5 European Semi-enclosed Seas
161
The typical Mediterranean thermohaline circulation (Fig. 5.19) determined by
the simulations of Beuvier et al. (2010) is quite complicated. At the surface the low
density Atlantic water enters the western Mediterranean Sea at the Strait of Gibraltar
and flows along the African coast towards the eastern Mediterranean Sea (Millot
1999). Winter convection forms dense waters in the following four main areas: (1)
the Western Mediterranean Deep Water in the Gulf of Lions, (2) the Adriatic Deep
Water (ADW) in the Adriatic Sea, (3), the Cretan Intermediate Water in the southern
part of the Aegean Sea, and (4) the Levantine Intermediate Water in the Levantine
basin (mainly in the Rhodes gyre). The Levantine Intermediate Water, which is the
most important intermediate water mass, flows at a depth of about 300 to 500 m
from the Levantine basin towards the western Mediterranean Sea.
5.3.3 Numerical Modelling of the Estuarine Circulation:
The Baltic Sea Case
The DMI/BSHcmod model is an appropriate tool to study estuarine dynamics because it has up-to-date physical parameterizations and allows a two-way nesting.
The setup of this model to study processes in the transition zone between the North
Sea and the Baltic Sea has been described by Lu et al. (2012). The coarse model
domain has a horizontal resolution of 3 nautical miles; the fine one covering the
area from Skagerrak to the Bornholm Basin (Fig. 5.20) has a horizontal resolution
of 0.5 nautical miles. The upper 30 m thick layer is resolved using 1 m thick layers to enable a precise replication of the topography of straits and sills, as well as
of the thermohaline stratification. Below the depth of 30 m the layer thickness is
2 m. The model is forced by 6-hourly meteorological forcing (10 m winds, 2 m
air temperature, mean sea level pressure, surface humidity and cloud cover) from
the DMI operational weather prediction model HIRLAM (High Resolution Limited
Area Model) with a horizontal resolution of 12 km. The surface heat flux is parameterized with bulk aerodynamic formulae using atmospheric data and simulated
sea surface temperature. River runoff is provided monthly for 31 rivers from the
BALTEX Hydrological Data Centre (BHDC, http://www.smhi.se/sgn0102/bhdc/).
The similarity of the Baltic Sea transition zone with the tidal estuaries is highlighted below using the profiles of the mean salinity and meridional velocity along a
zonal section line in the Great Belt (see Fig. 5.20 for the position), averaged for the
inflow and outflow conditions during December 1992–January 1993 (Figs. 5.21a, b).
Part of this period was known as one of the largest MBI events.
The following analysis, which is also relevant to the Bosporus Straits (Fig. 5.11),
aims to illustrate the basic characteristics of inflows and outflows. Obviously, the
outflow phase resembles the typical estuarine circulation: export of low salinity water occurs in the surface layers while saltier water is imported in the bottom layer. As
the mean for the entire section could not be fully representative for the conditions
in the axis of the channel, Fig. 5.21 also provides the profiles for the deepest area
(dashed lines). The two profiles of each pair in Fig. 5.21 are similar with slightly
161
The typical Mediterranean thermohaline circulation (Fig. 5.19) determined by
the simulations of Beuvier et al. (2010) is quite complicated. At the surface the low
density Atlantic water enters the western Mediterranean Sea at the Strait of Gibraltar
and flows along the African coast towards the eastern Mediterranean Sea (Millot
1999). Winter convection forms dense waters in the following four main areas: (1)
the Western Mediterranean Deep Water in the Gulf of Lions, (2) the Adriatic Deep
Water (ADW) in the Adriatic Sea, (3), the Cretan Intermediate Water in the southern
part of the Aegean Sea, and (4) the Levantine Intermediate Water in the Levantine
basin (mainly in the Rhodes gyre). The Levantine Intermediate Water, which is the
most important intermediate water mass, flows at a depth of about 300 to 500 m
from the Levantine basin towards the western Mediterranean Sea.
5.3.3 Numerical Modelling of the Estuarine Circulation:
The Baltic Sea Case
The DMI/BSHcmod model is an appropriate tool to study estuarine dynamics because it has up-to-date physical parameterizations and allows a two-way nesting.
The setup of this model to study processes in the transition zone between the North
Sea and the Baltic Sea has been described by Lu et al. (2012). The coarse model
domain has a horizontal resolution of 3 nautical miles; the fine one covering the
area from Skagerrak to the Bornholm Basin (Fig. 5.20) has a horizontal resolution
of 0.5 nautical miles. The upper 30 m thick layer is resolved using 1 m thick layers to enable a precise replication of the topography of straits and sills, as well as
of the thermohaline stratification. Below the depth of 30 m the layer thickness is
2 m. The model is forced by 6-hourly meteorological forcing (10 m winds, 2 m
air temperature, mean sea level pressure, surface humidity and cloud cover) from
the DMI operational weather prediction model HIRLAM (High Resolution Limited
Area Model) with a horizontal resolution of 12 km. The surface heat flux is parameterized with bulk aerodynamic formulae using atmospheric data and simulated
sea surface temperature. River runoff is provided monthly for 31 rivers from the
BALTEX Hydrological Data Centre (BHDC, http://www.smhi.se/sgn0102/bhdc/).
The similarity of the Baltic Sea transition zone with the tidal estuaries is highlighted below using the profiles of the mean salinity and meridional velocity along a
zonal section line in the Great Belt (see Fig. 5.20 for the position), averaged for the
inflow and outflow conditions during December 1992–January 1993 (Figs. 5.21a, b).
Part of this period was known as one of the largest MBI events.
The following analysis, which is also relevant to the Bosporus Straits (Fig. 5.11),
aims to illustrate the basic characteristics of inflows and outflows. Obviously, the
outflow phase resembles the typical estuarine circulation: export of low salinity water occurs in the surface layers while saltier water is imported in the bottom layer. As
the mean for the entire section could not be fully representative for the conditions
in the axis of the channel, Fig. 5.21 also provides the profiles for the deepest area
(dashed lines). The two profiles of each pair in Fig. 5.21 are similar with slightly