A new dipole index for the North Pacific Victoria mode

A novel index, the Victoria mode Dipole Index (VMDI), is proposed to quantify the North Pacific Victoria mode (VM) variability. The VM demonstrates a distinctive ‘dipole’ configuration in sea surface temperature (SST) anomalies, characterized by two principal centers of action and fluctuations spanning annual to decadal periods. This pattern is encapsulated by the second empirical orthogonal function (EOF) of SST anomalies (SSTA) in the North Pacific. The VMDI is determined by calculating the variance in SSTA between the average values in the northwest and southeast areas of the North Pacific. The VMDI, which is not based on EOF, offers a simple method for tracking the variability of SST from year to decade that is linked to the VM. The VMDI time series exhibits a strong correspondence with previously established EOF-based indices while offering the benefits of a more straightforward computation and consistency with methods employed for other climate variability indices. The reliability of VMDI has been demonstrated through the evaluation of the modal patterns described, the analysis of the evolution of surface SST, subsurface SST, and low-level wind field, and the assessment of its impact on other climate modes. The VMDI proves to be a robust and reliable indicator of the VM in both observational and modeled datasets.