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| Titel |
Impact of atmospheric feedbacks on the stability of the thermohaline circulation in the Atlantic ocean |
| VerfasserIn |
Andrea Cimatoribus, Sybren Drijfhout, Henk Dijkstra |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033988
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| Zusammenfassung |
| How do atmospheric feedbacks affect the stability of thermohaline circulation in the Atlantic
ocean?
This question has been asked several times in literature during the last decade, but no final
answer is widely accepted. Idealised and simpler general circulation models apparently
contradict the results of state of the art computations. While the former ones hint at the
existence of a stable collapsed state and multiple equilibria, the latter do not show such
behaviour. Understanding the relative importance of the salt advection feedback in the ocean
and of the response of the atmosphere to a thermohaline circulation depression is a crucial
point in this work. A combined approach is developed to start answering these questions,
focusing on the physical mechanisms that may change the stability properties of density
driven circulation.
An atmosphere/ocean/sea–ice coupled general circulation model (Speedo/CLIO) is used
in two different setups. First, the statistical steady state of the model is recorded. In a second
experiment, a collapse of thermohaline circulation is induced with a freshwater pulse in the
north Atlantic. Thermohaline circulation does not recover even after the release of the pulse,
and a second steady state with no thermohaline circulation is attained. Using these two
runs, the anomalies can be computed as linear regressions on the local value of sea
surface temperature and on northern hemisphere average sea surface temperature
separately.
With this approach, both natural variability of atmospheric forcing due to local
temperature anomalies and large scale changes due to the collapse of thermohaline circulation
can be represented. Changes in freshwater and heat fluxes are the most significant. The
northern–southern Atlantic temperature dipole and the southward shift of intertropical
convergence zone, believed to be the main atmospheric signals in response to a collapse of
thermohaline circulation, are evident in the second experiment and well recorded by linear
regressions. The linearly perturbed climatology is used successfully as boundary
condition for the ocean–only component of Speedo/CLIO. The model shows only minor
drift (- 0.3-C in 1000 years) and variability is consistent with that of the coupled
model. |
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