3.2.1 Model construction

A 48-hr oil spill dispersion forecasting system was developed and implemented in the wider northern Aegean Sea. The system was based on wind, wave, and ocean circulation models, coupled with the operational systems ALERMO and SKIRON of the Department of Physics of the University of Athens, and an oil spill dispersion model by the Department of Civil Engineering of the Aristotle University of Thessaloniki. The basic components of the model are presented hereafter.

#### 3.2.1.1 Meteorological model

The meteorological model is part of the weather forecasting system SKIRON developed by the University of Athens, which is based on a Limited Area Model of Eta/NCEP, which provides high-resolution (of 1°) weather forecasts for 120 hrs [31]. In this work, the non-hydrostatic model Eta of the operational forecasting system SKIRON has been used, with an even higher resolution (of 1°/10) since the description of non-hydrostatic phenomena is necessary for the model to be applied for such a high resolution. The available data are: air temperature and humidity at 2 m, wind velocity and direction at 10 m, short- and long-wave radiation, atmospheric pressure at the sea level, and precipitation.

#### 3.2.1.2 Hydrodynamic model

The hydrodynamic forecasting model, which was developed for the area under study, is based on the well-known numerical model Princeton Ocean Model (POM) [21], a model that has been widely used for the simulation of open and coastal sea circulation. The Department of Physics at the University of Athens developed a POM-based sea circulation forecasting model, named ALERMO, under the European programs MFSPP and MFSTEP, which was made public in 2004 (http://www. phys.uoa.gr). Its resolution is 2 nm and it is coupled with the Mediterranean forecasting system MFS-OGCM (INGV, Italy), which also assimilates satellite data and field measurements (XBTs, CTDs, Profiling Float). ALERMO uses an innovative variational initialization technique (VIFOP) for its initial conditions and provides initial and boundary conditions to other coastal forecasting systems (e.g., Greece, Cyprus, and Israel). The developed hydrodynamic model has been applied to the area of interest (North Aegean: 38.7°–41.1° N, 22.5°–27.1° E) with horizontal resolution of 1°/60 (1 nm) and 25 σ-layers in the vertical. The open boundary conditions, as well as the initial conditions, are provided by ALERMO. Finally, the momentum, heat and water fluxes at the air-sea interface are calculated by using the weather forecasting data provided by the meteorological model. A series of sensitivity tests have been conducted, with respect to the atmospheric conditions and the inflow of water from the Black Sea [32].

#### 3.2.1.3 Wave model

The wave model WAM [33, 34] has been adapted and applied to the area under study, with a resolution of 1°/20 by the University of Athens. This model is a thirdgeneration numerical model, which has been widely used, as it best describes the evolution of the wave spectrum in the sea. WAM makes a distinction between deep and shallow waters, depending on the sea depth at the area, where the wave equations are being applied.

#### 3.2.1.4 Oil spill dispersion model

The oil spill transport and dispersion model, named NASOS (North Aegean Sea and Oil Slick), is based on the 3D model that has been developed by the civil engineering department of the Aristotle University of Thessaloniki [16, 17]. The produced operational code was updated and adapted to the area of interest (38.7°– 41.1° N, 22.5°–27.1° E), that is, the North Aegean Sea. This model assumes that the oil slick is described by a big number (equal to 104 ) of particles (or "parcels"), each of which represents many cubic meters of oil, and has individual physicochemical properties. The distinction of the oil spill in these "parcels" is supported by the fact

## Oil Spill Dispersion Forecasting Models DOI: http://dx.doi.org/10.5772/intechopen.81764

that oil contains a variety of hydrocarbon components with different physicochemical properties, and therefore makes the monitoring of the evolution of each "parcel" easier. This model recognizes four different oil types, enough to cover the variety of physicochemical properties and their effect on the environment. In terms of the simulation of the fate and transport of the oil spill in the sea, the model recognizes the following processes: initial spreading and transport, horizontal and vertical diffusion and dispersion, evaporation, emulsification, beaching, and sedimentation. The Mackay approach [26, 27] is again used for the computation of the evaporated volume fraction from each oil component. Emulsification is activated for oil fraction with densities and wave height/length ratios beyond critical values. The evaporation and emulsification processes lead on the one hand to the deficit of contained oil in the evaporated particles, and on the other hand to the creation of a mixture of water and oil, and formation of a floating mousse. Beaching, which expresses the entrapment of oil on the beach, is expressed by the duration of particles trapped on the coastal boundary. It strongly depends on the coastal morphology (rocky to flat sandy beach).
