@article{fdi:010066232,
  title = {{S}trong and moderate nonlinear {E}l {N}ino regimes},
  author = {{T}akahashi, {K}. and {D}ewitte, {B}oris},
  editor = {},
  language = {{ENG}},
  abstract = {{I}t has been previously proposed that two {E}l {N}io ({EN}) regimes, strong and moderate, exist but the historical observational record is too short to establish this conclusively. {H}ere, 1200 years of simulations with the {GFDL} {CM}2.1 model allowed us to demonstrate their existence in this model and, by showing that the relevant dynamics are also evident in observations, we present a stronger case for their existence in nature. {I}n {CM}2.1, the robust bimodal probability distribution of equatorial {P}acific sea surface temperature ({SST}) indices during {EN} peaks provides evidence for the existence of the regimes, which is also supported by a cluster analysis of these same indices. {T}he observations agree with this distribution, with the {EN} of 1982-1983 and 1997-1998 corresponding to the strong {EN} regime and all the other observed {EN} to the moderate regime. {T}he temporal evolution of various indices during the observed strong {EN} agrees very well with the events in {CM}2.1, providing further validation of this model as a proxy for nature. {T}he two regimes differ strongly in the magnitude of the eastern {P}acific warming but not much in the central {P}acific. {O}bservations and model agree in the existence of a finite positive threshold in the {SST} anomaly above which the zonal wind response to warming is strongly enhanced. {S}uch nonlinearity in the {B}jerknes feedback, which increases the growth rate of {EN} events if they reach sufficiently large amplitude, is very likely the essential mechanism that gives rise to the existence of the two {EN} regimes. {O}ceanic nonlinear advection does not appear essential for the onset of strong {EN}. {T}he threshold nonlinearity could make the {EN} regimes very sensitive to stochastic forcing. {O}bservations and model agree that the westerly wind stress anomaly in the central equatorial {P}acific in late boreal summer has a substantial role determining the {EN} regime in the following winter and it is suggested that a stochastic component at this time was key for the development of the strong {EN} towards the end of 1982.},
  keywords = {{ENSO} ; {E}l {N}ino ; {E}astern {P}acific ; {N}onlinear dynamics ; {B}jerknes feedback ; {GFDL} {CM}2.1 ; {PACIFIQUE} {EST}},
  booktitle = {},
  journal = {{C}limate {D}ynamics},
  volume = {46},
  numero = {5-6},
  pages = {1627--1645},
  ISSN = {0930-7575},
  year = {2016},
  DOI = {10.1007/s00382-015-2665-3},
  URL = {https://www.documentation.ird.fr/hor/fdi:010066232},
}