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| Titel |
Control of the Atlantic Meridional Circulation stability by freshwater transport: a framework to interpret results from climate models. |
| VerfasserIn |
Andrea Cimatoribus, Sybren Drijfhout, Matthijs den Toom, Henk Dijkstra |
| 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 |
250087908
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| Publikation (Nr.) |
 EGU/EGU2014-1967.pdf |
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| Zusammenfassung |
| The stability properties of the Atlantic Meridional Overturning Circulation (AMOC) have
been the subject of several numerical studies in the last decades. These studies, focusing in
particular on the impact of freshwater anomalies applied at the northern end of
the Atlantic Ocean, have produced widely different results for what concerns the
possibility of a permanent collapse of the AMOC. Furthermore, the comparison of
results using different freshwater anomalies has lead to some confusion between the
transient response of the system, highly dependent on the model used and on the
magnitude of the freshwater anomaly, and the possibly underlying steady states of the
system.
With the aim of clarifying these aspects, a series of numerical and analytical studies has
been conducted, focusing on the control of the AMOC stability by the freshwater budget of
the Atlantic Ocean. The role played by the different components of the freshwater budget are
investigated in a coarse resolution global climate model close to the steady state, by
adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the
surface. These anomalies alter in particular the basin-scale salt-advection feedback,
completely changing the response of the AMOC to perturbations. It is found that an
appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean
can collapse the AMOC entirely even without any further “hosing” in the North
Atlantic.
Furthermore, a simple model is developed, extending the Gnanadesikan pycnocline
model, that allows the study of different steady-state regimes of the AMOC driven
by the joint effect of winds over the Southern Ocean and the north–south density
difference.
Overall, the sensitivity of the AMOC to changes in basin integrated net evaporation is
highly dependent on the zonal salinity contrast at the southern border of the Atlantic. This
suggests a new view on the stability of the AMOC, controlled by processes in the South
Atlantic. Since climate models are strongly affected by biases in the salinity field and
freshwater budget in the South Atlantic region, we suggest that the different outcomes of
different studies of the AMOC stability may be caused by these biases, as well as to the use
of anomalies of different duration that probe the response of the system on different time
scales. |
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