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| Titel |
Atmospheric circulation in the early Holocene: Sensitivity of the North Atlantic winter climate to moderate changes in the ice-sheet configuration |
| VerfasserIn |
N. Merz, C. C. Raible, T. F. Stocker |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062961
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| Zusammenfassung |
| A prominent feature of interglacials, such as the Holocene, is the reduced size of the
continental ice sheets. At present-day, only two ice-sheets (namely Greenland and Antarctica)
exist which themselves are likely to retreat in the future due to global warming. Changes in
the global ice-sheet distribution have distinct consequences for the surface climate and the
atmospheric circulation since ice-masses shape the topography and define the local surface
characteristics.
Past interglacial periods offer the potential to study the climate dynamics and stability of
warm periods, also concerning the impact of changes in the ice-sheet distribution. For this
purpose, we use a comprehensive climate model to perform a set of time-slice simulations for
the present, the early-Holocene and the Eemian warm period. In particular, we perform
sensitivity experiments to assess the atmosphere’s reaction to modest changes in the global
ice-sheet distribution.
In a first attempt, we focus on a set of four early-Holocene simulations which include the
paleo-topographies from 9000BP, 8000BP, 7000BP and the present orography as lower
boundary conditions, respectively. The early Holocene orography differs from the
present-day state by the presence of remnants of the Laurentide ice-sheet and newly ice-free
regions in Scandinavia and North America with a higher altitude due to the post-glacial
rebound effect. For all simulations, the orbital forcing is set to the state of 8000BP, whereas
the solar constant and greenhouse gas concentrations are fixed on pre-industrial
levels.
The Northern Hemisphere (NH) winter surface climate shows moderate and mostly
non-significant changes due to the different lower boundaries. Significant differences in
surface temperature are limited to areas which experience a local change in orography.
However, there is a clear impact on the mid-level troposphere downstream of the Laurentide
ice sheet remnants leading to a cooling over the North Atlantic and a warming over Southern
Europe. These changes are likely associated with a change in the North Atlantic winter jet.
The analysis shows that the sub-tropical branch of the jet is intensified whereas the
eddy-driven jet is slightly weakened. Nevertheless, the induced changes in the jet do
not lead to a change in the main NH modes of atmospheric variability (e.g., the
North Atlantic Oscillation or the East Atlantic Pattern). This analysis illustrates that
although the impact of the lower boundaries is significant, the magnitude is too small
to lead to a significant reorganization of the mean atmospheric flow in the NH. |
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