期刊名称：Journal of Advances in Modeling Earth Systems
电子版ISSN：1942-2466
出版年度：2021
卷号：13
期号：6
页码：e2021MS002530
DOI：10.1029/2021MS002530
出版社：John Wiley & Sons, Ltd.
摘要：The impact of the El Niño-Southern Oscillation (ENSO) on the extratropics is investigated in an idealized, reduced-order model that has a tropical and an extratropical module. Unidirectional ENSO forcing is used to mimick the atmospheric bridge between the tropics and the extratropics. The variability of the coupled ocean-atmosphere extratropical module is then investigated through the analysis of its pullback attractors (PBAs). This analysis focuses on two types of ENSO forcing generated by the tropical module, one periodic and the other aperiodic. For a substantial range of the ENSO forcing, two chaotic PBAs are found to coexist for the same set of parameter values. Different types of extratropical low-frequency variability (LFV) are associated with either PBA over the parameter ranges explored. For periodic ENSO forcing, the coexisting PBAs exhibit only weak nonlinear instability. For chaotic forcing, though, they are quite unstable and certain extratropical perturbations induce transitions between the two PBAs. These distinct stability properties may have profound consequences for extratropical climate predictions: in particular, ensemble averaging may no longer help isolate the LFV signal. Plain Language Abstract The authors have investigated the variability of a simplified coupled ocean-atmosphere model for the Earth's midlatitudes, subject to the influence of the El Niño-Southern Oscillation (ENSO). This study reveals that multiple climates may coexist, each of which is characterized by distinct types of low-frequency variability (LFV) and predictability properties. When the ENSO forcing is periodic, these climates are fairly robust against perturbations, but when it is chaotic, small perturbations induce transitions between the different climates. These properties could have profound consequences for extratropical climate predictions, since ensemble averaging may no longer be a valid approach to ascertain the LFV signal.
