400
Abyssal Circulation
This important example emphasizes the fact that the direction of the
interior flow and the boundary layer flow can be directly opposed to that which
might be naively inferred from the knowledge of the source position and the
characteristics of the water at any location with respect to the source. Thus, for
example, the water in the western boundary current north of 30°N has its
source in the southern hemisphere. However, because of the strongly
recirculating character of the flow it is moving southward towards the source.
A flux equal to woR 2 (¢e-
Half of this flux is absorbed into the thermocline in the area south of 30°N. At
30°N, where Tw=O, the otherhalfofthe original mass flux, i.e. 0.5w 0 R 2 (cfJ.-cfJw)
enters the northern portion of the sector through the interior and upwells into the thermocline. However, a flux equal to the full flow across
the equator reaches the apex of the sector, i.e., a flux of woR 2 (
north of 30° which carries at the apex a flux, woR 2 ( ¢ e -
that entered the region north of 30°. The recirculation is twice as strong as the
flow involved in the mass circuit from the source in the western boundary layer
at the equator to the distributed sink in the northern portion of the gyre. The
ability of the source/sink flow to create strong recirculations tends to decouple
the local flow direction from the origin of the source water. This is true both for
the interior and the boundary layer.
Consider now an ocean basin bounded between the latitudes e. and en and
the longitudes, as before,
northern sector at the northern boundary, and a source Ss is placed at the
southern boundary of the basin. The longitude of each of the sources is
arbitrary. The situation is shown in Fig. 7.3.2 and presents a unifying and
generalizing arrangement of the previous two examples.
The total mass flux upwelling in the basin is:
= Ss +Sn
(7.3.18)
which relates the upwelling amplitude to the total source strength.
Consider the upwelling into the thermocline in the subregion north of the
latitude e. The flux leaving the abyss is given by the first line in (7.3.18) with e.
replaced with e. The mass balance for this region consists of balancing this sink
against the fluid that enters in the western boundary layer, the fluid delivered
by the source Sn and the interior flow (7.3.6) integrated across the latitude e.
When the balance is made the result requires a western boundary layer
transport:
Abyssal Circulation
This important example emphasizes the fact that the direction of the
interior flow and the boundary layer flow can be directly opposed to that which
might be naively inferred from the knowledge of the source position and the
characteristics of the water at any location with respect to the source. Thus, for
example, the water in the western boundary current north of 30°N has its
source in the southern hemisphere. However, because of the strongly
recirculating character of the flow it is moving southward towards the source.
A flux equal to woR 2 (¢e-
Half of this flux is absorbed into the thermocline in the area south of 30°N. At
30°N, where Tw=O, the otherhalfofthe original mass flux, i.e. 0.5w 0 R 2 (cfJ.-cfJw)
enters the northern portion of the sector through the interior and upwells into the thermocline. However, a flux equal to the full flow across
the equator reaches the apex of the sector, i.e., a flux of woR 2 (
north of 30° which carries at the apex a flux, woR 2 ( ¢ e -
that entered the region north of 30°. The recirculation is twice as strong as the
flow involved in the mass circuit from the source in the western boundary layer
at the equator to the distributed sink in the northern portion of the gyre. The
ability of the source/sink flow to create strong recirculations tends to decouple
the local flow direction from the origin of the source water. This is true both for
the interior and the boundary layer.
Consider now an ocean basin bounded between the latitudes e. and en and
the longitudes, as before,
northern sector at the northern boundary, and a source Ss is placed at the
southern boundary of the basin. The longitude of each of the sources is
arbitrary. The situation is shown in Fig. 7.3.2 and presents a unifying and
generalizing arrangement of the previous two examples.
The total mass flux upwelling in the basin is:
= Ss +Sn
(7.3.18)
which relates the upwelling amplitude to the total source strength.
Consider the upwelling into the thermocline in the subregion north of the
latitude e. The flux leaving the abyss is given by the first line in (7.3.18) with e.
replaced with e. The mass balance for this region consists of balancing this sink
against the fluid that enters in the western boundary layer, the fluid delivered
by the source Sn and the interior flow (7.3.6) integrated across the latitude e.
When the balance is made the result requires a western boundary layer
transport: