Non Stationary And Non Gaussian Character Of ENSO: The Role Of Climate Shifts And Nonlinearities
Abstract
ENSO is the dominant climate mode of variability in the Pacific, having socio-economical impacts on surrounding regions. ENSO exhibits a significant modulation at decadal to interdecadal timescales which is associated to changes of its characteristics (onset, amplitude, frequency, propagation, and predictability). Among these characteristics, some of them are generally ignored in ENSO studies, such as its asymmetry and the deviation of its statistics from those of the Gaussian distribution. These properties could be related to the ability of the current generation of coupled models to predict ENSO and its modulation. Here, the non-Gaussian nature and asymmetry of ENSO is diagnosed from in situ data and the outputs of a variety of models (from intermediate complexity models to full physics coupled general circulation models) using robust statistical tools. In particular alpha-stable laws are used as theoretical background material to quantify the non-Gaussian character of ENSO time series. It is shown that the Alpha-stable character of ENSO may result from the presence of climate shifts inducing non stationnarity in the time series. Also, cool (warm) periods are associated with ENSO statistics having a larger (weaker) tendency towards Gaussianity and a weaker (larger) asymmetry. This supports the hypothesis of ENSO being rectified by changes in mean state through non-linear processes. The relationship between change in mean state and non-linearity is investigated both in the Zebiak and Cane model and the IPCC models, which indicate that the propensity of a model to reproduce extreme events is related to its tendency to emphasize the non-linear interaction between mean state and ENSO variability. More particularly, high statistical moments i.e. high order nonlinearities seem to be involved in the feedback between extreme events occurrence and mean state shift triggering through inverse energy cascade, emphasizing the ENSO multifractal nature.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A13B0241B
- Keywords:
-
- 4468 Probability distributions;
- heavy and fat-tailed (3265);
- 4475 Scaling: spatial and temporal (1872;
- 3270;
- 4277);
- 4513 Decadal ocean variability (1616;
- 1635;
- 3305;
- 4215);
- 4522 ENSO (4922)