Tropical Pacific decadal variability induced by nonlinear rectification of El Nino-Southern Oscillation

On the basis of the 32 long-term simulations of the state-of-the-art coupled GCMs, we investigate relationship between tropical Pacific decadal variability (TPDV) and El Niño-Southern Oscillation (ENSO). The first Empirical Orthogonal Function (EOF) mode for the 11-year moving sea surface temperatures (SST) in the coupled models is commonly characterized by El Niño-like decadal variability with Bjerknes air-sea interaction. However, the second EOF mode can be separated into two groups: 1) some models have a zonal dipole SST pattern, and 2) other models are characterized by a meridional dipole pattern. We found that models with the zonal dipole pattern in the second mode tend to simulate strong ENSO amplitude and asymmetry compared with those of the other models. Also, the residual patterns, which are defined as the summation of El Niño and La Niña SST composite anomalies, are quite similar to the decadal dipole pattern, which suggests that ENSO residuals can cause the decadal dipole pattern. It is found that decadal modulation of ENSO variability in these models strongly depends on the phase of the dipole decadal variability. The decadal changes in ENSO residual correspond well with the decadal changes in the dipole pattern, and the nonlinear dynamic heating terms by ENSO anomalies are well matched with the decadal dipole pattern.