Extratropical low-frequency variability with ENSO forcing: a reduced-order coupled model study
Vannitsem, S.; Demaeyer, J.; Ghil, M. (2021). Extratropical low-frequency variability with ENSO forcing: a reduced-order coupled model study. J. Adv. Model. Earth Syst. 13(6): e2021MS002530. https://dx.doi.org/10.1029/2021MS002530 In: Journal of Advances in Modeling Earth Systems. American Geophysical Union: Washington. e-ISSN 1942-2466, more |   |
| Author keywords | ENSO forcing; midlatitude dynamics; reduced-order models; pullback attractors; ocean-atmosphere interaction; Lyapunov exponents |
| Authors | | Top | - Vannitsem, S., more
- Demaeyer, J., more
- Ghil, M.
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| Abstract | 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. |
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