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| Titel |
Retroflection from a double-slanted coastline: a model for the Agulhas leakage variability |
| VerfasserIn |
V. Zharkov, D. Nof, W. Weijer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 6, no. 4 ; Nr. 6, no. 4 (2010-12-13), S.997-1011 |
| Datensatznummer |
250003685
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| Publikation (Nr.) |
 copernicus.org/os-6-997-2010.pdf |
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| Zusammenfassung |
The Agulhas leakage to the South Atlantic exhibits a strong anti-correlation
with the mass flux of the Agulhas Current. When the Agulhas retroflection is
in its normal position near Cape Agulhas, leakage is relatively high and the
nearby South African coastal slant (angle of derivation from zonal) is very
small and relatively invariant alongshore. During periods of strong incoming
flux (low leakage), the retroflection shifts upstream to Port Elizabeth or
East London, where the coastline shape has a "kink", i.e., the slant
changes abruptly from small on the west side, to large (about 55°) on
the east side. Here, we show that the variability of rings shedding and
anti-correlation between Agulhas mass flux and leakage to the South Atlantic
may be attributed to this kink.
To do so, we develop a nonlinear analytical model for retroflection near a
coastline that consists of two sections, a zonal western section and a
strongly slanted eastern section. The principal difference between this and
the model of a straight slanted coast (discussed in our earlier papers)
is that, here, free purely westward propagation of eddies along the zonal
coastline section is allowed. This introduces an interesting situation in
which strong slant of the coast east of the kink prohibits the formation and
shedding of rings, while the almost zonal coastal orientation west of the
kink encourages shedding. Therefore, the kink "locks" the position of the
retroflection, forcing it to occur just downstream of the kink. Rings are
necessarily shed from the retroflection area in our kinked model, regardless
of the degree of eastern coast slant. In contrast, a no-kink model with a
coastline of intermediate slant indicates that shedding is almost completely
arrested by that slant.
We suggest that the observed difference in ring-shedding intensity during
times of normal retroflection position and times when the retroflection is
shifted eastward is due to the change in the retroflection location with
respect to the kink. When the incoming flux detaches from the coast north of
the kink, ring transport is small; when the flux detaches south of the kink,
transport is large. Simple process-oriented numerical simulations are in
fair agreement with our analytical results. |
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