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| Titel |
On the modulation of the periodicity of the Faroe Bank Channel overflow instabilities |
| VerfasserIn |
E. Darelius, I. Fer, T. Rasmussen, C. Guo, K. M. H. Larsen |
| 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 ; 11, no. 5 ; Nr. 11, no. 5 (2015-10-26), S.855-871 |
| Datensatznummer |
250117298
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| Publikation (Nr.) |
 copernicus.org/os-11-855-2015.pdf |
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| Zusammenfassung |
| The Faroe Bank Channel (FBC) is one of the major pathways where dense, cold water
formed in the Nordic Seas flows southward as a bottom-attached energetic
plume towards the North Atlantic. The plume region downstream of the FBC sill
is characterized by high mesoscale variability, quasi-regular oscillations
and intense mixing. Here, 1 year long time series of velocity and
temperature from ten moorings deployed in May 2012 in the plume region are
analysed to describe variability in
the strength and period of the oscillations. The eddy kinetic energy (EKE)
associated with the oscillations changes by a factor of 10 during the year
and the dominant period of the oscillations is modulated and varies between 3
to 4 and 6 days, where the shorter-period oscillations are more energetic.
The dense water is observed on a wider portion of the slope (both deeper and
shallower) during periods with energetic, short-period oscillations. The
observations are complemented by results from a regional, high-resolution
model that shows a similar variability in EKE and a gradual change in
oscillation period of between 3 and 4 days. The observed variability in
oscillation period is directly linked to changes in the volume transport
across the sill: the oscillation period increases from approximately 3 days
to about 6 days when the transport decreases from 2.4 to 1.9 Sv. A similar
relation is obtained from the model. This is in agreement with results from a
linear baroclinic instability analysis, which suggests that the period
increases while the growth rate decreases for decreased plume thickness.
Advective effects, caused by the variable background current, further
modulate the observed periodicity by up to 1 day. In addition, it is shown
that about 50 % of the transport variability across the sill is explained
by changes in the local sea surface height gradient. |
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