(a) Niño-3.4 values in SODA ( y axis) vs Niño-3.4 hindcasts based on a linear function of WWV and DMI 14 months before ( x axis). The date on which the forecast is issued is indicated by the gray bar, and the peak of ENSO in NDJ of year 1 is indicated by the light red bar. The significance of the increase in variance obtained from this method is indicated within brackets (bold when 90% significant). The plot shows the mean value over cross-validations leaving 50% of the samples (randomly chosen) to train the prediction model and keeping 50% for its evaluation. (a) Increased variance due to DMI (i.e., first predictor is SON WWV and second predictor is SON DMI). Increase of explained Niño-3.4 variance when a second predictor of ENSO is used in addition to WWV. The 90% significance level is indicated by the horizontal dashed lines ( t test for 100 degrees of freedom see caption of Fig.

The rightmost column represents the CMIP5 multimodel mean, and the error bars indicate the 90% confidence interval on the mean ( t value, all CMIP5 distributions being normally distributed at the 99% confidence level according to a Shapiro–Wilk test).Ĭorrelation between DMI in SON (shown by the gray bar) and lagged monthly Niño-3.4 in 21 CMIP5 models. The bars falling between the two dashed lines cannot be considered as different from the random proportion of 25% (90% confidence interval based on Monte Carlo statistical method see text). (c) Proportion of pIODs followed by La Niña 14 months later (orange) and of nIODs followed by El Niño 14 months later (blue). (b) Proportion of pIODs immediately followed by El Niño (red) and of nIODs immediately followed by La Niña (blue). (a) Proportion (%) of El Niños followed by La Niña (yellow) and of La Niñas followed by El Niño (green). The 90% level of statistical significance for 100 degrees of freedom is indicated by the dashed line (see caption of Fig. (b) Autocorrelation between Niño-3.4 in NDJ (gray bar) and lagged monthly Niño-3.4 for 21 CMIP5 models (colors), the CMIP5 multimodel mean (solid black), and the multiobservation mean (dashed black). (a) Correlation between Niño-3.4 in NDJ (gray bar) and lagged monthly WWV for 21 CMIP5 models (colors), the CMIP5 multimodel mean (solid black), the SODA reanalysis (long-dashed black), and the NOAA–BMRC observational dataset (short-dashed black). (c),(d) As in (a),(b), but the curve is normalized (anomaly with respect to the mean, divided by the standard deviation).

Standard deviation of (a) Niño-3.4 and (b) DMI for 23 CMIP5 models (color lines), the CMIP5 multimodel mean (solid black), and the observational multidataset mean (dashed black), in kelvin.

The 90% significance level is indicated by the horizontal dashed lines. Correlation between DMI in SON (show by the gray bar) and lagged monthly Niño-3.4 in four observational datasets over 1890–2012.

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