130
6 Rotational Effects
Fig. 6.4 Bathymetry for Exercise 16
on the velocity scale and lengthscale of dynamical perturbations that develop in
interaction with variable bathymetry.
The total simulation time of experiments is 20 days with data outputs at every
6 h. A narrow source of Eulerian tracer concentration of unity is prescribed at the
western boundary to visualise the structure of the fl w. Wind-stress forcing and
lateral momentum diffusion are ignored. Zero-gradient conditions are employed for
all variables at open boundaries. Additional smoothing algorithms are implemented
near the western and eastern open boundaries to avoid reflectio of topographic
Rossby waves.
6.5.4 Caution
The f rst-order Shapiro filte does not work well for processes dominated by the
geostrophic balance. This filte operates to gradually decrease sea-level gradients,
hence diminishing the barotropic horizontal pressure-gradient force that is the principal driver of geostrophic f ows in the ocean. For this reason, the Shapiro filte is
disabled in this and most of the subsequent model applications, if not stated otherwise.
6.5.5 Sample Code
The folder “Exercise 16” of the CD-ROM contains the computer codes for this
exercise. The f le “info.txt” gives additional information.
6.5.6 Results
In Scenario 1, the f ow largely follows bathymetric contours and the topographic
steering mechanism appears to work (Fig. 6.5). Given that the f ow enters the model
domain through the upstream boundary with zero relative vorticity, the conservation
principle of potential vorticity (6.23) has the solution:
6 Rotational Effects
Fig. 6.4 Bathymetry for Exercise 16
on the velocity scale and lengthscale of dynamical perturbations that develop in
interaction with variable bathymetry.
The total simulation time of experiments is 20 days with data outputs at every
6 h. A narrow source of Eulerian tracer concentration of unity is prescribed at the
western boundary to visualise the structure of the fl w. Wind-stress forcing and
lateral momentum diffusion are ignored. Zero-gradient conditions are employed for
all variables at open boundaries. Additional smoothing algorithms are implemented
near the western and eastern open boundaries to avoid reflectio of topographic
Rossby waves.
6.5.4 Caution
The f rst-order Shapiro filte does not work well for processes dominated by the
geostrophic balance. This filte operates to gradually decrease sea-level gradients,
hence diminishing the barotropic horizontal pressure-gradient force that is the principal driver of geostrophic f ows in the ocean. For this reason, the Shapiro filte is
disabled in this and most of the subsequent model applications, if not stated otherwise.
6.5.5 Sample Code
The folder “Exercise 16” of the CD-ROM contains the computer codes for this
exercise. The f le “info.txt” gives additional information.
6.5.6 Results
In Scenario 1, the f ow largely follows bathymetric contours and the topographic
steering mechanism appears to work (Fig. 6.5). Given that the f ow enters the model
domain through the upstream boundary with zero relative vorticity, the conservation
principle of potential vorticity (6.23) has the solution: