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| Titel |
Southern Annular Mode responsible for frontal variability South of Australia |
| VerfasserIn |
C. O. Dufour, J. Le Sommer, M. H. England, T. Penduff, B. Barnier |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024525
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| Zusammenfassung |
| A global 1-4- ocean model simulation, performed during the DRAKKAR project, is used to
investigate the interseasonal to interannual variability of thermohaline properties in
subsurface waters across the Antarctic Circumpolar Current (ACC) South of Australia over
the last decades. In the model simulation, subsurface variability appears to be dominated by a
mode whose main characteristics are the following: a maximum of variability located at the
interface between the Subantarctic Mode Water (SAMW) and the Antarctic Intermediate
Water (AAIW), and an intermittent interseasonal period. This dominant mode appears
to be consistent with previous studies based on hydrographic sections along the
WOCE-SR3 line where the mode was observed and named the Pulsation Mode. Further
investigations show that the Pulsation Mode is associated with ACC frontal variability
constrained by topography. In particular, our detailed study shows that the Pulsation
Mode corresponds to a baroclinic adjustment of the ACC to changes in atmospheric
winds. Indeed, this mode exhibits a close correlation both with zonal wind stress
South of Australia and with the Southern Annular Mode (SAM), the dominant
atmospheric mode of Southern Hemisphere variability. On interseasonal to interannual
periods, the regional ocean circulation is thus shown to switch between two typical
states depending on the phase of the SAM. Although it is still unclear whether
the Pulsation Mode induces changes in water masses formation, we emphasize
that the structure of hydrographic sections South of Australia depends strongly
on the SAM phase, which should therefore be considered when analysing in-situ
data.
In this study, model data are used to provide a detailed description of ocean variability
and to analyse the associated physical processes. This study thus examplifies how ocean
model simulations driven by atmospheric reanalyses can compensate for the scarcity of
observational data in the Southern Ocean and offer a complementary view in order to get a
better understanding of ocean variability. |
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