I've been looking some more at last winter...turns out 2016-17 had a historically significant (at least with regards to modern observations) disconnect between the ENSO state and the PDO phase. Completely out of sync. The DJF ONI was -0.4, qualifying as cold neutral bordering on a weak Nina. However, the DJF averaged monthly PDO was a whopping +0.88, which is something you might expect in a weak/moderate Nino event.
The last time we saw such a degree of +PDO in conjunction with an ONI as low as -0.4 during DJF was during the 1980s. We had a run of three straight winters from 1983-86 that saw the following ONI/PDO values:
1983-84: ONI -0.5; PDO +1.47
1984-85: ONI -0.9; PDO +1.01
1985-86: ONI -0.4; PDO +1.04
That streak came at the tail end of a remarkable 8 year run of +ENSO domination that had prevailed since 1976. I've heard the PDO described before as nothing more than a decadal expression of the background ENSO state, since the two coupled oceanic/atmospheric indices are teleconnected. The fact that we were able to maintain such a remarkably positive +PDO despite transitioning to -ENSO conditions in the mid-1980s perhaps lends credence to that idea.
Either way, it's interesting that we had gone more than 30 years without seeing a similar disconnect between ENSO conditions and PDO during boreal winter.
Yeah, ENSO/PDO/PNA are a part the same mechanical "equilibration" system, which includes the NAM/SAM. From a multidecadal perspective, the boreal winter -NAM/-SAM circulation(s) constructively teleconnect to -ENSO/-PDO, and visa versa. The opposite holds true on millennial timescales but that's another topic altogether.
It's no coincidence that -PDO/-PNA/-NAM winters cluster in multiyear stretches with -PDO/-PNA dominance. It's also no coincidence that the flip to +NAM (starting in boreal winter 2011/12) was followed by the flip to +PDO/+PNA one year later, and it's no coividehcd that the last several years have featured huge +NAM/+NAO circulations during DJF.
- The 1950s to 1970s were predominantly -NAM/-PNA/-PDO
- The 1980s & 1990s were predominantly +NAM/+PNA/+PDO
- The late 2000s & early 2010s were mostly -NAM/-PNA/-PDO
- The 2013-present period is mostly +NAM/+PNA/+PDO
The leading variable is in fact the boreal winter NAO, which is a solid long term statistical predictor of the PDO and global temperature tendency years in the future.
- The abrupt flip to +NAO in the 1910s was followed by an transition to +PDO a few years later. The +NAO continued through the 1920s/1930s and began to decline in the 1940s.
- The steady decline in the NAO during the 1940s was followed by a flip to -PDO. The NAO continued to decline into the late 1960s and remained in its multidecadal negative state until the middle 1970s, during that multi-year super niña.
- The flip to +NAO in the mid/late 1970s corresponds to the "great Pacific climate shift" to +PDO thereafter. The +NAO continued until the early 2000s, peaking from the late 1980s to middle 1990s, in the heart of the +PDO era.
- The decline in the NAO during the early/mid 2000s was followed by a flip to -PDO during the mid/late 2000s. The late 2000s and early 2010s were largely -PDO/-NAO.
- The most recent example being the flip to +NAO, starting in winter 2011/12 (to present), was followed by the flip to +PDO a year later. Winter 2014/15 had one of the most prolific +NAOs ever recorded for DJF.