Variations of the Atlantic meridional overturning circulation in control and transient simulations of the last millennium

Hofer, Dominik; Raible, Christoph C.; Stocker, Thomas F. (2011). Variations of the Atlantic meridional overturning circulation in control and transient simulations of the last millennium. Climate of the past, 7(1), pp. 133-150. Göttingen: Copernicus Publications 10.5194/cp-7-133-2011

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The variability of the Atlantic meridional overturing circulation (AMOC) strength is investigated in control experiments and in transient simulations of up to the last millennium using the low-resolution Community Climate System Model version 3. In the transient simulations the AMOC exhibits enhanced low-frequency variability that is mainly caused by infrequent transitions between two semi-stable circulation states which amount to a 10 percent change of the maximum overturning. One transition is also found in a control experiment, but the time-varying external forcing significantly increases the probability of the occurrence of such events though not having a direct, linear impact on the AMOC. The transition from a high to a low AMOC state starts with a reduction of the convection in the Labrador and Irminger Seas and goes along with a changed barotropic circulation of both gyres in the North Atlantic and a gradual strengthening of the convection in the Greenland-Iceland-Norwegian (GIN) Seas. In contrast, the transition from a weak to a strong overturning is induced by decreased mixing in the GIN Seas. As a consequence of the transition, regional sea surface temperature (SST) anomalies are found in the midlatitude North Atlantic and in the convection regions with an amplitude of up to 3 K. The atmospheric response to the SST forcing associated with the transition indicates a significant impact on the Scandinavian surface air temperature (SAT) in the order of 1 K. Thus, the changes of the ocean circulation make a major contribution to the Scandinavian SAT variability in the last millennium.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Climate and Environmental Physics

UniBE Contributor:

Hofer, Dominik; Raible, Christoph and Stocker, Thomas

ISSN:

1814-9324

Publisher:

Copernicus Publications

Language:

English

Submitter:

Factscience Import

Date Deposited:

04 Oct 2013 14:27

Last Modified:

27 Dec 2014 20:08

Publisher DOI:

10.5194/cp-7-133-2011

Web of Science ID:

000288992700012

BORIS DOI:

10.7892/boris.10133

URI:

https://boris.unibe.ch/id/eprint/10133 (FactScience: 215979)

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