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| Titel |
The vertical structure of oceanic Rossby waves: a comparison of high-resolution model data to theoretical vertical structures |
| VerfasserIn |
F. K. Hunt, R. Tailleux, J. J.-M. Hirschi |
| 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 ; 8, no. 1 ; Nr. 8, no. 1 (2012-01-13), S.19-35 |
| Datensatznummer |
250005394
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| Publikation (Nr.) |
 copernicus.org/os-8-19-2012.pdf |
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| Zusammenfassung |
| Tests of the new Rossby wave theories that have been developed over the past
decade to account for discrepancies between theoretical wave speeds and
those observed by satellite altimeters have focused primarily on the surface
signature of such waves. It appears, however, that the surface signature of
the waves acts only as a rather weak constraint, and that information on the
vertical structure of the waves is required to better discriminate between
competing theories.
Due to the lack of 3-D observations, this paper uses high-resolution model
data to construct realistic vertical structures of Rossby waves and compares
these to structures predicted by theory. The meridional velocity of a
section at 24° S in the Atlantic Ocean is pre-processed using the Radon
transform to select the dominant westward signal. Normalized profiles are
then constructed using three complementary methods based respectively on: (1)
averaging vertical profiles of velocity, (2) diagnosing the amplitude of the
Radon transform of the westward propagating signal at different depths, and
(3) EOF analysis. These profiles are compared to profiles calculated using
four different Rossby wave theories: standard linear theory (SLT), SLT plus
mean flow, SLT plus topographic effects, and theory including mean flow and
topographic effects. Our results support the classical theoretical
assumption that westward propagating signals have a well-defined vertical
modal structure associated with a phase speed independent of depth, in
contrast with the conclusions of a recent study using the same model but for
different locations in the North Atlantic. The model structures are in
general surface intensified, with a sign reversal at depth in some regions,
notably occurring at shallower depths in the East Atlantic. SLT provides a
good fit to the model structures in the top 300 m, but grossly overestimates
the sign reversal at depth. The addition of mean flow slightly improves the
latter issue, but is too surface intensified. SLT plus topography rectifies
the overestimation of the sign reversal, but overestimates the amplitude of
the structure for much of the layer above the sign reversal. Combining the
effects of mean flow and topography provided the best fit for the mean model
profiles, although small errors at the surface and mid-depths are carried
over from the individual effects of mean flow and topography respectively.
Across the section the best fitting theory varies between SLT plus
topography and topography with mean flow, with, in general, SLT plus
topography performing better in the east where the sign reversal is less
pronounced. None of the theories could accurately reproduce the deeper sign
reversals in the west. All theories performed badly at the boundaries. The
generalization of this method to other latitudes, oceans, models and
baroclinic modes would provide greater insight into the variability in the
ocean, while better observational data would allow verification of the model
findings. |
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