The North Pacific Victoria mode: More effective prediction signal for the Central Pacific El Nino than the North Pacific Oscillation

By use of observational reanalysis data and the CMIP5 data, the relationships of the Central Pacific (CP) El Nino and the Victoria Mode (VM)/North Pacific Oscillation (NPO) are compared. The VM/NPO and the CP El Nino are physically related via negative feedback process of air-sea interaction. The VM/NPO has a delay effect on the CP ENSO in the subsequent winter. Nevertheless, the impact of VM on the CP El Nino is more effective relative to the NPO. When the conventional ENSO (hereafter as ENSO) own cycle is removed, the former's correlation with the EMI (El Nino Modoki index) in the Dec(+1) only decreases from 0.48 to 0.31, which is still significant. But the latter's correlation dose not reach 95% confidence level. Composition analysis also shows that during the D(+1)JF(+2), very few SST anomalies could be found over 95% significant level whether in positive or negative NPO phase. While for the VM cases, a large area of the CP ENSO-like SST anomalies is observed significantly in the tropical Pacific. Especially, for non-ENSO year, CP El Nino occurs in 50% positive VM cases' following winter. Although in previous studies, the VM is only considered as a transition stage during the process of NPO affecting the CP El Nino, the regression analysis shows that the VM is a partly natural mode, most of its variation is contributed by its internal evolution. The CP El Nino would still occur during positive VM cases even when NPO phase is negative. Their relationship remains stable in the CMIP5 RCP8.5 simulations, that is, the global warming does not interfere with the impact of positive VM on the CP El Nino. In conclusion, the VM may be a more effective prediction signal for the CP El Nino than the NPO.