Validation of Numerical Climate Models for the El Niño-Southern Oscillation System

Abstract

Statistical properties of the observed bi-variate ENSO time series (sea surface temperature within the Niño area 3.4 and the Southern Oscillation Index) from 1876 through 2005 are compared with respective properties of 46 CMIP5 models used in the historical experiment, one run per model. The models were found to exaggerate linear trend rates of SST; mean value and variance estimates have a large scatter, most probability densities are Gaussian, the shape of spectra is reproduced correctly in most cases though the spectra of simulated Southern Oscillation have a negative bias. Most estimates of coherence correctly reproduce the behavior of coherence between the observed SST and SOI that exceeds 0.9 at moderate frequencies. The average coherent spectrum of simulated SST is close to the “observed” coherent spectrum and has a negative bias in the SOI case. The results for the time domain require improvement; the frequency domain results are satisfactory.