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E.V. Stanev and X. Lu
5.3 Water Mass Formation
5.3.1 Numerical Modelling of Wind and Thermohaline Circulation
5.3.1.1 Models
The hydrodynamic equations solved by the ocean models (see Chaps. 2, 3 and 4)
are discretized vertically and horizontally in a finite number of grid elements as
described in Chap. 3 based on several simple examples. In order to resolve all of the
important thermo-hydrodynamic processes the grid resolution has to be sufficiently
fine. This would necessitate very big computer resources, which are not presently
available. Therefore optimal model set-ups are sought under which grid resolution
is fine enough to sufficiently resolve ocean eddies (‘eddy-resolving models’). With
respect to the demand to resolve the complicated geometry and topography one
promising approach is to use unstructured grids, however this type of modelling has
not yet been developed enough for simulating baroclinic processes in the European
semi-enclosed seas and will not be considered below.
In the vertical direction different types of grids are used when modelling different
ocean regimes (e.g., surface, coastal, or deep ocean, Stanev 2005, see also Chap. 3).
The early versions of the Black Sea, Baltic Sea and Mediterranean Sea models
(Stanev et al. 1989; Stanev 1990; Krauss and Brügge 1991) used the MOM, which
is a z-coordinate model based on the so-called ‘box-concept’ (Bryan 1969). These
studies have been followed by a few others using terrain following (σ -coordinates)
models, one example of which is the Princeton Ocean Model (POM, Blumberg and
Mellor 1983). Its application to the three basins under consideration has been first
documented by Oguz and Malanotte-Rizzoli (1996) for the Black Sea, Lascaratos
and Nittis (1998) for the Mediterranean Sea and Laanemets et al. (2011) for the
Baltic Sea. Of similar origin, but with two σ -layers, is the GeoHydrodynamics and
Environment Research (GHER) model, which has been extensively used by Stanev
and Beckers (1999) and Beckers (1991) to model the Black Sea and Mediterranean
Sea circulation.
The application of isopycnal models, one of the most widely used being the Hybrid Coordinate Ocean Model (HYCOM, Bleck 2002), to the Black Sea is described
by Kara et al. (2005). The hybrid coordinates of HYCOM allow the model to behave like a conventional sigma- (terrain-following) model in very shallow oceanic
regions, like a z-level coordinate model in the mixed layer or other unstratified regions, and like an isopycnal coordinate model in stratified regions. One big challenge was to apply this model to resolving the Mediterranean outflow in the Black
Sea (Stanev 2005) and the Gulf of Cádiz (Xu et al. 2007). These applications demonstrated the potential of this model to realistically simulate the spreading of the outflowing plumes and the downstream evolution of temperature and salinity. Of similar
type is the model recently developed by Dick and Kleine (2007) using general vertical coordinates or the model of Hofmeister et al. (2011) using non-uniform adaptive
vertical grids.
E.V. Stanev and X. Lu
5.3 Water Mass Formation
5.3.1 Numerical Modelling of Wind and Thermohaline Circulation
5.3.1.1 Models
The hydrodynamic equations solved by the ocean models (see Chaps. 2, 3 and 4)
are discretized vertically and horizontally in a finite number of grid elements as
described in Chap. 3 based on several simple examples. In order to resolve all of the
important thermo-hydrodynamic processes the grid resolution has to be sufficiently
fine. This would necessitate very big computer resources, which are not presently
available. Therefore optimal model set-ups are sought under which grid resolution
is fine enough to sufficiently resolve ocean eddies (‘eddy-resolving models’). With
respect to the demand to resolve the complicated geometry and topography one
promising approach is to use unstructured grids, however this type of modelling has
not yet been developed enough for simulating baroclinic processes in the European
semi-enclosed seas and will not be considered below.
In the vertical direction different types of grids are used when modelling different
ocean regimes (e.g., surface, coastal, or deep ocean, Stanev 2005, see also Chap. 3).
The early versions of the Black Sea, Baltic Sea and Mediterranean Sea models
(Stanev et al. 1989; Stanev 1990; Krauss and Brügge 1991) used the MOM, which
is a z-coordinate model based on the so-called ‘box-concept’ (Bryan 1969). These
studies have been followed by a few others using terrain following (σ -coordinates)
models, one example of which is the Princeton Ocean Model (POM, Blumberg and
Mellor 1983). Its application to the three basins under consideration has been first
documented by Oguz and Malanotte-Rizzoli (1996) for the Black Sea, Lascaratos
and Nittis (1998) for the Mediterranean Sea and Laanemets et al. (2011) for the
Baltic Sea. Of similar origin, but with two σ -layers, is the GeoHydrodynamics and
Environment Research (GHER) model, which has been extensively used by Stanev
and Beckers (1999) and Beckers (1991) to model the Black Sea and Mediterranean
Sea circulation.
The application of isopycnal models, one of the most widely used being the Hybrid Coordinate Ocean Model (HYCOM, Bleck 2002), to the Black Sea is described
by Kara et al. (2005). The hybrid coordinates of HYCOM allow the model to behave like a conventional sigma- (terrain-following) model in very shallow oceanic
regions, like a z-level coordinate model in the mixed layer or other unstratified regions, and like an isopycnal coordinate model in stratified regions. One big challenge was to apply this model to resolving the Mediterranean outflow in the Black
Sea (Stanev 2005) and the Gulf of Cádiz (Xu et al. 2007). These applications demonstrated the potential of this model to realistically simulate the spreading of the outflowing plumes and the downstream evolution of temperature and salinity. Of similar
type is the model recently developed by Dick and Kleine (2007) using general vertical coordinates or the model of Hofmeister et al. (2011) using non-uniform adaptive
vertical grids.