10 Applications of the Inverse Problem of Pollution Propagation
331
that had a thickness of 2 m). The model has shown excellent performance in different applications, from basin-scale estimates of the upwelling features in the entire
Baltic Sea (Myrberg and Andrejev 2003; Myrberg et al. 2010a), mean circulation
and water age (Andrejev et al. 2004a, 2004b) and various hydrophysical features of
the Gulf of Finland (Myrberg et al. 2010b) down to the small-scale reproduction of
surface buoy drift (Gästgifvars et al. 2006) and test simulations using a resolution
of up to 0.25 nm (Viikmäe et al. 2010).
The OAAS model setup, boundary conditions and forcing data are discussed in
Andrejev et al. (2010, 2011). The model was forced with the same meteorological
data as the RCO model. River discharge was approximated in the OAAS model
using monthly mean values for 1970–1990 (Bergström and Carlsson 1994). As a
first approximation, the salinity of river water was set to zero and its temperature
equal to the ambient sea water temperature at the river mouth. This approximation
(equivalent to ignoring both salinity and heat flux from the rivers) is sensible in the
Baltic Sea conditions, where the river water salinity is almost zero and the difference
in river and sea water temperature in shallow river mouth areas is moderate.
The modelling in the Gulf of Finland started from the resting water masses and
with the sea level in equilibrium with atmospheric pressure. The initial fields (water temperature and salinity) and the boundary information (the 3D structure of
the salinity and temperature and sea level information) at the entrance to the gulf
(Fig. 10.1) were extracted (and optionally interpolated) from the output of the RCO
model at 6-hour resolution. To smooth the potential impact of the difference in the
resolution between the models, the lateral diffusivity coefficient was increased in
the OAAS model towards the boundary following a sine function in a sponge layer
of a width of 16 nm. The modelled fields were plausible from the very beginning of
calculations. The spin-up of the surface layer dynamics took ca 1–2 weeks.
10.4.3 The DMI/BSHcmod Model
Another circulation model, DMI/BSHcmod, was applied in the studies of the dynamics in the southern Baltic Sea. This is also a 3D primitive-equation, hydrostatic,
free-surface ocean model. It was developed originally by the German Federal Maritime and Hydrographic Agency (BSH) (Kleine 1994; Dick et al. 2001) and further developed by the Danish Meteorological Institute (DMI). Its version developed
for the Baltic Sea conditions is now known as the HIROMB-BOOS community
model (Funkquist 2001) and inter alia serves as the underlying circulation model of
Seatrack Web, the official web-based HELCOM tool for simulation of the propagation and fate of oil pollution in the Baltic Sea (Ambjörn 2007, 2008).
In order to accurately resolve the water exchange between the Baltic Sea and
North Sea through the Danish Straits, three nesting levels were applied by Lu et al.
(2012) (see also Chap. 5). A 2D model with a horizontal resolution of 6 nm covering
a large part of the north-eastern Atlantic provided boundary conditions for a local
3D Baltic Sea–North Sea model, with a horizontal resolution of 3 nm. A finer 3D
331
that had a thickness of 2 m). The model has shown excellent performance in different applications, from basin-scale estimates of the upwelling features in the entire
Baltic Sea (Myrberg and Andrejev 2003; Myrberg et al. 2010a), mean circulation
and water age (Andrejev et al. 2004a, 2004b) and various hydrophysical features of
the Gulf of Finland (Myrberg et al. 2010b) down to the small-scale reproduction of
surface buoy drift (Gästgifvars et al. 2006) and test simulations using a resolution
of up to 0.25 nm (Viikmäe et al. 2010).
The OAAS model setup, boundary conditions and forcing data are discussed in
Andrejev et al. (2010, 2011). The model was forced with the same meteorological
data as the RCO model. River discharge was approximated in the OAAS model
using monthly mean values for 1970–1990 (Bergström and Carlsson 1994). As a
first approximation, the salinity of river water was set to zero and its temperature
equal to the ambient sea water temperature at the river mouth. This approximation
(equivalent to ignoring both salinity and heat flux from the rivers) is sensible in the
Baltic Sea conditions, where the river water salinity is almost zero and the difference
in river and sea water temperature in shallow river mouth areas is moderate.
The modelling in the Gulf of Finland started from the resting water masses and
with the sea level in equilibrium with atmospheric pressure. The initial fields (water temperature and salinity) and the boundary information (the 3D structure of
the salinity and temperature and sea level information) at the entrance to the gulf
(Fig. 10.1) were extracted (and optionally interpolated) from the output of the RCO
model at 6-hour resolution. To smooth the potential impact of the difference in the
resolution between the models, the lateral diffusivity coefficient was increased in
the OAAS model towards the boundary following a sine function in a sponge layer
of a width of 16 nm. The modelled fields were plausible from the very beginning of
calculations. The spin-up of the surface layer dynamics took ca 1–2 weeks.
10.4.3 The DMI/BSHcmod Model
Another circulation model, DMI/BSHcmod, was applied in the studies of the dynamics in the southern Baltic Sea. This is also a 3D primitive-equation, hydrostatic,
free-surface ocean model. It was developed originally by the German Federal Maritime and Hydrographic Agency (BSH) (Kleine 1994; Dick et al. 2001) and further developed by the Danish Meteorological Institute (DMI). Its version developed
for the Baltic Sea conditions is now known as the HIROMB-BOOS community
model (Funkquist 2001) and inter alia serves as the underlying circulation model of
Seatrack Web, the official web-based HELCOM tool for simulation of the propagation and fate of oil pollution in the Baltic Sea (Ambjörn 2007, 2008).
In order to accurately resolve the water exchange between the Baltic Sea and
North Sea through the Danish Straits, three nesting levels were applied by Lu et al.
(2012) (see also Chap. 5). A 2D model with a horizontal resolution of 6 nm covering
a large part of the north-eastern Atlantic provided boundary conditions for a local
3D Baltic Sea–North Sea model, with a horizontal resolution of 3 nm. A finer 3D