The Atlantic Multidecadal Variability in Observations and in a Large Historical Multimodel Ensemble: Forced and Internal Variability.
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| Title: | The Atlantic Multidecadal Variability in Observations and in a Large Historical Multimodel Ensemble: Forced and Internal Variability. |
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| Authors: | Christiansen, Bo1 (AUTHOR) boc@dmi.dk, Yang, Shuting1 (AUTHOR), Drews, Annika1 (AUTHOR) |
| Source: | Journal of Climate. Jun2025, Vol. 38 Issue 12, p2761-2781. 21p. |
| Subjects: | North Atlantic oscillation, Atmospheric models, Definitions, Ocean, Polynomials |
| Abstract: | We investigate the Atlantic multidecadal variability (AMV) in observations and in a large CMIP6 historical climate model ensemble. We compare four different definitions of the AMV aimed at extracting the variability intrinsic to the Atlantic region. They are based on removing from the Atlantic temperature the linear or polynomial trend, the part congruent to the global average, or the part congruent to the multimodel mean of the global average. The definitions agree on the well-known low-frequency oscillatory variability in observations but show larger differences for the models. In general, large differences between ensemble members are found. We estimate the forced response in the AMV as the mean of the multimodel ensemble. This response converges fast with the ensemble size and saturates for a size of around 25. The forced response resembles the observed low-frequency oscillatory variability for the detrended AMV definitions, but these definitions are also the most ineffective in removing the forced global mean signal. The forced response is very weak for the other definitions, and few of their individual ensemble members show oscillatory variability and even fewer with the observed phase. The observed spatial temperature pattern related to the AMV is well captured for all AMV definitions but is more confined for the definitions with the global means removed. These definitions also depend the least on the considered period. The observed instantaneous connection between NAO and AMV is well represented in the models for all definitions. Only nonsignificant evidence of NAO leading the AMV on decadal time scales is found. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| Abstract: | We investigate the Atlantic multidecadal variability (AMV) in observations and in a large CMIP6 historical climate model ensemble. We compare four different definitions of the AMV aimed at extracting the variability intrinsic to the Atlantic region. They are based on removing from the Atlantic temperature the linear or polynomial trend, the part congruent to the global average, or the part congruent to the multimodel mean of the global average. The definitions agree on the well-known low-frequency oscillatory variability in observations but show larger differences for the models. In general, large differences between ensemble members are found. We estimate the forced response in the AMV as the mean of the multimodel ensemble. This response converges fast with the ensemble size and saturates for a size of around 25. The forced response resembles the observed low-frequency oscillatory variability for the detrended AMV definitions, but these definitions are also the most ineffective in removing the forced global mean signal. The forced response is very weak for the other definitions, and few of their individual ensemble members show oscillatory variability and even fewer with the observed phase. The observed spatial temperature pattern related to the AMV is well captured for all AMV definitions but is more confined for the definitions with the global means removed. These definitions also depend the least on the considered period. The observed instantaneous connection between NAO and AMV is well represented in the models for all definitions. Only nonsignificant evidence of NAO leading the AMV on decadal time scales is found. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 08948755 |
| DOI: | 10.1175/JCLI-D-24-0310.1 |
