Relative contributions to ENSO of the seasonal footprinting and trade wind charging mechanisms associated with the Victoria mode

The Victoria mode (VM), as a basin-scale sea surface temperature (SST) pattern over the North Pacific, is suggested to facilitate subsequent development of El Niño–Southern Oscillation (ENSO) through both the seasonal footprinting mechanism (SFM) and the trade wind charging (TWC) mechanism. The present study aims at investigating the distinct roles and relative contributions to ENSO of the SFM and the TWC mechanism associated with the VM using atmospheric and oceanic reanalysis data as well as modeling simulations. Our results reveal that the positive SST anomalies (SSTAs) over the subtropical northeast Pacific (SNP) related to the VM effectively trigger the initiation of ENSO via the SFM, which emphasizes an air–sea surface thermodynamic-coupling process. In contrast, the negative SSTAs over the western North Pacific (WNP) associated with the VM primarily induce ENSO via a thermocline–SST feedback process, known as the TWC mechanism. Further analysis indicates that the SFM related to the VM may play a relatively independent role in affecting ENSO and is more closely linked to ENSO than is the TWC mechanism related to the VM, which is shown to be reasonably reproduced by the Community Earth System Model. Additionally, the SFM associated with the positive (negative) SNP SSTAs may induce fewer El Niño events (more La Niña events) than the TWC mechanism related to the positive (negative) WNP SSTAs. Our findings suggest that the SFM and the TWC mechanism associated with the VM both contribute to enhanced predictive skill for ENSO. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.