MEDSLIK-II, a Lagrangian marine surface oil spill model for short-term forecasting – Part 1: Theory

The processes of transport, diffusion and transfor- mation of surface oil in seawater can be simulated using a Lagrangian model formalism coupled with Eulerian circu- lation models. This paper describes the formalism and the conceptual assumptions of a Lagrangian marine surface oil slick numerical model and rewrites the constitutive equations in a modern mathematical framework. The Lagrangian nu- merical representation of the oil slick requires three different state variables: the slick, the particle and the structural state variables. Transformation processes (evaporation, spreading, dispersion and coastal adhesion) act on the slick state vari- ables, while particle variables are used to model the transport and diffusion processes. The slick and particle variables are recombined together to compute the oil concentration in wa- ter, a structural state variable. The mathematical and numer- ical formulation of oil transport, diffusion and transforma- tion processes described in this paper, together with the many simplifying hypothesis and parameterizations, form the basis of a new, open source Lagrangian surface oil spill model, the so-called MEDSLIK-II, based on its precursor MEDSLIK (Lardner et al.,1998, 2006;Zodiatis et al.,2008a). Part 2 of this paper describes the applications of the model to oil spill simulations that allow the validation of the model re- sults and the study of the sensitivity of the simulated oil slick to different model numerical parameterizations