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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 3
Nonlin. Processes Geophys., 13, 275–285, 2006
https://doi.org/10.5194/npg-13-275-2006
© Author(s) 2006. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

Special issue: Complex dynamics in geosciences: analysis techniques for observational...

Nonlin. Processes Geophys., 13, 275–285, 2006
https://doi.org/10.5194/npg-13-275-2006
© Author(s) 2006. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  13 Jul 2006

13 Jul 2006

A conceptual ENSO model under realistic noise forcing

J. Saynisch, J. Kurths, and D. Maraun J. Saynisch et al.
  • Nonlinear Dynamics Group, University Potsdam, Germany

Abstract. We investigated the influence of atmospheric noise on the generation of interannual El Niño variability. Therefore, we perturbed a conceptual ENSO delay model with surrogate windstress data generated from tropical windspeed measurements. The effect of the additional stochastic forcing was studied for various parameter sets including periodic and chaotic regimes. The evaluation was based on a spectrum and amplitude-period relation comparison between model and measured sea surface temperature data. The additional forcing turned out to increase the variability of the model output in general. The noise-free model was unable to reproduce the observed spectral bandwidth for any choice of parameters. On the contrary, the stochastically forced model is capable of producing a realistic spectrum. The weakly nonlinear regimes of the model exhibit a proportional relation between amplitude and period matching the relation derived from measurement data. The chaotic regime, however, shows an inversely proportional relation. A stability analysis of the different regimes revealed that the spectra of the weakly nonlinear regimes are robust against slight parameter changes representing disregarded physical mechanisms, whereas the chaotic regime exhibits a very unstable realistic spectrum. We conclude that the model including stochastic forcing in a parameter range of moderate nonlinearity best matches the real conditions. This suggests that atmospheric noise plays an important role in the coupled tropical pacific ocean-atmosphere system.

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