Nonlinear Processes in Oceanic and Atmospheric Flows

Presentation

The non-stationary and non-Gaussian nature of ENSO: the role of climate shifts and nonlinearities.

Author: Julien Boucharel, LEGOS.

Names and affiliation of other authors:
Dewitte B. (2),
Garel B. (3),
Du Penhoat Y. (1)
Bosc C. (1)

(1) : Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS)
(2) : LEGOS / IRD / IMARPE
(3) : Institut de Mathématiques de Toulouse (LSP)

Oral or poster: Poster

Downloadable poster file:

The non-stationary and non-Gaussian nature of ENSO: the role of climate shifts and nonlinearities.

(Poster_Castro_Shift.pdf, 3901358 bytes)

Abstract:
ENSO is the dominant climate mode of variability in the Pacific, impacting surrounding regions with large socio-economical aspects. ENSO exhibits a significant modulation at interdecadal timescales, also associated to changes of its characteristics. Among these characteristics, some of them are generally ignored in ENSO studies, such as asymmetry and deviation of its statistics from those of an assumed Gaussian distribution. Here, statistical tests are performed to quantify the non-Gaussian nature and asymmetry of typical ENSO indices from long in situ records and intermediate complexity models. A low frequency modulation, dominated by climate shifts, is evidenced in the statistical distribution of the phenomenon, which oscillate between warm heavy-tailed periods (α-stable distribution) and cool Gaussian phases. This supports the mechanism of ENSO rectification by the change in mean state to produce decadal variability. We highlight the role of nonlinearities in the process leading to change in statistical properties. During periods characterized by a warm ocean background, nonlinearities emphasize phase’s relationships between temperature and currents fields which facilitate the growth of extreme events responsible for the variance burst and thus the switch of representative statistics. Conversely, this nonlinear activity is almost inhibited throughout cool mean state phases, giving back a more Gaussian nature to ENSO proxies.

Formatted version of the abstract or additional information

*Satellite images from NASA and ESA

Nonlinear Processes in Oceanic and Atmospheric Flows. July 2-4, 2008. Castro Urdiales, Cantabria, Spain.