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6 Rotational Effects
6.10 Exercise 19: Baroclinic Compensation
6.10.1 Background
Adjustment toward a steady state is in our previous model of the wind-driven midlatitude circulation only possible if f ow convergence in the upper ocean is compensated by f ow divergence in deeper layers of the ocean. Whereas the convergence of
Ekman drift leads to establishment of a centre of elevated sea level, it is obvious the
fl w divergence in the ocean interior leads to downward displacements of density
interfaces. Hence, density interfaces in the ocean interior tend to be an amplifie
mirror image of the shape of the sea surface. The process that leads to this structure
is sometimes referred to as baroclinic compensation.
Baroclinic compensation implies that the horizontal pressure-gradient force
becomes weaker with depth and so do the associated geostrophic f ows. Consequently, large-scale wind-driven geostrophic f ows tend to becomes vanishingly
small below depths of 1500–3000 m. Whereas the sea level can approach an equilibrium state, as described by the Sverdrup relation (Eqs. 6.47 and 6.48), density
interfaces in the ocean interior reach an equilibrium only in the presence of additional ageostrophic effects such as provided by lateral momentum diffusion.
6.10.2 Aim
The real ocean has a density stratification Excess of solar heating at tropical and
subtropical latitudes produces a warm surface layer that is separated from the cold
abyss by a temperature transition zone, called the permanent thermocline. Dependent on location, the permanent thermocline extends to depths of 500–2000 m.
The simplest model of this stratificatio is a two-layer ocean in which the density
interface represents the thermocline. The aim of this exercise to explore the winddriven circulation of the ocean in a flui of two superimposed layers of different
densities.
6.10.3 Task Description
The exercise is a repeat of Exercise 18 (Scenario 3), but with consideration of a
two-layer ocean. The top layer has an initial thickness of 200 m and a density of
1025 kg/m
3
. The bottom layer has an initial thickness of 800 m and a density of
1030 kg/m
3
. The nonlinear terms are enabled. Horizontal eddy viscosity is set to
500 m
2
/s and the bottom-friction coefficien is chosen as r = 0.001 m/s. The total
simulation time is 100 days with data outputs at every 2.5 days. The time step is set
to Δt = 20 s.
6 Rotational Effects
6.10 Exercise 19: Baroclinic Compensation
6.10.1 Background
Adjustment toward a steady state is in our previous model of the wind-driven midlatitude circulation only possible if f ow convergence in the upper ocean is compensated by f ow divergence in deeper layers of the ocean. Whereas the convergence of
Ekman drift leads to establishment of a centre of elevated sea level, it is obvious the
fl w divergence in the ocean interior leads to downward displacements of density
interfaces. Hence, density interfaces in the ocean interior tend to be an amplifie
mirror image of the shape of the sea surface. The process that leads to this structure
is sometimes referred to as baroclinic compensation.
Baroclinic compensation implies that the horizontal pressure-gradient force
becomes weaker with depth and so do the associated geostrophic f ows. Consequently, large-scale wind-driven geostrophic f ows tend to becomes vanishingly
small below depths of 1500–3000 m. Whereas the sea level can approach an equilibrium state, as described by the Sverdrup relation (Eqs. 6.47 and 6.48), density
interfaces in the ocean interior reach an equilibrium only in the presence of additional ageostrophic effects such as provided by lateral momentum diffusion.
6.10.2 Aim
The real ocean has a density stratification Excess of solar heating at tropical and
subtropical latitudes produces a warm surface layer that is separated from the cold
abyss by a temperature transition zone, called the permanent thermocline. Dependent on location, the permanent thermocline extends to depths of 500–2000 m.
The simplest model of this stratificatio is a two-layer ocean in which the density
interface represents the thermocline. The aim of this exercise to explore the winddriven circulation of the ocean in a flui of two superimposed layers of different
densities.
6.10.3 Task Description
The exercise is a repeat of Exercise 18 (Scenario 3), but with consideration of a
two-layer ocean. The top layer has an initial thickness of 200 m and a density of
1025 kg/m
3
. The bottom layer has an initial thickness of 800 m and a density of
1030 kg/m
3
. The nonlinear terms are enabled. Horizontal eddy viscosity is set to
500 m
2
/s and the bottom-friction coefficien is chosen as r = 0.001 m/s. The total
simulation time is 100 days with data outputs at every 2.5 days. The time step is set
to Δt = 20 s.