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Simulated Atlantic Multidecadal Oscillation during the Holocene

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Citation:
Wei, W. and Lohmann, G. (2011): Simulated Atlantic Multidecadal Oscillation during the Holocene , AGU 2011 Fall Meeting, San Francisco, USA .
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Abstract:

In this study, the Atlantic Multidecadal Oscillation (AMO) under different boundary conditions during the Holocene, i.e. orbital change, greenhouse gas concentration, the Laurentide ice sheet and its melting, are examined in several long-term simulations using the Earth system model COSMOS. The simulated AMO indices exhibit a quasi-multidecadal periodicity, consistent with the typical 50-80 year cycle of the AMO indicated by the observation data. A warm phase of the AMO accompanies a hemispheric scale warming in the NH, with the maximum warming over the North Atlantic and part of the Arctic. Such a warming favors more evaporation and thus more precipitation over most part of the North Atlantic, especially enhancing the Atlantic intertropical convergence zone. Concerning the forcing mechanism of the AMO, the most common believed physical process involves the variation of the Atlantic meridional overturning circulation (AMOC). Although a fully understanding of such a process is beyond the scope of this study, our results show the strong correlation between the AMO index and AMOC index on multidecadal timescales and, during a warm phase of the AMO, the AMOC is intensified significantly. The climate influence of the AMO during the Holocene demonstrates that there is no remarkable change in its spatial pattern under different climate background conditions, which further reveals that the AMO is an internal variability of the climate system. However, we imply that this influence can be distinguished regarding the regional scale feature and its magnitude. It has been supported by a previous study, which suggests that the regional response to the AMO can be modulated by orbitally induced shifts in large-scale ocean-atmosphere circulation. Moreover, we argue that the climate influence of the AMO might be amplified by a vigorous background climate condition, in particular during a cold period.

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