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| Titel |
Variability of the Atlantic meridional overturning circulation in the last millennium and two IPCC scenarios |
| VerfasserIn |
Pablo Ortega, Marisa Montoya, Fidel González-Rouco, Juliette Mignot, Stephanie Legutke |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055129
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| Zusammenfassung |
| The variability of the Atlantic meridional overturning circulation (AMOC) is investigated in
several climate simulations with the ECHO-G atmosphere-ocean general circulation model
(AOGCM), including two forced integrations of the last millennium, one millennial-long
control run, and two future scenario simulations of the 21st century. This constitutes a new
framework in which the AMOC response to future climate change conditions is addressed in
the context of both its past evolution and its natural variability. The main mechanisms
responsible for the AMOC variability at interannual and multidecadal time scales are
described. At interannual timescales the AMOC is directly responding to local
changes in the Ekman transport, associated to three different teleconnection indices: El
Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the East
Atlantic (EA) pattern. At multidecadal timescales the AMOC is largely controlled by
convection activity south of Greenland. Again, the atmosphere is found to play a leading
role on these variations. Positive anomalies of convection are preceded in 1 year
by intensified zonal winds, associated in the forced runs to a positive NAO-like
pattern.
Finally, the sensitivity of the AMOC to three different forcing factors is investigated. The
major impact is associated to increasing greenhouse gases (GHG), given their strong and
persistent radiative forcing. Starting in the Industrial Era and continuing in the future
scenarios, the AMOC experiences a final decrease of up to 40% with respect to the
preindustrial average, well below the range of natural AMOC variability simulated for the
past millennium and the control simulation. This final weakening is associated with a
reduced meridional density gradient and with decreased convection in the North
Atlantic, both mainly responding to changes in the atmospheric water transport.
Also, a weak but significant AMOC strengthening is found in response to the major
volcanic eruptions, which produce colder and saltier surface conditions over the main
convection regions. In contrast, no meaningful impact of the solar forcing on the
AMOC is observed. Indeed, solar irradiance only affects convection in the Nordic
Seas, with a marginal contribution to the AMOC variability in the ECHO-G runs. |
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