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| Titel |
Decadal Variability in an OGCM Southern Ocean: intrinsic modes, forced modes and metastable states |
| VerfasserIn |
Terence O'Kane, Richard Matear, Matthew Chamberlain, James Risbey, Illia Horenko, Bernadette Sloyan |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087123
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| Publikation (Nr.) |
 EGU/EGU2014-1140.pdf |
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| Zusammenfassung |
| An Ocean General Circulation Model (OGCM) is used to identify a Southern Ocean
southeast Pacific intrinsic mode of low frequency variability. Using CORE data a
comprehensive suite of experiments were carried out to elucidate excitation and amplification
responses of this intrinsic mode to low frequency forcing (ENSO, SAM) and stochastic
forcing due to high frequency winds. Subsurface anomalies were found to teleconnect the
Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC) thermocline. The
Pacific region of the ACC is characterised by intrinsic baroclinic disturbances that respond to
both SAM and ENSO, while the Atlantic sector of the ACC is sensitive to higher frequency
winds that act to amplify thermocline anomalies propagating downstream from the Pacific.
Non-stationary cluster analysis was used to identify the system’s dynamical regimes
and characterise meta-stability, persistence and transitions between the respective
states. This analysis reveals significant trends, indicating fundamental changes to
the meta-stability of the ocean dynamics in response to changes in atmospheric
forcing. Intrinsic variability in sea-ice concentration was found to be coupled to
thermocline processes. Sea-ice variability localised in the Atlantic was most closely
associated with high frequency weather forcing. The SAM was associated with a
circumpolar sea-ice response whereas ENSO was found to be a major driver of sea-ice
variability only in the Pacific. This simulation study identifies plausible mechanisms that
determine the predictability of the Southern Ocean climate on multi-decadal timescales. |
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