Establishment of the Abyssal Circulation
419
is independent of the ridge. The fate of the flow when it impinges on the ridge is
determined by the stagnation point structure, and the flow through the gaps in
the ridge is completely determined in turn by the eastern interior
streamfunction and the position of the gaps (or, equivalently, on the value
of the constant streamfunction on each segment). Thus the flow is drawn
through the gaps to satisfy the conditions already determined in the eastern
basin rather than being forced through the gaps by the flow in the western
basin. The zonal jets are forced in the western basin as a reaction to the mass
drawn though the ridge gaps in the manner already familiar from the
discussion of the Stommel-Arons theory in Section 7.4.
Pedlosky (1994b) suggested that these recirculations, anchored to the
ridges and their gaps, are responsible for the subplanetary recirculations seen in
the data, as described in Section 7.1 (e.g., Fig. 7.1.4). Extension of the theory to
a stratified model, in the context of a two-layer model (Pedlosky 1994a) shows
that the presence of the recirculation is strongest within the layers actually
blocked by the ridge, but that the recirculation extends upward, at least
weakly, into the unblocked layer above the ridge.
7.6 Establishment of the Abyssal Circulation
The Stommel-Arons theory relates the structure of the abyssal circulation to a
widespread upwelling into the thermocline. The horizontal structure of the
upwelling is fixed a priori in the model. This, with the specification of the
position of the sources of deep water, determines the boundary-current
transports required to close the circulation as well. The distribution of the
upwelling into the thermocline is really, of course, not completely independent
of the motion of the waters of the abyss, and this dependence can be expected
to alter the horizontal structure of the upwelling and the resulting horizontal
circulation. At the same time, baroclinic effects can be expected also to be
important in determining the form of the circulation, for, as we noted in
Section 7.1, the circulation as observed has a strong baroclinic character. One
important feature of the baroclinic circulation is that the way in which
information is signaled involves slow baroclinic Rossby waves and baroclinic
Kelvin waves as well as the rapid barotropic Rossby wave, and this affects both
the structure of the steady circulation and the process of adjustment of the
circulation to changes in the sources or sinks of the flow. A similar dependence
was noted in Chapter 3.
A very illuminating model of the abyssal circulation which attempts to
extend the ideas of Stommel and Arons along the direction of these concerns
has been presented by Kawase (1987). Although the assumption of linearity of
the dynamics is maintained, the upwelling from the abyss into the thermocline
is coupled to the abyssal motion in a direct way. Indeed, while the interior
upwelling in the Stommel-Arons model is independent of the abyssal motion,
419
is independent of the ridge. The fate of the flow when it impinges on the ridge is
determined by the stagnation point structure, and the flow through the gaps in
the ridge is completely determined in turn by the eastern interior
streamfunction and the position of the gaps (or, equivalently, on the value
of the constant streamfunction on each segment). Thus the flow is drawn
through the gaps to satisfy the conditions already determined in the eastern
basin rather than being forced through the gaps by the flow in the western
basin. The zonal jets are forced in the western basin as a reaction to the mass
drawn though the ridge gaps in the manner already familiar from the
discussion of the Stommel-Arons theory in Section 7.4.
Pedlosky (1994b) suggested that these recirculations, anchored to the
ridges and their gaps, are responsible for the subplanetary recirculations seen in
the data, as described in Section 7.1 (e.g., Fig. 7.1.4). Extension of the theory to
a stratified model, in the context of a two-layer model (Pedlosky 1994a) shows
that the presence of the recirculation is strongest within the layers actually
blocked by the ridge, but that the recirculation extends upward, at least
weakly, into the unblocked layer above the ridge.
7.6 Establishment of the Abyssal Circulation
The Stommel-Arons theory relates the structure of the abyssal circulation to a
widespread upwelling into the thermocline. The horizontal structure of the
upwelling is fixed a priori in the model. This, with the specification of the
position of the sources of deep water, determines the boundary-current
transports required to close the circulation as well. The distribution of the
upwelling into the thermocline is really, of course, not completely independent
of the motion of the waters of the abyss, and this dependence can be expected
to alter the horizontal structure of the upwelling and the resulting horizontal
circulation. At the same time, baroclinic effects can be expected also to be
important in determining the form of the circulation, for, as we noted in
Section 7.1, the circulation as observed has a strong baroclinic character. One
important feature of the baroclinic circulation is that the way in which
information is signaled involves slow baroclinic Rossby waves and baroclinic
Kelvin waves as well as the rapid barotropic Rossby wave, and this affects both
the structure of the steady circulation and the process of adjustment of the
circulation to changes in the sources or sinks of the flow. A similar dependence
was noted in Chapter 3.
A very illuminating model of the abyssal circulation which attempts to
extend the ideas of Stommel and Arons along the direction of these concerns
has been presented by Kawase (1987). Although the assumption of linearity of
the dynamics is maintained, the upwelling from the abyss into the thermocline
is coupled to the abyssal motion in a direct way. Indeed, while the interior
upwelling in the Stommel-Arons model is independent of the abyssal motion,