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| Titel |
Chaotic variability of the meridional overturning circulation on subannual to interannual timescales |
| VerfasserIn |
J. J.-M. Hirschi, A. T. Blaker, B. Sinha, A. Coward, B. Cuevas, S. Alderson, G. Madec |
| 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 ; 9, no. 5 ; Nr. 9, no. 5 (2013-09-09), S.805-823 |
| Datensatznummer |
250085242
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| Publikation (Nr.) |
 copernicus.org/os-9-805-2013.pdf |
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| Zusammenfassung |
| Observations and numerical simulations have shown that the meridional
overturning circulation (MOC) exhibits substantial variability on sub- to
interannual timescales. This variability is not fully understood. In
particular it is not known what fraction of the MOC variability is caused by
processes such as mesoscale ocean eddies and waves which are ubiquitous in
the ocean. Here we analyse twin experiments performed with a global ocean
model at eddying (1/4°) and non-eddying (1°) resolutions. The
twin experiments are forced with the same surface fluxes for the 1958 to 2001
period but start from different initial conditions. Our results show that on
subannual to interannual timescales a large fraction of MOC variability
directly reflects variability in the surface forcing. Nevertheless, in the
eddy-permitting case there is an initial-condition-dependent MOC variability
(hereinafter referred to as "chaotic" variability) of several Sv
(1Sv = 106 m3 s−1) in the Atlantic and the Indo-Pacific. In
the Atlantic the chaotic MOC variability represents up to 30% of the
total variability at the depths where the maximum MOC occurs. In comparison
the chaotic MOC variability is only 5–10% in the non-eddying case. The
surface forcing being almost identical in the twin experiments suggests that
mesoscale ocean eddies are the most likely cause for the increased chaotic
MOC variability in the eddying case. The exact formation time of eddies is
determined by the initial conditions which are different in the two model
passes, and as a consequence the mesoscale eddy field is decorrelated in the
twin experiments. In regions where eddy activity is high in the
eddy-permitting model, the correlation of sea surface height variability in
the twin runs is close to zero. In the non-eddying case in contrast, we find
high correlations (0.9 or higher) over most regions. Looking at the sub- and
interannual MOC components separately reveals that most of the chaotic MOC
variability is found on subannual timescales for the eddy-permitting model.
On interannual timescales the amplitude of the chaotic MOC variability is
much smaller and the amplitudes are comparable for both the eddy-permitting
and non-eddy-permitting model resolutions. Whereas the chaotic MOC
variability on interannual timescales only accounts for a small fraction of
the total chaotic MOC variability in the eddy-permitting case, it is the main
contributor to the chaotic variability in the non-eddying case away from the
Equator. |
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