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| Titel |
Another look at low-frequency variability in climate dynamics, from the ergodic theory of dynamical systems |
| VerfasserIn |
M. D. Chekroun |
| 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 |
250070204
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| Zusammenfassung |
| Climate variability, oceanic currents, and geophysical turbulent flows in general
exhibit recurrent large-scale patterns which although evolving irregularly in time,
exhibit characteristic dominant frequencies across a large range of time-scales from
intraseasonal through seasonal-interannual up to interdecadal. The understanding
of the associated low-frequency variability (LFV) is essential for simulation and
prediction of the irregularly occurring events in each of these bands. In the case of
El-Niño-Southern Oscillation (ENSO), Chekroun et al. (PNAS, 108, 2011) showed that a
better understanding of these modes — and their interactions with higher-frequency
variability — allows an extension of predictability for a stochastic model exhibiting
the appropriate LFV (for ENSO, the quasi-biennial and quasi-quadrennial modes
essentially).
Several approaches have been proposed to explain the origin of such LFV over the past
decades such as the mechanisms of nonlinear resonance or the ones of noise-sustained
oscillations from non-normal modes, to name a few. In this talk, new perspectives stemming
from the ergodic theory of dynamical systems will be presented which will point out other
mathematical representations of LFV as arising in dissipative chaotic systems subject to
random disturbance or not. The theory of time-dependent Sinaï-Ruelle-Bowen
measures (Chekroun et al., Physica D, 240, 2011) and the theory of Koopman operator
will serve us in that perspective. Idealized models of intermediate complexity will
illustrate our theoretical approach and challenges for more realistic models will be
discussed. |
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