@article{fdi:010076046,
  title = {{I}nfluence of {W}esterly {W}ind {E}vents stochasticity on {E}l {N}ino amplitude : the case of 2014 vs. 2015},
  author = {{P}uy, {M}. and {V}ialard, {J}{\'e}r{\^o}me and {L}engaigne, {M}atthieu and {G}uilyardi, {E}. and {D}i{N}ezio, {P}. {N}. and {V}oldoire, {A}. and {B}almaseda, {M}. and {M}adec, {G}. and {M}enk{\`e}s, {C}hristophe and {M}c{P}haden, {M}. {J}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he weak {E}l {N}ino of 2014 was preceded by anomalously high equatorial {P}acific {W}arm {W}ater {V}olume ({WWV}) and strong {W}esterly {W}ind {E}vents ({WWE}s), which typically lead to record breaking {E}l {N}ino, like in 1997 and 2015. {H}ere, we use the {CNRM}-{CM}5 coupled model to investigate the causes for the stalled {E}l {N}ino in 2014 and the necessary conditions for extreme {E}l {N}inos. {T}his model is ideally suited to study this problem because it simulates all the processes thought to be critical for the onset and development of {E}l {N}ino. {I}t captures {E}l {N}ino preconditioning by {WWV}, the {WWE}s characteristics and their deterministic behaviour in response to warm pool displacements. {O}ur main finding is, that despite their deterministic control, {WWE}s display a sufficiently strong stochastic component to explain the distinct evolutions of {E}l {N}ino in 2014 and 2015. {A} 100-member ensemble simulation initialized with early-spring equatorial conditions analogous to those observed in 2014 and 2015 demonstrates that early-year elevated {WWV} and strong {WWE}s preclude the occurrence of a {L}a {N}ina but lead to {E}l {N}inos that span the weak (with few {WWE}s) to extreme (with many {WWE}s) range. {S}ensitivity experiments confirm that numerous/strong {WWE}s shift the {E}l {N}ino distribution toward larger amplitudes, with a particular emphasis on summer/fall {WWE}s occurrence which result in a five-fold increase of the odds for an extreme {E}l {N}ino. {A} long simulation further demonstrates that sustained {WWE}s throughout the year and anomalously high {WWV} are necessary conditions for extreme {E}l {N}ino to develop. {I}n contrast, we find no systematic influence of easterly wind events ({EWE}s) on the {E}l {N}ino amplitude in our model. {O}ur results demonstrate that the weak amplitude of {E}l {N}ino in 2014 can be explained by {WWE}s stochastic variations without invoking {EWE}s or remote influences from outside the tropical {P}acific and therefore its peak amplitude was inherently unpredictable at long lead-time.},
  keywords = {{E}l {N}ino ; {W}esterly {W}ind {E}vents ; {E}asterly wind events ; {P}redictability ; {E}xtreme {E}l {N}ino events ; {E}l {N}ino predictors ; {PACIFIQUE} ; {ZONE} {EQUATORIALE} ; {ZONE} {TROPICALE}},
  booktitle = {},
  journal = {{C}limate {D}ynamics},
  volume = {52},
  numero = {12},
  pages = {7435--7454},
  ISSN = {0930-7575},
  year = {2019},
  DOI = {10.1007/s00382-017-3938-9},
  URL = {https://www.documentation.ird.fr/hor/fdi:010076046},
}