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| Titel |
Depth dependence of westward-propagating North Atlantic features diagnosed from altimetry and a numerical 1/6° model |
| VerfasserIn |
A. Lecointre, T. Penduff, P. Cipollini, R. Tailleux, B. Barnier |
| 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 ; 4, no. 1 ; Nr. 4, no. 1 (2008-03-18), S.99-113 |
| Datensatznummer |
250001537
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| Publikation (Nr.) |
 copernicus.org/os-4-99-2008.pdf |
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| Zusammenfassung |
| A 1/6° numerical simulation is used to investigate the vertical
structure of westward propagation between 1993 and 2000 in the North Atlantic ocean.
The realism of the simulated westward propagating signals, interpreted
principally as the signature of first-mode baroclinic Rossby waves (RW),
is first assessed by comparing the simulated amplitude and zonal phase
speeds of Sea Level Anomalies (SLA) against TOPEX/Poseidon-ERS
satellite altimeter data. Then, the (unobserved) subsurface signature of
RW phase speeds is investigated from model outputs by means of the
Radon Transform which was specifically adapted to focus on first-mode
baroclinic RW. The analysis is performed on observed and simulated
SLA and along 9 simulated isopycnal displacements spanning the
0–3250 m depth range. Simulated RW phase speeds agree well with
their observed counterparts at the surface, although with a slight slow
bias. Below the surface, the simulated phase speeds exhibit
a systematic deceleration with increasing depth, by a factor that appears
to vary geographically. Thus, while the reduction factor is about 15–18%
on average at 3250 m over the region considered, it appears to be
much weaker (about 5–8%) in the eddy-active Azores Current, where westward
propagating structures might be more coherent in the vertical. In the context
of linear theories, these results question the often-made normal mode assumption
of many WKB-based theories that the phase speed is independent of depth.
Alternatively, these results could also suggest that the vertical structure of
westward propagating signals may significantly depend on their degree of
nonlinearity, with the degree of vertical coherence possibly increasing
with the degree of nonlinearity. |
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