150
5 3D Level Modelling
5.8.3 Results
The gradual density increase in the formation region creates a Deep Western Boundary Current that spreads southward along the western side of the model domain
(Fig. 5.19). This boundary current is initiated by the Coriolis force which pushes
deep water against the coast. The resultant upward doming of the density interface
and geostrophic adjustment lead to steady-state dynamics. Note that an anticyclonic
eddy appears in bottom layers of the dense-water formation region. Owing to a net
influx of low-density water, the density excess in the formation region reaches a
steady value of around 2 kg/m
3 . This implies that density in a formation region is
bounded by an upper limit.
A return flow establishes in the upper ocean spanning the entire length of the
Deep Western Boundary Current (Fig. 5.20). This return flow is created by a drop
of the coastal sea level as consequence of the geostrophic adjustment of the dense
bottom layer. The adjacent ocean remains largely at rest. A counterclockwise rotating eddy appears in surface layers of the dense-water formation region. Upwelling
along the path of the boundary current leads to entrainment of bottom water into the
surface return flow. There is some indication of meandering of the boundary current, but the inherent dynamics are grossly biased by the coarse lateral grid spacing
chosen.
In contrast to the Stommel-Arons model, a vertical rather than horizontal overturning circulation establishes here being concentrated to a narrow zone along the
western boundary. The final locations of selected Lagrangian floats nicely reveal
the boundary current (Fig. 5.21) together with the return flow that establishes in the
surface ocean (Fig. 5.22). This model application does not create any return flows in
Fig. 5.19 Exercise 24. Distributions of density (shading and contours) and horizontal flow field
(arrows) in the lowermost 200 m of the water column domain after 120 days of simulation. Arrows
for speeds <1 cm/s are omitted. Velocities are averaged over 2 × 2 grid cells
5 3D Level Modelling
5.8.3 Results
The gradual density increase in the formation region creates a Deep Western Boundary Current that spreads southward along the western side of the model domain
(Fig. 5.19). This boundary current is initiated by the Coriolis force which pushes
deep water against the coast. The resultant upward doming of the density interface
and geostrophic adjustment lead to steady-state dynamics. Note that an anticyclonic
eddy appears in bottom layers of the dense-water formation region. Owing to a net
influx of low-density water, the density excess in the formation region reaches a
steady value of around 2 kg/m
3 . This implies that density in a formation region is
bounded by an upper limit.
A return flow establishes in the upper ocean spanning the entire length of the
Deep Western Boundary Current (Fig. 5.20). This return flow is created by a drop
of the coastal sea level as consequence of the geostrophic adjustment of the dense
bottom layer. The adjacent ocean remains largely at rest. A counterclockwise rotating eddy appears in surface layers of the dense-water formation region. Upwelling
along the path of the boundary current leads to entrainment of bottom water into the
surface return flow. There is some indication of meandering of the boundary current, but the inherent dynamics are grossly biased by the coarse lateral grid spacing
chosen.
In contrast to the Stommel-Arons model, a vertical rather than horizontal overturning circulation establishes here being concentrated to a narrow zone along the
western boundary. The final locations of selected Lagrangian floats nicely reveal
the boundary current (Fig. 5.21) together with the return flow that establishes in the
surface ocean (Fig. 5.22). This model application does not create any return flows in
Fig. 5.19 Exercise 24. Distributions of density (shading and contours) and horizontal flow field
(arrows) in the lowermost 200 m of the water column domain after 120 days of simulation. Arrows
for speeds <1 cm/s are omitted. Velocities are averaged over 2 × 2 grid cells