The Victoria mode in the North Pacific linking extratropical sea level pressure variations to ENSO

The Victoria mode (VM) represents the second dominant mode (empirical orthogonal function, EOF2) of North Pacific variability, independent of the Pacific Decadal Oscillation and is defined as the EOF2 of SST anomalies in the North Pacific poleward of 20°N. The present study indicates that the VM is closely linked to the development of El Niño--Southern Oscillation (ENSO). The VM may effectively act as an ocean bridge (or conduit) through which the extratropical atmospheric variability in the North Pacific influences ENSO. The VM can trigger the onset of ENSO via the following two dominant processes: (1) surface air-sea coupling associated with the VM in the subtropical/tropical Pacific and (2) evolution of subsurface ocean temperature anomalies along the equator associated with the VM. These two processes may force sufficient surface warming to occur in the central eastern equatorial Pacific from spring to summer, which in turn initiates an ENSO event. The VM influence on ENSO relies on a basin-scale air-sea interaction dynamic, as opposed to more local-scale dynamics typically associated with the seasonal footprinting mechanism or Pacific meridional mode. The majority of VM events are followed by ENSO events. These ENSO events triggered by VM include El Niño Modoki (EM) as well as conventional El Niño. There is no evidence that the VM tends to be more conducive to the initialization of EM than conventional El Niño.