of a better description of the atmosphere-sea surface boundary layer, that would then furnish a better estimation of the driving forces for surface pollutants (such as, but not only, oil slicks). In practice oil spill system are required to import and make use of gridded meteo-ocean data, since the spill can move through geographically varying meteo-ocean conditions. The performance of models during operations, especially during storms, is highly dependent on such input data and their quality. This part of the project, being, from a scientific point of view, a very advanced (and risky) one, has produced a deep literature review on model coupling issues, taking into account of physical studies, existing algorithmic tools and the State-of-the-Art of scientific/operational systems where model coupling strategies have been defined and implemented.

CLEOPATRA system is constituted by meteorological, marine (i.e. hydrodynamic), surface waves and oil dispersal/diffusion model components. Traditionally, atmospheric forcing and winds are the main driving forces for the ocean, especially near the sea surface where more critical may be the concentration of pollutant substances such as oil. Here both surface ocean currents and wind stress acting directly on the slick cause the diffusion/dispersion of oil. Sea waves usually are not fully integrated in the model chain. The possibility to couple the atmospheric, ocean and wave models, which are strongly connected, has been analysed, with the aim of a better description of the dynamics of the sea surface boundary layer.

In fact atmosphere to ocean interactions have mainly be studied in climatology (so when the spatial/temporal scales of interest are much bigger then the typical scale of an oil slick problem, that is local). In CLEOPATRA models chain, information at local scales (high resolution models) are derived from low resolution model. These models communicate each other via "standard" forcing, that is: atmosphere forcing (winds) drive sea waves, while both winds, surface heating and salinity fluxes (evaporation/ precipitation rates) cause the ocean dynamics (wind-driven and termohaline currents). Information for pollution spill is obtained from both winds, waves and, mainly, ocean currents. Here the feedback waves to atmosphere (in fact sea surface roughness, as determined by the sea motion, can have a strong influence on local winds), waves to ocean (meaning: how waves transfer momentum and turbulence to the oceanic scales - roughly speaking to the ocean currents), and ocean to waves (meaning: how currents influence sea waves, that may be important in some areas such as straits or in coastal areas) is studied. 'In situ' and 'Earth Observation' data can be used as (additional) initial condition to run the models (of course the spilling model can start from a satellite pollutant observation, but also from an accident notification). Finally the connection between 'in situ' and 'Earth Observation' data with models is also important for calibration/validation purposes.

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